ilitjrarp ANATOMY |)KSCRIITIVE AND APPLIED BY HENRY GRAY, F.R.S. FELLOW OF THE ROYAL COLLEGE OF SURGEONS; LECTURER ON ANATOMY AT ST. GEORGE's HOSPITAL MEDICAL SCHOOL, LONDON A NEW AMERICAN FROM THE EICtHTEENTH ENGLISH EDITION THOROUGHLY REVISED AND RE-EDITED AVITH THE BASLE ANATOMICAL NOMENCLATUEE IN ENGLISH BY ROBERT HOWDEN, M.A., M.B., CM. PROFESSOR OF ANATOMY IN THE UNIVERSITY OF DURHAM, ENGLAND 1I^u9trate^ wttb 1126 jeuQravinQS LEA & FEBIGER PHILADELPHIA AND NEW YORK 1913 a 11 Entered according to the Act of Congress, in the 3'ear 1913, by LEA & FEBIGER in the Office of the Librarian of Congress. All rights reserved. THE FIRST EDITION OF THIS WORK WAS DEDICATED TO SIR BENJAMIN COLLINS BRODTE, Bart., F.R.S., D.C.L. IN ADMIRATION OF HIS GREAT TALENTS AND IN REMEMBRANCE OF MANY ACTS OF KINDNESS SHOWN TO THE ORIGINAL AUTHOR OF THE BOOK FROM AN EARLY PERIOD OF HIS PROFESSIONAL CAREER PREFACE. nnHE outstanding modification in the text of this edition is the use of the Basle nomenclature. Except in one or two instances, this nomenclature has been adopted in its entirety; in most cases English translations of the Latin terms are employed, but in those cases where the Latin terms have become fixed by routine usage it has been deemed desirable to retain them. Where the Basle nomenclature differs materially from the older terminology, the latter has been added in brackets, and for further convenience a glossary is appended showing (a) the terms adopted in the text, (b) the Basle, and (c) the old terminology. The paragraphs on Surface Anatomy, which in previous editions were appended separatel}^ to the descriptions of the various structures, have been collected and recast into a special chapter — an arrangement which admits of more easy reference. The section on Histology has been shortened. The elementary tissues are described in it, but the complex tissues are considered along with, the organs to which they are specially related. The whole text has been thoroughly revised and, where necessary, rewritten. About two hundred new engravings have been added; some of them replace older figures, but many are additional, and the majority are drawn from original preparations. The notes on Applied Anatomy have been revised by A. J. Jex-Blake, jNI.A., M.B., B.Ch., F.R.C.P., Assistant Physician to St. George's Hospital, London, and W. Fedde Fedden, M.S., F.R.C.S., Assistant Surgeon and Lecturer on Surgical Anatomy in St. George's Hospital, London, England. I am deeply indebted to Dr. J. Ackworth Menzies, Lecturer on Physiology, and to Drs. J. Dunlop Lickley and J. C. Boileau Grant, Demonstrators of Anatomy in this University. Dr. Menzies revised the histological part of the book, and furnished a number of microscopic preparations for drawings. Dr. Lickley helped to revise the text, arranged the chapter on Surface Anatomy and Surface jNIarkings, and passed the book through the press. Dr. Grant prepared the dissections for the new illustrations and assisted in the revision of the text. I am also indebted to that skilled anatomical artist Mr. Sydney T. Sewell, who made the drawings for the new illustrations and who spared no pains to produce clear and accurate figures. ROBERT HOWDEN. University of Durham College of Medicine, Newcastle-upon-Tyne, 1913. Digitized by the Internet Archive in 2010 with funding from Open Knowledge Commons http://www.archive.org/details/anatomydescripti1913gray PUBLISHPJRS' NOTE. Books, like men, have characters that can be analyzed to a certain point, but beyond or below lies a quality, subtle as life, and incapable of analysis or imitation, which is called personality. The greater the author, and the more intense his mental action in creating his book, the more it partakes of this element. This principle, so clear as to be almost axiomatic, is illustrated to the fullest extent in the work in hand. Henry Gray combined two faculties, either one sufficient to make his name famous. He was a great anatomist and a great teacher. He possessed a thorough knowledge of anatomy and an equal insight into the best methods of imparting it to other minds. His text was unequalled in clearness, and he united with it a series of incomparable illustrations. He devised the method of engraving the names of the parts directly upon them, thereby exliibiting at a glance not only their nomenclature, but also their position, extent, and relations. His work, still unique in this respect, was also the first to employ colors. Summing all, it is hardly to be wondered at that students and teachers alike find their labors reduced and the permanence of knowledge increased by the use of this book. On its original appearance, over half a centur}' ago, Gray immediately took the leading place, and it has not only maintained its position in its own subject, but has also become the best-known work in all medical literature. It is incomparably the greatest text-book in medicine, measured by the number of students who use it, and it is unique also in being the one work which is certain to be carried from college to afford guidance in the basic questions underlying practice. The consequent demand is evidenced in the number of editions, which collec- tively represent the labors of many of the leading anatomists since the early death of its talented author. In this new revision every line has been carefully considered, any possible obscurity has been clarified, the latest accessions to anatomical knowledge have been introduced, and much has been rewritten. Care has been exercised to make the text a homogeneous, sequential, and complete presentation of the subject, meeting every need of the student, physician, or surgeon. As directions are given for dissecting, this volume will serve every requirement of the student throughout his course. The Basle Anatomical Nomenclature in English has been used in the text and on the engravings, this being preferable to the Latin form in the judgment of such eminent anatomists as Professor Howden and Professor ^Nlall. A Glossary exhibiting the three accepted nomenclatures in parallel columns will be found a great convenience. The Table of Contents is so arranged as to give a complete conspectus of anatomy, a feature of obvious value. The whole book is thoroughly'- organized in its headings and the sequence of subjects, so that the student receives his knowledge of the parts in their anatomical dependence. As a teaching instrument the new Gray's Anatomy embodies all that careful thought and unstinted expenditure can combine in a text-book. CONTENTS. HISTOLOGY. The Animal Cell. Protoplasm Nucleus .... Reproduction of Cells Prophase Metaphase . Anaphase Telophase Epithelium. Pavement Epi- Simple Epithelium . Simple Squamous thelium Columnar or Cylindrical Epithelium Glandular Epithelium .... Ciliated Epithelium Stratified Epithelium Transitional Epithelium Connective Tissue. The Connective Tissues Proper .... Areolar Tissue Adipose Tissue White Fibrous Tissue Yellow Elastic Tissue Mucous Tissue Retiform or Reticular Tissue Basement Membranes Vessels and Nerves of Connective Tissue Pigment Applied Anatomy Development of Connective Tissue . 33 34 34 35 36 36 36 37 37 37 37 37 39 40 40 40 42 43 44 44 44 45 46 46 46 47 Cartilage Hyaline Cartilage White Fibrocartilage .... Yellow or Elastic Fibrocartilage Bone Structure and Physical Properties Periosteum Marrow Vessels and Nerves of Bone . Ossification Applied Anatomj- The Circulating Fluids. Blood General Composition of the Blood Lymph The Muscular Tissue. Striped or Voluntary Muscle .... Vessels and Nerves of Striped Muscle Unstriped Plain or Involuntary Muscle . Cardiac Muscular Tissue . . . . Development of Muscle Fibres 47 47 49 50 50 50 51 51 52 56 59 61 61 64 64 67 67 68 69 The Nervous Tissue. Neuroglia 70 Nerve Cells 70 Nerve Fibres 73 Wallerian Degeneration 76 Non-medullated Fibres 76 EMBRYOLOGY. The Ovum. Yolk ...... Germinal Vesicle Coverings of the Ovum Maturation of the Ovum The Spermatozoon Fertilization of the Ovum Segmentation of the Fertilized Oviun. The Formation of the Primitive Streak Mesoderm Ectoderm Entoderm Mesoderm . The Neural Groove and Tube The Notochord . The Primitive Segments Separation of the Embryo 92 The Yolk-sac .... 93 Development of the Fetal Membranes and Placenta. The Allantois 93 The Amnion 94 The Umbilical Cord and Body-stalk ... 96 Implantation or Imbedding of the Ovum . 97 The Decidua • 98 The Chorion 99 The Placenta 100 Fetal Portion 100 Maternal Portion 100 Separation of the Placenta . 101 Development of the Parieties. The Skeleton 102 The Vertebral Column 102 The Ribs 104 12 CONTENTS The Skeleton— The Sternum 105 The Skull 105 The Nose and Face Ill The Limbs 113 Development of the Joints 115 Development of the Muscles 116 Development of the Skin, Glands, and Soft Parts . . . . 116 Development of the Nervous System and Sense Organs. The Medulla Spinalis The Spinal Nerves The Brain The Rhombencephalon or Hind-brain The Mesencephalon or Mid-brain . The Prosencephalon or Fore-brain . The Diencephalon The Telencephalon The Cerebral Nerves . The Sympathetic System Chromaffin Organs The Suprarenal Glands The Nose .... The Eye The Ear Development of the Valvular System. Further Development of the Heart The Valves of the Heart . Further Development of the Arteries The Anterior Ventral Aortse . The Aortic Arches The Dorsal Aortse . . . Further Development of the Veins The Visceral Veins The Parietal Veins Inferior Vena Cava 117 119 120 122 125 125 126 127 132 133 133 134 134 134 138 145 151 152 152 153 154 155 155 157 157 Peculiarities of the Fetal Heart .... 161 The Lymphatic Vessels 161 Developmejit of the Digestive and Respiratory Apparatus. The Digestive Tube The Mouth . . The Salivary Glands The Tongue . . The Thyroid Gland The Palatine Tonsils The Thymus . . The Parathyroid Bodies The Hjrpophysis Cerebri Further Development of the Tube The Rectum and Anal Canal The Liver The Pancreas .... The Spleen The Respiratory Organs D igestive Developinent of the Body Cavities 162 163 164 164 165 165 165 166 166 168 172 174 175 176 176 178 Development of the Urinary and Generative Organs. The The The The The The The The The and Pronephros and Wolffian Duct . Mesonephros, Miillerian Duct, Genital Glands Ovary Testis Descent of the Testes Descent of the Ovaries ... Metanephros and the Permanent Kidney Urinary Bladder .... Prostate External Organs of Generation Urethra 180 180 184 186 186 187 187 188 189 190 190 The Form of the Embryo at Different Stages of its Growth . . . : . .191 OSTEOLOGY. Long Bones . Short Bones . Flat Bones . Irregular Bones . Surfaces of Bones The Vertebral Column. General Characteristics of a Vertebra. The Cervical Vertebrae The First Cervical Vertebra . The Second Cervical Vertebra The Seventh Cervical Vertebra The Thoracic Vertebra The First Thoracic Vertebra The Ninth Thoracic Vertebra The Tenth Thoracic Vertebra The Eleventh Thoracic Vertebra The Twelfth Thoracic Vertebra The Lumbar Vertebrae The Fifth Lumbar Vertebra . The Sacral and Coccygeal Vertebrae The Sacrum The Coccyx • Ossification of the Vertebral Column The Vertebral Column as a Whole. Curves Surfaces 198 199 200 201 201 203 204 204 204 204 204 205 205 206 209 210 212 213 195 Base .... 196 Vertebral Canal 196 Applied Anatomy 196 196 The Thorax. Boundaries The Sternum Manubrium Body Xiphoid Process The Ribs Common Characteristics of the Ribs Peculiar Ribs First Rib Second Rib Tenth Rib Eleventh and Twelfth Ribs The Costal Cartilages .... Applied Anatomy The Skull. The Cranial Bones. The Occipital Bone The Squama Lateral Parts Basilar Parts The Parietal Bone 214 214 214 216 216 216 218 220 220 221 223 223 224 224 224 224 225 227 227 229 230 231 The Frontal Boue Sqiuiiua .... Orbital or Horizontal Par The Temporal Bone The Squama Mastoid Portion Petrous Portion Tympanic Part Styloid Process The Sphenoidal Bone . Body The Great Wings . The Small ^^■in!J:s . Pterygoid Processes The Sphenoidal Concha? Ethmoidal bono Crihrifonu plate Pcrpciulicular Plate Lal)\ rinth or Lateral Mass Sutural or Wormian Bones Applied Anatomy The Facial Bones. The Nasal Bones The Maxillte (Upper Jaw) The Maxillary Sinus or Antrum of High- more 259 The Zygomatic Process 260 The Frontal Process 260 The Alveolar Process 260 The Palatine Process 260 Changes Produced in the Maxilla by Age 262 The Lacrimal Bone 263 The Zygomatic Bone 263 The Palatine Bone 265 The Horizontal Part 266 The Vertical Part .266 The Pyramidal Process or Tuberosity . 267 The Orbital Process 267 The Sphenoidal Process 268 The Inferior Nasal Concha 268 The Vomer 269 Applied Anatomy 271 The Mandible (Lower Jaw) . . . . .271 Changes Produced in the Mandible by A-e 275 The Hyoid Bone 275 Applied Anatomy 277 CONTENTS . 233 The Scapula . 234 The Spine . 235 The Acromion .... . 237 The Coracoid Process . 237 Applied Anatomy . . 239 The Humerus 241 Upi)er Extremity . 243 The Head . . . ■ 244 The Anatomical Neck . 245 The Greater Tubercle 24G The Lesser Tubercle . 248 The Body or Shaft . 249 The Lower Extremity . 250 Applied Anatomy . 250 The Ulna . 251 The Upper Extremity 252 The Olecranon . 252 The Coronoid Process 253 The Semilunar Notch 255 The Radial Notch . 255 The Body or Shaft . . The Lower Extremity The Radius The Upper Extremity 255 The Body or Shaft . . . 256 The Lower Extremity 13 304 306 306 307 309 309 309 309 309 309 309 311 312 313 314 315 315 315 315 318 318 318 319 320 320 321 The Exterior of the Skull. Norma Verticalis .... Norma Basalis Norma Lateralis .... The Temporal Fossa . The Infratemporal Fossa The Pterygopalatine Fossa Norma Occipitalis .... Norma Frontalis ... The Orbits . . . The Interior of the Skull. Inner Surface of the Skull-cap Under Surface of the Base of the Skull The Anterior Fossa The Middle Fossa The Posterior Fossa The Nasal Cavities Anterior Nasal Aperture Differences in the Skull Due to Age Sexual Differences in the Skull Craniology . .- . Applied Anatomy .... The Extremities. The Bones of the Uj^per Extremity. The Clavicle The Sternal Extremity .... The Acromial Extremity .... Applied Anatomy 277 278 281 282 283 284 284 285 286 288 288 288 290 291 292 294 294 295 Applied Anatomy of the Ulna and Radius 321 The Hand. The Carpus 323 Common Characteristics of the Carpal Bones 323 Bones of the Proximal Row .... 323 The Naviculaj- Bone .... 323 The Lunate Bone 323 The Triangular Bone .... 324 The Pisiform Bone 326 Bones of the Distal Row .... 326 The Greater Multangular Bone 326 The Lesser Multangular Bone . 327 The Capitate Bone 327 The Hamate Bone 328 The Metacarpus 329 Common Characteristics of the Meta- carpal Bones 329 Characteristics of the Individual Meta- carpal Bones 329 The First Metacarpal Bone 329 The Second Metacarpal Bone . 329 The Third Metacarpal Bone 330 The Fourth Metacarpal Bone . 330 The Fifth Metacarpal Bone 330 The Phalanges of the Hand 331 Ossification of the Bones of the Hand . 331 Applied Anatomy of the Bones of the Hand 332 The Bones of the Lower Extremity. The Hip Bone . The Ilium . The Body The Ala The Ischium The Body The Superior Ramus The Inferior Ramus The Pubis .... The Body . . The Superior Ramus The Inferior Ramus The Acetabulum . The Obturator Foramen The Pelvis 295 i The Greater or False Pelvis 297 ; The Lesser or True Pelvis Axes Position of the Pelvis Differences- between Male and Pelves Applied Anatomy . The Femur 301 : The Upper Extremity 303 ' The Head 303 ! The Neck .... 303 ' The Trochanters . Female 333 333 333 333 336 336 337 337 337 337 337 338 339 339 340 340 340 342 342 343 344 345 345 345 345 346 14 CONTENTS The Femur — The Bodv or Shaft, 348 The Lower Extremity 349 Applied Anatomy 352 The PateUa 354 Applied Anatomy 355 The Tibia 355 The Upper Extremity 355 The Body or Shaft 356 The Lower Extremity 358 The Fibula 359 The Upper Extremity or Head . 359 The Body or Shaft 359 The Lower Extremity or Lateral Malleolus 360 Applied Anatomy of the Tibia and Fibula 361 The Foot. The Tarsus . . The Calcaneus 362 362 The Tarsus— The Talus The Cuboid Bone The Navicular Bone The First Cuneiform Bone The Second Cuneiform Bone The Third Cuneiform Bone . The Metatarsus Common Characteristics of the Meta tarsal Bones Characteristics of the Individual Meta tarsal Bones The First Metatarsal Bone . The Second Metatarsal Bone The Third Metatarsal Bone The Fourth Metatarsal Bone . The Fifth Metatarsal Bone The Phalanges of the Foot Ossification of the Bones of the Foot Comparison of the Bones of the Hand and Foot Applied Anatomy of the Bones of the Foot The Sesamoid Bones 366 367 368 369 369 370 371 371 371 371 372 372 372 372 373 374 375 375 376 SYXDESMOLOGY. Bone 379 Articular Cartilage 375 Ligaments 379 Classification of Joints. Synarthrosis 380 Sutura 380 Schindylesis 381 Gomphosis 381 Synchondrosis 381 Amphlarthrosis 381 Diathrosis 381 Ginglimus 382 Trochoid 382 Condyloid 382 Articulation by Reciprocal Reception . 382 Enarthrosis 382 Arthrodia 382 The Kind of Movement Admitted in Joints. Gliding Movement 383 Angular Movement 383 Circumduction 383 Rotation 383 Ligamentous Action of Muscles .... 383 Applied Anatomy 383 Articulations of the Trunk. Articulations of the Vertebral Column . Articulations of Vertebral Bodies The Anterior Longitudinal Liga- ment The Posterior Longitudinal Liga ment The Intervertebral Fibrocartilages Structure Applied Anatomy .... Articulations of Vertebral Arches The Articular Capsules . The Ligamenta Flava The Supraspinal Ligament . The Ligamentum Nuchae The Interspinal Ligaments . The Intertransverse Ligaments Articulation of the Atlas with the Epistro pheus or Axis The Articular Capsules .... The Anterior Atlantoaxial Ligament The Posterior Atlantoaxial Ligament The Transverse Ligament of the Atlas 384 384 384 385 385 386 386 386 386 386 387 387 387 387 388 389 389 389 389 Articulations of the Vertebral Column with the Cranium Articulation of the Atlas with the Occipital Bone The Articular Capsules ... The Anterior Atlantooccipital Mem- brane The Posterior Atlantooccipital Mem- brane The Lateral Ligaments .... Ligaments Connecting the Axis with the Occipital Bone The Membrana Tectoria The Alar Ligaments Articulation of the Mandible The Artictdar Capsule The Temporomandibular Ligament The Sphenomandibular Ligament The Articular Disk The Stylomandibular Ligament . Applied Anatomy Costovertebral Articulations Articulations of the Heads of the Ribs . The Articular Capsule .... The Radiate Ligament .... The Interarticular Ligament Costotransverse Articulations The Articular Capsule .... The Anterior Costotransverse Liga- ment The Posterior Costotransverse Liga- ment The Ligament of the Neck of the Rib The Ligament of the Tubercle of the Rib Sternocostal Articulations The Articular Capsules The Radiate Sternocostal Ligaments The Interarticular Sternocostal Liga- ment The Costoxiphoid Ligaments Interchondral Articulations . Costochondral Articulations .... Articulation of the Manubrium and Body of the Sternum Mechanism of the Thorax . . . Articulation of the Vertebral Column with the Pehris The Iliolumbar Ligament Articulations of the Pehas Sacroiliac Articulation The Anterior Sacroiliac Ligament The Posterior Sacroiliac Ligament The Interosseous Sacroiliac Liga ment 392 392 392 392 392 392 393 393 393 393 394 394 395 395 395 396 396 396 396 396 397 397 398 398 398 399 399 399 399 399 400 401 401 401 401 401 403 404 404 404 404 404 404 CONTENTS 15 Articulations of the Pelvis — ■ Ligaments Connecting the Sacrum and Ischium 404 The Sacrotuberous Ligament 404 The Sacrospinous Ligament 405 Sacrococcygeal Symphysis .... 406 The Anterior Sacrococcygeal Liga- ment 406 The Posterior Sacrococcygeal Liga- ment 406 The Lateral Sacrococcygeal Liga- ment 406 The Interarticular Ligaments . 406 The Pubic Symphysis 406 The Anterior Pubic Ligament 407 The Posterior Pubic Ligament . 407 The Superior Pubic Ligament . 407 The Arcuate Pubic Ligament 407 The Interpubic Fribrocartilaginous Lamina 407 Mechanism of the Pelvis 408 Articulations of the Upper Extremity. Liga Sternoclavicular Articulation The Articular ("apsule The Anterior Sternoclavicular Ligament The Posterior Sternoclavicular Liga- ment The Intercla\'icular Ligament The Costoclavicular Ligament The Articular Disk . . . Applied Anatomy .... Acromioclavicular Articulation The Articular Capsule The Superior AcromioclaAdcul^r Liga ment The Inferior Acromiocla'vdcular ment The Articular Disk .... The CoracoclaAdcular Ligament . The Trapezoid Ligament The Conoid Ligament Applied Anatomy The Ligaments of the Scapula The Coracoacromial Ligament The Superior Transverse Ligament The Inferior Transverse Ligament Humeral Ai-ticulation or Shoulder-joint The Articular Capsule The Coracohumeral Ligament Glenohumeral Ligaments The Transverse Humeral Ligament The Glenoidal Labrum Bursae Applied Anatomy . Elbow-joint The Anterior Ligament The Posterior Ligament The Ulnar Collateral Ligament . The Radial Collateral Ligament Applied Anatomy Radioulnar Articulation Proximal Radioulnar Articulation The Annular Ligament . Applied Anatomy .... Middle Radioulnar Union The Oblique Cord .... The Interosseous Membrane Distal Radioulnar Articulation . The Volar Radioulnar Ligament The Dorsal Radioulnar Ligament The Articular Disk .... Radiocarpal Articulation or Wrist-joint . The Volar Radiocarpal Ligament The Dorsal Radiocarpal Ligament . The Ulnar Collateral Ligament . The Radial Collateral Ligament Applied Anatomy Intercarpal Articulations Articulations of the Proximal Row of Carpal Bones .... The Dorsal Ligaments . The Volar Ligaments The Interosseous Ligaments 409 410 410 410 410 410 410 411 411 411 411 412 412 412 412 412 413 413 413 413 413 414 414 415 415 415 415 415 417 418 418 418 418 419 421 422 422 422 423 423 423 423 423 424 424 424 425 426 426 426 426 426 427 427 427 427 427 Intercarpal Articulations — Articulations of the Distal Row of Carpal Bones . . The Dorsal Ligaments The Volar Ligaments The Interosseous Ligaments Articulations of the Two Rows of Carpal Bones with Each Other The V'olar Ligaments The Dorsal Ligaments The Collateral Ligaments Carpometacarpal Articulations Carpometacarpal Articulation of the Trunk Articulations of the Other Four Meta- carpal Bones with the Carpus The Dorsal Ligaments The Volar Ligaments The Interosseous Ligaments Intermetacarpal Articulations The Transverse Metacarpal Ligament Metacarpophalangeal Articulations The Volar Ligaments The Collateral Ligaments Articulations of the Digits .... 427 427 427 427 427 428 428 428 429 429 429 429 429 429 430 430 430 430 430 431 Articulations of the Lower Extremity. Coxal Articulation or Hip-joint .... 432 The Articular Capsule 432 The Iliofemoral Ligament .... 433 The Pubocapsular Ligament 433 The Ischiocapsular Ligament 433 The Ligamentum Teres Femoris 434 The Glenoidal Labrum 434 The Transverse Acetabular Ligament 434 Applied Anatomy 437 The Knee-joint 438 The Articular Capsule 438 The Ligamentum Patellae .... 439 The Oblique Popliteal Ligament 439 The Tibial Collateral Ligament ... 439 The Fibular Collateral Ligament 440 The Cruciate Ligaments 441 The Anterior Cruciate Ligament . 441 The Posterior Cruciate Ligament . 441 The Menisci 441 The Medial Meniscus .... 442 The Lateral Meniscus .... 442 The Transverse Ligament .... 442 Bursas 443 Applied Anatomy 446 Articulations between the Tibia and Fibula. 447 Tibiofibular Articulation .... 448 The Articular Capsule .... 448 The Anterior Ligament .... 448 The Posterior Ligament 448 Interosseous Membrane 448 Tibiofibular Syndesmosis .... 448 The Anterior Ligament .... 448 The Posterior Ligament . . 448 The Inferior Transverse Ligament 449 The Interosseous Ligament 449 Talocrural Articulation or Ankle-joint 449 The Articular Capsule 449 The Deltoid Ligament 450 The Anterior Talofibular Ligament 450 The Posterior Talofibular Ligament . 451 The Calcaneofibular Ligament 451 Applied Anatomy 452 Intertarsal Articulations 452 Talocalcaneal Articulation .... 452 The Articular Capsule .... 452 The Anterior Talocalcaneal Liga- ment 452 The Posterior Talocalcaneal Liga- ment 453 The Lateral Talocalcaneal Liga- ment 453 The Medial Talocalcaneal Liga- ment 453 The Interosseous Talocalcaneal Ligament 453 Talocalcaneona\"icular Articulation . 454 16 CONTENTS Intertarsal Articulations — Talocalcaneonavicular Articulat ion — The Articular Capsule .... The Dorsal Talonavicular Ligament Calcaneocuboid Articulation The Articular Capsule The Dorsal Calcaneocuboid Liga- ment The Bifurcated Ligament The Long Plantar Ligament The Plantar Calcaneocuboid Liga ment The Ligaments Connecting the Calca- neus and Navicular Tile Plantar Calcaneonavicular Ligament Applied Anatomy Cuneonavicular Articulation The Dorsal Ligaments The Plantar Ligaments . Cuboideonavicular Articulation . The Dorsal Ligament The Plantar Ligament 454 454 454 454 454 454 454 454 455 455 456 456 456 456 457 457 457 Intertarsal Articulations Cuboideonavicular Articulation — The Interosseous Ligament Intercuneiform and (Juncocuboid Art lation The Dorsal Ligaments The Plantar Ligaments . The Interosseous Ligaments Applied Anatomy Tarsometatarsal Articulations The Dorsal Ligaments The Plantar Ligaments The Interosseous Ligaments . Intermetatarsal Articulations . The Dorsal Ligaments The Plantar Ligaments . The Interosseous Ligaments . The Transverse Metatarsal Ligament Metatarsophalangeal Articulations The Plantar Ligaments . The Collateral Ligaments Articulations of the Digits Arches of the Foot 457 457 457 457 457 457 457 457 458 458 458 458 458 458 458 459 459 459 459 459 MYOLOGY. Applied Anatomy of Muscles 462 Tendons, Aponeuroses, and Fascice. Tendons . Aponeuroses Fasciae 463 463 463 The Fasciae and Muscles of the Head. The Muscles of the Scalp. Dissection 464 The Skin of the Scalp 465 The Superficial Fascia 465 Epicranius 465 Occipitalis ... .... 446 Frontalis 466 Galea Aponeurotica ... 466 Applied Anatomy 466 The Muscles of the Eyelid. Dissection Orbicularis Oculi Corrugator . The Muscles of the Nose. Procerus Nasalis Depressor Septi Dilator Naris Posterior Dilator Naris Anterior The Muscles of the Mouth. Dissection Quadratus Labii Superioris Caninus Zygomaticus Mentalis Quadratus Labii Inferioris Triangularis Buccinator Relations Pterygomandibular Raphe Orbicularis Oris .... Risorius 467 467 468 469 469 469 469 469 469 469 470 470 470 470 470 470 470 471 471 472 Masseter — Relations .... Temporal Fascia Dissection Temporalis Relations .... Dissection .... Pterygoideus Externus Relations . Pterygoideus Internus Relations . The Muscles of Mastication. 472 473 473 473 473 474 474 474 474 474 The Fascia and Muscles of the Antero- LATERAL REGION OF THE NecK. The Superficial Cervical Muscle. Dissection Superficial Fascia Platysma The Lateral Cervical Muscles. The Fascia Colli . . Applied Anatomy . Sternocleidomastoideus Triangles of the Neck Relations . . . . Applied Anatomy . The Supra- and Infrahyoid Muscles. Dissection Digastricus . Relations Stylohyoideus The Stylohyoid Mylohyoideus Relations Dissection . Geniohyoideus Dissection Sternohyoideus . Sternothyreoideus Thyreohyoideus Omohyoideus The Anterior Vertebral Muscles. Ligament Parotideomasseteric Fascia Masseter Longus Colli Longus Capitis . 472 i Rectus Capitis Anterior 472 ! Rectus Capitis Lateralis 475 475 475 476 478 478 478 478 479 480 480 481 481 481 481 481 481 481 482 482 482 482 482 483 484 484 484 CONTENTS 17 The Lateral Vertebral Muscles. Scalenus Anterior Relations Scalenus Medius Relations Scalenus Posterior 484 484 484 485 485 The Fasci-k and Muscles of the Trunk. The Deep Muscles of the Back. Dissection of the Muscles of the Back by Layers 485 The Lumbodorsal Fascia 486 Splenius Capitis 486 Splenius Cervicis 487 Sacrospinalis 488 Iliocostalis Lumborum Iliocostalis Dorsi . Iliocostalis Cervicis Longissimus Dorsi Lougissimus Cervicis . . . 488 Longissimus Capitis . 489 Spinalis Dorsi .... 489 Spinalis Cervicis . . ... 489 Spinalis Capitis . . 489 Semispinalis Dorsi .... 489 Semispinalis Cervicis 489 Semispinalis Capitis 489 Multifidus 489 Rotatores 490 Interspinales 490 Extensor Coccygis 490 Intertransversarii 490 The Suboccipital Muscles. Rectus Capitis Posterior Major .... 491 Rectus Capitis Posterior Minor .... 491 Obliquus Capitis Inferior 491 Obliquus Capitis Superior 491 The Suboccipital Triangle 491 Applied Anatomj' 492 1 The Muscles of the Thorax. \ Intercostal Fascia 492 j Intercostales 492 1 Intercostales Externi 492 Intercostales Interni 492 i Subcostales 492 Transversus Thoracis 492 Levatores Costarum 493 : Serratus Posterior Superior 493 Serratus Posterior Inferior 493 Diaphragma 493 i Medial Lumbocostal Arch 495 ; Lateral Lumbocostal Arch .... 495 ' The Crura 495 The Central Tendon 495 Openings in the Diaphragma 495 ! Relations 496 I Mechanism of Respiration 497 i The Muscles and Fasciae of the Abdomen. The Antero-lateral Muscles of the Abdomen 498 Dissection 498 The Superficial Fascia 49S Obliquus Externus Abdominis . 499 Aponeurosis of the Obliquus Externus Abdominis . 499 Subcutaneous Inguinal Ring . 500 The Inter crural Fibres 501 The Inguinal Ligament 501 The Lacunar Ligament 502 The Reflected Inguinal Liga- ment .-502 Ligament of Cooper 502 Dissection 503 Obliquus Internus Abdominis 503 Cremaster 504 Dissection 504 Tlie Antero-lateral Muscles of the Abdomen— Transversus Abdominis 504 Inguinal Aponeurotic Falx 505 Dissection 505 Rectus Al)doniinis 506 Pyrainidalis 507 The Linca Alba ... 507 The Lineac Semilunarcs 507 The Transversalis Fascia ... 508 The Abdominal Inguinal Ring 508 The Inguinal Canal 508 Extraperitoneal Connective Tissue . 509 The Deep Crural Arch 509 The Posterior Muscles of the Abdomen . 510 The Fascia Covering the Quadratus Lumborum 510 Quadratus Lumborum 510 The Muscles and Fascice of the Pelrt Pelvic Fascia Levator Ani . Relations Coccygeus The Muscles and Fascice of the Perineum 510 513 514 514 Muscles of the Anal Region 515 The Superficial Fascia 515 The Deep Fascia 515 Ischiorectal Fossa 515 Applied Anatomy 516 The Corrugator Cutis Ani 516 Sphincter Ani Externus 516 Sphincter Ani Internus 516 The Muscles of the Urogenital Region in the Male 517 Superficial Fascia 517 The Central Tendinous Point of the Perineum 518 Bulbocavernosus 518 Ischiocavernosus 518 The Deep Fascia 519 Transversus Perinaei Profundus 520 Sphincter Urethrae Membranaceae . 520 The Muscles of the Urogenital Region in the Female 520 Transversus Perinaei Superficialis 520 Bulbocavernosus 520 Ischiocavernosus 521 Transversus Perinaei Profundus 521 The Fascia and Muscles of the Upper Extremity. The Muscles Connecting the Upper Extreinity to the Vertebral Column. Superficial Fascia Deep Fascia Trapezius Latissimus Dorsi Rhomboideus Major Rhomboideus Minor Levator Scapulae 522 522 522 524 525 525 525 The Muscles Connecting the Upper Extremity to the Anterior and Lateral Thoracic Walls. Dissection of Pectoral Region and Axilla Superficial Fascia Applied Anatomy Pectoralis Major Relations Dissection Coracoclavicular Fascia Pectoralis Minor Relations Subclavius Relations Serratus Anterior Relations Applied Anatomy 525 526 526 526 528 528 528 528 528 528 529 529 530 530 18 CONTENTS The Muscles and Fasciae of (he Shoulder. The Dissection 530 Deep Fascia 530 Deltoideus 530 Relations 531 Applied Anatomy 531 Dissection 531 Subscapular Fascia 531 Subscapularis 531 Dissection 532 Supraspinatous Fascia 532 Supraspinatus 532 Infraspinatous Fascia 533 Infraspinatus 533 Teres Minor 533 Teres Major 533 The Muscles and Fasciae of the Arm. Dissection 533 Brachial Fascia 534 Coracobrachialis 534 Relations 534 Biceps Brachii 534 Relations 535 Brachialis 535 Relations 535 Applied Anatomy 535 Triceps Brachii 535 Applied Anatomy 536 The Muscles and Fascia of the Forearm. Dissection 536 Antibrachial Fascia ' 536 The Volar Antibrachial Muscles .... 537 The Superficial Group 537 Pronator Teres 537 Applied Anatomy .... 537 Flexor Carpi Radialis .... 537 Palmaris Longus 538 Flexor Carpi Ulnaris ... 539 Flexor Digitorum Sublimis 539 The Deep Group 539 Dissection 539 Flexor Digitorum Profundus . . 540 Fibrous Sheaths of the Flexor Tendons 540 Flexor Pollicis Longus 540 Pronator Quadratus 540 The Dorsal Antibrachial Muscles .... 542 The Superficial Group 542 Dissection 542 Brachioradialis 542 Extensor Carpi Radialis Longus . 542 Extensor Carpi Radialis Brevis 542 Extensor Digitorum Communis 544 Extensor Digiti Quinti Proprius 544 Extensor Carpi Ulnaris .... 544 Anconaeus 544 The Deep Group 544 Supinator 544 Abductor Pollicis Longus 545 Extensor Pollicis Brevis 545 Extensor Pollicis Longus 545 Extensor Indicis Proprius 546 Applied Anatomy 546 The Muscles and Fasciae of the Hand. Dissection 546 Volar Carpal Ligament 547 Transverse Carpal Ligament 547 The Mucous Sheaths of the Tendons on the Front of the Wrist 548 Dorsal Carpal Ligament 550 The Mucous Sheaths of the Tendons on the Back of the Wrist 550 ! Palmar Aponeurosis 550 The Applied Anatomy 551 | The Lateral Volar Muscles 552 Abductor Pollicis Brevis 552 Opponens Pollicis 553 Flexor Pollicis Brevis 553 The Lateral Volar Muscles — Adductor Pollicis (Obliquus) Adductor Pollicis (Transversus) The Medial Volar Muscles Palmaris Brevis Abductor Digiti Quinti Flexor Digiti Quinti Brevis Opponens Digiti Quinti The Intermediate Muscles Lumbricales .... Interossei Interossei Dorsales Interossei Volares Applied Anatomy of the Muscles Upper Extremity .... of the 554 554 554 554 554 554 555 555 555 555 555 556 556 The Muscles and Fascia of the Lower Extremity. The Muscles and Fasciae of the Iliac Region. Dissection 559 The Fascia Covering the Psoas and Iliacus 559 Psoas Major 560 Relations 561 Psoas Minor 561 Iliacus 561 Relations 561 Applied Anatomy 562 The The The Muscles and Fascice of the Thigh. Anterior Femoral Muscles Dissection . Superficial Fascia . Deep Fascia The Fossa Ovalis . Tensor Fasciae Latae Sartorius Relations . Quadriceps Femoris Rectus Femoris Vastus Lateralis Vastus Medialis Vastus Intermedins Articularis Genu . Applied Anatomy Medial Femoral Muscles Dissection . Gracilis .... Pectineus Relations . Adductor Longus . Relations . Adductor Brevis Relations . Adductor Magnus Relations . Applied Anatomy . Muscles of the Gluteal Region Dissection . Glutaeus Maximus BurssB . Relations . Dissection . Glutaeus Medius . Glutaeus Minimus Piriformis Relations . Obturator Membrane Dissection . Obturator Internus Relations . Gemelli .... Gemellus Superior Gemellus Inferior Quadratvis Femoris Obturator Externus Posterior Femoral Muscles Dissection . Biceps Femoris Semitendinosus Semimembranosus Applied Anatomy . 562 562 562 563 564 565 565 565 565 565 566 566 566 566 567 567 567 567 567 567 567 567 568 568 568 569 569 569 569 569 570 570 570 570 570 571 571 572 572 572 573 573 573 573 573 573 574 574 574 575 575 575 CONTEXTS 19 The Muscles and Fascia: of the Log. The Anterior Crural Muscles 570 Dissection ... 576 Deep Fascia . . 57G Dissection 570 Tibialis Anterior 570 Extensor Hallucis Longus 577 Extensor DiKitorum Longus 577 Peronaeus Tertius . . 57s The Posterior Crural Muscles 578 Dissection 578 The Superficial Group 578 Gastrocnemius 578 Relations 578 Soleus 579 Relations. 579 Tendo Calcaneus 579 Plantaris 579 The Deep Group ... 579 Dissection .... 579 Deep Transverse Fascia 580 Dissection .... 581 Popliteus 581 Relations. 581 Flexor Hallucis Longus . 581 Relations 581 Flexor Digitorum Longus 581 Relations 582 Tibialis Posterior 582 Relations . 582 The Lateral Crural Muscles 582 Dissection .... 582 Peronaeus Longus . 582 Peronaeus Bre\'is . 583 Applied Anatomy . 583 The Fascia: Around the Ankle. Transverse Crural Ligament 584 Cruciate Crural Ligament 584 Laciniate Ligament 585 Peroneal Retinacula . . 585 Th(! Mucous Slieaths of the Tendons Around llu! Ankle 586 The Muscles and Fascia; uf (he Fool. The Dorsal Muscle of the Foot 586 Extensor Digitorum Brevis 580 The Plantar Muscles of the Foot 580 Plantar Aponeurosis 580 The First Layer 587 . Dissection . . 587 Abductor Hallucis 587 Flexor Digitorum Brevis 588 Fibrous Sheaths of the Flexor Tendons 588 Abductor Digiti Quinti . 588 Dissection 588 The Second Layer 589 Quadratus Plantae 589 Lumbricales 589 Dissection 589 The Third Layer 589 Flexor Hallucis Brevis ... 589 Adductor Hallucis 589 Flexor Digiti Quinti Brevis 590 The Fourth Layer 590 Interossei 590 Interossei Dorsales .... 591 Interossei Plantares .591 Applied Anatomy of the Muscles of the Lower Extremity 592 ANGIOLOGY. Structure of Arteries Capillaries . Sinusoids Structure of Veins . The Thoracic Cavity. The Cavity of the Thorax . . . The Upper Opening of the Thorax The Lower Opening of the Thorax The Pericardium. Structure of the Pericardium . Applied Anatomy The Heart. Size Component Parts 596 Right Atrium . 606 598 Sinus Venarum . 606 599 Auricula . 606 599 Dissection . 607 Right Ventricle . 608 Dissection . 609 Left Atrium . . 610 Auricula . 610 60n Dissection . 611 001 Left Ventricle . 611 001 Ventricular Septum 612 Structure of the Heart . 613 Applied Anatomy 614 The Cardiac Cvcle and the . Vctiont ot the 601 Valves . 615 603 Applied Anatomy . 615 Peculiarities in the Vascular Systein in the Fetus. 604 Fetal Circulation 616 604 Changes in the Vascular System at Birth 618 THE ARTERIES. Applied Anatomy The Pulmonary Artery Relations Applied Anatomj' . 619 620 620 621 The Arch of the Aorta. The Aorta. The Ascending Aorta. Relations Branches The Coronary Arteries Right Coronarj^ Arterj- Left Coronary Artery Applied Anatomy Relations . . . . Applied Anatomj^ . The Innominate Artery Relations Branches Thj'reoidea Ima Applied Anatomy . 023 024 025 025 025 626 626 622 The Arteries of the Head and Neck. 622 622 The Common Carotid Artery. 622 623 Relations 627 623 Pecuharities 628 20 CONTENTS Applied Anatomy . 629 The External Carotid Artery .... . 630 Relations . 630 Applied Anatomy . 630 Branches 630 Superior Thyroid Artery . 631 Relations 631 Branches . 631 Applied Anatomy . 631 1 Lingual Artery . 631 Relations . 632 Branches 632 1 Applied Anatomy . 632 External Maxillary Artery . . 633 Relations . 633 Branches . 634 Peculiarities . . 635 Applied Anatomy . 635 Occipital Artery . 635 Course and Relations . 635 Branches . 636 Posterior Auricular Artery . . 636 Branches . 636 Ascending Pharyngeal Artery . 637 Branches .... . 637 Applied Anatomy . 637 Superficial Temporal Artery 637 Relations .... . 637 Branches ... . 637 Applied Anatomy . 638 Internal Maxillary Artery . 638 Branches .... . 639 The Triangles of the Neck . . . 642 Anterior Triangle . 642 Inferior Carotid or Muscular Tri- angle . 643 Superior Carotid or Carotid Tri- angle . 643 Submaxillary or Digastric Tri- angle . 644 Suprahyoid Triangle . 644 Posterior Triangle .... 644 Occipital Triangle 645 Subcla\ian Triangle . . 645 The Internal Carotid Artery . 645 Course and Relations .... . 645 Cer\'ical Portion . 646 Petrous Portion 647 Cavernous Portion . 647 Cerebral Portion . . 647 Peculiarities . . 647 Applied Anatomy . . . 647 Branches . . . 648 Caroticotympanic . . 648 Artery of the Pterygoid Canal . . 648 Cavernous . . 648 Hypophyseal . . 648 Anterior Meningeal . . . 648 Ophthalmic artery . . 648 Branches ... . . 648 Anterior Cerebral Artery . . 651 Branches .... . . 652 Middle Cerebral Arterj' . 652 Branches .... . . 653 Posterior Communicating Arte ry . 653 Anterior Choroid il Artery . . . 653 The Arteries of the Brain. The Ganglionic System .... The Cortical Arterial System . 654 654 The Arteries of the Upper Extremity. The Subclavian Artery. First Part of the Right Subclavian Artery . 655 Relations 655 First Part of the Left Subclavian Artery 655 Relations 655 Second and Third Parts of the Subclavian Artery 656 Relations 656 Relations 657 Peculiarities 657 Applied Anatomy 657 Branches 659 Vertebral Arterj^ 659 Relations . 659 Branches . . . 660 Applied Anatomy 661 Thyrocervical Trunk 662 Branches 662 Peculiarities 644 Internal Mammary Artery 604 Relations 664 Branches 664 The Costoccrvical Trunk ... 666 The Axilla. Boundaries 667 Contents 667 Applied Anatomj- 667 The Axillary Artery 668 Relations 668 Applied Anatomy 669 Branches 670 The Highest Thoracic Arterj' . 670 The Thoracoacromial Artery 670 The Lateral Thoracic Artery 671 The Subscapular Arterj^ 671 The Posterior Humeral Circumflex Artery 671 The Anterior Humeral Circumflex Artery 672 Peculiarities 672 The Brachial Artery 672 Relations 672 The Anticubital Fossa 672 Peculiarities 672 Applied Anatomy 673 Branches 674 The Arteria Profunda Brachii 674 The Nutrient Arterj- .... 674 The Superior Llnar Collateral Artery 674 The Inferior Ulnar Collateral Artery 675 Muscular Branches 675 The Anastomosis Around the Elbow- joint 675 The Radial Artery 676 Relations 676 Peculiarities 676 Applied Anatomy 676 Branches 678 Radial Recurrent Artery 678 Musciilar 678 Volar Carpal 678 Superficial Volar 678 Dorsal Carpal 678 Arteria Princeps Pollicis . . 678 Arteria Volaris Indicis Radialis 679 Deep Volar Arch 679 Volar Metacarpal Arteries . 679 Perforating 679 Recurrent 679 The Ulnar Artery 679 Relations 679 Peculiarities 679 Applied Anatomy , . 680 Branches 680 Anterior Ulnar Recurrent Artery . 680 Posterior Ulnar Recurrent Artery . 680 Common Interosseous Artery 680 Muscular 682 Volar Carpal 682 Dorsal Carpal 682 Deep Volar 682 Superficial Volar 682 Relations 682 Applied Anatomy .... 682 The Arteries of the Trunk. The Descending Aorta. The Thoracic Aorta 683 Relations 683 Peculiarities 6»3 cox TEXTS 21 The Thoracic Aort:^" Applied Anatomy Branches Pericardial Bronchial . CEsophaKcal Mediastinal Intercostal Arteries . Branches Applied Anatomy Subcostal Arteries Superior Phrenic . The Abdominal Aorta . Relations Applied Anatomy . Branches The Coeliac Artery Relations The Superior Mesenteric Artery Dissection Branches The Inferior Mesenteric Artery Dissection Branches Applied Anatomy The ^liddle Suprarenal Arteries The Renal Arteries The Internal Spermatic Arteries The Ovarian Arteries The Inferior Phrenic Arteries The Lumbar Arteries The iMiddle Sacral Artery The Common Iliac Arteries. Peculiarities .... AppUed Anatomy The Hj'pogastric Artery Peculiarities Applied Anatomy . Branches Superior Vesical Artery ^Middle Vesical ATter3^ Inferior Vesical Artery Middle Hemorrhoidal Artery Uterine Artery Vaginal Artery Obturator Artery Branches Pectiliarities Internal Pudendal Artery Relations Peculiarities Branches Inferior Gluteal Ai'tery . Branches Lateral Sacral Arteries Superior Gluteal Artery Apphed Anatomy The External Ihac Artery . Relations Applied Anatomy .... Branches Inferior Epigastric Arterj Branches Peculiarities . AppUed Anatomy . Deep Iliac Circumflex Arterj 683 G85 685 685 685 685 685 686 686 686 686 686 687 687 688 688 688 691 692 692 694 695 695 696 696 696 697 697 697 698 698 700 700 700 700 701 701 701 701 701 701 701 702 702 702 703 703 703 704 704 706 706 707 707 708 70S 708 708 709 709 709 709 710 710 Knee The Arteries of the Lower Extremity. The Femoral Artery. The Femoral Sheath The Femoral Triangle 710 712 The Adductor Canal .... Relations of the Femoral Arterj- . Peculiarities of the Femoral Artery Ajiplied Anatomj' Branches Superficial Epigastric Artery Superficial Iliac Circumflex Artery . Superficial External Pudendal Artery Deep External Pudendal Artery Muscular Profunda Femoris Artery Relations .... Peculiarities Branches .... Highest Genicular Artery The Popliteal Fossa. Dissection Boundaries Contents The Popliteal Artery Relations Peculiarities Applied Anatomj' Branches Superior Muscular Sural Arteries Cutaneous Branches Superior Genicular Arteries Middle Genicular Artery- Inferior Genicular Arteries . The Anastomosis Around the joint The Anterior Tibial Artery Relations Peculiarities Applied Anatomy . . Branches Posterior Tibial Recurrent Artery Fibular Artery Anterior Tibial Recurrent Arterj- Muscular Branches .... Anterior Medial Malleolar Artery Anterior Lateral Malleolar Ajrterj- The Arteria Dorsalis Pedis Relations .... Peculiarities Applied Anatomy . Branches .... Lateral Tarsal Artery Medial Tarsal Artery Arcuate Artery Deep Plantar Artery The Posterior Tibial Artery Relations .... Peculiarities Applied Anatomy . Branches .... Peroneal Artery . Peculiarities . Branches Nutrient Artery . Muscular Branches Posterior Medial Malleolar Arterj- Communicating Branch Medial Calcaneal . Medial Plantar Artery Lateral Plantar Artery Applied Anatomj" Branches THE VEINS. The Pulmonary Veins . 730 The Systemic Veins. The Veins of the Heart. Coronary Sinus 730 Tributaries 730 The Veins of the Head and Xeck. The Veins of the Exterior of the Head and Face 732 The Frontal Vein 732 The Supraorbital ^'ein 733 The Angtdar Vein 733 The Anterior Facial Vein .... 733 22 CONTENTS The Veins of the Exterior of the Head and Face — The Anterior Facial Vein — Tributaries 733 Applied Anatomy 733 The Superficial Temporal Vein . 733 Tributaries 734 The Pterygoid Plexus 734 The Internal Maxillary Vein . 734 The Posterior Facial Vein .... 734 The Posterior Auricular Vein 734 The Occipital Vein 734 The Veins of the Xeck 734 The External Jugular Vein .... 734 Tributaries 735 Applied Anatomy . . 736 The Posterior External Jugular Vein 736 The Anterior Jugular Vein ... 736 The Internal Jugular Vein ... 736 Tributaries 736 Applied Anatomy 737 The Vertebral Vein 738 Tributaries 738 The Diploic Veins 738 The Veins of the Brain 739 The Cerebral Veins 739 The External Veins 739 The Superior Cerebral Vein 739 The Middle Cerebral Vein . . 739 The Inferior Cerebral Vein . 739 The Internal Cerebral Veins 740 The Great Cerebral Vein 740 The Cerebellar Veins 740 The Sinuses of the Dura Mater. Ophthalmic Veins and Emissary Veins . . 740 The Superior Sagittal Sinus .... 740' Applied Anatomy 741 The Inferior Sagittal Sinus .... 741 The Straight Sinus 741 The Transverse Sinuses 742 The Occipital Sinus 743 The Confluence of the Sinuses 743 The Cavernous Sinuses 744 Applied Anatomj- 745 The Ophthalmic Veins . . . 745 The Superior Ophthalmic Vein . 745 The Inferior Ophthalmic Vein . 746 The Intercavernous Sinuses ... 746 The Superior Petrosal Sinus ... 746 The Inferior Petrosal Sinus .... 746 The Basilar Plexus 746 The Emissary Veins 746 Applied Anatomy 747 The Veins of the Upper Extremity and Thorax. The Superficial Veins of the Upper Extremity 747 Digital Veins 747 The Cephalic Vein . . . 747 The Accessory Cephalic Vein 748 The Basilic Vein 748 The Median Antibrachial Vein . 749 Applied Anatomy 749 The Deep Veins of the Upper Extremity 750 Deep Veins of the Hand 750 Deep Veins of the Forearm .... 750 The Brachial Veins 750 The AxUlary Vein 750 Applied Anatomy 750 The SubclaA-ian Vein 750 Tributaries 751 The Veins of the Thorax 751 The Innominate Veins . . 751 The Right Innominate Vein . . 751 The Left Innominate Vein . . . 751 Tributaries 751 Peculiarities 751 The Veins of the Thorax — The Internal Mammary Veins 751 The Inferior Thyroid Veins . 751 The Highest Intercostal Vein 753 The Superior Vena Cava . 753 Relations 753 The Azygos Vein 753 Tributaries 753 The Hemiazygos Veins 753 The Accessory Hemiazygos Veins 753 Applied Anatomy 754 The Bronchial Veins 754 The Veins of the Vertebral Column . 754 The External Vertebral Venous Plexuses 754 The Internal Vertebral Venous Plexuses 755 The Basivertebral Veins 755 The Veins of the Medulla Spinalis . 755 The Veins of the Lower Extremity, Abdomen, and Pelvis. The Superficial Veins of the Lower Extremity The Dorsal Digital Veins . The Great Saphenous Vein Tributaries The Small Saphenous V ein AppUed Anatomy . The Deep Veins of the Lower Extremity The Plantar Digital Veins The Posterior Tibial Veins The Anterior Tibial Veins The Popliteal Vein The Femoral Vein The Deep Femoral Vein The Veins of the Abdomen and Peh-is The External Iliac Vein Tributaries The Hypogastric Veins Tributaries The Hemorrhoidal Plexus The Pudendal Plexus . The Vesical Plexus AppKed Anatomy The Dorsal Veins of the Penis The Uterine Plexuses . The Vaginal Plexuses The Common Iliac Veins The Middle Sacral Veins Peculiarities The Inferior Vena Cava . Relations .... Peculiarities . Applied Anatomy Tributaries Lumbar Veins Spermatic Veins Applied Anatomy I Ovarian Veins I Renal Veins . Suprarenal Veins \ Inferior Phrenic Veins Hepatic Veins The Portal System of Veins. The Portal Vein .... Tributaries .... The Lienal Vein . Tributaries The Superior Mesenteric Vein Tributaries . The Coronary Vein . The Pyloric Vein The Cystic Vein . The Parumbilical Veins ■ AppUed Anatomy . THE LYMPHATIC SYSTEM. Structure of Lvmphatic Vessels .... 768 The Lymph Glands 768 Structure of Lymph Glands .... 769 Applied Anatomy 770 The Thoracic Duct. The Cisterna Chyli Tributaries 756 756 756 756 757 757 758 758 758 758 758 758 759 759 759 760 760 760 761 761 761 761 761 761 762 762 762 762 762 762 762 762 763 763 763 763 764 764 764 764 764 764 765 765 766 766 766 766 766 767 767 767 772 772 CONTENTS 23 The Right Lymphatic Duct Tributaries Applied Anatomy . 772 773 773 Thk Lymphatics of thk Hkad, Face, and Neck. The Lviiiph Glands of the Hoad ... 774 The Occipital Cilands 774 The Posterior Auricular Glauds . 774 The Anterior Auricular Glands . 775 The Parotid Glands 775 The Facial (Jhunls . ' 775 The Deep Ivicial Glands 775 The Lingual Glands 775 The Retropharyngeal Glands . 776 The Lymphatic Vessels of the Scalp . 776 The Lymphatic Vessels of the Auricula and External Acoustic Meatus 776 The Lymphatic Vessels of the Face 776 The Lymphatic Vessels of the Nasal Cavities 776 The Lymphatic Vessels of the Mouth . 777 The Lymphatic Vessels of the Palatine Tonsil 777 The Lymphatic Vessels of the Tongue . 778 The Lymph Glands of the Neck .... 778 The Submaxillary Glands . 778 The Submental or Suprahyoid Glands . 778 The Superficial Cervical Glands . 778 The Anterior Cervical Glands ... 778 The Deep Cervical Glands . . . . . 778 The Lymphatic Vessels of the Skin and Muscles of the Neck 779 The Lymphatics of the Upper Extremity. The Lymph Glands of the Upper Extremity 779 The Superficial Lvmph Glands . . 779 The Deep Lymph Glands .... 780 The Axillary Glands .... 780 Applied Anatomy 781 The Lymphatic Vessels of the Upper Extremity 781 The Superficial Lymphatic Vessels . 781 The Deep Lymphatic Vessels . . 782 The Lymphatics of the Lower Extremity. The Lymph Glands of the Lower Extremity 782 The Anterior Tibial Gland .... 782 The Popliteal Glands 782 The Inguinal Glands 783 Applied Anatomy 784 The Lvmphatic Vessels of the Lower Extremity 784 The Superficial Lymphatic Vessels . 784 The Deep Lymphatic Vessels . . 785 The Lymphatics of the Abdomen and Pelvis. ' The The Lymph Glands of the Abdomen and Pelvis . . • The Parietal Glands .... The External Iliac Glands . The Common Iliac Glands . The Epigastric Glands . The Iliac Circumflex Glands The Hypogastric Glands The Sacral Glands The Lumbar Glands The Lymphatic Vessels of the Abdomen Pelvis The Superficial Vessels The Deep Vessels .... The Lymphatic Vessels of the Perineum and External Genitals and 785 786 786 786 786 786 786 787 787 787 787 787 787 The Jj.\iiiphatic Vessels of the Abdonieu and Pelvis — Tiie Visceral Glands 787 Tlie Gastric Glands 788 The JbriKilic Glands .... 788 The Pancreaticolienial Glands . 788 The Superior Mesenteric Glands 789 The Mesenteric Glands .... 789 Ai)plied Anatomy 789 The Ileocolic Glands 789 The Mesocolic Glands . . 791 The Inferior Mesenteric Glands 791 The Lymphatic Vessels of the Abdominal and Pelvic Viscera 791 The Lymphatic Vessels of the Subdia- phragmatic Portions of the Digestive Tube 791 The Lymphatic Vessels of the Stomach 792 The Lymphatic Vessels of the Duodenum 792 The Lymphatic Vessels of the Jejunum and Ileum 792 The Lj'-mphatic Vessels of the Vermiform Process and Cecum 792 The Lymphatic Vessels of the Colon 792 The Lymphatic Vessels of the Anus, Anal Canal, and Rectum .... 792 The Lymphatic Vessels of the Liver 792 The Lymphatic Vessels of the Gall- bladder 793 The Lymphatic Vessels of the Pancreas 793 The Lymphatic Vessels of the Spleen and Suprarenal Glands 793 The Lymphatic Vessels of the Urinary Organs 793 The Lymphatic Vessels of the Kidney 793 The Lymphatic Vessels of the Ureter 793 The Lymphatic Vessels of the Bladder , 793 The Lymphatic Vessels of the Prostate 794 The Lymphatic Vessels of the Urethra 794 The Lymphatic Vessels of the Repro- ductive Organs 794 The Lvmphatic Vessels of the Testes 794 The Lymphatic Vessels of the Ductus Deferens 794 The Lymphatic Vessels of the Ovary 795 The Lvmphatic Vessels of the Uterine Tube 795 The Lymphatic Vessels of the Uterus 795 The Lymphatic Vessels of the Vagina 795 The Lymphatics of the Thorax. The Parietal Lymph Glands 796 The Sternal Glands 796 The Intercostal Glands 797 The Diaphragmatic Glands .... 797 Superficial Lymphatic Vessels of the Thoracic Wall 797 The Lymphatic Vessels of the Mamma . 797 The Deep Lymphatic Vessels of the Thoracic Wall 797 The Visceral Lymph Glands 798 The Anterior Mediastinal Glands . 798 The Posterior Mediastinal Glands . 798 The Tracheobronchial Glands ... 798 Applied Anatomy 798 Lymphatic Vessels of the Thoracic Viscera 799 The Lymphatic Vessels of the Heart . 799 The Lymphatic Vessels of the Lungs 799 The Lymphatic Vessels of the Pleura 800 The Lymphatic Vessels of the Thymus 800 The Lymphatic Vessels of the CEso- phagus 800 The 24 CONTENTS NEUROLOGY. Structure of the Peripheral Nerves and Ganglia SOI The Medulla Spinalis or Spinal Cord. The Dissection Enlargements Fissures and Sulci The Anterior Median Fissure The Posterior Median Sulcus Internal Structure of the Medulla Spinalis The Gray Substance Structure of the Gray Substance The White Substance Nerve Fasciculi Roots of the Spinal Nerves The Anterior Nerve Root The Posterior Root Applied Anatomy .... The Encephalon or Brain. Dissection General Considerations and Di\-isions The Rhombencephalon or Hind-brain. The Medulla Oblongata The Anterior Median Fissure The Posterior Median Fissure Internal Structure of the Medulla Oblongata The Cerebrospinal Fasciculi Gray Substance of the Medulla Oblongata . Restiform Bodies Formatio Reticularis Applied Anatomy The Pons Structure .... Applied Anatomy . The Cerebellum Lobes of the Cerebellum Internal Structure of the Cerebellum The White Substance Projection Fibres The Gray Substance Microscopic Appearance Cortex . Applied Anatomy . The Fourth Ventricle . Angles . _ . Lateral Boundaries Choroid Plexuses . Openings in the Roof Rhomboid Fossa . of the 805 808 808 80S 809 810 814 814 818 819 819 820 821 821 822 822 822 826 826 829 830 832 833 833 834 836 836 836 839 839 840 842 842 844 845 845 845 846 847 847 The Dicncephalon — The Optic Tracts . The Third Ventricle . . The Interpeduncular Fossa The Telencephalon .... The Cereljrul Hemispheres The Longitudinal Cerebral Fissure . The Surfaces of the Cerebral Hemi- spheres The Lateral Cerebral Fissure The Central Sulcus The Parietooccipital Fissure . The Calcarine Fissure The Cingulate Sulcus The Collateral Fissure The Sulcus Circularis The Lobes of the Hemispheres The Frontal Lobe The Parietal Lobe The Occipital Lobe . The Temporal Lobe . The Insula .... The Limbic Lobe . The Rliinencephalon The Olfactory Lobe . The Interior of the Cerebral spheres .... The Corpus CaUosum The Lateral Ventricles The Fornix The Interventricular Foramen The Anterior Commissure The Septum Pellucidum . The Choroid Plexus of the Ventricle .... Structure of the Cerebral spheres ... Structure of the Cerebral Cortex Special Types of Cerebral Cortex Weight of Encephalon . Cerebral Localization Applied Anatomy . Hemi- Lateral Hemi- 863 864 865 865 865 865 867 868 868 869 869 869 869 869 869 870 871 871 873 873 874 874 875 876 877 885 887 887 887 887 889 891 893 894 894 895 The Motor and Sensory Tracts. The Motor Tract 89& The Sensory Tract 897 Applied Anatomy 89& The Meninges of the Brain and Medulla Spinalis. The Mesencephalon or Mid-brain. The Cerebral Peduncles Structure of the Cerebral Peduncles The Gray Substance The White Substance The Corpora Quadrigemina .... Structure of the Corpora Quadrigemina The Cerebral Aqueduct The Prosencephalon or Fore-brain. The Diencephalon . The Thalamencephalon Structure . Connections The Metathalamus The Epithalanius . The Hypothalamus Applied Anatomy The Optic Chiasma 849 850 851 853 854 854 855 855 856 857 858 859 860 862 862 The Dura Mater The Cerebral Dura Mater Processes . Structure . The Spinal Dura Mater Structure . The Arachnoid .... The Cerebral Part The Spinal Part . . Structure . . The Subarachnoid Cavity The Subarachnoid Cisternse The Arachnoid Granulations Structure . . . • . The Pia Mater The Cerebral Pia Mater . The Spinal Pia Mater The Ligamentum Denticulatum Applied Anatomy .... 900 900 900 902 902 903 903 903 903 904 904 904 905 906 906 906 906 907 907 The Cerebral Nerves. The Olfactory Nerves. Applied Anatomy 909 The Optic Nerve. The Optic Tract 909 The Optic Chiasma 909 Applied Anatomy 911 cox TEXTS 20 The Oculomotor Nerve. Applied Anatomy The Trochlear Nerve. Applied Anatomy The Trigeminal Nerve. The Semilunar Ganglion The Ophthalmic Nerve The Lacrimal Nerve The Frontal Nerve The Nasociliary Nerve The Ciliary Ganglion . The Maxillarj' Nerve Branches .... The Middle Meningeal Ncrv The Zygomatic Nerve The Sphenopalatine. The Posterior Superior Alveolar The Middle Superior Alveolar The Anterior Superior Alveolar The Inferior Palpebral The External Nasal . The Superior Labial The Sphenopalatine Ganglion The Mandibular Nerve .... Branches The Nervus Spinosus The Internal Pterygoid Nerve The Masseteric Nerve The Deep Temporal Nerves The Buccinator Nerve The External Pterygoid Nerve The Auriculotemporal Nerve The Lingual Nerve The Inferior Alveolar Nerve The Otic Ganglion . The Submaxillary Ganglion Applied Anatomy of the Trigeminal Nerve Trigeminal Nerve Reflexes .... The Abducent Nerve. Applied Anatomy The Facial Nerve. 913 914 914 915 915 916 916 917 917 917 917 917 918 918 919 919 919 919 919 919 921 921 921 921 921 922 922 922 923 923 923 924 925 925 925 929 The Ganglion Nodosum — The Auricular Branch The Pharyngeal Branch . The Superior Laryngeal Nerve The Recurrent Nerve The Superior Cardiac Branches The Inferior Cardiac Branches The Anterior Bronchial Branches The Posterior Bronchial Branches The CEsophageal Branches The Gastric Branches The Coeliac Branches The Hepatic Branches Applied Anatomy of the Vagus Nerve The Accessory Nerve. The Cerebral Part The Spinal Part Applied Anatomy The Greater Superficial Petrosal Ner\-e . 931 The Nerve to the Stapedius 932 The Chorda Tj-mpani Nerve 932 The Posterior Auricular Nerve .... 933 The Digastric Branch 933 The Stylohyoid Branch 933 The Temporal Branches 933 The Zygomatic Branches 933 The Buccal Branches 933 The Mandibular Branch 933 The Cer^-ical Branch 933 Applied Anatomy 933 The Acoustic Nerve. The Vestibular Root 935 The Cochlear Root 935 Applied Anatomy 936 The Glossopharyngeal Nerve. The Superior Ganglion -938 The Petrous Ganglion 939 The Tympanic Nerve 939 The Carotid Branches 939 The Pharyngeal Branches .... 940 The Muscular Branches 940 The Tonsillar Branches 940 The Lingual Branches 940 The Vagus Nerve. The Jugular Ganglion 941 The Ganglion Nodosum 941 The Meningeal Branch 941 The Hypoglossal Nerve. Branches of Communication Branches of Distribution . The Meningeal Branches The Descending Ramus The Thyrohyoid Branch The ^luscular Branches The Spinal Nerves. 941 942 942 942 942 943 943 943 943 943 943 943 943 944 945 945 946 947 947 947 947 947 Nerve Roots . 948 The Anterior Root . 948 The Posterior Root . . . 948 The Spinal Ganglia . 948 Structure .... . 949 Applied Anatomy . . 950 Di-\"isions of the Spinal_ Nerves 951 The Posterior Di^nsions . . 951 The Cervical Nerves . 951 The Thoracic Nerves . 952 The Lumbar Nerves . 953 The Sacral Nerves . . 953 The Coccygeal Nerve . 954 The Anterior Di^^sions . 954 The Cervical Nerves . 954 The Cervical Plexus . 954 Great Auricular Nerve . 956 Cutaneous Cer^-ical N erve 957 Supraclavicular Nerve s 957 Communicantes Cer\d cales 957 Phrenic Nerve . . 957 Applied Anatomy . 958 The Brachial Plexus . 958 Relations . 959 Dorsal Scapular Nerv e . 960 Suprascapular Nerve . 960 Nerve to Subclavius . 960 Long Thoracic Nerve . 960 Anterior Thoracic Nei ves 961 Subscaptilar Nerves . . 960 Thoracodorsal Nerve . . 960 Axillary Nerve . . 960 Musculocutaneous Ne rve 962 Medial Antibrachial C uta- neous Nerve . . 964 :Medial Brachial Cut 1- neous Nerve . . 964 Median Nerve . . . 965 Radial Nerve . . . 968 Applied Anatomy . . . 970 The Thoracic Nerves . . 972 First Thoracic Nerve . . . 972 LTpper Thoracic Nerves . . 972 Lower Thoracic Nerves . . 973 Applied Anatomj- . . . 974 The Lumbosacral Plexus . . 974 The Lumbar Nerves . . 974 The Lumbar Plexus . . 975 Iliohypogastric N erve 976 Ilioinguinal Nerv 3 . 977 Genitofem( jral Ne rve 977 26 COXTEXTS Divisions of the Spinal Nerves — The Anterior Divisions — The Lumbosacral Plexus — The Lumbar Nerves — The Lumbar Plexus — Lateral Femoral Cuta- neous Nerve Obturator Nerve Accessory Obturator Nerve .... Femoral Nerve Saphenous Nerve. The Sacral and Coccygeal Nerves The Sacral Plexus Relations Nerve to Quadratus Femoris and Gemellus Inferior Nerve to Obturator luternus and Ge- mellus Superior . Nerve to Piriformis Superior Gluteal Nerve .... Inferior Gluteal Nerve .... Posterior Femoral Cutaneous Nerve Sciatic Nerve Tibial Nerve Lateral Plantar Nerve Common Peroneal Nerve .... Deep Peroneal Nerve Superficial Peroneal Nerve .... The Pudendal Plexus Perforating Cuta- neous Nerve . Pudendal Nerve Anococcygeal Nerve Applied Anatomy .... The Sympathetic Nerves. The Sympathetic Trunks Connections -n-ith the Spinal Nerves 977 979 The Cephalic Portion of the Sympathetic System. The Internal Carotid Plexus .... 996 The Cavernous Plexus 996 The Cervical Portion of the Sympathetic System. 980 The 980 981 The 982 The 982 982 Superior Cervical Ganglion . . 997 Branches . . 997 Middle Cer\acal Ganglion 997 Branches 997 Inferior Cervical Ganglion . 998 Branches . . 998 984 984 984 984 985 985 986 987 989 989 990 990 991 991 991 992 992 995 995 The The The The Thoracic Portion of the Sympathetic System. Greater Splanchnic Nerve .... 998 Lesser Splanchnic Nerve .... 999 Lowest Splanchnic Nerve .... 999 The Abdominal Portion of the Sympathetic System .... 1001 The Pelvic Portion of the Sympathetic System .... 1001 The Great Plexuses of the Symjjathetic System. The Cardiac Plexus . 1001 The Coeliac Plexus . . 1002 Phrenic Plexus 1003 Hepatic Plexus 1004 Lienal Plexus 1004 Superior Gastric Plexus 1004 Suprarenal Plexus 1004 Renal Plexus . 1004 Spermatic Plexus 1004 Applied Anatomv 1004 Superior Alesenteric Plexus 1004 Abdominal Aortic Plexus 1004 Inferior Alesenteric Plexus 1005 The Hypogastric Plexus . 1005 The Pehdc Plexuses . 1005 Applied Anatomy 1005 THE ORGANS OF THE SENSES AND THE COMMON INTEGUMENT. The Peripheral Organs of the Special Senses. The Organs of Taste. Structure 1007 The Organ of Smell. The External Nose 1008 Structure 1008 The Nasal Cavitv 1010 The Lateral Wall 1010 The Medial Wall 1012 The Mucous Membrane .... 1012 Structure 1012 The Accessory Sinuses of the Nose . . 1014 The Frontal Sinuses 1014 The Ethmoidal Air Cells . . . . 1014 The Sphenoidal Sinuses 1014 The MaxUlary Sinus 1015 Applied Anatomy of the Nose .... 1015 The Organ of Sight. The Tunics of the Eye The Fibrous Tunic The Sclera . Structure The Cornea . Structure 1017 1017 1017 1018 1018 1019 The Tunics of the Eye — Dissection .... The Vascular Tunic . The Choroid . . Structure Dissection The Ciliary Body . Structure The Iris .... Structure Membrana PupUlaris The Retina .... Structure The Refracting Media The Aqueous Humor The Vitreous Body . The Crystalline Lens Structure Applied Anatomy of the Organ of Sight The Accessory Organs of the Eye The Ocular Muscles .... Dissection Levator Palpebrae Superioris The Recti Obliquus Oculi Superior Obliquus Oculi Inferior The Fascia Bulb The Orbital Fascia Applied Anatomy The Eyebrows The Eyelids . . . 1021 1021 1021 1021 1022 1023 1023 1024 1025 1026 1026 1027 1030 1030 1030 1030 1031 1031 1034 1034 1034 1034 1035 1035 1036 1037 1038 1038 1038 1038 CONTEXTS 27 The Accessory Organs of the Eye — The Eyelids — The Lateral Palpebral Commis sure The Eyelashes .... Structure of the Eyelids The Tarsal Glauds . . Sti'ucture The Conjunctiva The Palpebral Portion The Bulbar Portion The Lacrimal Apparatus Tlie Lacrimal Gland Structure The Lacrimal Ducts The Lacrimal Sac Structure The Nasolacrimal Duct Applied Anatomy The Organ of Hearing. The External Ear The Auricula or Pinna Structure The External Acoustic Meatus Relations Applied Anatomy ... The ]\Iiddle Ear or Tvmpanic Cavitv The Tegumental Wall or Roof . The Jugular Wall or Floor . The Membranous or Lateral Wall The Tympanic Membrane . Structure The Labyrinthic or Medial Wall The Mastoid or Posterior Wall The Carotid or Anterior Wall . The Auditory Tube . The Auditorv Ossicles The ]Malleus . . . The Incus The Stapes Articulations of the Auditory Ossicles Ligaments of the Ossicles The Muscles of the Tympanic Cavity 1038 1038 1039 1040 1040 1040 1040 1041 1041 1041 1041 1041 1042 1042 1042 1042 1043 1044 1044 1046 1047 1048 1049 1049 1049 1049 1050 1050 1050 1051 1052 1052 1053 1053 1054 1054 1054 1054 1055 The Auditory Ossicles — The Muscles of the Tympanic Cavity The Tensor Tympani The Stapedius ... Applied Anatomy .... The Internal Ear or Lal)yrint!< . The Osseous Labyrinth . The Vestibule .... The Bony Semicircular Canals The Cochlea .... The Membranous Labyrinth The Utricle The Saccule The Semicircular Ducts Structure .... The Ductus Cochlearis The Basilar Membrane Hair Cells Applied Anatomy .... 1055 1055 1056 1057 1057 1058 1058 1059 1061 1062 1062 1062 1063 1063 1065 1067 1068 Peripheral Terminations of Nerves of General Sensations. Free Nerve-endings Special End-organs End-bulbs of Krause . Tactile Corpuscles of Grandry Pacinian Corpuscles . Corpuscles of Golgi and Mazzoni Tactile Corpuscles of Wagner and Meissner Neurotendinous Spindles Neuromuscular Spindles The Comon Integument. The Epidermis, Cuticle, or Scarf Skin The Corium, Cutis Vera, Dermis, or True Skin The Appendages of the Skin. The Nails The Hairs The Sebaceous Glands ...... The Sudoriferous or Sweat Glands . 1069 1069 1069 1069 1069 1069 1070 1070 1070 1071 1074 1075 1075 1077 1078 SPLANCHNOLOGY. The Respiratory Apparatus. The Pleura;. The Larynx. The Cartilages of the Larynx The Thyroid Cartilage . The Cricoid Cartilage The Arytenoid Cartilage The Corniculate Cartilages . The Cuneiform Cartilages . The Epiglottis .... Structure The Ligaments of the Larynx The Extrinsic Ligaments The Intrinsic Ligaments The Interior of the Larynx The Ventricular Folds The Vocal Folds .... The Ventricle of the Larynx The Rima Glottidis . The Muscles of the Larynx Cricothj-reoideus Cricoarytaenoideus Posterior Cricoarj-taenoideus Lateralis Arytaenoideus .... Thyreoarvtaenoideus The Trachea and Bronchi. Relations The Right Bronchus The Left Bronchus Structure Applied Anatomy 1079 1080 1081 1081 1081 1082 1082 1082 1082 1082 1083 1085 1085 1086 1086 1087 1088 1088 1088 1088 1088 1089 Reflections of the Pleura .... Pulmonary Ligament Structure of Pleura ... Applied Anatomy The Mediastinal Cavity Superior Mediastinal Cavity Anterior Mediastinal Cavity Middle Mediastinal Cavity . Posterior Mediastinal Cavity Applied Anatomy The Lungs. The Apex of the Lungs The Base of the Lungs Surfaces of the Lungs Borders of the Lungs . Fissures and Lobes of the Lungs The Root of the Lung Divisions of the Bronchi . Structure of the Lungs Applied Anatomy .... The Digestive Apparatus. 1095 1097 1097 1098 1098 1100 1101 1101 1101 1101 1102 1102 1103 1104 1105 1105 1106 1108 „Q^ The Mouth. 1092 I The Vestibule of the Mouth 1110 1092 i The Mouth Cavity Proper 1110 1092! Structure IHO 1093 The Lips IHO 28 CONTEXTS The Mouth Cavity Proper The Labial Glands The Cheeks . . . Structure . The Gums .... Applied Anatomy The Palate .... The Hard Palate The Soft Palate . The Palatine Aponeurosis The Muscles of the Palate Levator Veli Palatini Tensor Veli Palatini Musculus L"^^ilae Glossopalatinus . Phar>'ngopalatinus . Dissection Applied Anatomy The Teeth General Characteristics . The Permanent Teeth The Canine Teeth . The Premolar or Bicuspid Teeth The Molar Teeth . The Deciduous Teeth Structure of the Teeth . Development of the Teeth Eruption of the Teeth Applied Anatomy The Tongue The Root of the Tongue The Apex of the Tongue The Dorsum of the Tongue The Papillae of the Tongue The Muscles of the Tongue Genioglossus Hyoglossus . Relations Chondroglossus Styloglossus . Longitudinalis Linguae Superior Longitudinalis Linguae Inferior Transversus Linguae Verticalis Linguae . Applied Anatomy . Structure of the Tongue Glands of the Tongue Applied Anatomy .... The Salivarv Glands The Parotid Gland .... Structures within the Gland The Parotid Duct . Structure The Submaxillarj' Gland The Submaxillarj- Duct The Sublingual Gland Structure of the Salivary Gland Accessory Glands .... Applied Anatomy . . The Pharynx. The Xasal Part of the Pharj'nx . The Oral Part of the Pharj-nx . The Palatine Tonsils Structure Applied Anatomy The Laryngeal Part of the Pharynx The Muscles of the Pharynx Dissection Constrictor Pharj^ngis Inferior Relations .... Constrictor Pharj^ngis Medius Relations .... Constrictor Pharyngis Superior Relations .... Stylopharj-ngeus .... Salpingopharj'ngeus . Structure of the Pharynx Applied Anatomy The CEsopfuigus. Relations Applied Anatomy 1110 1110 1110 1111 1112 1112 1112 1112 1112 1113 1113 1113 1114 1114 1114 1114 1115 1115 1116 1117 1117 Ills 1118 1118 1119 1121 1124 1125 1125 1126 1126 1126 1127 1128 1129 1129 1129 1130 1130 1130 1130 1130 1130 1130 1131 1131 1132 1133 1133 1135 1135 1135 1135 1136 1137 1137 1138 1138 1139 1139 1139 1141 1141 1141 1141 1141 1141 1142 1142 1142 1142 1142 1142 1143 1143 1143 1144 1146 the Omental of the Peri or Appen The Abdomen. Boundaries of the Abdomen The Apertures in the Walls of the Abdomen Regions of the Abdomen The Peritoneum Vertical Dispositions of the Main Perl toneal Cavity . Vertical Disposition of Bursa .... Horizontal Disposition toneum In the Pelvis In the Lower Abdomen In the Upper Abdomen The Omenta . The Mesenteries . The Peritoneal Recesses or Fossae The Duodenal Fossae The Cecal Fossae The Intersigmoid Fossa Applied Anatomy The Stomach Openings of the Stomach Curv'atures of the Stomach Surfaces of the Stomach Component Parts of the Stomach Position of the Stomach Interior of the Stomach Pyloric Valve Structure of the Stomach The Gastric Gland Applied Anatomy The Small Intestine . The Duodenum Relations The Jejunum and Ileum ^kleckel's Diverticulum Structure .... The Large Intestine The Cecum The Vermiform Process dix Structure The Colic Valve . The Colon .... The Ascending Colon The Transverse Colon The Descending Colon The Iliac Colon The Sigmoid Colon The Rectum .... Relations of the Rectum The Anal Canal Structure of the Colon Applied Anatomy of the Intestines The Liver ...... Surfaces of the Liver Fosste of the Liver Lobes of the Liver Ligaments of the Liver . Structure of the Liver Excretory Apparatus of the The Hepatic Duct . The Gall-bladder Relations Structure The Common Bile Duct Relations Applied Anatomy The Pancreas . Dissection Relations . The Pancreatic Duct Structure . Applied Anatomy The Urogenital Appabatcs. The Urinary Organs. The Kidneys 120& Relations 1207 Surfaces 1207 Liver CONTENTS 29 The Kidneys- The Fcm^ile Geiiilal Organs. Borders 1209 Extremities . 1209 The Ovaries 1243 Fixation of the Kidney . . . . 1209 The Epoophoron 1244 General Structure of the Kidney 1210 The Paroophoron 1245 Applied Anatomy 1214 Structure 1245 The Ureters 1216 Vesicular Ovarian P^ollicles . 1245 The Ureter Proper 1216 Applied Anatomy . 1246 Structure 1217 The Uterine Tube 1247 Applied Anatomy 1218 Structure ... 1247 The Urinary Bladder 1218 Applied Anatomy . . 1247 1218 The Uterus 1248 Tlip Dii^tonHprl T^InrlHpr 1219 The Body 1249 The Bladder in the Child 1220 The Cervix 1249 The Female Bladder 1221 The Interior of the Uterus . 1250 The Ligaments of the Bladder 1221 The Ligaments of the Uterus 1250 The Interior of the Bladder 1222 Structure 1252 Structure 1223 Applied Anatomy 1254 Applied Anatomy 1224 The Vagina 1255 The Male Urethra 1225 Relations . 1255 The Prostatic Portion . . 1225 Structure 1255 1226 The External Organs . 1256 The Cavernous Portion .... 1226 The Mons Pubis . 1256 Structure 1226 The Labia Majora 1256 Applied Anatomy 1226 The Labia Minora 1257 The Female Urethra 1228 The Clitoris . . 1257 Structure 1228 The Vestibule 1257 The Bulb of the Vestibule . . 1257 Th Male Genital Organs. The Greater Vestibular Glands 1258 The Mammae 1258 The Testes and their Coverings . 1228 The Mammary Papilla or Nipple . 1258 The Scrotum 1228 Structure 1258 The Intercrural Fascia .... 1229 Applied Anatomy 1260 The Cremaster Muscle .... 1229 The Infundibuliform Fascia 1229 The Tunica Vaginalis .... 1229 The Ductless Glands. The Inguinal Canal 1229 The Spermatic Cord .... 1229 The Thyroid Gland. Structure of the Spermatic Cord 1230 1230 Structure 1262 Applied Anatomy Applied Anatomy . 1263 The Testes _ 1230 The Epididymis .... Appendages of the Testis and Epi 1231 The Parathyroid Glands. didymis 1231 1231 1232 Structure 1264 The Tunica Vaginalis The Tunica Albuginea Applied Anatomy 1264 The Tunica Vasculosa 1232 Structure 1232 The Thymus. Applied Anatomy .... 1234 The Ductus Deferens 1235 Structure 1264 The Ductuli Aberrantes 1236 Applied Anatomy 1266 Paradidj-mis 1236 Structure 1236 The Spleen. The Vesiculae Seminales 1236 Structure 1237 Relations 1266 Applied Anatomy 1237 Structure . 1267 The Ejaculatory Ducts . 1237 Applied Anatomy 1270 Structure 1237 The Penis . 1237 The Suprarenal Glands. The Corpora Cavernosa Penis . . 1238 The Corpus Cavernosum Urethrae . 1238 Relations ......... . 1270 . 1239 Structure Applied Anatomy 1271 Applied Anatomy The Prostate 1240 1241 . 1272 Structxire Applied Anatomy 1241 1242 The Carotid Skeins . . 1273 The Bulbourethral Glands ... 1243 Structure . 1243 The Coccygeal Skein . 1273 SURFACE ANATOMY AND SURFACE MARKINGS. Surface Anatomy of the Head and Neck. The Cranium — Bony Landmarks The Bones 1275 The Brain .... The Joints and Muscles 1276 ! Vessels The Arteries 1278 I The Face External Maxillary Artery Surface Markings of Special Regions of the Head Trigeminal Nerve and Neck. Parotid Gland The Nose The Cranium 1279 The Mouth The Scalp 1279 The Eye 1279 1280 1282 1282 1282 1283 1283 1284 1284 1287 30 CONTEXTS The Ear 1288 Descending Colon 1307 The Tympanic Antrum 1289 Iliac Colon . 1307 The Neck " 1289 Liver 1307 Muscles 1290 Pancreas 1307 Arteries ... ... 1290 Spleen 1307 Veins 1291 Kidneys 1308 Nerves 1291 Ureters . 1308 Submaxillary Gland 1291 Vessels . Nerves . 1309 1309 Surface Anatomy of the Back. Surface Anatomy of the Perineum. Bones 1291 Muscles 1292 Skin 1309 Bones 1309 Surface Markings of the Back. Muscles and Ligaments 1309 Bony Landmarks Medulla Spinalis Spinal Nerves . Surface Anatomy of the Thorax. 1293 I Surface Markings of the Perineum. 1293 1295 Rectum and Anal Canal 1310 Male Urogenital Organs 1310 Female Urogenital Organs 1311 Bones Muscles Mamma Surface Markings of the Thorax. Bonj' Landmarks Diaphragma Surface Lines PleuriBe Lungs Trachea CEsophagus Heart Arteries Veins . Surface Anatomy of the Abdornen. Skin Bones Muscles Vessels Viscera Surface Markings of the Abdomen. Bony Landmarks . Muscles Surface Lines Stomach Duodenum . Small Intestine Cecum and Vermiform Process Ascending Colon Transverse Colon . 1295 1295 1296 1296 1297 1297 1297 1298 1299 1299 1299 1300 1300 1301 1301 1301 1301 1301 1303 1303 1303 1305 1306 1306 1307 1307 1307 Surface Anatomy of the Upper Extremity. Skin . . Bones Articulations Muscles Arteries Veins Nerves . 1312 1313 1315 1315 1318 1318 1318 Surface Markings of the Upper Extremity. Bony Landmarks Articulations Muscles Mucous Sheaths Arteries Nerves 1319 1319 1319 1319 1320 1323 Surface Anatomy of the Lower Extremity. Skin . . Bones Articulations Muscles Arteries Veins Nerves . 1323 1324 1325 1326 1328 1329 1329 Surface Markings of the Lower Extremity. Bony Landmarks Articulations Muscles Arteries Veins Nerves . 1329 1330 1330 1331 1334 1334 INTRODUCTION. T^HE term human anaiomy comprises a consideration of the various structures which make up the human organism. In a restricted sense it deals merely with the parts which form the fully developed individual and which can be ren- dered evident to the naked eye by various methods of dissection. Regarded from such a standpoint it may be studied by two methods: (1) the various structures may be separately considered- — systematic anatomy; or (2) the organs and tissues ma}' be studied in relation to one another — topographical or regional anatomy. It is, however, of much advantage to add to the facts ascertained by naked- eye dissection those obtained by the use of the microscope. This introduces two fields of investigation, viz., the study of the minute structure of the various component parts of the body — histology — and the study of the human organism in its immature condition, i. e., the various stages of its intrauterine develop- ment from the fertilized ovum up to the period when it assumes an independent existence — embryology. Owing to the difficulty of obtaining material illustrating all the stages of this early development, gaps must be filled up by observations on the development of lower forms^ — comparative embryology, or by a consideration of adult forms in the line of human ancestry — comparative anatomy. The direct application of the facts of human anatomy to the various pathological conditions which may occur constitutes the subject of applied anatomy. Finally, the appre- ciation of structures on or immediately underlying the surface of the body is frequently made the subject of special study — surface anatomy. Systematic Anatomy. — The various systems of which the human body is composed are grouped under the following headings: 1. Osteology — the bony system or skeleton. 2. Syndesmology — the articulations or joints. 3. Myology — the muscles. With the description of the muscles it is convenient to include that of the fasciae which are so intimately connected with them. 4. Angiology — the vascular system, comprising the heart, bloodvessels, lymphatic vessels, and lymph glands. 5. Neurology — the nervous system. The organs of sense may be included in this system. 6. Splanchnology — the visceral system. Topographically the viscera form two groups, viz., the thoracic viscera and the abdominopelvic viscera. The heart, a thoracic viscus, is best considered with the vascular system. The rest of the viscera may be grouped according to their functions: {a) the respiratory apparatus; (6) the digestive apparatus; and (c) the urogenital apparatus. Strictly speaking, the third subgroup should include only such components of the urogenital apparatus as are included within the abdominopehdc cavity, but it 32 INTRODUCTION is convenient to study under this heading certain parts which he in relation to the surface of the body, e. g., the testes and the external organs of generation. For descriptive purposes the body is supposed to be in the erect posture, with the arms hanging by the sides and the palms of the hands directed forward. The median plane is a vertical antero-posterior plane, passing through the centre of the trunk. This plane will pass approximately through the sagittal suture of the skull, and hence any plane parallel to it is termed a sagittal lAane. A vertical plane at right angles to the median plane passes, roughly speaking, through the central part of the coronal suture or through a line parallel to it; such a plane is known as a frontal plane or sometimes as a coronal plane. A plane at right angles to both the median and frontal planes is termed a transverse plane. The terms anterior or ventral, and j)osterior or dorsal, are employed to indicate the relation of parts to the front or back of the body or limbs, and the terms superior or cephalic, and inferior or caudal, to indicate the relative levels of different structures; structures nearer to or farther from the median plane are referred to as medial or lateral respectively. The terms superficial and deep) are strictly confined to descriptions of the relative depth from the surface of the various structures; external and internal are reserved almost entirel}' for describing the walls of cavities or of hollow viscera. In the case of the limbs the words proximal and distal refer to the relative distance from the attached end of the limb. DESCRIPTIYE AND APPLIED ANATOMY. HISTOLOGY. THE ANIMAL CELL (Fig. 1). A LL the tissues and organs of the body originate from a microscopic structure ■^^ (the fertilized ovum), which consists of a soft jelly-like material enclosed in a membrane and containing a vesicle or small spherical body inside which are one or more denser spots. This may be regarded as a complete cell. All the solid tissiles consist largely of cells essentially similar to it in nature but differing in external form. Cell wall Vacuole Centrosome consisting of cen- trosphere enclosing two cen- trioles ~ Nucleolus Net-knot of chromatin form- ing a pseudo-nucleolus Chromatin network Cell- inclusions (paraplasm) Fig. 1. — Diagram of a cell. (Modified froni Wilson.) In the higher organisms a cell may be defined as "a nucleated mass of proto- plasm of microscopic size." Its two essentials, therefore, are: a soft jelly-like material, similar to that found in the ovum, and usually styled protoplasm, and a small spherical body imbedded in it, and termed a nucleus. Some of the unicellular protozoa contain no nuclei but granular particles .which, like true nuclei, stain with basic d^'es. The other constituents of the ovum, viz., its limiting membrane and-- the denser spot contained in the nucleus, called the nucleolus, are not essential to the type cell, and in fact many cells exist without them. Protoplasm (cytoplasm) is a material probably of variable constitution during life, but yielding on its disintegration bodies chiefly of proteid nature. Lecithin and cholesterin are constantly found in it, as well as inorganic salts, chief among which are the phosphates and chlorides of potassium, sodium, and calcium. It is of a semifluid viscid consistence, and in the living condition appears to be homo- 3 34 HISTOLOGY geneous and structureless. When, however, cells have been "fixed" by reagents a fibrillar or granular appearance can often be made out under a high power of the microscope. The filjrils are usually arranged in a network or reticulum, to which the term spongioplasm is applied, the clear substance in the meshes being termed hyaloplasm. A granular appearance is often caused by the knots of the network; but, in addition to these, protoplasm frequently contains true granules, some of which are proteid in nature and probably essential constituents; others are fat, glycogen, or pigment granules, and are regarded as adventitious material taken in from without, and hence are styled cell-inclusions or paraplasm. The size and shape of the meshes of the spongioplasm vary in different cells and in different parts of the same cell. The relative amounts of spongioplasm and hyaloplasm also vary in different cells, the latter preponderating in the young cell and the former in- creasing at the expense of the hyaloplasm as the cell grows. The peripheral layer of a cell is in all cases modified, either by the formation of a definite cell membrane as in the ovum, or more frequently in the case of animal cells, by a transformation, probably chemical in nature, which is only recognizable by the fact that the surface of the cell behaves as a semipermeable membrane. Nucleus. — The nucleus is a minute body, imbedded in the protoplasm, and usually of a spherical or oval form, its size having little relation to that of the cell. It is surrounded by a well-defined wall, the nuclear membrane; this encloses the nuclear substance {nuclear matrix), which is composed of a homogeneous material or karyoplasm containing a network or karyomitome. The former is probably of the same nature as the hyaloplasm of the cell, but the latter, which forms also the wall of the nucleus, differs from the spongioplasm of the cell substance. It con- sists of fibres or filaments arranged in a reticular manner. These filaments are composed of a homogeneous material known as linin, which stains with acid dyes and contains embedded in its substance particles which have a strong affinity for basic dyes. These basiphil granules have been named chromatin or basichromatin and owe their staining properties to the presence of nucleic acid. ^Yithin the nuclear matrix are one or more highly refracting bodies, termed nucleoli, connected with the nuclear membrane by the nuclear filaments. They are regarded as being of two kinds. Some are mere local condensations (" net- knots") of the chromatin; these are irregular in shape and are termed pseudo- nucleoli; others are distinct bodies differing from the pseudo-nucleoli both in nature and chemical composition; they may be termed true nucleoli, and are usually found in resting cells. The true nucleoli are oxyphil, i. e., they stain with acid dyes. Most living cells contain, in addition to their protoplasm and nucleus, a small particle which usually lies near the nucleus and is termed the centrosome. In the middle of the centrosome is a minute body called the centriole, and surrounding this is a clear spherical mass known as the centrosphere. The protoplasm surround- ing the centrosphere is frequently arranged in radiating fibrillar rows of granules, forming what is termed the attraction sphere. Reproduction of Cells. — Reproduction of cells is effected either by direct or by indirect division. In reproduction by direct division the nucleus becomes constricted in its centre, assuming an hour-glass shape, and then divides into two. This is fol- lowed by a cleavage or division of the whole protoplasmic mass of the cell; and thus two daughter cells are formed, each containing a nucleus. These daughter cells are at first smaller than the original mother cell; but they grow, and the process may be repeated in them, so that multiplication may take place rapidly. Indirect divsion or karyokinesis (karyomitosis) has been observed in all the tissues — genera- tive cells, epithelial tissue, connective tissue, muscular tissue, and nerve tissue. It is possible that cell division may always take place by the indirect method, and that in those cases in which direct division has been described the intermediate stages may not have been seen, owing to the process occurring more rapidly than usual. rilE AXIMAL CELL 35 The process of indirect cell division is characterized by a series of complex changes in the nucleus, leading to its subdivision; this is followed by cleavage of tlie cell protoplasm. Starting with the nucleus i)i tlu> quiescent or resting stage, these changes may be briefly grouped under the f«iur following phases (Fig. 2). I ,' - ^X^ 3©^ VI ^ ^^^ r \t:i ,. - VIII ..-■ Y Fig 2 —Diagram showing the changes which occur in the centrosomes and nucleus of a^ cell in the i recess of mitotic ■ ■ division. (Schafer.) I to IV, prophase; T" and TT, metaphase; T II and T III, anaph, se. 1. Prophase.— The nuclear network of chromatin filaments assumes the form of a twisted skein or spirem, while the nuclear membrane and nucleolus disappear. The convoluted skein of chromatin divides into a definite number of ^ -shaped segments or chromosomes. The number of chromosomes varies in different animals, but is constant for all the cells in an animal of any given species; in man the number is given by Flemming and Duesberg as twenty-four.^ Coincidently with or pre- ceding these changes the centriole, which usually lies by the side of the nucleus, undergoes subdivi'sion, and the two resulting centrioles, each surrounded by a centrosphere, are seen to be connected by a spindle of delicate achromatic fibres 1 Dr. J. Duesberg, Anat. Anz., Band xsviii, S. 475. 36 HISTOLOGY the achromatic spindle. The centrioles moN'e away from each other — one toward either extremity of the nucleus — and the fibrils of the achromatic spindle are cor- respondingly lengthened. A line encircling the spindle midway between its ex- tremities or poles is named the equator, and around this the V-shaped chromosomes arrange themselves in the form of a star, thus constituting tlie mother star or monaster. 2. Metaphase. — Each \"-shaped chromosome now undergoes longitudinal cleavage into two equal parts or daughter chromosomes, the cleavage commencing at the apex of the V and extending along its di\'ergent limbs. The daughter chromosomes, thus separated, travel in opposite directions along the fibrils of the achromatic spindle toward the centrioles, around which they group themselves, and thus two star-like figures are formed, one at either pole of the achromatic spindle. This constitutes the diaster. 3. Anaphase. — The daughter chromosomes now^ arrange themselves into a skein or spirem, and eventually form the network of chromatin which is character- istic of the resting nucleus. The nuclear membrane and nucleolus are also differ- entiated during this phase. The cell protoplasm begins to appear constricted around the equator of the achromatic spindle, where double rows of granules are also sometimes seen. The constriction deepens and the original cell gradually becomes divided. 4. Telophase. — In this stage the cell is completely divided into two new cells, each with its own nucleus and centrosome, which assume the ordinary positions occupied b}' such structures in the resting stage. EPITHELIUM. All the surfaces of the body — the external surface of the skin, the internal surfaces of the digestive, respiratory, and genito-urinary tracts, the closed serous cavities, the inner coats of the vessels, the acini and ducts of all secreting and ex- creting glands, the ventricles of the brain and the central canal of the medulla spinalis — are covered by one or more layers of simple cells, called epithelium or epithelial cells. These cells are also present in the terminal parts of the organs of special sense, and in some other structures, such as the hypophysis cerebri and the thyroid gland. They serve various purposes, in some cases forming a protective layer, in others acting as agents in secretion and excretion, and again in others being concerned in the elaboration of the organs of special sense. Thus, in the skin, the main purpose served by the epithelium (here called the epidermis) is that of protection. iVs the surface is worn away by the agency of friction new cells are supplied, and thus the true skin and the vessels and nerves which it contains are defended from damage. In the gastro-intestinal mucous membrane and its glands, the epithelial cells appear to be the principal agents in preparing the diges- tive secretions, and in selecting and modifying materials for absorption. In other situations (as the nose, fauces, and respiratory passages) an important office of the epithelial cells appears to be to maintain an equable temperature by the moisture with which they keep the surface always slightly lubricated. In the serous cavities they also keep the opposed layers moist, and thus facilitate their movements on each other. Finally, in all internal parts, they ensure a perfectly smooth surface. Epithelium consists of one or more layers of cells usually supported on a base- ment membrane and united together by an interstitial cement substance which appears to be similar in chemical composition to the matrix or ground substance of the connective tissues. It is naturally grouped into two classes according as to whether there is a single layer of cells (simple epithelium), or more than one (stratified epithelium and transitional epithelium). EPITHELIUM 37 Simple Epithelium. — The (lill'eivnt xaricties of simple epithelium are squamous or j)a\'euieut. columnar, glandular, and ciliated. Simple Squamous or Pavement Epithelium (Fig. 3) is composed of flat, nucleated scales of dill'erent shapes, usually polygonal, and varying in size. These cells fit together by their edges, like the tiles of a mosiac pax'ement. The nucleus is gen- erally flattened, hut may be spheroidal; the flattening depends upon the thinness of the cell. The protoplasm of the cell presents a fine reticulum or honey-combed network, which gives to the cell the appearance of granulation. This kind of epi- thelium forms the lining of the air-sacs of the lungs. The so-called endothelium, \\hicli covers the serous membranes, and which lines the heart, bloodvessels, and lymphatics, is also of the pavement type, being composed of a single layer of flattened transparent squamous cells, joined edge to edge in such a manner as to form a membrane of cells. ms — Stf^ Fig. 3. — Simple pavement epithelium. Fig. 4. — Columnar epithelial cells of the rabbit's intes- tine. (Schafer.) str, striated border; n, nucleus. Columnar or Cylindrical Epithelium (Fig. 4) is formed of cylindrical or rod-shaped cells set together so as to form a complete layer, resembling, when viewed in pro- file, a palisade. The cells have a prismatic figure, flattened from mutual pressure, and are set upright on the surface on which they are supported. Their protoplasm is always more or less reticulated, and fine longitudinal striae may be seen in it; the nucleus of each is oval in shape and contains an intranuclear network. In the case of the intestinal villi, the outer free border of each of these cells is dis- tinctly marked ofT from the rest of the protoplasm, and contains well-defined vertical striations. Columnar epithelium covers the mucous membrane and nearly the whole gastro-intestinal tract and its glands, the greater part of the male urethra, the ductus deferens, the prostate, the bulbo-urethral glands of Cowper, and the vestibular glands of Bartholin. In a modified form it also covers the ovary. Goblet or chalice cells are modified columnar cells. The goblet cell appears to be formed by an alteration in shape of a columnar cell (ciliated or otherwise) con- sequent on the formation of granules, w^hich consist of a substance called mucigen, in the interior of the cell. This distends the upper part of the cell, while the nucleus is pressed dow^n toward its deep part, until the cell bursts and the mucus is dis- charged on to the surface of the mucous membrane (Fig. 5), the cell then assuming the shape of an open cup or chalice. Glandular Epithelium (Fig. 6) is composed of polyhedral, columnar, or cubical cells. As in other forms of epithelial cells, the protoplasm shows a fine reticulum, which gives to the cells the appearance of granulation. Granular cells are found in the terminal recesses of secreting glands, and the protoplasm of the cells usually contains the materials which the cells secrete. Ciliated Epithelium (Fig. 7) generally inclines to the columnar shape. It is dis- tinguished by the presence of minute processes, like hairs or eyelashes (cilia) standing up from the free surface. The cilia (Fig. 8) at their points of attachment 38 HISTOLOGY to the free border of the cell possess small nodular enlargements (basal knobs of Engelmaiin) ; within the cell they converge, and according to some authorities meet at or near the attraction sphere. If the cells be examined during life or immediately on removal from the living body (for which in the human subject the removal of a nasal polypus offers a convenient opportunity') in a weak solution of salt, the cilia will be seen in lashing motion; and if the cells be separated, they will often be seen to be moved about in the field bv this ciliarv action. ' %& Fro. 6. — Isolated liver cells of rabbit. X 500. Fig. 5.— Goblet cells of frog. X 500. Fig. 7. — Ciliated epithelium from trachea of kitten. X 255. lifn'HrHHT"' Sasal knobs Fig. 8. — Isolated ciliated cell (semidiagrammatic). Fig. 9. — Stratified epithelium from the oesophagus. The situations in which ciliated epithelium is found in the human body are: the respiratory tract from the nose downward to the smallest ramifications of the bronchial tubes, except the lower part of the pharynx and the surfaces of the vocal folds; the tympanic cavity and auditory tube; the uterine tube and the body of the uterus; the vasa efferentia, coni vasculosi and the first part of the ductus deferens; the ventricles of the brain and the central canal of the medulla spinalis. EPITHELIUM 39 Stratified Epithelium (Fig. 9). — Stratificil epithelium consists of several layers of cells varying greatly in shape. The cells of the deepest layer are for the most part columnar, and are placed vertically on the basement membrane; above these are several layers of polyhedral cells, which as they approach the surface become more and more compressed, until the superficial ones are found to consist of flat- tened scales (Fig. 10), the margins of which overlap one another so as to present an imbricated appearance. The protoplasm of the superficial cells is completely converted into a horny substance termed keratin. An intermediate body, eleidin, is often present in the deeper layers of this superficial portion; it exists in the form of coarse granules, and is especially well seen in the stratum granulosum of the epidermis (Fig. 11). The most superficial layers lose their nuclei, die, and are thrown or worn oflF. Fig. 10.— Epithelial cells from the oral cavity of man. X 3.50. a, large; h, middle sized; c. the same with two nuclei. Priclie-cells of stratum — ■< Malpighii Fig. 11. — Portion of epidermis from a section of the skin of the finger. (Ran\'ier.) The cells of the deeper layers of stratified squamous epithelium are called prickle cells; they possess short, fine fibrils, which pass from their margins to those of neighboriiig cells, serving to connect them together. They are not closely joined together by cement-substance, but are separated from each other by intercellular channels, across which the fibrils may be seen bridging. When a cell is isolated, it appears to be covered over with a number of short spines, in consequence of the fibrils being broken through. These cells were first described by Max Schultze and Virchow, and it was believed by them that the cells were dovetailed together. Martyn subsequently showed that this was not the case and that the prickles were attached to each other by their apices; and Delepine believes the prickles to be parts of fibrils forming internuclear bundles between the nuclei of the cells of an epithelium in a state of active growth. 40 HISTOLOGY Stratified epithelium is found in the skin, in the conjunctiva, in the nuicous membrane of the nose, excepting the olfactory portion, and in the mucous membrane of the mouth, lower part of the pharynx, and oesophagus. Transitional Epithelium. — Transitional epithelium occurs in the ureters and urinary bladder. Here the cells of the most superficial layer are large and flat- tened, with depressions on their under surfaces, to fit on to the rounded ends of the cells of the second layer, which are pear-shaped, the apices touching the basement membrane. Between the tapering points of the cells of the second layer is a third variety of cells of smaller size than those of the other two layers Fig. 12.— Transitional epithelium. (Fig. 12). CONNECTIVE TISSUES. The term connective tissue includes a number of tissues which support and con- nect the other tissues of the body; they are composed of cells separated from one another b}' an intercellular material. The connective tissues may differ con- siderably from each other in appearance, but they present many points of relation- ship, and are, moreover, developed from the same layer of the embryo, the meso- derm. They are divided into three great groups: (1) the connective tissues proper, (2) cartilage, and (3) bone. The circulating fluids, although functionally and prob- ably developmentally different from the others, are regarded by some histologists as a form of connective tissue, and are dealt with therefore in this section. The Connective Tissues Proper. — Several varieties of connective tissue are recognized: (Ij Areolar tissue. (2) White fibrous tissue. (3) Yellow elastic tissue. (4) Mucous tissue. (5) Retiform tissue. They are all composed of a homogeneous matrix, in which are imbedded cells and fibres — the latter of two kinds, white, and yellow or elastic. The distinction between the different varieties depends upon the relative preponderance of one or other kind of fibre, of cells, or of matrix. Areolar Tissue. — This is so called because its meshes can be easily distended with air or fluid and thus separated into areolae or spaces, which open freely into each other. Such spaces, however, do not exist in the natural condition of the body, the whole tissue forming one unbroken membrane composed of a number of inter- lacing fibres. The chief use of areolar tissue is to bind parts together, while by the laxity of its fibres, and the permeability of its areolae, it allows them to move on each other, and affords a ready exit for inflammatory and other effused fluids. It is quite the most extensively distributed of all the tissues. It is found beneath the skin in a continuous layer all over the body, connecting it to the subjacent parts. In the same way it is situated beneath the mucous and serous membranes. It is also found between muscles, vessels, and nerves, forming investing sheaths for them, and connecting them with surrounding structures. In addition to this it is present in the interior of organs, binding together the ^'arious lobes and lobules of the compound glands, the various coats of the hollow viscera, the fibres of muscles, etc., and thus forms the most important connecting medium of the various struc- tures or organs of which the body is made up. In many parts the areolae or inter- spaces of areolar tissue are occupied by fat cells, constituting adipose tissue, which will presently be described. Areolar tissue presents to the naked eye an appearance somewhat like spun silk. When stretched out, it is seen to consist of delicate soft elastic threads CONNECTIVE TISSUES 41 interlacing witli each other in every direction, and forming a network of extreme deHcacy. When examined nnder the microscope (Fig. 13) it is found to be com- posed of white fibres and yellow elastic fibres intercrossing in all directions, and united together by a homogeneous cement or ground substance, the matrix, showing cell-si)aces wherein lie the connective tissue corpuscles; these contain the protoplasm out of which the whole is developed and regenerated. Plasma cell White fibres Elastic fibres Fibrillaied cell Lamellar cell Fig. 13. — Subcutaneous tissue from a young rabbit. Highly magnified. (Schafer.) The white fibres are arranged in wavy bands or bundles of minute transparent homogeneous filaments or fibrillse. The bundles have a tendency to split up longitudinally or send off slips to join neighboring bundles, and receive others in return, but the individual fibres are unbranched, and never join other fibres. The yellow elastic fibres have well-defined outlines and are considerably larger in size than the white fibrillse, but vary much, being from 1 to 6 /x in diameter. They form bold and wide curves, branch, and freely anastomose with each other; they are homogeneous in appearance, and tend to curl up, especially at their broken ends. The cells of areolar tissue are of four principal kinds: (1) Flattened lamellar cells, which may be either branched or unbranched. The branched lamellar cells are composed of clear cytoplasm, and contain oval nuclei; the processes of these cells may unite so as to form an open network, as in the cornea. The unbranched cells are joined edge to edge like the cells of an epithelium; the " tendon cells," pres- ently to be described, are examples of this variety. (2) Clasmatocytes, large irregular cells characterized by the presence of granules or vacuoles in their protoplasm, and containing oval nuclei. (3) Granule cells {MastzeUen) , which are ovoid or spheroidal in shape. They are formed of a soft protoplasm, containing granules which are basiphil in character. (4) Plasma cells of Waldeyer, usually spheroidal and distinguished by containing a vacuolated protoplasm. The vacuoles are filled 42 HISTOLOGY with fluid, and the protoplasm between the spaces is clear, with occasionally a few scattered basiphil granules. In addition to these four typical forms of connective-tissue corpuscles, areolar tissue may be seen to possess wandering cells, i. e., leucocytes which have emigrated from the neighboring vessels; in some instances, as in the choroid coat of the eye, cells filled with granules of pigment (pigment cells) are found. The cells lie in spaces in the ground substance between the bundles of fibres, and these spaces may be brought into view by treating the tissue with nitrate of silver and exposing it to the light. This will color the ground substance and leave the cell-spaces unstained. Adipose Tissue. — In almost all parts of the body the ordinary areolar tissue contains a variable quantity of fat. The principal situations where it is not found are the subcutaneous tissue of the eyelids, of the penis and scrotum, of the labia minora; within the cavity of the cranium; and in the lungs, except near their roots. The distribution of adipose tissue is not uniform; in some parts it is in great abundance, as in the subcutaneous tissue, especially of the abdomen, around the kidneys, and in some other situations. Lastly, fat enters largely into the for- mation of the marrow of bones. Fig. 14. — Adipose tissue. Highly magnified, o, star-like appearance, from crystallization of fatty acids. Adipose tissue consists of small vesicles, fat cells, lodged in the meshes of areolar tissue. Fat cells (Fig. 14) vary in size, but are of about the average diameter of 50m; each consists of an exceedingly delicate protoplasmic membrane, filled with fatty matter, which is liquid during life, but becomes solidified after death. They are round or spherical where they have not been subjected to pressure; otherwise they assume a more or less polygonal outline. A nucleus is always present under the cell membrane and can be easily demonstrated by staining with hematoxylin; in the natural condition it is so compressed by the contained oily matter as to be scarcely recognizable. The fat cells are contained in clusters in the areolae of fine connective tissue, and are held together mainly by the network of capillary blood- vessels which is distributed to them. Chemically the oily material in the cells is composed of the fats, olein, palmitin, and stearin, which are glycerin compounds with fatty acids. Sometimes fat crystals form in the cells after death (Fig. 14, a). By boiling the tissue in ether or strong alcohol the fat may be extracted from the vesicles, leaving them empty and shrunken. Fat may be first detected in the human embryo about the fourteenth week. The fat cells are formed bv the transformation of connective-tissue corpuscles. CONNECTIVE TISSUES 43 Small droplets of oil are formed in the protoplasm, and these coalesce to produce a larger drop, which increases until it distends the corpuscles, the remaining proto- plasm and the nucleus being displaced toward the periphery of the cell (Fig. 15). Fig. 15. — Development of fat. (Kloiii and Xoble Smith ) a, minute artery ; v, minute vein; e, capillary bloodvessels in the course of formation ; they are not yet completely hol- lowed out, there being still left in them protoplasmic septa; the ground substance, containing numerous nucleated cells, some of which are more distinctly branched and flattened than others, and appear therefore more spindle-shaped. Fig. 16. -White fibres of areolar tissue. X 400. (Sharpey.) ijlll, ^^ 9ii!|i' I 1 u Fig. 17. — Tendon of mouse's tail, stained with [logwood, showing chains of cells be- tween '"(the tendon bundles. (From Quain's "Anatomy." E. A. Schafer.) Fig. is. — Transverse section of tendon of rat. X 120. White .Fibrous Tissue (Fig. 16) is a true connecting structure, and serves three purposes in the animal economy. In the form of ligaments it binds bones together; in the form of tendons it connects muscles to bones or other structures; and it constitutes investing or protecting structures to various organs in the form of membranes. Examples of such membranes are to be found in the muscular fasciae or sheaths, the periosteum, and the perichondrium; the investments of the various glands (such as the tunica albuginea testis, the capsule of the kidney, etc.); the investing sheaths of the nerves (epineurium) , and of various organs, as the penis and the eye. In white fibrous tissue, as its name implies, the white fibres predomi- 44 HISTOLOGY nate; the matrix is apparent only as a cement-substance, the yellow elastic fibres are comparatively few, while the tissue cells are arranged in a special manner. It presents to the naked eye the appearance of silvery white glistening fibres, covered over with a quantity of loose flocculent tissue which binds the fibres together and carries the bloodvessels. It is not possessed of any elasticity, and only the very slightest extensibility; it is exceedingly strong, so that upon the applica- tion of any external violence, a bone with which it is connected may fracture before the fibrous tissue gives way. In ligaments and tendons the bundles of fibres run parallel with each other; in membranes they intersect one another. The cells found in white fibrous tissue are often called tendon cells. They are situated on the surfaces of groups of bundles and are quadrangular in shape, arranged in rows, in single file, each cell being separated from its neighbors by a narrow line of cement- substance. The nucleus is generally situated at one end of the cell, the nucleus of the adjoining cell being in close proximity to it (Fig. 17). The tendon cells have wing-like processes which pass between the bundles of fibres, giving a stel- late appearance in transverse section (Fig. 18). Upon the addition of acetic acid white fibrous tissue swells up into a glassy looking indistinguishable mass. When boiled in water it is converted almost completely into gelatin, the white fibres being composed of the albuminoid collagen, which is often regarded as the anhydride of gelatin. Yellow Elastic Tissue. — In certain parts of the body a tissue is found which when viewed in mass is of a yellowish color, and is possessed of great elasticity, so that it is capable of considerable extension, and when the extending force is withdrawn returns at once to its original condition. This is yelloiv elastic tissue; it may be regarded as a connective tissue in which the yellow elastic fibres have developed to the practical exclusion of the other elements. It is found in the ligamenta flava, in the vocal folds, in the mucous membrane of the trachea and bronchi, in the coats of the bloodvessels, especially the larger arteries, and to a very considerable extent in the hyothyroid, cricothyroid, and stylohyoid ligaments. It is also found in the ligamentum nuchae of the lower animals (Fig. 19). In some parts where the fibres are broad and large and the network close, the tissue presents the appearance of a membrane, with gaps or perforations corresponding to the intervening spaces. This is to be found in the inner coat of the arteries, and to it the name of fenestrated membrane has been given by Henle. The yellow elastic fibres remain unaltered by acetic acid; chemically they are composed of the albuminoid body elastin. Mucous Tissue. — jMucous tissue exists chiefly in the "jelly of \Yharton," which forms the bulk of the umbilical cord, but is also found in other situations in the fetus, chiefly as a stage in the development of connective tissue. It consists of a matrix, largely made up of mucin, in which are nucleated cells with branching and anastomosing processes (Fig. 20). Few fibres are seen in typical mucous tissue, although at birth the umbilical cord shows a considerable development of fibres. In the adult the vitreous humor of the eye is a persistent form of mucous tissue, in w^hich there are no fibres, and from which the cells have disappeared, leaving only the mucinous ground substance. Retiform or Reticular Tissue (Fig. 21) is found extensively in many parts of the body, constituting the framework of some organs and entering into the construc- tion of manv mucous membranes. It is a varietv of connective tissue, in which Fig 19. — Elastic fibres. (Sharpey.) X 200. CONNECTIVE TISSUES 45 the intercellular or gound substance has, in great measure, disappeared, and is replaced by fluid. It is apparently composed almost entirely of extremely fine bundles of white fibrous tissue, forming an intricate network, and chemically it yields gelatin. The fibres are covered and concealed in places by flattened branched connective tissue cells. In many situations the interstices of the network are filled with rounded lymph-corpuscles, and the tissue is then termed lymphoid or adenoid tissue. Fig. 20.— Mucous tissue from the umbilical cord of the human fetus of four months. ■f Fig. 21. — Retiform tissue, from a lymph gland. Basement Membranes, formerly described as homogeneous membranes, are in most cases really a form of connective tissue. They constitute the supporting membrane, or membrana propria, on which is placed the epithelium of mucous membranes or secreting glands, and they are also found in other situations. Bv 46 HISTOLOGY means of staining with nitrate of silver they may be shown to consist usually of flattened cells in close apposition, and joined together by their edges, thus forming an example of an epithelioid arrangement of connective tissue cells. In some situations the cells, instead of adhering by their edges, give off branching processes which join with similar processes of other cells, and so form a network rather than a continuous membrane. Some basement membranes are composed of elastic tissue, as in the cornea, others are merely condensed matrix. Vessels and Nerves of Connective Tissue. — The bloodvessels of connective tissue are very few — that is to say, there are few actually destined for the tissue itself, although many vessels carrying blood to other structures may permeate one of its forms, the areolar tissue. In white fibrous tissue the bloodvessels usually run parallel to the longitudinal bundles and between them, sending transverse com- municating branches across; in some forms, as in the periosteum and dura mater they are fairly numerous. In yellow elastic tissue, the bloodvessels also run between the fibres, and do not penetrate them. Lymphatic vessels are very numer- ous in most forms of connective tissue, especially in the areolar tissue beneath the skin and the mucous and serous surfaces. They are also found in abundance in the sheaths of tendons, as well as in the tendons themselves. Nerves are to be found in the white fibrous tissue, where they end in a special manner; but it is doubtful whether any nerves end in areolar tissue; at all events, they have not yet been demonstrated, and the tissue is possessed of very little sensibility. Pigment. — In various parts of the body pigment is found; most frequently in epithelial cells and in the cells of connective tissue. Pigmented epithelial cells are found in the external layer of the retina, on the posterior surface of the iris, in the olfactory region of the nose, and in the membranous labyrinth of the ear. Pig- ment is likewise found in the cells of the deeper laj'ers of the cuticle and in the hairs; in the skin of the colored races it is abun- dantly present, but in the white races it is well-marked only in the areolee around the nipples and in irregular colored patches. In the connective tissue cells pigment is frequently met with in the lower verte- brates. In man it is found in the choroid coat of the eye (Fig. 22), and in the iris of all but the light blue eyes and the albino. It is also occasionally met with in the cells of retiform tissue and in the pia mater of the upper part of the medulla spinalis. The cells are characterized by their large size and by branched processes, w^hich are also filled with granules. In the retina the pro- cesses of the cells can be withdrawn or protruded under the influence of light in order to protect the delicate rods and cones. The pigment (melanin) consists of dark brown or black granules of very small size closely packed together within the cells, but not invading the nucleus. Occasionally the pigment is yellow, and when occurring in the cells of the cuticle constitutes "freckles." In the retina another variety of pigment occurs, known as rhodopsin or visual purple, which is bleached on exposure to light. Applied Anatomy. — Abnormal pigmentation of the skin may be congenital, when it often takes the form of dark brown or black nevi (moles), scattered over a greater or smaller area of the body. It may also result from the prolonged consumption of various drugs, particularly of salts of silver or arsenic, being most marked wherever the skin is exposed to the action of light. Fig. 22. — Pigment cells from the choroid coat of the eyeball. CONNECTIVE TISSUES 47 Progressive darkening or bronzing of tlic skin is also highlj' suggestive of Addison's disease, which commonly follows destruction or tuberculosis of the suprarenal glands; it is then most obvious in regions where the skin is normally pigmented or is subjected to pressure or irritation from the clothes. Pigmentation is also associated with certain disorders of the skin, of the female genitaUa, and of the thyroid gland, and with the later stages of wasting diseases such as cancer and phthisis. It does not yield to any medical treatment as a rule. Development of Connective Tissue. — Connective tissue is developed from cells of the meso- derm. Tlu'se cells nudtijjly and form a syncytium containing many nuclei. Later the proto- plasm increases rapidly in amount, and in the vicinity of each nucleus is differentiated into two pai'ts: (1) a portion sm-rounding the nucleus and forming ultimately the cytoplasm of the con- nective tissue cell; (2) an outlying portion in which fibrillation takes place. Both the white and the yellow elastic fibres are laid down in the same manner. Cartilage. — Cartilage is a non-vascular structure which is found in various parts of the body — in adult life chiefly in the joints, in the parietes of the thorax, and in various tubes, such as the trachea and bronchi, nose, and ears, which require to be kept permanently open. In the fetus, at an early period, the greater part of the skeleton is cartilaginous; as this cartilage is afterward replaced by bone, it is called temporary, in contradistinction to that which remains unossified during the whole of life, and is called permanent. Cartilage is di^'ided, according to its minute structure, into hyaline cartilage, white fibrocartilage, and yellow or elastic fibrocartilage. Besides these varieties met with in the adult human subject, there is a variety called cellular cartilage, which consists entirely, or almost entirely, of cells, separated from each other by their capsules only, which in this kind of cartilage are extremely well-marked. Cellular cartilage is found in the external ears of rats, mice, and some other animals, and is present in the notochord of the human embryo, but is not found in any other human structure. The various cartilages in the body are also classified, according to their functions and positions, into articular, interarticular, costal, and membraniform. Hyaline Cartilage. — Hyaline cartilage consists of a gristly mass of a firm consist- ence, but of considerable elasticity and pearly bluish color. Except where it coats the articular ends of bones, it is covered externally by a fibrous membrane, the perichondrium, from the vessels of which it imbibes its nutritive fluids, being itself destitute of bloodvessels. It contains no nerves. Its intimate structure is very simple. If a thin slice be examined under the microscope, it will be found to consist of cells of a rounded or bluntly angular form, lying in groups of two or more in a granular or almost homogeneous matrix (Fig. 23). The cells, when arranged in groups of two or more, have generally straight outlines where they are in contact with each other, and in the rest of their circumference are rounded. They consist of clear translucent protoplasm in which fine inter- lacing filaments and minute granules are sometimes present; imbedded in this are one or two round nuclei, having the usual intranuclear network. The cells are contained in cavities in the matrix, called cartilage lacunae; around these the matrix is arranged in concentric lines, as if it had been formed in successive portions around the cartilage cells. This constitutes the so-called capsule of the space. Each lacuna is generally occupied by a single cell, but during the division of the cells it may contain two, four, or eight cells. The matrix is transparent and apparently without structure, or else presents a Fig. 23. — Human cartilage cells from the cricoid cartilage. X 350 48 HISTOLOGY dimly granular appearance, like ground glass. Some observers have shown that the matrix of hyaline cartilage, and especially of the articular variety, after pro- longed maceration, can be broken up into fine fibrils. These fibrils are probably of the same nature, chemically, as the white fibres of connective tissue. It is believed by some histologists that the matrix is permeated by a number of fine channels, which connect the lacunse with each other, and that these canals com- municate with the lymphatics of the perichondrium, and thus the structure is permeated by a current of nutrient fluid. Articular cartilage, costal cartilage, and temporary cartilage are all of the hyaline variety. They present differences in the size, shape, and arrangement of their cells. In Articular Cartilage (Fig. 24), which shows no tendency to ossification, the matrix is finely granular; the cells and nuclei are small, and are disposed parallel to the surface in the superficial part, while nearer to the bone they are arranged in vertical rows. Articular cartilages have a tendency to split in a vertical direction; in disease this tendency becomes very manifest. The free surface of articular cartilage, where it is exposed to friction, is not covered by perichondrium, although a layer of connective tissue continuous with that of the synovial membrane can be I Superficial flAiUened cells '. Irruption tne periCnondnUm, entirely similar to the of the subperiosteal tissue, v- Fibrous layer of the perios- pmhrvonir- pnnnppfi\ra fiQcnf^ nlr^nrl-^/ teum o. Layer of osteoblasts, irn. Subperiosteal bony emoryomc connective ^ tissue aireaay deposit. (From Qualn's "Anatomy," E. a. Schafer.) described as constituting the basis of membrane bone; on the inner surface of this — that is to say, on the surface in contact with the cartilage — are gathered the formative cells, the osteoblasts. By the agency of these cells a thin layer of bony tissue is formed between the peri- chondrium and the cartilage, by the intramemhranous mode of ossification just described. There are then, in this first stage of ossification, two processes going on simultaneously: in the centre of the cartilage the formation of a number of oblong spaces, formed of calcified matrix and containing the withered cartilage cells, and on the surface of the cartilage the formation of a layer of true mem- brane bone. The second stage consists in the prolongation into the cartilage of processes of the deeper or osteogenetic layer of the perichondrium, which has now become periosteum (Fig. 35, ir). The processes consist of bloodvessels and 5tM«. 58 HISTOLOGY cells — osteoblasts, or bone-formers, and osteoclasts, or bone-destroyers. The latter are similar to the giant cells (myeloplaxes) found in marrow, and they excavate passages through the new-formed bony layer by absorption, and pass through it into the calcified matrix (Fig. 36). Wherever these processes come in con- tact with the calcified walls of the primary areolae they absorb them, and thus cause a fusion of the original cavities and the formation of larger spaces, which are termed the secondary areolae or medullary spaces. These secondary spaces become filled with embryonic marrow, consisting of osteoblasts and vessels, derived, in the manner described above, from the osteogenetic layer of the periosteum (Fig. 36). Thus far there has been traced the forma- tion of enlarged spaces (secondary areolae), the perforated walls of which are still formed by calcified cartilage matrix, containing an embryonic marrow derived from the processes sent in from the osteogenetic layer of the periosteum, and consisting of bloodvessels and osteoblasts. The walls of these secondary areolae are at this time of only inconsiderable thickness, but they become thickened by the deposition of layers of true bone on their sur- face. This process takes place in the follow- ing manner: Some of the osteoblasts of the embryonic marrow, after undergoing rapid division, arrange themselves as an epithelioid layer on the surface of the wall of the space (Fig. 37). This layer of osteoblasts forms a bony stratum, and thus the wall of the space becomes gradually covered with a layer of Osteoclasts- Fig. 36. — Part of a longitudinal section of the developing femur of a rabbit, a. Flattened cartilage cells, h. Enlarged cartUage cells, c, d. Xewly formed bone. e. Osteoblasts. /. Giant cells or osteoclasts. g, h. Shrunken cartilage cells. (From "Atlas of Histology," Klein and Noble Smith.) Osteoblasts Fig. 37. — Osteoblasts and osteoclasts on trabecula of lower jaw of calf embryo. (KolUker.; true osseous substance in which some of the bone-forming cells are included as bone corpuscles. The next stage in the process consists in the removal of these primary bone spicules by the osteoclasts. One of these giant cells may be found lying in a Howship's foveola at the free end of each spicule. The removal of the primary spicules goes on j^^ri -passu with the formation of permanent bone by the periosteum, and in this way the medullary cavity of the body of the bone is formed. This series of changes has been gradually proceeding toward the end of the body of the bone, so that in the ossifying bone all the changes described above may be seen in different parts, from the true bone at the centre of the body to the hyaline cartilage at the extremities. CONNECTIVE TISSUES 59 AYhilc the ossification of tlie cartilaginous body is extending toward the articular ends, the cartilage immediately in advance of the osseous tissue continues to grow until the length of the adult bone is reached. During the period of growth the articular end, or epiphysis, remains for some time entirely cartilaginous, then a bony centre appears, and initiates in it the process of intracartilaginous ossification; but this process never extends to any great distance. The epiphysis remains separated from the body by a narrow cartilaginous layer for a definite time. This layer ultimately ossifies, the distinc- tion between body and epiphysis is obliterated, and the bone assumes its completed form and shape. The same remarks also apply to such processes of bone as are separately ossified, e. g., the trochanters of the femur. The bones therefore con- tinue to grow until the body has acquired its full stature. They increase in length b}' ossification continuing to extend behind the epiphysial cartilage, which goes on growing in advance of the ossifying process. They increase in circumference by deposition of new bone, from the deeper layer of the periosteum, on their exter- nal surface, and at the same time an absorption takes place from within, by which the medullary cavities are increased. The permanent bone formed by the periosteum when first laid down is cancellous in structure. Later the osteoblasts contained in its spaces become arranged in the concentric layers characteristic of the Haversian systems, and are included as bone corpuscles. The number of ossific centres varies in different bones. In most of the short bones ossification commences at a single point near the centre, and proceeds toward the surface. In the long bones there is a central point of ossification for the body or diaphysis: and one or more for each extreinity, the epiphysis. That for the body is the first to appear. The times of union of the epiphyses with the body vary inversely with the dates at which their ossifications began (with the exception of the fibula) and regulate the direction of the nutrient arteries of the bones. Thus, the nutrient arteries of the bones of the arm and forearm are directed toward the elbow, since the epiphyses at this joint become united to the bodies before those at the opposite extremities. In the lower limb, on the other hand, the nutrient arteries are directed away from the knee: that is, upward in the femur, downward in the tibia and fibula; and in them it is observed that the upper epiphysis of the femur, and the lower epiphyses of the tibia and fibula, unite first with the bodies. Where there is only one epiphysis, the nutrient artery is directed toward the other end of the bone; as toward the acromial end of the clavicle, toward the distal ends of the metacarpal bone of the thumb and the metatarsal bone of the great toe, and toward the proximal ends of the other metacarpal and metatarsal bones. Parsons^ groups epiphyses under three headings, viz.: (1) pressure epiphyses, appearing at the articular ends of the bones and transmitting "the weight of the body from bone to bone;" (2) traction epiphyses, associated with the insertion of muscles and "originally sesamoid structures though not necessarily sesamoid bones;" and (3) atavistic epiphyses, representing parts of the skeleton, which at one time formed separate bones, but which have lost their function, " and only appear as separate ossifications in early life." Applied Anatomy. — It has been stated above that the bones increase firstty in length bj^ ossifi- cation continuing to extend in the epiphysial cartilage, which goes on growing in advance of the ossifying process; and secondly, in circumference by deposition of new bone from the deeper layer of the periosteum, on the external sm-face. A careful study of osseous development is of the very greatest utihty in the proper understand- ing of bone disease; and, moreover, an accm-ate knowledge of the blood supply of a long bone 1 Jour, of Anat. and Phys., vols, xsxviii, xxxix, and xlii. 60 HISTOLOGY has also many important bearings. The outer portion of the compact tissue being supphed by periosteal vessels, which reach the bone through muscular attachments, it follows that where the muscular structures are well developed, and therefore amply supphed with blood, the perios- teum will also be well-nourished and the bones proportionately well-developed in girth; this is well seen in strong muscular men with well-marked ridges on the bones. Conversely, if the mus- cular development be poor, the bones are correspondingly thin and hght, and if from any cause a hmb has been paralyzed from early childhood, the whole of the bones of that extremity are remarkable for their extreme thinness — that is to say, the periosteal blood supply has been insuffi- cient to nourish that membrane, and consequently very httle fresh osseous tissue has been added to the bones from the outside. The best example of this condition is seen in connection with the disease known as infantile paralysis, where a hmb becomes paralyzed at a very early period of childhood, where the muscles become flaccid and atonic, and where the blood supply is in consequence very greatly diminished. In such cases, although the hmb does continue to grow in length from the epiphysial lines, its length is considerably less than on the normal side, owing to the imperfect nutrition; but the most striking feature about all the long bones of the Umb is their remarkable tenuity, little or no addition having been made to their circumferences. In cases where the periosteum has been separated from the compact tissue by extensive injury or inflammatory exudation, necrosis or death of the underlying portion of bone takes place owing to its blood supply having been cut off, and the dead portion or sequestrum has to be separated and subsequently cast off. Cases, however, occur where the inflammatory process affects the whole or a great portion of the diaphysis of a long bone, and here extensive death of the affected portion takes place, and the condition goes by the name of acute infective periostitis. Where this occurs the body of the bone dies very rapidly, especiaUy if the single nutrient artery be thrombosed at the same time. The pus which has formed beneath the periosteum is set free by timely incision, or bursts on the surface; the periosteum then falls back on the necrosed diaphysis and rapidly forms a layer of new periosteal bone, surrounding the sequestrum. This layer is called the involucrum, and the openings in it through which the pus escapes the cloacce. When the inflammatory process affects mainly the medullary canal, the condition is spoken of as osteomyelitis, and the two conditions very frequently coexist, and then go by the name of acute infective necrosis of bone or acute diaphysitis . When the medullary cavity is filled with pus, septic thrombosis of the veins in the Haversian canals takes place, and there is a very great danger of septic emboh being displaced and carried into the general circulation, thus setting up a fatal pyemia. In fact, pyemia is more frequently due to septic bone conditions than to any other cause. In the pre-antiseptic days, pyemia frequently resulted from, amputations, where the medullary canal of a long bone was opened by the saw cut. Osteomyehtis ensued, and if the patient sur- vived, a tubular sequestrum of the divided shaft subsequently separated. A proper knowledge of the epiphyses is of the utmost possible importance, and greatly simphfies many of the problems in the pathology of bone disease. Speaking generally, the long bones have at either end an epiphysis from the cartilage of which growth occurs, and hence the body of the bone increases in length from both ends. In every case, however, one epiphysis is the more active, and also continues in its activity for a longer time. This actively growing epiphysis is always the one from which the nutrient foramen in the diaphysis points, and it imites to the diaphysis at a later date. It follows, therefore, that the increase in length of a bone is largely dependent on this epiphysis, and hence anything which interferes with the growth from this epiphysial hne at any time prior to the union of the epiphysis with the diaphysis must result in a cessation of growth in length of that bone. Thus when deal- ing with disease in the neighborhood of this actively growing epiphysis very great care should be taken not to excise or destroy its line of imion with the diaphysis. These epiphyses are par- ticTilarly prone to become the seat of tuberculous disease, which especially tends to attack the soft, highly vascular canceUous tissue. Again, the actively growing epiphysial plate is the portion of a long bone which is in the vast majority of cases afTected by tumor growth in bone, whether it be innocent or malignant, the former (e. g., osteoma) usually appearing about puberty, and the latter (e. g., sarcoma) usually toward the end of the active period of epiphysial growth. Epiphysial growth, moreover, has to be considered by the surgeon when he is about to ampu- tate in a child. If the amputation is being performed through a bone, the actively growing epiphysis of which is at the upper end, and which will continue to grow for several years (e. g., humerus and tibia), it will be necessary to make allowance for this and to cut the flaps long; as otherwise, owing to continued growth, the sawn end of the bone will ultimately project through the stump, and a condition known as "conical stump" wiU result. This requires removal of a further portion of the bone. An inflammatory condition termed acute epiphysitis also occurs, although it is not so frequent as the acute infective conditions of the diaphysis, owing to the freer blood supply of the epiphysis; THE CIRCULATING FLUIDS 61 in late years it lias been shown that acute epipliysitis in (children is very frequently the result of a pneumococcal infection, and it may pass on to complete separation of the epiphysis. In this connection it is worthy of note that some of the epiphysial lines lie entirely within the cap- sules of their corresponding joints, in other cases entirely witliout the capsules; and it must follow that in the former case epiphysial disease, acute or chronic, becomes, ipso facto, practically synony- mous with disease of that joint. The best examples of intra-articular epiphyses are those for the head of the femur and head of the humerus, and the vast majority of all cases of tuberculous disease of the hip start as a tuberculous epiphysitis about the intra-articular epiphysial plate of the femur; again cases of acute septic arthritis of the shoulder or hip joints generally have their origins in these intra-articular epiphysial lines, and often result in separation of the affected epiphysis. Those of the other class, or extra-articular epiphyses, when diseased, do not tend to involve the neighboring joint so readily; and it should be the surgeon's duty to keep the disease from involv- ing the joint. For example, the trochanteric epiphysis of the femur is extra-articular as regards the hip-joint, and the epiphysial line of the head of the tibia is well below the level of the knee- joint, and should a chronic tuberculous abscess form in the latter situation, it should be attacked from the outside before it has time to spread up and involve the cartilage of the head of the tibia. It is therefore of great surgical interest to note in every case the relations which the various epiphysial lines bear to their respective joint capsules. A knowledge of the exact periods when the epiphyses become joined to the shaft is often of great importance in medicolegal inquiries. It also aids the surgeon in the diagnosis of many of the injuries to which the joints are hable; for it not infrequently happens that, on the apphcation of severe force to a joint, the epiphysis becomes separated from the diaphysis, and such injuries may be mistaken for fracture or dislocation. THE CIRCULATING FLUIDS. The circulating fluids of the body are the blood and the lymph. Blood. — The blood is an opaque, rather viscid fluid, of a bright red or scarlet color when it flows from the arteries, of a dark red or purple color when it flows from the veins. It is salt to the taste, and has a peculiar faint odor and an alkaline reaction. Its specific gravity is about 1.06, and its temperature is generally about 37° C, though varying slightly in different parts of the body. General Composition of the Blood. — Blood consists of a faintly yellow fluid, the plasma or liquor sanguinis, in which are suspended numerous minute particles, the blood corpuscles, the majority of which are colored and give to the blood its red tint. If a drop of blood be placed in a thin layer on a glass slide and examined under the microscope, a number of these corpuscles will be seen floating in the plasma. The Blood Corpuscles are of /^^X /<^IiX M^^ ^^ b three kinds: (1) colored cor- puscles or erythrocytes; (2) color- less corpuscles or leucocytes; (3) blood platelets. 1. Colored or red corpuscles (erythrocytes) , when examined under the microscope, are "seen to be circular disks, biconcave in profile. The disk has no nucleus, but, in consequence of its bicon- cave shape, presents, according to the alterations of focus under an ordinary high power, a central part, sometimes bright, sometimes dark, which has the appearance of a nucleus (Fig. 38, a). It is to the aggregation of the red corpuscles that the blood owes its red hue, although when examined by transmitted light their color appears to be only a faint reddish yellow. The corpuscles vary slightly in size even in the same drop of blood, but the average Fig. 38. — Human red blood corpuscles. Highly magnified, a. Seen from the surface, b. Seen in profile and forming rouleaux. c. Rendered spherical by water, d. Rendered crenate by salt solution. 62 HISTOLOGY diameter of each is about 7.5m/ and the thickness about 2)u, Besides these there are found certain smaller corpuscles of about one-half of the size just indicated; these are termed microcytes, and are very scarce in normal blood; in diseased con- ditions (e. g., anemiaj, however, they are more numerous. The number of red corpuscles in the blood is enormous; between 4,000,000 and 5,000,000 are con- tained in a cubic millimetre. Power states that the red corpuscles of an adult would present an aggregate surface of about 3000 square yards. If the web of a living frog's foot be spread out and examined under the micro- scope the blood is seen to flow in a continuous stream through the vessels, and the corpuscles show no tendency to adhere to each other or to the wall of the vessel. Doubtless the same is the case in the human- body; but when human blood is drawn and examined on a slide without reagents the corpuscles tend to collect into heaps like rouleaux of coins (Fig. 38, b). It has been suggested that this phenomenon may be explained by alteration in surface tension. During life the red corpuscles may be seen to change their shape under pressure so as to adapt themselves, to some extent, to the size of the vessel. They are, however, highly elastic, and speedily recover their shape when the pressure is removed. They are readily influenced by the medium in which they are placed. In water they swell up, lose their shape, and become globular (endosmosis) (Fig. 38, c). Subsequently the hemoglobin is dissolved out, and the envelope can barely be distinguished as a faint circular outline. Solutions of salt or sugar, denser than the plasma, give them a stellate or crenated appearance (exosmosis) (Fig. 38, d), but the usual shape may be restored by diluting the solution to the same tonicity as the plasma. The crenated outline may be produced as the first effect of the passage of an elec- tric shock: subsequently, if sufficiently strong, the shock ruptures the envelope. A solution of salt, isotonic with the plasma, merely separates the blood corpuscles mechanically, without changing their shape. Two views are held with regard to the structure of the erythrocytes. The older view, that of Rollett, supposes that the corpuscle consists of a sponge work or stroma permeated by a solution of hemo- globin. Schafer, on the other hand, believes that the hemoglobin solution is con- tained within an envelope or membrane, and the facts stated above with regard to the osmotic behavior of the erythrocyte support this belief. The envelope consists mainly of lecithin, cholesterin, and nucleoprotein. The colorless corpuscles or leucocytes are of various sizes, some no larger, others smaller, than the red corpuscles, In human blood, however, the majority are rather larger than the red corpuscles, and measure about lO/i in diameter. On the average from 7000 to 12,000 leucocytes are found in each cubic millimetre of blood. They consist of minute masses of nucleated protoplasm, and exhibit several varieties, which are differentiated from each other chiefly by the occurrence or non-occurrence of granules in their protoplasm, and by the staining reactions of these granules when present (Fig. 39). (1) The most numerous (60 per cent.) and important are irregular in shape, possessed of the power of amoeboid movement, and are characterized by nuclei which often consist of two or three parts (multi- partite) connected together by fine threads of chromatin. The protoplasm is clear, and contains a number of very fine granules, which stain with acid dyes, such as eosin, or with neutral dyes, and are therefore called oxyphil or neutrophil (Fig. 39, P). These cells are termed the poljnnorphonuclear leucocytes. (2) A second variety comprises from 1 to 4 per cent, of the leucocytes; they are larger than the previous kind, and are made up of coarsely granular protoplasm, the granules being highly refractile and grouped around single nuclei of horse-shoe shape (Fig. 39, E). The granules stain deeply with eosin, and the cells are there- ' A micromillimetre C") is 1/1000 of a millimetre or 1/25000 of an inch. THE CIRCULATING FLUIDS 63 fore often termed eosinophil corpuscles. (3) The third variety is called the hyaline cell or macrocyte (Fig-. 39, //). This is usually about the same size as the eosino- phil cell, and, when at rest, is spherical in shape and contains a single round 6r oval nucleus. The protoplasm is free from granules, but is not quite transparent, having the appearance of ground glass. (4) The fourth kind of colorless corpuscle is designated the lymphocyte (Fig. 39, i), because it is identical with the cell derived from the lymph glands or other lymphoid tissue. It is the smallest of the leuco- cytes, and consists chiefly of a spheroidal nucleus with a very little surrounding protoplasm of a homogeneous nature; it is regarded as the immature form of the Fig. 39. — Varieties of leucocytes found in human blood. Highly magnified. hyaline cell. The third and fourth varieties together constitute from 20 to 30 per cent, of the colorless corpuscles, but of these two varieties the lymphocj-tes are by far the more numerous. Leucoc^i:es having in their protoplasm granules which stain with basic dyes (basiphil) have been described as occurring in human blood, but they are rareh' found except in disease. The colorless corpuscles are very various in shape in living blood (Fig. 40), because many of them have the power of constantly changing their form by pro- truding finger-shaped or filamentous processes of their substance, by which they move and take up granules from the surrounding medium. In locomotion the corpuscle pushes out a process of its substance — a pseudopodium, as it is called m % ^- Fig. 40. — Human colorless blood corpuscle, showing its successive changes of outline within ten minutes when kept moist on a warm stage. (Schofield.) — and then shifts the rest of the body into it. In the same way w'hen any granule or particle comes in its way the corpuscle wraps a pseudopodium around it, and then withdraws the pseudopodium with the contained particle into its own substance. By means of these amoeboid properties the cells have the power of wandering or emigrating from the bloodvessels by penetrating their walls and thus finding their way into the extravascular spaces. A chemical investigation of the proto- plasm of the leucocytes shows the presence of nucleoprotein and of a globulin. The occurrence of small amounts of fat, lecithin, and glycogen may also be demonstrated. 64 HISTOLOGY The blood platelets (Fig. 41) are discoid or irregularly shaped, colorless, refractile bodies, much smaller than the red corpuscles. Each contains a central chromatin mass resembling a nucleus. Blood platelets possess the power of amoeboid move- ment. When blood is shed they rapidly disintegrate and form granular masses, setting free prothrombin and the substance called by Howell thromboplastin. It is doubtful whether they exist normally in circulating blood. Lymph. — Lymph is a transparent, colorless, or slightly yellow fluid, which is conveyed by a set of vessels, named lymphatics, into the blood. These vessels arise in nearly all parts of the body as lymph capillaries. They take up the fluid which has exuded from the blood capillaries for the nourish- ment of the tissue elements and return it into the veins. The greater number of these lymphatics empty themselves into one main duct, the thoracic duct, which passes upward along the front of the vertebral column and opens into the large veins on „ ^, Di J w w Tj- 1,1 the left side of the root of the neck. The remainder Fig. 41. — Blood platelets. Highly . mi i • i i • magnified. (After Kopsch.) empty thcmsclves mto a smaller duct which ends m the corresponding veins on the right side of the neck. Lymph is a watery fluid of specific gravity about L015; it closely resembles the blood plasma, but is more dilute. When it is examiner' under the microscope, leucocytes of the lymphocyte class are found floating in the transparent fluid; they are always increased in number after the passage of the lymph through lymphoid tissue, as in lymph glands. THE MUSCULAR TISSUE. Muscular tissue is composed of bundles of reddish fibres endowed with the prop- erty of contractility. There are three varieties of muscle: (1) transversely striated fibres, which are for the most part under the control of the will, although some are not so, such as the muscles of the pharynx and upper part of the oesophagus. This variety is called skeletal, striped, or voluntary; (2) transversely striated cardiac fibres, which are not under the control of the will; (3) plain or unstriped fibres, which are involuntary and controlled by a different part of the nervous system from that which controls the activity of the voluntary muscles; such are the muscular walls of the stomach and intestine, of the uterus and bladder, of the bloodvessels, etc. Striped or Voluntary Muscle. — Striped or voluntary muscle is composed of bundles of fibres each enclosed in a delicate web called the perimysium in contradistinction to the sheath of areolar tissue which invests the entire muscle, the epimysium. The bundles are termed fasciculi; they are prismatic in shape, of different sizes in different muscles, and are for the most part placed parallel to one another, though they have a tendency to converge toward their tendinous attachments. Each fasciculus is made up of a strand of fibres, which also run parallel with each other, and are separated from one another by a delicate connective tissue derived from the perimysium and termed endomysium. This does not form the sheath of the fibres, but serves to support the bloodvessels and nerves ramifying between them. A muscular fibre may be said to consist of a soft contractile substance, enclosed in a tubular sheath named by Bowman the sarcolemma. The fibres are cylindrical or prismatic in shape (Fig. 42), and are of no great length, not exceeding, as a rule, THE MUSCULAR TISSUE 65 40 inm. Their bretultli varies in man from 0.01 to 0.1 mm. As a rule, the fibres do not divide or anastomose; but occasionally, especially in the tongue and facial muscles, they may be seen to divide into several branches. In the substance of the muscle, the fibres end by tapering extremities which are joined to the ends of other fibres by the sarcolemma. At the tendinous end of the muscle the sarco- lemma appears to blend with a small bundle of fibres, into which the tendon becomes subdivided, while the muscular substance ends abruptly and can be readily made to retract from the point of junction. The areolar tissue between the fibres appear to be prolonged more or less into the tendon, so as to form a kind of sheath around the tendon bundles for a longer or shorter distance. When muscular fibres are attached to skin or mucous membranes, their fibres become continuous with those of the areolar tissue. ^I'l^tS-" Fig. 42. — Transverse section of 'man striped muscle fibres. X 255. Fig. 43. — Striped muscle fibres from tongue of cat. X 250. The sarcolemma, or tubular sheath of the fibre, is a transparent, elastic, and apparently homogeneous membrane of considerable toughness, so that it some- times remains entire when the included substance is ruptured. On the internal surface of the sarcolemma in mammalia, and also in the substance of the fibre in frogs, elongated nuclei are seen, and in connection with these is a little granular protoplasm. Upon examination of a voluntary muscular fibre by transmitted light, it is found to be marked by alternate light and dark bands or striae, which pass trans- versely across the fibre (Fig. 43). When examined by polarized light the dark bands are found to be doubly refracting (anisotropic), while the clear stripes are singly refracting (isotropic) . The dark and light bands are of nearly equal breadth, and alternate with great regularity; they vary in breadth from about 1 to 2/i. If the surface be carefully focussed, rows of granules will be detected at the points of junction of the dark and light bands, and very fine longitudinal lines may be seen running through the dark bands and joining these granules together. By treating the specimen with certain reagents {e. g., chloride of gold) fine lines may be seen running transversely between the granules and uniting them together. This appearance is believed to be due to a reticulum or network of interstitial substance lying betw^een the contractile portions of the muscle. The longitudinal striation gives the fibre the appearance of being made up of a bundle of fibrils which have been termed sarcostyles or muscle columns, and if the fibre be hardened in alcohol, it can be broken up longitudinally and the sarcostjdes separated from each other (Fig. 44.) The reticulum, with its longitudinal and transverse meshes, is called sarcoplasm. 66 HISTOLOGY In a transverse section, the muscular fibre is seen to be divided into a number of areas, called the areas of Cohnheim, more or less polyhedral in shape and con- sisting of the transversely divided sarcostyles, surrounded by transparent sarco- plasm (Fig. 42). Upon closer examination, and by somewhat altering the focus, the appearances become more complicated, and are susceptible of various interpretations. The transverse striation, which in Fig. 43 appears as a mere alternation of dark and light bands, is resolved into the appearance seen in Fig. 44, which shows a series of broad dark bands, separated by light bands, each of which is divided into two by a dark dotted line. This line is termed Dobie's line or Krause's mem- brane (Fig. 45, k), because it was believed by Krause to be an actual membrane, continuous with the sar- colemma, and dividing the light band into two compartments. In addition to the membrane of Krause, fine clear lines may be made out, with a sufficiently high power, cross- ing the centre of the dark band; these are known as the lines of Hensen (Fig. 45, H). Schafer has worked out the minute anatomy of muscular fibre, particu- larly in the wing muscles of insects, which are peculiarly adapted for this purpose on account of the large amount of interstitial sarcoplasm which sepa- rates the sarcostyles. In the following description that given by Schafer will be closely followed. ^ fig ^SM I Fig. 44. — A. Portion of a medium sized human muscular fibre. Magnified nearly 800 diameters B Separated bundles of fibrils, equallj- magnified, a, a. Larger, and b, b, smaller collections, c. Still smaller, d, d. The smallest which could be detached. S.E. H S.E. B Fig. 45. — Diagram of a sarcomere. (After Schafer.) A. In moderately extended condition. B. In a contracted condition, k, k. Membranes of Krause. H. Line or plane of Hensen. S.E. Poriferous sarcous element. A sarcostyle may be said to be made up of successive portions, each of which is termed a sarcomere. The sarcomere is situated between two membranes of Krause and consists of (1) a central dark part, which forms a portion of the dark band of the whole fibre, and is named a sarcous element. This sarcous element really consists of two parts, superimposed one on the top of the other, and when the fibre is stretched these two parts become separated from each other at the line of Hensen THE MUSCULAR TISSUE 67 (Fig. 45, A). (2) On either side of this central dark portion is a clear layer, most visible when the fibre is extended; this is situated between the dark centre and the membrane of Krause, and when the sarcomeres are joined together to form the sarcostyle, constitutes the light band of the striated muscular fibre. AYhon the sarcostyle is extended, the clear intervals are well-marked and plainly to be seen; when, on the other hand, the sarcostyle is contracted, that is to say, when the muscle is in a state of contraction, these clear portions are very small or they may have disappeared altogether (Fig. 45, B). When the sarcostyle is stretched to its full extent, not only is the clear portion well-marked, but the dark portion — the sarcous element — is separated into its two constituents along the line of Hensen. The sarcous element does not lie free in the sarcomere, for when the sarcostyle is stretched, so as to render the clear portion visible, very fine lines, which are probably septa, may be seen running through it from the sarcous element to the membrane of Krause. Schafer explains these phenomena in the following way: He considers that each sarcous element is made up of a number of longitudinal channels, which open into the clear part toward the membrane of Krause but are closed at the line of Hensen. When the muscular fibre is contracted the clear part of the muscular substance is driven into these channels or tubes, and is therefore hidden from sight, but at the same time it swells up the sarcous element and widens and shortens the sarcomere. When, on the other hand, the fibre is extended, this clear sub- stance is driven out of the tubes and collects between the sarcous element and the membrane of Krause, and gives the appearance of the light part between these two structures; by this means it elongates and narrows the sarcomere. If this view be true, it is a matter of great interest, and, as Schafer has shown, harmonizes the contraction of muscle with the amoeboid action of protoplasm. In an amoeboid cell, there is a framework of spongioplasm, which stains with hematoxylin and similar reagents, enclosing in its meshes a clear substance, hyalo- plasm, which will not stain with these reagents. Under stimulation the hyaloplasm passes into the pores X)f the spongioplasm; without stimulation it tends to pass out as in the formation of pseudopodia. In muscle there is the same thing, viz., a framework of spongioplasm staining with hematoxylin — the substance of the sarcous element — and this encloses a clear hyaloplasm, the clear substance of the sarcomere, which resists staining with this reagent. During contraction of the muscle — i. e., stimulation — this clear substance passes into the pores of the spongio- plasm; while during extension of the muscle — i. e., when there is no stimulation — it tends to pass out of the spongioplasm. In this way the contraction is brought about: under stimulation the proto- plasmic material (the clear substance of the sarcomere) recedes into the sarcous element, causing the sarcomere to widen out and shorten. The contraction of the muscle is merely the sum total of this widening out and shortening of these bodies. Vessels and Nerves of Striped Muscle. — The capillaries or striped muscle are very abundant, and form a sort of rectangular network, the branches of which run longitudinally in the endomysium between the muscular fibres, and are joined at short intervals by transverse anastomosing branches. In the red muscles of the rabbit dilatations occur on the transverse branches of the capillary network. The larger vascular channels, arteries and veins, are found only in the perimysium, between the muscular fasciculi. Nerves are profusely distributed to striped muscle. Their mode of termination is described on page 803. The existence of lymphatic vessels in striped muscle has not been ascertained, though they have been found in tendons and in the sheaths of the muscles. Unstriped, Plain, or Involuntary Muscle. — Unstriped, plain, or involuntary muscle is found in the following situations : in the lower half of the oesophagus and the whole of the remainder of the gastro-intestinal tube; in the trachea and bronchi; 68 HISTOLOGY in the gall-bladder and common bile duct; in the large ducts of the salivary and pancreatic glands; in the pelvis and calices of the kidney, the ureter, bladder, and urethra; in the female sexual organs — viz., the ovary, the uterine tubes, the uterus (enormously developed in pregnancy), the vagina, the broad ligaments, and the corpora cavernosa of the clitoris; in the male sexual organs — viz., the dartos of the scrotum, the ductus deferens and epididymis, the vesiculae seminales, th'e prostate, and the corpora cavernosa of the penis and urethra; in the capsule and trabeculse of the spleen; in the mucous membranes, forming the muscularis mucosae; in the skin, forming the Arrectores pilorum, and also in the sweat glands; in the arteries, veins, and lym- phatics; in the iris and the ciliary muscle. Plain or unstriped muscle is made up of spindle- shaped cells, called contractile fibre cells, collected into bundles and held together by a cement substance (Fig. 46). These bundles are further aggregated into larger fasciculi, or flattened bands, and bound together by ordinary connective tissue. The contractile fibre cells are elongated, spindle- shaped, nucleated cells of various sizes, averaging from 40 to 80m in length, and 6 to 7 fx in breadth. On transverse section they are more or less polyhedral in shape, from mutual pressure. Each presents a faint longitudinal striation and consists of an elastic cell wall containing a central bundle of fibrillse, representing the contractile substance, and an oval or rod-like nucleus, which includes, within a membrane, a fine net-work communicating at the poles of the nucleus with the contractile fibres (Klein). The fibres are attached to one another by a certain amount of interstitial cement substance which reduces nitrate* of silver, but in some regions, e. g., the muscular coats of the intestines, the muscle cells are also connected bj^ "bridges" similar to those which occur in the prickle cells of the epidermis. Unstriped muscle, except the ciliary muscle, is not under the control of the will, neither is the contraction rapid nor does it, as a rule, involve the whole muscle, as is the case with the voluntary muscles. The membranes which are composed of unstriped muscle slowly contract in a part of their extent, generally under the influence of a mechanical stimulus, as that of distension or of cold ; and then the contracted part slowly relaxes while another portion of the membrane takes up the contrac- tion. This peculiarity of action is most strongly marked in the intestines, constituting their vermicular motion. Cardiac Muscular Tissue. — The fibres of the heart differ very remarkably from those of other striped muscles. They are smaller by one-third, and their trans- verse striae are by no means so well-marked. They show faint longitudinal striation. The fibres are made up of distinct quadrangular cells, joined end to end so as to form a syncytium (Fig. 47). Each cell contains a clear oval nucleus, situated near its centre. The extremities of the cells have a tendency to branch or divide, the subdivisions uniting with offsets from other cells, and thus producing an anastomosis of the fibres. The connective tissue between the bundles of fibres is much less than in ordinary striped muscle, and no sarcolemma has been proved to exist. Fig. 46. — Muscle fibres from small intestine. (Schafer.) A. Complete cell. B. Broken cell showing delicate external layer. THE NERVOUS TISSUE 69 Purkinje Fibres (Fig. 48). — Between the endocardium and the ordinary cardiac muscle are found, imbedded in a small amount of connective tissue, peculiar fibres known as Purkinje fibres. They are found in certain mammals and in birds, and can be best seen in the sheep's heart, where they form a considerable portion of the moderator band and also appear as gelatinous-looking strands on the inner walls of the atria and ^'ent^icles. They also occur in the human heart associated with the terminal distributions of the bundle of His (see p. 614). The fibres are very much larger in size than the cardiac cells and differ from them in several ways. In longitudinal section they are quadrilateral in shape, being about twice as long as they are broad. The central portion of each fibre contains one or more nuclei and is made up of granular protoplasm, with no indication of striations, while the peripheral portion is clear and has distinct transverse striations. The fibres are intimately connected with each other, possess no definite sarcolemma, and do not branch. .,— r^- re[^i=^ '^ Fig. 47. — Anastomosing muscular fibres of the heart seen in a longitudinal section. On the right the limits of the separate cells with their nuclei are exhibited somewhat dia- grammatically. Fig. 48. — Purkinje fibres from the sheep's heart. The Bundle of His (see p. 614) is composed of cells which differ from ordinary cardiac muscle cells in being more spindle-shaped. They are, moreover, more loosely arranged and have a richer vascular supply than the rest of the heart muscle. Development of Muscle Fibres. — Voluntary muscular fibres are developed from the mesoderm, the embryonic cells of which elongate, show multipHcation of nuclei, and eventually become striated; the striation is first obvious at the side of the fibres, spreads around the circumference, and ultimately extends to the centre. The nuclei, at first situated centrally, gradually pass out to assume their final position immediately beneath the sarcolemma. In the case of involuntary muscle the mesodermal cell assumes a pointed shape at the extremities and becomes flattened, the nucleus also lengthening out to its permanent rod-like form. THE NERVOUS TISSUE. The nervous tissues of the body comprise the brain, the medulla spinalis or spinal cord, the cerebral, spinal, and sympathetic nerves, and the ganglia connected with them. 70 HISTOLOGY The nervous tissues are composed of nerve cells and their various processes, together with a supporting tissue called neuroglia, which, however, is found only in the brain and medulla spinalis. Certain long processes of the nerve cells are of special importance, and it is convenient to consider them apart from the cells; they are known as nerve fibres. To the naked eye a difference is obvious between certain portions of the brain and medulla spinalis, viz., the gray substance and the white substance. The gray substance is largely composed of nerve cells, while the white substance contains only their long processes, the nerve fibres. It is in the former that nervous impres- sions are received, stored, and transformed into efferent impulses, and by the latter that they are conducted. Hence the gray substance forms the essential constituent of all the ganglionic centres, both those in the isolated ganglia and those aggregated in the brain and medulla spinalis; while the white substance forms the bulk of the commissural portions of the nerve centres and the peripheral nerves. Fig. 49. — Neuroglia cells of brain shown by Golgi's method. (After Andriezen.) A. Cell with branched processes B. Spider cell with unbranched processes. Neuroglia. — Neuroglia, the peculiar ground substance in which are imbedded the true nervous constituents of the brain and medulla spinalis, consists of cells and fibres. Some of the cells are stellate in shape, with ill-defined cell body, and their fine processes become neuroglia fibres, which extend radially and unbranched (Fig. 49, B) among the nerve cells and fibres which they aid in supporting. Other cells give off fibres which branch repeatedly (Fig. 49, A). Some of the fibres start from the epithelial cells lining the ventricles of the brain and central canal of the medulla spinalis, and pass through the nervous tissue, branching repeatedly to end in slight enlargements on the pia mater. Thus, neuroglia is evidently a connective tissue in function but is not so in development; it is ectodermal in origin, whereas all connective tissues are mesodermal. Nerve Cells (Fig. 50). — Nerve cells are largely aggregated in the gray substance of the brain and medulla spinalis, but smaller collections of these cells also form the swellings, called ganglia, seen on many nerves. These latter are found chiefly upon the spinal and cerebral nerve roots and in connection with the sympathetic nerves. The nerve cells vaiy in shape and size, and have one or more processes. They may be divided for purposes of description into three groups, according to the number of processes which they possess: (1) Unipolar cells, which are found in the spinal ganglia; the single process, after a short course, divides in a T-shaped THE NERVOUS TISSUE 71 manner (Fig. 50, E). (2) Bipolar cells, also found in the spinal ganglia (Fig. 51), when the cells are in an embryonic condition. They are best demonstrated in the spinal ganglia of fish. Sometimes the processes come off from opposite poles of Fig. 50. — Various forms of nerve cells. A. Pyramidal cell. B. Small multipolar cell, in which the axon quickly divides into numerous branches. C. Small fusiform cell. D and E. Ganglion cells {E shows T-shaped division of axon), ax. Axon. c. Capsule. Sheath of cell body Nucleus Cell protoplasm '~ Axon Nucleolus Fig. 52. — Motor nerve cell from ventral horn of medulla spinalis of rabbit. (After Nissl.) The angular and spindle- shaped Nissl bodies are well shown. the cell, and the cell then assumes a spindle shape; in other cells both processes emerge at the same point. In some cases where two fibres are apparently connected with a cell, one of the fibres is really derived from an adjoining nerve cell and is passing to end in a ramification around the ganglion cell, or, again, it may be coiled spirally around the nerve process which is issuing from the cell. (3) Multipolar cells, which are pyramidal or stellate in shape, and characterized by their large size and by the numerous processes which issue from them. The processes are of two kinds: one of them is termed the axis- cylinder process or axon because it becomes the axis-cylinder of a nerve fibre -Dendron Myelin sheath Fig. 51. — Bipolar nerve cell from the spinal gan glion of the pike. (After Kolliker.) HISTOLOGY (Figs. 52, 53, 54). The others are termed the protoplasmic processes or dendrons; they begin to divide and subdivide as soon as they emerge from the cell, and finally end in minute twigs and become lost among the other elements of the nervous tissue. The body of the nerve cell, known as the cyton, consists of a finely fibrillated protoplasmic material, of a reddish or yellowish-brown color, which occasionally presents patches of a deeper tint, caused by the aggregation of pigment granules at one side of the nucleus, as in the substantia nigra and locus caeruleus of the brain. The protoplasm also contains peculiar angular granules, which stain deeply 53. — Pyramidal cell from the cerebral cortex of a mouse. (After Ramon y Cajal.) Fig 54 — Cell of Purkinje from the cerebellum. Golgi method. (Cajal.) a. Axon. b. Collateral, c and d. Dendrons. with basic dyes, such as methylene blue; these are known as Nissl's granules (Fig. 52). Thev extend into the dendritic processes but not into the axis-cylinder; the small clear area at the point of exit of the axon is termed the cone of origin. These granules disappear {chromatolysis) during fatigue or after prolonged stimulation of the nerve fibres connected with the cells. They are supposed to represent a store of nervous energy, and in various mental diseases are deficient or absent. The nucleus is, as a rule, a large, well-defined, spherical body, often presenting an intranuclear network, and containing a well-marked nucleolus. THE NERVOUS TISSUE 73 In addition to the protoplasmic network described above, each nerve cell may be shown to have delicate neurofibrils running through its substance (Fig. 55); these fibrils are continuous with the fibrils of the axon, and are believed to convey nerve impulses. Golgi has also described an extracellular network, which is probably a supporting structure. Nerve Fibres. — Xerve fibres are found universally in the peripheral nerves and in the white substance of the brain and medulla spinalis. They are of two kinds — viz., medullated or white fibres, and non-medullated or gray fibres. Fig. 55. — Nerve cells of kitten, showing neurofibrils. (Cajal.) a. Axon. 6. Cyton. c. Nucleus, d. Neurofibrils. The medullated fibres form the white part of the brain and medulla spinalis, and also the greater part of every cerebral and spinal nerve, and give to these structures their opaque, white aspect. When perfectly fresh they appear to be homogeneous; but soon after removal from the body each fibre presents, when examined by trans- mitted light, a double outline or contour, as if consisting of two parts (Fig. 56). The central portion is named the axis - cylinder ; around this is a shea*h of fatty material, staining black with osmic acid, named the white substance of Schwann or medullary sheath, which gives to the fibre its double contour, and the whole is enclosed in a delicate membrane, the neurolemma, primitive sheath, or nucleated sheath of Schwaim (Fig. 58). The axis-cylinder is the essential part of the nerve fibre, and is always present; the medullary sheath and the neurolemma are occasionally absent, expecially at the origin and termination of the nerve fibre. The axis-cylinder undergoes no interruption from its origin in the nerve centre to its peripheral termination, and 74 HISTOLOGY must be regarded as a direct prolongation of a nerve cell. It constitutes about one-half or one-third of the nerve fibre, being greater in proportion in the fibres of the central organs than in those of the nerves. It is quite transparent, and is therefore indistinguishable in a perfectly fresh and natural state of the nerve. It is made up of exceedingly fine fibrils, which stain darkly with gold chloride Fig. 56.— Medullated nerve fibres. (Bidder and Volkmann.) j-jQ ,57_ — Longitudinal and transverse sec- tions of medullated nerve fibre of frog, showing node of Ranvier, medullary segments and fibrils of axis cylinder. Osmic acid. (Biedermann.) Fig. 58. — Diagram of medullated nerve fibres stained with osmic acid, ' X 425. (Schiifer.) R. Nodes of Ran- vier. a. Neurolemma, c. Nucleus. (Fig. 57), and at its termination may be seen to break up into these fibrilla. The fibrillee have been termed the primitive fibrillse of Schultze. The axis-cylinder is said by some to be enveloped in a special reticular sheath, which separates it from the medullary sheath, and is composed of a substance called neurokeratin. The more common opinion is that this network or reticulum is contained in the white THE NERVOUS TISSUE 75 matter of Schwann, and by some it is believed to be produced by the action of the reagents employed to show it. The medullary sheath, or white matter of Schwami (Fig. 57), is regarded as being a fatty matter in a fluid state, which insulates and i)r()tects the essential part of the nerve — the axis-cylinder. It varies in thickness, in some forming a layer of extreme thinness, so as to be scarcely distinguishable, in others forming about one-half the nerve jfibre. The variation in diameter of the nerve fibres (from 2 to 16/x) depends mainly upon the amount of the wdiite substance, though the axis cylinder also varies within certain limits. The medullary sheath undergoes interruptions in its continuity at regular intervals, giving to the fibre the appearance of constriction at these points: these are known as the nodes of Ranvier (Figs. 57 and 58). The portion of nerve fibre between two nodes is called an internodal segment. The neurolemma or primitive sheath is not interrupted at the nodes, but passes over them as a continuous membrane. If the fibre be treated with silver nitrate the reagent penetrates the neurolemma at the nodes, and on exposure to light reduction takes place, giving rise to the appearance of black crosses, Ranvier's crosses, on the axis-cvlinder. There mav also be seen transverse lines bevond the nodes termed I- Node of Eanvier Frommann^s lines Fig. 59. — Medullated nerve fibres stained with silver nitrate. Fig. 60. — A small nervous branch from the sympathetic of a mammal. a. Two medullated nerve fibres among a number of gray nerve fibres, h. Frommann's lines (Fig. 59) ; the significance of these is not understood. In addi- tion to these interruptions oblique clefts may be seen in the medullary sheath, subdividing it into irregular portions, which are termed medullary segments, or segments of Lantermann (Fig. 57); there is reason to believe that these clefts are artificially produced in the preparation of the specimens. Medullated nerve fibres, when examined in the fresh condition, frequently present a beaded or vari- cose appearance: this is due to manipulation and pressure causing the oily matter to collect into drops; and in consequence of the extreme delicacy of the primitive sheath, even slight pressure wdll cause the transudation of the fatty matter, which collects as drops of oil outside the membrane. The neurolemma or primitive sheath presents the appearance of a delicate, structureless membrane. Here and there beneath it, and situated in depressions in the white matter of Schwann, are nuclei surrounded by a small amount of protoplasm. The nuclei are oval and somewhat flattened, and bear a definite relation to the nodes of Ranvier, one nucleus generally lying in the centre of each internode. The primitive sheath is not present in all medullated nerve fibres, being absent in those fibres wdiich are found in the brain and medulla spinalis. 76 HISTOLOGY Wallerian Degeneration. — When nerve fibres are cut across, the central ends of the fibres degenerate as far as the first node of Ranvier; but the peripheral ends degenerate simultaneously throughout their whole length. The axons break up into fragments and become surrounded by drops of fatty substance which are formed from the breaking down of the medullary sheath. The nuclei of the primitive sheath proliferate, and finally absorption of the axons and fatty substance occurs. If the cut ends of the nerve be sutured together regeneration of the nerve fibres takes place by the downgrowth of axons from the central end of the nerve. At one time it was beheved that the regeneration was peripheral in origin, but this has been disproved, the proUferated nuclei in the peripheral portions taking part merely in the formation of the so-called scaffolding along which the new axons pass. Non-meduUated Fibres. — Most of the fibres of the sympathetic system, and some of the cerebrospinal, consist of the gray or gelatinous nerve fibres {fibres of Remak) (Fig. 60). Each of these consists of an axis-cylinder to which nuclei are applied at intervals. These nuclei are believed to be in connection with a delicate sheath corresponding with the neurolemma of the meduUated nerve fibre. In external appearance the non-medullated nerve fibres are semitransparent and gray or yellowish gray. The individual fibres vary in size, generally averaging about half the size of the medullated fibres. EMBRYOLOGY. rpHE term Embryology, in its widest sense, is applied to the various changes -*- which take place during the growth of an animal from the egg to the adult condition: it is, however, usually' restricted to the phenomena which occur before birth. Embryology may be studied from two aspects: (1) that of ontogeny, which deals only with the development of the individual; and (2) that of phylogeny, which concerns itself with the evoluntionary history of the animal kingdom. In vertebrate animals the development of a new being can only take place when a female germ cell or ovum has been fertilized by a male germ cell or spermatozoon. The ovum is a nucleated cell, and all the complicated changes by which the various tissues and organs of the body are formed from it, after it has been fertilized, are the result of two general processes, viz., segmentation and differentiation of cells. Thus, the fertilized ovum undergoes repeated segmentation into a number of cells which at first closely resemble one another, but are, sooner or later, differentiated into two groups: (1) somatic cells, the function of which is to build up the various tissues of the body; and (2) germinal cells, which become imbedded in the sexual glands — the ovaries in the female and the testes in the male — and are destined for the perpetuation of the species. Having regard to the main purpose of this work, it is impossible, in the space available in this section, to describe fully, or illustrate adequately, all the phenom- ena which occur in the different stages of the development of the human body. Only the principal facts are given, and the student is referred for further details to one or other of the text-books^ on human embryology. THE OVUM. The ova are developed from the primitive germ cells which are imbedded in the substance of the ovaries. Each primitive germ cell gives rise, by repeated divisions, to a number of smaller cells termed cogonia, from which the ova or primary oocytes are developed. Human ova are extremely minute, measuring about 0.2 mm. in diameter, and are enclosed within the egg follicles of the ovaries; as a rule each follicle contains a single ovum, but sometimes two or more are present. ^ By the enlargement and subsequent rupture of a follicle at the surface of the ovary, an ovum is liberated and conveyed by the uterine tube to the cavity of the uterus. Unless it be fertilized it undergoes no further development and is discharged from the uterus, but if fertilization take place it is retained within the uterus and is developed into a new being. In appearance and structure the ovum (Fig. 61) differs little from an ordinary cell, but distinctive names have been applied to its several parts; thus, the cell substance is known as the yolk or ooplasm, the nucleus as the germinal vesicle, and the nucleolus as the germinal spot. The ovum is enclosed within a thick, trans- 1 JNIanual of Human Embryology, Keibel and Mall; Handbuch der vergleichenden und experimentellen Entwickel- ungslehre der Wirbeltiere, Oskar Hertwig; Lehrbuch der Entwickelungsgeschichte, Bonnet; The Physiology of Reproduction, Marshall. ^ See description of the ovarj' on a future page. 78 EMBRYOLOGY parent envelope, the zona striata or zona pellucida, adhering to the outer surface of which are several layers of cells, derived from those of the follicle and collectively constituting the corona radiata. Yolk. — The yolk comprises (1) the cytoplasm of the ordinary animal cell witli its spongioplasm and hyaloplasm; this is frequently termed the formative yolk; (2) the nutritive yolk or duetoplasm, which consists of numerous rounded granules of fatty and albuminoid substances imbedded in the cytoplasm. In the mammalian ovum the nutritive yolk is extremely small in amount, and is of service in nourish- ing the embryo in the early stages of its development only, whereas in the egg of the bird there is sufficient to supply the chick with nutriment throughout Fig. 61. — Human ovum examined fresh in tlie liquor folliculi. (Waldeyer.) The zona pellucida is seen as a thick clear girdle surrounded by the cells of the corona radiata. The egg itself shows a central granular deutoplasmic area and a peripheral clear layer, and encloses the germinal vesicle, in which is seen the germinal spot. the whole period of incubation. The nutritive yolk not only varies in amount, but in its mode of distribution within the egg; thus, in some animals it is almost uniformly distributed throughout the cytoplasm; in some it is centrally placed and is surrounded by the cytoplasm; in others it is accumulated at the lower pole of the ovum, while the cytoplasm occupies the upper pole. A centrosome and centriole are present and lie in the immediate neighborhood of the nucleus. Germinal Vesicle. — The germinal vesicle or nucleus is a large spherical body which at first occupies a nearly central position, but becomes eccentric as the growth of the ovum proceeds. Its structure is that of an ordinary cell-nucleus, viz., it consists of a reticulum or karyomitome, the meshes of which are filled with THE OVUM 79 karyoplasm, while coimected with, or imhcdded in, tiie reticuluin are a number of chromatin masses or chromosomes, which may present the appearance of a skein or may assimie the form of rods or loops. The nucleus is enclosed by a delicate nuclear membrane, and contains in its interior a well-defined nucleolus or germinal spot. Coverings of the Ovum. — The zona striata or zona pellucida (Fig. (jlj is a thick membrane, which, under the higher powers of the microscope, is seen to be radially striated. It persists for some time after fertilization has occurred, and may serve for protection during the earlier stages of segmentation. It is not yet determined whether the zona striata is a product of the cytoplasm of the ovum or of the cells of the corona radiata, or both. The corona radiata (Fig. 61) consists or two or three strata of cells; they are derived from the cells of the follicle, and adhere to the outer surface of the zona striata when the ovum is set free from the follicle; the cells are radially arranged around the zona, those of the innermost layer being columnar in shape. The cells of the corona radiata soon disappear; in some animals they secrete, or are replaced by, a layer of adhesive protein, which may assist in protecting and nourishing the ovum. The phenomena attending the discharge of the ova from the follicles belong more to the ordinary functions of the ovary than to the general subject of embry- ology, and are therefore described with the anatomy of the ovaries.^ f.pn Fig. 62, — Formation of polar bodies in Asterias glacialis. (Slightly modified from Hertwig.) In I the polar spindle {.sp) has advanced to the surface of the egg. In // a small elevation (pfei) is formed which receives half of the spindle. In III the elevation is constricted off, forming the first polar body (pb^), and a second spindle is formed. In IV is seen a second elevation which in V has been constricted off as the second polar body (pfc^) Out of the remainder of the spindle (/.pra in VI) the female pronucleus is developed. Maturation of the Ovum. — Before an ovum can be fertilized it must undergo a process of maturation or ripening. This takes place previous to or immediately after its escape from the follicle, and consists essentially of an unequal subdivision of the ovum (Fig. 62) first into two and then into four cells. Three of the four cells are small, incapable of further development, and are termed polar bodies or polocytes, while the fourth is large, and constitutes the mature ovum. The process of maturation has not been observed in the human ovum, but has been carefully studied in the ova of some of the lower animals, to which the following description applies. It was pointed out on page 35 that the number of chromosomes found in the nucleus is constant for all the cells in an animal of any given species, and that in man the number is probably twenty-four. This applies not only to the somatic 1 See description of the ovary on a future page. 80 EMBRYOLOGY cells but to the primitive ova and their descendants. For the purpose of illustrating the process of maturation a species may be taken in which the number of nuclear chromosomes is four (Fig. 36). If an ovum from such be observed at the beginning of the maturation process it will be seen that the number of its chromosomes is apparently reduced to two. In reality, however, the number is doubled, since each chromosome consists of four granules grouped to form a tetrad. During the metaphase (see page 36) each tetrad divides into two dyads, which are equally distributed between the nuclei of the two cells formed by the first division of the ovum. One of the cells is almost as large as the original ovum, and is named the secondary oocyte; the other is small, and is termed the first polar body. The secondary oocyte now undergoes subdivision, during which each dyad divides and contributes a single chromosome to the nucleus of each of the two resulting cells. Primary oocyte Primary oocyte commencing muturdtion) Secondary oocyte First 'polar body /*e\ /^Q\ /*0\ Polar bodies Fig. 63. — Diagram showing the reduction in number of the chromosomes in the process of maturation of the ovum. This second division is also unequal, producing a large cell which constitutes the mature ovum, and a small cell, the second polar body. The first polar body fre- quently divides while the second is being formed, and as a final result four cells are produced, viz., the mature ovum and three polar bodies, each of which con- tains two chromosomes, i. e., one-half the number present in the nuclei of the somatic cells of members of the same species. The nucleus of the mature ovum is termed the female pronucleus. THE SPERMATOZOON. The spermatozoa or male germ cells are developed in the testes and are present in enormous numbers in the seminal fluid. Each consists of a small but greatly modified cell. The human spermatozoon possesses a head, a neck, a connecting piece or body, and a tail (Fig. 64). The head is oval or elliptical, but flattened, so that Avhen viewed in profile it is pear-shaped. Its anterior two-thirds are covered by a layer of modified proto- THE SPERMATOZOON 81 plasm, which is named the head-cap. This, in some animals, e. g., the salanaander, is prolonged into a barbed spear-like process or perforator, which probably facilitates the entrance of the spermatozoon into the ovum. The posterior part of the head exliibits an affinity for certain reagents, and presents a transversely striated appear- ance, being crossed by three or four dark bands. In some animals a central rod- like filament extends forward for about two-thirds of the length of the head, w^hile in others a rounded body is seen near its centre. The head contains a mass of chromatin, and is generally regarded as the nucleus of the cell surrounded by a thin envelope. Head Connecting piece •Perforator ) ycf/.- Tail'. Evd-picce ■ Head-cap interior centriole ---'Posterior centriole -Spiral tliread -JlitocJioiidria sheath Terminal disc Axial filainent Fig. 64.— Human spermatozoon. Diagrammatic. A. Surface view. B. Profile view, and connecting piece are more mgnly magmtied. In C the head, neck. The neck is less constricted in the human spermatozoon than m those of some of the lower animals. The anterior centriole, represented by two or three rounded particles, is situated at the junction of the head and neck, and behind it is a band of homogeneous substance. The connecting piece or body is rod-like, and is limited behmd by a terminal disk. The posterior centriole is placed at the junction of the body and neck and, like the anterior, consists of two or three rounded particles. From this centriole an axial filament, surrounded by a sheath, runs backward through the body and tail. In the body the sheath of the axial filament is encircled by a spiral tliread, around which is an envelope containing mitochondria granules, and termed the mitochondria sheath. 6 82 EMBRYOLOGY The tail is of great length, and consists of the axial thread or filament, sur- rounded by its sheath, which may contain a spiral thread or may present a striated appearance. The terminal jjortion or end-piece of the tail consists of the axial filament only. Krause gives the length of the human spermatozoon as between 52^i and G2/Li, the head measuring 4 to 5/^, the connecting piece fV, and the tail from 41 ^ to 52 /i. By virtue of their tails, which act as propellers, the spermatozoa are capable of free movement, and if placed in favorable surroundings, e. g., in the female pas- sages, will retain their vitalit}' and power of fertilizing for several days. In certain animals, e. g., bats, it has been proved that spermatozoa retained in the female passages for several months are capable of fertilizing. Primary oocyte Primary spermatocyte Secondary f ^ /^ ,^ \ /^ \ Sprrmdary oocyte K J ">.^y \ J \ J sptrrnatocytes Mature /''~\ ovum \ ) Polar bodies Spermatids Fig. 65. — Scheme showing analogies in the process of maturation of the ovum and the development of the spermatida (young .spermatozoa). The spermatozoa are developed from the primitive germ cells which have become imbedded in the testes, and the stages of their development are very similar to those of the maturation of the ovum. The primary germ cells undergo division and produce a number of cells termed spermatogonia, and from these the primary spermatocytes are derived. Each primary- spermatocyte divides into two secondary spermatocytes, and each secondary spermatocyte into two spermatids or young spermatozoa; from this it will be seen that a primary spermatocyte gives rise to four spermatozoa. On comparing this process with that of the maturation of the ovum (Fig. 65; it will be observed that the primary spermatocyte gives rise to two cells, the secondary spermatocytes, and the primary oocyte to two cells, the secondary oocyte and the first polar body. Again, the two secondary sperma- tocytes by their subdivision give origin to four spermatozoa, and the secondary oocyte and first polar body to four cells, the mature ovum and three polar bodies. In the development of the spermatozoa, as in the maturation of the ovum, there is a reduction of the nuclear chromosomes to one-half of those present in the primary spermatocyte. But here the similarity ends, for it must be noted that the four spermatozoa are of equal size, and each is capable of fertilizing a mature ovum, whereas the three polar bodies are not only very much smaller than the mature ovum but are incapable of further development, and may be regarded as abortive ova. FERTILIZATION OF THE OVUM. Fertilization consists in the union of the spermatozoon with the mature ovum (Fig. 66j. Nothing is known regarding the fertilization of the human ovum, but FERTILIZATION OF THE OVUM 83 the various stages of the process have been studied in other mammals, and from the knowledge so obtained it is believed that fertilization of the human ovum takes place in the lateral or ampuUary part of the uterine tube, and the ovum is then conveyed along the tube to the cavity of the uterus — a journey probably occupy- ing seven or eight days and during which the ovum loses its corona radiata and zona striata and undergoes segmentation. Sometimes the fertilized ovum is arrested in the uterine tube, and there undergoes development, giving rise to a tubal preg- nancy; or it may fall into the abdominal cavity and produce an abdominal preg- nancy. Occasionally the ovum is not expelled from the follicle when the latter ruptures, but is fertilized within the follicle and produces what is known as an ovarian pregnancy. Under normal conditions only one spermatozoon enters the 1. Polar bodies Female pronucleus Male pronucleus Female pronuchiis Male pronucleus Segmentntion nucleus - Female pro n ucleus Male pronucleus Fused pronuclei Segmentation nucleus [commencing division) Fig. 66. — The process of fertilization in the ovum of a mouse. (After Sobotta.) yolk and takes part in the process of fertilization. At the point where the sperma- tozoon is about to pierce, the yolk is drawn out into a conical elevation, termed the cone of attraction. As soon as the spermatozoon has entered the yolk, the per- ipheral portion of the latter is transformed into a membrane, the vitelline membrane w^hich prevents the passage of additional spermatozoa. Occasionally a second spermatozoon may enter the yolk, thus giving rise to a condition of polyspermy: when this occurs the ovum usually develops in an abnormal manner and gives rise to a monstrosity. Having pierced the yolk, the spermatozoon loses its tail, while its head and connecting piece assume the form of a nucleus containing a cluster of chromosomes. This constitutes the male pronucleus, and associated with it there are a centriole and centrosome. The male pronucleus passes more deeply into the yolk, and coincidently with this the granules of the cytoplasm surrounding it becomes radially arranged. The male and female pronuclei migrate toward each other, and, 84 EMBRYOLOGY meeting near the centre of the yolk, fuse to form a new nucleus, the segmentation nucleus, which therefore contains both male and female nuclear substance; the former transmits the individualities of the male ancestors, the latter those of the female ancestors, to the future embryo. By the union of the male and female pronuclei the number of chromosomes, is restored to that which is present in the nuclei of the somatic cells. SEGMENTATION OF THE FERTILIZED OVUM. The early segmentation of the human ovum has not yet been observed, but judging from what is known to occur in other mammals it may be regarded as certain that the process starts immediately after the ovum has been fertilized, i. e., while the ovum is in the uterine tube. The segmentation nucleus exhibits the usual mitotic changes, and these are succeeded by a division of the ovum into two cells of nearly equal size.^ The process is repeated again and again, so that the two cells are succeeded by four, eight, sixteen, thirty-two, and so on, with the result that a mass of cells is found within the zona striata, and to this mass the term Fig. 67. — First stages of segmentation of a mammalian ovum. Semidiagrammatic. (From a drawing by Allen Thomson.) z.p. Zona striata, p.gl. Polar bodies, a. Two-cell stage. 6. Four-cell stage, c. Eight-ceU stage. d, e. Morula stage. morula is applied (Fig. 67). The segmentation of the mammalian ovum may not take place in the regular sequence of two, four, eight, etc., since one of the two first formed cells may subdivide more rapidly than the other, giving rise to a three- or a five-cell stage. The cells of the morula are at first closely aggregated, but soon they become arranged into an outer or peripheral layer, the trophoblast, which does not contribute to the formation of the embryo proper, and an inner cell-mass, from which the embryo is developed. Fluid collects between the trophoblast and the greater part of the inner cell-mass, and thus the morula is converted into 1 In the mammalian ova the nutritive yolk or deutoplasm is small in amount and uniformly distributed through- out the cytoplasm; such ova undergo complete division during the process of segmentation, and are therefore termed holoblastic. In the ova of birds, reptiles, and fishes where the nutritive yolk forms by far the larger portion of the egg, the cleavage is limited to the formative yolk, and is therefore only partial; such ova are termed meroblastic._ Again, it has been observed, in some of the lower animals, that the pronuclei do not fuse but merely he in apposition. At the commencement of the segmentation process the chromosomes of the two pronuclei group themselves around the equator of the nuclear spindle and then divide; an equal number of male and female chromosomes travel to the opposite poles of the spindle, and thus the male and female pr9nuclei subscribe equal shares of chromatin to the nuclei of the two cells which result from the subdivision of the fertihzed ovum. SEGMENTATION OF THE FERTILIZED OVUM 85 a vesicle, the blastodermic vesicle (Fig. 68). The inner cell-mass remains in con- tact, however, with the trophoblast at one pole of the ovum; this is named the embryomic pole, since it indicates the situation where the future embryo will be de\'cluped. The cells of the trophoblast become differentiated into two strata: an outer, termed the syncytium or syncytiotrophoblast, so named because it consists of a layer of protoplasm studded with nuclei, but showing no evidence of subdivision into cells; and an inner layer, the cjrtotrophoblast or layer of Langhans, in which Inner cell-mass Entoderm Blastodermic vesicle Trophoblast FlQ. 68. — Blastodermic vesicle of Vespertilio murinus. (After van Beneden.) Inner cell-mass Trofhoblast Emhryonic ectoderm Entoderm Fig. 69. — Section through embryonic disk of VespertUio murinus. (After van Beneden.) Maternal bloodvessels Amniotic cavity Syncytiotrophoblast Cytotrophoblast Embryonic ectoderm Entoderm Fig. 70. — Section through embryonic area of Vespertilio murinus to show the formation of the amniotic cavity. (After van Beneden,) the cell outlines are defined. As already stated, the cells of the trophoblast do not contribute to the formation of the embryo proper; they form the ectoderm of the chorion and play an important part in the development of the placenta. On the deep surface of the inner cell-mass a layer of flattened cells, the entoderm, is differ- entiated and quickly assumes the form of a small sac, the yolk-sac. Spaces appear between the remaining cells of the mass (Fig. 69), and by the enlargement and coalescence of these spaces a cavity, termed the amniotic cavity (Fig. 70), is gradually 86 EMBRYOLOGY developed. The floor of this ca^•ity is formed by the embryonic disk composed of a layer of prismatic cells, the embryonic ectoderm, deri\ed from the inner cell- mass and lying in apposition with the entoderm. The Primitive Streak; Formation of the Mesoderm. — The embryonic disk becomes oval and then pear-shaped, the wider end being directed forward. Near the narrow, posterior end an opaque streak, the primitive streak (Figs. 71 and 72), makes its appearance and extends along the middle of the disk for about one-half of its length; at the anterior end of the streak there is a knob- like thickening termed Hensen's knot. A shallow groove, the primitive groove, appears on the surface of the streak, and the anterior end of this groove communicates by means of an aperture, the blastopore, with the yolk-sac. The primitive streak is produced by a thickening of the axial part of the ectoderm, the cells of which multiply, grow downward, and blend with those of the subjacent entoderm (Fig. 73). From the sides of the primitive streak a third layer of cells, the mesoderm, extends lateralward between the ectoderm and entoderm; the caudal end of the primitive streak forms the cloacal membrane. The extension of the mesoderm takes place throughout the whole of the embry- onic and extra-embryonic areas of the ovum, except in certain regions. One of these is seen immediately in front of the neural tube. Here the mesoderm extends forward in the form of two crescentic masses, which meet in the middle line so as -Surface view of (After rabbit. Kolliker.) arg. Embryonic disk. pr. Primitive streak Yolk- A')nnion Allatitois in body-stalk — Notochord ~~ Amnion y^ Neurenteric canal Primitive streak Fig. r2. — Surface view of embryo of Hylobates concolor. (After Selenka.) The amnion has been opened to expose the embryonic disk. to enclose behind them an area which is devoid of mesoderm. Over this area the ectoderm and entoderm come into direct contact wdth each other and constitute a thin membrane, the buccopharyngeal membrane, which forms a septum between the primitive mouth and pharynx. In front of the buccopharyngeal area, where the lateral crescents of mesoderm fuse in the middle line, the pericardium is SEGMENTATION OF THE FERTILIZED OVUM 87 afterward developed, and this region is therefore designated the pericardial area. A second region where the mesoderm is al)sent, at least for a time, is that imme- diately in front of the pericarchal area. This is termed the proamniotic area, and is the region where the proairmion is developed; in man, however, a proamnion is apparently never formed. A third region is at the hind end of the embryo where the ectoderm and entoderm come into apposition and form the cloacal membrane. ^im^pi%f%% Fig. 73. — Series of transverse sections through the embryonic disk of Tarsius. (After Hubrecht ) Section I passes through the disk, in front of Hensen's knot and shows only the ectoderrti and entoderm. Sections//, ///, and IV pass through Hensen's knot, which is seen in V tapering away into the primitive streak. In ///, IV, and V the mesoderm is seen springing from the keel-like thickening of the ectoderm, which in /// and IV is observed to be continuous into the entoderm. The blastoderm now" consists of three layers, named from without inward: ectoderm, mesoderm, and entoderm; each has distinctive characteristics and gives rise to certain tissues of the bod3^^ Ectoderm. — ^The ectoderm consists of columnar cells, which are, however, somewhat flattened or cubical tow^ard the margin of the embryonic disk. It forms the whole of the nervous system, the epidermis of the skin, the lining cells of the sebaceous, sudoriferous, and mammary glands, the hairs and nails, the epithelium of the nose and adjacent air sinuses, and that of the cheeks and roof of the mouth. From it also are derived the enamel of the teeth, and the anterior lobe of the hypophysis cerebri, the epithelium of the cornea, conjunctiva, and lacrimal glands, and the neuro-epithelium of the sense organs. Entoderm. — The entoderm consists at first of flattened cells, which subsequently become columnar. It forms the epithelial lining of the whole of the digestive tube excepting part of the mouth and pharynx and the terminal part of the rectum 1 The mode of formation of the germ layers in the human ovum has not j'et been observed; in the youngest known human ovum (viz., that described by Bryce and Teacher), all three layers are already present and the mesoderm is split into its two layers. The extra-embryonic coelom is of considerable size, and scattered mesodermal strands are seen stretching between the mesoderm of the yolk-sac and that of the chorion. EMBRYOLOGY (which are hned by involutions of the ectoderm), the hning cells of all the glands which open into the digestive tube, including those of the liver and pancreas, the epithelium of the auditory tube and tympanic cavit}-, of the trachea, bronchi, and air cells of the lungs, of the urinary bladder and part of the urethra, and that which lines the follicles of the thyroid gland and thymus. Mesoderm. — The mesoderm consists of loosely arranged branched cells sur- rounded by a considerable amount of intercellular fluid. From it the remaining tissues of the body are developed. The endothelial lining of the heart and blood- vessels and the blood corpuscles are, however, regarded by some as being of ento- dermal origin. ect mes h Fig. 74. — A series of transverse sections through an embryo of the dog. (After Bonnet.) Section / is the most anterior. In F the neural plate is spread out nearly flat. The series shows the uprising of the neural folds to form the neural canal, a. Aortse. c. Intermediate ceU mass. ect. Ectoderm, ent. Entoderm, h, h. Rudiments of endothelial heart tubes. In III, IV, and V the scattered cells represented between the entoderm and splanchnic layer of meso- derm are the vasoformative cells which give origin in front, according to Bonnet, to the heart tubes, h; l.p. Lateral plate still undivided in /, //, and III; in JF and V split into somatic (sm) and splanchnic (sp) layers of mesoderm. mes. Mesoderm, p. Pericardium, so. Primitive segment. As the mesoderm develops between the ectoderm and entoderm it is separated into lateral halves by the neural tube and notochord, presently to be described. A longitudinal groove appears on the dorsal surface of either half and divides it into a medial column, the paraxial mesoderm, lying on the side of the neural tube, and a lateral portion, the lateral mesoderm. The mesoderm in the floor of the groove connects the paraxial with the lateral mesoderm and is known as the intermediate cell-mass; in it the genito-urinary organs are developed. The lateral mesoderm splits into two layers, an outer or somatic, which becomes applied to the inner surface of the ectoderm, and with it forms the somatopleure ; and an inner or splanchnic, which adheres to the entoderm, and with it forms the splanchnopleure (Fig. 74). The space between the two layers of the lateral mesoderm is termed the coelom. THE NEURAL GROOVE AXD TUBE 89 THE NEURAL GROOVE AND TUBE. In front of the primitive streak two longitiuiinal ridges, eaused by a folding up of the ectoderm, make their appearance, one on either side of the middle line (Fig. 74). These are named the neural folds; they commence some little distance behind the anterior end of the embryonic disk, where they are continuous with each other, and from there gradually extend backward, one on either side of the anterior end of the primitive streak. Between these folds is a shallow median groove, the neural groove (Figs. 74, 75). The groove gradually deepens as the neural folds become elevated, and ultimatel}^ the folds meet and coalesce in the middle line and convert the groove into a closed tube, the neural tube or canal (Fig. 76), the ectodermal wall of which forms the rudiment of the nervous system. By the coalescence of the neural folds over the anterior end of the primitive streak, the blastopore no longer opens on the surface but into the closed canal of the neural J oik, bac Neurenteric canal Primitive streak Body-stalk Fig. 75. — Human embryo — length, 2 mm. Dorsal view, with the amnion laid open. X 30. (After Graf Spee.) tube, and thus a transitory communication, the neurenteric canal, is established between the neural tube and the primitive digestive tube. The coalescence of the neural folds occurs first in the region of the hind-brain, and from there exterids forward and bacb^^ard; toward the end of the third week the front opening (anterior neuropore) of the tube finally closes at the anterior end of the future brain, and forms a recess which is in contact, for a time, with the overlying ectoderm; the hinder part of the neural groove presents for a time a rhomboidal shape, and to this expanded portion the term sinus rhomboidalis has been applied (Fig. 76). Before the neural groove is closed a ridge of ectodermal cells appears along the prominent margin of each neural fold; this is termed the neural crest or ganglion ridge, and from it the spinal and cerebral nerve ganglia and the ganglia of the sympathetic nervous system are developed. By the upward growth of the mesoderm the neural tube is ultimately separated from the overlying ectoderm. The cephalic end of the neural groove exhibits several dilatations, which, when the tube is closed, assume the form of three vesicles; these constitute the three primary cerebral vesicles, and correspond respectively to the future prosencephalon 90 EMBRYOLOGY (fore-brain), mesencephalon (mid-brain), and rhombencephalon (^hind-brain j (Fig. 76). The walls of the vesicles are developed into the nervous tissue and neuroglia of the brain, and their cavities are modified to form its ventricles. The remainder of the tube forms the medulla spinalis or spinal cord; from its ectodermal wall the nervous and neuroglial elements of the medulla spinalis are developed while the cavity persists as the central canal. Head fold of amnion partlp covering the fore-brain 2Iid-brain -r Uind-hrain l^erve ganglion Auditory vesicle - Vitelline vein Fourteenth primitive segment Paraxial mesoderm Neural fold, Sinus rhomboidalis JRemains of primitive streak HeaH Fig. 76. — Chick embrv'O of thirty-three hours' incubation, viewed from the dorsal aspect. X 30. (From Duval's "Atlas d'Embryologie."; THE NOTOCHORD. The notochord (Fig. 77) consists of a rod of cells situated on the ventral aspect of the neural tube; it constitutes the foundation of the axial skeleton, since around it the segments of the vertebral column are formed. Its appearance synchronizes THE PRIM in VE SEGMENTS 91 with that of the neural tube. On the ventral aspect of the neural groove an axial thickening of the entoderm takes place; this thickening assumes the appearance of a furrow — the chordal furrow — the margins of which come into contact, and so convert it into a solid rod of cells — the notochord — which is then separated from the entoderm. It extends throughout the entire length of the future vertebral Ectoderm ., Neural canal Primitive Wolffia7i segment duct Ccelom Somatic mesoderm Entoderm ^' Fig. Notochord Aorta Splanchnic mesoderm -Transverse section of a chick embryo of forty-five hours' incubation. (Balfour.) column, and reaches as far as the anterior end of the mid-brain, where it ends in a hook-like extremity in the region of the future dorsum sellae of the sphenoid bone. It lies at first between the neural tube and the entoderm of the yolk-sac, but soon becomes separated from them by the mesoderm, which grows medial- ward and surrounds it. From the mesoderm surrounding the neural tube and notochord, the skull and vertebral column, and the membranes of the brain and medulla spinalis are developed. THE PRIMITIVE SEGMENTS. Czit edge of amnion Primitive segments Tow^ard the end of the second week transverse segmentation of the paraxial mesoderm begins, and it is converted into a series of well-defined, more or less cubical masses, the primitive segments (Figs. 76, 77, 78), which occupy the entire length of the trunk on either side of the middle line from the occipital region of the head. Each segment contains a central cavity — myocoel — ^w^hich, however, is soon filled with angular and spindle-shaped cells. The primitive segments lie immediately under the ectoderm on the lateral aspect of the neural tube and notochord, and are con- nected to the lateral mesoderm by the inter- mediate cell-mass. Those of the trunk may be arranged in the following groups, viz.: cervical 8, thoracic 12, lumbar 5, sacral 5, and coccygeal from 5 to 8. Those of the occipital region of the head are usually described as being four in number. In mammals primitive segments of the head can only be recognized in the occipital region, but a study of the lower vertebrates leads to the belief that they are present also in the anterior part of the head, and that altogether nine segments are represented in the cephalic region. Yolk-sac Fig Neural folds Neurenteric canal Dorsum of human embryo, 2.11 mm. in length. (After Eternod.) 92 EMBRYOLOGY SEPARATION OF THE EMBRYO. The embryo increases rapidly in size, but the circumference of the embryonic disk, or Hne of meeting of the embryonic and amniotic parts of the ectoderm, is of relatively slow growth and .gradually comes to form a constriction between the embryo and the greater part of the 3^olk-sac. By means of this constriction, which corresponds to the future umbilicus, a small part of the yolk-sac is enclosed within the embryo and constitutes the primitive digestive tube. The embryo increases more rapidly in length than in width, and its cephalic and caudal ends soon extend -beyond the corresponding parts of the circumference of the embryonic disk and are bent in a ventral direction to form the cephalic and caudal folds respectively (Figs. 84 and 85). The cephalic fold is first formed, and Villi of chorion Amnion Embryo7iic disc Bitdiment of heart Mesoder Chorion i"?"^ Mesoderm Body-stalk Primitive streak Allantois toderm Bloodvessel Fig. 79. — Section through the embryo which is represented in Fig. 75. (After Graf Spee.) as the proamniotic area (page 87) lying immediately in front of the pericardial area (page 87) forms the anterior limit of the circumference of the embryonic disk, the forward growth of the head necessarily carries with it the posterior end of the pericardial area, so that this area and the buccopharyngeal membrane are folded back under the head of the embryo which now encloses a diverticulum of the yolk-sac named the fore-gut. The caudal end of the embryo is at first connected to the chorion by a band of mesoderm called the body-stalk, but with the formation of the caudal fold the body-stalk assumes a ventral position; a diverticulum of the yolk-sac extends into the tail fold and is termed the hind-gut. Between the fore-gut and the hind-gut there exists for a time a wide opening into the yolk-sac, but the latter is gradually reduced to a small pear-shaped sac (sometimes termed the umbilical vesicle), and the channel of communication is at the same time narrowed and elongated to form a tube called the vitelline duct. DEVELOPMENT OF THE FETAL MEMBRANES AND THE PLACENTA 93 THE YOLK-SAC. The yolk-sac (Figs. 79 and SO) is situated on the ventral aspect of the embryo; it is lined by entoderm, outside of which is a layer of mesoderm. It is filled with fluid, the vitelline fluid, which possibly may be utilized for the nourishment of the embryo during the earlier stages of its existence. Blood is conveyed to the wall of the sac by the primitive aortae, and after circulating through a wide-meshed capil- lary plexus, is returned by the vitelline veins to the tubular heart of the em- Heart bryo. This constitutes the vitelline circulation, and by means of it nutri- tive material is absorbed from the yolk-sac and conveyed to the embryo. At the end of the fourth week the yolk- sac presents the appearance of a small pear-shaped vesicle (umbilical vesicle) opening into the digestive tube by a long narrow tube, the vitelline duct. The vesicle can be seen in the after- birth as a small, somewhat oval-shaped body whose diameter varies from 1 mm. to 5 mm.; it is situated between the amnion and the chorion and may lie on or at a varying distance from the placenta. As a rule the duct undergoes complete obliteration during the seventh week, but in about three per cent, of cases its proximal part persists as a diverticulum from the small intestine, Meckel's diverticulum, which is situated about three or four feet above the ileocolic junction, and may be attached by a fibrous cord to the abdominal wall at the umbilicus. Sometimes a narrowing of the lumen of the ileum is seen opposite the site of attachment of the duct. Fig. 80.- Hind limb Human embryo from thirty-one to thirty-four days. (His.) DEVELOPMENT OF THE FETAL MEMBRANES AND THE PLACENTA. The AUantois (Figs. 82 to 85).— The allantois arises as a tubular diverticulum of the posterior part of the yolk-sac; when the hind-gut is developed the allantois is carried backw^ard with it and then opens into the cloaca or terminal part of the hind-gut: it grows out into the body-stalk, a mass of mesoderm which lies below and around the tail end of the embryo. The diverticulum is lined by entoderm and covered by mesoderm, and in the latter are carried the allantoic or umbilical vessels. In reptiles, bhds, and many mammals the allantois becomes expanded into a vesicle which projects into the extra-embryonic coelom. If its finther development be traced in the bnd, it is seen to project to the right side of the embryo, and, gradually expanding, it spreads over its dorsal surface as a flattened sac between the amnion and the serosa, and extending in all directions, ultimately surrounds the yolk. Its outer wall becomes applied to and fuses with the serosa, which lies immediately inside the shell membrane. Blood is carried to the allantoic sac by the two allantoic or umbilical arteries, which are continuous with the primitive aortse, and after circulating through the allantoic capillaries, is returned to the primitive heart by the two umbilical veins. In this way the allantoic cnculation, which is of the utmost importance in connection with the respiration and nutrition 94 EMBRYOLOGY of the chick, is estabHshed. Oxygen is taken from, and carbonic acid is given up to the atmosphere through the egg-shell, while nutriti\'e materials are at the same time absorbed by the blood from the yolk. Amniotic cavity Amniotic cavity Yolk-sac Chorion Body-stalk Allantois Yolk-sac Chorion Fig. 81. — Diagram showing earliest observed stage of human ovum. Fig. 82. — Diagram illustrating early formation allantois and differentiation of body-stalk. In man and other primates the nature of the allantois is entirely different from that just described. Here it exists merely as a narrow, tubular diverticulum of the hind-gut, and never assumes the form of a vesicle outside the embryo. With the formation of the amnion the embryo is, in most animals, entirely separated from the chorion, and is only again united to it when the allantoic mesoderm spreads over and becomes applied to its inner surface. The human embryo, on the other hand, as was pointed out by His, is never wholly separated from the chorion, its tail end being from the first connected with the chorion by means of a thick band of mesoderm, named the body-stalk (Bauchstiel) ; into this stalk the tube of the allantois extends (Fig. 79). Amniotic cavity Embryo Body-stalk Placental villi Allantois Yolk-sac Chorion Heart Fig. 83. — Diagram showing later stage of allan- toic development with commencing constriction of the yolk-sac. Body-stalk Allantois Yolk-sac Heart Fore-gut Embryo Amniotic cavity Fia. 84. — Diagram showing the expansion of amnion and delimitation of the umbiUcus. The Amnion. — The amnion is a membranous sac which surrounds and protects the embryo. It is developed in reptiles, birds, and mammals, wdiich are hence called "Amniota;" but not in amphibia and fishes, which are consequently termed " Anamnia." In the human embryo the earliest stages of the formation of the amnion have not been observed; in the youngest embryo which has been studied the amnion was already present as a closed sac (Figs. 81 and 88), and, as indicated on page 85, DEVELOPMENT OF THE FETAL MEMBRANES AND THE PLACENTA 95 appears in the iiiiuT cell-mass as a cavity. This ca^•ity is roofed in by a single stratum of flattened, ectodermal cells, the amniotic ectoderm, and its floor consists of the prismatic ectoderm of the embryonic disk — the continuity between the roof and floor being established at the margin of the embryonic disk. placental villi Outside the amniotic ectoderm is a thin layer of mesoderm, which is continuous with that of the somatopleure and is connected by the body-stalk with the meso- dermal lining of the chorion. When first formed the amnion is in contact with the body of the embryo, but about the fourth or fifth week fluid (liquor amnii) be- gins to accumulate within it. This fluid increases in quantity and causes the amnion to expand and ultimately to adhere to the inner surface of the chorion, so that the extra-embryonic part of the coelom is obliterated. The liquor amnii increases in quantity up to the sixth or seventh month of preg- nancy, after which it diminishes somewhat; at the end of preg- nancy it amounts to about 1 litre. It allows of the free movements of the fetus during the later stages of pregnancy, and also protects it by diminishing the risk of injury from without. It contains less than 2 per cent, of solids, consisting of Yolk-sac Umbilical cord Allantois Heart Digestive tube Fig. 85. E^nbryo Amniotic cavity -Diagram illustrating a later stage in the development of the umbilical cord. false amnion or serosa \ villi of Fig. 86. — Diagram of a transverse section, showing the mode of formation of the amnion in the chick. The amniotic folds have nearly united in the middle Une. (From Quain's Anatomy.) Ectoderm, blue; mesoderm, red; entoderm and notochord, black. urea and other extractives, inorganic salts, a small amount of protein, and frequently a trace of sugar. That some of the liquor amnii is swallowed by the fetus is proved by the fact that epidermal debris and hairs have been found among the contents of the fetal alimentarv canal. 96 EMBRYOLOGY In reptiles, birds, and many mammals the amnion is developed in the following manner: At the point of constriction where the primitive digestive tube of the embryo joins the yolk-sac a reflection of folding upward of the somatopleure takes place. This, the amniotic fold (Fig. 86), first makes its appearance at the cephalic extremity, and subsequently at the caudal end and sides of the embryo, and grad- ually rising more and more, its different parts meet and fuse over the dorsal aspect of the embryo, and enclose a cavity, the amniotic cavity. After the fusion of the edges of the amniotic fold, the two layers of the fold become completely separated, the inner forming the amnion, the outer the false amnion or serosa. The space between the amnion and the serosa constitutes the extra-embryonic coelom, and for a time communicates with the embryonic coelom. Somatic mesoderm Splanchnic mesoderm Entoderm Vitelline veim Amniotic cavity Amnion Neural groove Fig. 87. — Model of human embrj-o 1.3 mm. long. (After Eternod.) The Umbilical Cord and Body-stalk. — The umbilical cord (Fig. 85) attaches the fetus to the placenta; its length at full time, as a rule, is about equal to the length of the fetus, i. e., about 50 cm., but it may be greatly diminished or increased. The rudiment of the umbilical cord is represented by the tissue which connects the rapidly growing embryo with the extra-embryonic area of the ovum. Included in this tissue are the body-stalk and the vitelline duct— the former containing the allantoic diverticulum and the umbilical vessels, the latter forming the communica- tion between the digestive tube and the yolk-sac. The body-stalk is the posterior segment of the embryonic area, and is attached to the chorion. It consists of a plate of mesoderm covered by thickened ectoderm on which a trace of the neural groove can be seen, indicating its continuity with the embryo. Running through its mesoderm are the two umbilical arteries and the two umbilical veins, together with the canal of the allantois— the last being lined by entoderm (Fig. 87). Its dorsal surface is covered by the amnion, while its ventral surface is bounded by the extra- embryonic coelom, and is in contact with the vitelline duct and yolk-sac. With the rapid elongation of the embryo and the formation of the tail fold, the body stalk comes to lie on the ventral surface of the embryo (Figs. 84 and 85), where its mesoderm blends with that of the yolk-sac and the vitelline duct. The lateral leaves of somatopleure then grow round on each side, and, meeting on the ventral DEVELOPMENT OF THE FETAL MEMBRANES AND THE PLACENTA 97 aspect of the allantois, enclose the viteUiiie duct and vessels, together with a part of the extra-embryonic coelom; the latter is ultimately obliterated. The cord is covered by a layer of ectoderm which is continuous with that of the amnion, and its various constitutents are enveloped by embryonic gelatinous tissue, jelly of Wharton. The vitelline vessels and duct, together with the right umbilical vein, undergo atrophy and disappear; and thus the cord, at birth, contains a pair of umbilical arteries and one (the left) umbilical vein. a.e. Fig. 88. — ^Section through ovum imbedded in the uterine decidua. Semidiagrammatic. (After Peters.) am. Amniotic cavity, b.c. Blood-clot. b.s. Body-stalk, ect. Embryonic ectoderm, ent. Entoderm. Tries. Mesoderm. m.v. Maternal vessels, tr. Trophoblast. u.e. Uterine epithelium, u.g. Uterine glands, y.s. Yolk-sac. Implantation or Imbedding of the Ovum. — As described (page 82), fertilization of the ovum occurs in the lateral or ampullary end of the uterine tube and is immediately followed by segmentation. On reaching the cavity of the uterus the segmented ovum adheres like a parasite to the uterine mucous membrane, destroys the epithelium over the area of contact, and excavates for itself a cavity in the mucous membrane in which it becomes imbedded. In the ovum described by Bryce and Teacher^ the point of entrance was visible as a small gap closed by a mass of fibrin and leucocytes; in the ovum described by Peters^ the opening was covered by a mushroom-shaped mass of fibrin and blood-clot (Fig. 88), the narrow stalk of which plugged the aperture in the mucous membrane. Soon, however, all trace of the opening is lost and the ovum is then completely surrounded by the uterine mucous membrane. The structure actively concerned in the process of excavation is the trophoblast of the ovum, which possesses the power of dissolving and absorbing the uterine ^ Contribution to the study of the early development and imbedding of the human ovum, 1908. - Die Einbettung des menschUchen Eies, 1899. 98 EMBRYOLOGY Mucous membrane Muscular fibres Stratum compactum tissues. The trophoblast proliferates rapidly and forms a network of branching processes which cover the entire ovum and invade and destroy the maternal tissues and open into the maternal bloodvessels, with the result that the spaces in the trophoblastic n£twork are filled with maternal blood; these spaces com- municate freely with one another and become greatly distended and form the intervillous space. The Decidua. — Before the fertilized ovum reaches the uterus, the mucous membrane of the body of the uterus undergoes important changes and is then known as the decidua. The thickness and vascularity of the mucous mem- brane are greatly increased; its glands are elongated and open on its free surface by funnel-shaped orifices, while their deeper portions are tortu- ous and dilated into irregular spaces. The interglandular tissue is also in- creased in quantity, and is crowded with large round, oval, or polygonal cells, termed decidual cells. These changes are well advanced by the second month of pregnancy, when the mucous membrane consists of the following strata (Fig. 89): (1) stratum compactum, next the free surface; in this the uterine glands are only slightly expanded, and are lined by columnar cells; (2) stratum spongiosum, in which the gland tubes are greatly dilated and very tortuous, and are ultimately separated from one another by only a small amount of inter- glandular tissue, while their lining cells are flattened or cubical; (3) a thin Unaltered or boundary layer, next the uterine muscular fibres, contain- ing the deepest parts of the uterine glands, which are not dilated, and are lined with columnar epithelium; it is from this epithelium that the epithelial lining of the uterus is re- generated after pregnancy. Distinc- tive names are applied to different portions of the decidua. The part which covers in the ovum is named the decidua capsularis; the portion which intervenes between the ovum and the uterine wall is named the decidua basalis or decidua placentalis; it is here that the placenta is subsequently developed. The part of the decidua which lines the remainder of the body of the uterus is known as the decidua vera or decidua parietalis. Coincidently with the grow^th of the embryo, the decidua capsularis is thinned and extended (Fig. 90) and the space between it and the decidua vera is gradually obliterated, so that by the third month of pregnancy the two are in contact. By Stratum spongiosum Unaltered or boundary layer Muscular fibres Fig. 89. — Diagrammatic sections of the uterine mucous membrane: A. The non-pregnant uterus. B. The preg- nant uterus, showing the thicltened mucous membrane and the altered condition of the uterine glands. (Kundrat and Engelmann.) DEVELOPMENT OF THE FETAL MEMBRANES AND THE PLACENTA 99 the fifth month of pregnancy the deciduu ('ai)sulari.s has jiractically disappeared, wliile during; the snc('ee.■ 7^ LVii^ Intervertebral fibrocartilage Notochord Fig. 95. — Scheme showing the manner in which each vertebral centrum is developed from portions of two adjacent segments. and costal arches are derivatives of the posterior part of the segment in front of the intersegmental septum with which they are associated. 104 EMBRYOLOGY This stage is succeeded by that of the cartilaginous vertebral column. In the fourth week two cartilaginous centres make their aj^ijearancc, one on either side of the notochord; these extend around the notochord and form the body of the cartil- aginous vertebra. A second pair of cartilaginous foci appear in the lateral parts of the vertebral bow, and grow backward on either side of the neural tube to form the cartilaginous vertebral arch, and a separate cartilaginous centre appears for each costal process. By the eighth week the cartilaginous arch has fused with the body, and in the fourth month the two halves of the arch are joined on the dorsal aspect of the neural tube. The spinous process is developed from the junction of the two halves of the vertebral arch. The transverse process grows out from the vertebral arch behind the costal process. In the upper cervical vertebrae a band of mesodermal tissue connects the ends of the vertebral arches across the ventral surfaces of the intervertebral fibrocartilages. This is termed the hypochordal bar or brace; in all except the first it is transitory and disappears by fusing with the fibrocartilages. In the atlas, however, the entire bow persists and undergoes chondrification; it develops into the anterior arch of the bone, while the cartilage representing the body of the atlas forms the dens or odontoid process which fuses with the body of the second cervical vertebra. Anterior longitudinal ligamevt P osier io'rlong it udinal ligament Cartilaginous end of vertebral body Nucleus pidjjosus Intervertebral fibro- cartilage Slight enkirgemerii of ivotocJiord in the cartilagirums vertebral body Fig. 96. — Sagittal section through an intervertebral fibrocartilage and adjacent parts of two vertebrsE of an advanced sheep's embrj-o. (Kolliker.) The portions of the notochord which are surrounded by the bodies of the verte- brse atrophy, and ultimately disappear, while those which lie in the centres of the intervertebral fibrocartilages undergo enlargement, and persist throughout life as the central nucleus pulposus of the fibrocartilages (Fig. 96). The Ribs. — The ribs are formed from the ventral or costal processes of the primitive vertebral bows, the processes extending between the muscle-plates. In the thoracic region of the vertebral column the costal processes grow lateralward to form a series of arches, the primitive costal arches. As already described, the transverse process grows out behind the vertebral end of each arch. It is at first connected to the costal process by continuous mesoderm, but this becomes differ- entiated later to form the costotransverse ligament; between the costal process and the tip of the transverse process the costotransverse joint is formed by absorption. The costal process becomes separated from the vertebral bow by the development of the costocentral joint. In the cervical vertebras (Fig. 97) the trans- verse process forms the posterior boundary of the foramen transversarium, while the costal process corresponding to the head and neck of the rib fuses with the DEVELOPMENT OF THE PARIETES 105 body of the vertebra, and forms the antero-lateral boundary of the foramen. The distal portions of the primitive costal arches remain undeveloped; occasionally the arch of the seventh cervical vertebra undergoes greater development, and by the formation of costovertebral joints is separated off as a rib. In the lumbar region the distal portions of the primitive costal arches fail; the proximal portions fuse with the trans^'erse processes to form the transverse processes of descriptive anatomy. Occasionally a movable rib is developed in connection with the first lumbar ^•ertebra. In the sacral region costal processes are developed only in connection with the upper three, or it may be four, vertebrae; the processes of adjacent segments fuse with one another to form the lateral parts of the sacrum. The coccygeal vertehrce are devoid of costal processes. CERVICAL LUMBAR THORACIC SACRAL Fig. 97. — Diagrams showing the portions of the adult vertebrse derived respectively from the bodies, vertebral arches, and costal processes of the embryonic vertebrae. The bodies are represented in yellow, the vertebral arches in red, and the costal processes in blue. The Sternum. — ^The ventral ends of the ribs become united to one another by a longitudinal bar termed the sternal plate, and opposite the first seven pairs of ribs these sternal plates fuse in the middle line to form the manubrium and body of the sternum. The xiphoid process is formed by a backward extension of the sternal plates. The Skull,- — Up to a certain stage the development of the skull corresponds with that of the vertebral column; but it is modified later in association with the expan- sion of the brain-vesicles, the formation of the organs of smell, sight, and hearing, and the development of the mouth and pharynx. 106 EMBRYOLOGY Fossa hypophyseos Mesoderm of base of skull Parachordal cartilage The notochord extends as far forward as the anterior end of the mid-})rain, and becomes partly surrounded by mesoderm (Fig. 98). The posterior part of this meso- dermal investment corresponds with the basilar part of the occipital bone, and shows a subdivision into four segments, which are separated by the roots of the hypo- glossal nerve. The mesoderm then extends over the brain-vesicles, and thus the entire brain is enclosed by a mesodermal investment, which is termed the membran- ous cranium. From the inner layer of this the bones of the skull and the membranes of the brain are developed; from the outer layer the muscles, bloodvessels, true skin, and subcutaneous tissues of the scalp. In the shark and dog-fish this membranous cranium undergoes complete chondrifi- cation, and forms the cartilaginous skull or chondrocranium of these animals. In mammals, on the other hand; the process of chondrification is limited to the base of the skull — the roof and sides being covered in by membrane. Thus the bones of the base of the skull are preceded by cartilage, those of the roof and sides by membrane. The posterior part of the base of the skull is developed around the notochord, and exhibits a segmented condition analogous to that of the vertebral column, while the anterior part arises in front of the notochord and shows no regular segmentation. The base of the skull may therefore be divided into (a) a chordal or vertebral, and (6) a prechordal or prevertebral portion. Situation of olfactory pit Ethmoid plate and nasal Olfactory organ Anterior arch of atlas Notochord Body of axis Third cervical vertebra Fig. 98. — Sagittal section of cephalic end of chord. (Keibel.) Fossa hypophyseos Trahecula _ cranii Situation of auditory vesicle Parachordal ' cartilage Notochord' Extension around olfactory organ Foramina for olfactory nerves Eyeball Fossa hypophyseos --Basilar plate --Auditory vesicle Notochord Fig. 99. — Diagrams of the cartilaginous cranium. (Wiedersheim.) In the lower vertebrates two pairs of cartilages are developed, viz., a pair of parachordal cartilages, one on either side of the notochord; and a pair of pre- chordal cartilages, the trabeculae cranii, in front of the notochord (Fig. 99). The parachordal cartilages (Fig. 99) unite to form a basilar plate, from which the car- tilaginous part of the occipital bone and the basi-sphenoid are developed. On the lateral aspects of the parachordal cartilages the auditory vesicles are situated. DEVELOPMENT OF THE PARIETES \o: and tlie mesodt^rni en('l()sin<>; them is soon converted into cartilage, forming the cartilaginous ear-capsules. These cartiUiginous ear-capsules, which are of an oval shape, fuse with the sides of the basilar plate, and from them arise the petrous and mastoid portions of the temporal bones. The trabeculae cranii (Fig. 99) are two curved bars of cartilage which embrace the hypophysis cerebri; their posterior ends soon unite with the basilar ])late, while their anterior ends join to form the ethmoidal plate, which extends forward between the fore-brain and the olfactory pits. Later the trabeculae meet and fuse below the hypophysis, forming the floor Crista galll Cribriform plate MecheVs cartilage Malleus Incus Int. acoustic meat. Jugular foramen Fossa subarcuata Canal for hypoglossal nerve Small wing of sphenoid Optic foramen Great wing of sphenoid Sella turcica Do7'sum sellae Canal for facial nerve Ear capsule — Ductus endol. Foramen magnum Fig. 100. — Model of the chondrocranium of a human embryo, 8 cm. long. not represented. (Hertwig. The membrane bones are of the fossa hypophyseos and so cutting off the anterior lobe of the hypophysis from the stomodeum. The median part of the ethmoidal plate forms the bony and cartilaginous parts of the nasal septum. From the lateral margins of the trabeculae cranii three processes grow out on either side. The anterior forms the ethmoidal labyrinth and the lateral and alar cartilages of the nose; the middle gives rise to the small wing of the sphenoid, while from the posterior the great wing and lateral pterygoid plate of the sphenoid are developed (Figs. 100, 101). The bones of the vault are of membranous formation, and are termed dermal or covering bones. They are partly developed from the mesoderm of the membranous 108 EMBRYOLOGY cranium, and partly from that which lies outside the entoderm of the fore- gut. They comprise the upper part of the occipital squama (interparietal), the squamse and tympanic parts of the temporals, the parietals, the frontal, the vomer, the medial pterj^goid plates, and the bones of the face. Some of them remain distinct throughout life, e. g., parietal and frontal, while others join with the bones of the chondrocranium, e. g., interparietal, squamse of temporals, and medial pterygoid plates. Recent observations have shown that, in mammals, the basi-cranial cartilage, both in the chordal and prechordal regions of the base of the skull, is developed as a single plate which extends from behind forward. In man, however, its posterior part shows an indication of being developed from two chondrifying centres which fuse rapidly in front and below. The anterior and posterior thirds of the cartilage surround the notochord, but its middle third lies on the dorsal aspect of the noto- chord, which in this region is placed between the cartilage and the wall of the pharynx. Optic foramen Small wing of sphenoid Great wing of iphenoid Nasal capsule Vomer Palatine bone Mandible Thyroid cart. Canal for hypoglossal nerve Fig. 101. -The same model as shown in Fig. 100 from the left side. Certain of the membrane bones of the right side are represented in yellow. The Branchial or Visceral Arches and Pharyngeal Pouches.— In the lateral walls of the anterior part of the fore-gut five pharyngeal pouches appear (Fig, 104) ; each of the upper four pouches is prolonged into a dorsal and a ventral diverticulum. Over these pouches corresponding indentations of the ectoderm occur, forming what are known as the branchial or outer pharyngeal grooves. The intervening mesoderm is pressed aside and the ectoderm comes for a time into contact with the ento- dermal lining of the fore-gut, and the two layers unite along the floors of the grooves to form thin closing membranes between the fore-gut and the exterior. Later the mesoderm again penetrates between the entoderm and the ectoderm. In gill-bearing animals the closing membranes disappear, and the grooves become complete clefts, the gill-clefts, opening from the pharynx on to the exterior; perfor- ation, however, does not occur in birds or mammals. The grooves separate a series of rounded bars or arches, the branchial or visceral arches, in which thickening of the mesoderm takes place (Figs. 102 and 103). The dorsal ends of these arches are attached to the sides of the head, while the ventral extremities ultimately meet in the middle line of the neck. In all, six arches make their appearance, DEVELOPMENT OF THE PARIETES 109 but of these only the first four are visible externally. The first arch is named the mandibular, and the second the hyoid; the others have no distinctive names. In each arch a cartilaginous bar, consisting of right and left halves, is developed, and with each of these there is one of the primitive aortic arches. Mid-hrain Forc-hrain Stomodeum Muiidibal((r arch Heart 11 tnd-hrain Auditory vesicle V isceral arches Imnion (cut) Olfactory pit Maxillary process Mandibular arch Hyoid aich i Third arch " Fig. 102. — Embryo between eighteen and twenty-one days. (His.) Fig. 103. — Head end of human embryo, about the end of the fourth week. (From model by Peter.) Lateral tongue Thyroid elevations diverticulum The mandibular arch lies between the first branchial groove and the stomodeum; from it are developed the lower lip, the mandible, the muscles of mastication, and the anterior part of the tongue. Its cartilaginous bar is formed by what are known as Meckel's cartilages (right and left) (Fig. 105). The dorsal ends of these cartilages are connected with the ear- capsules and are ossified to form two of the bones of the middle ear, the malleus and incus; the ventral ends meet each other in the region of the symphysis menti, and are usually regarded as undergoing ossification to form that portion of the mandible which contains the incisor teeth. The intervening part of the cartilage disappears; the portion immediately adjacent to the malleus and incus is replaced by fibrous membrane, which constitutes the spheno-mandibular ligament, while from the connective tissue covering the remainder of the cartilage the greater part of the mandible is ossified. From the dorsal ends of the mandibular arch a triangular process, the maxillary process, grows forward on either side and forms the cheek and lateral part of the upper lip. The second or hyoid arch assists in forming the side and front of the neck. From its cartilage are developed the styloid process, stylohyoid ligament, and lesser cornu of the hyoid bone. The cartilage of the third arch gives origin to the greater cornu of the hyoid bone. The ventral ends of the second and third arches unite with those of the opposite side, and form a transverse band, from which the body of Fig. Entrance to larynx 104. — Floor of pharynx of embrvo shown in Fig. 103. no EMBRYOLOGY the hyoid bone and the posterior part of tlie tongue are developed. The ventral portions of the cartilages of the fourth and fifth arches unite to form the thyroid cartilage; from the cartilages of the sixth arch the cricoid and arytenoid cartilages and the cartilages of the trachea are developed. The mandibular and hyoid arches grow more rapidly than those behind them, with the result that the latter Malleus Incus ,,'' Tympanic ring .'''Mandible _./Z- MeckeVs cartilage - Hyoid hone Fig. 105. — Head and neck of a human embrvo eighteen weeks old, with Meckel's cartilage and hyoid bar exposed. (After Kolliker.) become, to a certain extent, telescoped within the former, and a deep depression, the sinus cervicalis, is formed on either side of the neck. This sinus is bounded in front by the hyoid arch, and behind by the thoracic wall; it is ultimately obliterated by the fusion of its walls. Membranous capsule over cerebral hemisphere \ Fronto-nasal process Stomodeum Lateral nasal process Eye Globular process Maxillary process Mandibular arch Hyonuindibidar cleft Fig. 106. — Under surface of the head of a human embryo about twenty-nine days old. (After His.) From the first branchial groove the concha auriculae and external acoustic meatus are developed, while around the groove there appear, on the mandibular and hyoid arches, a number of swellings from which the auricula or pinna is formed. The first pharyngeal pouch is prolonged dorsally to form the auditory tube and the tympanic cavity; the closing membrane between the mandibular and hyoid arches DEVELOPMENT OF THE PARIETES 111 is invaded by mesoderm, and forms the tympanic membrane. No traces of the second, third, and fourth branchial grooves persist. The inner part of the second pliaryngeal pouch is named the sinus tonsillaris; in it the tonsil is developed, above which a trace of the sinus persists as the suj)rat()nsillar fossa. The fossa of Rosen- miiller or lateral recess of the pharynx is by some regarded as a persistent part of the second pharyngeal pouch, but it is probably developed as a secondary forma- tion. From the third pharyngeal pouch the thymus arises as an entodermal diver- ticulum on either side, and from the fourth pouches small diverticula project and become incorporated with the thymus, but in man these diverticula probably never form true thymus tissue. The parathyroids also arise as diverticula from the third and fourth pouches. From the fifth pouches the ultimobranchial bodies originate and are enveloped by the lateral prolongations of the median thyroid rudiment; they do not, however, form true thyroid tissue, nor are any traces of them found in the human adult. Future apex of nose Medial nasal 'process Olfactory pit Lateral nasal process Glcbular process Maxillary process Stomodeum Mandibular arch Future apex of iwse Medial nasal process Olfactory pit Lateral nasal process Clohidar process Maxillary process Roof of plmrynx Hypophyseal diverticidmn Dorsal wall of pharynx Fig. 107. — Head end of human embryo of about thirty to thirty-one days. (From model bj^ Peter.) Fig. 108. — Same embryo as shown in Fig. 107, with front wall of pharynx removed. The Nose and Face. — During the third week tw^o areas of thickened ectoderm, the olfactory areas, appear immediately under the fore-brain in the anterior wall of the stomodeum, one on either side of a region termed the fronto-nasal process (Fig. 106). By the upgrowth of the surrounding parts these areas are converted into pits, the olfactory pits, which indent the fronto-nasal process and divide it into a medial and two lateral nasal processes (Fig. 107). The rounded lateral angles of the medial process constitute the globular processes of His. The olfactory pits form the rudiments of the nasal cavities, and from their ectodermal lining the epithe- lium of the nasal cavities, with the exception of that of the inferior meatuses, is deriA^ed. The globular processes are prolonged backward as plates, termed the nasal laminae: these laminte are at first some distance apart, but, gradually approach- ing, they ultimately fuse and form the nasal septum; the processes themselves meet in the middle line, and form the premaxillse and the philtrum or central part of the upper lip (Fig. 110). The depressed part of the medial nasal process between the globular processes forms the lower part of the nasal septum or columella; while above this is seen a prominent angle, which becomes the future 112 EMBRYOLOGY apex (Figs. 107, 108), and still higher a flat area, the future l>ri(lge, of the nose. The lateral nasal processes form the alte of the nose. Continuous with the dorsal end of the mandibular arch, and growing forward from its cephalic border, is a triangular process, the maxillary process, the ventral extremity of which is separated from the mandibular arch by a ^ shaped notch (Fig. 106). The maxillary process forms the lateral wall and floor of the orbit, and in it are ossified the zygomatic bone and the greater part of the maxilla; it meets with the lateral nasal process, from which, however, it is separated for a time by a groove, the naso-optic furrow, that extend from the furrow encircling the eyeball to the olfactory pit. The maxillary processes ultimately fuse with the lateral nasal and globular processes, and form the lateral parts of the upper lip and the posterior boundaries of the nares (Figs. 109, 110). From the third to the fifth month the nares are filled by masses of epithelium, on the breaking down and disappearance of which the permanent openings are produced. The maxillary process also gives rise to the lower portion of the lateral wall of the nasal cavity. Lateral nasal pro- cess Globular processes Fig. 109. — Head of a human embryo of about eight weeks, in which the nose and mouth are formed. (His.) Fig. 110. — Diagram showing the regions of the adult face and neck related to the fronto-nasal process and the branchial arches. The roof of the nose and the remaining parts of the lateral wall, viz., the ethmoidal labyrinth, the inferior nasal concha, the lateral cartilage, and the lateral crus of the alar cartilage, are developed in the lateral nasal process. By the fusion of the maxillary and nasal processes in the roof of the stomodeum the primitive palate (Fig. Ill) is formed, and the olfactory pits extend backward above it. The pos- terior end of each pit is closed by an epithelial membrane, the bucconasal membrane, formed by the apposition of the nasal and stomodeal epithelium. By the rupture of these membranes the primitive choanse or openings between the olfactory pits and the stomodeum are established. The floor of the nasal cavity is completed by the development of a pair of shelf-like palatine processes which extend medial- ward from the maxillary processes (Figs. 112 and 113); these coalesce with each other in the middle line, and constitute the entire palate, except a small part in front which is formed by the premaxillary bones. Two apertures persist for a time between the palatine processes and the premaxillse and represent the permanent channels which in the lower animals connect the nose and mouth. The union of the parts which form the palate commences in front, the premaxillary and palatine processes joining in the eighth week, while the region of the future hard palate is completed by the ninth, and that of the soft palate by the eleventh week. By DFA'ELOl'MEXT OF THE I'AHIETES 113 the t'onipletion of the palate tiie permanent choanae are formed and are situated a considerable distance behind tlie primitive chc.ana-. The (k-formity known as cleft palate results from a non-union of the pahitiiit- processes, an. %4. Lateral part nasal capsul Injerior concha — ^ ;.tf! ' >f^ ' :;; :/.V^ -:.'^ f'-^-t-^ f;. ."••■:-;■. ■ .'- :'. W'-'- •.•.•-" Cartilage of nasal septuirk Inferior meatus Vomeronasal cartilage Palatine process Vomeronasal organ of Jacohson ■ Inferior meatus Cavity of mouth Fig. 113. — Frontal section of nasal cavities of a human embryo 28 mm. long. (Kollmann.) of the upper limb ; and the medial epicondyle of the femur, the tibia, and the great toe along the corresponding border of the lower limb. The preaxial part is derived from the anterior segments, the postaxial from the posterior segments of the limb- bud; and this explains, to a large extent, the innervation of the adult limb, the nerves of the more anterior segments being distributed along the preaxial (radial or tibial), and those of the more posterior along the postaxial (ulnar or fibular) border of the limb. The limbs next undergo a rotation or torsion through an angle of 90° around their long axes the rotation being effected almost entirely at the limb girdles. In the upper limb the rotation is outward and forward; in the lower limb, inward and backward. As a consequence of this rotation the preaxial (radial) border of the fore-limb is directed lateralward, and the preaxial (tibial) border of the hind-limb is directed medialward; thus the flexor surface of the fore-limb is turned forward, and that of the hind-limb backward. DEVELOPMENT OF THE JOISTS 115 DEVELOPMENT OF THE JOINTS. The mesuckTin from wliicli tlie dilt'crcnt parts of tlio skeleton are formed at first shows no differentiation into masses corresponding with the individual bones. Thus continuous cores of mesoderm form the axes of the Hml)-l)uds and a continu- ous cohnnii of mesotlerm the future vertebral column. The first indications of the bones and joints are circumscribed condensations of the mesoderm; these condensed parts become chondrified antl finally ossified to form the bones of the skeleton. The interN'ening non-condensed portions consist at first of undifferentiated meso- derm, which may develop in one of three directions. It may be converted into fibrous tissue as in the case of the skull bones, a synarthrodia! joint being the result, or it may become partly cartilaginous, in which case an amphiarthrodial joint is formed. Again, it may become looser in texture and a cavity ultimately appear in its midst; the cells lining the sides of this cavity form a synovial mem- brane and thus a diarthrodial joint is developed. Hyoid arch MamLhitlai a)ch Maxillary piocess Heart Foie-limb Fig. 114.- Hind-limb -Human embryo from thirty-one to thirty- four days. (His.) Auricula Fore-limb Hind-limh Vmhilical cord Fig. 115. — Embryo of about six weeks. (His.) The tissue surrounding the original mesodermal core forms fibrous sheaths for the developing bones, i. e., periosteum and perichondrium, which are continued between the ends of the bones over the synovial membrane as the capsules of the joints. These capsules are not of uniform thickness, so that in them may be recognized especially strengthened band which are described as ligaments. This, however, is not the only method of formation of ligaments. In some cases by modification of, or derivations from, the tendons surrounding the joint, additional ligamentous bands are provided to further strengthen the articulations. In several of the movable joints the mesoderm which originally existed between the ends of the bones does not become completely absorbed — a portion of it persists and forms an articular disk. These disks may be intimately associated in their development with the muscles surrounding the joint, e. g., the menisci of the knee-joint, or with cartilaginous elements, representatives of skeletal structures, which are vestigial in human anatomy, e. g., the articular disk of the sterno- clavicular joint. 116 EMBRYOLOGY DEVELOPMENT OF THE MUSCLES. The voluntary muscles are developed from the mycjtomes of the primitive segments. Portions of the myotomes retain their position on the sides of the neural tube, where they may remain distinct from each other and form the short muscles of the vertebral column, or fuse with corresponding portions of neighboring myotomes to form the Sacrospinales and their continuations. Other portions of the myotomes extend into the trunk wall, where again they may retain their segmental condition, as in the Intercostales, or may fuse with adjacent segments to form the flat muscles of the abdominal wall. Finally, por- tions of the myotomes wander into the limb-buds and there undergo fusions and alterations in form to produce the limb muscles. The original segmental character of the limb muscles is therefore lost, but their segmental nerve supplies are retained. Some of the limb muscles expand and migrate secondarily toward the mid-dorsal line, e. g., Trapezius and Latissimus dorsi, or toward the mid-ventral line, e. g., Pectoralis major. Again, muscles may migrate in a cephalic direction, e. g., the facial muscles which are derived from the hyoid arch, or in a caudal direc- tion, e. g., the Serratus anterior. In all cases the muscles carry with them the segmental nerves of the myotomes from which they were originally derived; two examples of this will suffice, viz., the Diaphragma, which is derived from the third and fourth and the Serratus anterior, from the fifth, sixth, and seventh cervical segments as is indicated by their nerves of supply. In man and the higher verte- brates many of the derivatives of the myotomes degenerate and are converted into aponeuroses, e. g., galea aponeurotica, and the aponeuroses of the abdominal muscles, or ligaments, e. g., sacrotuberous ligament and fibular collateral ligament of the knee. The involuntary muscles are derived from the splanchnopleure mesoderm. DEVELOPMENT OF THE SKIN, GLANDS, AND SOFT PARTS. The epidermis and its appendages, consisting of the hairs, nails, sebaceous and sweat glands, are developed from the ectoderm, while the corium or true skin is of mesodermal origin, being derived from the cutis-plates of the primitive seg- ments. About the fifth week the epidermis consists of two layers of cells, the deeper one corresponding to the rete mucosum. The subcutaneous fat appears about the fourth month, and the papillae of the true skin about the sixth. A considerable desquamation of epidermis takes place during fetal life, and this desquamated epidermis, mixed with sebaceous secretion, constitutes the vemix caseosa, with which the skin is smeared during the last three months of fetal life. The nails are formed at the third month, and begin to project from the epidermis about the sixth. The hairs appear between the third and fourth months in the form of solid downgrowths of the deeper layer of the epidermis, the growing extremities of which become inverted by papillary projections from the corium. The central cells of the solid downgrowths undergo alteration to form the hair, while the peripheral cells are retained to form the lining cells of the hair-follicle. About the fifth month the fetal hairs {lanugo) appear, first on the head and then on the other parts; they drop off after birth, and give place to the permanent hairs. The cellular structures of the sudoriferous and sebaceous glands are formed from the ectoderm, while the connective tissue and bloodvessels are derived from the mesoderm. The mamma is also formed partly from mesoderm and partly from ectoderm — its bloodvessels and connective tissue being derived from the former, its cellular elements from the latter. Its first rudiment is seen. about the third month, in the DEVELOPMEXT OF THE XERVOVS SYSTEM AXD SEXSE ORGAXS 117 form of a lunnbtT of small inward projections of the ectoderm, which invade the mesoderm; from these, secondary tracts of cellular elements radiate and sub- sequently give rise to the epithelium of the glandular follicles and ducts. The development of the follicles, however, remains imperfect, except in the parous female. DEVELOPMENT OF THE NERVOUS SYSTEM AND SENSE ORGANS. The entire nervous system is of ectodermal origin, and its first rudiment is seen in the neural groove which extends along the dorsal aspect of the embryo (Fig. 75). By the elevation and ultimate fusion of the neural folds, the groove is con- verted into the neural tube (Fig. 77). The anterior end of the neural tube becomes expanded to form the three primary brain- vesicles; the cavity of the tube is sub- sequently modified to form the ventricular cavities of the brain, and the central canal of the medulla spinalis ; from the wall the nervous elements and the neuroglia of the brain and medulla spinalis are developed. Eoof-plaie Oval bundle Posterior nerve root Central canal Ependynial layer Mantle layer Anterior nerve- rooUi ■Marginal layer Floor-plate Fig. ,116. — Section of medulla spinalis of a four weeks' embryo. (His.) The Medulla Spinalis. — J^t first the wall of the neural tube is composed of a single laj^er of columnar ectodermal cells. Soon the side-walls become thickened, while the dorsal and ventral parts remain thin, and are named the roof- and floor- plates (Figs. 116, 118). A transverse section of the tube at this stage presents an oval outline, while its lumen has the appearance of a slit. The cells which constitute the wall of the tube proliferate rapidly, lose their cell-boundaries and form a syncytium. This syncytium consists at first of dense protoplasm with closely packed nuclei, but later it opens out and forms a looser meshw^ork with the cellular strands arranged in a radiating manner from the central canal. Three layers may now be defined — an internal or ependymal, an intermediate or mantle, and an external or marginal. The ependymal layer is ultimately converted into the ependyma of the central canal; the processes of its cells pass outward toward the periphery of the medulla spinalis. The marginal layer is devoid of nuclei, and later forms the supporting framework for the white funiculi of the medulla spinalis. The mantle layer represents the whole of the future gray columns of the medulla 118 EMBRYOLOGY spinalis; in it tlie cells are differentiated into two sets, viz., (a) spongioblasts or young neuroglia cells, and (6) germinal cells, which are the parents of the neuroblasts or young nerve cells (Fig. 117). The spongioblasts are at first connected to one another by filaments of the syncytium; in these, fibrils are developed, so that as the Germinal cell Neuroblast Nuclei of spongioblasts 'yncylium Fig. 117. -Transverse section of the medulla spinalis of a human embryo at the beginning of the fourth week. (After His.) The left edge of the figure corresponds to the fining of the central canal. neuroglial cells become defined they exhibit their characteristic mature appearance with multiple processes proceeding from each cell. The germinal cells are large, round or oval, and first make their appearance between the ependymal cells on the sides of the central canal. They increase rapidly in number, so that by the Eoof-plate Alar lamina Oval bundle Posterior nerve-root Central canal Ependymal layer Lateral funiculus Basal lamina ntenor nerve-root Floor-plate Anterior funiculus Fasciculus gracilis \Po.sterior Fasciculus cuneatus) funiculus -Post, nerve-root Lateral funiculus Central canal Anterior funiculus B Fig. 118. — Transverse sections through the medullae spinales of human embryos. A. Aged about four and a half weelis. B. Aged about three months. (His.) fourth week they form an almost continuous layer on each side of the tube. No germinal cells are found in the roof- or floor-plates; the roof-plate retains, in certain regions of the brain, its epithelial character; elsewhere, its cells become spongio- blasts. By subdivision the germinal cells give rise to the neuroblasts or young DEVELOPMENT OF THE NERVOUS SYSTEM AND SENSE ORGANS 119 nerve cells, which migrate outward from the sides of the central canal into the mantle layer and neural crest, and at the same time become pear-shaped; the tapering part of the cell undergoes still further elongation, and forms the axis- cylinder of the cell. The lateral walls of the medulla spinalis contiiuie to increase in thickness, and the canal widens out near its dorsal extremity, and assumes a somewhat lozenge- shaped appearance. The widest part of the canal serves to subdivide the lateral wall of the neural tube into a dorsal or alar, and a ventral or basal lamina (Fig. 118), a subdivision which extends forward into the brain. At a later stage the ventral part of the canal widens out, while the dorsal part is first reduced to a mere slit and then becomes obliterated by the approximation and fusion of its walls; the ventral part of the canal persists and forms the central canal of the adult medulla spinalis. The caudal end of the canal exhibits a conical expansion which is known as the terminal ventricle. The ^'entral part of the mantle layer becomes thickened, and on cross-section appears as a triangular patch between the marginal and ependymal layers. This thickening is the rudiment of the anterior column of gray substance, and contains many neuroblasts, the axis-cylinders of w^hich pass out through the marginal layer and form the anterior roots of the spinal nerves (Figs. 116, 118). The thickening of the mantle layer gradually extends in a dorsal direction, and forms the posterior column of gray substance. The axons of many of the neuroblasts in the alar lamina run forward, and cross in the floor-plate to the opposite side of the medulla spinalis; these form the rudiment of the anterior white commissure. About the end of the fourth week nerve fibres begin to appear in the marginal layer. The first to develop are the short intersegmental fibres from the neuro- blasts in the mantle zone, and the fibres of the dorsal nerve roots which grow into the medulla spinalis from the cells of the spinal ganglia. By the sixth week these dorsal root fibres form a well-defined oval bundle in the peripheral part of the alar lamina; this bundle gradually increases in size, and spreading toward the middle line forms the rudiment of the posterior funiculus. The long intersegmental fibres begin to appear about the third month and the cerebrospinal fibres about the fifth month. All nerve fibres are at first destitute of medullary sheaths. Different groups of fibres receive their sheaths at different times — the dorsal and ventral nerve roots about the fifth month, the cerebrospinal fibres after the ninth month. By the growth of the anterior columns of gray substance, and by the increase in size of the anterior funiculi, a furrow is formed between the lateral halves of the cord anteriorly; this gradually deepens to form the anterior median fissure. The mode of formation of the posterior septum is somewhat uncertain. Many believe that it is produced by the growing together of the walls of the posterior part of the central canal and by the development from its ependymal cells of a septum of fibrillated tissue which separates the future fvmiculi graciles. Up to the third month of fetal life the medulla spinalis occupies the entire length of the vertebral canal, and the spinal nerves pass outward at right angles to the medulla spinalis. From this time onward, the vertebral column grows more rapidly than the medulla spinalis, and the latter, being fixed above through its continuity wdth the brain, gradually assumes a higher position within the canal. By the sixth month its lower end reaches only as far as the upper end of the sacrum ; at birth it is on a level with the third lumbar vertebra, and in the adult with the lower border of the first or upper border of the second lumbar vertebra. A delicate filament, the filum terminale, extends from its lower end as far as the coccyx. The Spinal Nerves.^ — Each spinal nerve is attached to the medulla spinalis by an anterior or ventral and a posterior or dorsal root. The fibres of the anterior roots are formed by the axons of the neuroblasts which lie in the ventral part of the mantle layer; these axons grow out through the 120 EMBRYOLOGY overlving marginal la^'e^ and become grouped to f(jrm the anterior nerve root (Fig. -117). The fibres of the posterior roots are developed from the cells of the spinal ganglia. Before the neural groove is closed to form the neural tube a ridge of ectodermal cells, the ganglion ridge or neural crest (Fig. 119), appears along the prominent margin of each neural fold. When the folds meet in the middle line the two gan- glion ridges fuse and form a wedge-shaped area along the line of closure of the tube. The cells of this area proliferate rapidly opposite the primitive segments and then migrate in a lateral and ventral direction to the sides of the neural tube, where they ultimately form a series of oval-shaped masses, the future spinal ganglia. These ganglia are arranged symmetrically on the two sides of the neural tube and, except in the region of the tail, are equal in number to the primitive segments. The cells of the ganglia, like the cells of the mantle layer, are of two kinds, viz., spongio- blasts and neuroblasts. The spongioblasts develop into the neuroglial cells of the ganglia. The neuroblasts are at first round or oval in shape, but soon assume the form of spindles the extremities of which gradually elongate into central and peripheral processes. The central processes grow medial ward and, be- coming connected with the neural tube, constitute the fibres of the posterior nerve roots, while the per- ipheral processes grow lateralward to mingle with the fibres of the anterior root in the spinal nerve. As de- velopment proceeds the bipolar form of the cells the two processes become mated until they ultimately arise from a single stem in a T-shaped manner. Only in the ganglia of the acoustic nerve is the bipolar form retained . More recent observers hold, however, that the T-form is derived from the branching of a single pro- cess which grows out from the cell. The anterior or ventral and the pos- terior or dorsal nerve roots join imme- diately beyond the spinal ganglion to form the spinal nerve, which then divides into anterior, posterior, and visceral divisions. The anterior and posterior divisions proceed directly to their areas of distribution without further association with ganglion cells (Fig. 120). The visceral divisions are distributed to the thoracic, abdominal, and pelvic viscera, to reach which they pass through the sympathetic trunk, and many of the fibres form arborizations around the ganglion cells of this trunk. Visceral branches are not given off from all the spinal nerves; they form two groups, viz., (a) thoracico-lumbar, from the first or second thoracic, to the second or third lumbar nerves; and (6) pelvic, from the second and third, or third and fourth sacral nerves. The Brain. — The brain is developed from the anterior end of the neural tube, which at an early period becomes expanded into three vesicles, the primary cerebral vesicles (Fig. 76). These are marked off from each other by intervening con- strictions, and are named the prosencephalon or fore-brain, the mesencephalon or mid-brain, and the rhombencephalon or hind-brain — the last being continuous w^ith the medulla spinalis. As the result of unequal growth of these different parts three flexures are formed and the embryonic brain becomes bent on itself original changes; approxi- FiG. 119. — Two stages in the development of the neural crest in the human embryo. (Lenhossek.) DEVELOP m' EN T OF THE NERVOUS SYSTEM AND SENSE ORGANS 121 in a somewhat zigzag fasliion; the two earliest flexures are eoneave ventrally and are assoeiated with corresponding flexures of the whole head. The first flexure appears in the region of the raid-brain, and is named the ventral cephalic flexure (Fig. 125). By means of it the fore-brain is bent in a ventral direction around the anterior end of the notochord and fore-gut, with the result that the floor of the fore-brain comes to lie almost parallel with that of the hind-brain. This flexure causes the mid-brain to become, for a time, the most prominent part of A udilory vesicle Facial and acoustic Ns. Trigeminal N, Trochlear N. Glossopluiryugeal N. Vagus N. Accessoi'y N. Hypoglossal N. Mesencephalon Octdomotor N. Dienceplialon — i- Cerebral hemisphere Froriep's ganglion •/• Cervical Vitelline loop Tail ' /. Coccygeal — V Sacral Fig. 120. — Reconstruction of peripheral nerves of a human embryo of 10.2 mm. (After His.) The abducent nerve is not labelled, but is seen passing forward to the eye under the mandibular and maxillary nerves. the brain, since its dorsal surface corresponds with the convexity of the curve. The second bend appears at the junction of the hind-brain and medulla spinalis. This is termed the cervical flexure (Fig. 127), and increases from the third to the end of the fifth week, when the hind-brain forms nearly a right angle with the medulla spinalis; after the fifth week erection of the head takes place and the cervi- cal flexure diminishes and disappears. The third bend is named the pontine flexure (Fig. 127), because it is found in the region of the future pons Varoli. It differs 122 EMBRYOLOGY from the other two in that (a) its convexity is forward, and (6) it does not affect the head. The lateral walls of the brain-tube, like those of the medulla spinalis, are divided bv internal furrows into alar or dorsal and basal or ventral lamina? (Fig. 121). Fig. 121. — Diagram to illustrate the alar and basal laminae of brain vesicles. (His.) Eoof-plate Alar lamina Furrow between alar and ba-sal laminae Basal lamina Vagus nerve Hypoglossal nerve Floor-plate Fig. 122. — Transverse section of medulla oblongata of human embryo. X 32. (Kollmann.) The Rhombencephalon or Hind-brain. — The cavity of the hind-brain becomes the fourth ventricle. At the time when the ventral cephalic flexure makes its appearance, the length of the hind-brain exceeds the combined lengths of the other two vesicles. Immediately behind the mid-brain it exhibits a marked constriction, the isthmus rhombencephali (Fig. 125, Isthmus), which is best seen when the brain is viewed from the dorsal aspect. From the isthmus the anterior medullary velum Rhomhic Up Vagus nerve Hypoglossal nerve Floor-plate Fig. 123. — Transverse section of medulla oblongata of human embrj-o. (After His.) and the brachia conjunctiva of the cerebellum are formed. It is customary to divide the rest of the hind-brain into two parts, viz., an upper, called the meten- cephalon, and a lower, the myelencephalon. The cerebellum is developed by a thickening of the roof, and the pons by a thickening in the floor and lateral walls of the metencephalon. The floor and lateral walls of the myelencephalon are developSiext of the xervous system AXD SEXSE ORGAXS 123 thickened to form the ineduHa oblongata; its roof remains thin, and, retaining to a great extent its epithehal nature, is expanded in a hiteral direction. Later, by the growth and backward extension of the cerebelkim, the roof is folded inward toward the cavity of the fourth ventricle; it assists in completing the dorsal wall of this cavity, and is also invaginated to form the ependymal covering of its choroid plexuses. Above it is continuous with the posterior medullary velum; below, with the obex and liguhe. Taenia Rhombic lip Fig. 124. — Hind-brain of a human embryo of three months — viewed from behind and partly from left side. (From model by His.) 125. — Exterior of brain of human embryo of four and a half weeks. (From model by His.) The development of the medulla oblongata resembles that of the medulla spinalis, but at the same time exhibits one or two interesting modifications. On transverse section the myelencephalon at an early stage is seen to consist of two lateral walls, connected across the middle line by floor- and roof-plates (Figs. 122 and 123). Each lateral w^all consists of an alar and a basal lamina, separated by an internal furrow, the remains of which are represented in the adult brain by the sulcus limitans on the rhomboid fossa. The contained cavity is more or less triangular in outline, the base being formed by the roof-plate, which is thin and greatly expanded transversely. Pear-shaped neuroblasts are developed in the alar and basal laminae, and their narrow stalks are elongated to form the axis-cylinders of the nerve fibres. Opposite the furrow or boundary between the alar and basal laminae a bundle of nerve fibres attaches itself to the outer surface of the alar lamina. This is named the tractus solitarius (Fig. 123), and is formed by the sensory fibres of the glossopharyngeal and vagus nerves. It is the homologue of the oval bundle seen in the medulla spinalis, and, like it, is developed by an ingrowth of fibres from the ganglia of the neural crest. At first it is applied to the outer surface of the alar lamina, but it soon becomes buried, owing to the growth over it of the neighboring parts. By the fifth w^eek the dorsal part of the alar lamina bends in a lateral direction along its entire length, to form what is termed the rhombic lip (Figs. 123, 124). Within a few days this lip becomes applied to, and unites 124 EMBRYOLOGY with, the outer surface of the main part of the alar lamina, and so covers in the tractus solitarius and also the spinal root of the trigeminal nerve; the nodulus and flocculus of the cerebellum are developed from the rhombic lip. Neuroblasts accumulate in the mantle layer; those in the basal lamina corre- spond with the cells in the anterior gray column of the medulla spinalis, and, like them, give origin to motor nerve fibres; in the medulla oblongata they are, however, arranged in groups or nuclei, instead of forming a continuous column. From the alar lamina and its rhombic lip, neuroblasts migrate into the basal lamina, and become aggregated to form the olivary nuclei, while many send their axis-cylinders through the floor-plate to the opposite side, and thus constitute the rudiment of the raphe of the medulla oblongata. By means of this thickening of the ventral portion, the motor nuclei are buried deeply in the interior, and, in the adult, are found close to the rhomboid fossa. This is still further accentuated: (a) by the development of the p^Tamids, which are formed about the fourth month by the downward growth of the motor fibres from the cerebral cortex ; and (6) by the fibres which pass to and from' the cerebellum. On the rhomboid fossa a series of six tem- porary furrows appears; these are termed the rhombic grooves. They bear a definite relationship to certain of the cerebral nerves; thus, from before backward the first and second grooves overlie the nucleus of the trigeminal; the third, the nucleus of the facial; the fourth, that of the ab- ducent; the fifth, that of the glosso- pharyngeal; and the sixth, that of the vagus. The pons is developed from the ventro-lateral wall of the meten- cephalon by a process similar to that which has been described for the medulla oblongata. The cerebellum is developed in the roof of the anterior part of the hind-brain (Figs. 124 to 129). The alar laminae of this region become thickened to form two lateral plates which soon fuse in the middle line and produce a thick lamina which roofs in the upper part of the cavity of the hind-brain vesicle; this constitutes the rudiment of the cerebellum, the outer surface of which is originally smooth and convex. The fissures of the cerebellum appear first in the vermis and floccular region, and traces of them are found during the third month; the fissures on the cerebellar hemispheres do not appear until the fifth month. The primitive fissures are not developed in the order of their relative size in the adult — thus the hori- zontal sulcus in the fifth month is merely a shallow groove. The best marked of the early fissures are: (a) the fissura prima between the developing culmen and declive, and {h) the fissura secunda between the future pyramid and uvula. The flocculus and nodule are developed from the rhombic lip, and are therefore recog- nizable as separate portions before any of the other cerebellar lobules. The groove produced by the bending over of the rhombic lip is here known as the Ganglia of VII. and VIII. Ns. Auditory vesicle Fig. 126.— Brain of human embryo of four and a half weeks, showing interior of fore-brain. (From model by His.) DF.VELOPMEXT OF THE XERVOrS SYSTE.\r AXD SEXSE ORGANS 125 floccular fissure; when the two hiteral walls fuse, the right and left Hoccular fissures join in the middle line and their central part becomes the post-nodular fissure. On the ventricular surface of the cerebellar lamina a transverse furrow, the incisura fastigii, appears, and deepens to form the tent-like recess of the roof of the fourth ventricle. The rudiment of the cerebellum at first projects in a dorsal direction ; but, by the backward growth of the cerebrum, it is folded downward and somewhat flattened, and the thin roof-plate of the fourth ventricle, originally continuous with the posterior border of the cerebellum, is projected inward toward the cavity of the ventricle. The Mesencephalon or Mid-brain. — The mid-brain (Figs. 125 to 129) exists for a time as a thin-walled cavity of some size, and is separated from the isthmus rhom- encephali behind, and from the fore-brain in front, by slight constrictions. Its cavity becomes relatively reduced in diameter, and forms the cerebral aqueduct of the adult brain. Its basal laminae increase in thickness to form the cerebral peduncles, which are at first of small size, but rapidly enlarge after the fourth month. Ganglion hubenulce I Fig. 127. — Exterior of brain of human embryo of five weeks. (From model by His.) The neuroblasts of these laminae are grouped in relation to the sides and floor of the cerebral aqueduct, and constitute the nuclei of the oculomotor and trochlear nerves, and of the mesencephalic root of the trigeminal nerve. By a similar thickening process its alar laminae are developed into the quadrigeminal lamina. The dorsal part of the wall for a time undergoes expansion, and presents an internal median furrow and a corresponding external ridge; these, however, disappear, and the latter is replaced by a groove. Subsequently two oblique furrows extend medialward and backward, and the thickened lamina is thus subdivided into the superior and inferior colliculi. The Prosencephalon or Fore-brain. — A transverse section of the early fore-brain shows the same parts as are displayed in similar sections of the medulla spinalis and medulla oblongata, viz., a pair of thick lateral walls connected by thin floor- and roof-plates. Moreover, each lateral wall exhibits a division into a dorsal or alar and a ventral or basal lamina separated internally by a furrow termed the sulcus 126 EMBRYOLOGY of Monro. This sulcus ends anteriorly at the medial end of the optic stalk, and in the adult brain is retained as a slight groove extending backwarrl from the inter- ventricular foramen to the cerebral aqueduct. At a very early period — in some animals before the closure of the cranial jjart of the neural tube — two lateral diverticula, the optic vesicles, appear, one on either side of the fore-brain; for a time they communicate with the cavity of the fore-})rain by relatively wide openings. The peripheral parts of the vesicles expand, while the proximal parts are reduced to tubular stalks, the optic stalks. The optic vesicle gives rise to the retina and the epithelium on the back of the ciliary body and iris; the optic stalk is invaded by nerve fibres to form the optic nerve. The fore-l)rain then grows forward, and from the alar laminae of this front portion the cerebral hemispheres originate as diverticula which rapidly expand to form two large pouches, one on either side. The cavities of these diverticula are the rudiments of the lateral ventricles; they communicate with the median part of the fore-brain cavity by relatively wide openings, which ultimately form the interventricular Recessus infundibuli Tuber cinereum Corpus mmniliare Cervical flexure Fig. 128. — Interior of brain of human embryo of five weeks. (From model by His.) foramen. The median portion of the wall of the fore-brain vesicle consists of a thin lamina, the lamina terminalis (Figs. 129, 132), which stretches from the interventricular foramen to the recess at the base of the optic stalk. The anterior part of the fore-brain, including the rudiments of the cerebral hemi- spheres, is named the telencephalon, and its posterior portion is termed the diencephalon ; both of these contribute to the formation of the third ventricle. The Diencephalon. — From the alar lamina of the diencephalon, the thalamus, metathalamus, and epithalamus are developed. The thalamus (Figs. 125 to 129) arises as a thickening which involves the anterior two-thirds of the alar lamina. The two thalami are visible, for a time, on the surface of the brain, but are subse- quently hidden by the cerebral hemispheres w^hich grow backward over them. The thalami extend medialward and gradually narrow the cavity between them into a slit-like aperture which forms the greater part of the third ventricle; their medial surfaces ultimately adhere, in part, to each other, and the intermediate DEVELOPMENT OF THE XERVOVS SYSTEM AXD SEXSE ORGANS 127 mass of the \eiitricle is developed aert)ss the area of eontact. The metathalamus comprises the ^eiiieiihite bodies which originate as sliglit outward bulgings of the alar lamina. In the adult the lateral geniculate body appears as an eminence on the lateral part of the posterior end of the thalamus, while the medial is situated on the lateral aspect of the mesencephalon. The epithalamus includes the pineal body, the posterior commissure, and the trigonum habenulae. The pineal body arises as an upward e\agination of the roof-plate immediately in front of the mid- brain; this evagination becomes solid with the exception of its proximal part, which persists as the recessus i)inealis. In lizards the pineal evagination is elongated into a stalk, and its peripheral extremity is expanded into a vesicle, in which a ruilimentary lens and retina are formed; the stalk becomes solid and nerve fibres make their appearance in it, so that in these animals the pineal body forms a rudimentary eye. The posterior commissure is formed by the ingrowth of fibres into the depression behind and below the pineal evagination, and the trigonum habenulae is developed in front of the pineal recess. Choroidal fissure Bypophysis Itecesstis infundibidi Fig. 129. — Median sagittal section of brain of human embrj-o of three months. (From model by His.) From the basal laminae of the diencephalon the pars mamillaria hypothalami is developed; this comprises the corpora mamillaria and the posterior part of the tuber cinereum. The corpora mamillaria arise as a single thickening, which becomes divided into two by a median furrow during the third month. The roof-plate of the diencephalon, in front of the pineal body, remains thin and epithelial in character, and is subsequently invaginated by the choroid plexuses of the third ventricle. The Telencephalon. — This consists of a median portion and two lateral diver- ticula. The median portion forms the anterior part of the cavity of the third ventricle, and is closed below and in front by the lamina terminalis. The lateral diverticula consist of outward pouchings of the alar laminae; the cavities represent the lateral ventricles, and their walls become thickened to form the nervous 128 EMBRYOLOGY matter of the cerebral hemispheres. The roof-plate of the telencephalon remains thin, and is continuous in front with the lamina terminalis and behind with the roof-plate of the diencephalon. In the basal laminae and floor-plate the pars optica hypothalami is developed; this comprises the anterior part of the tuber cinereum, the infundibulum and posterior lobe of the hypophysis, and the optic chiasma. The anterior part of the tuber cinereum is derived from the posterior part of the floor of the telencephalon; the infundibulum and posterior lobe of the hypophysis arise as a downward diverticulum from the floor. The most dependent part of the diverticulum becomes solid and forms the posterior lobe of the hypo- physis; the anterior lobe of the hypophysis is developed from a diverticulum of the ectodermal lining of the stomodeum (page 166), The optic chiasma is formed by the meeting and partial decussation of the optic nerves, which subsequently grow backward as the optic tracts and end in the diencephalon. The cerebral hemispheres arise as diverticula of the alar laminae of the telen- cephalon (Figs. 125 to 129); they increase rapidly in size and ultimately overlap the structures developed from the mid- and hind-brains. This great expansion of the hemispheres is a char- acteristic feature of the brains of mammals, and attains its maximum development in the brain of man. Elliott- Smith divides each cerebral hemisphere into three funda- mental parts, viz., the rhinen- cephalon, the corpus striatum, and the neopallium. The rhinencephalon (Fig. 130) represents the oldest part of the telencephalon, and forms almost the whole of the hemisphere in fishes, amphibians, and reptiles. In man it is feebly developed in comparison with the rest of the hemisphere, and com- prises the following parts, viz., the olfactory lobe (con- sisting of the olfactory tract and bulb and the trigonum olfactorium), the anterior perforated substance, the septum pellucidum, the subcallosal, supracallosal, and dentate gyri, the fornix, the hippocampus, and the uncus. The rhinencephalon appears as a longitudinal elevation, with a corresponding internal furrow, on the under surface of the hemisphere close to the lamina terminalis; it is separated from the lateral surface of the hemisphere by a furrow, the external rhinal fissure, and is continuous behind with that part of the hemisphere, which will ultimately form the anterior end of the temporal lobe. The elevation becomes divided by a groove into an anterior and a posterior part. The anterior grows forward as a hollow stalk the lumen of which is continuous with the anterior part of the ven- tricular cavity. During the third month the stalk becomes solid and forms the rudiment of the olfactory bulb and tract; a strand of gelatinous tissue in the interior of the bulb indicates the position of the original cavity. From the posterior part the anterior perforated substance and the pyriform lobe are developed; at the begin- ning of the fourth month the latter forms a curved elevation continuous behind with the medial surface of the temporal lobe, and consisting, from before backward, of the gyrus olfactorius lateralis, gyrus ambiens, and gyrus semilunaris, parts which Gyr. olf. med. .— -^___^ Gyr. olf.laL. J-r-tC Gyr. ambiens Gyr. diagonalis Gyr. semilunaris Cerebellum Olive Fig. 130.- -Inferior surface of brain of embrj'o at beginning of fourth month. (From Kollmann.) DEVELOPMENT OF THE NERVOUS SYSTEM AND SENSE ORGANS 129 in the adult brain are represented by the hiteral root of the olfactory tract and the uncus. The position and connections of the remaining portions of the rhinen- cephalon are described with the anatomy of the brain. The corpus striatum (Figs. 126 and 128) appears in the fourth week as a triangular thickening of the floor of the telencephalon between the optic recess and the interventicular foramen, and continuous behind with the thalamic part of the diencephalon. It increases in size, and by the second month is seen as a swelling in the floor of the future lateral ventricle; this swelling reaches as far as the posterior end of the primitive hemisphere, and when this part of the hemisphere grows backward and downward to form the temporal lobe, the posterior part of the corpus striatum is carried into the roof of the inferior horn of the ventricle, where it is seen as the tail of the caudate nucleus in the adult brain. During the fourth and fifth months the corpus striatum becomes incompletely subdivided by the fibres of the internal capsule into two masses, an inner, the caudate nucleus, and an outer, the lentiform nucleus. In front, the corpus striatum is continuous with the anterior perforated substance; laterally it is confluent for a time with that portion of the wall of the vesicle which is developed into the insula, but this continuity is sub- sequently interrupted by the fibres of the external capsule. Falx cerebri Hippocampal fissure Cs. Corpus striatum. ' Th. Thalamus. Fig. 131. — Diagrammatic coronal section of brain to show relations of neopallium. (After His.) Cs. Corpus striatum. Th. Thalamus. The neopallium (Fig. 131) forms the remaining, and by far the greater, part of the cerebral hemisphere. It consists, at an early stage, of a relatively large, more or less hemispherical cavity — the primitive lateral ventricle — enclosed by a thin wall from which the cortex of the hemisphere is developed. The vesicle expands in all directions, but more especially upward and backward, so that by the third month the hemispheres cover the diencephalon, by the sixth they overlap the mid-brain, and by the eighth the hind-brain. The median lamina uniting the two hemispheres does not share in their expan- sion, and thus the hemispheres are separated by a deep cleft, the forerunner of the longitudinal fissure, and this cleft is occupied by a septum of mesodermal tissue which constitutes the primitive falx cerebri. Coincidently with the expan- 9 130 EMBRYOLOGY sion of the vesicle, its cavity is drawn out into three prolongations which represent the horns of the future lateral ventricle; the hinder end of the vesicle is carried down- ward and forward and forms the inferior horn; the posterior horn is produced somewhat later, in association with the backward growth of the occipital lobe of the hemisphere. The roof-plate of the primitive fore-brain remains thin and of an epithelial character; it is invaginated into the lateral ventricle along the medial wall of the hemisphere. This invagination constitutes the choroidal fissure, and extends from the interventricular foramen to the posterior end of the vesicle. Mes- odermal tissue, continuous with that of the primitive falx cerebri, and carrying bloodvessels with it, spreads between the two layers of the invaginated fold and forms the rudiment of the tela choroidea; the margins of the tela become highly vascular and form the choroid plexuses which for some months almost completely fill the ventricular cavities; the tela at the same time invaginates the epithelial roof of the diencephalon to form the choroid plexuses of the third ventricle. By the downward and forward growth of the posterior end of the vesicle to form the temporal lobe the choroidal fissure finally reaches from the interventricular fora- men to the extremity of the inferior horn of the ventricle. Gyrus dentatus Taenia thalami Tlialamus Choroidal fissure Post, commissure Corpora quadrigemina Cerebral aqueduct — ,^- Cerebral peduncle ■ ' 1 — V ™ Cerebellum IV. ventricle Corpus callosum Septum pellucidum Anterior commissure Mft--^^ ^^y^ - Lamina terminalis Rhinencephalon Optic cJiiasma Hypophysis \ III. ventricle Pons r /\ Medulla oblongata Fig. 132. — Median sagittal section of brain of human embryo of four months. (Marchand.) Parallel with but above and in front of the choroidal fissure the medial wall of the cerebral vesicle becomes folded outward and gives rise to the hippocampal fissure on the medial surface and to a corresponding elevation, the hippocampus, within the ventricular cavity. The gray or ganglionic covering of the wall of the vesicle ends at the inferior margin of the fissure is a thickened edge; beneath this the marginal or reticular layer (future white substance) is exposed and its lower thinned edge is continuous with the epithelial invagination covering the choroid plexus (Fig. 131). As a result of the later downward and forward growth of the temporal lobe the hippocampal fissure and the parts associated with it extend from the interventricular foramen to the end of the inferior horn of the ventricle. The thickened edge of gray substance becomes the gyrus dentatus, the fasciola cinerea and the supra- and subcallosal gyri, while the free edge of the white sub- stance forms the fimbria hippocampi and the body and crus of the fornix. The corpus callosum is developed within the arch of the hippocampal fissure, and the upper part of the fissure forms, in the adult brain, the callosal fissure on the medial surface of the hemisphere. DEVELOPMENT OF THE NERVOUS SYSTEM AND SENSE ORGANS 131 Parietal operculum The Commissures (Fig. 132). — The development of the posterior commissure has already been referred to (page 127). The great commisssures of the hemi- spheres, viz., the corpus callosum, the fornix, and anterior commissure, arise from the hmiina terminahs. About the fourth month a small thickening appears in this lamina, immediately in front of the interventricular foramen. The lower part of this thickening is soon constricted off, and fibres appear in it to form the anterior commissure. The upper part continues to grow with the hemispheres, and is invaded by two sets of fibres. Transverse fibres, extending between the hemisjiheres, pass into its dorsal part, which is now differentiated as the corpus callosum (in rare cases the corpus callosum is not developed). Into the ventral part longitudinal fibres from the hippocampus pass to the lamina terminalis, and through that structure to the corpora mamillaria; these fibres constitute the fornix. A small portion, lying antero-inferiorly between the corpus callosum and fornix, is not invaded by the commissural fibres; it remains thin, and later a cavity, the cavit}' of the septum pellucidum, forms in its interior. Fissures and Sulci. — The outer surface of the cerebral hemisphere is at first smooth, but later it exhibits a number of elevations or convolutions, separated from each other by fissures and sulci, most of which make their appearance during the sixth or seventh months of fetal life. The term, fissure is applied to such grooves as involve the entire thickness of the cere- bral wall, and thus produce correspond- ing eminences in the ventricular cavit}^ while the sulci aflfect only the superficial part of the wall, and therefore leave no impressions in the ventricle. The fissures comprise the choroidal and hippocampal already described, and two others, viz., the calcarine and collateral, which pro- duce- the swellings known respectively as the calcar avis and the collateral eminence in the ventricular cavity. Of the sulci the following may be referred to, viz., the central sulcus {fissure of Rolando), which is developed in two parts; the intraparietal sulcus in four parts; and the cingulate sulcus in two or three parts. The lateral cerebral or Sylvian fissure differs from all the other fissures in its mode of development. It appears about the third month as a depres- sion, the Sylvian fossa, on the lateral surface of the hemisphere (Fig. 133); this fossa corresponds with the position of the corpus striatum, and its fioor is moulded to form the insula. The intimate connection which exists between the cortex of the insula and the subjacent corpus striatum prevents this part of the hemis- phere wall from expanding at the same rate as the portions which surround it. The neighboring parts of the hemisphere therefore gradually grow over and cover in the insula, and constitute the temporal, parietal, frontal, and orbital opercula of the adult brain. The frontal and orbital opercula are the last to form, but by the end of the first year after birth the insula is completely submerged by the approxi- mation of the opercula. The fissures separating the opposed margins of the oper- cula constitute the composite lateral cerebral fissure. If a section across the wall of the hemisphere about the sixth week be examined microscopically it will be found to consist of a thin marginal or reticular layer, a thick ependymal layer, and a thin intervening mantle layer. Neuroblasts from the Temporal operculum Sylvian fossa Frontal operculum Fig. 133. — Outer surface of cerebral hemisphere of human embryo of about five months. 132 EMBRYOLOGY ependymal and mantle layers migrate into the deep part of the marginal layer and form the cells of the cerelDral cortex. The nerve fibres which form the underlying white substance of the hemispheres consist at first of outgrowths from the cells of the corpora striata and thalami; later the fibres from the cells of the cortex are added. Medullation of these fibres begins about the time of birth and continues until puberty. A summary of the parts derived from the brain vesicles is given in the following table : Rhombencephalon or Hind-brain 1. Myelencephalon 2. Metencephalon Isthmus rhomb- encephali Mesencephalon or Mid-brain Prosencephalon or Fore-brain 1. Diencephalon 2. Telencephalon Medulla oblongata Lower part of fourth ventricle. Pons Cerebellum Intermediate part of fourth ventricle. Anterior medullary velum Brachia conjunctiva cerebelli. Upper part of fourth ventricle. Cerebral peduncles Lamina quadrigemina Cerebral aqueduct. Thalamus Metatbalamus Epithalamus Pars mamillaria hypo- thalami Posterior part of third ventricle. Anterior part of third ventricle Pars optica hypo- thalami Cerebral hemispheres Lateral ventricles Interventricular foramen. The Cerebral Nerves. — With the exception of the olfactory, optic, and acoustic nerves, which will be especially considered, the cerebral nerves are developed in a similar manner to the spinal nerves (see page 119). The sensory or afterent nerves are derived from the cells of the ganglion rudiments of the neural crest. The cen- tral processes of these cells grow into the brain and form the roots of the nerves, while the peripheral processes extend outward and constitute their fibres of dis- tribution (Fig. 120). It has been seen, in considering the development of the medulla oblongata (page 123), that the tractus solitarius (Fig. 135), derived from the fibres which grow inward from the ganglion rudiments of the glossopharyn- geal and vagus nerves, is the homologue of the oval bundle in the cord which had its origin in the posterior nerve roots. The motor or efferent nerves arise as out- growths of the neuroblasts situated in the basal laminae of the mid- and hind- brain. While, however, the spinal motor nerve roots arise in one series from the basal lamina, the cerebral motor nerves are grouped into two sets, according as they spring from the medial or lateral parts of the basal lamina. To the former set belong the oculomotor, trochlear, abducent, and hypoglossal nerves; to the developmIent of the nervous system and sense organs 133 latter, the accessory and the motor fibres of the tri^eiiiinal, facial, glossopharyn- geal, vagus nerves (Figs. 134, 135). The Sympathetic System. — The ganglion cells of the sympathetic system are derived from the cells of the neural crests. As these crests move forward along the sides of the neural tube and become segmented off to form the spinal ganglia, certain cells detach themselves from the ventral margins of the crests and migrate toward the sides of the aorta, where some of them are grouped to form the ganglia of the sympathetic trunks, while others undergo a further migration and form the ganglia of the prevertebral and visceral plexuses. The ciliary, sphenopalatine, otic, and submax- illary ganglia which are found on the branches of the trigeminal nerve are formed by groups of cells which have migrated from the part of the neural crest which gives rise to the semilunar ganglion. Some of the cells of the ciliary ganglion are said to migrate from the neural tube along the oculomotor ■Boof-plate 'ilar lamina Furrow between alar and basal lamincB Basal lamina Vagus nerve Hypoglossal nerve Floor-plate Fig. 134. — Transverse section of medulla oblongata of human embryo. X 32. (Kollmann.) nerve. Chromaffin Organs. — The tissue from which the sympathetic ganglia are formed is at first a syncytium of cells termed sympatho-chromaffin cells, but later two kinds of cells become differentiated from it; the smaller cells (sympathoblasts) are transformed into the sympathetic nerve cells, the larger become chromafiin cells, and, separating from the others, accumulate to form the chromaffin organs. Rhombic lip Vagus nerve Hypoglossal nerve Floor-plate Fig. 135. — Transverse section of medulla oblongata of human embryo. (After His.) In the gangliated trunk of the sympathetic the chromaffin bodies are situated in depressions in the ganglia. In connection with certain, but not all, of the secondary plexuses of the sympathetic system chromaffin organs are found; the largest mem- bers of this series are the aortic bodies, which lie along the sides of the abdominal aorta between the superior mesenteric and common iliac arteries; to this group 134 EMBRYOLOGY belong also the carotid skeins. After birth the chromaffin organs degenerate and can no longer be isolated by gross dissection, but chromaffin tissue can be recognized with the microscope in the sites originally occupied by them. The Suprarenal Glands. — Each suprarenal gland consists of a cortical portion derived from the coelomic epithelium and a medullary portion originally composed of sympatho-chromaffin tissue. The cortical portion is first recognizable about Cavity of fore-brain Invagination of ectoderm to form lens rudiment Pigmented layer of retina Margin of optic cup Nervous layer of retina Optic vesicle Fig. 136. — Transverse section of head of chick embryo of forty-eight hours' incubation. (Duval.) the beginning of the fourth week as a series of buds from the coelomic cells at the root of the mesentery. Later it becomes completely separated from the coelomic epithelium and forms a suprarenal ridge projecting into the coelom between the mesonephros and the root of the mesentery. Into this cortical portion cells from the neighboring masses of sympatho-chromaffin tissue migrate along the line of its central vein to reach and form the medullary portion of the gland. The Nose. — The development of Cavity of fore-brain ^he nose has already been con- sidered (pages 111, 112). The olfactory nerves are developed from the cells of the ectoderm which lines the olfactory pits; these cells undergo proliferation and give rise to what are termed the olfactory cells of the nose. The axons of the olfactory cells grow into the over- lying olfactory bulb and form the olfactory nerves. The Eye. — The eyes begin to develop as a pair of diverticula from the lateral aspects of the fore- brain. These diverticula make their appearance before the closure of the anterior end of the neural tube; after the closure of the tube they are knowai as the optic vesicles. They project toward the sides of the head, and the peripheral part of each expands to form a hollow bulb, while the proximal part remains narrow and constitutes the optic stalk (Figs. 136, 137). The ectoderm overlying the bulb becomes thickened, invaginated, and finally severed from the ectodermal covering of the head as a vesicle of cells, the lens vesicle, which con- stitutes the rudiment of the crystalline lens. The outer wall of the bulb becomes thickened and invaginated, and the bulb is thus converted into a cup, the optic cup, Pigmented layer of retina Ectoderin Lens Nervous layer of retina Optic stalk Fig. 137. — Transverse section of head of chick embrj'o of fifty-two hours' incubation. (Duval.) DEVELOPMENT OF THE XERVOUS SYSTEM AND SENSE ORGANS 135 consisting of two strata of cells (Fig. 137). These two strata are continuous with each other at the cup margin, which ultimately overlaps the front of the lens and reaches as far forward as the future aperture of the pupil. The invagination is not limited to the outer wall of the bulb, but invoh-es also its postero-inferior surface and extends in the form of a groove for some distance along the optic stalk, so that, for a time, a gap or fissure, the choroidal fissure, exists in the lower part of the cup (Fig. 138). Through the groove and fissure the mesoderm extends into the optic stalk and cup, and in this mesoderm a blood\'essel is developed; during the seventh week the groove and fissure are closed and the vessel forms the central artery of the retina. Sometimes the choroidal fissure persists, and wheii this occurs the choroid and iris in the region of the fissure remain undeveloped, giving rise to the condition known as colobonia of the choroid or iris. TJialameiicepkalon ■ — f Optic stalk Telenceplmlon ^ Ed^e of optic cup Choroidal fissure Arteria centralis retinae Fig. 138. — Optic cup and choroidal fissure seen from below, from a human embrj-o of about four weeks. (Kollmann.) The retina is developed from the optic cup. The outer stratum of the cup persists as a single layer of cells which assume a columnar shape, acquire pigment, and form the pigmented layer of the retina; the pigment first appears in the cells near the edge of the cup. The cells of the inner stratum proliferate and form a layer of considerable thickness from which the nervous elements and the susten- tacular fibres of the retina, together w^ith a portion of the vitreous body, are developed. In that portion of the cup which overlaps the lens the inner stratum is not differentiated into nervous elements, but forms a layer of columnar cells which is applied to the pigmented layer, and these two strata form the pars ciliaris and pars iridic a retinae. The cells of the inner or retinal layer of the optic cup become differentiated into spongioblasts and germinal cells, and the latter by their subdivisions give rise to neuroblasts. From the spongio- blasts the sustentacular fibres of Miiller, the outer and inner limiting membranes, together with the groundwork of the molecular layers of the retina are formed. The neuroblasts become arranged to form the gangUonic and nuclear layers. The layer of rods and cones is first developed in the central part of the optic cup, and from there gradually extends toward the cup margin. All the layers of the retina are completed by the eighth month of fetal life. The optic stalk is converted into the optic nerve by the obliteration of its cavity and the growth of nerve fibres into it. ]\Iost of these fibres are centripetal, and grow backward into the optic stalk from the nerve cells of the retina, but a few extend in the opposite direction and are derived from nerve cells in the brain. The fibres of the optic nerve receive their medullary sheaths about the tenth week after 136 EMBRYOLOGY birth. The optic chiasma is formed by the meeting and partial decussation of the fibres of the two optic nerves. Behind the chiasma the fibres grow backward as the optic tracts to the thalami and mesencephalon. The crystalline lens is developed from the lens \'esicle, which recedes within the margin of the cup, and becomes separated from the overlying ectoderm by mes- oderm. The cells forming the posterior wall of the vesicle lengthen and are con- verted into the lens fibres, which grow forward and fill up the cavity of the vesicle (Fig. 139). ^ The cells forming the anterior wall retain their cellular character, and form the epithelium on the anterior surface of the adult lens. By the second month the lens is invested by a vascular mesodermal capsule, the capsula vasciilosa lentis ; the bloodvessels supplying the posterior part of this capsule are derived from the hyaloid artery; those for the anterior part from the anterior ciliary arteries; the portion of the capsule which covers the front of the lens is named the pupillary Rudiment of choroid y Rectus muscle Optic nerve Retina Pigm,ented layer w Vitreous body (shrunken) • « Cornea Mernbrana pupillaris Pari ciham and pars iridica retinae Fig. 139. — Horizontal section through the ej-e of an eighteen days' embryo rabbit. X 30. (Kolliker.) membrane. By the sixth month all the vessels of the capsule are atrophied except the hyaloid artery, which disappears during the ninth month; the position of this artery is indicated in the adult by the hyaloid canal, which reaches from the optic disk to the posterior surface of the lens. With the loss of its bloodvessels the cap- sula vasculosa lentis disappears, but sometimes the pupillary membrane persists at birth, giving rise to the condition termed congenital atresia of the piipil. The vitreous body is developed between the lens and the optic cup. The lens rudiment and the optic vesicle are at first in contact with each other, but after the closure of the lens vesicle and the formation of the optic cup the former withdraws itself from the retinal layer of the cup; the two, however, remain connected by a net- work of delicate protoplasmic processes. This network, derived partly from the cells of the lens and partly from those of the retinal layer of the cup, constitutes the primitive vitreous body (Figs. 140, 141). At first these protoplasmic processes spring from the whole of the retinal layer of the cup, but later are limited to the DEVELOPMENT OF THE NERVOUS SYSTEM AND SENSE ORGANS 137 ciliary region, where by a process of condensation they appear to form the zonula ciliaris. The mesoderm which enters the cup through the choroidal fissure and around the equator of the lens becomes intimately united with this reticular tissue, and contributes to form the vitreous body, which is therefore derived partly from the ectoderm and partly from the mesoderm. Pig III c nk'd M esode riii ul layer of 'part of Rtuliment Upper eyelid retina vitreous body of sclera "= ~ ■a. b <.^- ^^^'^^3s^%^^^^t-'^t€\ 9?b%^c."'<^ CIS <25» e3> O O'^^^a ^ * fSS^'^tf £S> O Mesoderm Ectodermal NervoiLs layer part of of retina vitreous body Fig. 140. — Sagittal section of eye of human embryo of six weeks. (KoUmann.) The anterior chamber of the eye appears as a cleft in the mesoderm separating the lens from the overlying ectoderm. The layer of mesoderm in front of the cleft forms the substantia propria of the cornea, that behind the cleft the stroma of the iris and the pupillary membrane. The fibres of the ciliary muscle are derived from the mesoderm, but those of the Sphincter and Dilatator pupillae are of ectodermal origin, being developed from the cells of the pupillary part of the optic cup. The sclera and choroid are derived from the mesoderm surrounding the optic cup. The eyelids are formed as small cutaneous folds (Figs. 139, 140), which about the middle of the third month come together and unite in front of the cornea. They remain united until about the end of the sixth month. The lacrimal sac and nasolacrimal duct result from a thickening of the ectoderm in the groove, nasobptic furrows, between the lateral nasal and maxillary processes. This thickening forms a solid cord of cells which sinks into the mesoderm; during the third month the central cells of the cord break down, and a lumen, the naso- lacrimal duct, is established. The lacrimal ducts arise as buds from the upper part 138 EMBRYOLOGY of the cord of cells and secondarily establish openings (puncta lacrimalia) on the margins of the lids. The epithelium of the cornea and conjunctiva, and that which lines the ducts and alveoli of the lacrimal gland, are of ectodermal origin, as are also the eyelashes and the lining cells of the glands which ojjcn on the lid-margins. Lens Blood-vessel Primitive vitreous hody Retina Outer layer of optic cup' Fig 141. — Section of developing eye of trout. (Szily.) The Ear. — The first rudiment of the internal ear appears shortly after that of the eye, in the form of a patch of thickened ectoderm, the auditory plate, over the region of the hind-brain. The auditory plate becomes depressed and converted into the auditory pit (Fig. 142). The mouth of the pit is then closed, and thus a shut sac, the auditory vesicle, is formed (Fig. 143) ; from it the epithelial lining of the Cavity of hind-brain / Auditory pit Ectoderm Notochord Fig. 142. — Section through the head of a human embryo, about twelve days old, in the region of the hind brain. (Kollmann.) Hind-brain Auditory vesicle Fig. 143. — Section through hind brain and audi- tory vesiclesof an embryo more advanced than that of Fig. 142. (After His.) membranous labyrinth is derived. The vesicle becomes pear-shaped, and the neck of the flask is obliterated (Fig. 144). From the vesicle certain diverticula are given off which form the various parts of the membranous labyrinth. One from the middle part forms the ductus and saccus endolymphaticus, another from the anterior end gradually elongates, and, forming a tube coiled on itself, becomes the DEVELOPMliXT OF THE XERVOiS SYSTEM AXD SEXSE ORGAXS 139 cochlear duct, the vestibuhir extremity of which is siibseciueutly constricted to form the canalis reuniens. Three others appear as (Usk-Hke cNa^iiiatioiis on the surface of the vesicle; the central })arts of the walls of the disks coalesce and disappear, while the jieripheral portions persist to form the semicircular ducts; of these the Aiiditory vesicle Ductus endo- lymphaiictis Saccns endohjmphnticus Superior semi- circular duct Lateral semicircular duct Posterior semi- circular duct Rudiment of cochlear duct Fig. 144. — Left auditory vesicle of a human embryo of four weeks, seen from the outer surface. (W. His, Jr.) Fig. 145. — Left auditory vesicle of a human embryo of five weeks, seen from the outer surface. (W. His, Jr.) superior is the first and the lateral the last to be completed (Figs. 145, 146). The central part of the vesicle represents the membranous vestibule, and is subdivided by a constriction into a smaller ventral part, the saccule, and a larger dorsal and posterior part, the utricle. This subdivision is effected by a fold which extends Ductus endolymphaticus Ganglion cochleare Superior seini- circular duct Utricle Saccule Lateral semi- circular duct Ductus cochlearis Fig. 146. — Transverse section through head of fetal sheep, in the region of the labyrinth. X 30. (After Boettcher.) deeply into the proximal part of the ductus endolymphaticus, with the result that the utricle and saccule ultimately communicate with each other by means of a Y-shaped canal. The saccule opens into the cochlear duct, through the canalis reuniens, and the semicircular ducts communicate with the utricle (Fig. 147). 140 EMBRYOLOGY The mesodermal tissue surrounding the various parts of the epithelial labyrinth is converted into a cartilaginous ear-capsule, and this is finally ossified to form the bony labyrinth. Between the cartilaginous capsule and the epithelial structures is a stratum of mesodermal tissue which is differentiated into three layers, viz., Fig. 147. — Left membraaous labyrinth of a human embryo of 30 mm. (From model by W. His, Jr.) an^outer, forming the periosteal lining of the bony labyrinth; an inner, in direct contact with the epithelial structures; and an intermediate, consisting of gelatinous tissue : by the absorption of this latter tissue the perilymphatic spaces are developed. The modiolus and osseous spiral lamina of the cochlea are not preformed in cartil- age but are ossified directly from connective tissue. Embryonic cotmective tissue Cochlear duct Ligamentmn spirale Scala tytnpani Epithelium of the spiral organ of Corti Fig. 148. — Transverse section of the cochlear duct of a fetal cat. (After Boettcher and Ayres.) The middle ear and auditory tube are developed from the first pharyngeal pouch. The entodermal lining of the dorsal end of this pouch is in contact with the ecto- derm of the corresponding pharyngeal groove; by the extension of the mesoderm between these two layers the tympanic membrane is formed. During the sixth or DEVELOPMENT OF THE VASCULAR SYSTEM 141 seventh month the tympanic antrnm appears as an upward and backward expan- sion of the tympanic cavity. With regard to the exact mode of development of the ossicles of the middle ear there is some difference of opinion. The view generally held is that the incus and malleus are developed from the proximal end of the mandibular (Meckel's) cartilage (Fig. 105) and that the stapes is formed from the proximal end of the second arch. The malleus, with the exception of its anterior process, is ossified from a single centre which appears near the neck of the bone; the anterior process is ossified separately in membrane and joins the main part of the bone about the sixth month of fetal life. The incus is ossified from one centre which appears in the upper part of its long crus and ultimately extends into its lenticular process. The stapes first appears as a ring {annidus stapedius) encircling a small vessel, the stapedial artery, which subsequently undergoes atrophy; it is ossified from a single centre which appears in its base. The external acoustic meatus is developed from the first branchial groove. The lower part of this groove extends inward as a funnel-shaped tube (primary meatus) from which the cartilaginous portion and a small part of the roof of the osseous portion of the meatus are developed. From the lower part of the funnel-shaped tube an epithelial lamina extends downward and inward along the inferior wall of the primitive tympanic cavity; by the splitting of this lamina the inner part of the meatus (sec- ondary meatus) is produced, while the inner portion of the lamina forms the cutaneous stratum of the tympanic membrane. The auricula or pinna is developed by the gradual differentiation of six tubercles (Fig. 149) which appear around the margin of the first branchial groove. Two tubercles appear on the posterior edge of the mandibular arch; these represent the rudiments of the tragus and crus helicis. Three are found on the hj^oid arch, and indi- cate, from below upward, the lobule, antitragus, and antihelix. One arises above the groove, and grows downward behind the antitragus and antihelix; from it and its downward pro- longation the upper part of the helix and the Cauda helicis are developed (Figs. 150, 151). Some observers, however, maintain that the lowest tubercle on the hyoid arch becomes the antitragus, and that the lobule is developed later as an independent formation. The rudiment of the acoustic nerve appears about the end of the third week as a group of ganglion cells closely applied to the cephalic edge of the audi- tory vesicle. Whether these cells are derived from the ectoderm adjoining the auditory vesicle, or have migrated from the wall of the neural tube, is as yet un- certain. Each cell gives off a proximal fibre which passes into the neural tube, and a distal which is distributed to the epithelial cells of the auditory vesicle. Maiulibular arch Maxillary process Fig. 149. — Tubercles from which the different parts of the auricula are developed. (His.) 1, 2. Tubercles on mandibular arch. 3. Tuber- cle above cleft. 3, c. Prolongation of 3 down- ward. 4, 5, 6. Tubercles on hyoid arch. o.v. Auditory vesicle. DEVELOPMENT OF THE VASCULAR SYSTEM Bloodvessels first make their appearance in several scattered vascidar areas (Fig. 152) which are developed simultaneously between the entoderm and the meso- derm of the yolk-sac, i. e., outside the body of the embryo.^ Here the cells become 1 No definite statement can be made as to whether the earliest vessels are derived from the entoderm of the yolk- sac or from the mesoderm overlying it; the most recent view favors the entoderm as the original source of the blood corpuscles and endothelium of the vessels. 142 EMBRYOLOGY arranged into solid strands or cords which join to form a close-meshed network, the area vasculosa, which covers the whole yolk-sac. The peripheral cells of these Helix Cms helicis Aniihehz Cms helicis Tragus Anhtragus Mandible Lobule Tragus »Ueh Antihelix Antitragus Mandible -^^^^^^^ Fig. 150. — Left auriculse of human embryos estimated at thirty-five and thirty-eight days respectively. (After His.) strands become flattened and joined to each other by their edges to form the endo- thelium of the walls of the primitive bloodvessels. Fluid collects within the strands and converts them into tubes, and the more centrally situated cells of the cell-cords are thus pushed to the sides of the vessels and appear as masses of loosely arranged cells projecting toward the lumen of the tube. These masses are termed blood islands (Fig. 153); their cells are detached to form the blood corpuscles. The earliest blood- vessels, therefore, are formed at several separate centres; from the walls of these vessels buds grow out, become vascularized and converted into new vessels, and join with those of neighboring areas to form a close meshwork. It is uncertain whether the vessels within the body of the embryo are ex- tensions from this network (His) or whether they are of new formation. Most observers agree, however, that, after the aortse have appeared, no other independent vessels are laid down, i. e., all new vessels are derived from preexisting ones. Antihelix — Crus helicis — Antitragus Lobule Tragus . 2Iandible Fig 151 — \uricula m a more advanced stage of development than those repre- sented in Fig. 150. Mesoderm Blood island Mesoderm Vascular cells Entoderm Endothelial wall of vessel Entoderm Fig. 152. — Section through vascular area to show differ- entiation of primitive vascular cells. Diagrammatic. Fig. 153. — Section through developing bloodvessel. Diagrammatic. The red and the colorless corpuscles of the blood are all derived from the nucleated cells of the blood islands — mesamoeboid cells of Minot — and the earliest blood corpuscles are thus all nucleated; they are also capable of subdivision and of bEVELOPMEXr OF THE VASCULAR SYSTEM 143 FiQ. 154. — Transverse section through the region of the heart in a rabbit embryo of nine days. X 80. (Kolliker.) j, j. Jugular veins, ao. Aorta, ph. Pharynx, soni. Somatopleure. hi. Proamnion. ect. Ectoderm, enl. Entoderm, p. Pericardium, spl. .Splanchno- pleure. ah. Outer wall of heart, ih. Endothelial lining of heart, e'. Septum between heart tubes. executino- amcrboid movoinents. Some of these cells acquire coloring matter {heiiKHjJobin); their nuclei ilisintegrate and are expelled and the non-nucleated red corpuscles result. Other mesam- oeboid cells retain their nuclei; 7, some remain in the blood as the leucocytes; others wander out into the tissues, particularly into the liver, lymphoid tissues, and marrow of the bones, where they form specialized masses from which the corpuscles of the blood are regenerated. From the mesamoeboid cells five chief forms are derived: (1) erythro- cytes, (2) lymphocytes, (3) finely granular or neutrophil leuco- cytes, (4) coarsely granular or eosinophil leucocytes, (5) degen- erating or basiphil leucocytes. The first rudiment of the heart appears as a pair of tubular vessels which are developed in the splanchnopleure of the peri- cardial area (Fig. 154). These are named the primitive aortse, and a direct continuity' is soon established between them and the vessels of the yolk-sac. Each receives anteriorly a vein — the vitelline vein — from the yolk-sac, and is prolonged backw^ard on the lateral aspect of the noto- chord under the name of the dorsal aorta. The dorsal aortse give brandies to the yolk-sac, and are continued backward through the body-stalk as the umbilical arteries to the villi of the chorion. Eternod^ describes the circu- lation in an embryo which he estimated to be about thirteen days old (Fig. 155). The rudi- ment of the heart is situated immediately below the fore-gut and consists of a short stem. It gives oft' two vessels, the primi- tive aortse, which run backward, one on either side of the noto- chord, and then pass into the body-stalk along which they are carried to the chorion. From the chorionic villi the blood is returned by a pair of umbilical veins wliich unite in the body-stalk Umbilical . Umbilical Allantoic diverticulum Body-stalh Fig. 15.5. — Diagram of the vascular channels in a human embryo of the second week. (After Eternod.) The red lines are the dorsal aortas continued into the umbiUcal arteries. The red dotted lines are the ventral aortse, and the blue dotted Lines the vitelline veins. Anat. Anzeiger, 1899, vol. xv. 144 EMBRYOLOGY to form a single vessel and subsequently encircle the mouth of the yolk-sac and open into the heart. At the junction of the ;]>'olk-sac and body-stalk each vein is joined by a branch from the vascular plexus of the yolk-sac. From his observations it seems that, in the human embryo, the chorionic circulation is established before that on the yolk-sac. Dorsal aorta Primitive jugular vein Amnion Cardinal vein Dorsal aorta Body-stalk Chorionic villi Fig. 156. — Human embryo of about fourteen days old with yolk-sac. (After His.) By the forward growth and flexure of the head the pericardial area and the anterior portions of the primitive aortse are folded backward on the ventral aspect of the fore-gut, and the original relation of the somatopleure and splanchnopleure Fore-brain Bulbus cordis Atrium — Optic vesicle Ventricle — Vitelline vei% Fig. 157. — Head of chick embryo of about thirtj -eight hours' uicubj,tiuu, viewed from the ventral surface. X 26. (Duval.) layers of the pericardial area is reversed. Each primitive aorta now consists of a ventral and a dorsal part connected anteriorly by an arch (Fig. 156) ; these three parts are named respectively the anterior ventral aorta, the dorsal aorta, and the first cephalic arch. The vitelline veins which enter the embrj^o through the DEVELOPMENT OF THE VASCULAR SYSTEM 145 anterior wall of the umbilical orifice are now continuous with the posterior ends of the anterior ventral aorta. With the formation of the tail-fold the posterior i)arts of the primitive aortje are carried forward in a ventral direction to form the pos- terior ventral aortie and primary caudal arches.^ In the pericardial region the two primitive aortse grow together, and fuse to form a single tubular heart (Fig. 157), the i)osterior end of which receives the two vitelline veins, while from its anterior end the two anterior \'entral aortae emerge.- The first cephalic arches pass through the mandibular arches, and behind them five additional pairs subsequently develop, so that altogether six pairs of aortic arches are formed; the fifth arches are very transitory vessels connecting the ventral aortae wdth the dorsal ends of the sixth arches. By the rhythmical contraction of the tubular heart the blood is forced through the aortae and bloodvessels of the vascular area, from which it is returned to the heart by the vitelline veins. This constitutes the vitelline circulation (Fig. 156), and by means of it nutriment is absorbed from the yolk vitellus. The vitelline veins at first open separately into the posterior end of the tubular heart, but after a time their terminal portions fuse to form a single vessel. The vitelline \eins ultimately drain the blood from the digestive tube, and are modified to form the portal vein. This is caused by the growth of the liver, which interrupts their direct continuity with the heart; and the blood returned by them circulates through the liver before reaching the heart. With the atrophy of the yolk-sac the vitelline circulation diminishes and ulti- mately ceases, while an increasing amount of blood is carried through the umbilical arteries to the villi of the chorion. Subsequently, as the non-placental chorionic villi atrophy, their vessels disappear; and then the umbilical arteries convey the whole of their contents to the placenta, whence it is returned to the heart by the umbilical veins. In this manner the placental circulation is established, and by means of it nutritive materials are absorbed from, and waste products given up to, the maternal blood. The umbilical veins, like the vitelline, undergo interruption in the developing liver, and the blood returned by them passes through this organ before reaching the heart. Ultimately the right umbilical vein shrivels up and disappears, as will be explained later (page 156). During the occurrence of these changes great alterations take place in the primitive heart and bloodvessels. Further Development of the Heart. — Between the endothelial lining and the outer wall of the heart there exists for a time an intricate trabecular network of mesodermal tissue from which, at a later stage, the musculi papillares, chordae tendineae, and trabeculae carneae are developed. The simple tubular heart, already described, becomes elongated and bent on itself so as to form an S-shaped loop, the anterior part bending to the right and the posterior part to the left (Fig. 157). The intermediate portion arches transversely from left to right, and then turns sharply forward into the anterior part of the loop. Slight constrictions make their appearance in the tube and divide it from behind forward into five parts, viz.: (1) the sinus venosus; (2) the primitive atrium; (3) the primitive ventricle; (4) the bulbus cordis, and (5) the truncus arteriosus (Figs. 158, 159). The constriction between the atrium and ventricle constitutes the atrial canal, and indicates the site of the future atrioventricular valves. The sinus venosus is at first situated in the septum transversum (a layer of mesoderm in w^hich the liver and the central tendon of the Diaphragma are devel- oped) behind the primitive atrium, and is formed by the union of the vitelline veins. The veins or ducts of Cuvier from the body of the embryo and the umbilical veins from the placenta subsequently open into it (Fig. 160). The sinus is at first * Young and Robinson, Journal of Anatomy and Physiology, vol. xxxii. ' In most fishes and in the amphibia the heart originates as a single median tube. 10 U6 EMBRYOLOGY place transversely, and opens by a median aperture into the primitive atrium. Soon, however, it assumes an obhque position, and becomes crescentic in form; its right half or horn increases more rapidly than the left, and the opening into the atrium now communicates with the right portion of the atrial ca^'ity. The right horn and transverse portion of the sinus ultimately become incorporated with and form a part of the adult right atrium, the line of union between it and the auricula Bulbils cordis Ventricle Airimti Si7ius venosus Vitelline vein Fig. 158. — Diagram to illustrate the simple tubular condition of the heart. (Drawn from Ecker-Ziegler model.) Fig. 159. — Heart of human embryo of about fourteen days. (From model by His.) being indicated in the interior of the atrium hj a vertical crest, the crista terminalis of His. The left horn, which ultimately receives only the left duct of Cuvier, persists as the coronary sinus (Fig. 161). The vitelline and umbilical veins are soon replaced by a single vessel, the inferior vena cava, and the three veins (inferior vena cava and right and left Cuvierian ducts) open into the dorsal aspect of the atrium by a common slit-like aperture (Fig. 162). The upper part of this aperture repre- sents the opening of the permanent superior vena cava, the lower that of the inferior Maxillary process Stomodeum Mandibular arch Bulbus cordis — Ventricle Duct of Cuvier Cardinal vein Atrium Bile-duct Umbilical vein Fig. 160. — Heart of human embryo of about fifteen days. (Reconstruction by His.) vena cava, and the intermediate part the orifice of the coronary sinus. The slit- like aperture lies obliquely, and is guarded by two halves, the right and left venous valves; above the opening these unite with each other and are continuous with a fold named the septum spurium; below the opening they fuse to form a triangular thickening — the spina vestibuli. The right venous valve is retained; a small septum, the sinus septum, grows from the posterior wall of the sinus venosus to fuse d'evelopment of the vascl lar system 147 with the valve and divide it into two i)arts — an iii)j)er, the valve of the inferior vena cava, and a lower, the \alve of the coronary sinus (Fig. 105). The extreme Left duel of Curii r Openincj lata lliijJtl dad of iitridni, Cuvicr Fig. 161. — Dorsal surface of heart of human embryo of thirty-five days. (From model by His.) tSeptum spuriwm I Opening cf sinics vcnosus Left venous valve Septum primutn Right venous valve Spina vestibul Posterior endocard cushio Atrial canal Septum inferius Fig. 162. — Interior of dorsal half of heart from a human embryo of about thirty da>-s. (From model by His.) upper portion of the right venous valve, together with the septum spurium, form the crista terminalis already mentioned. The upper and middle thirds of the left 148 EMBRYOLOGY venous valve disappear; the lower third is continued into the spina vestibuli, and later fuses with the septum secundum of the atria and takes part in the forma- tion of the limbus fossae ovalis. Eight atrimn Bulhus cordis — Left atrium - Atrial canal Ventricle Fig. 163. — Heart showing expansion of the atria. (Drawn from Ecker-Zeigler model.) The atrial canal is at first a short straight tube connecting the atrial with the ventricular portion of the heart, but its growth is relatively slow, and it becomes overlapped by the atria and ventricles so that its position on the surface of the heart is indicated only by an annular constriction (Fig. 163). Its lumen is reduced to a transverse slit, and tw^o thickenings appear, one on its dorsal and another on its Septum secundum Opening of coronary sinus j Spina vestibuli fused with Septum ■spurium j j septum, primum Bight venous Right atrioventricidnr opening atrioventricular opening Septum intermedium Srptmii i)iffrius Fig. 164. — Interior of dorsal half of heart of human embryo of about thirty-five days. (From model by His.) ventral wall. These thickenings, or endocardial cushions (Fig. 162) as they are termed, project into the canal, and, meeting in the middle line, unite to form the septum intermedium which divides the canal into two channels, the future right and left atrioventricular orifices. DEVELOPMENT OF THE VASCULAR SYSTEM 149 The primitive atrium grows rapidly and partially encircles the bulbus cordis; the groove against whicii the bulbus cordis lies is the first indication of a division into right and left atria. The cavity of the primitive atrium becomes subdivided into right and loft chambers by a septum, the septiim primum (Fig. 1G2), which grows downward into the cavity. For a time the atria communicates with each other by an opening, the ostium primum of Born, below the free margin of the septum. This opening is closed by the union of the septum primum with the septum inter- medium, and the communication between the atria is reestal)lished through an opening which is dcvcl()i)cd in the upper part of the septum primum; this opening is known as the foramen ovale {ostiiini secundum of Born) and persists until birth. A second septum, the septum secundum (Figs. 164, 165), semilunar in shape, grows downward from the upper wall of the atrium immediately to the right of the primary septum and foramen ovale. Shortly after birth it fuses with the primary septum, and by this means the foramen ovale is closed, but sometimes the fusion is incomplete and the upper part of the foramen remains patent. The limbus fossae Left duel of Cuviej Opening of coronanj sinus roramen ovale Probe in aorta Aortic septum ^Scptivm intermedium Septum inferius Fig. 165. — Same heart as in Fig. 164, opened on right side. (From model by His.) ovalis denotes the free margin of the septum secundum. Issuing from each lung is a pair of pulmonary veins; each pair unites to form a single vessel, and these in turn join in a common trunk which opens into the left atrium. Subsequently the common trunk and the two vessels forming it expand and form the vestibule or greater part of the atrium, the expansion reaching as far as the openings of the four vessels, so that in the adult all four veins open separately into the left atrium. The primitive ventricle becomes divided by a septum, the septum inferius or ventricular septum (Figs. 162, 164, 165), which grows upward from the lower part of the ventricle, its position being indicated on the surface of the heart by a furrow. Its dorsal part increases more rapidly than its ventral portion, and fuses with the dorsal part of the septum intermedium. For a time an interventricular foramen exists above its ventral portion (Fig. 165), but this foramen is ultimately closed by the fusion of the aortic septum with the ventricular septum. When the heart assumes its S-shaped form the bulbus cordis lies ventral to and in front of the primitive ventricle. The adjacent walls of the bulbus cordis and ventricle approximate, fuse, and finally disappear, and the bulbus cordis now 150 EMBRYOLOGY communicates freely with the riglit \entricle, while the junction of the hulbus with the truncus arteriosus is brought directly ventral to and applied to the atrial canal. Fig. 166. — Diagrams to illustrate the transformation of the bulbus cordis. (Keith.) Ao. Truncus arteriosus. Au. Atrium. B. Bulbus cordis. RV. Right ventricle. LV. Left ventricle. P. Pulmonary artery. By the upgrowth of the ventricular septum the bulbus cordis is in great measure separated from the left ventricle, but remains an integral part of the right ventricle, of which it forms the infundibulum (Fig. 166). Aortic septum Common atrio- ventr icular aperture Right ^ ventricle Septum Left inferius ventricle Aortic septum Pulmonary artery Aorta Eight atrio- ventricular orifice Bight ventricle Left atrio- ventricular orifice Left ventricle Septum inferius Fig. 167. — Diagrams to show the development of the septum of the aortic bulb and of the ventricles. (Born.) The truncus arteriosus and bulbus cordis are divided by the aortic septum (Fig. 167). This makes its appearance in three portions. (1) Two distal ridge-like Aorta Aorta Aorta Pulmonary artery Pulmo- nary artery Pulmonary artery Fig. 168. — Transverse sections through the aortic bulb to show the growth of the aortic septum. The lowest section is on the left, the highest on the right of the figure. (After His.) thickenings project into the lumen of the tube; these increase in size, and ultimately meet and fuse to form a septum, which takes a spiral course toward the proximal DEVELOPMENT OF THE VASCULAR SYSTEM 151 end of the truncus arteriosus. It divides the distal part of the truncus into two vessels, the aorta and i)uhn()nary artery, which lie side by side above, but near the heart the puhnouary artery is in front of the aorta. (2) Four endocardial cnsliions appear in the proximal i)art of the truncus arteriosus in the region of the future semilunar valves; the manner in which these are related to the aortic septum is described below. (3) Two endocardial thickenings — anterior and posterior — develop in the bulbns cordis and unite to form a short septum; this joins above with the aortic septum and below with the ventricular septum. The septum grows down into the ventricle as an oblique partition, which ultimately blends with the ven- tricular septum in such a way as to bring the bulbus cordis into communication with the pulmonary artery, and through the latter with the sixth pair of aortic arches; while the left ventricle is brought into continuity with the aorta, which communicates with the remaining aortic arches. Second aortic arch Third aortic arch First aortic arch Atulitory vesicle Primitive jugular vein Fourth aortic arch Sixth aortic arch Dorsal aorta Cardinal vein Digestive tiibe Himl-gut Vnibilical vein Olfactory pit Maxillary process First branchial groove Mandibular arch Bulbus cordis A trinm Duct of Cuvier Ventricle Vitelline vein Yolk-sac Allantois Unibilical artery Fig. 169. — Profile view of a human embryo estimated at twenty or twenty-one days old. (After His.) The Valves of the Heart. — The atrioventricular valves are developed in relation to the atrial canal. By the upward expansion of the bases of the ventricles the canal becomes invaginated into the ventricular cavities. The invaginated margin forms the rudiments of the lateral cusps of the atrioventricular valves; the mesial or septal cusps of the valves are developed as downward prolongations of the septum intermedium (Fig. 164). The aortic and pulmonary semilunar valves are formed from four endocardial thickenings — an anterior, a posterior, and two lateral — 152 EMBRYOLOGY which appear at the proximal end of the truncus arteriosus. As the aortic septum grows downward it divides each of the lateral thickenings into two, thus giving rise to six thickenings — the rudiments of the semilunar valves — three at the aortic and three at the pulmonary orifice (Fig. 1G8). Further Development of the Arteries.— Recent observations show that practi- cally none of the main vessels of the adult arise as such in the embryo. In the site of each vessel a capillary network forms, and by the enlargement of definite paths in this the larger arteries and veins are developed. The branches of the main arteries are not always simple modifications of the vessels of the capillary network, but may arise as new outgrowths from the enlarged stem. EocUrnal carotid Ventral aorta — j Internal carotid Common carotid Aortic arch Right subclavian artery Might pulmonary artery Ductus arteriosus Vertebral artery Subclavian artery Trunk of pulmonary artery Left pulmonary artery Fig. 170. — Scheme of the aortic arches and their destination. (Modified from KoUmann.) It has been seen (page 145) that each primitive aorta consists of a ventral and a dorsal part which are continuous through the first aortic arch . The dorsal aortse at first run backward separately on either side of the notochord, but about the third week they fuse from about the level of the fourth thoracic to that of the fourth lumbar segment to form a single trunk, the descending aorta. The first aortic arches run through the mandibular arches, and behind them five additional pairs are developed within the visceral arches; so that, in all, six pairs of aortic arches are formed (Figs. 169, 170). The first and second arches pass between the ventral and dorsal aortse, while the others arise at first by a common trunk from the truncus arteriosus, but end separately in the dorsal aortse. As the neck elongates, the ventral aortse are drawn out, and the third and fourth arches arise directly from these vessels. In fishes these arches persist and give off branches to the gills, in which the blood is oxygenated. In mammals some of them remain as permanent structures, while others disappear or become obliterated (Fig. 170). The Anterior Ventral Aortse. — These persist on both sides. The right forms (a) the innominate artery, (6) the right common and external carotid arteries. The left gives rise to (a) the short portion of the aortic arch, which reaches from the DEVELOPMENT OF THE VASCULAR SYSTEM 153 origin of the innominate artery to that of the left common carotid artery; (h) the left common and external carotid arteries. The Aortic Arches. — The first and second arches disappear early, but the dorsal end of the second gives origin to the stapedial artery (Fig. 171), a vessel which atrophies in man but persists in some mammals. It passes through the ring of the stapes and divides into supraorbital, infraorbital, and mandibular branches which follow the three divisions of the trigeminal nerve. The infraorbital and man- dibular arise from a common stem, the terminal part of which anastomoses with Post, cerebral a. Ant. cerebral a. Supraorbital br. of stapedial a. Trigeminal nerve Maxillary nerve Infraorbital a. Stapedial a. Mandibular ? Mandibidar a. Ext. max. a. Lingual a. Sup. thyroid a. Common carotid a. Int. carotid a. Aortic ar Pulmonary arch Pulmonary art. Dorsal aorta Fig. 171. — Diagram showing the origins of the main branches of the carotid arteries. (Founded on Tandler.) the external carotid. On the obliteration of the stapedial artery this anastomosis enlarges and forms the internal maxillary artery, and the branches of the stapedial artery are now branches of this vessel. The common stem of the infraorbital and mandibular branches passes between the two roots of the auriculotemporal nerve and becomes the middle meningeal artery; the original supraorbital branch of the stapedial is represented by the orbital twigs of the middle meningeal. The third aortic arch constitutes the commencement of the internal carotid artery, and is therefore named the carotid arch. The fourth right arch forms the right sub- clavian as far as the origin of its internal mammary branch; while the fourth left arch constitutes the arch of the aorta between the origin of the left carotid artery and the termination of the ductus arteriosus. The fifth arch disappears on both sides. The sixth right arch disappears; the sixth left arch gives off the pulmonary 154 EMBRYOLOGY arteries and forms the ductus arteriosus; this duct remains pervious during the whole of fetal life, but is obliterated a few days after birth. His showed that in the early embryo the right and left arches each gives a branch to the lungs, but that later both pulmonary arteries take origin from the left arch. The Dorsal Aortse. — In front of the third aortic arches the dorsal aortae persist and form the continuations of the internal carotid arteries; these arteries pass to the brain and each divides into an anterior and a posterior branch, the former giving off the ophthalmic and the anterior and middle cerebral arteries, while the latter turns back and joins the cerebral part of the vertebral artery. Behind the third arch the right dorsal aorta disappears as far as the point where the two dorsal aortse fuse to form the descending aorta. The part of the left dorsal aorta between the third and fourth arches disappears, while the remainder persists to form the descending part of the arch of the aorta. A constriction, the aortic isthmus, is sometimes seen in the aorta between the origin of the left subclavian and the attachment of the ductus arteriosus. Sometimes the right subclavian artery arises from the aortic arch distal to the origin of the left subclavian and passes upward and to the right behind the trachea and oesophagus. This condition may be explained by the persistence of the right dorsal aorta and the obliteration of the fourth right arch. In birds the fourth right arch forms the arch of the aorta; in reptiles the fourth arch on both sides persists and gives rise to the double aortic arch in these animals. The heart originally lies on the ventral aspect of the pharynx, immediately ■behind the stomodeum. With the elongations of the neck and the development of the lungs it recedes within the thorax, and, as a consequence, the anterior ventral aortse are drawn out and the original position of the fourth and fifth arches is greatly modified. Thus, on the right side the fourth recedes to the root of the neck, while on the left side it is withdrawn within the thorax. The recurrent nerves originally pass to the larynx under the sixth pair of arches, and are there- fore pulled backward with the descent of these structures, so that in the adult the left nerve hooks around the ligamentum arteriosum; owing to the disappearance of the fifth and the sixth right arches the right nerve hooks around that immediately above them, /. e., the commencement of the subclavian artery. Segmental arteries arise from the primitive dorsal aortee and course between successive segments. The seventh segmental artery is of special interest, since it forms the lower end of the vertebral artery and, when the forelimb bud appears, sends a branch to it (the subclavian artery). From the seventh segmental arteries the entire left subclavian and the greater part of the right subclavian are formed. The second pair of segmental arteries accompany the hypoglossal nerves to the brain and are named the hypoglossal arteries. Each sends forward a branch which forms the cerebral part of the vertebral artery and anastomoses with the posterior branch of the internal carotid. The two vertebrals unite on the ventral surface of the hind-brain to form the basilar artery. Later the hypoglossal artery atrophies and the vertebral is connected with the first segmental artery. The cervical part of the vertebral is developed from a longitudinal anastomosis between the first seven segmental arteries, so that the seventh of these ultimately becomes the source of the artery. As a residt of the growth of the upper limb the subclavian artery increases greatly in size and the vertebral then appears to spring from it. Recent observations show that several segmental arteries contribute branches to the upper limb-bud and form in it a free capillary anastomosis. Of these branches, only one, viz., that derived from the seventh segmental artery, persists to form the subclavian artery. The subclavian artery is prolonged into the limb under the names of the axillary and brachial arteries, and these together constitute the arterial stem for the upper arm, the direct continuation of this stem in the forearm is the volar interosseous artery. A branch which accompanies the median nerve DEVELOPMENT OF THE VASCULAR SYSTEM 155 soon increases in size and forms the main vessel (median artery) of the forearm, while the volar interosseous diminishes. Later the radial and ulnar arteries are developed as branches of the brachial part of the stem and coincidently with their enlargement the median artery recedes; occasionally it persists as a vessel of some considerable size and then accompanies the median nerve into the palm of the hand. The primary arterial stem for the lower limb is formed by the inferior gluteal (sciatic) artery, which accompanies the sciatic nerve along the posterior aspect of the thigh to the back of the knee, whence it is continued as the peroneal arter}'. This arrangement exists in reptiles and amphibians. The femoral artery arises later as a branch of the common iliac, and, passing down the front and medial side of the thigh to the bend of the knee, joins the inferior gluteal artery. The femoral quickly enlarges, and, coincidently with this, the part of the inferior gluteal immediately above the knee undergoes atrophy. The anterior and posterior tibial arteries are branches of the main arterial stem. Anterior detached portions of utnbilical veins Venae revehentes Stomach Venae advehentes Pancreas Bile-duct Obliterated portions of venovjS rings Right umbilical vein Ductus venosus Liver Left umbilical vein Duodenum Portal vein Vitelline Fig. 172. — The liver and the veins in connection with it, of a human embrj'^o, twenty-four or twenty-five days old; as seen from the ventral surface. (After His.) Further Development of the Veins. — The formation of the great veins of the embryo may be best considered by dividing them into two groups, visceral and parietal. The Visceral Veins. — The visceral veins are the two vitelline or omphalomesenteric veins bringing the blood from the yolk-sac, and the two umbilical veins returning the blood from the placenta; these four veins open close together into the sinus venosus. The Vitelline Veins run upward at first in front, and subsequently on either side of the intestinal canal. They unite on the ventral aspect of the canal, and beyond this are connected to one another by two anastomotic branches, one on the dorsal, and the other on the ventral aspect of the duodenal portion of the intestine, which is thus encircled by two venous rings (Fig. 172) ; into the middle or dorsal anastomosis the superior mesenteric vein opens. The portions of the veins above the upper ring become interrupted by the developing liver and broken up by it into a plexus of small capillary-like vessels termed sinusoids (Minot). The branches conveying the blood to this plexus are named the venae advehentes, and become 156 EMBRYOLOGY the branches of the portal vein; while the vessels draining the plexus into the sinus venosus are termed the venae revehentes, and form the future hepatic veins (Figs. 172, 173). Ultimately the left vena revehens no longer communicates directly with the sinus venosus, but opens into the right vena revehens. The persistent part of the upper venous ring, above the opening of the superior mes- enteric vein, forms the trunk of the portal vein. Eight primitive jugular vein Eight cardinal^ lein ^, Eight duct of Cuviei Sinus venosus Eight hepatic vein Portal vein Portal vein Eight umbilical vein Umbilical cord- Left primitive jugular vein Left cardinal vein Left duct of Cuvier Left hepatic vein Left umbilical vein Left umbilical vein Fio. 173. — Human embryo with heart and anterior body-wall removed to show the sinus venosus and its tributaries. (After His.) The two Umbilical Veins fuse early to form a single trunk in the body-stalk, but remain separate within the embryo and pass forward to the sinus venosus in the side walls of the body. Like the vitelline veins, their direct connection with the sinus venosus becomes interrupted by the developing liver, and thus at this stage the whole of the blood from the yolk-sac and placenta passes through the substance of the liver before it reaches the heart. The right umbilical and right vitelline veins shrivel and disappear; the left umbilical, on the other hand, becomes enlarged and opens into the upper venous ring of the vitelline veins; with the atrophy of the yolk-sac the left vitelline vein also undergoes atrophy and disappears. Finally a direct branch is established between this ring and the right hepatic vein; this branch is named the ductus venosus, and, enlarging rapidly, it forms a wdde channel through which most of the blood, returned from the placenta, is carried direct to the heart without passing through the liver. A small proportion of the blood from the placenta is, how^ever, conveyed from the left umbilical vein to the liver through the left vena advehens. The left umbilical vein and the ductus venosus undergo atrophy and obliteration after birth, and form respectively the ligamentum teres and ligamentum venosum of the liver. DEVELOPMENT OF THE VASCULAR SYSTEM 157 The Parietal Veins. — The first indication of a parietal system consists in the appearance of two short transverse veins, the ducts of Cuvier, which open, one on either side, into the sinus venosus. Each of these ducts receives an ascending and descending vein. The ascending veins return the blood from the parietes of the trunk and from the Wolffian bodies, and are called cardinal veins. The descending veins return the blood from the head, and are called primitive jugular veins (Hg. 174). The blood from the lower limbs is collected by the right and left iliac and hypogastric ^'eins, which, in the earlier stages of development, open into the corresponding right and left cardinal veins ; later, a transverse branch (the left common iliac vein) is developed between the lower parts of the two cardinal veins (Fig. 176), and through this the blood is carried into the right cardinal vein. The portion of the left cardinal vein below the left renal vein atrophies and dis- appears up to the point of entrance of the left spermatic vein; the portion above the left renal vein persists as the hemiazygos and accessory hemiazygos veins and the lower portion of the highest left intercostal vein. The right cardinal vein Sinus venosus Primitive jugtilar Subclavian Duct of Cuvier Vitelline Umbilical Cardinal Svbcardinal Eenal External iliac Hypogastric Fig. 174. — Scheme of arrangement of parietal veins. Internal jugular External jugular Subclavian Duct of Cuvier Left cardinal Ductus venosus ■Renal — Subcardinal External iliac /\ / Hypogastric Fig. 175. — Scheme showing early stages of development of the inferior vena cava. which now receives the blood from both lower extremities, forms a large venous trunk along the posterior abdominal wall; up to the level of the renal veins it forms the lower part of the inferior vena cava. Above the level of the renal veins the right cardinal vein persists as the azygos vein and receives the right intercostal veins, while the hemiazygos veins are brought into communication with it by the development of transverse branches in front of the vertebral column (Figs. 176, 177) Inferior Vena Cava. — The development of the inferior vena cava is associated with the formation of two veins, the subcardinal veins (Figs. 174, 175). These lie parallel to, and on the ventral aspect of, the cardinal veins, and originate as longitudinal anastomosing channels which link up the tributaries from the mes- entery to the cardinal veins ; they communicate with the cardinal veins above and below, and also b}' a series of transverse branches. The two subcardinals are for a time connected with each other in front of the aorta by cross branches, but these disappear and are replaced by a single transverse channel at the level where the renal veins join the cardinals, and at the same level a cross communication is 158 EMBRYOLOGY established on either side between the cardinal and subcardinal (Fig. 175). The portion of the right subcardinal behind this cross communication disappears, while that in front, i. e., the prerenal part, forms a connection with the ductus venosus Left inriomlnale Might innominate Superior vena cava Prerenal part of inferior vena cava Postrenal part of inferior vena cava •Internal jugular ■External jugular Duct of Cuvier Left carelinal Left suprarenal Left rejial Left common iliac External iliac Hypogastric Fig. 176. — Diagram showing development of main cross branches between jugulars and between cardinals. at the point of opening of the hepatic veins, and, rapidity enlarging, receives the blood from the postrenal part of the right cardinal through the cross communica- te/^ innominate Right iymominate Superior vena cava Azygos vein Prerenal pari of inferior vena cava Internal jugular External jugular Subclavian — Highest left intercostal Ligament of left vena cava ^- j^ Oblique vein of left atrium ^~ — C Coronary sinus Accessory hemiazygos vein Hemiazygos vein Left suprarenal Left renal Left internal spermatic Fig. 177. — Left common iliac External iliac Hypogastric -Diagram showing completion of development of the parietal veins. tion referred to. In this manner a single trunk, the inferior vena cava (Fig. 177), is formed, and consists of the proximal part of the ductus venosus, the prerenal part of the right subcardinal vein, the postrenal part of the right cardinal vein, and the bEVELOPMEXT OF THE VASCCLAR SYSTEM 159 cross branch which joins these two veins. The left suhcardinal (lisai)pears, except the part immeiHatcly in front of the renal vein, which is retained as the left supra- renal vein. The spermatic (or ovarian) vein opens into the postrenal part of the corresponding cardinal vein. This portion of the right cardinal, as already explained, forms the h)wer part of the inferior vena cava, so tliat the right sjiermatic opens directly into that vessel. The postrenal segment of the left cardinal dis- appears, with the exception of the portion between the spermatic and renal vein, which is retained as the terminal part of the left spermatic vein. In consequence of the atro- ^-1 uditory vesicle Primitive jugular vein Vena capitis medialis Trigeminal nerve Ophthalmic vein Vena capitis _g^ lateralis Superior sagittal sinus Fig. its. — Diagram of veins of head of an embrjo four weeks old. (After Mall.) phy of the Wolffian bodies the cardinal veins diminish in size; the primitive jugular veins, on the other hand, become enlarged, owing to the rapid development of the head and brain. They are further aug- mented by recei^'ing the veins (subclavian) from the upper ex- tremities, and so come to form the chief veins of the Cuvierian ducts; these ducts gradually assume an almost vertical position in consequence of the descent of the heart into the thorax. The right and left Cuvierian ducts are originally of the same diameter, and are frequently termed the right and left superior venge cavae. By the development of a transverse branch, the left innominate vein between the two primitive jugular veins, the blood is carried across from the left to the right primitive jugular (Figs. 176, 177). The portion of the right primitive jugular vein between the left innominate and the azygos vein forms the upper part of the superior vena cava of the adult; the lower part of this vessel, i. e., below the entrance of the azygos vein, is formed by the right Cuvierian duct. Below the origin of the transverse branch the left Posterior cerebral vein' Audit vesii . 1 ory le Middle cerebral vein Anterior cerebral vein \ Torcular Herophili \\ /^ ^^^^.^^^Superior sagittal \ If y \/ sinus Jugular vein- 'Trigeminal nerve Vena capitis lateralis Ophthalmic vein Fig. 179. — Diagram of veins of head of an embryo five weeks old. (-\fter Mall.) primitive jugular vein and left Cuvierian duct atrophy, the former constituting the upper part of the highest left intercostal vein, while the latter is represented by the ligament of the left vena cava, vestigial fold of Marshall, and the oblique vein of the left atrium, oblique vein of Marshall (Fig. 177). Both right and left superior vense cavse are present in some animals, and are occasionally found in the adult human being. The oblique vein of the left atrium passes downward across the back of the left atrium to open into the coronary sinus, which, as already indicated, represents the persistent left horn of the sinus venosus. The primitive jugular veins drain the blood from the brain, and their proximal parts form the internal jugular veins. The distal portion of each has been named the vena capitis medialis (Fig. 178); it runs on the medial side of the auditory 160 EMBRYOLOGY vesicle and cerebral nerve roots, and the portion of it situated in the neighborhood of the trigeminal nerve becomes the cavernous sinus. The greater part of the vena capitis medialis is replaced, however, by the vena capitis lateralis (Fig. 179j, which is developed on the lateral aspect of the cerebral nerves from the trigeminal to the hypoglossal. This vein receives three principal tributaries, viz., the anterior cerebral vein from the eye, fore-brain, and mid-brain, the middle cerebral vein Torcular Hcrophili Middle cerebral vein Posterior cerebral vein Superior sagittal sinus Vena capitis lateralis Ophthalmic Anterior vein cerebral vein Auditory Trigeminal vesicle nerve Fig. 180. — Diagram of veins of head at the beginning of the third month. (After Mall.) from the cerebellum, and the posterior cerebral vein from the lower part of the hind- brain. At this stage, therefore, practically the whole of the blood from the brain is drained into the vena capitis lateralis, which leaves the skull in company with the facial nerve and opens into the internal jugular vein. The terminal branches of the two anterior cerebral veins anastomose in the middle line and thus form the Torcular Herophili Straight sinus Inferior sagittal sinus Superior petrosal sinus Transverse sinus Great cerebral vein Superior sagittal sinus Middle cerebral vein Anterior cerebral vein Sphenoparietal sinics Auditory vesicle Inferior petrosal sinus Trigeminal nerve Ophthalmic vein Fig. 181. — Diagram of veins of head of an older embryo. (After Mall.) superior sagittal sinus (Fig. 180). By the backward growth of the cerebral hemis- pheres this sinus comes to anastomose with the middle and posterior cerebral veins, the latter of which leaves the skull through the jugular foramen; this last anastomo- sis forms the greater part of the transverse sinus. The vena capitis lateralis under- goes atrophy; the middle cerebral vein forms the superior petrosal sinus (Fig. 181). The inferior petrosal sinus is a later formation. The external jugular vein DEVELOPMEXT OF THE VASCULAR SYSTEM 101 at first drains the region behind the ear (posterior auricuUir) and enters the primi- tive juguhir as a hiteral tributary. A group of veins from tiie face and lingual region converge to form a common vein, the linguo-facial/ which also terminates in the primitive jugular. Later, cross communications develop between the external jugular antl the linguo-facial, with the result that the posterior group of facial veins is transferred to the external jugular. Peculiarities of the Fetal Heart. — In early fetal life the heart is placed directly under the head and is relatively of large size. Later it assumes its position in the thorax, but lies at first in the middle line; toward the end of pregnancy it gradu- ally becomes oblique in direction. The atrial portion is at first larger than the ventricular part, and the two atria communicate freely through the foramen ovale. In consequence of the communication through the ductus arteriosus, between the pulmonary artery and the aorta, the contents of the right ventricle are mainly carried into the latter vessel instead of to the lungs, and hence the wall of the right ventricle is as thick as that of the left. At the end of fetal life, however, the left ventricle is thicker than the right, a difference which becomes more and more emphasized after birth. The fetal circulation and the changes which take place in the circulation after birth are described on pages 616 to 618. Left innominate Jugular lymph-sac Eight innominate S'lperior vena cava Prereiml part of inferior vena cava Postrenal part of inferior veiui cava Cisterna chyli Posterior lymph-sac Internal jugular External jugular Duct of Cuvier Left cardinal Left suprarenal Left renal Eetro-peritoneal lymph- sac Left common iliac External iliac Hypogastric Fig. 1S2. — Scheme showing relative positions of primary lymph sacs based on the description given by Florence Sabin. The Lymphatic Vessels. — The lymphatic system begins as a series of sacs- at the points of junction of certain of the embryonic veins. These lymph-sacs are developed by the confluence of numerous venous capillaries, which at first lose their connections with the venous system, but subsequently, on the formation of the sacs, regain them. The lymphatic system is therefore developmentally an offshoot of the venous system, and the lining walls of its vessels are always endothelial. In the human embryo the lymph sacs from which the lymphatic vessels are derived are six in number; two paired, the jugular and the posterior lymph-sacs; and two unpaired, the retroperitoneal and the cisterna chyli. In lower mammals ' Le-n-is, American Journal of Anatomy, February, 1909, No. 1, vol. is. 2 Sabin, ibid. 11 162 EMBRYOLOGY an additional pair, subclavian, is present, hut in the human embryo these are merel}' extensions of the jugular sacs. The position of the sacs is as follows: (1) jugular sac, the first to appear, at the junction of the subclavian vein with the primitive jugular; (2) posterior sac, at the junction of the iliac vein with the cardinal; (3) retroperitoneal, in the root of the mesentery near the suprarenal glands; (4) cisterna chyli, opposite the third and fourth lumbar vertebrae (Fig. 182). From the lymph-sacs the lymphatic vessels bud out along fixed lines corresponding more or less closely to the course of the embryonic blood\-essels. Both in the body-wall and in the wall of the intestine,^ the deeper plexuses are the first to be developed; by continued growth of these the vessels in the superficial layers are gradually formed. The thoracic duct is probably formed from anastomosing outgrowths from the jugular sac and cisterna chyli. At its connection with the cisterna chyli it is at first double, but the two vessels soon join. All the lymph-sacs except the cisterna chyli are, at a later stage, divided up by slender connective tissue bridges and transformed into groups of lymph glands. The lower portion of the cisterna chyli is similarly converted, but its upper portion remains'as the adult cisterna. A m nion Allantois Hind-gut Fig. 183. — Diagram of a sagittal section of a mammalian embryo. Very early. (After Quain.) DEVELOPMENT OF THE DIGESTIVE AND RESPIRATORY APPARATUS. The Digestive Tube.— As already indicated (page 92), the primitive digestive tube consists of two parts, viz.: (1) the fore-gut, within the cephalic flexure, and dorsal to the heart; and (2) the hind-gut, within the caudal flexure (Figs. 183, 184). Between these is the wide opening of the yolk-sac, which is gradually narrowed and reduced to a small foramen leading into the vitelline duct. At first the fore- gut and hind-gut end blindly. The anterior end of the fore-gut is separated from 1 Heuer, American Journal of Anatomy, vol. ix, No, 1, February. 1909. DEVELOPMEXT OF DIGESTIVE AXD RESPIRATORY APPARATUS 163 the stomodeum by the biiccopliaryngeal membrane (Fig. 184); the hind-gut ends in the cloaca, which is closed by the cloacal membrane. The Mouth. — The mouth is developed partly from the stomodeum, and partly from the floor of the anterior portion of the fore-gut. By the gro\\i;h of the head ' end of the embryo, and the formation of the cephalic flexure, the pericardial area and the buccopharyngeal membrane come to lie on the ventral surface of the embryo. ^Yith the further expansion of the brain, and the forward bulging of the pericardium, the buccopharyngeal membrane is depressed between these two prominences. This depression constitutes the stomodeum (Fig. 184). It is lined by ectoderm, and is separated from the anterior end of the fore-gut by the bucco- pliaryngeal membrane. This membrane is devoid of mesoderm, being formed by the apposition of the stomodeal ectoderm with the fore-gut entoderm; at the end of the third week it disappears, and thus a communication is established Thalamencephalon Optic vesicle Mid-hrain B uccopharyngeal viemhrane Pharynx Auditory pit Bulbus cordis Stomach Stomodeum Ventricle Liver Cloaca Body-stalk Uitibilical vein Yolk-sac Hind-gut Allantois Umbilical artery Fig. 184. — Human embryo about fifteen days old. Brain and heart represented from right side. Digestive tube and yolk sac in median section. (After His.) between the mouth and the future pharynx. No trace of the membrane is found m the adult; and the communication just mentioned must not be confused with the permanent isthmus faucium. The lips, teeth, and gums are formed from the walls of the stomodeum, but the tongue is developed in the floor of the pharynx. The visceral arches extend in a ventral direction between the stomodeum and the pericardium; and with the completion of the mandibular arch and the formation of the maxillary processes, the mouth assumes the appearance of a pentagonal orifi.ce. The orifice is bounded in front by the fronto-nasal process, behind by the mandibular arch, and laterally by the maxillary processes (Fig. 185). With the inward growth and fusion of the palatine processes (Figs. 112, 113), the stomodeum is divided into an upper nasal, and a lower buccal part. Along the free margins of the processes bounding the mouth cavity a shallow groove appears; this is termed the primary labial groove, and from the bottom of it a downgrowth of 164 EMBRYOLOGY ectoderm takes place into the underlying mesoderm. The central cells of the ectodermal downgrowth degenerate and a secondary labial groove is formed; by the deepening of this, the lips and cheeks are separated from the alveolar processes of the maxillae and mandible. The Salivary Glands. — The salivary glands arise as buds from the epithelial lining of the mouth; the parotid appears during the fourth week in the angle between the maxillary process and the mandibular arch; the submaxillary ap- pears in the sixth week, and the sublin- gual during the ninth week in the hollow between the tongue and the mandibular arch. The Tongue (Figs. 186 to 188).— The tongue is developed in the floor of the pharynx, and consists of an anterior or buccal and a posterior or pharyngeal part which are separated in the adult by the V-shaped sulcus terminalis. During the third week there appears, immediately behind the ventral ends of the two halves of the mandibular arch, a rounded swelling named the tuberculum impar, which was described by His as un- dergoing enlargement to form the buccal part of the tongue. ]More re- cent researches, however, show that this part of the tongue is mainly, if not entirely, developed from a pair of lateral . swellings which rise from the inner surface of the mandibular arch and meet in the middle line. The tuber- culum impar is said to form the central part of the tongue immediately in front of the foramen cecum, but Hammar insists that it is purely a transitory structure and forms no part of the adult tongue. From the ventral ends of the fourth arch Future a'pex of nose Medial nasal process Olfactory pit Lateral nasal process Glchular process Maxillary process Stomodeum Mandibidar arch Fig. 185. — Head end of human embryo of about thirty to thirty-one days. (From model by Peter.) Lateral tongue Thyroid swellings diverticulum Lateral tongue swellings Entrance to larynx Fig. 186. — Floor of pharynx of human embryo about twenty-six days old. (From model by Peter.) Entrance to larynx Arytenoid swellings Fig. 187. — Floor of pharj'nx of human embryo of about the end of the fourth week. (From model by Peter.) there arises a second and larger elevation, in the centre of which is a median groove or furrow. This elevation was named by His the furcula, and is at first separated from the tuberculum impar by a depression, but later by a ridge, the copula, formed by the forward growth and fusion of the ventral ends of the second and third arches. The posterior or pharyngeal part of the tongue is developed from DEVELOPMENT OF DIGESTIVE AXD RESPIRATORY APPARATUS 165 the copula, which extends forward in the form of a V, so as to embrace between its two limbs the buccal part of the tongue. At the apex of the V a pit-like invagination occurs, to form the thyroid gland, and this depression is represented in the adult by the foramen cecum of the tongue. In the adult the union of the anterior and posterior parts of the tongue is marked by the V-shaped sulcus terminalis, the apex of which is at the foramen cecum, while the two limbs run lateralward and forward. ])arallel tt). l)ut a little behind, the vallate papilUe. The Thyroid Gland. — The thyroid gland is developed from a median diverticulum (Fig. 189), which appears about the fourth week on the summit of the tuberculum impar, but later is found in the furrow immediately behind the tuberculum (Fig. 186). It grows downward and backward as a tubular duct, which bifurcates and subsequently subdivides into a series of cellular cords, from which the isthmus and lateral lobes of the thyroid gland are developed. As already stated (page 111), the ultimobranchial bodies from the fifth pharyngeal pouches are enveloped by the lateral lobes of the thyroid gland; they undergo atrophy and do not form true thyroid tissue. The connection of the diverticulum with the pharynx is termed the thyroglossal duct; its continuity is subsequently interrupted, and it undergoes degeneration, its upper end being represented by the foramen cecum of the tongue, and its lower by the pyramidal lobe of the thyroid gland. Arytenoid swellings Fig. ISS. — Floor of pharynx of human embryo about thirty days old. (From model by Peter.) Thyroid gland Parathyroids Thymus UUimo-hranchial body Fig. 189. — Scheme showing development of bran- chial epithelal bodies. (^Modified from Kohn.) /, //, III, IV. Branchial pouches. The Palatine Tonsils. — The palatine tonsils are developed from the dorsal angles of the second branchial pouches. The entoderm which lines these pouches grows in the form of a number of solid buds into the surrounding mesoderm. These buds become hollowed out by the degeneration and casting off of their central cells, and by this means the tonsillar crypts are formed. Lymphoid cells accumulate around the crypts, and become grouped to form the lymphoid follicles; the latter, however, are not well-defined until after birth. The Thymus. — The thymus appears in the form of two flask-shaped entodermal diverticula, which arise, one on either side, from the third branchial pouch (Fig. 189), and extend lateralward and backward into the surrounding mesoderm in front of the ventral aortse. Here they meet and become joined to one another by connective tissue, but there is never any fusion of the thymus tissue proper. The pharyngeal opening of each diverticulum is soon obliterated, but the neck of the flask persists for some time as a cellular cord. By further proliferation of the cells lining the flask, buds of cells are formed, which become surrounded and isolated 166 EMBRYOLOGY by the invading mesoderm. In the latter, numerous lymphoid cells make their appearance, and are aggregated to form lymphoid foil ides. These lymphoid cells are probably derivatives of the entodermal cells which lined the original diverticula and their subdivisions. Additional portions of thymus tissue are sometimes developed from the fourth branchial pouches. Thymus continues to grow until the time of puberty and then Ijegins to atrophy. The Parathyroid Bodies. — The parathyroid bodies are developed as outgrowths from the third and fourth branchial pouches (P'ig. 189). A pair of diverticula arise from the fifth branchial pouch and form what are termed the ultimobranchial bodies (Fig. 189): these fuse with the thyroid gland, but probably contribute no true thyroid tissue. The Hypophysis Cerebri. — This in the adult consists of a large anterior, and a small posterior, lobe: the former is derived from the ecto- derm of the stomodeum, the latter from the floor of the fore-brain. About the fourth week there appears a pouch- like diverticulum of the ecto- dermal lining of the roof of the stomodeum. This diver- ticulum, pouch of Rathke (Fig. 190), is the rudiment of the anterior lobe of the hypo- physis; it extends upward in front of the cephalic end of the notochord and the rem- nant of the buccopharyngeal membrani and comes into contact wnh the under sur- face of the fore-brain. It is then constricted off to form a closed vesicle, but remains for a time connected to the ectoderm of the stomodeum by a solid cord of cells. Masses of epithelial cells form on either side and in the front wall of the vesicle, and by the growth between these of a stroma from the mesoderm the development of the anterior lobe is completed. The upwardly directed hypo- physeal involution becomes applied to the antero-lateral aspect of a downwardly directed diverticulum from the base of the fore-brain (page 128). This divertic- ulum constitutes the future infundibulum in the floor of the third ventricle while its inferior extremity becomes modified to form the posterior lobe of the hj^Dophysis. In some of the low^er animals the posterior lobe contains nerve cells and nerve fibres, but in man and the higher vertebrates these are replaced by connective tissue. A canal, craniopharyngeal canal, is sometimes found extending Fig. 190. — Vertical sections of the heads of early embryos of the rab- bit. ^Magnified. (From Mihalkovics.) A. From an embryo 5 mm. long. B. From an embryo 6 mm. long. C. Vertical section of the anterior end of the notochord and hypophysis, etc., from an embrj'O 16 mm. long. In A the buccopharyngeal membrane is still present. In B it is in the process of disappearing, and the stomodeum now communi- cates with the primitive pharynx, am. Amnion, c. Fore-brain, ch. Notochord. /. Anterior extremity of fore-gut, i. h. Heart, if. Infun- dibulum. m. Wall of brain cavity, mc. Mid-brain. mo. Hind-brain. p. Original position of hypophyseal diverticulum, py. ph. Pharynx. sp.e. Sphenoethmoidal, be. Central, sp.o. Sphenooccipital parta of basis cranii. tha. Thalamus. DEVELOPMENT OF DIGESTIVE AND RESPIRATORY APPARATUS 167 / from the anterior part of the fossa hypophyseos of the sphenoid bone to tlie under I surface of the skuU, and marks the original position of Ratiike's pouch; while at :t •^ NotocJwrd RathJce\s pouch Li(nrj diverticulum -- Stomach Liver -- Opening into yolk-sac Allantois I — Mandilular arch — Postallantoic part of hind-gut Wolffian duct Lung diverticuhin. (Esophagus ^ ^y^ Stomach -~ -/ Pancreas • Bile-duct i Vitelline duct" Allantois - Thyroid gland Mandibular arch I I Notochord — Rathhe's pouch Postallantoic part of hind-gut -J- Wolffian duct Fig. 191. — Sketches in profile of two stages in the development of the human digestive tube. (His.) A X 30. B X 20. the junction of the septum of the nose with the palate traces of the stomodeal end are occasionally present (Frazer). 168 EMBRYOLOGY The Further Development of the Digestive Tube.— The upper part of the fore-gut becomes dilated to form the pharynx (Fig. 184), in relation to which the branchial arches are developed (see page 108) ; the succeeding i)art remains tubular, and with the descent of the stomach is elongated to form the (vsophagus. About the fourth week a fusiform dilatation, the future stomach, makes its appearance, and beyond this the gut opens freely into the yolk-sac (Fig. 191, A and B). The opening' is at first wide, but is gradually narrowed into a tubular stalk, the yolk-stalk or vitelline duct. Between the stomach and the mouth of the yolk-sac the li\er diverticulum appears. From the stomach to the rectum the alimentary canal is attached to the notochord by a band of mesoderm, from which the common mesentery of the gut is subsequently developed. The stomach has an additional attachment, viz., to the ventral abdominal wall as far as the umbilicus by the septum transversum. The cephalic portion of the septum takes part in the formation of the Diaphragma, while the caudal portion into which the liver grows forms the ventral mesoga:-;trium (Fig. 193). The stomach undergoes a further dilatation, and its two curvatures, can be recognized (Figs. 191, B, and 192), the greater directed toward the vertebral Trachea — -1 (Esophagus Stomach Bile-duct ■ Lung -- Trachea \f-sha]>ed loop of small intestine - Vitelline duct - Cloaca • >■ — Pancreas Bile-duct- Pancreas Lung (Esophagus ■Stomach Fig. 192. — Front view of two successive stages in the development of the digestive tube. (His.) column and the lesser toward the anterior wall of the abdomen, while its two surfaces look to the right and left respectively. Behind the stomach the gut undergoes great elongation, and forms a V-shaped loop which projects downward and forward; from the bend or angle of the loop the vitelline duct passes to the umbilicus (Fig. 193). For a time a considerable part of the loop extends beyond the abdominal cavity into the umbilical cord, but by the end of the third month it is withdrawn within the cavity. With the lengthening of the tube, the mesoderm, which attaches it to the future vertebral column and carries the bloodvessels for the supply of the gut, is thinned and drawn out to form the posterior common mesentery. The portion of this mesentery attached to the greater curvature of the stomach is named the dorsal mesogastrium, and the part wdiich suspends the colon is termed the mesocolon (Fig. 194). About the sixth week a diverticulum of the gut appears just behind the opening of the vitelline duct, and indicates the future cecum and vermiform process. The part of the loop on the distal side of the cecal diverticulum increases in diameter and forms the future ascending and transverse portions of the large intestine. Until the fifth month the cecal diverticulum has a uniform calibre, but from this time onward its distal part DEVELOPMENT OF DIGESTIVE AXD RESPIRATORY APPARATUS 169 remains rudimentary and forms the vermiform process, while its proximal part expands to form the cecum. Changes also take place in the shape and position of the stomach. Its dorsal part or greater curvature, to which the dorsal meso- Septwm transvcrsum Livd Falciform ligament of Uvei Lesser omentum Umbilical vein Vmbilical cord Aorta Dorsal mesogastrium Stomach Intestinal \/-shaped loop Mesentery Colon Fig. 193. — The primitive mesentery of a six weeks' human embryo, half schematic. (Kollraann.) gastrium is attached, grows much more rapidly than its ventral part or lesser curvature to which the ventral mesogastrium is fixed. Further, the greater curva- ture is carried downward and to the left, so that the right surface of the stomach is Ventral mesogastrium Aorta Spleen Dorsal mesogastrium, Coeliac artery Pancreas Superior mesenteric artery Mesentery Inferior mesenteric artery Hind-gut Fig. 194. — Abdominal part of digestive tube and its attachment to the primitive or common mesentery. Human embryo of six weeks. (After Toldt.) now directed backward and the left surface forward (Fig. 195), a change in position which explains why the left vagus nerve is found on the front, and the right vagus on the back of the stomach. The dorsal mesogastrium being attached to the greater 170 EMBRYOLOGY curvature must necessarily follow its movements, and hence it becomes greatly elongated and drawn lateralward and ventralward from the vertebral column, and, as in the case of the stomach, the rigiit surfaces of both the dorsal and ventral mesogastria are now directed backward, and the left forward. In this way a pouch, the bursa omentalis, is formed behind the stomach, and this increases in size as the digestive tube undergoes further development; the entrance to the pouch constitutes the future foramen epiplolcum or foramen of Winslow. The duodenum is developed from that part of the tube which innnediately succeeds the stomach; it undergoes little elongation, being more or less fixed in position by the liver and Pericardium 8th cervical nerve 1st thoracic vertebra Lung Suprarenal gland Stomach 12th thoracic nerve Mesonephros Kidney 5lh Imnbar nerve Small intestine Ureter Wolffian duct Reconstruction of a human embryo of 17 mm. (After Mall.) pancreas, which arise as diverticula from it. The duodenum is at first suspended by a mesentery, and projects forward in the form of a loop. The loop and its mes- entery are subsequently displaced by the transverse colon, so that the jight surface of the duodenal mesentery is directed backward, and, adhering to the parietal peritoneum, is lost. The remainder of the digestive tube becomes greatly elongated, and as a consequence the tube is coiled on itself, and this elongation demands a corresponding increase in the width of the intestinal attachment of the mesentery, which becomes folded. At this stage the small and large intestines are attached to the vertebral column DEVELOPMENT OF DIGESTIVE AND RESPIRATORY APPARATUS 171 by a common meseiittTv, the coils of tlie small intestine falling to the right of the middle line, while the large intestine lies on the left side.^ The gut is now rotated upon itself, so that the large intestine is carried o\'er in front of the small intestine, and the cecum is i)la('ed inuncdiately below the liver; about the sixth month the cecum descends into the right iliac fossa, and the large intestine forms an arch consisting of the ascending, transverse, and descending portions of the colon — the transverse portion crossing in front of the duodenum and lying just below the greater curvature of the stomach; within this arch the coils of the small intestine are disposed (Fig. 197). Sometimes the downward progress of the cecum is arrested, so that in the adult it may be found lying imme- diately below the liver instead of in the right iliac region. Mesogastnum Small intestine Vitelline duct Greater curvature of stomach Greater omentum Point where intestinal loops cross each other Meso- gastriun, Duodenum Mesocolon Cecum Large Vermiform intestine process Mesentery Greater omenttnn Rectum, Vitelline duct Large intestine Small intestine Rectum Fig. 196.- -Diagrams to illustrate two stages in the development of the digestive tube and its mesentery. The arrow indicates the entrance to the bursa omentalis. Further changes take place in the bursa omentalis and in the common mesenter}^, and give rise to the peritoneal relations seen in the adult. The bursa omentalis, which at first reaches only as far as the greater curvature of the stomach, grows downward to form the greater omentum, and this downward extension lies in front of the transverse colon and the coils of the small intestine (Fig. 198). Above, before the pleuro-peritoneal opening is closed, the bursa omentalis sends up a diverticulum on either side of the oesophagus; the left diverticulum soon disappears, but the right is constricted off and persists in most adults as a small sac lying within the thorax on the right side of the lower end of the oesophagus. The anterior layer of the transverse mesocolon is at first distinct from the posterior layer of the greater omentum, but ultimately the two blend, and hence the greater omentum appears as if attached to the transverse colon (Fig. 199). The mesenteries of the ascending and descending parts of the colon disappear in the majority of cases, while that of the small intestine assumes the oblique attachment characteristic of its adult condition. 1 Sometimes this condition persists throughout life, and it is then found that the duodenum does not cross from the right to the left side of the vertebra! column, but lies entirely on the right side of the median plane, where it is continued into the jejunum; the arteries to the small intestine (aa. intestinales) also arise from the right instead of the left side of the superior mesenteric artery. 172 EMBRYOLOGY The lesser omentum is formed, as indicated above, by a thinning of the meso- derm or ventral mesogastrium, which attaches the stomach and ckiodenum to the anterior abdominal wall. By the subsequent growth of the liver this leaf of mesoderm is divided into two parts, viz., the lesser omentum between the stomach and li^•e^, and the falciform and coronary ligaments between the liver and the abdominal wall and Diaphragma (Fig. 198). The Rectum and Anal Canal.— The hind-gut is at first prolonged backward into the body-stalk as the tube of the allantois; but, with the growth and flexure of the tail-end of the embryo, the body-stalk, with its contained allantoic tube, is carried forward to the ventral aspect of the body, and consequently a bend is formed at the junction of the hind-gut and allantois. This bend becomes dilated into a pouch, which constitutes the entodermal cloaca; into its dorsal part the hind-gut opens, and from its ventral part the allantois passes forward. At a later stage the Wolffian and Miillerian ducts open into its ventral portion. The cloaca is, for a time, shut Fig. 197. — Final disposition of the intestines and their vascular relations. (Jonnesco.) A. Aorta. H. Hepatic artery. M, Col. Branches of superior mesenteric artery. m,_ m'. Branches of inferior mesenteric artery. S. Splenic artery. Ventral mesogastrium Liver Umbilical vein. Border of ventral mesogastrium Stomach Bursa omentalis Pancreas Dorsal mesogastrium Duodenum Greater omentum Tran.sverse mesocolon Transverse colon Fig. 198. -Schematic figure of the bursa omentaUs, etc. embryo of eight weeks. (Kollmann.) Human off from the anterior by a membrane, the cloacal membrane, formed by the apposi- tion of the ectoderm and entoderm, and reaching, at first, as far forward as the future umbilicus. Behind the umbilicus, however, the mesoderm subsequently extends to form the lower part of the abdominal wall and symphysis pubis. By the growth of the surrounding tissues the cloacal membrane comes to lie at the bottom of a depression, which is lined by ectoderm and named the ectodermal cloaca (Fig. 200). The entodermal cloaca is divided into a dorsal and a ventral part by means of a partition, the urorectal septum (Fig. 201), which grows downward from the ridge separating the allantoic from the cloacal opening of the intestine and ultimately fuses with the cloacal membrane and divides it into an anal and a urogenital part. The dorsal part of the cloaca forms the rectum, and the anterior part of the uro- genital sinus and bladder. For a time a communication named the cloacal duct exists between the two parts of the cloaca below the urorectal septum; this duct DEVELOPMENT OF DIGESTIVE AND RESPIRATORY APPARATUS 173 occasionally persists as a passage between the rectnni and urethra. The anal canal is formed by an invagination of the ectoderm behind the urorectal septum. J)taphragi»a \ Liner Lomer omentum Jiiirna oitientalit:-- StoDiach- Pancrea s Greater omentum - Transverse mesocolon - Transverse colon - Lesser omentum -- Bursa omental is Stoinack Pancreas Ohlitcnticd part of mesogastrium --- Dnoilniuiii Transverse colon Mesentery Small intestine Small intcst Fig. 199. ^Diagrams to illustrate the development of the greater omentum and transverse mesocolon. Wolffian duct if Ectodermal cloaca — f^ij Cloacal membra nc~/ ~7 i nioicn Notochord Fig. 200. — Tail end of human embryo from fifteen to eighteen days old. (From model by Keibel.) Wolffian d%ict ■ \ — Rectum Septum Fig. 201. — Cloaca of human embryo from twenty-five to twenty-seven days old. (From model by Keibel.) Ureter. Wolffian duct Mulleiianduct Bhddi'i Glans penis Urethra Vertebral column Fig. 202. — Tail end of human embryo, from eight and a half to nine weeks old. (From model by Keibel.) 174 EMBRYOLOGY This invagination is termed the proctodcEum, and it meets with the entoderm of the hind-gut and forms witli it the anal membrane. By the absorption of this membrane the anal canal becomes continuous witli the rectum (Fig. 202). A small part of the hind-gut projects backward beyond the anal membrane; it is named the post-anal gut (Fig. 200), and usually becomes obliterated and disappears.^ The Liver. — The liver arises in the form of a diverticulum or hollow outgrowth from the \'entral surface of that portion of the gut which afterward becomes the descending part of the duodenum (Figs. 191, 203). This diverticulum is lined by entoderm, and grows upward and forward into the septum transversum, a mass of mesoderm between the vitelline duct and the pericardial cavity, and there gives ofif two solid buds of cells which represent the right and the left lobes of the liver. The solid buds of cells grow into columns or cylinders, termed the hepatic cylinders, which branch and anastomose to form a close meshwork. This network invades the vitelline and umbilical veins, and breaks up these vessels into a series of capil- lary-like vessels termed sinusoids (Minot), which ramify in the meshes of the cellular network and ultimately form the venous capillaries of the liver. By the continued Pericardial cavity Anterior wall of pericardium Loiver wall of pericardium Liver Bile duct Truncus arteriosus Dorsal mesocardium Atrium '^~- Cuvierian dud Uir)bilical vein Vitelline vein Communication between pericardial and peritoneal cavities Vitelline duel Peritoneal cavity Fig. 203. — Liver with the septum transversum. Human embryo 3 mm. long. (After model and figure by His.) growth and ramification of the hepatic cylinders the mass of the liver is gradually formed. The original diverticulum from the duodenum forms the common bile- duct, and from this the cystic duct and gall-bladder arise as a solid outgrowth which later acquires a lumen. The opening of the common duct is at first in the ventral wall of the duodenum; later, owing to the rotation of the gut, the opening is carried to the left and then dorsalward to the position it occupies in the adult. As the liver undergoes enlargement, both it and the ventral mesogastrium of the fore-gut are gradually differentiated from the septum transversum; and from the under surface of the latter the liver projects downward into the abdominal cavity. By the growth of the liver the ventral mesogastrium is divided into two parts, of which the anterior forms the falciform and coronary ligaments, and the posterior the lesser omentum. About the third month the liver almost fills the abdominal cavity, and its left lobe is nearly as large as its right. From this period 1 Consult, in this connection, the following article: "A Contribution to the Morphology of the Human Urino- genital Tract," by D. Berry Hart, M.D., F.R.C.P.E., Journal of Anatomy and Physiology, April, 1901, vol. xxxv. DEVELOPMEXr OF DIGESTIVE AXD RESPIRATORY APPARATUS 175 the relative development of the liver is less acti\e, more espeeially that of the left lobe, which actually uiulergoes some degeneration and becomes smaller than the right; but up to the end of fetal life the liver remains relatively larger than in the adult. The Pancreas (Figs. 204, 205). — The pancreas is developed in two parts, a dorsal and a ventral. The former arises as a diverticulum from the dorsal aspect of the duodenum a short distance above the hepatic diverticulum, and, growing upward and backward into the dorsal mesogastrium, forms a part of the head and uncinate process and the whole of the body and tail of the pancreas. The ventral Accessory 'pancreatic duct Dorsal pancreas Ventral pancreas Pancreatic duct Bile duct Fig. 204. — Pancreas of a human embrj-o of five weeks. (KoUmann.) Accessory pancreatic duct Dorsal pancreas Bile duct Fig. 205.- Ventral pancreas Pancreatic duct -Pancreas of a human embrj^o at end of sixth week. (Kollmann.) part appears in the form of a diverticulum from the primitive bile-duct and forms the remainder of the head and uncinate process of the pancreas. The duct of the dorsal part (accessory pancreatic duct) therefore opens independently into the duodenum, while that of the ventral part (pancreatic duct) opens w^th the common bile-duct. About the sixth week the two parts of the pancreas meet and fuse and a communication is established between their ducts. After this has occurred the terminal part of the accessory duct, i. e., the part between the duodenum and the point of meeting of the two ducts, undergoes little or no enlargement, while Liver Lesser omentum Liver Left suprarenal gland Right suprarenal gland Fig. 206. — Schematic and enlarged cross-section through the body of mesogastrium. Beginning of third month. i human embr\-o in the region of the (Toldt.) the pancreatic duct increases, in size and forms, the main duct of the gland. The opening of the accessory duct into the duodenum is sometimes obliterated, and even when it remains patent it is probable that the whole of the pancreatic secretion is conveyed through the pancreatic duct. At first the pancreas is directed upward and backward between the two layers of the dorsal mesogastrium, which give to it a complete peritoneal investment, and its surfaces look to the right and left. With the change in the position of the stomach the dorsal mesogastrium is drawn downward and to the left, and the right side of the pancreas is directed backward and the left forward (Fig. 206). The 176 EMBRYOLOGY right surface becomes applied to the posterior abdominal wall, and the peritoneum which covered it undergoes absorption (Fig. 207) ; and thus, in the adult, the gland appears to lie behind the peritoneal cavit}'. Lesser Stomach omentum Liver Liver suprarenal gland Left suprarenal gland Fig. 207. — Section through same region as in Fig. 206, at end of third month. (Toldt.) The Spleen (Fig. 194). — Although the spleen belongs to the group of ductless glands, its development may be conveniently referred to here. It appears about the fifth week as a localized thickening of the mesoderm in the dorsal mesogastrium above the tail of the pancreas. With the change in position of the stomach the spleen is carried to the left, and comes to lie behind the stomach and in contact with the left kidney. The part of the dorsal mesogastrium which intervened between the spleen and the greater curvature of the stomach forms the gastro- splenic ligament. Mouth of olfactory ])it Median fart of fronto- nasal process Processus globulari Hypophysis 1st branchial pouch Sinus cervicalis Laryngo-tracheal tube ' T, Lung Maxillary process 2Iandibular arch Future tympanic membrane Hyoid arch Third arch Fourth arch Fig. 208. — The head and neck of a human embryo thirty-two days old, seen from the ventral sxirface. The floor of the mouth and pharynx have been removed. (His.) The Respiratory Organs. — The rudiment of the respiratory organs appear as a median longitudinal groove in the ventral wall of the pharynx. The groove deepens and its lips fuse to form a septum which grows from below upward and converts the groove into a tube, the laryngo-tracheal tube (Fig. 208), the cephalic end of which opens into the pharynx by a slit-like aperture formed by the persistent anterior part of the groove. The tube is lined by entoderm from which the epithe- lial lining of the respiratory tract is developed. The cephalic part of the tube DEVELOPMENT OF DIGESTIVE AND RESPIRATORY APPARATUS 177 becomes the larynx, and its next succeeding part the trachea, while from its caudal end two lateral outgrowths, the right and left lung buds, arise, and from them the bronchi and lungs are developed. The first rudiment of the larynx consists of two arytenoid swellings, wliich appear, one on eitlier side of the cephalic end of the laryngo- tracheal grooN'c, and are continuous in front of the groove with a transverse Vidge (furcula of His) which lies between the ventral ends of the third branchial arches and from which the epiglottis is subsequently developed (Figs. 187, 188). After the separation of the trachea from the oesophagus, the arytenoid swellings come into contact with one another and with the back of the epiglottis, and the entrance to the larynx assumes the form of a T-shaped cleft, the margins of the cleft adhere to one another and the laryngeal entrance is for a time occluded. The mesodermal wall of the tube becomes condensed to form the cartilages of the larynx and trachea. The arytenoid swellings are differentiated into the arytenoid and corniculate car- tilages, and the folds joining them to the epiglottis form the aryepiglottic folds in which the cuneiform cartilages are developed as derivatives of the epiglottis. The thyroid cartilage appears as two lateral plates, each chondrified from two centres and united in the mid-ventral line by membrane in which an additional centre of chondrification develops. The cricoid cartilage arises from two cartil- aginous centres, which soon unite ventrally and gradually extend and ultimately fuse on the dorsal aspect of the tube. J. Ernest Frazeri has made an important investigation on the development of the larynx, and the following are his main conclusions: The opening of the pulmonary diverticulum lies between the two fifth arch masses and behind a "central mass" in the middle hne — the proximal end of the diverticulum is compressed between the fifth arch masses. The fifth arch is joined by the fourth to form a "lateral mass" on each side of the opening, and these "lateral masses" grow forward and overlap the central mass and so form a secondary transverse cavity, which is really a part of the cavity of the pharynx. The two parts of the cavity of the larynx are separated in the adult by a hne drawn back along the vocal fold and then upward along the border of the arytenoid eminence to the interarytenoid notch. The arytenoid and cricoid are developed in the fifth arch mass. The thyroid is primarily a fourth arch derivative, and if it has a fifth arch element this is a later addition. The epiglottis is derived from the "central mass," and has a third arch element in its oral and upper aspect; the arch value of the "central mass" is doubtful. Fig. 209. — Lung buds from a human embryo of about four weeks, showing commencing lobulations. (His.) Fig 210 — Lungs of a human embn o more advanced \n development (Hia ) The right and left lung buds grow out behind the ducts of Cuvier, and are at first symmetrical, but their ends soon become lobulated, three lobules appearing on the right, and two on the left; these subdivisions are the early indications of the corresponding lobes of the lungs (Figs. 209, 210). The buds undergo further sub- di-vision and ramification, and ultimately end in minute expanded extremities — the infundibula of the lung. After the sixth month the air-sacs begin to make their appearance on the infundibula in the form of minute pouches. The pulmonary arteries are derived from the sixth aortic arches. During the course of their development the lungs migrate in a caudal direction, so that by the time of birth 1 .lournal of Anatomy and Physiology, vol. xliv. 12 178 EMBRYOLOGY the bifurcation of the trachea is opposite the fourth thoracic vertebra. As the lungs grow they project into that part of the coelora which will ultimately form the pleural cavities, and the superficial layer of the mesoderm emcloping the lung rudiment expands on the growing lung and -is couNcrtcd into the pulmonary pleura. DEVELOPMENT OF THE BODY CAVITIES. In the human embryo described by Peters the mesoderm outside the embryonic disk is split into two layers enclosing an extra-embryonic coelom; there is no trace of an intra-embryonic coelom. At a later stage four cavities are formed within the embryo, ^•iz., one on either side within the mesoderm of the pericardial area, and one in either lateral mass of the general mesoderm. All these are at first independent of each other and of the extra-embryonic coelom, but later they become continuous. The two cavities in the general mesoderm unite on the ventral aspect of the gut and form the pleuro-peritoneal cavity, which becomes continuous with the remains of the extra-embryonic coelom around the umbilicus; the two cavities in the peri- cardial area rapidly join to form a single pericardial cavity, and from this two lateral Mesentery Pleuro- pericardial opening Pericardium," Mesoderm surrounding I net ofCuvier ' -Doibal mesocardium I "1 '-Heart Fig. 211. — Figure obtained by combining several successive sections of a human embryo of about the fourth week (From Kollmann.) The upper arrow is in the pleuroperitoneal opening, the lower in the pleuroperioardial. diverticula extend caudalward to open into the pleuro-peritoneal cavity (Fig. 211). Between the two latter diverticula is a mass of mesoderm containing the ducts of Cuvier, and this is continuous ventrally with the mesoderm in which the umbili- cal veins are passing to the sinus venosus. A septum of mesoderm thus extends across the body of the embryo. It is attached in front to the body-wall between the pericardium and umbilicus; behind to the body-wall at the level of the second cervical segment; laterally it is deficient where the pericardial and pleuro-peri- toneal cavities communicate, while it is perforated in the middle line by the fore- gut. This partition is termed the septum transversum, and is at first a bulky plate of tissue. As development proceeds the dorsal end of the septum is carried grad- ually caudalward, and when it reaches the fifth cervical segment muscular tissue with the phrenic nerve grow into it. It continues to recede, however, until' it reaches the position of the adult Diaphragma on the bodies of the upper lumbar vertebrae. As already described (page 174), the liver buds grow into the septum transversum and undergo development there. The lung buds meantime have grown out from the fore-gut, and project laterally into the forepart of the pleuro-peritoneal cavity ; the developing stomach and liver DEVELOPMEXT OF THE BODY CAVITIES 179 are iml^edded in the septum transversum; caudal to this the intestines project into the back i)art of the pleuro-peritoneal cavity (Fig. 212). Owing to the descent of the dorsal end of the septum transversum the hmg buds come to He al)ove the Left due of Cuvier (Edophayu^ Riyht duct of Cavin- Mesoderm surrouiidi luj duct Plruw-pericardiril opening Ridge, growing across opening Onienlal bursa Stomach -p^ — Dorsal mesentery ~ Peritoneal recess Fig. 212. — Upper part of ccelom of human embryo of 6.S mm., seen from behind. (From model by Piper.) septum and thus pleural and peritoneal portions of the pleuro-peritoneal cavity (still, however, in free communication with one another) may be recognized; the pericardial cavity opens into the pleural part. The ultimate separation of the permanent cavities from one another is effected by the growth of a ridge of tissue on either side from the mesoderm surrounding Aorta Pleural cavity _^ _ Lung (Esopliagus Inferior vena cava Body -wall Pericardium Fig. 213. — Diagram of transverse section through rabbit embryo. (After Keith.) the duct of Cuvier (Figs. 211, 212). The front part of this ridge grows across and obliterates the pleuro-pericardial opening; the hinder part grows across the pleuro- peritoneal opening. 180 EMBRYOLOGY With the continued growth of the hmgs the pleural cavities are pushed forward in the body-wall toward the ventral median line, thus separating the pericardium from the lateral thoracic walls (Fig. 213) . The further development of the peritoneal cavity has been described with the development of the digestive tube (page 168 et seq.). Spleen Colon Suprarenal gland Eleventh rib Twelfth ri Stemo-costal part of Diaphragina Central tendon of Diaphragma Inferior vena cava QP.sophagus Vertebral part of Diaphragma Posterior mediastinal cavity Aorta Spino-costal hiatus Left pleura Eight pleura Fig. 214. — The thoracic aspect of the Diaphragma of a newly born child in which the communication between the peritoneum and pleura has not been closed on the left side; the position of the opening is marked on the right side by the spinocostal hiatus. (After Keith.) DEVELOPMENT OF THE URINARY AND GENERATIVE ORGANS. The urinary and generative organs are developed from the intermediate cjll- mass which is situated between the primitive segments and the lateral plates of mesoderm. The permanent organs of the adult are preceded by a set of structures which are purely embryonic, and which with the exception of the ducts disappear almost entirely before the end of fetal life. These embryonic structures are on either side; the pronephros, the mesonephros, the metanephros, and the Wolffian and Miillerian ducts. The pronephros disappears very early; the structural elements of the mesonephros mostly degenerate, but in their place is developed the genital gland in association with w^hich the Wolffian duct remains as the duct of the male genital gland, the Miillerian as that of the female; some of the tubules of the metanephros form part of the permanent kidney. The Pronephros and Wolffian Duct. — In the outer part of the intermediate cell-mass, immediately under the ectoderm, in the region from the fifth cervical to the third thoracic segments, a series of short evaginations from each segment grow dorsalward and extend caudalward, fusing successively from before backward to form the pronephric duct. This continues to grow caudalward until it opens into the ventral part of the cloaca; beyond the pronephros it is termed the Wolffian duct. The original evaginations form a series of transverse tubules each of which com- municates by means of a funnel-shaped ciliated opening with the coelomic cavity, and in the course of each duct a glomerulus also is developed. Secondary glo- meruli are formed ventral to each of the others, and the complete group constitutes the pronephros. The pronephros undergoes rapid atrophy and disappears. The Mesonephros, Miillerian Duct, and Genital Gland. — On the medial side of the Wolffian duct, from the sixth cervical to the third lumbar segments, a series of tubules, the Wolffian tubules (Fig. 215), is developed; at a later stage in develop- ment they increase in number by outgrowths from the original tubules. These tubules first appear as solid masses of cells, which later become hollowed in the DEVELOPMENT OF THE URINARY AND GENERATIVE ORGANS 181 centre; one end grows toward and finally opens into the Wolffian duct, the other dilates and is invaginated by a tuft of capillary hloodwssels to form a glomerulus. The tubules collectively constitute the mesonephros or Wolffian body (Figs. 195, 210). By the fifth or sixth week this body forms an elongated spindle-shaped structure, termed the urogenital fold (Fig. 215), which projects into the coelomic cavity at the side of the dorsal mesentery, reaching from the sei)tum transversum r Stroma Genital j of ovary — - ridge j Primitive y ova Wolffian diict ^. Mullerian duct ---» Wolffian tubules Body-wall Fig. 215. — Section of the urogenital fold of a chick embryo of the fourth day. (Waldeyer.) in front to the fifth lumbar segment behind ; in this fold the reproductive glands are developed. The Wolffian bodies persist and form the permanent kidneys in fishes and amphibians, but in reptiles, birds, and mammals, they atrophy and for the most part disappear coincidently with the development of the permanent kidneys. The atrophy begins during the sixth or seventh week and rapidly proceeds, so that by the beginning of the fifth month only the ducts and a few of the tubules remain. In the male the Wolffian duct persists, and forms the tube of the epididymis, the ductus deferens and the ejaculatory duct, while the seminal vesicle arises during the third month as a lateral diverticulum from its hinder end. A large part of the head end of the mesonephros atrophies and dis- appears; of the remainder the anterior tubules form the efferent ducts of the testis; while the posterior tubules are represented by the ductuli aberrantes, and by the paradidymis, which is some- times found in front of the spermatic cord above the head of the epididymis (Fig. 219, C). In the female the Wolffian bodies and ducts atrophy. The remains of the Wolffian tubules are represented by the epobphoron or organ of Rosenmiiller, and the paroophoron, two small collections of rudimentary blind tubules wdiich are situated in the mesosalpinx (Fig. 217). The lower part of the Wolffian duct Fig. 216. — Enlarged view from the front of the left Wolffian body before the establishment of the distinction of sex. (From Farre, after Kobelt.) a, a, b, c, d. Tubular structure of the Wolffian body, e. Wolffian duct. /. Its upper extremity, g. Its termination in x, the urogenital sinus, h. The duct of Miiller. i. Its upper, funnel-shaped extremity. k. Its lower end, terminating in the urogenital sinus. I. The genital gland. 182 EMBRYOLOGY disappears, while the upper part i)ersists as tlie l()Il^■itu(lillal duct of the epoophoron or duct of Gartner^ (Fig. 219, B). The Miillerian Ducts. — Shortly after the formation of the Wolffian ducts a second pair of ducts is developed; these are named the Miillerian ducts. Each arises on the lateral aspect of the correspondino; Wolffian duct as a tu})ular inva- gination of the cells lining the ccelom (Fig. 21")). Th(> orifice of the invagination Fig. 217. — Broad ligament of adult, showing epoophoron. (From Farre, after Kobelt.) a, a. Epodphoron formed from the upper part of the Wolffian body. b. Remains of the uppermost tubes sometimes forming appendices, c. Middle set of tubes, d. Some lower atrophied tubes, e. Atrophied remains of the Wolffian duct. /. The terminal bulb or hydatid, h. The uterine tube, originally the duct of Miiller. i. Appendix attached to the extremity. I. The ovary. Miillerian ducts remains patent, and undergoes enlargement and modification to form the abdomi- nal ostium of the uterine tube. The ducts pass backward lateral to the Wolffian ducts, but toward the posterior end of the embryo they cross to the medial side of these ducts, and thus come to lie side by side between and behind the latter — the four ducts forming what is termed the genital cord (Fig. 218). The Miillerian ducts end in an epithelial elevation, the Miillerian eminence, on the ventral part of the cloaca between the orifices of the Wolflfian ducts; at a later date they open into the cloaca in this situation. In the male the Miillerian ducts atrophy, but traces of their anterior ends are repre- sented by the appendices testis {hydatids of Morgagni), while their terminal fused portions form the utriculus in the floor of the prostatic portion of the urethra (Fig. 219, C). In the female the Miillerian ducts persist and undergo further development. The por- tions which lie in the genital core fuse to form the uterus and vagina; the parts in front of this cord remain separate, and each forms the corresponding uterine tube — the abdomi- nal ostium of which is developed from the anterior extremity of the original tubular in- vagination from the coelom (Fig. 219, B). The fusion of the Miillerian ducts begins in the third month, and the septum formed by their fused medial walls disappears from below upward, and thus the cavities Fig. 218. — Urogenital sinus of female human embryo of eight and a half to nine weeks old. (From model by Keibel) ' Berry Hart {op. cit.) has described the Wolffian ducts as ending at the site of the future hymen in bulbous enlarge- ments, which he has named the Wolffian hilbs; and states that the hj'men is formed by these bulbs, "aided by a special involution from below of the cells lining the urogenital sinus. " He further believes that "the lower third of the vagina is due to the coalescence of the upper portion of the urogenital sinus and the lower ends of the Wolffian ducts," and that "the epithelial lining of the vagina is derived from the Wolffian bulbs. " He also regards the colliculus seminahs of the male urethra as being formed from the lower part of the Wolffian ducts. DEVELOPMENT OF THE URINARY AND GENERATIVE ORGANS 183 A Fig, 219. — Diagrams to show the develop- ment of male and female generative organs from a common type. (Allen Thomson.) A. — Diagram of the primitive urogenital organs in the embryo previous to sexual dis- tinction. 3. Ureter. 4. Urinary bladder. 5. I'rachus. cl. Cloaca, cp. Elevation which be- comes clitoris or penis, i. Lower part of the intestine. Is. Fold of integument from which the labia majora or scrotum are formed. m, m. Right and left Miillerian ducts uniting together and running with the Wolffian ducts in gc, the genital cord. of. The genital ridge from which either the ovary or testis is formed, ug. Sinus urogenitalis. W. Left Wolffian body, iv, lo. Right and left Wolffian duets. B. — Diagram of the female type of sexual organs. C. Greater vestibular gland, and immediately above it the urethra, cc. Corpus cavernosum clitoridis. dG. Remains of the left Wolffian duct, such as give rise to the duct of Gartner, represented by dotted lines; that of the right side is marked w. f. The abdominal opening of the left uterine tube. g. Round ligament, corresponding to guber- naculum. h. Situation of the hymen, i. Lower part of the intestine. I. Labium major, n. Labium minus, o. The left ovary, po. Epo- ophoron. sc. Corpus cavernosum urethrae. u. Uterus. The uterine tube of the right .side is marked m. v. Vulva, va. Vagina. W. Scattered remains of Wolffian tubes near it (paroophoron of Waldeyer). C. — Diagram of the male type of sexual organs. C. Bulbo-urethral gland of one side. cp. Corpora cavernosa penis cut short, e. Caput epididymis, g. The gubernaculum. I. Lower part of the intestine, m. Miillerian duct, the upper part of which remains as the hydatid of Morgagni; the lower part, represented bj' a dotted line descending to the prostatic utricle, constitutes the occa- sionally existing cornu and tube of the uterus masculinus. pr. The prostate, s. Scrotum. sp. Corpus cavernosum urethrae. t. Testis in the place of its original formation, t', together with the dotted lines above, indi- cates the direction in which the testis and epididymis descend from the abdomen into the scrotum. Dd. Ductus deferens. !)/i. Ductus aberrans. vs. The vesicula seminalis. W. Scattered remains of the Wolffian body, con- stituting the organ of Giraldes, or the para- didymis of Waldeyer. 184 EMBRYOLOGY Wolffian body MulleHan duct Wolffian duet of the vagina and uterus are produced. About the fifth month an annular con- striction marks the'position of the neck of the uterus, and after the sixth month the walls of the uterus begin to thicken. For a time the vagina is represented by a solid rod of epithelial cells, k ring-like outgrowth of this epithelium occurs at the lower end of the uterus and marks the future \-aginal fornices; about the fifth or sixth month the lumen of the vagina is produced by the breaking down of the central cells of the epithelium. The hymen represents the remains of the Miillerian eminence. Genital Glands. — The first appearance of the genital gland is essentially the same in the two sexes, and consists in a thickening of the epithelial layer which lines the peritoneal cavity on the medial side of the urogenital fold (Fig. 215). The thick plate of epithelium extends deeply, pushing before it the mesoderm and forming a distinct projection. This is termed the genital ridge (Fig. 215), and from it the testis in the male and the ovary in the female are developed. At first the mesonephros and genital ridge are suspended by a common mesentery, but as the embrj'o grows the genital ridge gradually becomes pinched off from the mesone- phros, with which it is at first continuous, though it still remains connected to the remnant of this body by a fold of peri- toneum, the mesorchium or mesovarium (Fig. 220). About the seventh week the distinction of sex in the genital ridge begins to be perceptible. The Ovary. — The ovary, thus formed from the genital ridge, is at first a mass of cells derived from the coelomic epi- thelium; later the mass is differentiated into a central part or medulla (Fig. 221) covered by a surface layer, the germinal epithelium. Between the cells of the germinal epithelium a number of larger cells, the primitive ova, are found, and these are carried into the subjacent stroma by bud-like ingrowths (genital cords) of the germinal epithelium (Fig. 222). The surface epithelium ultimately forms the permanent epithelial covering of this organ; it soon loses its connection with the central mass, and a tunica albuginea develops between them. The ova are chiefly derived from the cells of the central mass; these are separated from one another by the growth of connective tissue in an irregular manner; each ovum assumes a covering of connective tissue (follicle) cells, and in this way the rudi- ments of the ovarian follicles are formed (Fig. 222). According to Beard the primi- tive ova are early set apart during the segmentation of the ovum and migrate into the germinal ridge. t Medulla spinalis Spinal ganglion Notochord Sympathetic ganglion Inferior vena cava Common iliac artery Ureter Mesovarium Intestine Bladder ITmbilical artery Fig. 220. — Transverse section of human embryo eight and a half to nine weeks old. (From model by Keibel.) Waldeyer taught that the primitive germ cells are derived from the "germinal epithelium," covering the genital ridge. Beard, i on the other hand, maintains that in the skate they are not derived from this epithelium, but are probably formed during the later stages of cell cleavage, before there is any trace of an embryo; and a similar view was advanced by Nussbaum as to their origin in amphibia. Beard says: "At the close of segmentation many of the future germ cells lie in the segmentation cavity just beneath the site of the future embryo, and there is no doubt they subsequently wander into it." The germ cells, "after they enter the resting phase, are 1 Journal of Anatomy and Physiology, vol. xx.wiii. DEVELOPMENT OF THE URINARY AND GENERATIVE ORGANS 185 sharply marked off from the cells of the embryo by entire absence of mitoses among them." They can be further recognized by their irregular form and ama-boid processes, and by the fact Uterine tube Oerminal epithelium -, Medvlla — i--\- Epoophoron Rf.te Mesonephros Plica peritonalis tnbce Uterine tube Fig 221. — Longitudinal section of ovary of cat embryo of 9.4 cm. long. Schematic. (After Ccert.) that their cytoplasm has no affinity for ordinary stains, but assumes a brownish tinge when treated by osmic acid. The path along which they travel into the embryo is a very definite one, viz., "from the yolk sac upward between the splanchnopleure and gut in the hinder portion of the Genital cord Oerminal epithelium, Primitive ova Cell-nest Blood-vessel - Ovarian follicle - Fig. 222. — Section of the ovary of a newly born child. (Waldeyer.) embryo." This pathway, named by Beard the germinal path, "leads them directly to the posi- tion which they ought finally to take up in the 'germinal ridge' or nidus." A considerable number 186 EMBRYOLOGY apparently never reach their proper destination, since "vagrant germ cells are found in all sorts of places, but more particularly on the mesentery." Some of these may possibly find their way into the germinal ridge; some probably undergo atrr)])]iy, wliilc others may persist and become the seat of dermoid tumors. Epithelium ■ Tunica albuginea Supporting cell -Interstitial cell , Genital cell The Testis. — The testis is developed in much the same way as the ovary. Like the ovary, in its earhest stages it consists of a central mass of epithelium covered by a surface epithelium. In the central mass a series of cords appear (Fig. 223), and the periphery of the mass is converted into the tunica albuginea, thus excluding the surface epithelium from any part in the formation of the tissue of the testis. The cords of the central mass run together toward the future hilus and form a network which ultimately becomes the rete testis. From the cords the seminiferous tubules are developed, and between them connective tissue septa extend. The seminiferous tubules become connected with outgrowths from the Wolffian body, which, as before mentioned, form the efferent ducts of the testis. Descent of the Testes. — The testes, at an early period of fetal life, are placed at the back part of the abdominal cavity, behind the peritoneum, and each is attached by a peritoneal fold, the mesorchium, to the mesonephros. From the front of the mesonephros a fold of peritoneum termed the inguinal fold grows forward to meet and fuse with a peritoneal fold, the inguinal crest, which grows backward from the antero-lateral abdominal wall. The testis thus ac- quires an indirect connection with the anterior abdominal wall; and at the same time a portion of the peri- toneal cavity lateral to these fused folds is marked off as the future saccus vaginalis. In the inguinal crest a peculiar structure, the guber- naculum testis, makes its appearance. This is at first a slender band, ex- tending from that part of the skin of the groin which afterward forms the scrotum through the inguinal canal to the body and epididymis of the testis. As development advances, the peritoneum enclosing the gubernaculum forms two folds, one above the testis and the other below it. The one above the testis is the plica vascularis, and con- tains ultimately the internal spermatic vessels; the one below, the plica guber- natrix, contains the lower part of the gubernaculum, which has now grown into a thick cord; it ends below^ at the abdominal inguinal ring in a tube of peritoneum, the saccus vaginalis, which protrudes itself down the inguinal canal. By the fifth month the lower part of the gubernaculum has become a thick cord, while the upper part has disappeared. The lower part now consists of a central core of unstriped muscle fibre, and outside this of a firm layer of striped elements, con- nected, behind the peritoneum, with the abdominal wall. As the scrotum develops, the main portion of the lower end of the gubernaculum is carried, with the skin to which it is attached, to the bottom of this pouch; other bands are carried to the medial side of the thigh and to the perineum. The tube of peritoneum con- stituting the saccus vaginalis projects itself downward into the inguinal canal, and emerges at the cutaneous inguinal ring, pushing before it a part of the Obliquus internus and the aponeurosis of the Obliqims externus, which form respectively Fig 223. — Section of a genital cord of the testis of a human embryo 3.5 cm. long. (Felix and Buhler.) DEVELOPMENT OF THE URIXARY AXD GEXERATIVE ORG AX S 187 the Cremaster muscle and the iiitererural fascia. It forms a grachiahy elongating poiichj which eventually reaches the bottom of the scrotum, and behind this pouch the testis is drawn by the growth of the body of the fetus, for the gubernaculum does not grow commensurately with the growth of other parts, and therefore the testis, being attached by the gubernaculum to the bottom of the scrotum, is prevented from rising as the body grows, and is drawn first into the inguinal canal and eventually into the scrotum. It seems certain also that the guber- nacular cord becomes shortened as development proceeds, and this assists in caus- ing the testis to reach the bottom of the scrotum. By the end of the eighth month the testis has reached the scrotum, preceded by the saccus vaginalis, which com- municates by its upper extremity with the peritoneal cavity. Just before birth the upper part of the saccus vaginalis usually becomes closed, and this obliteration extends gradually downward to within a short distance of the testis. The process of peritoneum surrounding the testis is now entirely cut off from the general peri- toneal cavity and constitutes the tunica vaginalis. Descent of the Ovaries. — In the female there is also a gubernaculum, which effects a considerable change in the position of the ovary, though not so extensive a change as in that of the testis. The gubernaculum in the female lies in contact with the fundus of the uterus and contracts adhesions to this organ, and thus the ovary is prevented from descending below this level. The part of the guber- naculum between the ovary and the uterus becomes ultimately the proper ligament of the ovary, while the part between the uterus and the labium majus forms the round ligament of the uterus. A pouch of peritoneum analogous to the saccus vaginalis in the male accompanies it along the inguinal canal: it is called the canal of Nuck. In rare cases the gubernaculum may fail to contract adhesions to the uterus, and then the ovary descends through the inguinal canal into the labium majus, and under these circumstances its position resembles that of the testis. Wolffian duct AUantois \ Kidney diveiiicidum Umbilical cord I | ] Rectum J Umbilical vessch Hiiul-gut yofochord Fig. 224. — Tail end of human embryo twenty- five to twenty-nine daj'S old. (From model by Keibel.) Fig. 225. — Tail end of human embrj'o thirty-two to thirty-three days old. (From model by Keibel.) The Metanephros and the Permanent Kidney. — The rudiments of the perma- nent kidneys make their appearance about the end of the first or the beginning of the second month. Each kidney has a two-fold origin, part arising from the metanephros, and part as a diverticulum from the hind-end of the Wolffian duct, close to where the latter opens into the cloaca (Figs. 224, 225). The metanephros arises in the intermediate cell mass, caudal to the mesonephros, which it resembles in structure. The diverticulum from the Wolffian duct grows dorsalward and forward along the posterior abdominal wall, where its blind extremity expands and subsequently divides into several buds, which form the rudiments of the pelvis and calices of the kidney; by continued growth and subdivision it gives rise to the collecting tubules of the kidne}'. The proximal portion of the diver- ticulum becomes the ureter. The secretory tubules are developed from the 188 EMBRYOLOGY Ureter Wolffian duct \ MhUpi tan di Bladde-) Symphysis pubis metanephros, which is moulded over the growing end of the diverticuhim from the Wolffian duct. The tubules of the metanephros, unlike those of the pronephros and mesonephros, do not open into the Wolffian duct. One end expands to form a glomerulus, while the rest of the tubule rapidly elongates to form the convoluted and straight tubules, the loops of Henle, and the connecting tubules; these last join and establish communications with, the collecting tubules derived from the ultimate ramifications of the diverticulum from the Wolffian duct. The mesoderm around the tubules be- comes condensed to form the connec- tive tissue of the kidney. The ureter opens at first into the hind-end of the Wolffian duct; after the sixth week it separates from the Wolffian duct, and opens independently into the part of the cloaca which ultimately becomes the bladder (Figs. 226, 227). The secretory tubules of the kid- ney become arranged into pyramidal masses or lobules, and the lobulated condition of the kidneys exists for some time after birth, while traces of it may be found even in the adult. The kidnej^ of the ox and many other animals remains lobulated throughout life. The Urinary Bladder. — The bladder is formed partly from the entodermal cloaca and partly from the ends of the Wolffian ducts; the allantois takes no share in its formation. After the separation of the rectum from the dorsal part of the Glans penis Urethra Vertebral column Fig. 226. — Tail end of human embryo; from eight and a half to nine weeks old. (From model by Keibel.) Wolffian duct Hind-gut Bladder Outer zone\ > of kidney Inner zone) Pelvis of kidney Urogenital membrane Fig. 227. — Primitive kidney and bladder, from a reconstruction. (After Schreiner.) cloaca (p. 172), the ventral part becomes subdivided into three portions: (1) an anterior vesico-urethral portion, continuous with the allantois — into this portion the Wolffian ducts open; (2) an intermediate narrow channel, the pelvic portion; and (3) a posterior phallic portion, closed externally by the urogenital membrane (Fig. 227). The second and third parts together constitute the urogenital sinus. The DEVELOPMENT OF THE URIXARY AND GENERATIVE ORGANS 189 vesico-urethral portion absorbs the ends of the Wolffian ducts and the associated ends of the renal diverticula, and these give rise to the trigone of the bladder and part of the prostatic urethra. The remainder of the vesico-urethral portion forms the body of the bladder and part of the prostatic urethra; its apex is prolonged to the umbilicus as a narrow canal, which later is obhterated and becomes the medial umbilical ligament (urachus). Umbilical cord Genital tubercle Hind-linib Cloaca Tail Genital tubercle — • habiiun majus — — Labium mimm Urogenital meinbrane Glana penis Sci-otal swelling Edge of groove on phallus' Opening ofurogmital sin us PeriTietfm ~ Anus Glans clitoridie Labium majus Labium minus Opening of urogenital sinus Peri^iieum Glans penis Cavernous urethra Scrotum Raphe AniLS - Prepuce - Glans clitoridis Labium majits Labium miiiu-s Fig. 228. — Stages in the development of the external .sexual organs in the male and female. (Drawn from the Ecker-Ziegler models.) The Prostate.— The prostate originally consists of two separate portions, each of which arises as a series of diverticular buds from the epithelial lining of the uro- genital sinus and vesico-urethral part of the cloaca, between the third and fourth months. These buds become tubular, and form the glandular substance of the two lobes, which ultimately meet and fuse behind the urethra and also extend on to its ventral aspect. The isthmus or middle lobe is formed as an extension of the lateral 190 EMBRYOLOGY lobes between the common ejaculatory ducts and the })hidder. Skene's ducts in the female urethra are regarded as the homologues of the prostatic glands. The bulbo-urethral glands of Cowper in the male, and greater vestibular glands of Bartholin in the female, also arise as diverticula from the epithelial lining of the urogenital sinus. The External Organs of Generation (Fig. 22S). — As already stated (page 172), the cloacal membrane, composed of ectoderm and entoderm, originally reaches from the umbilicus to the tail. The mesoderm extends to the midventral line for some distance behind the umbilicus, and forms the lower part of the abdominal wall; it ends below in a prominent swelling, the cloacal tubercle. Behind this tubercle the urogenital part of the cloacal membrane separates the ingrowing sheets of mesoderm. The first rudiment of the penis (or clitoris) is a structure termed the phallus; it is derived from the phallic portion of the cloaca which has extended on to the end and sides of the under surface of the cloacal tubercle. The terminal part of the phallus representing the future glans becomes solid; the remainder, which is hollow, is converted into a longitudinal groove by the absorption of the urogenital membrane. In the female a deep groove forms around the phallus and separates it from the rest of the cloacal tubercle, which is now termed the genital tubercle. The sides of the genital tubercle grow backward as the genital swellings, which ultimately form the labia majora; the tubercle itself becomes the mons pubis. The labia minora arise by the continued growth of the lips of the groove on the under surface of the phallus; the remainder of the phallus forms the clitoris. In the male the early changes are similar, but the pelvic portion of the cloaca undergoes much greater development, pushing before it the phallic portion. The genital swellings extend around between the pelvic portion and the anus, and form a scrotal area; during the changes associated with the descent of the testes this area is drawn out to form the scrotal sacs. The penis is developed from the phallus. As in the female, the urogenital membrane undergoes absorption, forming a channel on the under surface of the phallus; this channel extends only as far forward as the corona glandis. The corpora cavernosa of the penis (or clitoris) and of the urethra arise from the mesodermal tissue in the phallus; they are at first dense structures, but later vascular spaces appear in them, and they gradually become cavernous. The prepuce in both sexes is formed by the growth of a solid plate of ectoderm into the superficial part of the phallus; on coronal section this plate presents the shape of a horseshoe. By the breaking down of its more centrally situated cells the plate is split into two lamellae, and a cutaneous fold, the prepuce, is liberated and forms a hood over the glans. "Adherent prepuce is not an adhesion really, but a hindered central desquamation" (Berry Hart, oy. cit.). The Urethra. — As already described, in both sexes the phallic portion of the cloaca extends on to the under surface of the cloacal tubercle as far forward as the apex. At the apex the walls of the phallic portion come together and fuse, the lumen is obliterated, and a solid plate, the urethral plate, is formed. The remainder of the phallic portion is for a time tubular, and then, by the absorption of the urogenital membrane, it establishes a communication with the exterior; this open- ing is the primitive urogenital ostium, and it extends forward to the corona glandis. In the female this condition is largely retained; the portion of the groove on the clitoris broadens out while the body of the clitoris enlarges, and thus the adult urethral opening is situated behind the base of the clitoris. In the male, by the greater growth of the pelvic portion of the cloaca a longer urethra is formed, and the primitive ostium is carried forward with the phallus, but it still ends at the corona glandis. Later it closes from behind forward. Mean- FORM OF THE EMBRYO AT DIFFERENT STAGES OF ITS GROWTH 191 while the urethral plate of the glaiis breaks down centrally to form a median groove continuous with the primitive ostium. This groove also closes from behind forward, so that the external urethral opening is shifted forward to the end of the glans. THE FORM OF THE EMBRYO AT DIFFERENT STAGES OF ITS GROWTH. First Week. — During this period the ovum is in the uterine tube. Having been fertilized in the upper part of the tube, it slowly passes down, undergoing segmentation, and reaches the uterus. Peters' described a specimen, the age of which he reckoned as from three to four days. It was imbedded in the decidua on the posterior wall of the uterus and enveloped by a decidua capsularis, the central part of which, however, consisted merely of a layer of fibrin. The ovum was in the form of a sac, the outer wall of which consisted of a layer of trophoblast; inside this was a thin layer of mesoderm composed of round, oval, and spindle-shaped cells. Numerous villous processes — some consisting of trophoblast only, others possessing a core of mesoderm — pi-ojected from the surface of the ovum into the surrounding decidua. Inside this sac the rudi- ment of the embryo was found in the form of a patch of ectoderm, covered by a small but com- pletely closed amnion. It possessed a minute yolk-sac and was surrounded by mesoderm, which was connected by a band to that Hning the trophoblast (Fig. 88).- Heart Amnion Bochj-stalh Chorion Fig. 229. — Human embryo about fifteen day.s old. (His.) Second Week. — By the end of this week the ovum has increased considerably in size, and the majority of its villi are vascularized. The embryo has assumed a definite form, and its cephahc and caudal extremities are easily distinguished. The neural folds are partly united. The embryo is more completely separated from the yolk-sac, and the paraxial mesoderm is being divided into the primitive segments (Fig. 229). Third Week. — By the end of the third week the embryo is strongly curved, and the primitive segments number about thirty. The primary divisions of the brain are visible, and the optic and auditory vesicles are formed. Four branchial grooves are present: the stomodeum is well- marked, and the buccopharyngeal membrane has disappeared. The rudiments of the limbs are seen as short buds, and the Wolffian bodies are visible (Fig. 230). Fourth Week. — The embryo is markedly curved on itself, and when viewed in profile is almost circular in outfine. The cerebral hemispheres appear as hoUow buds, and the elevations which form the rudiments of the auricula are visible. The hmbs now appear as oval flattened projec- tions (Fig. 231). Fifth Week. — The embryo is less curved and the head is relatively of large size. Differentiation of the limbs into their segments occurs. The nose forms a short, flattened projection. The cloacal tubercle is evident (Fig. 232). 1 Die Einbettung des niensohlichen Eies, 1899. - Bryce and Teacher (Earbj Deielopment and Imbedding of the Human Ovum, 190S) have described an ovum which they regard as thirteen to fourteen days old. In it the two vesicles, the amnion and yolk-sac, were present, but there was no trace of a layer of embryonic ectoderm. They are of opinion that the age of Peters' ovum has been understated, and estimate it as between thirteen and one-half and fourteen and one-half days. 192 EMBRYOLOGY Sixth Week. — The curvature of the embrj'o is further diniini.shed. The branchial grooves — except the first — have disappeared, and the rudiments of the fingers and toes can be recognized (Fig. 233). Mid-hrain y^ V/ Hind-hrain Fore-hrain ~~f hj On Auditor ij vesicle Sto7}iodeu7n ^ A, % yJQr-fvqJ Mandibular arch' \\ arches Heart \\ .*lJ1 a -Amnion {cut) Body-stalk Fig. 230. — Human embryo between eighteen and twenty-one days old. (His.) Seventh and Eighth Weeks. — The flexure of the head is gradually reduced and the neck is somewhat lengthened. The upper hp is completed and the nose is more prominent. The nostrils are directed forward and the palate is not completely developed. The eyehds are present in the shape of folds above and below the eye, and the different parts of the auricula are distinguish- able. By the end of the second month the fetus measures from 28 to 30 mm. in length (Fig. 234). Heart Fore-limb Hyoid arch 2Iandibular arch Maxillary process ^ Eye J' Olfactory pit Chorion Fig. 231. — Human embryo, twenty-seven to thirty days old. (His.) Third Month. — The head is extended and the neck is lengthened. The eyehds meet and fuse, remaining closed imtil the end of the sixth month. The hmbs are well-developed and nails appear on the digits. The external generative organs are so far differentiated that it is possible to dis- tinguish the sex. By the end of this month the length of the fetus is about 7 cm., but if the legs be included it is from 9 to 10 cm. Fourth Month. — The loop of gut which projected into the umbihcal cord is withdrawn within the fetus. The hairs begin to make their appearance. There is a general increase in size so that by the end of the fourth month the fetus is from 12 to 13 cm. in length, but if the legs be included it is from 16 to 20 cm. FORM OF THE EMBRYO AT DIFFERENT STAGES OF ITS GROWTH 193 Fifth Month. — It is during this mouth that the first movements of the fetus are usually ob- served. The erujition of hair on the head commences, and the veniix caseosa beguis to be deposited. Bj- the end of tliis month the total length of the fetus, including the legs, is from 25 to 27 cm. Heart Hyoid arch Mandibular a'>rJi Maxilla) y pi ore Ell Fore-limb Hind-limb Fig. 232. — Human embrj'o, thirty-one to thirtj'-foiir days old. (His.) Sixth Month. — The body is covered b}'- fine hairs (lanugo) and the deposit of vernix caseosa is considerable. The papillae of the skin are developed and the free border of the nail projects from the corium of the dermis. Measured from vertex to heels, the total length of the fetus at the end of this month is from 30 to 32 cm. Auricula Fore-limb Hind-linib Umbilical cord Fig. 23.3. — Human embrvo of about sis weeks. (His,) Fig. 234. — Human embryo about eight and a half weeks old. (His.) Seventh Month. — The pupillary membrane atrophies and the eyelids are open. The testis descends with the vaginal sac of the peritoneum. From vertex to heels the total length at the end of the seventh month is from 35 to 36 cm. The weight is a little over thi-ee pounds. 13 194 EMBRYOLOGY Eighth Month. — The skin assumes a pink color and is now entirely coated with vernix caseosa, and the lanugo begins to disappear. Subcutaneous fat has been developed to a considerable extent, and the fetus presents a plump appearance. The total length, i. e., from head to heels, at the end of the eighth month is about 40 cm., and the weight varies between four and one-half and five and one-half pounds. Ninth Month. — The lanugo has largely disappeared from the trunk. The umbilicus is almost in the middle of the body and the testes are in the scrotum. At full time the fetus weighs from six and one-half to eight pounds, and measm-es from head to heels about 50 cm. OSTEOLOGY. npHE general framework of the body is built up mainly of a series of bones, -L supplemented, however, in certain regions by pieces of cartilage; the bony part of the framework constitutes the skeleton. In comparative anatomy the term skeleton has a wider application, since in some of the lower animals hard, protecting and supporting structures are developed in association with the integumentary system. In such animals the skeleton is described as consisting of an internal or deep skeleton, the endoskeleton, and an external or superficial, the exoskeleton. In the human subject the exoskeleton is extremely rudimentary, its only important representatives being the nails and the enamel of the teeth. The term skeleton is, therefore, confined to the endoskeleton, and this is divisible into an axial part, which includes that of the head and trunk, and an appendicular part, which comprises that of the extremities or limbs. In the skeleton of the adult there are 206 distinct bones, as follows: — Axial Skeleton Vertebral column . . . . .26 Skull 22 Hyoid bone ... . . . .1 Ribs and sternum . . . . .25 74 Appendicular f Upper extremities . . . . .64 Skeleton \ Lower extremities . . . . .62 — 126 Auditory ossicles ........ 6 Total 206 The patellse are included in this enumeration, but the smaller sesamoid bones are not reckoned. Bones are divisible into four classes: Long, Short, Flat, and Irregular. Long Bones. — The long bones are found in the limbs, and each consists of a body or shaft and two extremities. The body, or diaphysis is cylindrical, with a central cavity termed the medullary canal; the wall consists of dense, compact tissue of considerable thickness in the middle part of the body, but becoming thinner toward the extremities; within the medullary canal is some cancellous tissue, scanty in the middle of the body but greater in amount toward the ends. The extremities are generally expanded, for the purposes of articulation and to afford broad surfaces for muscular attachment. They are usually developed from sep- arate centres of ossification termed epiphyses, and consist of cancellous tissue surrounded by thin compact bone. The medullary canal and the spaces in the cancellous tissue are filled with marrow. The long bones are not straight, but curved, the curve generally taking place in two planes, thus affording greater strength to the bone. The bones belonging to this class are: the clavicle, humerus, radius, ulna, femur, tibia, fibula, metacarpals, metatarsals, and phalanges. 196 OSTEOLOGY Short Bones. — Where a part of the skeleton is intended for strength and com- pactness combined with limited movement, it is constructed of a number of short bones, as in the carpus and tarsus. These consist of cancellous tissue covered by a thin crust of compact substance. The patellae, together with the other sesamoid bones, are by some regarded as short bones. Flat Bones. — Where the principal requirement is either extensive protection or the provision of broad surfaces for muscular attachment, the bones are expanded into broad, flat plates, as in the skull and the scapula. These bones are composed of two thin layers of compact tissue enclosing between them a variable quantity of cancellous tissue. In the cranial bones, the layers of compact tissue are famili- arly known as the tables of the skull; the outer one is thick and tough; the inner is thin, dense, and brittle, and hence is termed the vitreous table. The intervening cancellous tissue is called the diploe, and this, in certain regions of the skull, becomes absorbed so as to leave spaces filled with air {air-sinuses) between the two tables. The flat bones are: the occipital, parietal, frontal, nasal, lacrimal, vomer, scapula, os coxae {hiy hone), sternum, ribs, and, according to some, the patella. Irregular Bones. — The irregular bones are such as, from their peculiar form, cannot be grouped under the preceding heads. They consist of cancellous tissue enclosed within a thin layer of compact bone. The irregular bones are: the vertebrae, sacrum, coccyx, temporal, sphenoid, ethmoid, zygomatic, maxilla, mandible, palatine, inferior nasal concha, and hyoid. Surfaces of Bones. — If the surface of a bone be examined, certain eminences and depressions are seen. These eminences and depressions are of two kinds: articular and non-articular. Well-marked examples of articular eminences are found in the heads of the humerus and femur; and of articular depressions in the glenoid cavity of the scapula, and the acetabulum of the hip bone. Non-articular eminences are designated according to their form. Thus, a broad, rough, uneven elevation is called a tuberosity, protuberance, or process, a small, rough prominence, a tubercle ; a sharp, slender pointed eminence, a spine ; a narrow, rough elevation, running some way along the surface, a ridge, crest, or line. Non-articular depres- sions are also of variable form, and are described as fossae, pits, depressions, grooves, furrows, fissures, notches, etc. These non-articular eminences and depressions serve to increase the extent of surface for the attachment of ligaments and muscles, and are usually well-marked in proportion to the muscularity of the subject; the grooves, fissures, and notches transmit tendons, vessels, or nerves. The minute structure, growth, and composition of bone are described on pages 50 to 59. THE VERTEBRAL COLUMN (COLUMNA VERTEBRALIS ; SPINAL COLUMN). The vertebral column is a flexuous and flexible column, formed of a series of bones called vertebrae. The vertebrae are thirty-three in number, and are grouped under the names cervical, thoracic, lumbar, sacral, and coccygeal, according to the regions they occupy; there are seven in the cervical region, twelve in the thoracic, five in the lumbar, five in the sacral, and four in the coccygeal. This number is sometimes increased by an additional vertebra in one region, or it may be diminished in one region, the deficiency being supplied by an addi- tional vertebra in another. The number of cervical vertebrae is, however, very rarely increased or diminished. The vertebrae in the upper three regions of the column remain distinct through- out life, and are known as true or movable vertebrae; those of the sacral and GENERAL CHARACTERISTICS OF A VERTEBRA 197 coccygeal regions, on the other hand, are termed false or fixed vertebrai, because they are united with one another in the adult to form two bones — five forming the upper bone or sacrum, and four the terminal bone or coccyx. With the exception of tlio first and second cervical, the true or movable vertebrae present certain common characteristics which are best studied by examining one from the middle of the thoracic region. GENERAL CHARACTERISTICS OF A VERTEBRA. A typical vertebra consists of two essential parts — viz., an anterior segment, the body, and a posterior part, the vertebral or neural arch; these enclose a foramen, the vertebral foramen. The vertebral arch consists of a pair of pedicles and a pair of laminae, and supports seven processes — viz., four articular, two transverse, and one spinous. When the vertebrae are articulated with each other the bodies form a strong pillar for the support of the head and trunk, and the vertebral foramina constitute a canal for the protection of the medulla spinalis (spinal cord), while between every pair of vertebrae are two apertures, the intervertebral foramina, one on either side, for the transmission of the spinal nerves and vessels. Body {corpus vertebrae). — The body is the largest part of a vertebra, and is more or less cylindrical in shape. Its upper and lower surfaces are flattened and rough, and give attachment to the intervertebral fibrocartilages, and each presents a rim around its circumference. In front, the body is convex from side to side and concave from above downward. Behind, it is flat from above downward and slightly concave from side to side. Its anterior surface presents a few small apertures, for the passage of nutrient vessels; on the posterior surface is a single large, irregular aperture, or occasionally more than one, for the exit of the basi- vertebral veins from the body of the vertebra. Pedicles (radices arci vertebrae) . — The pedicles are two short, thick processes, which project backward, one on either side, from the upper part of the body, at the junction of its posterior and lateral surfaces. The concavities above and below the pedicles are named the vertebral notches; and when the vertebrae are articulated, the notches of each contiguous pair of bones form the intervertebral foramina, already referred to. Laminae. — The laminae are two broad plates directed backward and medialward from the pedicles. They fuse in the middle line posteriorly, and so complete the posterior boundary of the vertebral foramen. Their upper borders and the lower parts of their anterior surfaces are rough for the attachment of the ligamenta flava. Processes. — Spinous Process (processus spinosus). — The spinous process is directed backward and downward from the junction of the laminae, and serves for the attachment of muscles and ligaments. Articular Processes. — The articular processes, two superior and two inferior, spring from the junctions of the pedicles and laminae. The superior project upward, and their articular surfaces are directed more or less back\\^ard; the inferior project downward, and their surfaces look more or less forward. Transverse Processes (processus transmrsi). — ^The transverse processes, two in number, project one at either side from the point where the lamina joins the pedicle, between the superior and inferior articular processes. They serve for the attachment of muscles and ligaments. Structure of a Vertebra (Fig. 235). — The body is composed of cancellous tissue, covered by a thin coating of compact bone; the lat/ter is perforated by numerous orifices, some of large size 198 OSTEOLOGY for the passage of vessels; the interior of the bone is traversed by one or two large canals, for the reception of veins, which converge toward a single large, irregular apertun;, or several small apertures, at the posterior j)art of the body. The arch and processes pro- jecting from it have thick coverings . of compact tissue. Fig. 23.5. — Sagittal section of a lumbar vertebra. The Cervical Vertebrae (Verte- brae Cervicales). The cervical vertebrae (Fig. 236) are the .smallest of the true vertebrae, and can be readily distinguished from those of the thoracic or lumbar regions by the presence of a foramen in each transverse process. The first, second, and seventh present exceptional features and must be separately described; the following characteristics are common to the remaining four. The body is small, and broader from side to side than from before backward The anterior and posterior surfaces are flattened and of equal depth; the former is placed on a lower level than the latter, and its inferior border is prolonged downward, so as to overlap the upper and forepart of the vertebra below. The upper surface is concave transversely, and presents a projecting lip on either side; the lower surface is concave from before backward, convex from side to side, and presents laterally shallow concavities which receive the corresponding projecting lips of the subjacent vertebra. The pedicles are directed lateralward and backward, Aniei'ior tubercle of transverse process Foramen, transversariwtn Posterior tubercle of transverse process j Spinous ' process Fig. 236. — A cervical vertebra. Transverse process Superior articular process Inferior articular process and are attached to the body midway between its upper and lower borders, so that the superior vertebral notch is as deep as the inferior, but it is, at the same time, narrower. The laminae are narrow, and thinner above than below; the vertebral foramen is large, and of a triangular form. The spinous process is short and bifid, the two divisions being often of unequal size. The superior and inferior articular processes on either side are fused to form an articular pillar, which projects lateral- ward from the junction of the pedicle and lamina. The articular facets are flat and of an oval form: the superior look backward, upward, and slightly medial- ward: the inferior forward, downward, and slightly lateralward. The transverse processes are each pierced by the foramen trans versarium, which, in the upper six ^'ertebrae, gives passage to the vertebral artery and vein and a plexus of sympa- THE CERVICAL VERTEBRA 199 thetic nerves. Each process consists of an anterior and a posterior part. The anterior portion is the homologne of the rib in the thoracic region, and is there- fore named the costal process or costal element: it arises from the side of the body, is directed laterahvard in front of the foramen, and ends in a tubercle, the tuber- culum anterius. TJie posterior part, the true transverse process, springs from the vertebral arch behind the foramen, and is directed forward and lateralward; it ends in a flattened vertical tubercle, the tuberculum posterius. These two parts are joined, outside the foramen, by a bar of bone wliieli exhibits a deep sulcus on its upper surface for the passage of the corresponding spinal nerve.^ Chassaignac first pointed out that the common carotid artery can be easily compressed against the anterior tubercle of the transverse process of the sixth cervical vertebra, and therefore this tubercle is named the tuberculum caroticum or Chassaignac' s tubercle. It also constitutes an im- portant guide to the vertebral artery which enters the foramen transversarium of this vertebra. Anterior tubercle Transverse 'process Outline of section of odontoid process Outline of section of trans- verse atlantal ligament Foramen transver- sarium Groove for vertebral artery and first cervical nerve Posterior tubercle Fig. 237. — First cervical vertebra, or atlas. First Cervical Vertebra. — The first cervical vertebra (Fig. 237) is named the atlas because it supports the globe of the head. Its chief peculiarity is that it has no body, and this is due to the fact that the body of the atlas has fused with that of the next vertebra. Its other peculiarities are that it has no spinous process, is ring-like, and consists of an anterior and a posterior arch and two lateral masses. The anterior arch forms about one-fifth of the ring: its anterior surface is convex, and presents at its centre the anterior tubercle for the attachment of the Longus colli muscles; posteriorly it is concave, and marked by a smooth, oval or circular facet (fovea dentis), for articulation with the odontoid process {dens) of the axis. The upper and lower borders respectively give attachment to the anterior atlanto- occipital membrane and the anterior atlantoaxial ligament; the former connects it with the occipital bone above, and the latter with the axis below. The posterior arch forms about two-fifths of the circumference of the ring: it ends behind in the posterior tubercle, which is the rudiment of a spinous process and gives origin to the Recti capitis posteriores minores. The diminutive size of this process pre- vents any interference with the movements between the atlas and the skull. The posterior part of the arch presents above and behind a rounded edge for the attachment of the posterior atlantooccipital membrane, while immediately behind each superior articular process is a groove (sidciis arteriae vertehralis) , sometimes converted into a foramen by a delicate bony spiculum which arches backward from the posterior end of the superior articular process. This groove represents the superior vertebral notch, and serves for the transmission of the vertebral artery, which, after ascending through the foramen in the transverse ' The costal element of a cervical vertebra not only includes the portion which springs from the side of the body, but the anterior and posterior tubercles and the bar of bone which connects them (Fig. 97) . 200 OSTEOLOGY process, winds around the lateral mass in a direction backward and medialward; it also transmits the suboccipital (first spinal) nerve. On the under surface of the posterior arch, behind the articular facets, are two shallow grooves, the inferior vertebral notches. The lower border gives attachment to the posterior atlanto- axial ligament, which connects it with the axis. The lateral masses are the most bulky and solid parts of the atlas, in order to support the weight of the head. Each carries two articular facets, a superior and an inferior. The superior facets are of large size, oval, concave, and approach each other in front, but diverge behind: they are directed upward, medialward, and a little backward, each forming a cup for the corresponding condyle of the occipital bone, and are admirably adapted to the nodding movements of the head. Not infrequently they are partially subdivided by indentations which encroach upon their margins. The inferior articular facets are circular in form, flattened or slightly convex and directed downward and medialward, articulating with the axis, and permitting the rotatory movements of the head. Just below the medial margin of each superior facet is a small tubercle, for the attachment of the transverse atlantal ligament w^hich stretches across the ring of the atlas and divides the vertebral foramen into two unequal parts — the anterior or smaller receiving the odontoid process of the axis, the posterior transmitting the medulla spinalis and its membranes. This part of the vertebral canal is of considerable size, much greater than is required for the accommodation of the medulla spinalis, and hence lateral displacement of the atlas may occur without compression of this structure. The transverse processes are large; they project lateralward and downward from the lateral masses, and serve for the attachment of muscles which assist in rotating the head. They are long, and their anterior and posterior tubercles are fused into one mass; the foramen transversarium is directed from below, upward and backward. Odontoid process Rough surface for alar ligament Groove for transverse atlantal ligament Spinous process-^ Articular facet for anterior arch of atlas Body Transverse process Inferior articular process Fig. 238. — Second cervical vertebra, epistropheus, or axis. Second Cervical Vertebra. — The second cervical vertebra (Fig. 2.38) is named the epistropheus or axis because it forms the pivot upon which the first vertebra, carrying the head, rotates. The most distinctive characteristic of this bone is the strong odontoid process which rises perpendicularly from the upper surface of the body. The body is deeper in front than behind, and prolonged downward anteriorly so as to overlap the upper and fore part of the third vertebra. It pre- sents in front a median longitudinal ridge, separating two lateral depressions for the attachment of the Longus colli muscles. Its under surface is concave from before backw^ard and covex from side to side. The dens or odontoid process exliibits a slight constriction or neck, w^here it joins the body. On its anterior surface is an oval or nearly circular facet for articulation with that on the anterior arch THE THORACIC VERTEBRM 201 Body. of the atlas. On the back of the neck, and frequently extending on to its lateral surfaces, is a shallow groove for the transverse atlantal ligament which retains the process in position. The apex is pointed, and gives attachment to the middle alar ligament; below the apex the process is somewhat enlarged, and presents on either side a rough impression for the attachment of the lateral alar ligament; these ligaments connect the process to the occipital bone. The internal structure of the odontoid process is more compact than that of the body. The pedicles are broad and strong, especially in front, where they coalesce with the sides of the body and the root of the odontoid process. They are covered above by the superior articular surfaces. The laminae are thick and strong, and the vertebral foramen large, but smaller than that of the atlas. The transverse processes are very small, and each ends in a single tubercle; each is perforated by the foramen transversarium, which is directed obliquely upward and lateralward. The superior articular surfaces are round, slightly convex, directed upward and lateralward, and are supported on the body, pedicles, and transverse processes. The inferior articular surfaces have the same direction as those of the other cervical vertebrse. The supe- rior vertebral notches are very shal- low, and lie behind the articular processes; the inferior lie in front of the articular processes, as in the other cervical vertebrae. The spinous process is large, very strong, deeply channelled on its under surface, and presents a bifid, tuberculated extremity. The Seventh Cervical Vertebra (Fig. 239).— The most distinctive characteristic of this vertebra is the existence of a long and promi- nent spinous process, hence the name vertebra prominens. This pro- cess is thick, nearly horizontal in direction, not bifurcated, but ter- minating in a tubercle to which the lower end of the ligamentum nuchae is attached. The transverse processes are of considerable size, their posterior roots are large and prominent, while the anterior are small and faintly marked; the upper surface of each has usually a shallow sulcus for the eighth spinal nerve, and its extremity seldom presents more than a trace of bifurcation. The foramen transversarium may be as large as that in the other cervical vertebrae, but is generally smaller on one or both sides; occasionally it is double, sometimes it is absent. On the left side it occasionally gives passage to the vertebral artery; more frequently the vertebral vein traverses it on both sides; but the usual arrangement is for both artery and vein to pass in front of the transverse pro- cess, and not through the foramen. Sometimes the anterior root of the trans- verse process attains a large size and exists as a separate bone, which is known as a cervical rib. Spinous process Fig. 239. — Seventh cervical vertebra. The Thoracic Vertebrae (Vertebrae Thoracales). The thoracic vertebrae (Fig. 240) are intermediate in size between those of the cervical and lumbar regions; they increase in size from above downward the 202 OSTEOLOGY upper vertebrse being much smaller than those in the lower part of the region. They are distinguished by the presence of facets on the sides of the bodies for articulation with the heads of the ribs, and facets on the transverse processes of all, except the eleventh and twelfth, for articulation with the tubercles of the ribs. The bodies in the middle of the thoracic region are heart-shaped, and as broad in the antero-posterior as in the transverse direction. At the ends of the thoracic region they resemble respectively those of the cervical and lumbar vertebrae. They are slightly thicker behind than in front, flat above and below, convex from side to side in front, deeply concave behind, and slightly constricted laterally and in front. They present, on either side, two costal demi-facets, one above, near the root of the pedicle, the other below, in front of the inferior vertebral notch; these are covered with cartilage in the recent state, and, when the vertebrae are articulated with one another, form, with the intervening intervertebral fibro- cartilages, oval surfaces for the reception of the heads of the ribs. The pedicles are directed backward and slightly upward, and the inferior vertebral notches are of large size, and deeper than in any other region of the vertebral column. Superior articiilar process Facet for articular part of tubercle of rib ^ Demi-facet for head of rib Demi-facet for head of rib Inferior articular process Fig. 240. — A thoracic vertebra. The laminae are broad, thick, and imbricated — that is to say, they overlap those of subjacent vertebrae like tiles on a roof. The vertebral foramen is small, and of a circular form. The spinous process is long, triangular on coronal section, directed obliquely downward, and ends in a tuberculated extremity. These processes overlap from the fifth to the eighth, but are less obliciue in direction above and below.^ The superior articular processes are thin plates of bone projecting upward from the junctions of the pedicles and laminae; their articular facets are practi- cally flat, and are directed backw^ard and a little lateralward and upward. The inferior articular processes are fused to a considerable extent with the laminae, and project but slightly beyond their lower borders; their facets are directed forward and a little medialward and downward. The transverse processes arise from the arch behind the superior articular processes and pedicles; they are thick, strong, and of considerable length, directed obliquely backw-ard and lateralward, 1 In quadrupeds the majority of the spinous processes of the thoracic vertebrae project upward and backward, while those of the lumbar region are directed upward and forward. The change in inclination is effected in one of the lower thoracic vertebrae, the spine of which points almost directly upward. This vertebra is known as the anticlinal, and in man its representative is the eleventh thoracic. THE THORACIC VERTEBRA 203 and each ends in a clubbed extremity, on the front of which is a small, concave surface, for articulation with the tubercle of a rib. The first, ninth, tenth, eleventh, and twelfth thoracic vertebrae present certain peculiarities, and must be specially considered (Fip;. 241). An entire facet above, a demi-facct below A demi-facet above — One entire facet One entire facet. No facet on trans, proc. which is rudimentary One entire facet. (No facet on trans- I verse process. - Infer. artic.j}rocess convex and turned \lateralicards Fig. 241. — Peculiar thoracic vertebrae. The First Thoracic Vertebra has, on either side of the body, an entire articular facet for the head of the first rib, and a demi-facet for tlie upper half of the head of the second rib. The body is like that of a cervical vertebra, being broad trans- versely; its upper surface is concave, and lipped on either side. The superior articular surfaces are directed upward and backward; the spinous process is thick, long, and almost horizontal. The transverse processes are long, and the upper vertebral notches are deeper than those of the other thoracic vertebrae. 204 OSTEOLOGY The Ninth Thoracic Vertebra may have no demi-facets below. In some sub- jects however, it has two demi-facets on either side; when this occurs the tenth has only demi-facets at the upper part. The Tenth Thoracic Vertebra has (except in the cases just mentioned; an entire articular facet on either side, which is placed partly on the lateral surface of the pedicle. In the Eleventh Thoracic Vertebra the body approaches in its form and size to that of the lumbar vertebrse. The articular facets for the heads of the ribs are of large size, and placed chiefly on the pedicles, which are thicker and stronger in this and the next vertebra than in any other part of the thoracic region. The spinous process is short, and nearly horizontal in direction. The transverse processes are very short, tuberculated at their extremities, and have no articular facets. The Twelfth Thoracic Vertebra has the same general characteristics as the eleventh, but may be distinguished from it by its inferior articular surfaces being convex and directed lateraiward, like those of the lumbar vertebrae; by the general form of the body, laminae, and spinous process, in which it resembles the lumbar vertebrae; and by each transverse process being subdivided into three elevations, the superior, inferior, and lateral tubercles: the superior and inferior correspond to the mamillary and accessory processes of the lumbar vertebrae. Traces of similar elevations are found on the transverse processes of the tenth and eleventh thoracic vertebrae. Superior artiruUu p/ocf^ Fig. 242. — A lumbar vertebra seen from the side. The Lumbar Vertebrae (Vertebrae Lumbalesj. The lumbar vertebrae (Figs. 242 and 243) are the largest segments of the movable part of the vertebral column, and can be distinguished by the absence of a foramen in the transverse process, and by the absence of facets on the sides of the body. The body is large, wider from side to side than from before backward, and a little thicker in front than behind. It is flattened or slightly concave above and below, concave behind, and deeply constricted in front and at the sides. The pedicles are very strong, directed backward from the upper part of the body; consequently, the inferior vertebral notches are of considerable depth. The laminae are broad, short, and strong; the vertebral foramen is triangular, larger than in the thoracic, but smaller than in the cervical region. The spinous process is thick, broad, and somewhat quadrilateral; it projects backward and ends in a rough, uneven border, thickest below where it is occasionally notched. The superior and inferior articular processes are well-defined, projecting respectively upward and downward from the junctions of pedicles and laminae. The facets THE SACRAL AND COCCYGEAL VERTEBRA 205 on the superior processes are concave, and look backward and medialward; those on the inferior are convex, and are directed forward and lateralward. The former are wider apart than the hitter, since in the articuhited cokniin the inferior articular processes are em])raced by the superior processes of the subjacent vertebra. The transverse processes are long, slender, and horizontal in the upper three lumbar vertebrae; they incline a little upward in the lower two. In the upper three verte- brae they arise from the junctions of the pedicles and laminae, but in the lower two they are set farther forward and spring from the jjedicles and posterior parts (»f the bodies. They are situated in front of the articular processes instead of behind them as in the thoracic vertebrae, and are homologous with the ribs. Of the three tubercles noticed in connection with the transverse processes of the lower thoracic Transverse process Inferior articular process 2Iamillary process Accessory process Superior articular (—' process f Fig. 243 — \ lumbar -vertebra viewed obliquely from above. vertebrae, the superior one is connected in the lumbar region with the back part of the superior articular process, and is named the mamillary process; the inferior is situated at the back part of the base of the transverse process, and is called the accessory process (Fig. 243). Although in man these are comparatively small, in some animals they attain considerable size, and serve to lock the vertebrae more closely together. The Fifth Lumbar Vertebra is characterized by its body being much deeper in front than behind, which accords with the prominence of the sacrovertebral articulation; by the smaller size of its spinous process; by the wide interval between the inferior articular processes; and by the thickness of its transverse processes, which spring from the body as well as from the pedicles. The Sacral and Coccygeal Vertebrae. The sacral and coccygeal vertebrae consist at an early period of life of nine separate segments which are united in the adult, so as to form two bones, five entering into the formation of the sacrum, four into that of the coccyx. Some- times the coccyx consists of five bones; occasionally the number is reduced to three. 206 OSTEOLOGY The Sacrum (os sacrum). — The sacrum is a large, trianj^nilar bone, situated in the lower part of the vertebral column and at the upper and back part of the pelvic cavity, where it is inserted like a wedge between the two hip bones; its upper part or base articulates with the last lumbar vertebra, its apex with the coccyx. It is curved upon itself and placed very obliquely, its base projecting forward and forming the prominent sacrovertebral angle when articulated with the last lumbar vertebra; its central part is projected backward, so as to give increased capacity to the pelvic cavity. The sacrum is rather narrower at the level of the second segment than at the level of the third. It presents for examina- tion a pelvic, a dorsal, and two lateral surfaces, a base, an apex, and a central canal. Pronwnforu Fig. 244. — Sacrum, pelvic surface. Pelvic Surface (fades yehina). — The pelvic surface (Fig. 244) is concave from above downward, and slightly so from side to side. Its middle part is crossed by four transverse ridges, the positions of which correspond with the original planes of separation between the five segments of the bone. The portions of bone intervening between the ridges are the bodies of the sacral vertebrae. The body of the first segment is of large size, and in form resembles that of a lumbar vertebra; the succeeding ones diminish from above downward, are flattened from before backward, and curved so as to accommodate themselves to the form of the sacrum, being concave in front, convex behind. At the ends of the ridges are seen the anterior sacral foramina, four in number on either side, somewhat rounded in form diminishing in size from above downward, and directed lateralward and forward; they give exit to the anterior divisions of the sacral nerves and entrance to the lateral sacral arteries. Lateral to these foramina are the lateral parts of the sacrum, each consisting of five separate segments at an early period of life; in the adult, THE SACRAL AXD COCCYGEAL VERTEBRAE 20- these are blended with the bodies and with each other. Each lateral part is tra- versed by four broad, shallow grooves, which lodge the anterior divisions of the sacral nerves, and are separated by prominent ridges of bone which give origin to the Piriformis muscle. If a sagittal section be made through the centre of the sacrum (Fig. 240), the bodies are seen to be united at their circumferences by bone, wide intervals being left centrally, which, in the recent state, are filled by the inter\-ertebral fibro- cartilages. In some bones this union is more complete between the lower than the upper segments. Sacrospi)ialis Lafissimus dorsi Sacrospinalis •r half of fifth posterior sacral foramen Fig. 245. — Sacrum, dorsal surface. Dorsal Surface {fades dorsalis). — The dorsal surface (Fig. 245) is convex and narrower than the pelvic. In the middle line it displays a crest, the middle sacral crest, sm^mounted by three or four tubercles, the rudimentary spinous processes of the upper three or four sacral vertebrte. On either side of the middle sacral crest is a shallow groove, the sacral groove, which gives origin to the Multifidus, the floor of the groove being formed by the united lammse of the corresponding vertebrse. The laminae of the fifth sacral vertebra, and sometimes those of the fom-th, fail to meet behind, and thus a hiatus or deficiency occurs in the posterior wall of the sacral canal. On the lateral aspect of the sacral groove is a linear series of tubercles produced by the fusion of the articular processes which together form the indistinct sacral articular crests. The articidar processes of the first sacral vertebra are large and oval in shape; their facets are concave from side to side, look backv\"ard and medialward, and articulate with the facets on the inferior processes of the fifth lumbar vertebra. The tubercles which represent the inferior articular processes of the fifth sacral vertebra are prolonged downward as rounded processes, which are named the sacral comua, and are coimected to the cornua 208 OSTEOLOGY of the coccyx. Lateral to the articular processes are the four posterior sacral foramina; they are smaller in size and less regular in form than the anterior, and transmit the posterior divisions of the sacral nerves. On the lateral side of the posterior sacral foramina is a series of tubercles, which represent the transverse processes of the sacral vertebrae, and form the lateral crests of the sacrum. The transverse tubercles of the first sacral vertebra are large and very distinct; they, together with the transverse tubercles of the second vertebra, give attachment to the horizontal parts of the posterior sacroiliac ligaments; those of the third vertebra give attachment to the oblique fasciculi of the posterior sacroiliac liga- ments; and those of the fourth and fifth to the sacrotuberous ligaments. Lateral Surface. — The lateral surface is broad above, but narrowed into a thin edge below. The upper half presents in front an ear-shaped surface, the auricular surface for articulation with the ilium. Behind it is a rough surface, the sacral tuberosity, on which are three deep and uneven impressions, for the attachment of the posterior sacroiliac ligament. The lower half is thin, and ends in a pro- jection called the inferior lateral angle; medial to this angle is a notch, which is converted into a foramen by the transverse process of the first piece of the coccyx, and transmits the anterior division of the fifth sacral nerve. The thin lower half of the lateral surface gives attachment to the sacrotuberous and sacrospinous ligaments, to some fibres of the Glutaeus maximus behind, and to the Coccygeus in front. Base {basis oss. sacri). — The base of the sacrum, which is broad and expanded, is directed upward and forward. In the middle is a large oval articular surface, the upper surface of the body of the first sacral vertebra, which is connected with the under surface of the body of the last lumbar vertebra by an intervertebral fibrocartilage. Behind this is the large triangular orifice of the sacral canal, which is completed by the laminae and spinous process of the first sacral vertebra. The superior articular processes project from it on either side; they are oval, concave, directed backward and medialward, like the superior articular processes of a lumbar vertebra. They are attached to the body of the first sacral vertebra and to the alse b}' short thick pedicles; on the upper surface of each pedicle is a vertebral notch, which forms the lower part of the foramen between the last lumbar and first sacral vertebrae. On either side of the body is a large triangular surface, which supports the Psoas major and the lumbosacral trunk, and in, the articulated pelvis is continuous with the iliac fossa. This is called the ala; it is slightly concave from side to side, convex from before backward, and gives attachment to a few of the fibres of the Iliacus. The posterior fourth of the ala represents the transverse process, and its anterior three-fourths the costal process of the first sacral segment. Apex {ayex oss. sacri). — The apex is directed downward, and presents an oval facet for articulation with the coccyx. Vertebral Canal (canalis sacralis; sacral canal). — The vertebral canal (Fig. 246) runs throughout the greater part of the bone; above, it is triangular in form; below, its posterior wall is incomplete, from the non-development of the laminae and spinous processes. It lodges the sacral nerves, and its walls are perforated by the anterior and posterior sacral foramina through which these nerves pass out. Structure. — The sacrum consists of cancellous tissue enveloped by a thin layer of compact bone. Articulations. — The sacrum articulates with four bones; the last lumbar vertebra above, the coccyx below, and the hip bone on either side. DifEerences in the Sacrum of the Male and Female. — In the female the sacrum is shorter and wider than in the male; the lower half forms a greater angle with the upper; the upper half is nearly straight, the lower half presenting the greatest amount of curvature. The bone is also directed more obUquely backward; this increases the size of the pelvic cavity and renders the sacrovertebral angle more prominent. In the male the curvature is more evenly distributed over the whole length of the bone, and is altogether greater than in the female. THE SACRAL AND COCCYGEAL VERTEBRAE 209 Variations. — The sacrum, in some cases, consists of six pieces; occasionally the number is reduced to four. Sometimes the uppermost transverse tubercles are not joined to the rest of the ala on one or both sides, or the sacral canal may be open throughout a considerable part of its length, in consequence of the imperfect development of the laminae and spinous processes. The sacrum, also, varies considerably with respect to its degree of curvature. Coruua Anterior Surface Riidim. Trans, prac. Fig. 246. — Median sagittal section of the sacrum. Posterior surface Fig. 217. — Coccyx. The Coccyx (os coccygis). — The coccyx (Fig. 247) is usually formed of four rudimentary vertebrse; the number may however be increased to five or diminished to three. In each of the first three segments may be traced a rudimentary body and articular and transverse processes; the last piece (sometimes the third) is a mere nodule of bone. All the segments are destitute of pedicles, laminae, and spinous processes. The first is the largest; it resembles the lowest sacral vertebra, and often exists as a separate piece; the last three diminish in size from above downward, and are usually fused with one another. Owing to the gradual diminu- tion in the size of the segments, the coccyx is triangular in form, and presents for examination an anterior and a posterior surface, two borders, a base, and an apex. Surfaces. — The anterior surface is slightly concave, and marked with three trans- verse grooves which indicate the junctions of the different segments. It gives attachment to the anterior sacrococc3'geal ligament and the Levatores ani, and supports part of the rectum. The posterior surface is convex, marked by transverse grooves similar to those on the anterior surface, and presents on either side a linear row of tubercles, the rudimentary articular processes of the coccygeal vertebrae. Of these, the superior pair are large, and are called the coccygeal comua; they 14 210 OSTEOLOGY project upward, and articulate with the cornua of the sacrum, and on either side complete the foramen for the transmission of the posterior division of the fifth sacral nerve. Borders. — The lateral borders are thin, and exhibit a series of small eminences, which represent the transverse processes of the coccygeal vertebrae. Of these, the first is the largest; it is flattened from before backward, and often ascends to join the lower part of the thin lateral edge of the sacrum, thus completing the foramen for the transmission of the anterior division of the fifth sacral nerve; the others diminish in size from above downward, and are often wanting. The borders of the coccyx are narrow, and give attachment on either side to the sacro- tuberous and sacrospinous ligaments, to the Coccygeus in front of the ligaments, and to the Glutaeus maximus behind them. Base. — The base presents an oval surface for articulation with the sacrum. Apex. — The apex is rounded, and has attached to it the tendon of the Sphincter ani externus. It may be bifid, and is sometimes deflected to one or other side. Ossification of the Vertebral Column. — Each vertebra is ossified from three primary centres (Fig. 248), two for the vertebral arch and one for the body.^ Ossification of the vertebral arches begins in the upper cervical vertebrae about the seventh or eighth week of fetal life, and gradually extends dovra. the column. The ossific granules first appear in the situations where the transverse processes afterward project, and spread backward to the spinous process forward into the pedicles, and lateralward into the transverse and articular processes. Ossification of the bodies begins about the eighth week in the lower thoracic region, and subsequently extends upward and down- ward along the column. The centre for the body does not give rise to the whole of the body of the adult vertebra, the postero-lateral portions of which are ossified by extensions from the verte- bral arch centres. The body of the vertebra during the first few years of hfe shows, therefore, two sjTichondroses, neurocentral synchondroses, traversing it along the planes of junction of the three centres (Fig. 249). In the thoracic region, the facets for the heads of the ribs lie behind the neurocentral sj'nchondroses and are ossified from the centres for the vertebral arch. At birth the vertebra consists of three pieces, the body and the halves of the vertebral arch. During the first year the halves of the arch unite behind, union taking place first in the lumbar region and then extending upward through the thoracic and cervical regions. About the thii'd year the bodies of the upper cervical vertebrae are joined to the arches on either side; in the lower lumbar vertebrae the union is not completed until the sixth year. Before puberty, no other changes occur, excepting a gi-adual increase of these primary centres, the upper and under sur- faces of the bodies and the ends of the transverse and spinous processes being cartilaginous. About the sixteenth year (Fig. 249), five secondary centres appear, one for the tip of each trans- verse process, one for the extremity of the spinous process, one for the upper and one for the lower surface of the body (Fig. 2.50). These fuse with the rest of the bone about the age of twenty-five. Exceptions to this mode of development occur in the first, second, and seventh cervical verte- brae, and in the lumbar vertebrae. Atlas. — The atlas is usually ossified from three centres (Fig. 251). Of these, one appears in each lateral mass about the seventh week of fetal life, and extends backward; at birth, these portions of bone are separated from one another behind by a narrow interval fiUed witli cartilage. Between the third and fourth years they unite either directly or through the medium of a separate centre developed in the cartilage. At birth, the anterior arch consists of cartilage; in this a separate centre appears about the end of the first year after birth, and joins the lateral masses from the sixth to the eighth year — the lines of union extending across the anterior portions of the superior articular facets. Occasionally there is no separate centre, the anterior arch being formed by the forward extension and ultimate junction of the two lateral masses; sometimes this arch is ossified from two centres, one on either side of the middle fine. Epistropheus or Axis. — The axis is ossified from five primary and two secondarj^ centres (Fig. 252). The body and vertebral arch are ossified in the same manner as the corresponding parts in the other vertebrae, viz., one centre for the body, and two for the vertebral arch. The centres for the arch appear about the seventh or eighth week of fetal life, that for the body about the foin-th or fifth month. The dens or odontoid process consists originally of a continuation upward of the cartilaginous mass, in which the lower part of the body is formed. About the sixth month of fetal life, two centres make their appearance in the base of this process: thej' are placed laterally, and join before birth to form a conical bilobed mass deeply cleft above; the interval 1 A vertebra is occasionally found in which the body consists of two lateral portions — a condition which proves that the body is sometimes ossified from two primarj- centres, one on either side of the middle line. THE SACRAL AND COCCYGEAL VERTEBRA 211 between the sides of the cleft and the summit of the process is formed by a wedge-shaped piece of cartihige. The base of the process is separated from th(> body by a cartilaginous disk, which tii'adually b(!(;oin(!S ossified at its cir- FiG. 248. — Ossification of a vertebra By 3 primary centres 1 Jor hody [Hlh wck] 1 for each vertebral arch [llh or 8th week) Fig. 249. By 3 secondary centres Neurocentral synchondrosis 1 for each trans, process I6th year 1 for spinous process {IGth year) Fig. 250. By 2 additional plates 1 for upper surface^ of body 1 for under surface of body IQth year Fig. 251— Atlas. By 3 centres I for anter. arch (end of 1st year) 1 for each \^aweelc lateral mass J Fig. 252.— Axis. By 7 centres <(P^ 2nd year 6th month 1 Jor each vertebral arch (7 th or 8th iceek) 1 for body {4th month) 1 for under surface of body Fig. 253. — Lumbar vertebra. 2 additional centres for mamillary processes cumference, Ijut remains cartilaginous in its centre until advanced age. In this cartilage, I'udiments of the lower epiphysial lamella of the atlas and the upper epiphysial lamella of the axis may sometimes be found. The apex of the odontoid process has a separate centre which api^ears in the second and joins about the twelfth year; this is the upper epiphysial lamella of the atlas. In addition to these there is a secondary centre for a thin epiphysial plate on the under surface of the body of the bone. Additional centres for costal elements * At birth Fig. 254 At 4J yrs Fig. 255 Two epiphysial plates for each lateral surface * At 25th year Fig. 256. — Ossification of the sacrum. The Seventh Cervical Vertebra. — The anterior or costal part of the transverse process of this vertebra is sometimes ossified from a separate centre which appears about the sixth month of 212 OSTEOLOGY fetal life, and joins the body and posterior part of the transverse process between the fifth and sixth years. Occasionally the costal part persists as a separate piece, and, becoming lengthened lateralward and forward, constitutes what is known as a cervical rib. Separate ossific centres have also been found in the costal processes of the fourth, fifth, and sixth cervical vertebrae. Lumbar Vertebrae. — The lumbar vertebrae (Fig. 253) have each two additional centres, for the mamillary processes. The transverse process of the first lumbar is sometimes developed as a separate piece, which may remain permanently ununited with the rest of the bone, thus form- ing a lumbar rib — a peculiarity, however, rarely met with. Sacrum (Figs. 254 to 257). — The body of each sacral vertebra is ossified from a primary centre and tico epiphysial plates, one for its upper and another for its under surface, while each vertebral arch is ossified from two centres. The anterior portions of the lateral -parts have six additional centres, two for each of the first three vertebrae; these represent the costal elements, and make their appearance above and lateral to the anterior sacral foramina (Figs. 254, 255). On each lateral surface two epiphysial plates are developed (Figs. 256, 257) : one for the auric- ular surface, and another for the remaining part of the thin lateral edge of the bone.^ Periods or Ossificatiox. — About the eighth or ninth week of fetal Ufe, ossification of the central part of the body of the first sacral vertebra commences, and is rapidly followed by deposit of ossific matter in the second and third; Centre for neural arch Centre for neural arch. Costal element Lateral epiphysis. Fig. 257. Centre for hody. Lateral epiphysis. -Base of young sacrum. ossification does not commence in the bodies of the lower two segments until between the fifth and eighth months of fetal life. Between the sixth and eighth months ossification of the vertebral arches takes place; and about the same time the costal centres for the lateral parts make their appearance. The junctions of the vertebral arches with the bodies take place in the lower vertebrae as early as the second year, but are not effected in the uppermost until the fifth or sixth year. About the sixteenth year the epiphysial plates for the upper and under sui-faces of the bodies are formed; and between the eighteenth and twentieth years, those for the lateral surfaces make their appearance. The bodies of the sacral vertebrae are, during early life, separated from each other by intervertebral fibrocartilages, but about the eighteenth year the two lowest segments become imited by bone, and the process of bony union gradually extends upward, with the result that between the twenty-fifth and thirtieth years of fife all the segments are united. On examining a sagittal section of the sacrum, the situa- tions of the intervertebral fibrocartilages are indicated by a series of oval cavities (Fig. 246). Coccyx. — The coccj^ is ossified from four centres, one for each segment. The ossific nuclei make their appearance in the following order: in the first segment between the first and fourth j^ears; in the second between the fifth and tenth j^ears; in the third between the tenth and fifteenth years; in the fourth between the ourteenth and twentieth years. As age advances, the segments unite with one another, the union between the first and second segments being freq ently delayed until after the age of twenty-five or thirty. At a late period of life, especially in females, the coccyx often fuses with the sacrum. THE VERTEBRAL COLUMN AS A WHOLE. The vertebral column is situated in the median line, as the posterior part of the trunk; its average length in the male is about 71 cm. Of this length the cervical part measures 12.5 cm., the thoracic about 28 cm., the lumbar 18 cm., and the sacrum and coccyx 12.5 cm. The female column is about 61 cm. in length. Curves. — Viewed laterally (Fig. 258), the vertebral column presents several curves, which correspond to the different regions of the column, and are called cervical, thoracic, lumbar, and pelvic. The cervical curve, convex forward, begins ' The ends of the spinous processes of the upper three sacral v^ertebrae are sometimes developed from separate epi- physes, and Fawcett (Anatomischer Anzeiger, 1907, Band xxx) states that a number of epiphysial nodules may be seen in the sacrum at the age of eighteen years. These are distributed as follows: One for each of the mamillar}' pro- cesses of the first sacral vertebra; twelve — six on either side — in connection with the costal elements (two each for the first and second and one each for the third and fourthj and eight for the transverse processes — four on either side — one each for the first, third, fourth, and fifth. He is further of opinion that the lower part of each lateral surface of the sacrum is formed by the extension and imion of the third and fourth "costal" and fourth and fifth "transverse" epiphyses. THE VERTEBRAL COLUMN AS A WHOLE 213 at the apex of the odontoid process, and ends at the middle of the second thoracic vertebra; it is the least marked of all the cn^^'es. The thoracic curve, concave for- ward, begins at the middle of the second and ends at the middle of the twelfth tho- racic vertebra. Its most prominent point behind corresponds to the spinous process of the seventh thoracic vertebra. The lumbar curve is more marked in the female than in the male; it begins at the middle of the last thoracic vertebra, and ends at the sacro vertebral angle. It is convex ante- riorly, the convexity of the lower three vertebrae being much greater than that of the upper two. The pelvic curve begins at the sacrovertebral articulation, and ends at the point of the coccyx; its concavity is directed downward and forward. The thoracic and pelvic curves are termed primary curves, because they alone are present during fetal life. The cervical and lumbar curves are compensatory or secondary, and are developed after birth, the former when the child is able to hold up its head (at three or four months), and to sit upright (at nine months), the latter at twelve or eighteen months, when the child begins to walk. The vertebral column has also a slight lateral curvature, the convexity of which is directed toward the right side. This may be produced by muscular action, most persons using the right arm in preference to the left, especially in making long-con- tinued efforts, when the body is curved to the right side. In support of this ex- planation it has been found that in one or two individuals who were left-handed, the convexity was to the left side. By others this curvature is regarded as being produced by the aortic arch and upper part of the descending thoracic aorta — a view which is supported by the fact that in cases where the viscera are transposed and the aorta is on the right side, the convexity of the curve is directed to the left side. Surfaces. — Anterior Surface. — When viewed from in front, the width of the bodies of the vertebrae is seen to increase from the second cervical to the first thoracic; there is then a slight diminution in the next three vertebrae; below this there is again a gradual and progressive increase in width 1st cervical or Atlas r ^ ^ Sndcervicfil -l''^^"'^'\ or Axis \^r, y^'^-<~^^^ 1st thoiacic V -'i' 4' ^^. >^ / for xiphoid \ Fig. 262. — Ossification of the sternum. Rarely unite, except in old age Between puberty and the 25th year Soon after puberty 6 \ Partly cartilaginous to advanced life Fig. 263 for first piece, two or more centres for second piece, itsually one for third ^ for fourth J for fifth 2, placed laterally Fig. 264. — Peculiarities. Arrest of ossification of lateral pieces, producing : -Sternal fissure, and Sternal foramen 220 OSTEOLOGY the intercostal spaces. ]Most of the cartilages belonging to the true ribs, as will be seen from the foregoing description, articulate with the sternum at the lines of junction of its primitive component segments. This is well seen in many of the lower animals, where the parts of the bone remain ununited longer than in man. Xiphoid Process (jjrocessus xiphoideiis; ensiform or xi-phoid appendix). — The xiphoid process is the smallest of the three pieces: it is thin and elongated, cartilaginous in structure in youth, but more or less ossified at its upper part in the adult. Surfaces. — Its anterior surface affords attachment on either side to the anterior costoxiphoid ligament and a small part of the Rectus abdominis; its posterior sur- face, to the posterior costoxiphoid ligament and to some of the fibres of the Dia- phragma and Transversus thoracis, its lateral borders, to the aponeuroses of the abdominal muscles. Above, it articulates with the lower end of the body, and on the front of each superior angle presents a facet for part of the cartilage of the seventh rib; below, by its pointed extremity, it gives attachment to the linea alba. The xiphoid process varies much in form; it may be broad and thin, pointed, bifid, perforated, curved, or deflected considerably to one or other side. Structure. — The sternum is composed of highly vascular cancellous tissue, covered by a thin layer of compact bone which is thickest in the manubrium between the articular facets for the clavicles. Ossification. — The sternum originally consists of two cartilaginous bars, situated one on either side of the median plane and connected with the cartilages of the upper nine ribs of its own side. These two bars fuse with each other along the middle line to form the cartilaginous sternum which is ossified frotn six centres: one for the manubrium, four for the body, and one for the xiphoid process (Fig. 262). The ossific centres appear in the intervals between the articular depressions for the costal cartilages, in the following order: in the manubrium and first piece of the body, dm-ing the sixth month; in the second and third pieces of the body, dm-ing the seventh month of fetal life; in its fourth piece, during the first year after birth; and in the xiphoid process, between the fifth and eighteenth years. The centres make their appearance at the upper parts of the seg- ments, and proceed gradually downward. "• To these may be added the occasional existence of two smaU episternal centres, which make their appearance one on either side of the jugular notch; they are probably vestiges of the episternal bone of the monotremata and lizards. Occasionally some of the segments are formed from more than one centre, the number and position of which vary (Fig. 264). Thus, the first piece may have two, three, or even six centres. When two are present, they are generally situated one above the other, the upper being the larger; the second piece has seldom more than one; the third, fourth, and fifth pieces are often formed from two centres placed laterally, the irregular union of which explains the rare occurrence of the sternal foramen (Fig. 265), or of the vertical fissm-e which occasionally intersects this part of the bone; these conditions are further explained by the manner in which the cartilaginous sternum is formed. Union of the various centres of the body begins about puberty, and proceeds from below upward (Fig. 263) ; by the age of twenty-five they are all united. The xiphoid process may become joined to the body before the age of thirty, but this occurs more frequently after forty; on the other hand, it sometimes remains unimited in old age. In advanced life the manubrium is occasionally joined to the body by bone. When this takes place, however, the bony tissue is generally only superficial, the central portion of the intervening cartilage remaining imossified. Articulations. — The sternum articulates on either side with the clavicle and upper seven costal cartilages. The Ribs (Costae). The ribs are elastic arches of bone, which form a large part of the thoracic skeleton. They are twelve in number on either side; but this number may be increased by the development of a cervical or lumbar rib, or may be diminished to eleven. The first seven are connected behind with the vertebral column, and in front, through the intervention of the costal cartilages, with the sternum (Fig. 259); they are called true or vertebro-sternal ribs.^ The remaining five are false 1 Out of 141 sterna between the time of birth and the age of sixteen years, Paterson (op. cit.) found the fourth or lowest centre for the body present only in thirty-eight cases — i. e., 26.9 per cent. 2 Sometimes the eighth rib cartilage articulates with the sternum; this condition occurs more frequently on the right than on the left side. THE RIBS 221 ribs; of thos{>, the first three have their cartihiges attached to the cartilage of the rib above (vertebro-chondral) : the hist two are free at their anterior extremities Non-articular pari of tubercle Articular part o," tubercle Fig. 266. — A central rib of the left side. Inferior aspect. and are termed floating or vertebral ribs. The ribs vary in their direction, the ni)per ones being less oblique than the lower; the obliquity reaches its maximum at the ninth rib, and gradually decreases from that rib to the twelfth. The ribs are situated one below the other in such a manner that spaces called intercostal spaces are left between them. The length of each space corresponds to that of the adjacent ribs and their cartilages; the breadth is greater in front than behind, and between the upper than the lower ribs. The ribs increase in length from the first to the seventh, below which they diminish to the twelfth. In breadth they decrease from above downward; in the upper ten the greatest breadth is at the sternal extremity. Common Characteristics of the Ribs (Figs. 266, 267).— A rib from the middle of the series should be taken in order to study the common characteristics of these bones. Each rib has two extremities, a posterior or vertebral, and an anterior or sternal, and an intervening portion — the body or shaft. Posterior Extremity. — The posterior or verte- bral extremity presents for examination a head, neck, and tubercle. The head is marked by a kidney-shaped articular surface, divided by a horizontal crest into two facets for articulation with the depression formed by the junction of the bodies of two contiguous thoracic verte- brae; the upper facet is the smaller; to the crest is attached the interarticular ligament. The neck is the flattened portion which extends lateralward from the head; it is about 2.5 cm. long, and is placed in front of the transverse process of the lower of the two vertebrae with which the head articulates. Its anterior surface is flat and smooth, its posterior rough for the attachment of the ligament of the 222 OSTEOLOGY neck, and perforated by numerous foramina. Of its two borders the superior presents a rough crest (crista colli costae) for the attachment of the antericjr costotransverse Hgament; its inferior border is rounded. On the posterior surface at the junction of the neck and body, and nearer the lower than the upper border, is an eminence — the tubercle; it consists of an articular and a non-articular portion. The articular jjortion, the lower and more medial of the two, presents a small, oval surface for articulation with the end of the transverse process of the lower of the two ^•e^tebrai to which the head is connected. The ncm-articvlar yrjrtion is a rough elevation, and affords attachment to the ligament of the tubercle. The tubercle is much more prominent in the upper than in the lower ribs. Body. — The body or shaft is thin and flat, with two surfaces, an external and an internal ; and two borders, a superior and an inferior. The external surface is convex, smooth, and marked, a little in front of the tubercle, by a prominent line, directed downward and lateralward; this gives attachment to a tendon of the Iliocostalis, and is called the angle. At this point the rib is bent in two directions, and at the same time twisted on its long axis. If the rib be laid upon its lower border, the portion of the body in front of the angle rests upon this border, while the portion behind the angle is bent medialward and at the same time tilted upward; as the Bemifacet for vertebra - Interarticular crest DemifrMet for vertebra Costal groove Fig. 267. — A central rib of the left side, vie-sved from behind. result of the twisting, the external surface, behind the angle, looks downward, and in front of the angle, slightly upward. The distance between the angle and the tubercle is progressively greater from the second to the tenth ribs. The portion between the angle and the tubercle is rounded, rough, and irregular, and serves for the attachment of the Longissimus dorsi. The external surface presents, toward its sternal end, an oblique line, the anterior angle. The internal surface is concave, smooth, directed a little upward behind the angle, a little downward in front of it, and is marked by a ridge which commences at the lower extremity of the head; this ridge is strongly marked as far as the angle, and gradually becomes lost at the junction of the anterior and middle thirds of the bone. Between it and the inferior border is a groove, the costal groove, for the intercostal vessels and nerve. At the back part of the bone, this groove belongs to the inferior border, but just in front of the angle, where it is deepest and broadest, it is on the internal surface. The superior edge of the groove is rounded and serves for the attach- ment of an Intercostalis internus; the inferior edge corresponds to the lower margin of the rib, and gives attachment to an Intercostalis externus. ^Yithin the groove are seen the orifices of numerous small foramina for nutrient vessels THE Rllii^, 223 which traverse the shaft ohHqiiely from l)et'()re backward. The superior border, thick and rounded, is marked by an external and an internal hp, more distinct behind than in front, which serve for the attachment of Interc^ostales externus and internus. The inferior border is thin, and has attached to it an Intercostahs extennis. Anterior Extremity.— The anterior or sternal extremity is flattened, and presents a porous, o\al, concave depression, into whicli tlie c(jstal cartilage is received. Fig. 268 Fig Aiigle- FiG. 271 Single articular facet Fig. 272 Single articular facet Figs. 268 to 272. — Peculiar ribs. Peculiar Ribs. — The first, second, tenth, eleventh, and twelfth ribs present certain variations from the common characteristics described above, and require special consideration. First Rib. — The first rib (Fig. 268) is the most curved and usually the shortest of all the ribs; it is broad and flat, its surfaces looking upward and downward, and its borders inward and outward. The head is small, rounded, and possesses 224 OSTEOLOGY only a single articular facet, for articulation with the body of the first thoracic vertebra. The neck is narrow and rounded. The tubercle, thick and prominent, is placed on the outer border. There is no angle, but at the tubercle the rib is slightly bent, with the convexity upward, so that the head of the bone is directed downward. The upper surface of the body is marked by two shallow grooves, separated from each other by a slight ridge prolonged internally into a tubercle, the scalene tubercle, for the attachment of the Scalenus anterior; the anterior groove transmits the subclavian vein, the posterior the subclavian artery and the lowest trunk of the brachial plexus.^ Behind the posterior groove is a rough area for the attachment of the Scalenus medius. The under surface is smooth, and destitute of a costal groove. The outer border is convex, thick, and rounded, and at its posterior part gives attachment to the first digitation of the Serratus anterior; the inner border is concave, thin, and sharp, and marked about its centre by the scalene tubercle. The anterior extremity is larger and thicker than that of any of the other ribs. Second Rib. — The second rib (Fig. 269) is much longer than the first, but has a very similar curvature. The non-articular portion of the tubercle is occasionally only feebly marked. The angle is slight, and situated close to the tubercle. The body is not twisted, so that both ends touch any plane surface upon which it may be laid; but there is a bend, with its convexity upward, similar to, though smaller than that found in the first rib. The body is not flattened horizontally like that of the first rib. Its external surface is convex, and looks upward and a little outward ; near the middle of it is a rough eminence for the origin of the lower part of the first and the whole of the second digitation of the Serratus anterior; behind and above this is attached the Scalenus posterior. The internal surface, smooth, and concave, is directed downward and a little inward: on its posterior part there is a short costal groove. Tenth Rib. — The tenth rib (Fig. 270) has only a single articular facet on its head. Eleventh and Twelfth Ribs. — The eleventh and twelfth ribs (Figs. 271 and 272) have each a single articular facet on the head, which is of rather large size; they have no necks or tubercles, and are pointed at their anterior ends. The eleventh has a slight angle and a shallow costal groove. The twelfth has neither; it is much shorter than the eleventh, and its head is inclined slightly downward. Sometimes the twelfth rib is even shorter than the first. Structure. — The ribs consist of highly vascular cancellous tissue, enclosed in a thin layer of compact bone. Ossification. — ^Each rib, with the exception of the last two, is ossified from four centres; a primary centre for the body, and three epiphysial centres, one for the head and one each for the articular and non-articular parts of the tubercle. The eleventh and twelfth ribs have each only two centres, those for the tubercles being wanting. Ossification begins near the angle toward the end of the second month of fetal Ufe, and is seen first in the sixth and seventh ribs. The epiphyses for the head and tubercle make their appearance between the sixteenth and twentieth years, and are united to the body about the twenty-fifth year. Fawcett^ states that "in all probability there is usually no epiphysis on the non-articular part of the tuberosity below the sixth or seventh rib. The Costal Cartilages (Cartilagines Costales). The costal cartilages (Fig. 259) are bars of hyaline cartilage w^hich serve to prolong the ribs forward and contribute very materially to the elasticity of the walls of the thorax. The first seven pairs are connected with the sternum; the next three are each articulated with the lower border of the cartilage of the pre- ceding rib; the last two have pointed extremities, which end in the wall of the abdomen. Like the ribs, the costal cartilages vary in their length, breadth, and lAnat. Anzeiger, 1910, Band xxxvi. . 2 Journal of Anatomy and Physiology, vol. xlv. THE COSTAL CARTILAGES 225 direction. They increase in length from the first to the seventh, then gradually decrease to the twelfth. Their breadth, as well as that of the intervals between them, diminishes from the first to the last. They are broad at their attachments to the ribs, and taper toward their sternal extremities, excepting the first two, which are of the same breadth throughout, and the sixth, seventh, and eighth, which are enlarged where their margins are in contact. They also vary in direc- tion: the first descends a little, the second is horizontal, the third ascends slightly, while the others are angular, following the course of the ribs for a short distance, and then ascending to the sternum or preceding cartilage. Each costal cartilage presents two surfaces, two borders, and two extremities. Surfaces. — The anterior surface is convex, and looks forward and upward: that of the first gives attachment to the costoclavicular ligament and the Subclavius muscle; those of the first six or seven at their sternal ends, to the Pectoralis major. The others are covered by, and give partial attachment to, some of the flat muscles of the abdomen. The posterior surface is concave, and directed backward and downward; that of the first gives attachment to the Sternothyroideus, those of the third to the sixth inclusive to the Transversus thoracis, and the six or seven inferior ones to the Transversus abdominis and the Diaphragma. Borders. — Of the two borders the superior is concave, the inferior convex; they afford attachment to the Intercostales interni : the upper border of the sixth gives attachment also to the Pectoralis major. The inferior borders of the sixth, seventh, eighth, and ninth cartilages present heel-like projections at the points of greatest convexity. These projections carry smooth oblong facets which articulate respec- tively with facets on slight projections from the upper borders of the seventh, eighth, ninth, and tenth cartilages. Extremities. — The lateral end of each cartilage is continuous with the osseous tissue of the rib to which it belongs. The medial end of the first is continuous with the sternum; the medial ends of the six succeeding ones are rounded and are received into shallow concavities on the lateral margins of the sternum. The medial ends of the eighth, ninth, and tenth costal cartilages are pointed, and are connected each with the cartilage immediately above. Those of the eleventh and twelfth are pointed and free. In old age the costal cartilages are prone to undergo superficial ossification. Applied Anatomy. — Fracture of the sternum is by no means common, owing, no doubt, to the elasticity of the ribs and their cartilages which support it like so many springs. The fracture usually occurs in the upper half of the body. Dislocation of the body from the manubrium may take place, and is sometimes described as a fracture. The bone is frequently the seat of gummatous tumors and not uncommonly is affected with caries. The ribs are frequently broken, though from their connections and shape they are able to withstand great force, yielding under the injury and recovering themselves hke a spring. The middle ribs are the most hable to fracture. The first and to a less extent the second, being pro- tected by the clavicle, are rarely fractured; and the eleventh and twelfth on account of their loose and floating condition enjoy a like immimity. The fracture generally occiirs from indirect violence, from forcible compression of the chest wall, and the bone then gives way at its weakest part, i. e., just in front of the angle. But the ribs may also be broken by direct violence, in which case the bone is driven inward at the point struck. Fractm-e of the ribs is frequently comphcated with some injury to the viscera contained within the thorax or upper part of the abdominal caAdty; this is most likely to occur in fractures from direct violence. Fracture of the costal cartilages or separation of the cartilages from the ribs, may also take place, though they are comparatively rare injuries. In workmen the pressure of tools may dis- place the xiphoid process inward. The ribs are frequently the seat of tuberculous disease, with the formation of a chronic abscess in the chest wall. This may not immediately overlie the carious portion of rib, as the pus is often directed a considerable distance along the. costal groove before appearing beneath the integument. Resection of a portion of a rib is often required in order to give efficient drainage to an empyema; this is referred to in the description of the respiratory organs. 15 226 OSTEOLOGY Cervical ribs derived from the seventh cervical vertebra (i)age 201) are of not infrequent occur- rence, and are important clinically because they may give rise to obscure nervous or vascular symptoms. The cervical rib may be a mere epiphysis articulating only with the transverse process of the vertebra, but more commonly it consists of a defined head, neck, and tubercle, with or without a body. It extends lateralward, or forward and lateralward, into the posterior triangle of the neck, where it may terminate in a free end or may join the first thoracic rib, the first costal cartilage, or the sternum.^ It varies much in shape, size, direction, and mobility. If it reach far enough forward, part of the brachial plexus and the subclavian artery and vein cross over it, and are apt to suffer compression in so doing. Pressure on the artery may obstruct the circula- tion so much that arterial thrombosis results, causing gangrene of the finger tips. Pressure on the nerves is commoner, and affects the eighth cervical and first thoracic nerves, causing paralysis of the muscles they supply, and neuralgic pains and paresthesia in the area of skin to which they are distributed : no oculopupillary changes are to be found. If these symptoms be severe, removal of the rib or as much of it as causes pressure on the vessels and nerves is called for. The operation is not free from difficulty, and has been followed by paralysis of the muscles and by subclavian aneiu'ism, due to injuries inflicted in the course of the operation. The thorax is frequently found to be altered in shape in certain diseases. In rickets, the ends of the ribs, where they join the costal cartilages, become enlarged, giving rise to the so-called "rickety rosary," which in mild cases is only found on the internal surface of the thorax. Lateral to these enlargements the softened ribs sink in, so as to present a groove passing downward and lateralward on either side of the sternum. This bone is forced forward by the bending of the ribs, and the antero-posterior diameter of the chest is increased. The ribs affected are the second to the eighth, the lower ones being prevented from falling in by the pres- ence of the liver, stomach, and spleen; and when the abdomen is distended, as it often is in rickets, the lower ribs may be pushed outward, causing a transverse groove (Harrison's sulcus) just above the costal arch. This deformity or forward projection of the sternum, often asymmetrical, is known as pigeon breast, and may be taken as evidence of active or old rickets except in cases of primary spinal curvature. In many instances it is associated in children with obstruction in the upper air passages, due to enlarged tonsils or adenoid growths. In some rickety children or adults, and also in others who give no history or further evidence of having had rickets, an opposite condition obtains. The lower part of the sternum and often the xiphoid process as well are deeply depressed backward, producing an oval hollow in the lower sternal and upper epigastric regions. This is known as funnel breast (German, Trichterbrust) ; it never appears to produce the least disturbance of any of the vital functions. The phthisical chest is often long and narrow, and with great obliquity of the ribs and projection of the scapulse In pulmonary empMjsejua the chest is enlarged in all its diameters, and presents on section an almost circular outhne. It has received the name of the barrel-shaped chest. In severe cases of lateral curvature of the vertebral column the thorax becomes much distorted. In consequence of the rotation of the bodies of the vertebrae which takes place in this disease, the ribs opposite the convexity of the dorsal curve become extremely convex behind, being thrown out and bulging, and at the same time flattened in front, so that the two ends of the same rib are almost parallel. Coincidently with this the ribs on the opposite side, on the concavity of the curve, are sunk and depressed behind, and bulging and convex in front. It is commonly said that in tuberculosis of the lungs the chest is characteristically "flat," that is to say, that the ratio of its antero-posterior to its transverse diameter is less than the normal. But by careful measurement in a large number of cases. Woods Hutchinson has shown that this is not so. Taking the transverse diameter of the chest at the nipple level as = 100, he finds that in the normal adult man between the ages of twenty and forty-four the antero-posterior diameter =71. In 82 phthisical subjects it was =79.5, and in 30 "flat-chested" persons was = 80. He explains the error as an optical illusion, due to rolUng forward of the shoulders in the "fiat chested;" the back is seen to be correspondingly rounded and protuberant, while the forward position of the shoulders and clavicles lends an appearance of flattening to the chest. More or less shrinkage of one side of the thorax is often seen as a consequence of adhesive pleurisy, in which the pulmonary and parietal pleural adhere closely to one another and the lung becomes collapsed and fibrosed. If this process be at all complete, great deformity of the chest results, the ribs on the affected side faUing in, together with obliteration of the intercostal spaces; the contents of the mediastinal cavity are pulled over toward the affected side, the other lung becomes emphysematous compensatorily. The vertebral column becomes scoUotic, with the concavity of the curve toward the affected side. THE SKULL. The skull is supported on the summit of the vertebral column, and is of an oval shape, wider behind than in front. It is composed of a series of flattened 1 W. Thorburn, The Medical Chronicle, Manchester, 1907, 4th series, xiv. No. 3. THE OCCIPITAL BONE 00" or irregular hones which, willi one exception (the mandible), are immovably jointed together. It is di\isihle into two ])arts: (1) the cranium, which lodges and protects the brain, consists of eight bones, and (2) the skeleton of the face, of fourteen, as follows: Skull, 22 bones Cranium, S bones ()ccii)ital. Two Parietals. Frontal. Two Temporals. Sphenoidal. Ethmoidal. I Face, 14 bones Two Nasals. Two Maxillae. Two Lacrimals. Two Zygomatics. Two Palatines. j Two Inferior Nasal Conchse. I Vomer. l^ Mandible. In the Basle nomenclature, certain bones developed in association with the nasal capsule, viz., the inferior nasal conchse, the lacrimals, the nasals, and the vomer, are grouped as cranial and not as facial bones. The hyoid bone, situated at the root of the tongue and attached to the base of the skull by ligaments, is described in this section. THE CRANIAL BONES (OSSA CRANII). The Occipital Bone (Os Occipitale). The occipital bone (Figs. 273, 274), situated at the back and lower part of the cranium, is trapezoid in shape and curved on itself. It is pierced by a large oval aperture, the foramen magnum, through which the cranial cavity communicate with the vertebral canal. The curved, expanded plate behind the foramen magnum is named the squama ; the thick, somewhat quadrilateral piece in front of the foramen is called the basilar part, whilst on either side of the foramen is the lateral portion. The Squama {squama occiijitalis) . — The squama, situated above and behind the foramen magnum, is curved from above downward and from side to side. Surfaces. — The external surface is convex and presents midway between the summit of the bone and the foramen magnum a prominence, the external occipital protuberance. Extending lateralward from this on either side are two curved lines, one a little above the other. The upper, often faintly marked, is named the highest nuchal line, and to it the galea aponeurotica is attached. The lower is termed the superior nuchal line. That part of the squama which lies above the highest nuchal lines is named the planum occipitale, and is covered by the Occipitalis muscle; that below, termed the planum nuchale, is rough and irregular for the attachment of several muscles. From the external occipital protuberance a ridge or crest, the median nuchal line, often faintly marked, descends to the fora- men magnum, and affords attachment to the ligamentum nuchae; running from the middle of this line across either half of the nuchal plane is the inferior nuchal line. Several muscles are attached to the outer surface of the squama, thus: the superior nuchal line gives origin to the Occipitalis and Trapezius, and insertion 228 OSTEOLOGY to the Stemocleidomastoideiis and Splenius capitis: into the surface between the superior and inferior nuchal hues the Semispinalis capitis and the Obhquus capitis superior are inserted, while the inferior nuchal line and the area below it receive the insertions of the Recti capitis posteriores major and minor. The posterior atlantooccipital membrane is attached around the postero-lateral part of the foramen magnum, just outside the margin of the foramen. Highest nuchal line Hypoglossal canal Fig. 273. — Occipital bone. Outer surface. The internal surface is deeply concave and divided into four fossae by a cruciate eminence. The upper two fossae are triangular and lodge the occipital lobes of the cerebrum; the lower two are quadrilateral and accommodate the hemispheres of the cerebellum. At the point of intersection of the four divisions of the cruciate eminence is the internal occipital protuberance. From this protuberance the upper division of the cruciate eminence runs to the superior angle of the bone, and on one side of it (generally the right) is a deep groove, the sagittal sulcus, which lodges the hinder part of the superior sagittal sinus; to the margins of this sulcus the falx cerebri is attached. The low^er division of the cruciate eminence is prominent, and is named the internal occipital crest; it bifurcates near the foramen magnum and gives attachment to the falx cerebelli; in the attached margin of this falx is the occipital sinus, which is sometimes duplicated. In the upper part of the internal occipital crest, a small depression is sometimes distinguishable; it is termed the vermian fossa since it is occupied by part of the vermis of the cerebellum. Transverse grooves, one on either side, extend from the internal occipital protuber- ance to the lateral angles of the bone; those grooves accommodate the transverse sinuses, and their prominent margins give attachment to the tentorium cerebelli. The groove on the right side is usually larger than that on the left, and is THE OCCIPITAL BONE 229 continuous with that for the superior sagittal sinus. Exceptions to this condition are, however, not infrequent; the left may he larger than the right or the two may be almost equal in size. Tlie angle of union of the superior sagittal and trans- verse sinuses is named the confluence of the sinuses {torcular Ilerophili^), and its position is indicated by a depression situated on one or other side of the protuberance. Sitlierio f A ng le ' S u // ej. Tnfe.Tiov Anqlp \^^ Fig. 274. — Occipital bone. Inner surface. Lateral Parts {pars lateralis). — The lateral parts are situated at the sides of the foramen magnum; on their under surfaces are the condyles for articulation with the superior facets of the atlas. The condyles are oval or reniform in shape, and their anterior extremities, directed forward and medialward, are closer together than their posterior, and encroach on the basilar portion of the bone; the posterior extremities extend back to the level of the middle of the foramen magnum. The articular surfaces of the condyles are convex from before backward and from side to side, and look downward and lateralward. To their margins are attached the capsules of the atlantooccipital articulations, and on the medial side of each is a rough impression or tubercle for the alar ligament. At the base of either condyle the bone is tunnelled by a short canal, the hypoglossal canal {anterior condyloid foramen) . This begins on the cranial surface of the bone immediately above the foramen magnum, and is directed lateralward and forward above the 1 The columns of blood coming in different directions were suppo.sed to be pressed together at this point {torcular, a wine press). 230 . OSTEOLOGY condyle. It may be partially or completely divided into two. by a spicule of bone; it trives exit to the hypoglossal or twelfth cerebral nerve, and entrance to a meningeal brancJi of the ascending pharyngeal artery. Behind either condyle is a depression, the condyloid fossa, which receives the posterior margin of the superior facet of the atlas when the head is bent backward; the floor of this fossa is sometimes perforated by the condyloid canal, through which an emissary' vein passes from the transverse sinus. p]xtending laterahvard from the posterior half of the condyle is a quadrilateral plate of bone, the jugular process, excavated in front by the jugular notch, which, in the articulated skull, forms the posterior part of the jugular fora- men. The jugular notch may be divided into two by a bony spicule, the intra- jugular process, which projects lateralward above the hypoglossal canal. The under surface of the jugular process is rough, and gives attachment to the Rectus capitis lateralis muscle and the lateral atlantooccipital ligament; from this surface an eminence, the paramastoid process, sometimes projects downward, and may be of sufficient length to reach, and articulate with, the transverse process of the atlas. Laterally the jugular process presents a rough quadrilateral or tri- angular area which is joined to the jugular surface of the temporal bone by a plate of cartilage; after the age of twenty-five this plate tends to ossify. The upper surface of the lateral part presents an oval eminence, the jugular tubercle, which overlies the hypoglossal canal and is sometimes crossed by an oblique groove for the glossopharyngeal, vagus, and accessory nerves. On the upper surface of the jugular process is a deep groove which curves medialward and forward and is continuous with the jugular notch. This groove lodges the terminal part of the transverse sinus, and opening into it, close to its medial margin, is the orifice of the condyloid canal. Basilar Part (/pars basilaris). — The basilar part extends forward and upward from the foramen magnum, and presents in front an area more or less quadrilateral in outline. In the young skull this area is rough and uneven, and is joined to the body of the sphenoid by a plate of cartilage. By the twenty-fifth yesLT this cartil- aginous plate is ossified, and the occipital and sphenoid form a continuous bone. Surfaces. — On its lower surface, about 1 cm. in front of the foramen magnum, is the pharyngeal tubercle which gives attachment to the fibrous raphe of the pharynx. On either side of the middle line the Longus capitis and Rectus capitis anterior are inserted, and immediately in front of the foramen magnum the anterior atlantooccipital membrane is attached. The upper surface presents a broad, shallow groove which inclines upward and forward from the foramen magnum; it supports the medulla oblongata, and near the margin of the foramen magnum gives attachment to the membrana tectoria. On the lateral margins of this surface are faint grooves for the inferior petrosal sinuses. Foramen Magnum. — The foramen magnum is a large oval aperture with its long diameter antero-posterior ; it is wider behind than in front where it is encroached upon by the condyles. It transmits the medulla oblongata and its membranes, the accessory nerves, the vertebral arteries, the anterior and posterior spinal arteries, and the membrana tectoria and alar ligaments. Angles. — The superior angle of the occipital bone articulates with the occipital angles of the parietal bones and, in the fetal skull, corresponds in position with the posterior fontanelle. The inferior angle is fused with the body of the sphenoid. The lateral angles are situated at the extremities of the grooves for the transverse sinuses: each is received into the interval between the mastoid angle of the parietal and the mastoid part of the temporal. Borders.^ — The superior borders extend from the superior to the lateral angles: they are deeply serrated for articulation with the occipital borders of the parietals, and form bv this union the lambdoidal suture. The inferior borders extend from THE PARIETAL BOXE 281 the lateral aii.ules to the inferior aii^le; the upper half of each articulates with the mastoid pt)rtion of the corresponding temporal, the lower half with the petrous part of the same bone. These two portions of the inferior border are separated from one another by the jugular i)r()cess, the notch on the anterior surface of which forms the i)osterior part of the jugular foramen. Planum occipitale Structure.— Tlu- occipital, like the otlier cranial bones, consists of two compact lamellie, called the fluler and inner tahlcti, between which is the cancellous tissue or diploe; the bone is especially thick at the rido;es, protuberances, condyles, and anterior part of the basilar jxirt; in the inferior fosste it is thin, semitransparent, and destitute of diploe. Ossification (^Fig. 275). — The planum occipitale of the squama is developed in membrane, and may remain separate throughout life when it constitutes the interparietal bone; the rest of the bone is developed in cartilage. The number of nuclei for the planum occipitale is usually given as four, two appearing near the middle hne about the second month, and two some little distance from the middle line about the third month of fetal life. The planum nuchale of the squama is ossified from two centres, which ap- pear about the seventh week of fetal life and soon unite to form a single piece. Union of the upper and lower portions of the squama takes place in the third month of fetal life. An occasional centre (Kerckring) appears in the posterior margin of the foramen magnum during the fifth month; this forms a separate ossicle (sometimes double) which unites with the rest of the squama before birth. Each of the lateral parts begins to ossify from a single centre during the eighth week of fetal hfe. The basilar portion is ossified from two centres, one in front of the other; these appear about the sixth week of fetal Ufe and rapidly coalesce. MalP states that the planum occipitale is ossified from two centres and the basilar portion from one. About the fourth year the squama and the two lateral portions unite, and about the sixth year the bone consists of a single piece. Between the eighteenth and twenty-fifth years the occipital and sphenoid become united, forming a single bone. Articulations. — The occipital articulates with six bones: the two parietals, the two temporals, the sphenoid, and the atlas. Lateral part Basila) part Fig. 275. — Occipital bone at birth. The Parietal Bone (Os Parietale). The parietal bones form, by their union, the sides and roof of the cranium. Each bone is irregidarly quadrilateral in form, and has two surfaces, four borders, and four angles. Surfaces. — The external surface (Fig. 276) is convex, smooth, and marked near the centre by an eminence, the parietal eminence (tuber parietale), which indicates the point where ossification commenced. Crossing the middle of the bone in an arched direction are two curved lines, the superior and inferior temporal lines; the former gives attacliment to the temporal fascia, and the latter indicates the upper limit of the muscular origin of the Temporalis. Above these lines the bone is covered by tlie galea aponeurotica; below tliem it forms part of the temporal fossa, and affords attachment to the Temporalis muscle. At the back part and close to the upper or sagittal border is tlie parietal foramen, which transmits a vein to the superior sagittal sinus, and sometimes a small branch of the occipital artery; it is not constantly present, and its size varies considerably. ' American Journal of Anatomy, 1906, vol. v. 232 OSTEOLOGY The internal surface (Fig. 277) is concave; it presents depressions corresponding to the cerebral convolutions, and numerous furrows for the ramifications of the middle meningeal vessel;^ the latter run upward and backward from the sphenoidal angle, and from the central and posterior part of the squamous border. Along the upper margin is a shallow groove, which, together with that on the opposite parietal, forms a channel, the sagittal sulcus, for the superior sagittal sinus; the edges of the sulcus afford attachment to the falx cerebri. Near the groove are several depressions, best marked in the skulls of old persons, for the arachnoid granulations {Pacchionian bodies). In the groove is the internal opening of the parietal foramen when that aperture exists. Articulates ivith opposite parietal bone J.. Articulates with frontal hone <^ '- v Pa rt'e taJ r m / , >nP ,0^ ?-"/"^"' ^'^v. Articidaies with occipita bo7ie With sphenoid Fig. 276. — Left parietal bone. With mastoid portion of temporal bone Outer surface. Borders. — The sagittal border, the longest and thickest, is dentated and articu- lates with its fellow of the opposite side, forming the sagittal suture. The squamous border is divided into three parts: of these, the anterior is thin and pointed, bevelled at the expense of the outer surface, and overlapped by the tip of the great wing of the sphenoid; the middle portion is arched, bevelled at the expense of the outer surface, and overlapped by the squama of the temporal; the posterior part is thick and serrated for articulation with the mastoid portion of the temporal. The frontal border is deeply serrated, and bevelled at the expense of the outer surface above and of the inner below; it articulates with the frontal bone, forming one- half of the coronal suture. The occipital border, deeply denticulated, articulates with the occipital, forming one-half of the lambdoidal suture. » Journal of Anatomy and Physiology, 1912, vol. xlvi. THE FRONTAL BONE 233 Angles. — The frontal angle is practically a right angle, and corresponds with the point of meeting of the sagittal and coronal sutures; this point is named the bregma; in the fetal skull and for about a year and a half after birth this region is membranous, and is called the anterior fontanelle. The sphenoidal angle, thin and acute, is received into the interval between the frontal bone and the great wing of the s{)henoid. Its inner surface is marked by a deep groove, sometimes a canal, for the anterior divisions of the middle meningeal artery. The occipital angle is rounded and corresponds with the point of meeting of the sagittal and lambdoidal sutures — a point which is termed the lambda; in the fetus this part of the skull is membranous, and is called the posterior fontanelle. The mastoid angle is truncated; it articulates with the occipital bone and with the mastoid portion of the temporal, and presents on its inner surface a broad, shallow groove which lodges part of the transverse sinus. The point of meeting of this angle with the occipital and the mastoid part of the temporal is named the asterion. l,^Uik''^-^— ^-^ Occipital angle Mastoid angle n Frontal angle Sphenoidal angle Fig. 277. — Left parietal bone. Inner surface. Ossification. — The parietal bone is ossified in membrane from a single centre, which appears at the parietal eminence about the eighth week of fetal life. Ossification gradually extends in a radial manner from the centre toward the margins of the bone; the angles are consequently the parts last formed, and it is here that the fontanelles exist. Occasionally the parietal bone is divided into two parts, upper and lowei*, by an antero-posterior suture. Articulations. — The parietal articulates with five bones: the opposite parietal, the occipital, frontal, temporal, and sphenoid. The Frontal Bone (Os Frontale). The frontal bone resembles a cockle-shell in form, and consists of two portions -a vertical portion, the squama, corresponding with the region of the forehead; 234 OSTEOLOGY and an orbital or horizontal portion, Avhich enters into tlie formation of the roofs of the orbital and nasal ca\ities. Squama (squama frontalis). — Surfaces. — The external surface (Fig. 278) of this portion is convex and usually exhibits, in the lower part of the middle line, the remains of the frontal or metopic suture; in infancy this suture divides the bone into two, a condition which may persist throughout life. On either side of this suture, about 3 cm. above the supraorbital margin, is a rounded elevation, the frontal emi- nence (tuber frontale). These eminences vary in size in different individuals, are occasionally unsymmetrical, and are especially prominent in young skulls; the sur- face of the bone above them is smooth, and covered by the galea aponeurotica. Below the frontal eminences, and separated from them by a shallow groove, are two arched elevations, the superciliary arches; these are prominent medially, and Zygomatic process Frontal U spine Fig. 278. — Frontal bone. Outer surface. are joined to one another by a smooth elevation named the glabella. They are larger in the male than in the female, and their degree of prominence depends to some extent on the size of the frontal air sinuses;^ prominent ridges are, how- ever, occasionally associated with small air sinuses. Beneath each superciliary arch is a curved and prominent margin, the supraorbital margin, which forms the upper boundary of the base of the orbit, and separates the squama from the orbital portion of the bone. The lateral part of this margin is sharp and prominent, affording to the eye, in that situation, considerable protection from injury; the medial part is rounded. At the junction of its medial and intermediate thirds is ' Some confusion is occasioned to students commencing the study of anatomy by the name "sinus" ha^dng been given to two different kinds of space connected with the slvuU. It may be as well, therefore, to state here that the "sinuses" in the interior of the cranium which produce the grooves on the inner surfaces of the bones are venous channels which convey the blood from the brain, while the "sinuses" external to the cranial cavity (the frontal, sphenoidal, ethmoidal, and maxillary) are hollow spaces in the bones themselves; they communicate with the nasal cavities and contain air. THE FROXTAL BOXE 235 a notch, sometimes eom-erted into a foramen, the supraorbital notch or foramen, which transmits the su})ra()rl)ital vessels and nerve. A small aperture in the upper part of the notch transmits a vein from the diploe to join the supraorbital vein. The supraorbital margin ends laterally in the zygomatic process, which is strong and j)rominent, and articulates with the zygomatic bone. Running upward and backward from this ])r()cess is a well-marked line, the temporal line, which divides into the upper and lower temporal lines, continuous, in the articulated skull, with the corresponding lines on the parietal bone. The area below and behind the tem- poral line forms the anterior part of the temporal fossa, and gives origin to the Temporalis muscle. Between the supraorbital margins the squama projects down- ward to a level below that of the zygomatic processes; this ])()rtion is known as the nasal part and presents a rough, uneven inte^^'al, the nasal notch, which articulates on either side of the middle line with the nasal bone, and laterally with the frontal process of the maxilla and with the lacrimal. The term nasion is applied to the middle of the frontonasal suture. From the centre of the notch the nasal process projects downward and forward beneath the nasal bones and frontal processes of the maxillse, and supports the bridge of the nose. The nasal process ends below in a sharp spine, and on either side of this is a small grooved surface which enters into the formation of the roof of the corresponding nasal cavity. The spine forms part of the septum of the nose, articulating in front with the crest of the nasal bones and behind with the perpendicular plate of the ethmoid. The internal surface (Fig. 279) of the squama is concave and presents in the upper part of the middle line a vertical groove, the sagittal sulcus, the edges of which unite below to form a ridge, the frontal crest; the sulcus lodges the superior sagittal sinus, while its margins and the crest afford attachment to the falx cerebri. The crest ends below in a small notch which is converted into a foramen, the fora- men cecum, by articulation with the ethmoid. This foramen varies in size in dift'erent subjects, and is frequently impervious; when open, it transmits a vein from the nose to the superior sagittal sinus. On either side of the middle line the bone presents depressions for the convolutions of the brain, and numerous small furrows for the anterior branches of the middle meningeal vessels. Several small, irregular fossae may also be seen on either side of the sagittal sulcus, for the reception of the arachnoid granulations. Orbital or Horizontal Part {pars orbitalis). — This portion consists of two thin triangular plates, the. orbital plates, which form the vaults of the orbits, and are separated from one another by a median gap, the ethmoidal notch. Surfaces. — The inferior surface (Fig. 279) of each orbital plate is smooth and concave, and presents, laterally, under cover of the zygomatic process, a shallow depression, the lacrimal fossa, for the lacrimal gland ; near the nasal part is a depres- sion, the fovea trochlearis, or occasionally a small trochlear spine, for the attach- ment of the cartilaginous pulley of the Obliquus oculi superior. The superior surface is convex, and marked by depressions for the convolutions of the frontal lobes of the brain, and faint grooves for the meningeal branches of the ethmoidal vessels. The ethmoidal notch separates the two orbital plates; it is quadrilateral, and filled, in the articulated skull, by the cribriform plate of the ethmoid. The margins of the notch present several half-cells which, when united with corresponding half-cells on the upper surface of the ethmoid, complete the ethmoidal air cells. Two grooves cross these edges transversely; they are converted into the anterior and posterior ethmoidal canals by the ethmoid, and open on the medial wall of the orbit. The anterior canal transmits the nasociliary nerve and anterior ethmoidal vessels, the posterior, the posterior ethmoidal nerve and vessels. In front of the ethmoidal notch, on either side of the frontal spine, are the openings of the frontal air sinuses. These are two irregular cavities, which extend backward, upward. 236 OSTEOLOGY and lateralward for a variable distance between the two tables of the skull; they are separated from one another by a thin bony septum, which often deviates to one or other side, with the result that the sinuses are rarely symmetrical. Absent at birth, they are usually fairly well-developed between the seventh and eighth years, but only reach their full size after puberty. They vary in size in different persons, and are larger in men than in women. ^ They are lined by mucous mem- brane, and each communicates with the corresponding nasal cavity by means of a passage called the frontonasal duct. Supraorbital foramen With Tnaxdla With nasal With perpendicular plate of ethmoid Fiontal sinus Under surface of nasal process forming part of roof of nose Fig. 279. — Frontal bone. Inner surface. Borders. — The border of the squama is thick, strongly serrated, bevelled at the expense of the inner table above, where it rests upon the parietal bones, and at the expense of the outer table on either side, where it receives the lateral pressure of those bones; this border is continued below into a triangular, rough surface, which articulates with the great wing of the sphenoid. The posterior borders of the orbital plates are thin and serrated, and articulate with the small wings of the sphenoid. Structure. — The squama and the zygomatic processes are very thick, consisting of diploic tissue contained between two compact laminae; the diploic tissue is absent in the regions occupied by the frontal air sinuses. The orbital portion is thin, translucent, and composed entirely of compact bone; hence the facihty with which instruments can penetrate the cranium through this part of the orbit ; when the frontal sinuses are exceptionally large they may extend backward for a considerable distance into the orbital portion, which in such cases also consists of only two tables. 1 Aldren Turner (The Accessory Sinuses of the Nose, 1901) gives the following measurements for a sinus of average size: height, IM inches; breadth, 1 inch; depth from before backward, 1 inch. THE TEMPORAL BONE 237 Ossification (Fig. 280). — The frontal bone is ossified in membrane from two primary centres, one for each half, which appear toward the end of the second month of fetal life, one above each supraorbital margin. From each of these centres ossification extends upward to form the corresponding half of the squama, and backward to form the orbital plate. The spine is ossified from a pair of secondary centres, on either side of the middle line; similar centres appear in the nasal part and zygo- matic processes. At birth the bone consists of two pieces, separated by the frontal suture, which is usually obliterated, except at its lower part, by the eighth year, but occasionally persists throughout life. It is generally maintained that the development of the frontal sinuses begins at the end of the first or beginning of the second year, but Onodi's recent researches indicate that development begins at birth. The sinuses are of considerable size by the seventh or eighth year, but do not attain their full proportions until after puberty. Articulations. — The frontal articulates with twelve bones: the sphenoid, the eth- moid, the two parietals, the two nasals, the two maxiUse, the two laci'imals, and the two zygomatics. Squama Nasal pai't Zygomatic process Spine Fig. 280.— Frontal bone at birth. The Temporal Bone (Os Temporale). The temporal bones are situated at the sides and base of the skull. Each consists of five parts, viz., the squama, the petrous, mastoid, and tympanic parts, and the styloid process. The Squama (squama temporalis). — The squama forms the anterior and upper part of the bone, and is scale-like, thin, and translucent. Surfaces.— Its outer surface (Fig. 281) is smooth and convex; it affords attach- ment to the Temporalis muscle, and forms part of the temporal fossa; on its hinder part is a vertical groove for the middle temporal artery. A curved line, the tem- poral line, or supramastoid crest, runs backward and upward across its posterior part; it serves for the attachment of the temporal fascia, and limits the origin of the Temporalis muscle. The boundary between the squama and the mastoid portion of the bone, as indicated by traces of the original suture, lies about 1 cm. below this line. Projecting from the lower part of the squama is a long, arched process, the zygomatic process. This process is at first directed lateralward, its two surfaces looking upward and downward; it then appears as if twisted inward upon itself, and runs forward, its surfaces now looking medialward and lateralward. The superior border is long, thin, and sharp, and serves for the attachment of the temporal fascia; the inferior, short, thick, and arched, has attached to it some fibres of the Masseter. The lateral surface is convex and subcutaneous; the medial is concave, and affords attachment to the Masseter. The anterior end is deeply serrated and articulates with the zygomatic bone. The posterior end is connected to the squama by two roots, the anterior and posterior roots. The posterior root, a prolongation of the upper border, is strongly marked; it runs backward above the external acoustic meatus, and is continuous with the temporal line. The anterior root, continuous with the lower border, is short but broad and strong; it is directed medialward and ends in a rounded eminence, the articular tubercle {eminentia articularis) . This tubercle forms the front boundary of the mandibular fossa, and in the recent state is covered with cartilage. In front of the articular tubercle is a small triangular area which assists in forming the infratemporal fossa; this area is separated from the outer surface of the squama by a ridge which is continu- ous behind with the anterior root of the zygomatic process, and in front, in the 238 OSTEOLOGY articulated skull, with the iufrateliiporal crest on the great wing of the sphenoid. Between the posterior wall of the external acoustic meatus and the posterior root of the zygomatic process is the area called the suprameatal triangle (JNIacewen), or mastoid fossa, through which an instrument ma}' be pushed into the tympanic antrum. At the junction of the anterior root with the zygomatic process is a pro- jection for the attachment of the temporomandibular ligament; and behind the anterior root is an oval depression, forming part of the mandibular fossa, for the reception of the condyle of the mandible. The mandibular fossa {glenoid fossa) is bounded, in front, by the articular tubercle; behind, by the tympanic part of the bone, which separates it from the external acoustic meatus; it is divided into two parts by a narrow slit, the petrotympanic fissure {Glaserian fissure). The Groove for middle temporal artery Parietal notch S iipi ameatal tnangle Occipitalis Articular tubercle Post- glenoid process Mandibular fossa Petrotympanic fissure Vaginal process Styloglossus \ Tympa7iic part Stylohyoidecs Styloid process Fig. 281. — Left temporal bone. Outer surface. Occipital gwove anterior part, formed by the squama, is smooth, covered in the recent state with cartilage, and articulates wdth the condyle of the mandible. Behind this part of the fossa is a small conical eminence; this is the representative of a prominent tubercle which, in some mammals, descends behind the condyle of the mandible, and prevents its backward displacement. The posterior part of the mandibular fossa, formed by the tympanic part of the bone, is non-articular, and sometimes lodges a portion of the parotid gland. The petrotympanic fissure leads into the middle ear or tympanic cavity; it lodges the anterior process of the malleus, and transmits the tympanic branch of the internal maxillary artery. The chorda tympani nerve passes through a canal {ccmal of Huguier), separated from the an- terior edge of the petrotympanic fissure by a thin scale of bone and situated on the lateral side of the auditory tube, in the retiring angle between the squama and the petrous portion of the temporal. THE TEMPORAL BONE 239 The internal surface of the scjuamn (Fiji". 2(S2) is ccmcave; it jjreseiits clepressions correspoiuliiii;' to the eomolutioiis of the temporal lobe of the brain, and grooves for the branches of the middle meningeal vessels. Borders, — The superior border is thin, and bevelled at the expense of the internal table, so as to oNcrhip the scjnanions border of the parietal bone, forming with it the sqnamosal sntnre. Posteriorly, the superior border forms an angle, the parietal notch, with the mastoid portion of the bone. The anteroinferior border is thick, serrated, and bevelled at the expense of the inner table above and of the outer below, for articulation with the great wing of the sphenoid. Mastoid Portion [yars mastoidea). — The mastoid portion forms the posterior part of the bone. tctl h ^n. Par ieial notch Emineniia arcuala Mastoid foramen ' Aquceductus vestibuli Aqiiceductiis cochlece Internal acoustic w^eatus Fig. 282. — Left temporal bone. Inner surface. Surfaces. — Its outer surface (Fig. 281) is rough, and gives attachment to the Occipitalis and Auricularis posterior. It is perforated by numerous foramina; one of these, of large size, situated near the posterior border, is termed the mastoid foramen; it transmits a vein to the transverse sinus and a small branch of the occipi- tal artery to the dura mater. The position and size of this foramen are very variable; it is not always present; sometimes it is situated in the occipital bone, or in the suture between the temporal and the occipital. The mastoid portion is continued below into a conical projection, the mastoid process, the size and form of which vary somewhat; it is larger in the male than in the female. This process serves for the attachment of the Sternocleidomastoideus, Spleniuss capitis, and Longissimus capitis. On the medial side of the process is a deep groove, the mastoid notch (digastric fossa), for the attachment of the Digastricus; medial to this is a shallow fvirrow, the occipital groove, which lodges the occipital artery. 240 OSTEOLOGY The inner surface of the mastoid portion presents a deep, curved groove, the sigmoid sulcus, which lodges part of the transverse sinus; in it may be seen the opening of the mastoid foramen. The groove for the transverse sinus is separated from the innermost of the mastoid air cells by a very thin lamina of bone, and even this may be partly deficient. Borders. — The superior border of the mastoid portion is broad and serrated, for articulation with the mastoid angle of the parietal. The posterior border, also serrated, articulates with the inferior border of the occipital between the lateral angle and jugular process. Anteriorly the mastoid portion is fused with the descending process of the squama above; below it enters into the formation of the external acoustic meatus and the tympanic cavity. Ti/m panic antrum Tegmen tynvpani . Prominence of lateral semicircular canal Prominence of facial canal Fenestra vestibuli Bristle in semicanal for Tensor tympani Septum canalis musculctubarii Bristle in hiatus of facial canal Carotid canal Bony part of auditory tube Promontory Bristle in pyramid Fenestra cochleae Sulcus tympanicus Mastoid cells ^nstle in stylomastoid fora^nen Fig. 283. — Coronal section of right temporal bone. A section of the mastoid process (Fig. 283) shows it to be hollowed out into a number of spaces, the mastoid cells, which exhibit the greatest possible variety as to their size and number. At the upper and front part of the process they are large and irregular and contain air, but toward the lower part they diminish in size, while those at the apex of the process are frequently quite small and contain marrow; occasionally they are entirely absent, and the mastoid is then solid throughout. In addition to these a large irregular cavity is situated at the upper and front part of the bane. It is called the tympanic antrum, and must be distin- guished from the mastoid cells, though it communicates with them. Like the mas- toid cells it is filled with air and lined by a prolongation of the mucous membrane of the tympanic cavity, with which it communicates. The tympanic antrum is bounded above by a thin plate of bone, the tegmen tympani, which separates it from the middle fossa of the base of the skull; below by the mastoid process; later- ally by the squama just below the temporal line, and medially by the lateral semi- circular canal of the internal ear which projects into its cavity. It opens in front into that portion of the tympanic cavity which is known as the attic or epitympanic THE TEMPO HAL BONE 241 recess. The tympanic antrum is a cavity of some considerable size at the time of hirth; the mastoid air cells may he ref>arded as diverticula from the antrum, and begin to appear at or before birth; by the fifth year they are well-marked, but tiieir development is not completed until toward puberty. Petrous Portion {pars petrosa [pyramis]). — The petrous portion or pyramid is pyramidal and is wedged in at the base of the skull between the sphenoid and occipital. Directed medialward, forward, and a little upward, it presents for examination a base, an apex, three surfaces, and three angles, and contains, in its interior, the essential parts of the organ of hearing. Base. — The base is fused with the internal surfaces of the squama and mastoid portion. Apex. — The apex, rough and uneven, is received into the angular inter\'al between the posterior border of the great wing of the sphenoid and the basilar part of the occipital; it presents the anterior or internal orifice of the carotid canal, and forms the postero-lateral boundary of the foramen lac- erum. Surfaces. — The anterior surface forms the posterior part of the middle fossa of the base of the skull, and is continuous with the inner surface of the squamous portion, to which it is united by the petrosquamous suture, remains of which are distinct even at a late period of life. It is marked by depressions for the convolutions of the brain, and presents six points for examination: (1) near the centre, an eminence {eminentia arcuata) which indicates the situation of the superior semi- circular canal; (2) in front of and a little lateral to this eminence, a depression indicating the position of the tympanic cavity: here the layer of bone which separates the tympanic from the cranial cavity is extremely thin, and is known as the tegmen tympani; (3) a shallow groove, sometimes double, leading lateral ward and backward to an oblique open- ing, the hiatus of the facial canal, for the passage of the greater superficial petrosal nerve and the petrosal branch of the middle meningeal artery; (4) lateral to the hiatus, a smaller opening, occasionally seen, for the passage of the lesser superficial petrosal nerve; (5) near the apex of the bone, the termination of the carotid canal, the w'all of w^hich in this situation is deficient in front; (6) above this canal the shallow trigeminal impression for the reception of the semilunar ganglion. The posterior surface (Fig. 282) forms the front part of the posterior fossa of the base of the skull, and is continuous with the inner surface of the mastoid portion. Near the centre is a large orifice, the internal acoustic meatus, the size of which varies considerably; its margins are smooth and rounded, and it leads into a short canal, about 1 cm. in length, which runs lateralward. It transmits the facial and acoustic nerves and the internal auditory branch of the basilar artery. The lateral end of the canal is closed by a vertical plate, which is divided by a horizontal crest, the crista falciformis, into two unequal portions (Fig. 284). Each portion is further subdivided by a vertical ridge into an anterior and a posterior part. In the portion beneath the crista falciformis are three sets of foramina; one group, just below the posterior part of the crest, situated in the area cribrosa media, consists of several small openings for the nerves to the saccule; below and 16 Fig. 284. — Diagrammatic view of the fundus of the right internal acoustic meatus. (Testut.) 1. Crista falciformis. 2. Area facialis, with (2') internal opening of the facial canal. 3. Ridge separating the area facialis from the area crib- rosa superior. 4. Area cribrosa superior, with (4') openings for nerve filaments. 5. Anterior inferior cribriform area, with (5') the tractus spiralis foraminosus, and (5") the canaUs cen- tralis of the cochlea. 6. Ridge separating the tractus spiralis foraminosus from the area crib- rosa media. 7. Area cribrosa media, with (7') orifices for nerves to saccule. 8. Foramen singulare. 242 OSTEOLOGY behind this area is the foramen singulare, or opening for the nerAe to the posterior semieircuhir duct; in front of and below the first is the tractus spiralis foraminosus, consisting of a number of small spirally arranged openings, which encircle the canalis centralis cochleae; these openings together with this central canal transmit the nerves to the cochlea. The portion above the crista falciformis presents behind, the area cribrosa superior, pierced by a series of small openings, for the passage of the nerves to the utricle and the superior and lateral semicircular ducts, and, in front, the area facialis, with one large opening, the commencement of the canal for the facial nerve (aquaeductus Fallopii). Behind the internal acoustic meatus is a small slit almost hidden by a thin plate of bone, leading to a canal, the aquae- ductus vestibuli, which transmits the ductus endolymphaticus together with a small artery and vein. Above and between these two openings is an irregular depression which lodges a process of the dura mater and transmits a small vein; in the infant this depression is represented by a large fossa, the subarcuate fossa, which extends backward as a blind tunnel under the superior semicircular canal. Semicanals for • auditory tube and Tensor tympa7ii Lev. veli palatin Rmcgh quadrilateral surface Opening of carotid canal Inferior tympanic canaliculus Aquaeductus cochleae JIastoid canaliculus Jugular fossa Vaginal process Styloid process Stylomastoid foramen Jugular surface Tympanomastoid fissure Stylopharyngeus Fig. 285. — Left temporal bone. Inferior surface. The inferior surface (Fig. 285) is rough and irregular, and fornis part of the exterior of the base of the skull. It presents eleven points for examination: (1) near the apex is a rough surface, quadrilateral in form, which serves partly for the attachment of the Levator veli palatini and the cartilaginous portion of the audi- tory tube, and partly for connection with the basilar part of the occipital bone through the intervention of some dense fibrous tissue; (2) behind this is the large circular aperture of the carotid canal, which ascends at first vertically, and then, making a bend, runs horizontally forward and medialward; it transmits into the cranium the internal carotid artery, and the carotid plexus of nerves; (3) medial to the opening for the carotid canal and close to its posterior border, in front of THE TEMPORAL BOXE 243 the juniilar fossii, is a triangular depression; at the apex of this is a small oj)ening, the aquaeductus cochleae, whieh lodges a tubular i)r<)l()n^ation of the dura mater and transmits a vein from the cochlea to join the internal jujj;ular; (4) behind these openings is a deep depression, the jugular fossa, of variabl(> d(>i)th and si/e in difl'erent skulls; it lodges the bulb of the internal jugular vein; (5) in the bony ridge dividing the carotid canal from the jugular fossa is the small inferior tympanic canaliculus for the passage of the tympanic branch of the glossoi)liaryngeal ner\-e; ((i) in the lateral part of the jugular fossa is the mastoid canaliculus for the entrance of the auricular branch of the vagus nerve; (7) behind the jugular fossa is a quadrilateral area, the jugular surface, covered with cartilage in the recent state, and articulating Avith the jugular process of the occipital bone; (8) extending backward from the carotid canal is the vaginal process, a sheath-like plate of bone, which di\'ides behind into two laminae; the lateral lamina is continuous with the tympanic part of the bone, the medial with the lateral margin of the jugular surface; (9) between these lamina? is the styloid process, a sharp spine, about 2.5 cm. in length; (10) between the styloid and mastoid processes is the stylomastoid foramen; it is the termination of the facial canal, and transmits the facial nerve and stylomastoid artery; (11) situated between the tympanic portion and the mastoid process is the tympanomastoid fissure, for the exit of the auricular branch of the vagus nerve. Angles. — The superior angle, the longest, is grooved for the superior petrosal sinus, and gives attachment to the tentorium cerebelli; at its medial extremity is a notch, in which the trigeminal nerve lies. The posterior angle is intermediate in length between the superior and the anterior. Its medial half is marked by a sulcus, w^hich forms, with a corresponding sulcus on the occipital bone, the channel for the inferior petrosal sinus. Its lateral half presents an excavation — the jugular fossa — which, with the jugular notch on the occipital, forms the jugular foramen ; an eminence occasionally projects from the centre of the fossa, and divides the foramen into two. The anterior angle is divided into two parts — a lateral joined to the squama by a suture {petrosquamous) , the remains of which are more or less distinct; a medial, free, which articulates with the spinous process of the sphenoid. At the angle of junction of the petrous part and the squama are two canals, one above the other, and separated by a thin plate of bone, the septum canalis musculotubarii {processus cochleariformis) ; both canals lead into the tympanic cavity. The upper one {semicanalis m. tensoris tympani) transmits the Tensor tympani, the lower one {semicanalis tuhae auditivae) forms the bony part of the auditory tube. The tympanic cavity, auditory ossicles, and internal ear, are described with the organ of hearing. Tympanic Part {pars tympanica). — The tympanic part is a curved plate of bone lying below the squama and in front of the mastoid process. Surfaces. — Its postero-superior surface is concave, and forms the anterior wall, the floor, and part of the posterior wall of the bony external acoustic meatus. Medially, it presents a narrow furrow, the tympanic sulcus, for the attachment of the tympanic membrane. Its antero-inferior surface is quadrilateral and slightly concave; it constitutes the posterior boundary of the mandibular fossa, and is in contact with the retromandibular part of the parotid gland. Borders. — Its lateral border is free and rough, and gives attachment to the car- tilaginous part of the external acoustic meatus. Internally, the tympanic part is fused wnth the petrous portion, and appears in the retreating angle between it and the squama, where it lies below and lateral to the orifice of the auditory tube. Posteriorly, it blends with the squama and mastoid part, and forms the anterior boundary of the tympanomastoid fissure. Its upper border fuses laterally with the back of the postglenoid process, while medially it bounds the petro- 244 OSTEOLOGY tympanic fissure. The medial part of tlie lower border is thin and sharp; its lateral part splits to enclose the root of the styloid process, and is therefore named the vaginal process. The central portion of the tympanic part is thin, and in a consid- erable percentage of skulls is perforated by a hole, the foramen of Huschke. The external acoustic meatus is nearly 2 cm. long and is directed inward and slightly forward: at the same time it forms a slight curve, so that the floor of the canal is convex upward. In sagittal section it presents an oval or elliptical shape with the long axis directed downward and slightly backward. Its anterior wall and floor and the lower part of its posterior wall are formed by the tympanic part; the roof and upper part of the posterior wall by the squama. Its inner end is closed, in the recent state, by the tympanic membrane; the upper limit of its outer orifice is formed by the posterior root of the zygomatic process, imme- diately below which there is sometimes seen a small spine, the suprameatal spine, situated at the upper and posterior part of the orifice. Styloid Process {processus styloideus). — The styloid process is slender, pointed, and of varying length; it projects downward and forw^ard, from the under surface of the temporal bone. Its proximal part {tymjMnokyal) is ensheathed by the vaginal process of the tympanic portion, while its distal part {styhhyal) gives attachment to the stylohyoid and stylomandibular ligaments, and to the Stylo- glossus, Stylohyoideus, and Stylopharyngeus muscles. The stylohyoid ligament extends from the apex of the process to the lesser cornu of the hyoid bone, and in some instances is partially, in others completely, ossified. Septum canalis musculotubarii Fenestra vestibuli Tympanic antrum ] Sulcus tympanicus Bristle in facial canal Lateral wall of tympanic antrum Fig. 286. — The three principal parts of the temporal bone at birth. 1. Outer surface of petromastoid part. 2. Outer surface of tjTnpanio ring. 3. Inner surface of squama. Structure. — The structure of the squama is hke that of the other cranial bones: the mastoid portion is spongy, and the petrous portion dense and hard. Ossification. — The temporal bone is ossified from eight centres, exclusive of those for the internal ear and the tympanic ossicles, viz., one for the squama including the zygomatic process, one for the tympanic part, four for the petrous and mastoid parts, and two for the styloid process. Just before the close of fetal hfe (Fig. 286) the temporal bone consists of three principal parts: 1. The squama is ossified in membrane from a single nucleus, which appears near the root of the zygomatic process about the second month. 2. The petromastoid part is developed from four centres, which make their appearance in the cartilaginous ear capsule about the fifth or sixth month. One (prootic) appears in the neighborhood of the eminentia arcuata, spreads in front and above the internal acoustic meatus and extends to the apex of the bone; it forms part of the cochlea, vestibule, superior semicircular canal, and medial wall of the tympanic cavity. A second {opisthoticy appears at the promontory on the medial wall of the tympanic cavity and surrounds the fenestra cochleae; it forms the floor of the tympanic cavity and vestibule, surrounds the carotid canal, inve.sts the lateral and lower part of the cochlea, and spreads medially below the internal THE SPHENOIDAL BONE 245 acoustic meatus. A third (plerotic) roofs in the tympanic cavity and antrum; while the fourth (epiotic) appears near the posterior semicircular canal and extends to form the mastoid process (VroUk). 3. The lympaidc ring is an incomplete circle, in the concavity of which is a groove, the tympanic sulcus, for the attachment of the circumference of the tyrn[)anic membrane. This ring expands to form the tympanic part, and is ossified in membrane from a single centre which appears about the third month. The styloid process is developed from the proximal part of the cartilage of the second branchial or hyoid arch by two centres: one for the proximal part, the tynipanohyal, appears before birth; the other, comprising the rest of the process, is named the stylohyal, and does not appear until after birth. The tympanic ring unites with the squama shortly before birth; the petromastoid part and squama join during the first year, and the tym- panohVal portion of the styloid process about the same time (Figs. 287, 288). The stylohyal does not unite with the rest of the bone until after puberty, and in some skulls never at all. Squama Squama Petrosquamous suture Petrosquamous suture Emineyitia arcuata Tympanic ring Petromastoid portion Fig. 287. — Temporal bone at birth. Outer aspect. Fossa suharcuata Internal acoustic meatus Fig. 288. — Temporal bone at birth. Inner aspect. The chief subsequent changes in the temporal bone apart from increase in size are: (1) The tympanic ring extends outward and backward to form the tympanic part. This extension does not, however, take place at an equal rate all around the circumference of the ring, but occurs most rapidly on its anterior and posterior portions, and these outgrowths meet and blend, and thus, for a time, there exists in the floor of the meatus a foramen, the foramen of Huschke; this foramen is usually closed about the fifth year, but may persist throughout fife. (2) The mandibular fossa is at first extremely shallow, and looks lateralward as well as downward; it becomes deeper and is ultimately directed downward. Its change in direction is accounted for as follows. The part of the squama which forms the fossa Ues at first below the level of the zygomatic process. As, however, the base of the skull increases in width, this lower part of the squama is directed hori- zontally inward to contribute to the middle fossa of the skull, and its sm-faces therefore come to look upward and downward; the attached portion of the zygomatic process also becomes everted, and projects like a shelf at right angles to the squama. (3) The mastoid portion is at first quite flat, and the stylomastoid foramen and rudimentary styloid process he immediately behind the tympanic ring. With the development of the air cells the outer part of the mastoid portion grows downward and forward to form the mastoid process, and the styloid process and stylomastoid foramen now come to he on the imder surface. The descent of the foramen is necessarily accompanied by a corresponding lengthening of the facial canal. (4) The dowTiward and forward growth of the mastoid process also pushes forward the tympanic part, so that the portion of it w-hich formed the original floor of the meatus and contained the foramen of Huschke is ultimately found in the anterior wall. (5) The fossa subarcuata becomes filled up and almost obhterated. Articulations. — The temporal articulates vfUhfive bones: occipital, parietal, sphenoid, mandible, and zygomatic. The Sphenoidal Bone (Os Sphenoidal; Sphenoid Bone). The sphenoidal bone is situated at the base of the skull in front of the temporals and basilar part of the occipital. It some^Yhat resembles a bat with its wings 246 OSTEOLOGY extended, and is divided into a median portion or body, two great and two small wings extending outward from the sides of the body, and two pterygoid processes which project from it below. Body (corpus syhenoidalis) . — The body, more or less cubical in shape, is hollowed out in its interior to form two large ca^-ities, the sphenoidal air sinuses, which are separated from each other by a septum. Surfaces, — The superior surface of the body (Fig. 289) presents in front a promi- nent spine, the ethmoidal spine, for articulation with the cribriform plate of the ethmoid; behind this is a smooth surface slightly raised in the middle line, and grooved on either side for the olfactory lobes of the brain. This surface is bounded behind by a ridge, which forms the anterior border of a narrow, transverse groove, the chiasmatic groove {oytic groove), above and behind which lies the optic chiasma; the groove ends on either side in the optic foramen, which transmits the optic nerve and opthalmic artery into the orbital cavity. Behind the chiasmatic groove is an olive-like elevation, the tuberculum sellae; and still more posteriorly, a deep depression, the sella turcica, the deepest part of which lodges the hypophysis Middle Clinoid process Posterior Clinoid process Ethmoidal spine Groove for i ^.,, olfactory ,Y . I fg I ethmoiC / al^-"^' Optic foramen Superior orbital fissure Foramen rotundum Foramen Vesalii Foramen ovale Foramen spinosum Spina angularis palatine Fig. 289. — Sphenoidal bone. Upper surface. cerebri and is known as the fossa hypophyseos. The anterior boundary of the sella turcica is completed by two small eminences, one on either side, called the middle clinoid processes, while the posterior boundary is formed by a square- shaped plate of bone, the dorsum sellae, ending at its superior angles in two tuber- cles, the posterior clinoid processes, the size and form of which vary considerably in different individuals. The posterior clinoid processes deepen the sella turcica, and give attachment to the tentorium cerebelli. On either side of the dorsum sellae is a notch for the passage of the abducent nerve, and below the notch a sharp process, the petrosal process, which articulates with the apex of the petrous portion of the temporal bone, and forms the medial boundary of the foramen lacerum. Behind the dorsum sellae is a shallow depression, the clivus, which slopes obliquely backward, and is continuous with the groove on the basilar portion of the occipital bone; it supports the upper part of the pons. The lateral surfaces of the body are united with the great wings and the medial pterygoid plates. Above the attachment of each great wing is a broad groove, curved something like the italic letter /; it lodges the internal carotid artery and THE SPHEXOIDAL BONE 247 the cavernous sinus, and is named the carotid groove. Ak)ng the posterior part of the lateral margin of this , and it is not until the third year that they become hollowed out and cone-shaped; about the fourth year they fuse with the labyi-inths of the ethmoid, and between the ninth and twelfth years the}^ unite with the sphenoid. Postsphenoid, — The first ossific nuclei are those for the great wings (ali-sphenoids) . One makes its appearance in each wing between the foramen rotundum and foramen ovale about the eighth week. The orbital plate and that part of the sphenoid which is found in the temporal fossa, as well as the lateral pterygoid plate, are ossified in membrane (Fawcett-). Soon after, the centres for the postsphenoid part of the body appear, one on either side of the sella turcica, and become blended together about the middle of fetal life. Each medial pterygoid plate (with the exception of its hamulus) is ossified in membrane, and its centre probably appears about the ninth or tenth w^eek; the hamulus becomes chondrified during the third month, and almost at once undergoes ossification (Fawcett^). The medial joins the lateral pterygoid plate about the sixth month. About the fourth month a centre appears for each lingula and speedily joins the rest of the bone. The presphenoid is united to the postsphenoid about the eighth month, and at birth the bone is in three pieces (Fig. 292) : a central, consisting of the body and small wings, and two lateral, each comprising a gi'eat wing and ptery- goid process. In the first year after birth the great wings and body unite, and the small wings extend inward above the anterior part of the body, and, meeting with each other in the middle line, form an elevated smooth surface, termed the jugum sphenoidale. By the twenty-fifth year the sphenoid and occipital are completely fused. Be- tween the pre- and postsphenoid there are occasionally seen the remains of a canal, the canalis craniopharyngeus, through which, in early fetal life, the hypophyseal diverticulum of the buccal ectoderm is transmitted (see page 166). The sphenoidal sinuses are present as minute cavities at the time of birth (Onodi), but do not attain their full size until after puberty. Certain intrinsic Ugaments are attached to the sphenoid. The more important of these are: the pterygospinous, stretching between the spina angularis and the lateral pterygoid plate (see cervical fascia); the interclinoid, a fibrous process joining the anterior to the posterior clinoid process; and the caroticoclinoid, connecting the anterior to the middle clinoid process. These ligaments occasionally ossify. Articulations. — The sphenoid articulates with twelve bones: fom- single, the vomer, ethmoid, frontal, and occipital; and four paired, the parietal, temporal, zygomatic, and palatine.* Fig. 292. — Sphenoidal bone at birth. Posterior aspect. The Ethmoidal Bone (Os Ethmoidale; Ethmoid Bone). The ethmoidal bone is exceedingly light and spongy, and cubical in shape; it is situated at the anterior part of the base of the cranium, between the two orbits, at the roof of the nose, and contributes to each of these cavities. It consists of four parts: a horizontal or cribriform plate, forming part of the base of the cranium; a perpendicular plate, constituting part of the nasal septum; and two lateral masses or labvrinths. 1 According to Cleland, each sphenoidal concha is ossified from four centres. 2 Journal of Anatomy and Physiology, 1910, vol. xliv. 2 Anatomischer Anzeiger, March, 1905. * It also sometimes articulates with the tuberosity of the maxilla (see page 257). 252 OSTEOLOGY Perpendicular plate Ala Crista gain Cribiform Plate (lamina cribrosa; horizontal lamina). — The cribriform plate (Fig. 293) is received into the ethmoidal notch of the frontal bone and roofs in the nasal cavities. Projecting upward from the middle line of this plate is a thick, smooth, triangular process, the crista galli, so called from its resemblance to a cock's comb. Its posterior border, long, thin, and slightly curved, serves for the attachment of the falx cerebri. Its anterior border, short and thick, articulates with the frontal bone, and presents two small pro- jecting alae, which are received into corresponding depressions in the frontal bone and complete the foramen cecum. Its sides are smooth, and sometimes bulging from the presence of a small air sinus in the interior. On either side of the crista galli, the cribri- form plate is narrow and deeply grooved; it supports the olfactory V , '£ ;-.\ j/ktl - Posterior ethmoidal bulb and is perforated by fora- •''^*^»' -■,--<>' y^ groove mina for the passage of the olfac- tory nerves. The foramina in the middle of the groove are small and transmit the nerves to the roof of the nasal cavity; those at the medial and lateral parts of the groove are larger — the former transmit the nerves to the upper part of the nasal septum, the latter those to the superior nasal concha. At the front part of the cribriform plate, on either side of the crista galli, is a small fissure which is occupied by a process of dura mater. Lateral to this fissure is a notch or foramen which trans- mits the nasociliary nerve; from this notch a groove extends backward to the anterior ethmoidal foramen. Cribriform jdate Anterior ethmoidal groove Fig. 293. — ^Ethmoidal bone from above. ^th EtAmoidtii Fig. 29-1. — Perpendicular plate of ethmoid. Shown by removnng the right labyrinth. Perpendicular Plate {lamina perpendicular is; vertical plate). — The perpendicular plate (Figs. 294, 295) is a thin, fiattened lamina, polygonal in form, which descends from the under surface of the cribriform plate, and assists in forming the septum of the nose; it is generally deflected a little to one or other side. The anterior border THE ETHMOIDAL BOXE 253 articulates with the spine of the frontal hone and the crest of the nasal hones. The posterior border articulates hy its upper half with the sphenoidal crest, b\' its lower with the vomer. The inferior border is thicker than the posterior, and serves for the attachment of the septal cartilage of the nose. The surfaces of the plate are smooth, except above, where numerous grooves and canals are seen; these lead from the medial foramina on the cribriform ])late and lodge filaments of the olfactory nerves. The Labyrinth or Lateral Mass Qahyriufhus ethmoidalis) consists of a number of thin-walled cellular cavities, the ethmoidal cells, arranged in three groups, anterior, middle, and yosterior, and inter- posed between two vertical plates of bone ; the lateral plate forms part of the orbit, the medial, part of the corresponding nasal cavity. In the disarticulated bone many of these cells are opened into, but when the bones are articulated, they are closed in at every part, except where they open into the nasal cavity. Surfaces. — The upper surface of the laby- rinth (Fig. 293) presents a number of half-broken cells, the walls of which are completed, in the articulated skull, by the edges of the ethmoidal notch of the frontal bone. Crossing this surface are two grooves, converted into canals by articulation with the frontal; they are the anterior and posterior ethmoidal canals, and open on the inner wall of the orbit. The posterior surface presents large irregular cellular cavities, which are closed in by articulation with the sphenoidal concha and orbital process of the palatine. The lateral surface (Fig. 296) is formed of a thin, smooth, oblong plate, the lamina papyracea {os planum), which covers in the middle and posterior ethmoidal cells Fig. 295. Crista fjalU Labyrinth Superior nasal concha Superior meatus Uncinate process Middle nasal concha Perpendicular plate Ethmoidal bone from behind. Ethmoidal cells Perpendicular plate Uncinate process Fig. 296. — Ethmoidal bone from the right side. and forms a large part of the medial wall of the orbit; it articulates above with the orbital plate of the frontal bone, below with the maxilla and orbital process of the palatine, in front with the lacrimal, and behind with the sphenoid. In front of the lamina papyracea are some broken air cells which are overlapped and completed by the lacrimal bone and the frontal process of the maxilla. A curved lamina, the uncinate process, projects downward and backward from this part of the labyrinth; it forms a small part of the medial wall of the maxillary sinus, and articulates with the ethmoidal process of the inferior nasal concha. 254 OSTEOLOGY The medial surface of the labyrinth (Fig. 297) forms part of the lateral wall of the corresponding nasal cavity. It consists of a thin lamella, which descends from the under surface of the cribriform plate, and ends below in a free, convoluted margin, the middle nasal concha. It is rough, and marked above by numerous grooves, directed nearly vertically downward from the cribriform plate; they lodge branches of the olfactory nerves, which are distributed to the mucous mem- brane covering the superior nasal concha. The back part of the surface is sub- divided by a narrow oblique fissure, the superior meatus of the nose, bounded above by a thin, curved plate, the superior nasal concha; the posterior ethmoidal cells open into this meatus. Below, and in front of the superior meatus, is the convex Frontal sinus -Crista galli Sella turcica Uncinate process of ethmoid Openings into maxillary sinus Medial pterygoid plate Hamulus Fig. 297. — Lateral wall of nasal cavity, showing ethmoidal bone in position. surface of the middle nasal concha; it extends along the wdiole length of the medial surface of the labyrinth, and its lower margin is free and thick. The lateral surface of the middle concha is concave, and assists in forming the middle meatus of the nose. The middle ethmoidal cells open into the central part of this meatus, and a sinuous passage, termed the infundibulum, extends upward and forward through the labyrinth and communicates with the anterior ethmoidal cells, and in about 50 per cent, of skulls is continued upward as the frontonasal duct into the frontal sinus. Ossification. — The ethmoid is ossified in the cartilage of the nasal capsule by three centres: one for the perpendicular plate, and one for each labyrinth. The labyrinths are first developed, ossific granules making their appearance in the region of the lamina papyia.cea between the fourth and fifth months of fetal life, and extending into the conchse. At birth, the bone consists of the two labyrinths, which are small and ill-developed. During the first year after birth, the perpendicular plate and crista gaUi begin to ossify from a single centre, and are joined to the labyrinths about the beginning of the second year. The cribriform plate is ossified partly from the perpendicular plate and partly from the labyrinths. The development of the ethmoidal cells begins during fetal life. THE NASAL BOXES 255 Articulations. — The ethmoid articulates with fifteen bones: four of the cranium — the frontal, the si)heiioi(l, and the two sphenoidal concha?; and eleven of the face — the two nasals, two maxilla;, two latrinials. two palatines, two inferior nasal concha?, and the vomer. Sutural or Wormian' Bones. — In addition to the usual centres of o.ssification of the craniinn, others may occin- in the course of the sutures, giving rise to irregular, isolated bones, termed sutural or Wormian bones. They occur most frequently in the course of the lambdoidal suture, but are occasionally seen at the fontanelles, especially the ])osterior. One, the plerion ossicle, sometimes exists between the sphenoidal angle of the i)arietal and the great wing of the .sphenoid. They have a tendency to be more or less symmetrical on the two sides of the .skull, and vary much in size. Their number is generally limited to two or three; but more than a hundred have been ftnmd in th(> skull of an adult hydrocephalic subject. Applied Anatomy. — An arrest in the ossifying process' may give rise to deficiencies, gaps, or fissures in the cranium, which are of importance from a medicolegal point of view, as thej^ arc liable to be mistaken for fractures. The fissures generally extend from the margins toward the centre of a bone, but the gaps may be found in the middle as well as at the edges. In course of time they maj' become filled with thin laminae of bone. In manj^ of these cases, however, the gaps must be regarded as due to absorption of bone already formed rather than as congenital deficiencies; this is especially the case when they appear in the centre of a bone such as the parietal, the ossification of which has already been described as occurring in a regular manner radiating from one centre. The condition is most commonly seen in verj^ badly nom'ished children affected with congenital syphilis, and is called cranioiabes. THE FACIAL BONES (OSSA FACIEI). The Nasal Bones (Ossa Nasalia) . The nasal bones are two small oblong bones, varying in size and form in different individuals; they are placed side by side at the middle and upper part of the face, FuitVi Joi lac) oiKil sac Infraorhiial foramen Fig. 298. — Articulation of nasal and lacrimal bones with maxilla. and form, by their junction, "the bridge" of the nose (Fig. 334). Each has two surfaces and four borders. ' Ole Worm, Professor of Anatomy at Copenhagen, 1624-1639, was erroneously supposed to have given the first detailed description of these bones. 256 OSTEOLOGY Surfaces. — The outer surface (Fig. 299) is concavoconvex from above downward, convex from side to side; it is covered by the Procerus and Compressor naris, and perforated about its centre by a foramen, for the transmission of a small vein. The inner surface (Fig. 300) is concave from side to side, and is traversed from above downward, by a groove for the passage of a branch of the nasociliary nerve. Borders. — The superior border is narrow, thick, and serrated for articulation with the nasal notch of the frontal bone. The inferior border is thin, and gives attach- ment to the lateral cartilage of the nose; near its middle is a notch which marks the end of the groove just referred to. The lateral border is serrated, bevelled at the expense of the inner surface above, and of the outer below, to articulate with the frontal process of the maxilla. The medial border, thicker above than below, articulates with its fellow of the opposite side, and is prolonged behind into a vertical crest, which forms part of the nasal septum : this crest articulates, from above downward, with the spine of the frontal, the perpendicular plate of the ethmoid, and the septal cartilage of the nose. nvi'^yi Foramen fci' vein Fig. 299. — Right nasal bone. Outer surface. Crest Groove for nerve Fig. 300. — Right nasal bone. Inner surface. Ossification. — Each bone is ossified from one centre, which appears at the beginning of the third month of fetal life in the membrane overlying the front part of the cartilaginous nasal capsule. Articulations. — The nasal articulates with four bones: two of the cranium, the frontal and ethmoid, and two of the face, the opposite nasal and the maxilla. The Maxillae (Upper Jaw). The maxillae are the largest bones of the face, excepting the mandible, and form; by their union, the whole of the upper jaw. Each assists in forming the boundaries of three cavities, viz., the roof of the mouth, the floor and lateral wall of the nose and the floor of the orbit; it also enters into the formation of two fossse, the infratemporal and pterygopalatine, and two fissures, the inferior orbital and pterygomaxillary. Each bone consists of a body and four processes — zygomatic, frontal, alveolar, and palatine. The Body {corpus maxillae). — The body is somewhat pyramidal in shape, and contains a large cavity, the maxillary sinus {antrum of Highmore). It has four surfaces — an anterior, a posterior or infratemporal, a superior or orbital, and a medial or nasal. Surfaces. — The anterior surface (Fig. 301) is directed forward and lateralward. It presents at its lower part a series of eminences corresponding to the positions of the roots of the teeth. Just above those of the incisor teeth is a depression, the incisive fossa, which gives origin to the Depressor alae nasi; to the alveolar border below the fossa is attached a slip of the Orbicularis oris; above and a little lateral to it, the Xasalis arises. Lateral to the incisive fossa is another depression. THE MAXILL.E 257 the canine fossa; it is larger and deeper than the incisive fossa, and is separated from it by a \ertical ridge, the canine eminence, corresponding to the socket of the canine tooth; tiie canine fossa gives origin to the Caninus. Above the fossa is the infraorbital foramen, the end of the infraorbital canal; it transmits the infra- orbital vessels and ncr\e. iVbove the foramen is the margin of the orbit, which affords attachment to part of the Quadratus labii superioris. Medially, the anterior surface is limited by a deep concavity, the nasal notch, the margin of which gives attachment to the Dilatator naris posterior and ends below in a pointed process, whic-h with its fellow of the opposite side forms the anterior nasal spine. Med. palp Dilatator naris posterior tubercle Incisive Jossa Alveolar canals Maxillary tuberosity Fig. 301. — Left maxilla Outer surface. The infratemporal surface (Fig. 301) is convex, directed backw^ard and lateral- ward, and forms part of the infratemporal fossa. It is separated from the anterior surface by the zygomatic process and by a strong ridge, extending upward from the socket of the first molar tooth. It is pierced about its centre by the apertures of the alveolar canals, which transmit the posterior superior alveolar vessels and nerves. At the lower part of this surface is a rounded eminence, the maxillary tuberosity, especially prominent after the growth of the wisdom tooth; it is rough on its lateral side for articulation with the pyramidal process of the palatine bone and in some cases articulates with the lateral pterygoid plate of the sphenoid. It gives origin to a few fibres of the Pterygoideus internus. Immediately above this is a smooth surface, which forms the anterior boundary of the pterygopalatine fossa, and presents a groove, for the maxillary nerve; this groove is directed lateral- ward and slightly upward, and is continuous with the infraorbital groove on the orbital surface. The orbital surface (Fig. 301) is smooth and triangular, and forms the greater part of the floor of the orbit. It is bounded mediaUy by an irregular margin which in front presents a notch, the lacrimal notch; behind this notch the margin articu- lates with the lacrimal, the lamina papyracea of the ethmoid and the orbital process of the palatine. It is bounded hehind by a smooth rounded edge which forms the anterior margin of the inferior orbital fissure, and sometimes articulates at its lateral extremity with the orbital surface of the great wing of the sphenoid. 17 258 OSTEOLOGY It is limited in front by part of the circumference of the orbit, which is continuous medially with the frontal process, and laterally with the zyogmatic prf)cess. Near the middle of the posterior part of the orbital surface is the infraorbital groove, for the passage of the infraorbital vessels and nerve. The groove begins at the middle of the posterior border, where it is continuous with that near the upper edge of the infratemporal surface, and, passing forward, ends in a canal, which subdivides into two branches. One of the canals, the infraorbital canal, opens just below the margin of the orbit; the other, which is smaller, runs downward in the substance of the anterior wall of the maxillary sinus, and transmits the anterior superior alveolar vessels and nerve to the front teeth of the maxilla. From the back part of the infraorbital canal, a second small canal is sometimes given off; it runs downward in the lateral wall of the sinus, and conveys the middle alveolar nerve to the premolar teeth. At the medial and forepart of the orbital surface, just lateral to the lacrimal groove, is a depression, which gives origin to the Obliquus oculi inferior. With frontal Bones 'partially closing orifice of sinus tnarked in red Ethmoid — Inferior nasal concha- Palatine th nasal hone Ant. nasal spine Bristle passed through incisive canal Fig. 302. — Left maxilla. Nasal surface. The nasal surface (Fig. 302) presents a large, irregular opening leading into the maxillary sinus. At the upper border of this aperture are some broken air cells, which, in the articulated skull, are closed in by the ethmoid and lacrimal bones. Below the aperture is a smooth concavity which forms part of the inferior meatus of the nasal cavity, and behind it is a rough surface for articulation with the per- pendicular part of the palatine bone; this surface is traversed by a groove, com- mencing near the middle of the posterior border and running obliquely downward and forward; the groove is converted into a canal, the pterygopalatine canal, by the palatine bone. In front of the opening of the sinus is a deep groove, the lacrimal groove, which is converted into the nasolacrimal canal, by the lacrimal bone and inferior nasal concha; this canal opens into the inferior meatus of the nose and transmits the nasolacrimal duct. More anteriorly is an oblique ridge, the conchal crest, for articulation with the inferior nasal concha. The shallow concavity above this ridge forms part of the atrium of the middle meatus of the nose, and that below it, part of the inferior meatus. THE MAXILL.E 259 The Maxillary Sinus or Antrum of Highmore {sinus maxillaris). — The maxillary sinus is a large pyramidal c'a\ity, within the body of the maxilla: its apex, directed laterahvard, is formed by the zygDmatic process; its base, directed mediahvard, by the lateral wall of the nose. Its walls are everywhere exceedingly thin, and correspond to the nasal orbital, anterior, and infratemporal surfaces of the body of the bone. Its nasal wall, or base, presents, in the disarticulated bone, a large, irregular aperture, connnnnicating with the nasal cavity. In the articulated skull this aperture is much reduced in size by the following bones: the uncinate process of the ethmoid above, the ethmoidal process of the inferior nasal concha below, the vertical part of the palatine behind, and a small part of the lacrimal above and in front (Figs. 302, 303) ; the sinus communicates with the middle meatus of the nose, generally by two small apertures left between the above-mentioned bones. In the recent state, usually only one small opening exists, near the upper Anterior ethmoidal Joraimn Fossa for lacrimal sac Uncinate process of ethmoid Openings of maxillary sinus Inferior nasal concha .Posterior ethmoidal foramen '^Orbital process of palatine Gplic forainen Sphenopalatine foramen Sella turcica I Probe in foramen rot undum -/ - - Pi obe in pterygoid canal Piobe in pteiygopalatine canal Palatine hone Lateral pteiygcid plate \' 'j ^ y^ Pyiamidai proce--s of palatine Fig. 303. — Left maxillary sinus opened from the exterior. part of the cavity; the other is closed by mucous membrane. On the posterior wall are the alveolar canals, transmitting the posterior superior alveolar vessels and nerves to the molar teeth. The floor is formed by the alveolar process of the maxilla, and, if the sinus be of an average size, is on a level with the floor of the nose; if the sinus be large it reaches below this level. Projecting into the floor of the antrum are several conical processes, correspond- ing to the roots of the first and second molar teeth ;^ in some cases the floor is perforated by the fangs of the teeth. The infraorbital canal usually projects into the cavity as a well-marked ridge extending from the roof to the anterior wall; additional ridges are sometimes seen in the posterior wall of the cavity, and 1 The number of teeth whose roots are in relation with the floor of the antrum is variable. The sinus "may extend so as to be in relation to all the teeth of the true maxilla, from the canine to the dens sapientiae." (Salter.) 260 OSTEOLOGY are caused by the alveolar canals. The size of the cavity varies in different skulls, and even on the two sides of the same skull. ^ Applied Anatomy. — -The extreme thinness of the walls of this cavity affords an explanation of the fact tliat a tumor growing from the maxillary sinus and encroaching upon the adjacent parts may push up the floor of the orbit, and displace the eyeball; may project into the nose; may protrude forward on to the cheek; or may make its way backward into the infratemporal fossa, or downward into the mouth. The Zygomatic Process (processus zygomaticus; malar lyrocess). — ^The zygomatic process is a rough triangular eminence, situated at the angle of separation of the anterior, zygomatic, and orbital surfaces. In front it forms part of the anterior surface; behind, it is concave, and forms part of the infratemporal fossa; above, it is rough and serrated for articulation with the zygomatic bone; while below, it presents the prominent arched border which marks the division between the anterior and infratemporal surfaces. The Frontal Process {processus frontalis; nasal process). — The frontal process is a strong plate, which projects upward, medialward, and backward, by the side of the nose, forming part of its lateral boundary. Its lateral surface is smooth, continuous with the anterior surface of the body, and gives attachment to the Quadratus labii superioris, the Orbicularis oculi, and the medial palpebral ligament. Its medial surface forms part of the lateral wall of the nasal cavity; at its upper part is a rough, uneven area, which articulates with the ethmoid, closing in the anterior ethmoidal cells; below this is an oblique ridge, the ethmoidal crest, the posterior end of which articulates with the middle nasal concha, while the anterior part is termed the agger nasi; the crest forms the upper limit of the atrium of the middle meatus. The upper border articulates with the frontal bone and the anterior with the nasal; the posterior border is thick, and hollowed into a groove, which is continuous below with the lacrimal groove on the nasal surface of the body: by the articulation of the medial margin of the groove with the anterior border of the lacrimal a corresponding groove on the lacrimal is brought into continuity, and together they form the lacrimal fossa for the lodgement of the lacrimal sac. The lateral margin of the groove is named the anterior lacrimal crest, and is con- tinuous below^ with the orbital margin; at its junction with the orbital surface is a small tubercle, the lacrimal tubercle, which serves as a guide to the position of the lacrimal sac. The Alveolar Process {processus alveolaris). — ^The alveolar process is the thickest and most spongy part of the bone. It is broader behind than in front, and exca- vated into deep cavities for the reception of the teeth. These cavities are eight in number, and vary in size and depth according to the teeth they contain. That for the canine tooth is the deepest; those for the molars are the widest, and are subdivided into minor cavities by septa; those for the incisors are single, but deep and narrow. The Buccinator arises from the outer surface of this process, as far forward as the first molar tooth. When the maxillae are articulated with each other, their alveolar processes together form the alveolar arch; the centre of the anterior margin of this arch is named the alveolar point. The Palatine Process {processus palatinus; palatal process). — -The palative process, thick and strong, is horizontal and projects medialward from the nasal surface of the bone. It forms a considerable part of the floor of the nose and the roof of the mouth and is much thicker in front than behind. Its inferior surface (Fig. 304) is concave, rough and uneven, and forms, with the palatine process of the opposite bone, the anterior three-fourths of the hard plate. It is perforated by numerous foramina for the passage of the nutrient vessels; is channelled at the 1 Aldren Turner (op. cit.) gives the following measurements as those of an average sized sinus: vertical height opposite first molar tooth, Ijl inch; transverse breadth, 1 inch; and antero-posterior depth, IJ^ inch. THE MAXILLA 261 back part of its lateral border by a groove, sometimes a canal, for the transmission of tlie descending;' i)alatine vessels and the anterior palatine nerve from the spheno- palatine ganglion; and presents little depressions for the lodgement of the palatine glands. When the two maxiihe are articulated, a funnel-shaped opening, the incisive foramen, is seen in the middle line, immediately behind the incisor teeth. In this opening the orifices of two lateral canals are visible; they are named the incisive canals or foramina of Stensen; through each of them passes the terminal branch of the descending palatine artery and the nasopalatine nerve. Occasionally two additional canals are present in the middle line; they are termed the foramina of Scarpa, and when present transmit the nasopalatine nerves, the left passing through the anterior, and the right through the posterior canal. On the under surface of the palatine process, a delicate linear suture, well seen in young skulls, mav sometimes be noticed extending lateralward and forward on either side from Incisive canals Jncisive foramen Foramina of Scarpa Palatine process of maxilla Horizontal plate of palatine hone Fig. 304. — The bony palate and alveolar arch. Greater palatine foramnen Lesser palatine foramina the incisive foramen to the interval between the lateral incisor and the canine tooth. The small part in front of this suture constitutes the premaxilla {os incisimim), which in most vertebrates forms an independent bone; it includes the whole thick- ness of the alveolus, the corresponding part of the floor of the nose and the anterior nasal spine, and contains the sockets of the incisor teeth. The upper surface of the palatine process is concave from side to side, smooth, and forms the greater part of the floor of the nasal cavit3\ It presents, close to its medial margin, the upper orifice of the incisive canal. The lateral border of the process is incorporated with the rest of the bone. The medial border is thicker in front than behind, and is raised above into a ridge, the nasal crest, which, with the corresponding ridge of the opposite bone, forms a groove for the reception of the vomer. The front part of this ridge rises to a considerable height, and is named the incisor crest; it is prolonged forward into a sharp process, which forms, together with a similar 262 OSTEOLOGY process of the opposite bone, the anterior nasal spine. The posterior border is ser- rated for artieuhition with the horizontal part of the pahitine bone. Ossification. — The maxilla is ossified in membrane. Mall' and P\iwcett- maintain that it is ossified from Iwo centres only, one for the maxilla proi)er and one for the ])renuixilla. These centres appear during the sixth week of fetal life and unite in the beginning of the third month, but the suture between the two portions persists on the palate until nearly middle life. Mall states that the frontal process is developed from both centres. The maxillary sinus appears as a shallow groove on the nasal surface of the bone about the fourth month of fetal life, but does not reach its full size until after the second dentition. The maxilla was formerly described as ossifying from six centres, viz., one, the orhilonasal, forms that portion of the body of the bone which lies medial to the infraorbital canal, including the medial part of the floor of the orbit and the lateral wall of the nasal cavity; a second, the zygomatic, gives origin to the portion which lies lateral to the infraorbital canal, including the zygomatic process; from a third, the palatine, is developed the palatine process posterior to the incisive canal together with the adjoining part of the nasal wall; a fourth, the premaxillary, forms the incisive bone which carries the incisor Fig. 305. — Anterior surface of maxilla at birth. Fig. 306. — Inferior surface of maxilla at birth. Maxillary sinus Fig. 307. Palatine process -Nasal surface of maxilla at birth. teeth and corresponds to the premaxilla of the lower vertebrates;^ a fifth, the nasal, gives rise to the frontal process and the portion above the canine tooth; and a sixth, the infravonierine, lies between the palatine and premaxillary centres and beneath the vomer; this centre, together with the corresponding centre of the opposite bone, separates the incisive canals from each other. Articulations. — The maxilla articulates with nine bones: two of the cranium, the frontal and ethmoid, and seven of the face, viz., the nasal, zygomatic, lacrimal, inferior nasal concha, palatine, vomer, and its fellow of the opposite side. Sometimes it articulates with the orbital surface, and sometimes with the lateral pterygoid plate of the sphenoid. CHANGES PRODUCED IN THE MAXILLA BY AGE. At birth the transverse and antero-posterior diameters of the bone are each greater than the vertical. The frontal process is well-marked and the body of the bone consists of little more than the alveolar process, the teeth sockets reaching almost to the floor of the orbit. The maxillary sinus presents the appearance of a furrow on the lateral wall of the nose. In the adult the vertical diameter is the greatest, owing to the development of the alveolar process and the increase in size of the sinus. In old age the bone reverts in some measure to the infantile condition; its height is diminished, and after the loss of the teeth the alveolar process is absorbed, and the lower part of the bone contracted and reduced in thickness. 1 American Journal of Anatomy, 1906, vol. v. 2 Journal of Anatomy and Physiology, 1911, vol. xlv. ' Some anatomists believe that the premaxillary bone is ossified by two centres (see page 299). THE ZYGOMATIC BONE 263 The Lacrimal Bone (Os Lacrimale). The lacrimal bone, the sniaUost and most fragile bone of the face, is situated at the front i)art of the medial wall of the orhit (I'^ig- 309). It has two surfaces and four borders. Surfaces. — The lateral or orbital surface (Fig. 308) is divided hy a vertical ridge, the posterior lacrimal crest, into two parts. In front of this crest is a longitudinal grooN'e, the lacrimal sulcus {sulcus lacrimcdls), the inner margin of which unites with the frontal process of the maxilla, and the lacrimal fossa is thus completed. The nj^per part of this fossa lodges the lacrimal sac, the lower part, tlie naso- lacrimal duct. The portion behind the crest is smootli, and forms part of the medial wall of the orbit. The crest, with, a part of the orl^ital surface imme- diately behind it, gives origin to the lacrimal part of the Orbicularis oculi and ends below in a small, hook-like projection, the lacrimal hamulus, which articu- lates with the lacrimal tubercle of the maxilla, and completes the upper orifice of the lacrimal canal; it sometimes exists as witAfrontai a separate piece, and is then called the lesser lacrimal bone. | ' J''^'^' The medial or nasal surface presents a longitudinal furrow, corresponding to the crest on the lateral surface. The area in front of this furrow forms part of the middle meatus of the nose; that behind it articulates with the ethmoid, and completes some of the anterior ethmoidal cells. Borders. — Of the jour borders the anterior articulates w^th the frontal process of the maxilla; the posterior with the lamina papyracea of the ethmoid; the superior with the frontal bone. infer, nasai concha The inferior is divided by the lower edge of the posterior lacri- fig. sos.— Left lacri- mal crest into tw^o parts: the posterior part articulates with f^ce.'^E'niarged'*''^ ^"'^" the orbital plate of the maxilla; the anterior is prolonged downward as the descending process, which articulates with the lacrimal process of the inferior nasal concha, and assists in forming the canal for the nasolacrimal duct. Ossification. — The lacrimal is ossified from a single centre, which appears about the twelfth week in the membrane covering the cartilaginous nasal capsule. Articulations. — The lacrimal articulates with four bones: two of the cranium, the frontal and ethmoid, and two of the face, the maxilla and the inferior nasal concha. The Zygomatic Bone (Os Zygomaticum; Malar Bone). The zygomatic bone is small and quadrangular, and is situated at the upper and lateral part of the face: it forms the prominence of the cheek, part of the lateral wall and floor of the orbit, and parts of the temporal and infratemporal fossse (Fig. 309). It presents a malar and a temporal surface; four processes, the frontosphenoidal, orbital, maxillary, and temporal; and four borders. Surfaces. — The malar surface (Fig. 310) is convex and perforated near its centre by a small aperture, the zygomaticofacial foramen, for the passage of the zygomatico- facial nerve and vessels; below this foramen is a slight elevation, w^hich gives origin to the Zygomaticus. The temporal surface (Fig. 311), directed backward and medialward, is concave, presenting medially a rough, triangular area, for articulation with the maxilla, and laterally a smooth, concave surface, the upper part of which forms the anterior boundary of the temporal fossa, the low^er a part of the infratemporal fossa. Near the centre of this surface is the zygomaticotemporal foramen for the transmission of the zygomaticotemporal nerve. 264 OSTEOLOGY Processes. — The frontosphenoidal process is thick and serrated, and articulates with the zygomatic process of the frontal bone. On its orbital surface, just within the orbital margin and about 11 mm. below the zygomaticofrontal suture is a tubercle of varying size and form, but present in 95 per cent, of skulls (WhitnalP). I' ro n tj u I I I' I-Ta V ill n Fig. 309. — Left zygomatic bone in situ. The orbital process is a thick, strong plate, projecting backward and medialward from the orbital margin. Its antero-medial surface forms, by its junction with the orbital surface of the maxilla and with the great wing of the sphenoid, part of the floor and lateral wall of the orbit. On it are seen the orifices of two canals, With Frontal Bristles passed through zygomatico- orhital foramina a}-. Fig. 310. — Left zygomatic bone. Malar surface. Fig. 311. — Left zygomatic bone. Temporal surface. the zygomaticoorbital foramina; one of these canals opens into the temporal fossa, the other on the malar surface of the bone; the former transmits the zygomatico- temporal, the latter the zygomaticofacial nerve. Its postero-Iateral surface, smooth ' Journal of Anatomy and Physiology, vol. xlv. The structures attached to this tubercle are: (1) the check ligament of the Rectus lateralis; (2) the lateral end of the aponeurosis of the Levator palpebrae superioris; (3) the suspensorj' ligament of the eye (Lockwood) ; and (4) the lateral extremities of the superior and inferior tarsi. THE PALATTXE BOXE 265 and convex, forms parts of the temporal and infratemporal fossae. Its anterior margin, smooth and rounded, is part of the circumference of the orbit. Its superior margin, rough, and directed horizontally, articulates with the frontal bone behind the zygomatic process. Its posterior margin is serrated for articulation, with the great wing of the sphenoid and the orbital surface of the maxilla. At the angle of junction of the sphenoidal and maxillary portions, a short, concave, non-articular part is generally seen; this forms the anterior boundary of the inferior orbital fissure: occasionally, this non-articular part is absent, the fissure then being completed by the junction of the maxilla and sphenoid, or by the interposition of a small sutural bone in the angular interval between them. The maxillary process presents a rough, triangular surface which articulates with the maxilla. The temporal process, long, narrow, and serrated, articulates with the zygomatic process of the temporal. Borders. — The antero-superior or orbital border is smooth, concave, and forms a considerable part of the circumference of the orbit. The antero-inferior or maxil- lary border is rough, and bevelled at the expense of its inner table, to articulate with the maxilla; near the orbital margin it gives origin to the Quadratus labii superioris. The postero-superior or temporal border, curved like an italic letter /, is continuous above with the commencement of the temporal line, and below with the upper border of the zygomatic arch; the temporal fascia is attached to it. The postero-inferior or zygomatic border affords attachment by its rough edge to the ^Nlasseter. Ossification. — The z^-gomatic bone is generally described as ossifying from three centres — one for the malar and two for the orbital portion; these appear about the eighth week and fuse about the fifth month of fetal hfe. ]\Iall describes it as being ossified from one centre which appears just beneath and to the lateral side of the orbit. After birth, the bone is sometimes divided by a horizontal sutm'e into an upper larger, and a lower smaller division. In some quad- rumana the z5-gomatic bone consists of two parts, an orbital and a malar. Articulations. — ^The zj-gomatic articulates with /our bones: the frontal, sphenoidal, temporal, and maxilla. Groove for nasolacrimal duct Maxilla) y sinus Orbital process Sphenopalatip notch Sphenoidal Cciichal crest Frontal process —Conchal crest Fig. 312. — Articulation of left palatine bone with maxilla. The Palatine Bone (Os Palatinum; Palate Bone). The palatine bone is situated at the back part of the nasal cavity between the maxilla and the pterygoid process of the sphenoid (Fig. 312). It contributes to the walls of three cavities: the floor and lateral wall of the nasal cavity, the 266 OSTEOLOGY roof of the mouth, and the floor of the orl)it ; it enters into the formation of two fossEe, the pterygopalatine and pterygoid fossae; and one fissure, the inferior orbital fissure. The palatine bone somewhat resem})les the letter L, and consists of a horizontal and a vertical part and three outstanding processes — viz., the pyramidal process, ^^hich is directed backward and lateralward from the junction of the two parts, and the orbital and sphenoidal porcesses, w^hich surmount the vertical part, and are separated by a deep notch, the sphenopalatine notch. The Horizontal Part (pans horizontalis; horizontal plate) (Figs. 313, 314.). — The horizontal part is quadrilateral, and has two surfaces and four borders. Surfaces. — The superior surface, concave from side to side, forms the back part of the floor of the nasal cavity. The inferior surface, slightly concave and rough, forms, with the corresponding surface of the opposite bone, the posterior fourth of the hard palate. Near its posterior margin may be seen a more or less marked transverse ridge for the attachment of part of the aponeurosis of the Tensor veli palatini. ^Ital Fpoc^ Maxillary surface Superior 'ineatub Sphenopalatine fora men ^1 > Maocillary ']yrocess Fig. 31.3. HORIZONTAL PAKT -Left palatine bone. Enlarged. to- I A <\^ 1 S'"^ 0' J- ^ 5 -CA Sphenopalatine forainen Sphenoidal process Articular portion Non-artimlar portion Posterior _ nasal Musculus nvulce spine Pyamidal process HORIZONTAL P4.RT Nasal aspect. Fig. 314. -Left palatine bone. Enlarged. Posterior aspect. Borders. — The anterior border is serrated, and articulates with the palatine process of the maxilla. The posterior border is concave, free, and serves for the attachment of the soft palate. Its medial end is sharp and pointed, and, when united with that of the opposite bone, forms a projecting process, the posterior nasal spine for the attachment of the Musculus uvulae. The lateral border is united with the lower margin of the perpendicular part, and is grooved by the lower end of the pterygopalatine canal. The medial border, the thickest, is serrated for articu- lation with its fellow of the opposite side; its superior edge is raised into a ridge, which, united with the ridge of the opposite bone, forms the nasal crest for articu- lation with the posterior part of the lower edge of the vomer. The Vertical Part {pars perpendicularis ; perpendicular plate) (Figs. 313, 314). — The vertical part is thin, of an oblong form, and presents two surfaces and four borders. Surfaces. — The nasal surface exhibits at its lower part a broad, shallow depres- sion, which forms part of the inferior meatus of the nose. Immediately above this is a well-marked horizontal ridge, the conchal crest, for articulation with the inferior nasal concha; stih higher is a second broad, shallow depression, which THE PALATINE BONE 267 forms part of the middle meatus, and is limited above by a horizontal crest less prominent than the inferior, the ethmoidal crest, for articulation with the middle nasal concha. Above the ethmoidal crest is a narrow, horizontal groove, which forms part of the superior meatus. The maxillary surface is rough and irregular throughout the greater part of its extent, for articulation \\'\t\\ the nasal surface of the maxilla; its upper and back part is smooth where it enters into the formation of the pterygopalatine fossa; it is also smooth in front, wdiere it forms the posterior part of the medial wall of the maxillary sinus. On the posterior part of this surface is a deep vertical groove, converted into the pterygopalatine canal, by articulation with the maxilla; this canal transmits the descending palatine vessels, and the anterior palatine nerve. Borders. — The anterior border is thin and irregular; opposite the conchal crest is a pointed, projecting lamina, the maxillary process, which is directed forw^ard, and closes in the lower and back part of the opening of the maxillary sinus. The posterior border (Fig. 314) presents a deep groove, the edges of which are serrated for articulation with the medial pterygoid plate of the sphenoid. This border is continuous above with the sphenoidal process; below it expands into the pyramidal process. The superior border supports the orbital process in front and the sphenoidal process behind. These processes are separated by the sphenopalatine notch, which is converted into the sphenopalatine foramen by the under surface of the body of the sphenoid. In the articulated skull this foramen leads from the pterygopalatine fossa into the posterior part of the superior meatus of the nose, and transmits the sphenopalatine vessels and the superior nasal and nasopalatine nerves. The inferior border is fused with the lateral edge of the horizontal part, and immediately in front of the pyramidal process is grooved by the lower end of the pterygopalatine canal. The Pyramidal Process or Tuberosity (^processus pyramidalis) . — The pyramidal process projects backward and lateralw^ard from the junction of the horizontal and vertical parts, and is received into the angular interval between the lower extremities of the pterygoid plates. On its posterior surface is a smooth, grooved, triangular area, limited on either side by a rough articular furrow. The furrows articulate with the pterygoid plates, while the grooved intermediate area completes the lower part of the pterygoid fossa and gives origin to a few^ fibres of the Pter}'- goideus internus. The anterior part of the lateral surface is rough, for articulation with the tuberosity of the maxilla; its posterior part consists of a smooth triangular area which appears, in the articulated skull, betw^een the tuberosity of the maxilla and the lower part of the lateral pterygoid plate, and completes the lower part of the infratemporal fossa. On the base of the pyramidal process, close to its union with the horizontal part, are the lesser palatine foramina for the transmis- sion of the posterior and middle palatine nerves. The Orbital Process {processus orhitalis). — The orbital process is placed on a higher level than the sphenoidal, and is directed upward and lateralward from the front of the vertical part, to which it is connected by a constricted neck. It presents five surfaces, which enclose an air cell. Of these surfaces, three are articu- lar and two non-articular. The articular surfaces are: (1) the anterior or maxillary, directed forward, lateralward, and downward, of an oblong form, and rough for articulation with the maxilla; (2) the posterior or sphenoidal, directed backward, upward, and medialward; it presents the opening of the air cell, which usually communicates with the sphenoidal sinus; the margins of the opening are serrated for articulation with the sphenoidal concha; (3) the medial or ethmoidal, directed forward, articulates with the labyrinth of the ethmoid. In some cases the air cell opens on this surface of the bone and then communicates with the posterior ethmoidal cells. More rarely it opens on both surfaces, and then communicates with the posterior ethmoidal cells and the sphenoidal sinus. The non-articular 268 OSTEOLOGY surfaces are: (1) the superior or orbital, directed upward and lateralward; it is triangular in shape, and forms the back part of the floor of the orbit; and (2) the lateral, of an oblong form, directed toward the pterygopalatine fossa; it is sejjarated from the orbital surface by a rounded border, which enters into the formation of the inferior orbital fissure. The Sphenoidal Process {processus sphenoidalis) . — The sphenoidal process is a thin, compressed plate, much smaller than the orbital, and directed upward and medialward. It presents three surfaces and two borders. The superior surface articulates with the root of the pterygoid process and the under surface of the sphenoidal concha, its medial border reaching as far as the ala of the vomer; it presents a groove which contributes to the formation of the pharyngeal canal. The medial surface is concave, and forms part of the lateral wall of the nasal cavity. The lateral surface is divided into an articular and a non-articular portion: the former is rough, for articulation w^ith the medial pterygoid plate; the latter is smooth, and forms part of the pterygopalatine fossa. The anterior border forms the posterior boundary of the sphenopalatine notch. The posterior border, serrated at the expense of the outer table, articulates with the medial pterygoid plate. The orbital and sphenoidal processes are separated from one another by the sphenopalatine notch. Sometimes the two processes are united above, and form between them a complete foramen (Fig. 313), or the notch may be crossed by one or more spicules of bone, giving rise to two or more foramina. Ossification. — The palatine bone is ossified in membrane from a single centre, which makes its appearance about the sixth or eighth week of fetal life at the angle of junction of the two parts of the bone. From this point ossification spreads medialward to the horizontal part, downward into the pyramidal process, and upward into the vertical part. Some authorities describe the bone as ossifying from four centres: one for the pyramidal process and portion of the vertical part behind the pterygopalatine groove; a second for the rest of the vertical and the horizontal parts; a third for the orbital, and a fourth for the sphenoidal process. At the time of birth the height of the vertical part is about equal to the transverse width of the horizontal part, whereas in the adult the former measures about twice as much as the latter. Articulations. — The palatine articulates with six bones: the sphenoid, ethmoid, maxilla, inferior nasal concha, vomer, and opposite palatine. The Inferior Nasal Concha (Concha Nasalis Inferior ; Inferior Turbinated Bone) . The inferior nasal concha extends horizontally along the lateral wall of the nasal cavity (Fig. 315) and consists of a lamina of spongy bone, curled upon itself like a scroll. It has two surfaces, two borders, and two extremities. The medial surface (Fig. 316) is convex, perforated by numerous apertures, and traversed by longitudinal grooves for the lodgement of vessels. The lateral surface is concave (Fig. 317), and forms part of the inferior meatus. Its upper border is thin, irregular, and connected to various bones along the lateral wall of the nasal cavity. It may be divided into three portions: of these, the anterior articulates wdth the conchal crest of the maxilla; the posterior wdth the conchal crest of the palatine; the middle portion presents three well-marked processes, which vary much in their size and form. Of these, the anterior or lacrimal process is small and pointed and is situated at the junction of the anterior fourth with the posterior three-fourths of the bone : it articulates, by its apex, with the descend- ing process of the lacrimal bone, and, by its margins, with the groove on the back of the frontal process of the maxilla, and thus assists in forming the canal for the nasolacrimal duct. Behind this process a broad, thin plate, the ethmoidal process, ascends to join the uncinate process of the ethmoid; from its lower border a thin lamina, the maxillary process, curves downward and lateralward; it articulates Avith the maxilla and forms a part of the medial wall of the maxillary sinus. The inferior border is free, thick, and cellular in structure, more especially in the middle THE VOMER 209 of the bone. Both extremities are more or less pouited, the posterior })eing the more tapering. Frontal sinus Griskt gain Sella turcica Uncinate process oj ethmoid Openings into maxillary sinus Medial pterygoid plate Pterygoid hamulus Fig. 315. — Lateral wall of right nasal cavity showing inferior concha uj situ. Ossification. — ^The inferior nasal concha is ossified from a single centre, wliicli appears about tlie fifth month of fetal Ufe in the lateral wall of the cartilaginous nasal capsule. Articulations. — The inferior nasal concha articulates with four bones: the ethmoid, maxilla, lacrimal, and palatine. Fig. 316. — Right inferior nasal concha. Medial surface. Fig. 317. — Right inferior nasal concha. Lateral surface. The Vomer. The vomer is situated in the median plane, but its anterior portion is frequently bent to one or other side. It is thin, somewhat quadrilateral in shape, and forms the hinder and lower part of the nasal septum (Fig. 318); it has two surfaces and four borders. The surfaces (Fig. 319) are marked by small furrows for blood- vessels, and on each is the nasopalatine groove, which runs obliquely downward and forward, and lodges the nasopalatine nerve and vessels. The superior border, the thickest, presents a deep furrow, bounded on either side by a horizontal pro- jecting ala of bone; the furrow receives the rostrum of the sphenoid, while the 270 OSTEOLOGY margins of the ala^ articulate with the vaginal processes of the medial pterygoid plates of the sphenoid behind, and with the sphenoidal processes of the palatine bones in front. The inferior border articulates with the crest formed by the maxillse and palatine bones. The anterior border is the longest and slopes downward and Crest of nasal bones Frontal spine Space for triangular cartilage of septum Fig. 318. — Median wall of left nasal cavity showing vomer in situ. forward. Its upper half is fused with the perpendicular plate of the ethmoid; its lower half is grooved for the inferior margin of the septal cartilage of the nose. The posterior border is free, concave, and separates the choanse. It is thick and bifid above, thin below. Ossification. — At an early period the septum of the nose consists of a plate of cartilage, the ethmovomerine cartilage. The postero-superior part of this cartilage is ossified to form the perpendicular plate of the eth- moid; its antero-inferior portion per- sists as the septal cartilage, while the vomer is ossified in the membrane covering its postero-inferior part. Two ossific centres, one on either side of the middle fine, appear about the eighth week of fetal life in this part of the membrane, and hence the vomer consists primarily of two lam- ellae. About the third month these unite below, and thus a deep groove growth proceeds, the union of the lamellae the intervening plate of cartilage undergoes almost completely united to form a median bone is seen in the everted alte of its upper Uh Maxilla: Fig. 319.— The vomer. is formed in which the cartilage is lodged. As extends upward and forward, and at the same time absorption. By the age of puberty the lamellae are plate, but evidence of the bilaminar origin of the border and the groove on its anterior margin. THE MANDIBLE 271 Articulations. — The vomer articulates with six bones: two of the cranium, the sphenoid and ethmoid; and four of the face, the two maxilla; and the two palatine bones; it also articulates with I lie .scplal cartilage of the nose. Applied Anatomy. — Tlie surfaces of the vomer are covered l)y nuicous membrane, which is intimately connected with the periosteum, little, if any, subnnu^ous connective tissue intcn-vcning. Hence polypi are rarely found growing from this surface, though they frecjuently grow from the lateral walls of the nasal cavities, where the submucous tissue is abundant. The Mandible (Mandibula ; Inferior Maxillary Bone; Lower Jaw). The mandible, the hirgest and strongest bone of the face, serves for the reception of the lower teeth. It consists of a curved, horizontal portion, the body, and two perpendicular portions, the rami, which unite with the ends of the body nearly at right angles. The Body (corpus mandihulae) . — The body is curved somewhat like a horseshoe, and has two surfaces and two borders. Coronoid process Condyle TEMPORALIS Mental protuberance Groove for external maxillary ai'tery Fig. 320. — Mandible. Outer surface. Side view. Surfaces. — The external surface (Fig. .320) is marked in the median line by a faint ridge, indicating the symphysis or line of junction of the two pieces of which the bone is composed at an early period of life. This ridge divides below and encloses a triangular eminence, the mental protuberance, the base of which is de- pressed in the centre but raised on either side to form the mental tubercle. On either side of the symphysis, just below the incisor teeth, is a depression, the incisive fossa, which gives origin to the Mentalis and a small portion of the Orbicularis oris. Below the second premolar tooth, on either side, midway between the upper and lower borders of the body, is the mental foramen, for the passage of the mental vessels and nerve. Running backward and upward from each mental tubercle is a faint ridge, the oblique line, which is continuous with the anterior border of the ramus; it affords attachment to the Quadratus labii inferioris and Triangularis; the Platysma is attached below it. The internal surface (Fig. 321) is concave from side to side. Near the lower part of the symphysis is a pair of laterally placed spines, termed the mental spines, which give origin to the Genioglossi. Immediately below these is a second pair of spines, or more frequently a median ridge or impression, for the origin of the 272 OSTEOLOGY Geniohyoidei. In some cases the mental spines are fused to form a single eminence, in others they are absent and their position is indicated merely by an irregularity of the surface. Above the mental spines a median foramen and furrow are some- times seen; they mark the line of union of the halves of the bone. Below the mental spines, on either side of the middle line, is an oval depression for the attachment of the anterior belly of the Digastricus. Extending upward and backward on either side from the lower part of the s^'mphysis is the mylohyoid line, which gives origin to the Mylohyoideus; the posterior part of this line, near the alveolar margin, gives attachment to a small part of the Constrictor pharyngis superior, and to the pterygomandibular raphe. Above the anterior part of this line is a smooth triangular area against which the sublingual gland rests, and below the hinder part, an oval fossa for the submaxillary gland. .iti'J'^-i*-., Genio- glossTis Genio- hyoideus Mylohyoid line BODT Fig. 321. — Mandible. Inner surface. Side view. Borders. — The superior or alveolar border, wider behind than in front, is holloM^ed into cavities, for the reception of the teeth; these cavities are sixteen in number, and vary in depth and size according to the teeth which they contain. To the outer lip of the superior border, on either side, the Buccinator is attached as far forward as the first molar tooth. The inferior border is rounded, longer than the superior, and thicker in front than behind; at the point where it joins the lower border of the ramus a shallow groove; for the external maxillary artery, may be present. The Ramus {ravms mandihulae; 'perpendicular portions). — The ramus is quadri- lateral in shape, and has two surfaces, four borders, and two processes. Surfaces. — The lateral surface (Fig. 320) is flat and marked by oblique ridges at its lower part; it gives attachment throughout nearly the whole of its extent to the Masseter. The medial surface (Fig. 321) presents about its centre the oblique mandibular foramen, for the entrance of the inferior alveolar vessels and nerve. The margin of this opening is irregular; it presents in front a prominent ridge, surmounted by a sharp spine, the lingula mandibulae, which gives attachment to the sphenomandibular ligament ; at its lower and back part is a notch from which the mylohyoid groove runs obliquely downward and forward, and lodges the mylo- hyoid vessels and nerve. Behind this groove is a rough surface, for the insertion THE MAXDIBLE 273 of the Ptengoideus internus. The mandibular canal runs ohlicjuely downward and forward in the ramus, and then liori/ontally forward in the body, where it is placed under tlie alveoli and communicates with them by small openings. On arriving at the incisor teeth, it turns back to communicate with the mental foramen, giving off two small canals which run to the cavities containing the incisor teeth. In the })osterior two-thirds of the bone the canal is situated nearer the internal surface of the mandii)le; and in the anterior third, nearer its external surface. It contains the inferior alveolar vessels and nerve, from which branches are dis- tributed to the teeth. The lower border of the ramus is thick, straight, and con- tinuous with the inferior Iwrder of the body of the bone. At its junction with the posterior border is the angle of the mandible, which may be either in\erted or everted and is marked by rough, oblique ridges on each side, for the attachment of the, Masseter laterally, and the Pterygoideus internus medially; the stylomandibular ligament is attached to the angle between these muscles. The anterior border is thin aboA'e, thicker below, and continuous with the oblique line. The posterior border is thick, smooth, rounded, and covered by the parotid gland. The upper border is thin, and is surmounted by two processes, the coronoid in front and the condyloid behind, separated by a deep concavity, the mandibular notch. The Coronoid Process (processus coronoideus) is a thin, triangular eminence, which is flattened from side to side and varies in shape and size. Its anterior border is convex and is continuous below with the anterior border of the ramus; its posterior border is concave and forms the anterior boundary of the mandibular notch. Its lateral surface is smooth, and affords insertion to the Temporalis and Masseter. Its medial surface gives insertion to the Temporalis, and presents a ridge which begins near the apex of the process and runs downward and forward to the inner side of the last molar tooth. Between this ridge and the anterior border is a grooved triangular area, the upper part of which gives attachment to the Temporalis, the lower part to some fibres of the Buccinator. The Condyloid Process {pjrocessus condyloideus) is thicker than the coronoid, and consists of two portions : the condyle, and the constricted portion which sup- ports it, the neck. The condyle presents an articular surface for articulation with the articular disk of the temporomandibular joint; it is convex from before back- ward and from side to side, and extends farther on the posterior than on the ante- rior surface. Its long axis is directed medialward and slightly backward, and if prolonged to the middle line will meet that of the opposite condyle near the ante- rior margin of the foramen magnum. At the lateral extremity of the condyle is a small tubercle for the attachment of the temporomandibular ligament. The neck is flattened from before backward, and strengthened by ridges which descend from the forepart and sides of the condyle. Its posterior surface is convex; its anterior presents a depression for the attachment of the Pterygoideus externus. The mandibular notch, separating the two processes, is a deep semilunar depres- sion, and is crossed by the masseteric vessels and nerve. Ossification. — The mandible is ossified in the fibrous membrane covering the outer sm-faces of Meckel's cartilages. These cartilages form the cartilaginous bar of the mandibular arch (see p. 109), and are two in number, a right and a left. Their proximal or cranial ends are connected with the ear capsules, and theii- distal extremities are joined to one another at the symphysis by mesodermal tissue. They run forward immediately below the condj'les and then, bending downward, he in a groove near the lower border of the bone; in front of the canine tooth they inchne upward to the sj^mphj-sis. From the proximal end of each cartilage the malleus and incus, two of the bones of the middle ear, are developed; the next succeeding portion, as far as the hngula, is replaced by fibrous tissue, which persists to form the sphenomandibular hgament. Between the lingula and the canine tooth the cartilage disappears, while the portion of it below and behind the incisor teeth becomes ossified and incorporated with this part of the mandible. Ossification takes place in the membrane covering the outer surface of the ventral end of Meckel's cartilage (Figs. 322 to 325), and each half of the bone is formed from a single centre IS 274 OSTEOLOGY which appears, near the mental foramen, about the sixth week of fetal Ufe. By the tenth week the portion of Meckel's cartilage which hes below and behind the incisor teeth is surrounded and invaded by the membrane bone. Somewhat later, accessory nuclei of cartilage make their appear- Mental nerve. Liur/iud itcivf Iiif alveola) n Mylohyoid nerve Fig. 322. — Mandible of human embryo of 24 mm. long. Outer aspect. (From model by Low.) ~ Stajies ~ 1 cicial nerve Mylohyoid nerve Chorda tympani ReicherVs cartilage Fig. 32.3. — Mandible of human embryo of 24 mm. long. Inner aspect. (From model by Low.) ance, viz., a wedge-shaped nucleus in the condyloid process and extending downward through the ramus; a small strip along the anterior border of the coronoid process; and smaller nuclei in the front part of both alveolar walls and along the fi'ont of the lower border of the bone. These acce.ssory nuclei possess no separate ossific centres, but are invaded by the surrounding membrane Mandibular loerve Meckel's caitilage Jlental nerve Anterior process of )tialleus Fig. 324. — Mandible of human embryo of 9.5 mm. long. Outer aspect. (From model by Low.) Nuclei of cartilage stippled. bone and undergo absorption. The inner alveolar border, usually described as arising from a separate ossific centre {s-plenial centre), is formed in the human mandible by an ingrowt^h from the main mass of the bone. At birth the bone consists of two parts, united by a fibrous symphysis, in which ossification takes place during the first year. Lingual nerve Auricidotemporal nerve Meckel's cartilage Ant. process of malleus Chorda tijmpani Symphysis Mylohyoid nerve Fig. 325. — Mandible of human embryo of 95 mm. long. Inner aspect. Nuclei of cartilage stippled. (From model by Low.) The foregoing description of the ossification of the mandible is based on the researches of Low^ and Fawcett,- and differs somewhat from that usually given. Articulations. — The mandible articulates with the iico temporal bones. 1 Proceedings of the Anatomical and Anthropological Society of the University of .\berdeen, 1905, and Journal of Anatomy and Physiology, vol. xliv. 2 Journal of the American Medical Association, September 2, 1905. TJIR If VOID HONK 275 CHANGES PRODUCED IN THE MANDIBLE 13Y AGE. At birth (Fig. 326), the body of the bone is a mere shell, containing the sockets of the two incisor, the canine, and the two deciduous molar teeth, imperfectly partitioned off from one another. The mandibular canal is of large size, and runs near the lower border of the bone; the mental foramen opens beneath the socket of the lirst deciduous molar tooth. The angle is obtuse (175°), and the condyloid portion is nearly in line with the body. The coronoid i)rocess is of comparatively large size, and projects above the level of the condyle. After birth (Fig. 327), the two segments of the bone become joined at the symphysis, from below upward, in the first year; but a trace of separation may be visible in the beginning of the second year, near the alveolar margin. The body becomes elongated in its whole length, but moi-e especially behind the mental foramen, to provide space for the three additional teeth devel- oped in this part. The depth of the body increases owing to increased growth of the alveolar part, to afford room for the roots of the teeth, and by thickening of the subdental portion which enables the jaw to withstand the powerful action of the masticatory muscles; but the alveolar portion is the deeper of the two, and, consequently, the chief part of the body hes above the oblique line. The mandibular canal, after the second dentition, is situated just above the level of the myloh3'oid Une; and the mental foramen occupies the position usual to it in the adult. The angle becomes less obtuse, owing to the separation of the jaws by the teeth; about the fourth year it is 140°. In the adult (Fig. 328), the alveolar and subdental portions of the body are usually of equa depth. The mental foramen opens midway between the upper and lower borders of the bone, and the mandibular canal runs nearly parallel with the mylohyoid line. The ramus is almost vertical in direction, the angle measuring from 110° to 120°. In old age (Fig. 329), the bone becomes greatly reduced in size, for with the loss of the teeth the alveolar process is absorbed, and, consequently, the chief part of the bone is below the oblique line. The mandibular canal, with the mental foramen opening from it, is close to the alveolar border. The ramus is obhque in direction, the angle measures about 140°, and the neck of the condyle is more or less bent backward. The Hyoid Bone (Os Hyoideum; Lingual Bone). The hyoid bone is shaped like a horseshoe, and is suspended from the tips of the styloid processes of the temporal bones by the stylohyoid ligaments. It consists of five segments, viz., a body, two greater cornua, and two lesser cornua. The Body or Basihyal {corpus oss. hyoidei). — The body or central part is of a quadrilateral form. Its anterior surface (Fig. 330) is convex and directed forward and upward. It is crossed in its upper half by a well-marked transverse ridge with a slight downward convexity, and in many cases a vertical median ridge divides it into two lateral halves. The portion of the vertical ridge above the transverse line is present in a majority of specimens, but the lower portion is evident only in rare cases. The anterior surface gives insertion to the Geniohyoid- eus in the greater part of its extent both above and below the transverse ridge; a portion of the origin of the Hyoglossus notches the lateral margin of the Genio- hyoideus attachment. Below the transverse ridge the Mylohyoideus, Sterno- hyoideus, and Omohyoideus are inserted. The posterior surface is smooth, concave, directed backward and downward, and separated from the epiglottis by the hyothyroid membrane and a quantity of loose areolar tissue ; a bursa intervenes between it and the hyothyroid membrane. The superior border is rounded, and gives attachment to the hyothyroid membrane and some aponeurotic fibres of the Genioglossus. The inferior border affords insertion medially to the Sternohyoideus and laterally to the Omohyoideus and occasionally a portion of the Thyreohyoideus. It also gives attachment to the Levator glandulae thyreoideae, when this muscle is present. In early life the lateral borders are connected to the greater cornua by synchondroses; after middle life usually by bony union. The Greater Cornua or Thyrohyals {cornua majora) . — The greater cornua project backward from the lateral borders of the body; they are flattened from above downward and diminish in size from before backward ; each ends in a tubercle to which is fixed the lateral hyothyroid ligament. The upper surface is rough 276 OSTEOLOGY Fig. 326.— At birth. Fig. 327. — In childhood. Fig. 32S.— In the adult. Fig. 329.— In old age. Side view of the mandible at different periods of life. THE EXTERIOH OF THE SKULL '.ii DIOASTRICUS & STYUiHYOIDEUS T'hyreohyoidecs Omohyoideus dose to its lateral border, for muscular attachments: the largest of these are the origins of the Hyoglossus and Constrictor pharyngis medius which extend along the whole length of the cornu; the Digastricus and Stylohyoideus have small insertions in front of these near the junction of the l)o(l\' /^Tk^ ^Greater coi~nu with the cornu. To the medial border the hyothyroid mem- brane is attached, while the anterior half of the lateral border gives insertion to the Thyreohyoideus. The Lesser Cornua or Cera- tohyals {cornua vunora). — The lesser cornu are two small, conical eminences, attached by their bases to the angles of junction between the body and greater cornua. They are con- nected to the body of the bone by fibrous tissue, and occasionally to the greater cornua by distinct diarthrodial joints, which usually persist throughout life, but occasionally become ankylosed. The lesser cornua are situated in the line of the transverse ridge on the bod>' and appear to be morphological continuations of it (Parsons^). The apex of each cornu gives attachment to the stylohyoid ligament ;2 the Chondroglossus rises from the medial side of the base. Ossification. — -The hyoid is ossified from six centres: two for the body, and one for each cornu. Ossification commences in the greater cornua toward 'the end of fetal hfe, in the body shortly afterward, and in the lesser cornua during the first or second year after birth. Applied Anatomy. — The hyoid bone is occasionally fractured, generally from direct violence, as in hanging, forcible grasping of the throat in garroting or throttling, or bj' a blow. The frac- ture generally occurs about the junction of the greater cornu with the body of the bone, but sometimes takes place through the latter; since the muscles of the tongue have important con- nections with this bone, there is great pain upon any attempt being made to move the tongue, as in speaking or swallowing. Mylohyoibkus sternohyoidebs Geniohyoideus Fig. .3.30. — Hyoid bone. Anterior surface. Enlarged. THE EXTERIOR OF THE SKULL. The skull as a whole may be viewed from different points, and the views so obtained are termed the normse of the skull; thus, it may be examined from above (norma verticalis), from below (norma basalis), from the side (norma lateralis), from behind (norma occipitalis), or from the front (norma frontalis). Norma Verticalis. — When viewed from above the outline presented varies greatly in different skulls; in some it is more or less oval, in others more nearly circular. The surface is traversed by three sutures, viz.: (1) the coronal sutures, nearly transverse in direction, between the frontal and parietals; (2) the sagittal sutures, medially placed, between the parietal bones, and deeply serrated in its anterior two-thirds; and (3) the upper part of the lambdoidal suture, between the parietals and the occipital. The point of junction of the sagittal and coronal suture is named the bregma, that of the sagittal and lambdoid sutures, the lambda; they indicate respectively the positions of the anterior and posterior fontanelles in the fetal skull. On either side of the sagittal suture are the parietal eminence and parietal 1 See article on "The Topography and Morphology of the Human Hyoid Bone," by F. G. Parsons, Journal of Anatomy and Physiology, vol. xliii. 2 These ligaments in many animals are distinct bones, and in man maj' undergo partial ossification. 278 OSTEOLOdY foramen — the latter, however, is freciuently absent on one or })oth sides. The skull is often somewhat flattened in the neighborhood of the parietal foramina, and the term obelion is applied to that point of the sagittal suture which is on a level with the foramina. In front is the glabella, and on its lateral aspects are the superciliary arches, and above these the frontal eminences. Immediately above the glabella may be seen the remains of the frontal suture; in a small percentage of skulls this suture persists and extends along the middle line to the bregma. Passing backward and upward from the zygomatic processes of the frontal bone are the temporal lines, which mark the upper limits of the temporal fossae. The zygomatic arches may or may not be seen projecting beyond the anterior portions of these lines. Norma Basalis (Fig. 331). — The inferior surface of the base of the skull, exclu- sive of the mandible, is bounded in front by the incisor teeth in the maxillae; behind, by the superior nuchal lines of the occipital; and laterally by the alveolar arch, the lower border of the zygomatic bone, the zygomatic arch and an imaginary line extending from it to the mastoid process and extremity of the superior nuchal line of the occipital. It is formed by the palatine processes of the maxillse and palatine bones, the vomer, the pterygoid processes, the under surfaces of the great wings, spinous processes, and part of the body of the sphenoid, the under surfaces of the squamse and mastoid and petrous portions of the temporals, and the under surface of the occipital bone. The anterior part or hard palate projects below the level of the rest of the surface, and is bounded in front and laterally by the alveolar arch containing the sixteen teeth of the maxillse. Immediately behind the incisor teeth is the incisive foramen. In this foramen are two lateral apertures, the openings of the incisive canals (foramina of Stensen) which transmit the anterior branches of the descending palatine vessels, and the nasopalatine nerves. Occasionalh' two additional canals are present in the incisive foramen; they are termed the foramina of Scarpa and are situated in the middle line; when present they transmit the nasopalatine nerves. The vault of the hard palate is concave, uneven, perforated by numerous foramina, marked by depressions for the palatine glands, and traversed by a crucial suture formed by the junction of the four bones of which it is composed. In the young skull a suture may be seen ex- tending on either side from the incisive foramen to the interval between the lateral incisor and canine teeth, and marking oft" the os incisivum or premaxillary bone. At either posterior angle of the hard palate is the greater palatine foramen, for the transmission of the descending palatine vessels and anterior palatine nerve; and running forward and medialward from it a groove, for the same vessels and nerve. Behind the posterior palatine foramen is the pyramidal process of the palatine bone, perforated by one or more lesser palatine foramina, and marked by the commence- ment of a transverse ridge, for the attachment of the tendinous expansion of the Tensor veli palatini. Projecting backward from the centre of the posterior border of the hard palate is the posterior nasal spine, for the attachment of the IMusculus uvulae. Behind and above the hard palate are the choanae, measuring about 2.5 cm. in their vertical and 1.25 cm. in their transverse diameters. They are separated from one another by the vomer, and each is bounded above by the body of the sphenoid, below by the horizontal part of the palatine bone, and laterally by the medial pterygoid plate of the sphenoid. At the superior border of the vomer may be seen the expanded alee of this bone, receiving between them the ros- trum of the sphenoid. Near the lateral margins of the alse of the vomer, at the roots of the pterygoid processes, are the pharyngeal canals. The pterygoid process presents near its base the pterygoid canal, for the transmission of a nerve and artery. The medial pterygoid plate is long and narrow^; on the lateral side of its base is the scaphoid fossa, for the origin of the Tensor veli palatini, and at its lower extremity the hamulus, around which the tendon of this muscle turns. The lateral pterygoid THE EXTERIOR OF THE SKULL 279 plate is broad; its lateral surface forms the mc.lial houiulan „[ tlie infratemporal tossa, and aftords attaolinicnt to tlie Pterviroidcus extcrnus. Incisors Canine Incisive canal Trammitu left nasopalatine nerve Traiixinits descendimj palatine vemiels Transnuts right nasupalatine nei-ve Lesser palatine foramina Posterior nasal spine Muscuhis uvulae Pteryrjoid hamulus Sphenoidal process of jjalaline Pharyrujeal caiiul Tensor tympani Pliaryngeal tubercle Situation of auditory tube and stmicanal for Tensor tympani Tenxor veli 'palatini Inferior li/uipanic canaliculua Aqiiarihidiix mclilrne Jvjiiihir fiii-Kiiicn M,ist,,„l n,,:„li,-iihis TyinpunvJiia-stuid fissure Fig. 331. — Base of skull. Inferior surface. 280 OSTEOLOGY Behind the nasal ca\-ities is the basihir portion of the occipital bone, presenting near its centre the pharyngeal tubercle for the attachment of the fibrous raphe of the pharynx, with depressions on either side for the insertions of the Rectus capitis anterior and Longus capitis. At the base of the lateral pterygoid plate is the foramen ovale, for the transmission of the mandi})ular nerve, the accessory meningeal artery, and sometimes the lesser superficial petrosal nerve; behind this are the foramen spinosum which transmits the middle meningeal vessels, and the promi- nent spina angularis (sphenoidal spine), which gives attachment to the spheno- mandibular ligament and the Tensor veli palatini. Lateral to the spina angularis is the mandibular fossa, divided into two parts by the petrotympanic fissure; the anterior portion, concave, smooth, bounded in front by the articular tubercle, serves for the articulation of the condyle of the mandible; the posterior portion, rough and bounded behind by the tympanic part of the temporal, is sometimes occupied by a part of the parotid gland. Emerging from between the laminae of the vaginal process of the tympanic part is the styloid process; and at the base of this process is the stylomastoid foramen, for the exit of the facial nerve, and entrance of the stylomastoid artery. Lateral to the stylomastoid foramen, between the tympanic part and the mastoid process, is the tympanomastoid fissure, for the auricular branch of the vagus. Upon the medial side of the mastoid process is the mastoid notch for the posterior belly of the Digastricus, and medial to the notch, the occipital groove for the occipital artery. At the base of the medial pterygoid plate is a large and somewhat triangular aperture, the foramen lacerum, bounded in front by the great wing of the sphenoid, behind by the apex of the petrous portion of the temporal bone, and medially by the body of the sphenoid and basilar portion of the occipital bone; it presents in front the posterior orifice of the ptery- goid canal; behind, the aperture of the carotid canal. The lower part of this opening is filled up in the recent state by a fibrocartilaginous plate, across the upper or cerebral surface of which the internal carotid artery passes. Lateral to this aperture is a groove, the sulcus tubae auditivae, between the petrous part of the temporal and the great wing of the sphenoid. This sulcus is directed lateralward and backward from the root of the medial pterygoid plate and lodges the cartilaginous part of the auditory tube; it is continuous behind with the canal in the temporal bone which forms the bony part of the same tube. At the bottom of this sulcus is a narrow cleft, the petrosphenoidal fissure, which is occupied, in the recent condition, by a plate of cartilage. Behind this fissure is the under surface of the petrous portion of the temporal bone, presenting, near its apex, the quadrilateral rought surface, part of which affords attachment to the Levator veli palatini; lateral to this surface is the orifice of the carotid canal, and medial to it, the depression leading to the aquaeductus cochleae, the former transmitting the internal carotid artery and the carotid plexus of the sympathetic, the latter serving for the passage of a vein from the cochlea. Behind the carotid canal is the jugular foramen, a large aperture, formed in front by the petrous portion of the temporal, and behind by the occipital; it is generally larger on the right than on the left side, and may be subdivided into three compartments. The anterior compartment transmits the inferior petrosal sinus; the intermediate, the glossopharyngeal, vagus, and accessory nerves; the posterior, the transverse sinus and some meningeal branches from the occipital and ascending pharyngeal arteries. On the ridge of bone di^■iding the carotid canal from the jugular foramen is the inferior tympanic canaliculus for the transmission of the tympanic branch of the glossopharyngeal nerve; and on the w^all of the jugular foramen, near the root of the styloid process, is the mastoid canaliculus for the passage of the auricular branch of the ^•agus nerve. Extending forward from the jugular foramen to the foramen lacerum is the petrooccipital fissure occupied, in the recent state, by a plate of cartilage. Behind the basilar portion of the occipital bone is the foramen magnum, bounded laterally by the occipital THE EXTERIOR OF THE SKULL 281 condyles, the medial sides of which are rough for tlie attachment of the alar ligaments. Lateral to each condyle is the jugular process which gives attachment to the Rectus capitis lateralis muscle and the hitcral athmtooccipital ligament. The foramen magnum transmits the medulla ol)longata and its membranes, the accessory nerves, the vertebral arteries, the anterior and posterior spinal arteries, and the ligaments connecting the occipital bone with the axis. The mid-points on the anterior and posterior margins of the foramen magnum are respectively termed the basion and the opisthion. In front of each condyle is the canal for the passage of the hypoglossal nerve and a meningeal artery. Behind each condyle is the condyloid fossa, perforated on one or both sides by the condyloid canal, for the transmission of a vein from the transverse sinus. Behind the foramen magnum is the median nuchal line ending above at the external occipital protuberance, while on either side are the superior and inferior nuchal lines; these, as well as the surfaces of bone between them, are rough for the attachment of the muscles which are enumerated on pages 227 and 22S. Parietal Ftontal Occipital Fig. 332. — Side view of the skull. Norma Lateralis (Fig. 332). — When \iewed from the side the skull is seen to consist of the cranium above and behind, and of the face below and in front. The cranium is somewhat ovoid in shape, but its contour varies in different cases and depends largely on the length and height of the skull and on the degree of promi- nence of the superciliary arches and frontal eminences. Entering into its formation are the frontal, the parietal, the occipital, the temporal, and the great wing of the sphenoid. These bones are joined to one another and to the zygomatic by the follow- 282 OSTEOLOGY ing sutures: the zygomaticotemporal between the zNgomatic })r()cess of the temporal and the temporal process of the zygomatic; the zygomaticofrontal uniting the zygo- matic bone with the zygomatic process of the frontal ; the sutures surrounding the great wing of the si)henoid, viz., the sphenozygomatic in front, the sphenofrontal and sphenoparietal above, and the sphenosquamosal behind. The si)lien()})arictal suture varies in length in different skulls, and is absent in those cases where the frontal articulates with the temporal squama. The point corresponding with the posterior end of the sphenoparietal suture is named the pterion; it is situated about 3 cm. behind, and a little above the level of the zygomatic process of the frontal bone. The squamosal suture arches backward from the pterion and connects the tem- poral squama with the lower border of the parietal: this suture is continuous behind with the short, nearly horizontal parietomastoid suture, which unites the mastoid process of the temporal with the region of the mastoid angle of the parietal. Extending from above downward and forward across the cranium are the coronal and lambdoidal sutures; the former connects the parietals with the frontal, the latter, the parietals with the occipital. The lambdoidal suture is continuous below^ with the occipitomastoid suture between the occipital and the mastoid portion of the temporal. In or near the last suture is the mastoid foramen, for the transmission of an emissary vein. The point of meeting of the parietomastoid, occipitomastoid, and lambdoidal sutures is known as the asterion. Immediately above the orbital margin is the superciliary arch, and, at a higher level, the frontal eminence. Near the centre of the parietal bone is the parietal eminence. Posteriorly is the ex- ternal occipital protuberance, from which the superior nuchal line may be followed forward to the mastoid process. Arching across the side of the cranium are the temporal lines, w^hich mark the upper limit of the temporal fossa. The Temporal Fossa {fossa temyoralis). — The temporal fossa is bounded above and behind by the temporal lines, wdiich extend from the zygomatic process of the frontal bone upward and backward across the frontal and parietal bones, and then curve downward and forward to become continuous with the supramastoid crest and the posterior root of the zygomatic arch. The point w^here the upper temporal line cuts the coronal suture is named the stephanion. The temporal fossa is bounded in front by the frontal and zygomatic bones, and opening on the back of the latter is the zygomaticotemporal foramen. Laterally the fossa is limited by the zygomatic arch, formed by the zygomatic and temporal bones; helow, it is separated from the infratemporal fossa by the infratemporal crest on the great wing of the sphenoid, and by a ridge, continuous wdth this crest, which is carried backward across the temporal squama to the anterior root of the zygomatic process. In front and below% the fossa communicates with the orbital cavity through the inferior orbital or sphenomaxillary fissure. The floor of the fossa is deeply concave in front and convex behind, and is formed by the zygomatic, frontal, parietal, sphenoid, and temporal bones. It is traversed by vascular furrows ; one, usually well-marked, runs upward above and in front of the external acoustic meatus, and lodges the middle temporal artery. Two others, frequently indistinct, may be observed on the anterior part of the floor, and are for the anterior and posterior deep temporal arteries. The temporal fossa contains the Temporalis muscle and its vessels and nerves, together with the zygomaticotemporal nerve. The zygomatic arch is formed by the zygomatic process of the temporal and the temporal process of the zygomatic, the two being united by an oblique suture; the tendon of the Temporalis passes medial to the arch to gain insertion into the coronoid process of the mandible. The zygomatic process of the temporal arises by two roots, an anterior, directed inward in front of the mandibular fossa, where it expands to form the articular tubercle, and a posterior, which runs backward above the external acoustic meatus and is continuous with the supramastoid Tiii<: kxti:rior of the skcll 283 crest. The iip])(>r honlcr of the areh gives attaclnnent to the teni])oral fascia; the lower border and medial surface gWe orij;in to the Masseter. Below the posterior root of the zygomatic arch is the elliptical orifice of the external acoustic meatus, bounded in front, below, and lu'liind by tlie tym])anic part of the temporal bone; to its outer margin the cartilaginous segment of the external acoustic meatus is attached. The small triangular area between the posterior root of the zygomatic arch and the postero-sui)erior part of the orifice is termed the suprameatal triangle, on the anterior border of which a small spinous process, the suprameatal spine, is sometimes seen. Between the tympanic part and the articular tubercle is the mandibular fossa, divided into two i)arts by the petrotympanic fissure. The anterior and larger part of the fossa articulates with the condyle of the mandible and is limited behind by the external acoustic meatus: the posterior part sometimes lodges a portion of the parotid gland. The styloid process extends downward and forward for a \^ariable distance from the lower part of the tympanic part, and gives attachment to the Styloglossus, StyJohy- oideus, and Stylopharyngeus, and to the stylohyoid and stylomandibular ligaments. Projecting downward behind the external acoustic meatus is the mastoid process, to the outer surface of which the Sternocleidomastoideus, Splenius capitis, and Longissimus capitis are attached. Pa rictf/I Inferim- orbital fissure Infratemporal crest Pierygomaxillary fisstire Pterygoid hamulus Fig. 333. — Left infratemporal fossa External acoustic meatus Tympanic part of temporal ijloicl process Mandibular cavity Zygomatic process {cut) Lateral pterygoid plate The Infratemporal Fossa (fossa infratemjjoral is; zygomatic fossa) (Fig. 333). — The infratemporal fossa is an irregularly shaped cavity, situated below and medial to the zygomatic arch. It is bounded, in front, by the infratemporal surface of the maxilla and the ridge which descends from its zygomatic process; behind, by the articular tubercle of the temporal and the spina angularis of the sphenoid; above, by the great wing of the sphenoid below the infratemporal crest, and by the under surface of 284 OSTEOLOGY the temporal squama; heloic, by the alveolar border of the maxilla; medially, by the lateral pterygoid plate. It contains the lower ])art of the Temporalis, the Pterygoidei internus and externus, the internal maxillary vessels, and the man- dibular and maxillary nerves. The foramen ovale and foramen spinosum open on its roof, and the alveolar canals on its anterior wall. At its u])per and medial part are two fissures, wliieli together form a T-shaped fissure, the horizontal limb being named the inferior orbital, and the vertical one the pterygomaxillary. The inferior orbital fissure {fissura orbitalis inferior; sphenomaxillary fissure), horizontal in direction, opens into the lateral and back part of the orbit. It is bounded above by the lower border of the orbital surface of the great wing of the sphenoid; hclow, by the lateral border of the orbital surface of the maxilla and the orbital process of the palatine bone; laterally, by a small part of the zygomatic bone:^ medially, it joins at right angles with the pterygomaxillary fissure. Through the inferior orbital fissure the orbit communicates with the temporal, infratem- poral, and pterygopalatine fossse; the fissure transmits the maxillary nerve and its zygomatic branch, the infraorbital vessels, the ascending branches from the sphenopalatine ganglion, and a vein which connects the inferior ophthalmic vein with the pterygoid venous plexus. The pterygomaxillary fissure is vertical, and descends at right angles from the medial end of the preceding; it is a triangular interval, formed by the diver- gence of the maxilla from the pterygoid process of the sphenoid. It connects the infratemporal with the pterygopalatine fossa, and transmits the terminal part of the internal maxillary artery. The Pterygopalatine Fossa (fossa pterygoimlatina; sphenomaxillary fossa). — The pterygopalatine fossa is a small, triangular space at the angle of junction of the inferior orbital and pterygomaxillary fissures, and placed beneath the apex of the orbit. It is bounded above by the under surface of the body of the sphenoid and by the orbital process of the palatine bone; in front, by the infratemporal surface of the maxilla; behind, by the base of the pterygoid process and lower part of the anterior surface of the great wing of the sphenoid; medially, by the vertical part of the palatine bone with its orbital and sphenoidal processes. This fossa communicates with the orbit by the inferior orbital fissure, with the nasal cavity by the sphenopalatine foramen, and with the infratemporal fossa by the pterygo- maxillary fissure. Five foramina open into it. Of these, three are on the posterior wall, viz., the foramen rotundum, the pterygoid canal, and the pharyngeal canal, in this order downward and medial ward. On the medial wall is the sphenopalatine foramen, and below is the superior orifice of the pterygopalatine canal. The fossa contains the maxillary nerve, the sphenopalatine ganglion, and the terminal part of the internal maxillary artery. Norma Occipitalis. — When viewed from behind the cranium presents a more or less circular outline. In the middle line is the posterior part of the sagittal suture connecting the parietal bones; extending downward and lateralward from the hinder end of the sagittal suture is the deeply serrated lambdoidal suture join- ing the parietals to the occipital and continuous below with the parietomastoid and occipitomastoid sutures; it frequentl}- contains one or more sutural bones. Near the middle of the occipital squama is the external occipital protuberance or inion, and extending lateralward from it on either side is the superior nuchal line, and above this the faintly marked highest nuchal line. The part of the squama above the inion and highest lines is named the planum occipitale, and is covered by the Occipitalis muscle; the part below is termed the planum nuchale, and is divided by the median nuchal line which runs downward and forward from the inion to the foramen magnum; this ridge gives attachment to the ligamentum nuchae. The ^ Occasionally the maxilla and the sphenoid articulate with each other at the anterior extremity of this fissure; the zygomatic is then excluded from it. THE EXTERIOR OF THE SKULL 285 muscles attached to the phinum niichale are enumerated on p. 227. Below and in front are the mastoid processes, convex laterally and grooved medially hy the mastoid notches. In or near the occipitomastoid suture is the mastoid foramen for the passage of the mastoid emissary vein. F r n t a I Supraorbital foramen Superior orbital fissure - Lamina papyracea of ethmoid - Laeritnal ■ Inferior orbital fissure ■ Zygomaticofacial 'foramen Infraorbital foramen Nasal cavity Inferior nasal concha u ; %st ^Ya //c' ' i ' Mentcd foramen Fig. 334.— The skull from the front. Norma Frontalis (Fig. 334). — When viewed from the front the skull exhibits a somewhat oval outline, limited above by the frontal bone, heloiv by the body of the mandible, and lateraUy by the zygomatic bones and the mandibular rami. The upper part, formed by the frontal squama, is smooth and convex. The lower part, made up of the bonesvof the face, is irregular; it is excavated laterally by the orbital cavities, and presents. in the middle line the anterior nasal aperture leading to the nasal cavities, and befcw this the transverse slit between the upper and lower dental arcades. Above, the frontal eminences stand out more or less prominently, and beneath these are the superciliary arches, joined to one another in the middle by the glabella. On and above the glabella a trace of the frontal suture sometimes persists; beneath it is the frontonasal suture, the mid-point of which is termed the nasion. Behind and below the frontonasal suture the frontal articulates with the frontal process of the maxilla and with the lacrimal. Arching transversely below 286 OSTEOLOGY the superciliary arches is the ujjper part of tlie maroin of the orbit, thin and promi- nent in its lateral two-thirds, rounded in its medial third, and presenting, at the junction of these two portions, the supraorbital notch or foramen for the supra- orbital nerve and vessels. The supraorbital margin ends laterally in the zygomatic process which articulates with the zygomatic bone, and from it the temporal line extends upward and backward. Below the frontonasal suture is the bridge of the nose, con^'ex from side to side, concavo-convex from abo\'e downward, and formed by the two nasal bones supported in the middle line by the perpendicular plate of the ethmoid, and laterally by the frontal jirocesses of the maxillae w^hich are prolonged upward between the nasal and lacrimal bones and form the lower and medial part of the circumference of each orbit. Below the nasal bones and between the maxillae is the anterior aperture of the nose, pyriform in shape, with the narrow end directed upward. Laterally this opening is bounded by sharp margins, to which the lateral and alar cartilages of the nose are attached; beloic, the margins are thicker and curve medialward and forward to end in the anterior nasal spine. On looking into the nasal cavity, the bony septum which separates the nasal cavities presents, in front, a large triangular deficiency; this, in the recent state, is filled up by the cartilage of the nasal septum; on the lateral wall of each nasal cavity the anterior part of the inferior nasal concha is visible. Below and lateral to the anterior nasal aperture are the anterior surfaces of the maxillee, each perforated, near the lower margin of the orbit, by the infraorbital foramen for the passage of the infraorbital nerve and vessels. Below and medial to this foramen is the canine eminence separating the incisive from the canine fossa. Beneath these fossse are the alveolar processes of the maxillae containing the upper teeth, which overlap the teeth of the mandible in front. The zygomatic bone on either side forms the prominence of the cheek, the lower and lateral portion of the orbital cavity, and the anterior part of the zygomatic arch. It articulates medially with the maxilla, behind with the zygomatic process of the temporal, and above with the great wing of the sphenoid and the zygomatic process of the frontal; it is per- forated by the zygomaticofacial foramen for the passage of the zygomaticofacial nerve. On the body of the mandible is a median ridge, indicating the position of the symphysis; this ridge divides below to enclase the mental protuberance, the lateral angles of which constitute the mental tubercles. Below the incisor teeth is the incisive fossa, and beneath the second premolar tooth the mental foramen which transmits the mental nerve and vessels. The oblique line runs upward from the mental tubercle and is continuous behind with the anterior border of the ramus. The posterior border of the ramus runs downward and forward from the condyle to the angle, which is frequently more or less everted. _ The Orbits (orbitae) (Fig. 334). — The orbits are two quadrilateral pyramidal cavi- ties, situated at the upper and anterior part of the face, their bases being directed forward and lateralward, and their apices backward and medialward, so that their long axes, if continued backward, would meet over the body of the sphenoid. Each presents for examination a roof, a floor, a medial and a lateral wall, a base, and an apex. The roof is concave, directed downward, and slightly forward, and formed in front by the orbital plate of the frontal; behind by the small wing of the sphenoid. It presents medially the trochlear fovea for the attachment of the cartilaginous pulley of the Obliquus oculi superior; laterally, the lacrimal fossa for the lacrimal gland; and posteriorly, the suture between the frontal bone and the small wing of the sphenoid. The floor is directed upward and lateralward, and is of less extent than the roof; it is formed chiefl}- by the orbital surface of the maxilla; in front and laterally, by the orbital process of the zygomatic bone, and behind and medially, to a small extent, by the orbital process of the palatine. At its medial angle is the upper THE EXTKRIOH OF THE SKILL 2.S'i opening oi the nasolacrimal canal, immediately to the lateral side of which is a depression for the origin of the ()l)li(iuus oculi inferior. On its lateral part is the sntnre between the maxilla and zygomatic hone, and at its posterior part that between the maxilla and the orbital i)r()c(\ss of the palatine. Running forward near the middle of the floor is the infraorbital groove, ending in front in the infra- orbital canal and transmitting the infraorbital nerve and vessels. The medial wall (I'ig. 'c>\\b) is nearly vertical, and is formed from before back- ward by the frontal process of the maxilla, the lacrimal, the lamina papyracea of the ethmoid, and a small part of the body of the sphenoid in front of the optic foramen. vSometimes the sphenoidal concha forms a i-mall part of this w^all (see page 250). It exhibits three vertical sutures, viz., the lacrimomaxillary, lacrimo- ethmoidal, and sphenoethmoidal. In front is seen the lacrimal groove, which lodges the lacrimal sac, and behind the groove is the posterior lacrimal crest, from wiiich Anterior ethmoidal foramen Posterior ethmoidal foramen Orbital process of palatine Oiiiic foramen Sphenopalatine foramen . Se^la turcica I Piobe iH foramen rotundwn Fossa f&>' . — , lacriinal sac \J Uncinate process . ^^ ""T^IB. of ethmoid \^-"i^m Openings of _ -— \ VmWiPr maxillary sinus Inferior nasal cotvcha Probe in pterygoid canal ( ^Prohe in pterygopalatine canal I ^ Palatine hone Lateral pterygoid plate Pyramidal process of palatine Fig. 335. — Medial wall of left orbit. the lacrimal part of the Orbicularis oculi arises. At the junction of the medial wall and the roof are the frontomaxillary, frontolacrimal, frontoethmoidal, and sphenofrontal sutures. The point of junction of the anterior border of the lacrimal with the frontal is named the dacryon. In the frontoethmoidal suture are the anterior and posterior ethmoidal foramina, the former transmitting the nasociliary nerve and anterior ethmoidal vessels, the latter the posterior ethmoidal nerve and vessels. The lateral wall, directed medialward and forw^ard, is formed by the orbital process of the zygomatic and the orbital surface of the great wing of the sphenoid ; these are united by the sphenozygomatic suture which terminates below at the front end of the inferior orbital fissure. On the orbital process of the zygomatic bone are the orbital tubercle (Whitnall) and the orifices of one or two canals which transmit the branches of the zvgomatic nerve. Between the roof and the lateral 288 OSTEOLOGY wall, near the apex of the orbit, is the superior orbital fissure. Through this fissure the oculomotor, the trochlear, the ophthahnic division of the trigeminal, and the abducent nerves enter the orbital cavity, also some filaments from the cavernous plexus of the sympathetic and the orbital branches of the middle meningeal artery. Passing backward through the fissure are the ophthalmic vein and the recurrent branch from the lacrimal artery to the dura mater. The lateral wall and the floor are separated posteriori^' by the inferior orbital fissure which transmits the maxillary nerve and its zygomatic branch, the infraorbital vessels, and the ascending branches from the sphenopalatine ganglion. The base of the orbit, quadrilateral in shape, is formed above by the supra- orbital arch of the frontal bone, in which is the supraorbital notch or foramen for the passage of the supraorbital vessels and nerve; beloiv b>' the zygomatic bone and maxilla, united by the zygomaticomaxillary suture; laterally by the zygomatic bone and the zygomatic process of the frontal joined by the zygomaticofrontal suture; medially by the frontal bone and the frontal process of the maxilla united by the frontomaxillary suture. The apex, situated at the back of the orbit, corresponds to the optic foramen^ a short, cylindrical canal, which transmits the optic nerve and ophthalmic artery. It will thus be seen that there are nine openings communicating with each orbit, viz., the optic foramen, superior and inferior orbital fissures, supraorbital foramen, infraorbital canal, anterior and posterior ethmoidal foramina, zygomatic foramen, and the canal for the nasolacrimal duct. THE INTERIOR OF THE SKULL. In order to study the interior of the skull the skull-cap should be removed by a saw-cut carried around the cranium about the level of the frontal eminences and the upper limits of the squapaosal sutures, cutting the occipital bone about 2.5 cm. above the external protuberance. Inner Surface of the Skull-cap. — The inner surface of the skull-cap is concaA'e and presents depressions for the convolutions of the cerebrum, together with numerous furrows for the lodgement of branches of the meningeal vessels. Along the middle line is a longitudinal groove, narrow in front, where it commences at the frontal crest, but broader behind; it lodges the superior sagittal sinus, and its margins afford attachment to the falx cerebri. On either side of it are several depressions for the arachnoid granulations, and at its back part, the openings of the parietal foramina when these are present. It is crossed, in front, by the coronal suture, and behind by the lambdoidal, while the sagittal lies in the medial plane between the parietal bones. Upper Surface of the Base of the Skull (Fig. 336). — The upper surface of the base of the skull or floor of the cranial cavity presents three fossae, called the anterior, middle, and posterior cranial fossae. Anterior Fossa (Jossa cranii anterior) . — The floor of the anterior- fossa is formed by the orbital plates of the frontal, the cribriform plate of the ethmoid, and the small wings and front part of the body of the sphenoid ; it is limited behind by the posterior borders of the small wings of the sphenoid and by the anterior margin of the chiasmatic groove. It is traversed by the frontoethmoidal, sphenoethmoidal, and sphenofrontal sutures. Its lateral portions roof in the orbital cavities and sup- port the frontal lobes of the cerebrum; they are convex and marked by depressions for the brain convolutions, and grooves for branches of the meningeal vessels. 1 Some anatomists describe the apex of the orbit as corresponding with the mediaf end of the superior orbital fissure. It seems better, however, to adopt the statement in the text, since the ocular muScles take origin around the optic foramen, and diverge from it to the bulb of the eye. THE INTERIOR OF THE SKULL 289 The central portion corresponds with the roof of the nasal cavity, and is markedly depressed on either side of the crista galli. It presents, in and near the median Groove for super, sagittal sintis — Grooves for anier. meningeal vessels Foramen cacum — Cn'nta galli Slit for n(isocili(i)-y nerve Groove fur iiasociiian/ verve Anterior ethmoidal foratnen Orifices for olfactory nerves Posterior ethmoidal foramen Ethmoidal spine Olfactory grooves Optic foramen Chiasmatic groove T'uberculum sellae Anterior clinoid process Middle clinoid process Posterior clinoid process Groove for abducent nerve Foramen lacerum Orifice of carotid canal Depression for semilunar ganglion Internal acoustic meattis Slit for dura mater Groove for supeiior petrosal sinus Jugular foramen Hypoglossal canal - Aquceductus vestibuli Condyloid foramen Mastoid foramen Posterior m,eningeal grooves fit'-'- Fig. 336. — Base of the skull. Upper surface. line, from before backward, the commencement of the frontal crest for the attach- ment of the falx cerebri; the foramen cecum, between the frontal bone and the crista galli of the ethmoid, which usually transmits a small vein from the nasal cavity 19 290 OSrEOWGY to the superior sagittal sinus; behind the foramen cecum, the crista galli, the free margin of which affords attachment to the falx cerebri; on either side of the crista galli, the olfactory groove formed by the cribriform plate, which supports the olfactory bulb and presents foramina for the transmission of the olfactory nerves, and in front a slit-like opening for the nasociliary nerve. Lateral to either olfactory groove are the internal openings of the anterior and posterior ethmoidal foramina; the anterior, situated about the middle of the lateral margin of the olfac- tory groove, transmits the anterior ethmoidal vessels and the nasociliary nerve; the nerve runs in a groove along the lateral edge of the cribriform plate to the slit-like opening above mentioned; the posterior ethmoidal foramen opens at the l)ack part of this margin under cover of the projecting lamina of the sphenoid, and transmits the posterior ethmoidal vessels and nerve. Farther back in the middle line is the ethmoidal spine, bounded behind by a slight elevation separating two shallow lon- gitudinal grooves which support the olfactory lobes. Behind this is the anterior margin of the chiasmatic groove, running laterahvard on either side to the upper margin of the optic foramen. The Middle Fossa {fossa cranii media). — The middle fossa, deeper than the pre- ceding, is narrow in the middle, and wide at the sides of the skull. It is bounded in front by the posterior margins of the small wings of the sphenoid, the anterior clinoid processes, and the ridge forming the anterior margin of the chiasmatic groove; hehincl, by the superior angles of the petrous portions of the temporals and the dorsum sellae; laterally by the temporal squamse, sphenoidal angles of the parietals, and great wings of the sphenoid. It is traversed by the squamosal, sphenoparietal, sphenosquamosal, and sphenopetrosal sutures. The middle part of the fossa presents, in frojit, the chiasmatic groove and tuber- culum sellae ; the chiasmatic groove ends on either side at the optic foramen, which transmits the optic nerve and ophthalmic artery to the orbital cavity. Behind the optic foramen the anterior clinoid process is directed backward and medialward and gives attachment to the tentorium cerebelli. Behind the tuberculum sellae is a deep depression, the sella turcica, containing the fossa hypophyseos, which lodges the hypophysis, and presents on its anterior wall the middle clinoid processes. The sella turcica is bounded posteriorly by a quadrilateral plate of bone, the dorsum sellae, the upper angles of which are surmounted by the posterior clinoid processes: these afford attachment to the tentorium cerebelli, and below each is a notch for the abducent nerve. On either side of the sella turcica is the carotid groove, which is broad, shallow, and curved somewhat like the italic letter /. It begins behind at the foramen lacerum, and ends on the medial side of the anterior clinoid process, where it is sometimes converted into a foramen (carotico-clinoid) by the union of the anterior with the middle clinoid process; posteriorly, it is bounded laterally by the lingula. This groove lodges the cavernous sinus and the internal carotid artery, the latter being surrounded by a plexus of sympathetic nerves. The lateral parts of the middle fossa are of considerable depth, and support the temporal lobes of the brain. They are marked by depressions for the brain convolutions and traversed by furrows for the anterior and posterior branches of the middle meningeal vessels. These furrows begin near the foramen spinosum, and the anterior runs forward and upward to the sphenoidal angle of the parietal, where it is sometimes converted into a bony canal; the posterior runs laterahvard and backward across the temporal squama and passes on to the parietal near the middle of its lower border. The following apertures are also to be seen. In front is the superior orbital fissure, bounded above by the small wing, below, by the great wing, and medially, by the body of the sphenoid; it is usually completed laterally by the orbital plate of the frontal bone. It transmits to the orbital cavity the oculomotor, the trochlear, the ophthalmic division of the trigeminal, and the abducent nerves, some filaments from the cavernous plexus of the THE INTERIOR OF THE SK[ILL 291 sympathetic, and tlic orbital hraiich of the iniddle inciiiii^cal artery; and from the orbital cavity a recurrent branch from the lacrimal artery to the dura mater, and the ophthalmic veins. Behind the medial end of the superior orbital fissure is the foramen rotundum, for the passage of the maxillary nerve. Behind and lateral to the foramen rotundum is the foramen ovale, which transmits the mandibular nerve, the accessory meningeal artery, and the lesser sujxTficial jjetrosal nerve. ^ Medial to the foramen o\'ale is the foramen Vesalii, which varies in size in different individuals, and is often absent; when present, it opens below at the lateral side of the scaphoid fossa, and transmits a small vein. Lateral to the foramen ovale is the foramen spinosum, for the passage of the middle meningeal vessels, and a recurrent branch from the mandibular nerve. Medial to the foramen ovale is the foramen lacerum; in the recent state the lower part of this aperture is filled up b}' a layer of fibrocartilage, while its upper and inner parts transmit the internal carotid artery surrounded by a plexus of sympathetic nerves. The nerve of the pterygoid canal and a meningeal branch from the ascending pharyngeal artery pierce the layer of fibrocartilage. On the anterior surface of the petrous portion of the temporal bone are seen the eminence caused by the projection of the superior semicircular canal; in front of and a little lateral to this a depression corresponding to the roof of the tympanic cavity; the groove leading to the hiatus of the facial canal, for the transmission of the greater superficial petrosal nerve and the petrosal branch of the middle meningeal artery; beneath it, the smaller groove, for the pas- sage of the lesser superficial petrosal nerve; and, near the apex of the bone, the depression for the semilunar ganglion and the orifice of the carotid canal. The Posterior Fossa (fossa cranii posterior). — The posterior fossa is the largest and deepest of the three. It is formed by the dorsum sellae and clivus of the sphenoid, the occipital, the petrous and mastoid portions of the temporals, and the mastoid angles of the parietal bones; it is crossed by the occipitomastoid and the parietomastoid sutures, and lodges the cerebellum, pons, and medulla oblongata. It is separated from the middle fossa in and near the median line by the dorsum sellae of the sphenoid and on either side by the superior angle of the petrous por- tion of the temporal bone. This angle gives attachment to the tentorum cerebelli, is grooved for the superior petrosal sinus, and presents at its medial end a notch upon which the trigeminal nerve rests. The fossa is limited behind by the grooves for the transverse sinuses. In its centre is the foramen magnum, on either side of which is a rough tubercle for the attachment of the alar ligaments; a little above this tubercle is the canal, which transmits the hypoglossal nerve and a meningeal branch from the ascending pharyngeal artery. In front of the foramen magnum the basilar portion of the occipital and the posterior part of the body of the sphenoid form a grooved surface which supports the medulla oblongata and pons; in the young skull these bones are joined by a synchondrosis. This grooved surface is separated on either side from the petrous portion of the temporal by the petro- occipital fissure, which is occupied in the recent state by a plate of cartilage; the fissure is continuous behind with the jugular foramen, and its margins are grooved for the inferior petrosal sinus. The jugular foramen is situated between the lateral part of the occipital and the petrous part of the temporal. The anterior portion of this foramen transmits the inferior petrosal sinus; the posterior portion, the transverse sinus and some meningeal branches from the occipital and ascending pharyngeal arteries; and the intermediate portion, the glossopharyngeal, vagus, and accessory nerves. Above the jugular foramen is the internal acoustic meatus, for the facial and acoustic nerves and internal auditory artery; behind and lateral to this is the slit-like opening leading into the aquaeductus vestibuli, which lodges the ductus endolymphaticus; while between these, and near the superior angle of 1 See footnote, page 248. 292 OSTEOLOGY the petrous portion, is a small triangular depression, the remains of the fossa sub- arcuata, which lodges a process of the dura mater and occasionally transmits a small vein. Behind the foramen magnum are the inferior occipital fossae, which support the hemispheres of the cerebellum, separated from one another by the internal occipital crest, which serves for the attachment of the falx cerebelli, and lodges the occipital sinus. The posterior fossae are surmounted by the deep grooves for the transverse sinuses. Each of these channels, in its passage to the jugular foramen, grooves the occipital, the mastoid angle of the parietal, the mastoid portion of the temporal, and the jugular process of the occipital, and ends at the back part of the jugular foramen. Where this sinus grooves the mastoid portion of the temporal, the orifice of the mastoid foramen may be seen; and, just previous to its termina- tion, the condyloid canal opens into it; neither opening is constant. Crest of nasal bones Frontal spine Space for triangular cartilage of septum Crest of palatines Crest of maxillce Fig. 337. — ^ledial wall of left nasal fossa. The Nasal Cavity (cavum nasi; nasal fossa). — The nasal cavities are two irregular spaces, situated one on either side of the middle line of the face, extending from the base of the cranium to the roof of the mouth, and separated from each other by a thin vertical septum. They open on the face through the pear-shaped anterior nasal aperture, and their posterior openings or choanse communicate, in the recent state, with the nasal part of the pharynx. They are much narrower above than below, and in the middle than at their anterior or posterior openings : their depth, which is considerable, is greatest in the middle. They communicate with the frontal, ethmoidal, sphenoidal, and maxillary sinuses. Each cavity is bounded by a roof, a floor, a medial and a lateral wall. The roof (Figs. 337, 338) is horizontal in its central part, but slopes down- ward in front and behind ; it is formed in front by the nasal bone and the spine of the frontal; in the middle, by the cribriform plate of the ethmoid; and behind, by the body of the sphenoid, the sphenoidal concha, the ala of the vomer and the sphenoidal process of the palatine bone. In the cribriform plate of the ethmoid THE INTERIOR OF THE SKULL 293 are the foramina for the olfactory nerves, and on the posterior part of the roof is the openin"' into the sphenoi(hil sinus. The floor is fhittened from before backward and concave from side to side. It is formed by the pahitine process of the maxilla and the horizontal part of the palatine bone; near its anterior end is the opening of the incisive canal. The medial wall (scpfioii nasi) (Fig. 337), is frequently deflected to one or other side, more often to the left than to the right. It is formed, in front, by the crest of the nasal bones and frontal spine; in the middle, by the perpendicular plate of the ethmoid; behind, by the vomer and the rostrum of the sphenoid; below, by the crest of the maxillte and palatine bones. It presents, in front, a large, triangular notch, which receives the cartilage of the septum; and behind, the free edge of the vomer. Its surface is marked by numerous furrows for vessels and nerves and by the grooves for the nasopalatine nerve, and is traversed by sutures connecting the bones of which it is formed. Xasal bone Frontal spine Cribriform plate of ethmoid Sphenoid Anterior nasal spine Palatine proc. of maxilla Horizontal part of palatine Posterior 'nasal spine Incisive canal Probe passed through nasolacrimal canal Bristle passed through infundibulum - Frontal proc. of maxilla - Lacrimal Ethmoid Uncinate proc. of ethmoid Inferior nasal concha Palatine Superior meatus Middle meatus Inferior meatus Fig. 338. — Roof, floor, and lateral wall of left nasal cavitJ^ The lateral wall (Fig. 338) is formed, in front, by the frontal process of the maxilla and by the lacrimal bone; in the middle, by the ethmoid, maxilla, and inferior nasal concha; behind, by the vertical plate of the palatine bone, and the medial pterygoid plate of the sphenoid. On this wall are three irregular antero- posterior passages, termed the superior, middle, and inferior meatuses of the nose. The superior meatus, the smallest of the three, occupies the middle third of the lateral wall. It lies between the superior and middle nasal conchse; the spheno- palatine foramen opens into it behind, and the posterior ethmoidal cells in front. The sphenoidal sinus opens into a recess, the sphenoethmoidal recess, which is placed above and behind the superior concha. The middle meatus is situated between the middle and inferior conchse, and extends from the anterior to the posterior end of the latter. The lateral wall of this meatus can be satisfactorily studied only after the removal of the middle concha. On it is a curved fissure, the hiatus semilunaris, 294 OSTEOLOGY limited below by the edge of the uncinate i)r()('ess of the ethmoid and above by an elevation named the bulla ethmoidalis ; the middle ethmoidal cells are contained within this bulla and open on or near to it. Through the hiatus semilunaris the meatus communicates with a curved passage termed the infundibulum, Avhich communicates in front with the anterior ethmoidal cells and in ratlier more than fifty per cent, of skulls is continued upward as the frontonasal duct into the frontal air-sinus; when this continuity fails, the frontonasal duct oi)ens directly into the anterior part of the meatus. Below the bulla ethmoidalis and hidden by the unci- nate process of the ethmoid is the opening of the maxillary sinus (ostium maxillare) ; an accessory opening is freciuently present above the posterior part of the inferior nasal concha. The inferior meatus, the largest of the three, is the space between the inferior concha and the floor of the nasal cavity. It extends almost the entire length of the lateral wall of the nose, is broader in front than behind, and presents anteriorly the lower orifice of the nasolacrimal canal. The Anterior Nasal Aperture (Fig. 334) is a heart-shaped or pyriform opening, whose long axis is vertical, and narrow end upward; in the recent state it is much contracted by the lateral and alar cartilages of the nose. It is bounded aboDe by the inferior borders of the nasal bones; laterally by the thin, sharp margins which separate the anterior from the nasal surfaces of the maxillae; and heloio by the same borders, where they curve medialward to join each other at the anterior nasal spine. The choanse are each bounded above by the under surface of the body of the sphenoid and ala of the vomer; below, by the posterior border of the horizontal part of the palatine bone; laterally, by the medial pterygoid plate; they are separated from each other by the posterior border of the vomer. DIFFERENCES IN THE SKULL DUE TO AGE. At birth the skull is large in proportion to the other parts of the skeleton, but its facial portion is small, and equals only about one-eighth of the bulk of the cranium as compared with one-half in the adult. The frontal and parietal eminences are prominent, and the greatest width of the skull is at the level of the latter; on the other hand, the glabella, superciliary arches, and mastoid processes are not developed. Ossification of the skull bones is not completed, and many of them, e. g., the occipital, temporals, sphenoid, frontal, and mandible, consist of more than one piece. Unossified membranous intervals, termed fontanelles, are seen at the angles of the parietal bones ; these fontanelles are six in number: two, an anterior and a posterior, are situated in the middle line, and two, an antero-lateral and a postero-lateral, on either side. Fig. 339. — Skull at birth showing anterior and posterior fontanelles. Fig. 340. — The lateral fontanelles. The anterior or hregmatic fontanelle (Fig. 339) is the largest, and is placed at the junction of the sagittal, coronal, and frontal sutures; it is lozenge-shaped, and measures about 4 cm. in its antero-posterior and 2.5 cm. in its transverse diameter. The posterior fontanelle is triangular CRANIOLOGY 295 in form and is situated at the junetion of the sagittal and lanibdoidal sutures. The lateral Jonla- nclles (Fig. 340) are small, irregular in shape, and correspond resi)ec-tivclj' with the sphenoidal and mastoid angles of the parietal bones. An additional fonlanelk; is sometimes seen in tlie sagittal suture at the region of the obelion. The fontanelles are usually closc'd by the growth and extension of the bones which surround them, but sometimes they are the sites of se]iarate ossific centres which develop into sutural bones. The posterior and lateral fontanelles are obliter- ated within a month or two after birth, but the anterior is not completely closed until ;ibout the middle of the second year. The smallness of the face at birth is mainly accounted for by the rudimentaiy condition of the maxilhe and mandible, the non-eruption of the teeth, and the small size of th(! maxillarj' air sinuses antl nasal cavities. At birth the nasal cavities lie almost entirely between the orbits, and the lower border of the anterior nasal aperture is only a httle below the level of the orbital floor. With the eruption of the deciduous teeth there is an enlargement of the face and jaws, and these changes are still more marked after the second dentition. The skull grows rapidly from birth to the seventh year, by which time the foramen magnum and petrous parts of the temporals have reached their full size and the orbital cavities are only a Httle smaller than those of the adult. Growth is slow from the seventh year until the approach of puberty, when a second period of activity occurs : this results in an increase in all directions, but it is especially marked in the frontal and facial regions, where it is associated with the develop- ment of the air sinuses. ObUteration of the sutures of the vault of the skull takes place as age advances. This process may commence between the ages of thirty and forty, and is first seen on the inner surface, and some ten years later on the outer surface of the skull. The dates given are, however, only approxi- mate, as it is impossible to state with anything like accuracy the time at which the sutures are closed. ObUteration usually occurs first in the posterior part of the sagittal suture, next in the coronal, and then in the lambdoidal. In old age the skull generally becomes thinner and lighter, but in a small proportion of cases it increases in thickness and weight, owing to an hypertrophy of the inner table. The most strik- ing featm'e of the old skull is the diminution in the size of the maxillge and mandible consequent on the loss of the teeth and the absorption of the alveolar processes. This is associated with a marked reduction in the vertical measurement of the face and with an alteration in the angles of the mandible. SEXUAL DIFFERENCES IN THE SKULL Until the age of puberty there is little difference between the skull of the female and that of the male. The skull of an adult female is, as a rule, lighter and smaller, and its cranial capacity about 10 per cent, less, than that of the male. Its walls are thinner and its muscular ridges less strongly marked; the glabella, superciliary arches, and mastoid processes are less prominent, and the corresponding air sinuses are small or rudimentary. The upper margin of the orbit is sharp, the forehead vertical, the frontal and parietal eminences prominent, and the vault some- what flattened. The contour of the face is more rounded, the facial bones are smoother, and the maxillae and mandible and their contained teeth smaller. From what has been said it will be seen that more of the infantile characteristics are retained in the skull of the adult female than in that of the adult male. A well-marked male or female skull can easily be recognized as such, but in some cases the respective characteristics are so indistinct that the determination of the sex may be difficult or impossible. CRANIOLOGY. Skulls vary in size and shape, and the term craniology is applied to the study of these varia- tions. The capacity of the cranial cavity constitutes a good index of the size of the brain which it contained, and is most conveniently arrived at by filUng the cavity with shot and measuring the contents in a graduated vessel. Skulls may be classified according to their capacities as follows: 1. Microcephalic, with a capacity of less than 1350 c.cm. — e. g., those of native Australians and Andaman Islanders. 2. Mesocephalic, wdth a capacity of from 1350 c.cm. to 1450 c.cm. — e. g., those of African negroes and Chinese. 3 Megacephalic, with a capacity of over 1450 c.cm. — e. g., those of Em'opeans, Japanese, and Eskimos. In comparing the shape of one skuU with that of another it is necessary to adopt some definite position in which the skulls should be placed during the process of examination. They should be so placed that a line carried through the lower margin of the orbit and upper margin of the external acoustic meatus is in the horizontal plane. The normse of one skull can then be com- pared with those of another, and the differences in contom- and surface form noted. Fm-ther, 296 OSTEOLOGY it is necessary that the various linear measurements used to determine the shape of the skull should be made between definite and easily locahzed points on its surface. The principal points may be divided into two groups: (1) those in the median plane, and (2) those on either side of it. The Points in the Median Plane are the: Mental Point. The most prominent i)oint of the chin. Alveolar Point or Prosthion. The central point of the anterior margin of the upper alveolar arch. Subnasal Point. The middle of the lower border of the anterior nasal aperture, at the base of the anterior nasal spine. Nasion. The central point of the frontonasal suture. Glabella. The point in the middle line at the level of the superciliaiy arches. Ophryon. The point in the middle line of the forehead at the level where the temporal hues most nearly approach each other. Bregma. The meeting point of the coronal and sagittal sutures. Obelion. A point in the sagittal suture on a level with the parietal foramina. Lambda. The point of junction of the sagittal and lambdoidal sutures. Occipital Point. The point in the middle line of the occipital bone farthest from the glabella. Inion. The external occipital protuberance. Opisthion. The mid-point of the posterior margin of the foramen magnum. Basion. The mid-point of the anterior margin of the foramen magnum. The Points on Either Side of the Median Plane are the: Gonion. The outer margin of the angle of the mandible. Dacryon. The point of union of the antero-superior angle of the lacrimal with the frontal bone and the frontal process of the maxilla. Stephanion. The point where the temporal line intersects the coronal suture. Pterion. The point where the great wing of the sphenoid joins the sphenoidal angle of the parietal. Auricular Point. The centre of the orifice of the external acoustic meatus. Asterion. The point of meeting of the lambdoidal, mastooccipital, and mastoparietal sutures. The horizontal circumference of the cranium is measured in a plane passing tkrough the glabella (Turner) or the ophryon (Flower) in front, and the occipital point behind; it averages about 50 cm. in the female and 52.5 cm. in the male. The occipitofrontal or longitudinal arc is measured from the nasion over the middle line of the vertex to the opisthion: while the basinasal length is the distance between the basion and the nasion. These two measurements, plus the antero-posterior diameter of the foramen magnum, represent the vertical circumference of the cranium. The length is measured from the glabella to the occipital point, while the breadth or greatest transverse diameter is usually foimd near the external acoustic meatus. The proportion of u J 1- 1 ,. (breadth X 100) breadth to length . -r- is termed the cephalic index or index of breadth. The height is usually measured from the basion to the bregma, and the proportion of height , (height X 100) to length , ..- constitutes the vertical or height index. In studying the face the principal points to be noticed are the proportion of its length and breadth, the shape of the orbits and of the anterior nasal aperture, and the degree of projection of the jaws. The length of the face may be measured from the ophryon or nasion to the chin, or, if the mandible be wanting, to the alveolar point; while its width is represented by the distance between the zygomatic arches. By comparing the length with the width of the face, skulls may be divided into two groups; dolichofacial or leptoprosope (long faced) and brachyfacial or chemoprosope (short faced) . The orbital index signifies the proportion which the orbital height bears to the orbital width, thus : orbita l height X 100 orbital width The rwsal index expresses the proportion which the width of the anterior nasal aperture bears to the height of the nose, the latter being measured from the nasion to the lower margin of the nasal aperture, thus : nas al width X 100 nasal height The degree of projection of the jaws is determined by the gnathic or alveolar index, which repre- sents the proportion between the basialveolar and basinasal lengths, thus: basialveolar length X 100 basinasal length CRANIOLOGY 297 The following table, modified from that given by Duckwoitli.i illustrates how these different indices may be utilized in the classification of skulls: Index. Classification. Below 75 Between 75 and SO Above SO Nomenclature. Examples. 1. Cephalic Dolichocephalic Mesaticephalic Brachycephalic Kaffirs and Native Australians. Europeans and Chinese. Mongolians and Andamans. 2. Orbital Below 84 Between 84 and 89 Above 89 Below 48 Between 48 and 53 Above 53 Below 98 Between 98 and 103 Above 103 Microseme Mesoseme Megaseme Tasmanians and Native Austra- lians. Europeans. Chinese and Polynesians. 3. Nasal Leptorhine Mesorhine Platyrhine Orthognathous Mesognathous Prognathous Europeans. Japanese and Chinese. Negroes and Native Australians. 4. Gnathic Europeans. Chinese and Japanese. Native Australians. Applied Anatomy. — Occasionally a protrusion of the brain or its membranes may take place through one of the sutures, owing to non-closure. When the protrusion consists of membranes only, and is filled with cerebrospinal fluid, it is called a meningocele; when it consists of brain as well as membranes, it is termed an ence'phalocele. These malformations are usually found in the middle line, and most frequently at the back of the head, the protrusion taking place between the centres of ossification of the occipital squama (see p. 231). They generally occur through the upper part of the vertical fissure, which is the last to close, but not micommonly through the lower part, when the foramen magnum may be incomplete. More rarely these protrusions are met with in other situations, as in the sagittal, lambdoidal, and other sutures, or through abnormal gaps at the sides or base of the skull. The chief function of the skull is to protect the brain, and therefore those portions of the skull which are most exposed to external violence are thicker than those which are shielded from injury by overlying muscles. Thus, the skull-cap is thick and dense, whereas the temporal squamae, being protected by the temporales muscles, and the inferior occipital fossae, being shielded by the muscles at the back of the neck, are thin and fragile. Fracture of the skull is further prevented by its elasticity, its roimded shape, and its construction of a number of secondary elastic arches, each made up of a single bone. The manner in which vibrations are transmitted through the bones of the skull is also of importance as regards its protective mechanism, at all events as far as the base is concerned. In the vault, the bones being of a fairly equal thickness and density, vibrations are transmitted in a uniform manner in all directions, but in the base, owing to the varying thickness and density of the bones, this is not so; and therefore in this situation there are special buttresses which serve to carry the vibrations in certain definite directions. At the front of the skull, on either side, is the ridge which separates the anterior from the middle fossa of the base; and behind, the ridge or buttress which separates the middle from the posterior fossa; and if any violence is appUed to the vault, the vibrations would be carried along these buttresses to the sella turcica, where they meet. This part has been termed the "centre of resistance," and here there is a special protective mechanism to guard the brain. The subarachnoid cavity at the base of the brain is dilated, and the cerebrospinal fluid which fills it acts as a water cushion to shield the brain from injury. In like manner, when violence is applied to the base of the skull, as in falls upon the feet, the vibrations are carried backward through the occipital crest, and forward through the basilar part of the occipital and body of the sphenoid to the vault of the skull. Fractures of the skull are best considered as affecting either the vault or the base. Fractures of the vault generally involve the whole thickness of the bone; but sometimes the inner table alone is fractured, and portions of it driven inward. As a rule, in fractures of the skull, the inner table is more splintered and comminuted than the outer, and this is due to several causes. It is thinner and more brittle; the force of the violence as it passes inward becomes broken up, and is more diffused by the time it reaches the inner table; the bone being in the form of an arch bends as a whole and spreads out, and thus presses the particles together on the convex surface of the arch, i. e., the outer table, and forces them asunder on the concave surface or inner table; and, lastly, there is nothing firm under the inner table to support it and oppose the force. Fractures of the vault may be either simple, or starred and comminuted, and the fragments may be de- pressed or elevated. Cases of fracture with elevation of the fractured portion are uncommon, and can only be produced by direct wound. In comminuted fracture, a portion of the skuU is 1 Morphology and Anthropology, by W. L. H. Duckworth, M.A., Cambridge University Press. 298 OSTEOLOGY broken into several pieces, the lines of fracture radiating from a centre where the chief impact of the blow was felt; if the fracture is also depressed, a fissure circumscribes the radiating lines, enclosing a portion of the skull. If this area is circular it is termed a "pond" fracture, and has probably been caused by a round instrument, as a life preserver or hammer; if elliptical in shape it is termed a "gutter" fracture, and owes its shape to the instrument which has produced it, as a poker. Fracture of the outer table alone only occurs in the region of the frontal sinuses where the two tables are completely separated. Fractures of the base of the skull may be produced by indirect or direct violence. I. In cases of the former class the violence is applied to the vertex or some part of the cranial convexity, as when a person falls from a height on to his head and a fracture of the base results. The mechan- ism of this form of fracture was formerly explained by the doctrine of conlre-coup, i. e., that the force was transmitted from one side of the skull to the other; but this view is no longer held, and there are at the present day two theories as to the mode of causation of these fractures, (a) According to Aran's theory of irradiation all fractures of the base are produced by a fissure, which starts from the point of injury and radiates to the base. There can be little doubt that many cases of fracture of the base, especially of the middle fossae, are caused in this way, but it is insufficient to explain all, since instances have been met with of fracture of the base of the skull in which there has been no fracture of the vault. (6) To explain these cases, another theory, known as the coni'pression or bursting theory, has been suggested. If a hollow, elastic sphere is compressed from above downward, it will bulge laterally, and, if the compression is sufficient, it will eventually burst in the situation where it bulges. Now, the skull is an elastic sphere, and when compression is applied to it, its diameter will be reduced along the line of greatest pressure and will therefore be increased in other directions, and may increase to such an extent that burst- ing occurs. In a hollow elastic sphere of uniform thickness, the bulging and subsequent bursting take place at the equatorial line midway between the two points of compression; but the skull is not of uniform thickness, and therefore the bulging and subsequent bursting take place at the weakest part. II. Direct violence may be apphed to the base of the skull in several different ways: by the impact of the vertebral column against the condyles of the occipital bone, in falls on the buttocks or feet; by the condyle of the mandible being driven against the mandibular fossa, in blows or falls on the chin; by the thrusting of a pointed instrument through the orbit or nose; by gunshot wounds through the mouth; and by a fall or a stab on the back of the head. In the majority of cases the fracture is compound. The most common place for fracture of the base to occur is through the middle fossa, and here the fissure usually takes a fairly definite course. Starting from the point struck, which is generally somewhere in the neighborhood of the parietal eminence, it runs downward through the parietal and the temporal squama and across the petrous portion, frequently traversing and implicating the internal acoustic meatus, to the foramen lacerum. From this it may pass across the body of the sphenoid, through the sella turcica, to the foramen lacerum of the other side, and may indeed travel around the whole cranium, so as to completely separate the anterior from the posterior part. The course of the fracture explains the symptoms to which fracture in this region may give rise : thus, if the fissure pass across the internal acoustic meatus, injury to the facial and acoustic nerves may result, with consequent facial paralysis and deafness; or the tubular prolongation of the arachnoid around these nerves in the meatus may be torn and thus permit of the escape of the cerebro- spinal fluid should there be a communication between the internal ear and the tympanic cavity together with rupture of the tympanic membrane, as is frequently the case: again, if the fissure pass across the sella turcica and the mucoperiosteum covering the under surface of the body of the sphenoid is torn, blood will find its way into the pharynx and be swallowed, and after a time vomiting of blood will result. Fractures of the anterior fossa, involving the bones forming the roof of the orbit and nasal cavity, are generally the result of blows on the forehead; but fracture of the cribriform plate of the ethmoid may be a complication of fracture of the nasal bone. When the fracture imphcates the roof of the orbit, the blood finds its way into this cavity, and, travelhng forward, appears as a subconjunctival ecchymosis. If the roof of the nasal cavity be fractured, the blood escapes from the nose. In rare cases there may be also escape of cerebrospinal fluid from the nose, should the dura mater and arachnoid have been torn. In fractures of the posterior fossa, extravasation of blood may appear at the nape of the neck, beneath the muscles attached to the superior nuchal line of the occipital bone. Diseases of the Skull. — An inflammatory condition affecting the bones and the pericranium together is generally caused by septic infection either of a scalp wound exposing and bruising the bone, or of a compound fracture, and is termed septic osteomyelitis. Occasionally it may occur independently of injury, and then follows the same course, and is due to the same causes as acute infective osteomyehtis in the long bones. The most common chronic disease of the skull is due to syphilis. In acquired syphilis the disease usually occurs as nodes, which arise most commonly in the pericranium, but may also arise in the diploe, or more rarely on the inner surface of the skull. The formation of gummaia under the periosteum generally leads to caries, which may be either limited, if the gumma is CRANIOLOGY 299 localized, or widespread if the gumma is diffuse. The caries is often complicated by necrosis, for a condition of sclerosis is frequently set up in the surrounding bone, and the vessels in the Haversian canals become compressed and the vitality of the bone is interfered with; hence we often find a central necrosing area surrounded by a zone of caries. Large carious sequestra may be thrown off after prolonged suppuration, leaving considerable areas of the dura mater exposed. A common result of syi)hilitic disease of the skull is the production of large hard masses of bone on its surface, which give it a tuberculated appearance; in other cases, the skull presents a curious worm-eaten appearance; this is due to the fact that the osteogenctic powers of the pericranium are small and the formation of bone on the surface slight. In hereditary sypldlis, in addition to the formation of gummata, which are usually of the subperiosteal varietj^ atrophic or hyper- trophic changes may take place. In the atrojohic cases the bone becomes abnormally thin, or even perforated. In the hj'pertro})hic cases, a deposit of porous bone takes place around the anterior fontanelle; these deposits are separated by the coronal and sagittal sutures and are known as Parrot's nodes; such a skull has received the name of naiiform, from its fancied resem- blance to the buttocks. Hj^pertrophic changes also occur in the skull in ostitis deformans, acromegaly, leontiasis ossea, and in rickets. In rickety cases the skull becomes enlarged from the formation of periosteal outgrowths of soft tissue on the outer side of the skull. These deposits are very rich in blood- vessels, and occur between the ridges of the cranial bones and their centres of ossification, and are symmetrically arranged — often about the anterior fontanelle. The anterior fontanelle itself, instead of closing between the eighteenth and twenty-fourth months, as it normally does, remains patent in rickets until the third or even the sixth year. The general shape of the skull alters. The forehead is high and square, with prominent frontal eminences, and the head tends to be cubical or box-shaped; the enlargement of the head in rickets appears to be greater than it really is because the development of the facial bones is retarded. The base of the nose may appear sunken, from retarded development of the basis cranii. In marked cases of rickets these changes in the shape of the skull are permanent. In congenital hydrocephalus, or enlargement of the head due to the presence of excess of fluid in the ventricles of the brain, the cranium becomes globular, and its bones are thin and atrophic. They are often widely separated, the intervening fontaneUes being much enlarged and partially filled in by numerous sutural bones; the atrophy of the cranium and brain may be so extreme that the light of a candle may be plainly visible through the whole thickness of the enlarged head. The tympanic antrum, situated in the mastoid portion of the temporal bone, is often the seat of suppuration as a result of infection extending backward from the tympanic cavity. In such cases, the surgeon has to open the antrum in order to give exit to the pus; this he does by intro- ducing his gouge in the suprameatal triangle (see p. 238). A line is drawn horizontally through the upper border of the bony external acoustic meatus, and a second vertically through the posterior wall of the meatus, and the gouge is applied in the angle where these two hnes intersect; if the instriunent be introduced at a higher level it will open the middle fossa of the skull. It is to be carried in the direction of the external acoustic meatus — inward, forward, and a little upward — for the distance of from 1 to 1.5 cm., when the antrum will be reached. In some cases of middle-ear trouble, septic thrombosis of the transverse sinus takes place, and it becomes neces- sary to work backward and explore the sinus. In cormection with the bones of the face a common malformation is cleft palate. The cleft usually starts posteriorly, and its most elementary form is a bifid uvula; or the cleft may extend through the soft palate; or the posterior part of the whole of the hard palate may be involved, the cleft extending as , ih'nn far forward as the incisive foramen. In the severest forms, the cleft extends through the alveolus and passes between Mesognathion^ the incisive or premaxillary bone and the rest of the max- Exognathion^ ilia; that is to say, between the lateral incisor and canine teeth. In some instances, the cleft runs between the central and lateral incisor teeth; and this has induced some anatomists to believe that the premaxillary bone is devel- oped from two centres (Fig. 341) and not from one, as was stated on p. 262. The medial segment, bearing a central ^'''- ^""^iftP^^A^hf.?'^ '*''"*^^^^^ incisor, is called an endognathion; the lateral segment, bear- ing the lateral incisor, is called a mesognathion. The cleft may affect one or both sides; if the latter, the central part is frequently displaced forward and re- mains miited to the septum of the nose, the deficiency in the alveolus being complicated with a cleft in the lip (hare-hp). On examining a cleft palate in which the alveolus is not implicated, the cleft will generally appear to be in the median line, but occasionally is unilateral and in some cases bilat- eral. To understand this it must be borne in mind that three processes are concerned in the formation of the palate — the palatine processes of the two maxillae, w^hich grow in horizontally and unite in the middle line, and the ethmovomerine process, which grows dowTiward from the base of the skull and frontonasal process to unite with the palatine processes in the middle line." In 300 OSTEOLOGY those cases where the palatine processes fail to unite with each other and with the medial process, the cleft of the palate is median; where one palatine process unites with the medial septum, the other faUing to do so, the cleft in the palate is unilateral. In some cases where the palatine pro- cesses fail to meet in the middle, the ethmovomerine process grows downward between them and thus produces a bilateral cleft. Occasionally there may be a hole in the middle line of the hard palate, the anterior part of the hard and the soft palate being perfect; this is rare, because, as a rule, the union of the various processes progresses from before backward, and therefore the posterior part of the palate is more frequently defective than the anterior. The bones of the face are sometimes fractured as the result of direct violence. Those most commonly broken are the nasal bones and the mandible; the latter is by far the most frequently fractured of all the facial bones. Fracture of the nasal bone is for the most part transverse, and takes place about 1.25 cm. from the free margin. The broken portion may be displaced back- ward or more generallj^ to one side by the force which produced the lesion. The zygomatic bone is probably never broken alone — that is to say, without fracture of some of the other bones of the face. The zygomatic arch is occasionally fractm'ed, and when this occurs as a result of direct violence the fragments may be displaced inward. Fractures of the maxilla may vary much in degree, from the chipping off of a portion of the alveolar arch, to an extensive comminution of the whole bone from severe violence, as the kick of a horse. The most common situation for a fracture of the mandible is in the neighborhood of the canine tooth, as at this spot the bone is weakened bj" the deep socket for the root of this tooth; it is next most frequently fractured at the angle; then at the sj'mphysis; and finally the neck of the condjde or the coronoid process may be broken. Occasionally a double fractui-e may occur, one in either half of the bone. The fractures are usually compound, from laceration of the mucous membrane covering the gums. Displacement readily occm-s and is difficult to rectify; it results in inequahty in the line of the teeth and is commonly due to the muscles attached in the region of the symphysis dragging this portion doTVTiward. The maxilla and the mandible are frequently the seat of necrosis; but the disease more often affects the lower than the upper jaw. It may be the result of periostitis from tooth irritation, injury, or the action of some specific poison, as syphihs, or from sahvation by mercmy; it some- times occiirs in children after attacks of the exanthematous fevers, and a special form occurs from the action of the fumes of phosphorus in persons engaged in the manufacture of matches. In the vast majority of cases, however, it is of dental origin. Tumors originate in the jaw bones not infrequently, and may be either innocent or malignant. In the maxilla, cysts may occur in the antrum; or in either jaw in connection with the teeth; those connected with the roots of fuUy developed teeth are known as dental cysts; those con- nected with unerupted teeth, dentigerous cysts. MaUgnant tumors show a marked degree of mahgnancy when occurring in the maxilla. The results of distention of the walls of the maxillary antrum are given on page 260. The maxilla sometimes requires removal for tumors or other conditions. In order to remove it, the patient should be placed in the recumbent position, in a good fight, with the head and shoulders just raised. The central incisor tooth on the affected side is then extracted. One incision is begun just below the medial canthus of the eye and passes along the side of the nose, around the ala, and down the middle fine of the upper fip into the mouth. A second incision is made from the commencement of the first, along the lower border of the orbit as far as the promi- nence of the zygomatic bone. The flap thus formed is reflected, so as to expose the bone. The periosteum attached along the lower margin of the orbit is now to be incised, and -R-ith the handle of the scalpel the periostevun covering the floor of the orbit is raised from the bone; for in aU cases it is essential that this fibrous layer should not be removed. The mouth is now widely opened with a gag, and the mucous membrane covering the hard palate incised do-mi to the bone in the middle fine, and the soft palate separated from the hard. The surgeon having first separated tfie ala of tfie nose from its bony attachment, proceeds to divide the connections of the bone with the other bones of the face. They are (1) the jimction with the zygomatic bone, the line of section being carried into the inferior orbital fissure; (2) tfie frontal process of the maxilla; a smaU portion of its upper extremity, cormected with the nasal bone in front, the lacrimal bone behind, and the frontal bone above, being left; (3) the connection with the opposite maxilla and with the palatine bone in the roof of the mouth. The bone is now firmly grasped with fion- forceps; and by means of a rocking movement upward and do-miward, the remaining attach- ments of the orbital plate with the ethmoid, and of the back of the bone with the palatine, are broken through. OccasionaUy, in removing the maxiUa, it wiU be found that the orbital plate can be saved, and this should always be done if possible. A horizontal saw-cut should then be made just below the infraorbital foramen. THE EXTREMITIES. The extremities, or limbs, are long, jointed appendages, each of which is con- nected to the trunk bv one end, and is free in the rest of its extent. Thev are THE CLAVICLE 301 four in number: an upper pair, connected with the thorax and suhservient mainly to prehension; and a lower pair, connected with the vetrebral cohimn and intended for support and locomotion. Both pairs are constructed after one common type, but certain differences are observed between the upper and lower, dependent on the peculiar offices they have to perform. The bones by which the upper and lower limbs are attached to the trunk con- stitute respectively the shoulder and pelvic girdles. The shoulder girdle or girdle of the superior extremity is formed by the scapulae and clavicles, and is imperfect in front and behind. In front, however, it is completed by the upper end of the sternum, with which the medial ends of the clavicles articulate. Behind, it is widely imperfect, the scapulae being connected to the trunk by muscles only. The pelvic girdle or girdle of the inferior extremity is formed by the hip bones, which articulate with each other in front, at the symphysis pubis. It is imperfect behind, but the gap is filled in by the upper part of the sacrum. The pelvic girdle, with the sacrum, is a complete ring, massive and comparatively rigid, in marked contrast to the lightness and mobility of the shoulder girdle. THE BONES OF THE UPPER EXTREMITY (OSS A EXTREMITATIS SUPERIORIS). The Clavicle (Clavicula; Collar Bone). The clavicle (Figs. 342, 343) forms the anterior portion of the shoulder girdle. It is a long bone, curved somewhat like the italic letter/, and placed nearly horizon- tally at the upper and anterior part of the thorax, immediately above the first rib. It articulates medially wdth the manubrium sterni, and laterally with the acromion of the scapula.^ It presents a double curvature, the convexity being directed forward at the sternal end, and the concavity at the scapular end. Its lateral third is flattened from above downward, while its medial two-thirds is of a rounded or prismatic form. Sternal extremity Acromial extremity Fig. 342. — Left clavicle. Superior surface. Lateral Third. — The lateral third has two surfaces, an upper and a lower; and two borders, an anterior and a posterior. Surface. — The upper surface is flat, rough, and marked by impressions for the attachments of the Deltoideus in front, and the Trapezius behind; between these impressions a small portion of the bone is subcutaneous. The under surface is flat. At its posterior border, near the point where the prismatic joins with the flattened portion, is a rough eminence, the coracoid tuberosity {conoid tubercle); this, in the natural position of the bone, surmounts the coracoid process of the 1 The clavicle acts especially as a fulcrum to enable the muscles to give lateral motion to the arm. It is accordingly absent in those animals whose fore-hmbs are used only for progression, but is present for the m9st part in animals whose anterior extremities are clawed and used for prehension, though in some of them — as, for instance, in a large number of the carnivora — it is merely a rudimentary bone suspended among the muscles, and not articulating with either the scapula or sternum. 302 OSTEOLOGY scapula, and gives attachment to the conoid Hgament. From tiiis tuberosity an oblique ridge, the oblique or trapezoid ridge, runs forward and laterahvard, and afford attachment to the trapezoid ligament. Borders. — The anterior border is concave, thin, and rough, and gives attachment to the Deltoideus; at its medial part there is frequentl.y a tubercle, the deltoid tubercle. The posterior border is convex, rough, thicker than the anterior, and gives attachment to the Trapezius. Medial Two-thirds. — The medial two-thirds constitute the prismatic portion of the bone, which is curved so as to be convex in front, concave behind, and is marked by three borders, separating three surfaces. Borders. — The anterior border is continuous with the anterior margin of the flat portion. Its lateral part is smooth, and corresponds to the interval between the attachments of the Pectoralis major and Deltoideus; its medial part forms the lower boundary of an elliptical surface for the attachment of the clavicular portion of the Pectoralis major, and approaches the posterior border of the bone. The superior border is continuous with the posterior margin of the flat portion, and separates the anterior from the posterior surface. Smooth and rounded laterally, it becomes rough toward the medial third for the attachment of the Sternocleido- mastoideus, and ends at the upper angle of the sternal extremity. The posterior or subclavian border separates the posterior from the inferior surface, and extends from the coracoid tuberosity to the costal tuberosity; it forms the posterior boun- dary of the groove for the Subclavius, and gives attachment to a layer of cervical fascia w^hich envelops the Omohyoideus. Articv^lar capsule Articular caps7ile Fig. 343. — Left clavicle. Inferior surface. Surfaces. — The anterior surface is included between the superior and anterior borders. Its lateral part looks upward, and is continuous wdth the superior sur- face of the flattened portion; it is smooth, convex, and nearly subcutaneous, being covered only by the Platysma. Medially it is divided by a narrow^ subcutaneous area into two parts: a lower, elliptical in form, and directed forward, for the attachment of the Pectoralis major; and an upper for the attachment of the Sternocleidomastoideus. The posterior or cervical surface is smooth, and looks backw^ard toward the root of the neck. It is limited, above, by the superior border; below, by the subclavian border; medially, by the margin of the sternal extremity; and laterally, by the coracoid tuberosity. It is concave medio-laterally, and is in relation, by its lower part, wdth the transverse scapular vessels. This surface, at the junction of the curves of the bone, is also in relation with the brachial plexus of nerves and the subclavian vessels. It gives attachment, near the sternal extremity, to part of the Sternohyoideus ; and presents, near the middle, an oblique foramen directed lateralward, which transmits the chief nutrient artery of the bone. Sometimes there are two foramina on the posterior surface, or one on the posterior and another on the inferior surface. The inferior or subclavian surface is THE CLAVICLE 303 bounded, in front, by the anterior border; behind, l)y the subehivian border. It is narrowed medially, but gradually increases in width laterally, and is contin- uous with the under surface of the flat portion. On its medial part is a broad rough surface, tlie costal tuberosity {rhoinlnnd iiiipn'.s.sioii), ratlier more than 2 cm. in length, for the attachment of the costoclavicular ligament. The rest of this surface is occupied by a groove, which gives attachment to the Subclavius; the coracoclavicular fascia, which splits to enclose the muscle, is attached to the margins of the groove. Not infrequently this groove is subdivided longitudinally by a line whicli gi\-cs attachment to the intermuscular sei)tum of the Subclavius. The Sternal Extremity {c.iireinifa.s' sternal is; intenial extreinify). — The sternal extremity of the clavicle is triangular in form, directed medialward, and a little downward and forward; it presents an articular facet, concave from before back- ward, convex from abo\'e downward, which articulates with the manubrium sterni through the intervention of an articular disk. The lower part of the facet is con- tinued on to the inferior surface of the bone as a small semi-oval area for articula- tion with the cartilage of the first rib. The circumference of the articular surface is rough, for the attachment of numerous ligaments; the upper angle gives attach- ment to the articular disk. The Acromial Extremity {cxtreniifas acromialis; outer extrcniiti/). — The acromial extremity presents a small, flattened, oval surface directed obliquely downward, for articulation with the acromion of the scapula. The circumference of the articular facet is rough, especially above, for the attachment of the acromio- clavicular ligaments. In the female, the clavicle is generally shorter, thinner, less curved, and smoother than in the male. In those persons who perform considerable manual labor it becomes thicker and more curved, and its ridges for muscular attachment are prominently marked. Structure. — The clavicle consists of cancellous tissue, enveloped by a compact layer, which is much thicker in the intermediate part than at the extremities of the bone. Ossification. — The clavicle begins to ossify before any other bone in the body; it is ossified from three centres — viz., two primary centres, a medial and a lateral, for the body,^ which appear during the fifth or sixth week of fetal life; and a secondary centre for the sternal end, which appears about the eighteenth or twentieth year, and unites with the rest of the bone about the twenty-fifth year. Applied Anatomy. — The clavicle is very frequently fractured, since it is much exposed to vio- lence, and is the only bony connection between the upper hmb and the trunk, acting as a buttress to keep the point of the shoulder away from the thorax. It is, moreover, slender, and is very superficial. It may be broken by direct or indirect violence. The most common cause is, however, indirect violence, as the result of force apphed to the hand or shoulder, and the bone then gives way at the junction of its lateral with its intermediate third, that is to say, at the junction of the two curves, for tliis is its weakest part. The fracture is generally oblique, and the displace- ment of the lateral fragment is downward, forward, and medialward. The deformitj' is mainly due to the weight of the arm acting upon the fragment when the buttress-hke action of the bone is gone, assisted by the muscles which pass from the thorax to the upper extremity. The medial fragment, as a rule, is little displaced. Beneath the bone the main vessels of the upper Umb and the great nerve cords of the brachial plexus Ue on the first rib and are liable to be woimded, espe- cially in fracture from direct violence, when the force of the blow drives the broken ends inward. Fortimately the subclavius intervenes between these structm-es and the clavicle, and often protects them from injury. The clavicle is occasionally the seat of sarcomatous tumors, rendering the operation of excision of the entire bone necessary. This is an operation of considerable difficulty and danger. It is best performed by exposing the bone freely, disarticulating at the acromial end, and tm-ning it forward. The removal of the lateral part is comparatively easy, but resection of the medial part is fraught with difficulty, the main danger being the risk of wounding the great veins which are in relation with its deep sm-face. Great deformity of the clavicle maj^ be met with in rickets, the natural curvatures of the bone being exaggerated until it takes on an S-shape, and "green-stick" fracture is not uncommonly seen associated therewith. 1 Mall, American Journal of Anatomy, vol. v; Fawcett, Journal of Anatomy and Physiology, vol. xlvii. 304 OSTEOLOGY The Scapula (Shoulder Blade). The scapula forms the posterior part of the shoulder girdle. It is a flat, trian- gular bone, with two surfaces, three borders, and three angles. Surfaces. — The costal or ventral surface (Fig. 344) presents a broad concavity, the subscapular fossa. The medial two-thirds of the fossa are marked by several oblique ridges, which run lateralward and upward. The ridges give attachment Articular capsule Coracoacromial ligament (^^ Articular , "^^ capsule Fig. 344. — Left scapula. Costal surface. to the tendinous intersections, and the surfaces between them to the fleshy fibres, of the Subscapularis. The lateral third of the fossa is smooth and covered by the fibres of this muscle. The fossa is separated from the vertebral border by smooth triangular areas at the medial and inferior angles, and in the interval between these by a narrow^ ridge which is often deficient. These triangular areas and the THE SCAPULA 305 intervening ridge afford attachment to the Serratus anterior. At the upper part of the fossa is a transverse depression, where the bone appears to be bent on itself along a line at right angles to and passing through the centre of the glenoid cavity, fornnng a considerable angle, called the subscapular angle; this gives greater strengtli to the body of the bone by its arched form, while the summit of the arch serves to support the spine and acromion. Coracohunicnd liqametd Coraco-acrGinial ligament Trapezoid ligament Fig. 345. — Left scapula. Dorsal surface. The dorsal surface (Fig. 345) is arched from above downward, and is subdivided into two unequal parts by the spine; the portion above the spine is called the supraspinatous fossa, and that below it the infraspinatous fossa. 20 306 OSrEOLOGY . The supraspinatous fossa, tlu^ sinalltT of the two, is concavo, smooth, and broader at its vertebral than at its humeral end; its medial two-thirds f2;ive orig'in to the Supraspinatus. The infraspinatous fossa is much larger than the preceding; toward its \'ertebral margin a shallow conca^'ity is seen at its upper j^art; its centre presents a promi- nent con^^exity, while near the axillary l)order is a dee]) groove which runs from the upper toward the lower part. The medial two-thirds of the fossa give origin to the Infraspinatus; the lateral third is covered by this muscle. The dorsal surface is marked near the axillary l)order by an elevated ridge, which runs from the lower part of the glenoid cavity, downward and backward to the vertebral border, about 2.5 cm. above the inferior angle. The ridge serves for the attachment of a fibrous septum, which separates the Infraspinatus from the Teres major and Teres minor. The surface between the ridge and the axillary border is narrow in the upper two-thirds of its extent, and is crossed near its centre by a groove for the passage of the scapular circumflex vessels; it affords attachment to the Teres minor. Its lower third presents a broader, somewhat triangular surface, which gives origin to the Teres major, and over which the Latis- simus dorsi glides; frequently the latter muscle takes origin bj'' a few fibres from this part. The broad and narrow portions above alluded to are separated by an oblique line, which runs from the axillary border, downward and backward, to meet the elevated ridge: to it is attached a fibrous septum which separates the Teres muscles from each other. The Spine {syina scapulae). — The spine is a prominent plate of bone, which crosses obliquely the medial four-fifths of the dorsal surface of the scapula at its upper part, and separates the supra- from the infraspinatous fossa. It begins at the vertical border by a smooth, triangular area over which the tendon of inser- tion of the lower part of the Trapezius glides, and, gradually becoming more ele- vated, ends in the acromion, which overhangs the shoulder-joint. The spine is triangular, and flattened from above downward, its apex being directed toward the vertebral border. It presents two surfaces and three borders. Its superior surface is concave; it assists in forming the supraspinatous fossa, and gives origin to part of the Supraspinatus. Its inferior surface forms part of the infraspinatous fossa, gives origin to a portion of the Infraspinatus, and presents near its centre the orifice of a nutrient canal. Of the three borders, the anterior is attached to the dorsal surface of the bone; the posterior, or crest of the spine, is broad, and presents two lips and an intervening rough interval. The Trapezius is attached to the supe- rior lip, and a rough tubercle is generally seen on that portion of the spine which receives the tendon of insertion of the lower part of this muscle. The Deltoideus is attached to the w^hole length of the inferior lip. The interval between the lips is subcutaneous and partly covered by the tendinous fibres of these muscles. The lateral border, or base, the shortest of the three, is slightly concave; its edge, thick and round, is continuous above with the under surface of the acromion, below with the neck of the scapula. It forms the medial boundary of the great scapular notch, which serves to connect the supra- and infraspinatous fossae. The Acromion. — The acromion forms the summit of the shoulder, and is a large, somewhat triangular or oblong process, flattened from behind forward, projecting at first lateralward, and then curving forward and upward, so as to overhang the glenoid cavity. Its superior surface, directed upward, backward, and lateralward, is convex, rough, and gives attachment to some fibres of the Deltoideus, and in the rest of its extent is subcutaneous. Its inferior surface is smooth and concaA^e. Its lateral border is thick and irregular, and presents three or four tubercles for the tendinous origins of the Deltoideus. Its medial border, shorter than the lateral, is concave, gives attachment to a portion of the Trapezius, and presents about its centre a small, oval surface for articulation with the acromial end of the clavicle. THE SCAPTLA 307 Its apex, which c'()rrosi)()iuls to tlie point oi meeting of these two borders in front, is thin, and has attached to it the coracoacromial ligament. Borders. — Of the three borders of the scapuhi, the superior is the shortest and thinnest; it is concave, and extends from the mecHtd angle to the l)ase of the cora- coid process. At its lateral part is a deej), semicircnlar notch, the scapular notch, formed partly by the base of the coracoid process. This notch is converted into a foramen by the superior transverse ligament, and serves for the passage of the suprascapular nerve; sometimes the ligament is ossified. The adjacent part of the superior border affords attachment to the Omohyoideus. The axillary border is the thickest of the three. It begins above at the lower margin of the glenoid cavity, and inclines obliquely downward and backward to the inferior angle. Immediately below the glenoid cavity is a rough impression, the infraglenoid tuberosity, about 2.5 cm. in length, which gives origin to the long head of the Tri- ceps brachii; in front of this is a longitudinal groove, which extends as far as the lower third of this border, and affords origin to part of the Subscapularis. The inferior third is thin and sharp, and serves for the attachment of a few fibres of the Teres major behind, and of the Subscapularis in front. The vertebral border is the longest of the three, and extends from the medial to the inferior angle. It is arched, intermediate in thickness between the superior and the axillary borders, and the portion of it above the spine forms an obtuse angle with the part below. This border presents an anterior and a posterior lip, and an intermediate narrow area. The anterior lip affords attachment to the Serratus anterior; the posterior lip, to the Supraspinatus above the spine, the Infraspinatus below; the area between the two lips, to the Levator scapulae above the triangular surface at the commencement of the spine, to the Rhomboideus minor on the edge of that surface, and to the Rhomboideus major below it; this last is attached by means of a fibrous arch, connected above to the lower part of the triangular surface at the base of the spine, and below to the lower part of the border. Angles. — Of the three angles, the medial, formed by the junction of the superior and vertebral borders, is thin, smooth, rounded, inclined somewhat laterahvard, and gives attachment to a few^ fibres of the Levator scapulae. The inferior angle, thick and rough, is formed by the union of the vertebral and axillary borders; its dorsal surface aft'ords attachment to the Teres major and frequently to a few fibres of the Latissimus dorsi. The lateral angle is the thickest part of the bone, and is sometimes called the head of the scapula. On it is a shallow pyriform, articular surface, the glenoid cavity, which is directed laterahvard and forward and articulates with the head of the humerus; it is broader below than above and its vertical diameter is the longest. The surface is covered with cartilage in the recent state; and its margins, slightly raised, give attachment to a fibro- cartilaginous structure, the glenoidal labrum, which deepens the cavity. x4t its apex is a slight elevation, the supraglenoid tuberosity, to which the long head of the Biceps brachii is attached. The neck of the scapula is the slightly constricted por- tion which surrounds the head; it is more distinct below and behind than above and in front. The Coracoid Process (processus coracoideus) . — The coracoid process is a thick curved process attached by a broad base to the upper part of the neck of the scapula ; it runs at first upward and medialward; then, becoming smaller, it changes its direction, and projects forward and lateralward. The ascending portion, flattened from before backward, presents in front a smooth concave surface, across which the Subscapularis passes. The horizontal portion is flattened from above down- ward; its upper surface is convex and irregular, and gives attachment to the Pec- toralis minor; its under surface is smooth; its medial and lateral borders are rough; the former gives attachment to the Pectoralis minor and the latter to the coraco- acromial ligament; the apex is embraced by the conjoined tendon of origin of the 308 OSTEOLOGY Coracobrachialis and short head of the Biceps brachii and gives attachment to the coracoclavicular fascia. On the medial part of the root of the coracoid process is a rough impression for the attachment of the conoid Hgament; and running from it obhquely forward and laterahvard, on to the upper surface of the horizontal portion, is an elevated ridge for the attachment of the trapezoid ligament. Structure. — -The head, processes, and the thickened parts of the bone, contain cancellous tissue; the rest consists of a thin layer of compact tissue. The central part of the supraspinatous fossa and the upper part of the infraspinatous fossa, but especially the former, are usually so thin as to be semitransparent ; occasionally the bone is found wanting in this situation, and the adjacent muscles are separated only by fibrous tissue. Ossification (Fig. 346). — ^The scapula is ossified from seven or more centres: one for the body, two for the coracoid process, two for the acromion, one for the vertebral border, and one for the inferior angle. .<^e^. Fig. .346. — Plan of ossification of the scapula. From seven centres. Ossification of the body begins about the second month of fetal life, by the formation of an irregular quadrilateral plate of bone, immediately behind the glenoid cavity. This plate extends so as to form the chief part of the bone, the spine growing up from its dorsal surface about the third month. At birth, a large part of the scapula is osseous, but the glenoid cavity, the coracoid process, the acromion, the vertebral border, and the inferior angle are cartilaginous. From the fifteenth to the eighteenth month after birth, ossification takes place in the middle of the coracoid process, which as a rule becomes joined with the rest of the bone about the fifteenth year. Between the fourteenth and twentieth years, ossification of the remaining parts takes place in quick succes- sion, and usually in the following order ; first, in the root of the coracoid process, in the form of a broad scale; secondly, near the base of the acromion; thirdly, in the inferior angle and contiguous part of the vertebral border; foiuthly, near the extremity of the acromion; fifthly, in the vertebral border. The base of the acromion is formed by an extension from the spine; the two separate nuclei of the acromion unite, and then join with the extension from the spine. The upper third of the glenoid cavity is ossified from a separate centre (subcoracoid), which makes its appear- ance between the tenth and eleventh years and joins between the sixteenth and the eighteenth. Further, an epiphysial plate appears for the lower part of the glenoid cavity, while the tip of the THE HUMERUS 309 coracoid process frequently presents a separate nucleus. These various epiphyses are joined to the bone by the twentj^-fifth year. Failure of bony union between the acromion and spine sometimes occui-s, the junction being effected by fibrous tissue, or by an imperfect articulation; in some cases of supposed fracture of the acromion with ligamentous union, it is probable that the detached segment was never united to the rest of the bone. Articulations. — The scapula articulates with the humerus and clavicle. Applied Anatomy. — Fractm-es of the body of the scapula are rare, owing to the mobility of the bone, the thick layers of muscles by wliich it is encased, and the elasticity of the ribs on which it rests. Fractm-e of the neck is also uncommon. The most frequent course of a fracture is from the scapular notch to the infraglenoid tuberosity, and it derives its principal interest from its simulation of a subglenoid dislocation of the humerus. The diagnosis can be made by noting the alteration in the position of the coracoid process. The acromion is more frequently broken than any other part of the bone, and fibrous union is very Uable to follow. The presence of "winged scapulae" {scapulae alatae) described in thin persons of feeble muscular development in whom the lower angles of the blade bones project unduly, is due partly to abnormal roundness of the thoracic wall ("barrel-shaped chest," p. 226), and partly to weakness and flaccidity of the Latissimus dorsi and Serratus anterior. The shoulders are held low in these subjects, and the clavicles slope downward and forward, carrying with them the scapula), which fit iU to the posterior wall of the chest and so tend to project from it. TuTQors of various kinds grow from the scapula. Of the innocent form probably the osteomata are the most common. When an osteoma grows from the venter of the scapula, as it sometimes does, it is of the compact variety, such as usually grows from membrane-formed bones, as the bones of the skull. Sarcomatous tumors sometimes grow from the scapula, and may necessitate removal of the bone, with or without amputation of the upper Umb. The bone may be excised by a T-shaped incision, and the flaps being reflected, the removal is commenced from the vertebral border, so that the subscapular vessels which he along the axillary border are among the last structures divided, and can be readily secured. The Humerus (Arm Bone). The humerus (Figs. 347, 348) is the longest and largest bone of the upper extremity; it is divisible into a body and two extremities. Upper Extremity. — The upper extremity consists of a large rounded head joined to the body by a constricted portion called the neck, and two eminences, the greater and lesser tubercles. The Head {caput humeri).- — The head, nearly hemispherical in form,^ is directed upward, medialward, and a little backward, and articulates with the glenoid cavity of the scapula. The circumference of its articular surface is slightly constricted, and. is termed the anatomical neck, in contradistinction to a constriction below the tubercles called the surgical neck which is frequently the seat of fracture. Fracture of the anatomical neck rarely occurs. The Anatomical Neck {collum anatomicum) is obliquely directed, forming an obtuse angle with the body. It is best marked in the lower half of its circum- ference ; in the upper half it is represented by a narrow groove separating the head from the tubercles. It affords attachment to the articular capsule of the shoulder- joint, and is perforated by numerous vascular foramina. The Greater Tubercle {tuberculum ma jus; greater tuberosity). — The greater tubercle is situated lateral to the head and lesser tubercle. Its upper surface is rounded and marked by three flat impressions : the highest of these gives insertion to the Supraspinatus ; the middle to the Infraspinatus; the lowest one, and the body of the bone for about 2.5 cm. below it, to the Teres minor. The lateral surface of the greater tubercle is convex, rough, and continuous with the lateral surface of the body. The Lesser Tubercle {tuberculum minus; lesser tuberosity). — The lesser tubercle, although smaller, is more prominent than the greater: it is situated in front, and 1 Though the head is nearly hemispherical in form, its margin, as Humphrj- has shown, is by no means a true circle. Its greatest diameter is, from the top of the intertubercular groove in a direction downward, medialward, and back- ward. Hence it follows that the greatest elevation of the arm can be obtained by rolling the articular surface in this direction — that is to say, obliquely upward, lateralward, and forward. 310 OSTEOLOGY Articular capsule Common origin oj Flexor carpi radialis Palmaris longus "^ Flexor digitorum suhlimis Flexor carpi ulnaris Brachioradialis Extensor carpi radicdis longus \] ^ Articular capsule Common origin of Extensor carpi rad. hrev. ,, digitorum, communis ,, digiti quinti prop. ,, carpi ulnaris Supinator Fig. 347. — Left humerus. Anterior view. THE HUMERUS 311 is directed mediahvard and forward. Above and in front it presents an im])ression for the insertion of the tendon of the Subscaijuhiris. The tubercles are separated from each other by a deep groove, the intertubercular groove (bicipital groove), which lodges the long tendon of the Biceps brachii and transmits a branch of the anterior humeral circumflex arter>' to the shoulder-joint. It runs obliquely down- ward, and ends near the junction of the upper with the middle third of the bone. In the recent state its upper part is covered with a thin layer of cartilage, lined by a prolongation of the synovial membrane of the shoulder- joint; its lower portion gives insertion to the tendon of the Latissimus dorsi. It is deep and narrow above, and becomes shallow and a little broader as it descends. Its lips are called, respectively, the crests of the greater and lesser tubercles (bicipital ridges), and form the upper parts of the anterior and medial borders of the body of the bone. The Body or Shaft (corpus humeri). — The body is almost cylindrical in the upper half of its extent, prismatic and flattened below, and has three borders and three surfaces. Borders. — The anterior border runs from the front of the greater tubercle above to the coro- noid fossa below, separating the antero-medial from the antero-lateral surface. Its upper part is a prominent ridge, the crest of the greater tubercle ; it serves for the insertion of the tendon of the Pectoralis major. About its centre it forms the anterior boundary of the deltoid tuberosity; below, it is smooth and rounded, affording attachment to the Brachialis. The lateral border runs from the back part of the greater tubercle to the lateral epicondyle, and separates the antero-lateral from the pos- terior surface. Its upper half is rounded and indistinctly marked, serving for the attachment of the low^er part of the insertion of the Teres minor, and below this giving origin to the lateral head of the Triceps brachii; its centre is tra- versed by a broad but shallow oblique depres- sion, the radial sulcus (musculospiral groove). Its lower part forms a prominent, rough margin, a little curved from behind forward, the lateral supracondylar ridge, which presents an anterior lip for the origin of the Brachioradialis above, and Extensor carpi radialis longus below% a posterior lip for the Triceps brachii, and an intermediate ridge for the attachment of the lateral intermuscular septum. Articular caysuLe Articular capsule Fig. 348. — Left humerus. Posterior view. 312 OSTEOLOGY The medial border extends from the lesser tii})erck> to the medial epicondyle. Its upper third consists of a prominent ridge, the crest of the lesser tubercle, which gives insertion to the tendon of the Teres major. About its centre is a slight impression for the insertion of the Coracobrachialis, and just below this is the entrance of the nutrient canal, directed downward; sometimes there is a second nutrient canal at the commencement of the radial sulcus. The inferior third of this border is raised into a slight ridge, the medial supracondylar ridge, which becomes very prominent below; it presents an anterior lip for the origins of the Brachialis and Pronator teres, a posterior lip for the medial head of the Triceps brachii, and an intermediate ridge for the attachment of the medial intermuscular septum. Surfaces. — The antero-lateral surface is directed lateralward above, where it is smooth, rounded, and covered by the Deltoideus; forward and lateralward below, where it is slightly concave from above downward, and gives origin to part of the Brachialis. About the middle of this surface is a rough, triangular elevation, the deltoid tuberosity for the insertion of the Deltoideus; below this is the radial sulcus, directed obliquely from behind, forward, and downward, and transmitting the radial nerve and profunda artery. The antero-medial surface, less extensive than the antero-lateral, is directed medialward above, forward and medialward below; its upper part is narrow, and forms the floor of the intertubercular groove which gives insertion to the tendon of the Latissimus dorsi ; its middle part is slightly rough for the attacliment of some of the fibres of the tendon of insertion of the Coracobrachialis; its lower part is smooth, concave from above downward, and gives origin to the Brachialis.^ The posterior surface appears somewhat twisted, so that its upper part is directed a little medialward, its lower part backward and a little lateralward. Nearly the whole of this surface is covered by the lateral and medial heads of the Triceps brachii, the former arising above, the latter below the radial sulcus. The Lower Extremity. — The lower extremity is flattened from before backward, and curved slightly forward; it ends below in a broad, articular surface, which is divided into two parts by a slight ridge. Projecting on either side are the lateral and medial epicondyles. The articular surface extends a little lower than the epicondyles, and is curved slightly forward; its medial extremity occupies a lower level than the lateral. The lateral portion of this surface consists of a smooth, rounded eminence, named the capitulum of the humerus; it articulates with the cup- shaped depression on the head of the radius, and is limited to the front and lower part of the bone. On the medial side of this eminence is a shallow groove, in which is received the medial margin of the head of the radius. Above the front part of the capitulum is a slight depression, the radial fossa, which receives the anterior border of the head of the radius, when the forearm is flexed. The medial portion of the articular surface is named the trochlea, and presents a deep depression be- tween two well-marked borders; it is convex from before backward, concave from side to side, and occupies the anterior, lower, and posterior parts of the extremity. The lateral border separates it from the groove which articulates with the margin of the head of the radius. The medial border is thicker, of greater length, and consequently more prominent, than the lateral. The grooved portion of the artic- ular surface fits accurately within the semilunar notch of the ulna ; it is broader and deeper on the posterior than on the anterior aspect of the bone, and is inclined 1 A small, hook-shaped process of bone, the supracondylar process, varying from 2 to 20 mm. in length, is not infre- quently found projecting from the antero-medial surface of the body of the humerus 5 cm. above the medial epicondyle. It is curved downward and forward, and its pointed end is connected to the medial border, just above the medial epicondyle, by a fibrous band, which gives origin to a portion of the Pronator teres; through the arch completed by this fibrous band the median nerve and brachial artery pass, when these structures de\'iate from their \isual_ course. Sometimes the ner\'e alone is transmitted through it, or the nerv-e may be accompanied by the ulnar artery, in cases of high division of the brachial. A weU-marked groove is usually found behind the process, in which the nerve and artery are lodged. This arch is the homologue of the supracondyloid foramen found in many animals, and probably serves in them to protect the nerve and artery from compression during the contraction of the muscles in this region. THE HUMERUS 313 obliquely dowmvartl and forwartl toward the medial side. Above the front part of the trochlea is a small depression, the coronoid fossa, which receives the coronoid process of the ulna during flexion of the forearm. Above the back part of the troch- lea is a deep triangular depression, the olecranon fossa, in which the summit of the olecranon is received in extension of the forearm. These fossse are separated from one another by a thin, transparent lamina of bone, which is sometimes perforated by a supratrochlear foramen; they are lined in the recent state by the synovial membrane of the elbow-joint, and their margins afford attachment to the anterior and posterior ligaments of this articulation. The lateral epicondyle is a small, tuberculated eminence, curved a little forward, and giving attachment to the radial collateral ligament of the elbow-joint, and to a tendon common to the origin of the Supinator and some of the Extensor muscles. The medial epicondyle, larger and more prominent than the lateral, is directed a little backward; it gives attach- ment to the ulnar collateral ligament of the elbow-joint, to the Pronator teres, and to a common tendon of origin of some of the Flexor muscles of the forearm; the ulnar nerve runs in a groove on the back of this epicondyle. The epicondjdes are continuous above with the supracondylar ridges. Structure. ^The extremities consist of cancellous tissue, covered with a thin, compact layer (Fig. 349) ; the body is composed of a cyUnder of compact tissue, thicker at the centre than toward the extremities,, and contains a large medullary canal which extends along its whole length. Ossification (Figs. 350, 351). — The humerus is ossi- fied from eight centres, one for each of the following Epiphysial liiie parts: the body, the head, the greater tubercle, the lesser tubercle, the capitulum, the trochlea, and one for each epicondyle. The centre for the body appears near the middle of the bone in the eighth week of fetal hfe, and soon extends toward the extremities. At birth the humerus is ossified in nearly its whole length, only the extremities remaining cartilaginous. Dm'ing the first year, sometimes before birth, ossification commences in the head of the bone, and dui-ing the thu'd year the centre for the greater tubercle, and during the fifth that for the lesser tubercle, make theii' appearance. By the sixth year the centres for the head and tubercles have joined, so as to foi-m a single large epiphysis, which fuses with the body about the twentieth year. The lower end of the humerus is ossified as foUows. At the end of the second year ossification begins in the capitulum, and extends medialward, to form the chief part of the articular end of the bone; the centre for the medial part of the trochlea appears about the age of twelve. Ossifi- cation begins in the medial epicondjde about the fifth year, and in the lateral about the thirteenth or four- teenth year. About the sixteenth or seventeenth year, the lateral epicondyle and both portions of the articu- lating sm-face, having aheady joined, unite with the Fig. 349. body, and at the eighteenth year the medial epicon- dyle becomes joined to it. Articulations. — The hmnerus articulates with the scapula, ulna, and radius. Applied Anatomy. — There are several points of surgical interest connected with the ossification of the humerus. The upper end, though the first to ossify, is the last to join the bodj', and the length of the bone is mainly due to growth from the upper epiphysial plate. Hence, in cases of amputation of the arm in j'oung subjects, the humerus continues to grow considerably, and the end of the bone which immediately after the operation was covered with a thick cushion of soft tissue begins to project, thinning the soft parts and rendering the stump conical. This may necessitate the removal of about 5 cm. of the bone, and even after this operation a recurrence of the conical stump may take place. The region of the upper epiphysis, moreover, is the common site for the growth of tumors, both innocent and mahgnant Fractures of the hmnerus present several points of surgical interest . The bone maj' be broken by direct or indirect violence, like the other long bones, but, in addition to this, it is probably more frequently fractured b}' muscular action than anj^ other bone of this class. It is usually -Longitudinal section of head of left humerus. 314 OSTEOLOGY the body, just below the insertion of the Deltoideus, which is tlius broken, and the accident has been known to happen from throwing a stone. Fractures of the upp(;r end may take place eitlier through the anatomical or surgical neck, or a separation of the greater tubercle may occur. Frac- ture of the anatomical neck is a very rare accident; in fact, it is doubted by some whether it ever occurs. Fracture of the surgical neck of the bone is not uncommon, and impaction may occur; on the other hand, the upper end of the lower fragment may be displaced into the axilla and may damage the vessels or nerves. The fracture somewhat closely simulates dislocation of the shoulder- joint, but can be distinguished by the fact that the head of the bone remains in its normal jiosi- tion and the great tubercle still forms the most prominent point of the shoulder. Separation of the upper epiphysis sometimes occurs in the young subject, and is marked by a characteristic deformity, consisting in the presence of an abrupt projection at the front of the joint some short distance below the coracoid process, caused by the upper end of the diaphy.sis. In fractures of Epiphyses of head a)id'\ j^^t tuberclesblendatfifthl j /\ year, and unite tvith body at twentieth year Unites with body\ at eighteenth year J t§* Blend ^f,,^'' Body Fig. 350. — Plan of ossification of the humerus. Fig. 351. — Epiphysial lines of humerus in a young adult. Anterior aspect. The lines of attachment of the articular capsules are in blue. the body of the humerus the lesion may take place at any point, but appears to be more common in the lower than the upper part of the bone. The points of interest in connection with these fractures are: (1) that the radial nerve may be injured as it lies in the groove on the bone, or may become involved in the callus which is subsequently thrown out; and (2) the frequency of non-union, which is believed to be more common in the humerus than in any other bone. An important distinction to make in fractures of the lower end is between those that involve the elbow-joint and those which do not; the former are always serious, as they may lead to impair- ment of the utility of the limb; they include the T-shaped fracture and oblique fractures which involve the articular surface. Those which do not involve the joint are the transverse fracture above the epicondyles, and the so-called epitrochlear fracture, where the tip of the medial epi- condyle is broken off, generally from direct violence. The Ulna (Elbow Bone), The ulna (Figs. 353, 354) is a long bone, prismatic in form, placed at the medial side of the forearm, parallel with the radius. It is divisible into a body and two extremities. Its upper extremity, of great thickness and strength, forms THE ULNA 315 Olecranon a laruv part of the clhow-joint; tlie hone (liininishcs in size from above downward, its lower extremity beinjj; very small, and excluded from the wrist-joint hy the inter})osition of an articular disk. The Upper Extremity [proxhiml r.rfrcinifi/) (Fig. 352). — The upper extremity presents two cur\ed j)r()cesses, the olecranon and the coronoid process; and two concave, articular cavities, the semilunar and radial notches. The Olecranon {oJccranon process). — The olecranon is a large, thick, curved eminence, situated at the upper and back part of the ulna. It is bent forward at the summit so as to present a prominent lip which is received into the olecranon fossa of the humerus in extension of the forearm. Its base is contracted where it joins the bod>' and the narrowest part of the upper end of the ulna. Its posterior surface, directed backward, is triangular, smooth, subcutaneous, and covered by a bursa. Its superior surface is of quadrilateral form, marked behind by a rough impression for the insertion of the Triceps brachii; and in front, near the margin, by a slight trans- verse groove for the attachment of part of the posterior ligament of the elbow-joint. Its anterior surface is smooth, concave, and forms the upper part of the semilunar notch. Its borders present continuations of the groove on the margin of the superior surface; they serve for the attachment of ligaments, viz., the back part of the ulnar collateral liga- ment medially, and the posterior ligament laterally. From the medial border a part of the Flexor carpi ulnaris arises; while to the lateral border the Anconaeus is attached. The Coronoid Process (processus coronoideus) . — The coronoid process is a triangular emi- nence projecting forward from the upper and front part of the ulna. Its base is continuous with the body of the bone, and of consider- able strength. Its apex is pointed, slightly curved upward, and inflexion of the forearm is received into the coronoid fossa of the humerus. Its upper surface is smooth, con- cave, and forms the lower part of the semi- lunar notch. Its antero-inferior surface is concave, and marked by a rough impression for the insertion of the Brachialis. At the junction of this surface w4th the front of the body is a rough eminence, the tuberosity of the ulna, which gives insertion to a part of the Brachialis; to the lateral border of this tuberosity the oblique cord is attached. Its lateral surface presents a narrow, oblong, articular depression, the radial notch. Its medial surface, by its prominent, free margin, serves for the attachment of part of the ulnar collateral ligament. At the front part of this surface is a small rounded eminence for the origin of one head of the Flexor digitorum sublimis; behind the eminence is a depression for part of the origin of the Flexor digitorum profundus; descending from the eminence is a ridge which gives origin to one head of the Pronator teres. Frequently, the Flexor pollicis longus arises from the lower part of the coronoid process by a rounded bundle of muscular fibres. The Semilunar Notch (incisura semilunaris; greater sigmoid cavity). — The semi- lunar notch is a large depression, formed by the olecranon and the coronoid process, and serving for articulation with the trochlea of the humerus. About the middle of either side of this notch is an indentation, which contracts it somewhat, and Coronoid process Fig. 352. — Upper extremity' of left ulna. Lateral aspect. 316 OSTEOLOGY Articular capsule Flexor digitorum suhlimis Occasional origin of Flexor poinds longus Articular capsule Styloid process Radial origin of Flexor digitorwrn sitblimis Brachioradialis Groove for Abductor poinds longus and Extensor pollicis brevis Styloid process Fig. 3.53. — Bones of left forearm. Anterior aspect. THE ULNA 3i: Arlicidar cwpsule '^ I' if' < '^lV\ Flexor difjiloruiii suldhnis r Abductor pollicis I Extensor pollicis [^ brevis For Ext. carpi radialis longus For Extensor carpi radialis brevis For Extensor pollicis longus Articular capsule For Extensor carpi ulnaris For Extensor digiti quinti proprius XI (Extensor indicis proprius \Extensor digitorum comm communis Fig. 354. — Bones of left forearm. Posterior aspect. 318 OSTEOLOGY indicates the junction of the olecranon and the coronoid process. The notcli is concave from above downward, and diA-ided into a me(Hal and a lateral portion by a smooth ridge running from the summit of the olecranon to the tip of the coronoid process. The medial portion is the larger, and is slightly concave transA'crsely; the lateral is convex above, slightly concave below. The Radial Notch (iiicisura radialis; lesser sigmoid cavity). — The radial notch is a narrow, oblong, articular depression on the lateral side of the coronoid process; it receives the circumferential articular surface of the head of the radius. It is concave from before backward, and its prominent extremities serve for the attach- ment of the annular ligament. The Body or Shaft {corpus ulnae). — The body at its upper part is prismatic in form, and curved so as to be convex behind and lateralward; its central part is straight; its lower part is rounded, smooth, and bent a little lateralward. It tapers gradually from above downward, and has three borders and three surfaces. Borders. — The volar border {niargo volaris; anterior border) begins above at the prominent medial angle of the coronoid process, and ends below in front of the styloid process. Its upper part, well-defined, and its middle portion, smooth and rounded, give origin to the Flexor digitorum profundus; its lower fourth serves for the origin of the Pronator quadratus. This border separates the volar from the medial surface. The dorsal border {margo dorsalis; posterior border) begins above at the apex of the triangular subcutaneous surface at the back part of the olecranon, and ends below at the back of the styloid process; it is well-marked in the upper three- fourths, and gives attachment to an aponeurosis which affords a common origin to the Flexor carpi ulnaris, the Extensor carpi ulnaris, and the Flexor digitorum pro- fundus; its lower fourth is smooth and rounded. This border separates the medial from the dorsal surface. The interosseous crest {crista inter ossea; exteri\al or interosseous border) begins above by the union of two lines, which converge from the extremities of the radial notch and enclose between them a triangular space for the origin of part of the Supinator; it ends below at the head of the ulna. Its upper part is sharp, its lower fourth smooth and rounded. This crest gives attachment to the interosseous mem- brane, and separates the volar from the dorsal surface. Surfaces.^ — The volar surface {fades volaris; anterior surface), much broader above than below, is concave in its upper three-fourths, and gives origin to the Flexor digitorum profundus; its lower fourth, also concave, is covered by the Pronator quadratus. The lower fourth is separated from the remaining portion by a ridge, directed obliquely downward and medialward, which marks the extent of origin of the Pronator quadratus. At the junction of the upper with the middle third of the bone is the nutrient canal, directed obliquely upward. The dorsal surface {fades dorsalis; posterior surface) directed backward and lateralward, is broad and concave above; convex and somewhat narrower in the middle; narrow, smooth, and rounded below. On its upper part is an oblique ridge, which runs from the dorsal end of the radial notch, downward to the dorsal border; the triangular surface above this ridge receives the insertion of the Anconaeus, while the upper part of the ridge affords attachment to the Supinator. Below this the surface is subdivided by a longitudinal ridge, sometimes called the perpendicular line, into two parts: the medial part is smooth, and covered by the Extensor carpi ulnaris; the lateral portion, wider and rougher, gives origin from above downward to the Supinator, the Abductor pollicis longus, the Extensor pollicis longus, and the Extensor indicis proprius. The medial surface {fades medialis; internal surface) is broad and concave above, narrow and convex below. Its upper three-fourths give origin to the Flexor digitorum profundus; its lower fourth is subcutaneous. THE RADIUS 319 The Lower Extremity ((ILsfcil extremity). — The lower extremity of the uhia is small, and presents two eminences; the lateral and larger is a rounded, articular eminence, termed the head of the ulna; the medial, narrower and more projecting, is a non-articular eminence, the styloid process. The head i)resents an articular surface, part of which, of an oval or semilunar form, is directed downward, and articulates with the upper surface of the triangular articular disk which separates it from the Avrist-joint; the remaining portion, directed lateralward, is narrow, convex, and received into the ulnar notch of the radius. The styloid process projects from the medial and back part of the bone; it descends a little lower than the head, and its rounded end affords attachment to the ulnar collateral ligament of the wrist-joint. The head is separated from the styloid process by a depression for the attachment of the apex of the triangular articular disk, and behind, by a shallow groove for the tendon of the Extensor carpi ulnaris. Olecranon Appears at — £^^\— '^°"''*' ^"'^^^ "^ tenth year p»;™™«| sixteenth year Is'i 4 Appears at fourth year Joins body at twentieth year Inferior extremity Fig. 355. — Plan of ossification of the ulna. From three centres. Fig. 356. — Epiphysial hnes of ulna in a young adult. Lateral aspect. The lines of attachment of the articular capsules are in blue. Structure. — The structure of the ulna is similar to that of the other long bones. Ossification (Figs. 355, 356) . — The ulna is ossified from three centres : one each for the body, the inferior extremity, and the top of the olecranon. Ossification begins near the middle of the body, about the eighth week of fetal life, and soon extends through the greater part of the bone. At bii'th the ends are cartilaginous. About the fourth year, a centre appears in the middle of the head, and soon extends into the styloid process. About the tenth year, a centre appears in the olecranon near its extremity, the chief part of this process being formed by an upward extension of the body. The upper epiphysis joins the body about the sixteenth, the lower about the twentieth year. Articulations. — The ulna articulates with the humerus and radius. The Radius. The radius (Figs. 353, 354) is situated on the lateral side of the ulna, which exceeds it in length and size. Its upper end is small, and forms only a small part of the elbow-joint; but its lower end is large, and forms the chief part of the wrist- 320 - OSTEOLOGY joint. It is a long bone, prismatic in form and slightly curved longitudinally. It -has a body and two extremities. The Upper Extremity (pn).vinial extremity). — The upper extremity presents a head, neck, and tuberosity. The head is of a cylindrical form, and on its upper surface is a shallow cup or fovea for articulation Avith the capitulum of the humerus. The circumference of the head is smooth; it is broad medially where it articulates with the radial notch of the ulna, narrow in the rest of its extent, which is embraced by the annular ligament. The head is supported on a round, smooth, and con- stricted portion called the neck, on the back of which is a slight ridge for the inser- tion of part of the Supinator. Beneath the neck, on the medial side, is an eminence, the radial tuberosity; its surface is divided into a posterior, rough portion, for the insertion of the tendon of the Biceps brachii, and an anterior, smooth portion, on which a bursa is interposed between the tendon and the bone. The Body or Shaft (corpus radii). — The body is prismoid in form, narrower above than below, and slightly curved, so as to be convex lateral ward. It presents three borders and three surfaces. Borders.^ — The volar border (margo wlaris; anterior border) extends from the lower part of the tuberosity above to the anterior part of the base of the styloid process below, and separates the volar from the lateral surface. Its upper third is promi- nent, and from its oblique direction has received the name of the oblique line of the radius ; it gives origin to the Flexor digitorum sublimis and Flexor pollicis longus ; the surface above the line gives insertion to part of the Supinator. The middle third of the volar border is indistinct and rounded. The lower fourth is prominent, and gives insertion to the Pronator quadratus, and attachment to the dorsal carpal ligament; it ends in a small tubercle, into which the tendon of the Brachioradialis is inserted. The dorsal border (margo dorsalis; posterior border) begins above at the back of the neck, and ends below at the posterior part of the base of the styloid process; it separates the posterior from the lateral surface. It is indistinct above and below, but well-marked in the middle third of the bone. The interosseous crest {crista interossea; internal or interosseous border) begins above, at the back part of the tuberosity, and its upper part is rounded and indis- tinct; it becomes sharp and prominent as it descends, and at its lower part divides into two ridges which are continued to the anterior and posterior margins of the ulnar notch. To the posterior of the two ridges the lower part of the interosseous membrane is attached, while the triangular surface between the ridges gives inser- tion to part of the Pronator quadratus. This crest separates the volar from the dorsal surface, and gives attachment to the interosseous membrane. Surface.- — The volar surface {fades volaris; anterior surface) is concave in its upper three-fourths, and gives origin to the Flexor pollicis longus; it is broad and flat in its lower fourth, and affords insertion to the Pronator quadratus. A prominent ridge limits the insertion of the Pronator quadratus below, and between this and the inferior border is a triangular rough surface for the attachment of the volar radiocarpal ligament. At the junction of the upper and middle thirds of the volar surface is the nutrient foramen, which is directed obliquely upward. The dorsal surface {fades dorsalis; posterior surface) is convex, and smooth in the upper third of its extent, and covered by the Supinator. Its middle third is broad, slightly concave, and gives origin to the Abductor pollicis longus above, and the Extensor pollicis brevis below. Its lower third is broad, convex, and covered by the tendons of the muscles which subsequently run in the grooves on the lower end of the bone. The lateral surface {fades lateralis; external surface) is convex throughout its entire extent. Its upper third gives insertion to the Supinator. About its centre is a rough ridge, for the insertion of the Pronator teres. Its lower part is narrow^ and covered by the tendons of the Abductor pollicis longus and Extensor pollicis brevis. THE RADIUS 321 The Lower Extremity.— ^The lower extremity is large, of quadrilateral form, and provided with two articular surfaces — one below, for the carpus, and another at the medial side, for the ulna. The carpal articular surface is triangular, concave, smooth, and divided by a slight antero-posterior ridge into two parts. Of these, the lateral, triangular, articulates with the navicular bone; the medial, quadri- lateral, with the lunate bone. The articular surface for the ulna is called the ulnar notch (sigmoid cariti/) of the radius; it is narrow, concave, smooth, and articulates with the head of the ulna. These two articular surfaces are separated by a promi- nent ridge, to which the base of the triangular articular disk is attached; this disk separates the wrist-joint from the distal radioulnar articulation. This end of the bone has three non-articular surfaces — volar, dorsal, and lateral. The volar surface, rough and irregular, affords attachment to the volar radiocarpal ligament. The dorsal surface is convex, affords attachment to the dorsal radiocarpal ligament, and is marked by three grooves. Enumerated from the lateral side, the first groove is broad, but shallow, and subdivided into two by a slight ridge; the lateral of these two transmits the tendon of the Extensor carpi radialis longus, the medial the tendon of the Extensor carpi radialis brevis. The second is deep but narrow, and bounded laterally by a sharply defined ridge; it is directed obliquely from above downward and lateralward, and transmits the tendon of the Extensor pollicis longus. The third is broad, for the passage of the tendons of the Extensor indicis proprius and Extensor digitorum communis. The lateral surface is prolonged obliquely downward into a strong, conical projection, the styloid process, which gives attachment by its base to the tendon of the Brachioradialis, and by its apex to the radial collateral ligament of the wrist-joint. The lateral surface of this process is marked by a flat groove, for the tendons of the Abductor pollicis longus and Extensor pollicis brevis. Structure. — The structure of the radius is Uke that of the other long bones. Ossification (Figs. 357, 358). — The radius is ossified from three centres: one for the body, and one for either extremity. That for the body malies its appearance near the centre of the bone, during the eighth week of fetal fife. About the end of the second year, ossification commences in the lower end; and at the fifth year, in the upper end. The upper epiphysis fuses with the body at the age of seventeen or eighteen years, the lower about the age of twenty. An additional centre sometimes found in the radial tuberosity, appears about the fourteenth or fifteenth year. Articulations. — The radius articulates with four bones: the humerus, ulna, navicular, and lunate. Applied Anatomy of the Ulna and Radius. — The two bones of the forearm are more often broken together, than is either the radius or ulna separately. It is therefore convenient to con- sider in the first instance the fractm-es of both bones and subsequently the principal fractures which take place in either bone. Fractures of both bones may be produced by either direct or indirect violence, though more commonly by direct violence. When indirect force is apphed to the forearm the radius as a rule gives way, though both bones may suffer. Fracture from indirect force generally takes place somewhere about the middle of the bones, while that from direct violence may occur at any part, but is most frequent in the lower half of the bones. The fracture is usually transverse, but may be more or less obhque. A point of interest in connection with these fractures is the tendency for the two bones to unite across the interosseous membrane; the limb should therefore be put up in a position midway between supination and pronation, which is not only the most comfortable position, but also separates the bones most widely from each other. Anterior and posterior splints are apphed in these cases, and should be rather wider than the limb, so as to prevent any side pressure on the bones. The special fractures of the ulna are: (1) Fractiire of the olecranon, which is usually caused by direct violence, by falls on the elbow with the forearm flexed, but occasionally by muscular action in sudden contraction of the Triceps brachii; the most common site of this fracture is at the constricted portion where the olecranon joins the body of the bone, and the fracture is usually transverse; but any part may be broken, and even a thin shell may be torn off. Fractures from direct violence are occasionally comminuted. If the fibrous structures around the process are not torn the displacement is slight, otherwise the olecranon may be drawn up for a very consider- able distance. (2) Fracture of the coronoid process may occur as a complication of dislocation backward of the bones of the forearm, but it is doubtful if it ever takes place as an uncomplicated injury. (3) Fractm-es of the body of the ulna may occur at any part, but usuallv take place at 21 322 OSTEOLOGY or a little below the middle of the bone. They are generally the result of direct violence, but may occur as a complication of dislocation of the radius. (4) The styloid process may be knocked ofT by direct violence. Fractm'es of the radius may consist of: (1) Fracture of the head of the bone; this for the most part takes place in conjunction with some other lesion, but may occur as an uncomplicated injury. (2) Fracture of the neck also may occur, but is usually complicated with other injury. (3) Frac- tures of the body of the radius are very common, and may take place at any part of the bone. They may be caused by direct or indirect violence. In fracture of the upper third of the body — that is to say, above the insertion of the Pronator teres — the displacement is very great. The upper fragment is strongly supinated by the biceps and supinator and flexed by the biceps; while the lower fragment is pronated and drawn toward the ulna by the two pronators. If such a fracture be put up in the ordinary position, midway between supination and pronation, the bone will unite with the upper fragment in a position of supination, and the lower one in the mid- position, and thus considerable impairment of the movement of supination will result; the Umb should therefore be put up with the forearm supinated. (4) The most important fracture of the Head Appears af_ fifth year Unites with body about pitberiy Appears at secotuL year Unites with body about twentieth Lower extremity year Fig. 357 -Plan of ossification of the radius. From three centres. Fig. 358. — Epiphysial lines of radius in a young adult. Anterior aspect. The line of attachment of the articular capsule of the wrist-joint is in blue. radius is that of the lower end (Colles' fracture). The fracture is transverse, and generally takes place about 2.5 cm. from the lower extremity. It is caused by falls on the palm of the hand, and is an injury of advanced life, occurring more frequently in the female than in the male. In conse- quence of the manner in which the fracture is caused, the upper fragment is driven into the lower, and impaction commonly is the result; excess of violence may, however, disimpact, the lower fi-agment being split into two or more pieces, so that no fixation occurs. Separation of the lower epiphysis of the radius may take place in the young. This injury and Colles' fracture may be distinguished from other injuries in this neighborhood — especially dislocation of the wrist, with which they are liable to be confounded — by observing the relative positions of the styloid processes of the ulna and radius. In the natural conditions of parts, with the arm hanging by the side, the styloid process of the radius is on a lower level than that of the ulna. After fracture or separa- tion of the epiphysis the styloid process of the radius is on the same level as, or on a higher level than, that of the ulna, whereas it would be imaltered in position in dislocation. Reduction in the case of Colles' fracture is usually easily effected by traction on the hand, the limb being subse- quently splinted with the hand deflected toward the ulnar side. THE CARPUS 323 THE HAND. The skeleton of the hand ( Fii^'s. iJoO, .')()()) is suhdh'ided into three semtacarpal Fig. 368.— The left hamate bone. The Hamate Bone (os liamatum; unciform hone) (Fig. 36S). — The hamate bone may be readily distinguished by its wedge-shaped form, and the hook-like process w^hich projects from its volar surface. It is situated at the medial and lower angle of the carpus, with its base downward, resting on the fourth and fifth metacarpal bones, and its apex directed upward and lateralward. The superior surface, the apex of the wedge, is narrow, convex, smooth, and articulates with the lunate. The inferior surface articulates with the fourth and fifth metacarpal bones, by concave facets which are separated by a ridge. The dorsal surface is triangular and rough for ligamentous attachment. The volar surface presents, at its lower and ulnar side, a curved, hook-like process, the hamulus, directed forward and lateralward. This process gives attachment, by its apex, to the transverse carpal ligament and the Flexor carpi ulnaris; by its medial surface to the Flexor brevis and Opponens digiti quinti; its lateral side is grooved for the passage of the Flexor tendons into the palm of the hand. It is one of the four eminences on the front of the carpus to which the transverse carpal ligament of the wrist is attached; the others being the pisiform medially, the oblique ridge of the greater multangular, and the tubercle of the navicular laterally. The medial surface articulates wdth the triangular bone by an oblong facet, cut obliquely from above, downward and medialward. The lateral surface articulates with the capitate by its upper and posterior part, the remaining portion being rough, for the attachment of ligaments. Articulations.— The hamate articulates with five bones: the lunate proximally, the fourth and fifth metacarpals distally, the triangular medially, the capitate laterally. THE METACARPUS 329 The Metacarpus. The metacarpus consists of five cylindrical bones which are numbered from the lateral side (ossct iitctacarpalia I-V); each consists of a body and two extremities. Common Characteristics of the Metacarpal Bones. — The Body {corpus; shaft). — The body is prismoid in form, and curved, so as to be convex in the longitudinal direction behind, concave in front. It presents three surfaces: medial, lateral, and dorsal. The medial and lateral surfaces are concave, for the attachment of the Interossei, and separated from one another by a prominent anterior ridge. The dorsal surface presents in its distal two-thirds a smooth, triangular, flattened area which is covered in the recent state, by the tendons of the Extensor muscles. This surface is bounded by two lines, which commence in small tubercles situated on either side of the digital extremity, and, passing upward, converge and meet some distance above the centre of the bone and form a ridge which runs along the rest of the dorsal surface to the carpal extremity. This ridge separates two sloping surfaces for the attachment of the Interossei dorsales. To the tubercles on the digital extremities are attached the collateral ligaments of the metacarpo- phalangeal joints. The Base or Carpal Extremity {basis) is of a cuboidal form, and broader behind than in front: it articulates with the carpus, and with the adjoining metacarpal bones; its dorsal and volar surfaces are rough, for the attachment of ligaments. The Head or Digital Extremity {capitulum) presents an oblong surface markedly convex from before backw^ard, less so transversely, and flattened from side to side; it articulates with the proximal phalanx. It is broader, and extends farther up- ward, on the volar than on the dorsal aspect, and is longer in the antero-posterior than in the transverse diameter. On either side of the head is a tubercle for the attachment of the collateral ligament of the metacarpophalangeal joint. The dorsal surface, broad and flat, supports the Extensor tendons; the volar surface is grooved in the middle line for the passage of the Flexor tendons, and marked on either side by an articular eminence continuous with the terminal articular surface. Characteristics of the Individual Metacarpal Bones. — The First Metacarpal Bone {os metacarpale I; metacarpal hone of the thiimh) (Fig. 369) is shorter and stouter than the others, diverges to a greater degree from the carpus, and its volar surface is directed toward the palm. The body is flattened and broad on its dorsal surface, and does not present the ridge which is found on the other metacarpal bones; its volar surface is concave from above downward. On its radial border is inserted the Opponens poUicis; its ulnar border gives origin to the lateral head of the first Interosseus dorsalis. The base presents a concavo-convex surface, for articulation with the greater multangular; it has no facets on its sides, but on its radial side is a tubercle for the insertion of the Abductor pollicis longus. The head is less convex than those of the other metacarpal bones, and is broader from side to side than from before backward. On its volar surface are two articular eminences, of which the lateral is the larger, for the two sesamoid bones in the tendons of the Flexor pollicis brevis. The Second Metacarpal Bone {os metacarpale II; metacarpal hone of the index finger) (Fig. 370) is the longest, and its base the largest, of the four remaining bones. Its base is prolonged upward and medialward, forming a prominent ridge. For greater multangular For greater multangular Fig. 369. — -The first metacarpal. (Left.) 330 OSTEOLOGY It presents four articular facets: three on the upper surface and one on the uhiar side. Of the facets on the upper surface the intermediate is the largest and is concave from side to side, convex from before backward for articulation with the lesser multangular; the lateral is small, flat and oval for articulation with the greater multangular; the medial, on the summit of the ridge, is long and narrow for articu- lation with the capitate. The facet on the ulnar side articulates with the third metacarpal. The Extensor carpi radialis longus is inserted on the dorsal surface and the Flexor carpi radialis on the volar surface of the base. For (jreatei- For lesaer multangular multangular For 3/ metacarpal For For lesser ca2ntate mult- angular Styloid For 2nd process meta- carpal For capitate For 4Ah metacarfal Fig. 370. — The second metacarpal. (Left.) Fig. 371. — The third metacarpal. (Left.) The Third Metacarpal Bone {os metacarijale III; metacarjjal bone of the middle finger) (Fig. 371) is a little smaller than the second. The dorsal aspect of its base presents on its radial side a pyramidal eminence, the styloid process, which extends upward behind the capitate; immediately distal to this is a rough surface for the attachment of the Extensor carpi radialis brevis. The carpal articular facet is concave behind, flat in front, and articulates with the capitate. On the radial side is a smooth, concave facet for articulation with the second metacarpal, and on the ulnar side two small oval facets for the fourth metacarpal. The Fourth Metacarpal Bone {os inetacarjxile IV; metacarixd hone of the ring finger) (Fig. 372) is shorter and smaller than the third. The base is small and quadrilateral; its superior surface presents two facets, a large one medially for articulation with the hamate, and a small one laterally for the capitate. On the radial side are two oval facets, for articulation with the third metacarpal ; and on the ulnar side a single concave facet, for the fifth metacarpal. The Fifth Metacarpal Bone {os metacariKile V; metacarpal bone of the little finger) (Fig. 373) presents on its base one facet on its superior surface, which is concavo- convex and articulates with the hamate, and one on its radial side, which articulates with the fourth metacarpal. On its ulnar side is a prominent tubercle for the inser- tion of the tendon of the Extensor carpi ulnaris. The dorsal surface of the body is divided by an oblique ridge, which extends from near the ulnar side of the base to the radial side of the head. The lateral part of this surface serves for the attach- THE PHALANGES OF THE HAXD 331 ment of the fourth Iiiterosseus I i ive secondary C >■ ( s ^ Fig. 37/ -Plan of ossification of the hip bone. The three primary centres unite through a Y-shaped piece about puberty. Epiphyses appear about puberty, and unite about twenty-fifth year. The Obturator Foramen {joramen obturatum; thyroid foramen). — The obturator foramen is a large aperture, situated between the ischium and pubis. In the male it is large and of an oval form, its longest diameter slanting obliquely from before backward; in the female it is smaller, and more triangular. It is bounded by a thin, uneven margin, to which a strong membrane is attached, and presents, superiorly, a deep groove, the obturator groove, which runs from the pelvis obliquely medial ward and downward. This groove is converted into a canal by a ligamentous band, a specialized part of the obturator membrane, attached to tw^o tubercles: one, the posterior obturator tubercle, on the medial border of the ischium, just in front of the acetabular notch; the other, the anterior obturator tubercle, on the 340 OSTEOLOGY obturator crest of the superior ramus of the pubis. Through the canal the obturator vessels and nerve pass out of the pelvis. Structure. — The thicker parts of the bone consist of cancellous tissue, enclosed between two layers of compact tissue; the thinner parts, as at the bottom of the acetabulum and centre of the iliac fossa, are usually semitransparent, and composed entirely of compact tissue. Ossification (Fig. 377). — The Mp bone is ossified from eight centres: three primaiy — one each for the ilium, ischimn, and pubis; and five secondary — one each for the crest of the ilium, the anterior inferior spine (said to occur more frequently in the male than in the female), the tuberosity of the ischium, the pubic symphysis (more frequent in the female than in the male), and one or more for the Y-shaped piece at the bottom of the acetabulum. The centres appear in the follow- ing order: in the lower part of the iUum, immediately above the greater sciatic notch, about the eighth or ninth week of fetal life; in the superior ramus of the ischium, about the third month; in the superior ramus of the pubis, between the fom'th and fifth months. At birth, the three primary centres are quite separate, the crest, the bottom of the acetabulum, the ischial tuberosity, and the inferior rami of the ischium and pubis being still cartilaginous. By the seventh or eighth year, the inferior rami of the pubis and ischium are almost completely united by bone. About the thirteenth or fourteenth year, the three primary centres have extended their growth into the bottom of the acetabulum, and are there separated from each other by a Y-shaped portion of cartilage, which now presents traces of ossification, often by two or more centres. One of these, the OS acetahuU, appears about the age of twelve, between the ihum and pubis, and fuses with them about the age of eighteen; it forms the pubic part of the acetabulum. The ilium and ischium then become joined, and lastly the pubis and ischium, through the intervention of this Y-shaped portion. At about the age of puberty, ossification takes place in each of the remaining portions, and they join with the rest of the bone between the twentieth and twenty-fifth years. Separate centres are frequently found for the pubic tubercle and the ischial spine, and for the crest and angle of the pubis. Articulations. — The hip bone articulates with its fellow of the opposite side, and with the sacrum and femur. The Pelvis. The pelvis, so called from its resemblance to a basin, is a bony ring, interposed between the movable vertebrse of the vertebral column which it supports, and the lower limbs upon which it rests; it is stronger and more massively constructed than the wall of the cranial or thoracic cavities, and is composed of four bones: the two hip bones laterally and in front and the sacrum and coccyx behind. The pelvis is divided by an oblique plane passing through the prominence of the sacrum, the arcuate and pectineal lines, and the upper margin of the symphysis pubis, into the greater and the lesser pelvis. The circumference of this plane is termed the linea terminalis or pelvic brim. The Greater or False Pelvis {pelvis major) . — The greater pelvis is the expanded portion of the cavity situated above and in front of the pelvic brim. It is bounded on either side by the ilium; in front it is incomplete, presenting a wide interval between the anterior borders of the ilia, which is filled up in the recent state by the parietes of the abdomen ; behind is a deep notch on either side between the ilium and the base of the sacrum. It supports the intestines, and transmits part of their weight to the anterior wall of the abdomen. The Lesser or True Pelvis (-pelvis minor). — The lesser pelvis is that part of the pelvic cavity which is situated below and behind the pelvic brim. Its bony walls are more complete than those of the greater pelvis. For convenience of descrip- tion, it is divided into an inlet bounded by the superior circumference, and outlet bounded by the inferior circumference, and a cavity. The Superior Circumference. — The superior circumference forms the brim of the pelvis, the included space being called the superior aperture or inlet (apertura pelvis [minoris] superior) (Fig. 378). It is formed laterally by the pectineal and arcuate lines, in front by the crests of the pubes, and behind by the anterior margin of the base of the sacrum and sacrovertebral angle. The superior aperture is somewhat heart-shaped, obtusely pointed in front, diverging on either side, and encroached upon behind by the projection forward of the promontory of the sacrum. It has THE PELVIC 341 three principal diameters: antero-])osteric)r, trans\erse, and oblique. The antero- posterior or conjugate diameter extends from the sacrovertebral angle to the sym- physis pubis; its average measurement is about 110 mm. in the female. The transverse diameter extends across the greatest width of the superior aperture, from the middle of the brim on one side to the same point on the opposite; its aver- age measurement is about 135 mm. in the female. The oblique diameter extends from the iliopectineal eminence of one side to the sacroiliac articulation of the opposite side; its average measurement is about 125 mm. in the female Fig. 378. — Diameters of superior aperture of lesser pelvis (female). The cavity of the lesser pelvis is bounded in front and below by the pubic sym- physis and the superior rami of the pubes; above and behind, by the pelvic surfaces of the sacrum and coccjrx, which, curving forward above and below, contract the superior and inferior apertures of the ca^•ity; laterally, by a broad, smooth, quadrangular area of bone, corresponding to the inner surfaces of the body and superior ramus of the ischium and that part of the ilium which is below the arcuate line. From this description it will be seen that the cavity of the lesser pelvis is a short, curved canal, considerably deeper on its posterior than on its anterior wall. It contains, in the recent subject, the pelvic colon, rectum, bladder, and some of the organs of generation. The rectum is placed at the back of the pelvis, in the curve of the sacrum and coccyx; the bladder is in front, behind the pubic sym- physis. In the female, the uterus and vagina occupy the interval between these viscera. The Lower Circumference. — The lower circumference of the pelvis is very irregular; the space enclosed by it is named the inferior aperture or outlet {apertura pelns [minoris] inferior) (Fig. 379), and is bounded behind by the point of the coccj'x, and laterally by the ischial tuberosities. These eminences are separated by three notches: one in front, the pubic arch, formed by the convergence of the inferior rami of the ischium and pubis on either side. The other notches, one on either side, are formed by the sacrum and coccyx behind, the iscliium in front, and the ilium above; they are called the sciatic notches; in the natural state they are converted into foramina by the sacrotuberous and sacrospinous ligaments. ^Mien the ligaments are in situ, the inferior aperture of the pelvis is lozenge-shaped, bounded, in front, by the pubic arcuate ligament and the inferior rami of the pubes and ischia; laterally, by the ischial tuberosities; and behind, by the sacro- tuberous ligaments and the tip of the coccjtj. 342 OSTEOLOGY The diameters of tlie outlet of the pel\-is are two, autero-posterior and trans- verse. The antero-posterior diameter extends from the tip of the coecyx to the lower part of the pubic symphysis; its measurement is from 90 to 115 mm. in the female. It varies with the length of the coccyx, and is capable of increase or diminution, on account of the mobility of that bone. The transverse diameter, measured between the posterior parts of the ischial tuberosities, is about 115 mm. in the female.^ Fig. 379. — Diameters of inferior aperture of lesser pelvis (female). Axes (Fig. .380). — A line at right angles to the plane of the superior aperture at its centre would, if prolonged, pass through the umbilicus above and the middle of the coccyx below; the axis of the superior aperture is therefore directed downward and backward. The axis of the inferior aperture, produced upward, would touch the base of the sacrum, and is also directed downward, and slightly backward. The axis of the cavity — i. e., an axis at right angles to a series of planes betweeii those of the superior and inferior apertures — is curved like the cavity itself: this curve corresponds to the concavity of the sacrum and coccyx, the extremities being indicated by the central points of the superior and inferior apertures. A knowledge of the direction of these axes serves to explain the course of the fetus in its passage through the pelvis during parturition. Position of the Pelvis (Fig. 380). — In the erect posture, the pelvis is placed obliquely with regard to the trunk: the plane of the superior aperture forms an angle of from 50° to 60°, and that of the inferior aperture one of about 15° with the horizontal plane. The pelvic surface of the symphysis pubis looks upward and backward, the concavity of the sacrum and coccyx downward and forward. The position of the pelvis in the erect posture may be indicated by holding it so that the anterior superior iliac spines and the front of the top of the symphysis pubis are in the same vertical plane. Fig. 380. -Median sagittal section of pelvis. ' The measurements of the pelvis given above are fairly accurate, but different figures are given by various authors no doubt due mainly to differences in the physique and stature of the population from whom the measurements have been taken. THE r/'JLV/S 343 Differences between the Male and Female Pelves. -Flie feiualc pelvis (Fig. 382) is distinguished from that of the male (Fig. 'ASl) l)y its bones being more delicate and its % i, 426. THE FEMUR 345 the entrance into the pelvis becoming reniform. lu other cases all the pelvic bones give way, so that a general diminution in all the diameters of the pelvis results, the pelvic entrance becom- ing triangular or asj^mmetrical. If the i)ubic symphysis be forced forward, the rickety pelvis maj' even come to resemble closely the deformed j:)clvis of osteomalacia; in this disease the weight of the trunk causes an increase in the sacrovertebral angle, and a lessening of the antero-posterior diameter of the superior aperture, and at the same time the pressure of the heads of the femora on the acetabula causes these cavities, with the adjacent bone, to be pushed upward and back- ward, so that the oblique diameters of the pelvis are also diminished, and the cavity of the pelvis assumes a triradiate shape, with the symphysis pubis pushed forward. The Femur (Thigh Bone). The femur (Figs. 384, 3S5), the longest and strongest bone in the skeleton, is almost perfectly cylindrical in the greater part of its extent. In the erect posture it is not vertical, being separated above from its fellow by a considerable interval, which corresponds to the breadth of the pelvis, but inclining gradualli' downward and medialward, so as to approach its fellow toward its lower part, for the purpose of bringing the knee-joint near the line of gravity of the body. The degree of this inclination varies in different persons, and is greater in the female than in the male, on account of the greater breadth of the pelvis. The femur, like other long bones, is divisible into a body and two extremities. Obturator internus cuid Gemelli y J Pnifoimis X^'lj j Insertion of Obturator '~~ exiernus Fovea capitis. ^ for lig, teres ■ Oixater trochanter Lesser trochanter . Fig. 383. — Upper extremity of right femur viewed from behind and above. The Upper Extremity {proximal extremity, Fig. 383). — The upper extremity presents for examination a head, a neck, a greater and a lesser trochanter. The Head (caput femoris) . — The head which is globular and forms rather more than a hemisphere, is directed upward, medialward, and a little forward, the greater part of its convexity being above and in front. Its surface is smooth, coated with cartilage in the recent state, except over an ovoid depression, the fovea capitis femoris, which is situated a little below and behind the centre of the head, and gives attachment to the ligamentum teres. The Neck {collum femoris). — The neck is a flattened pyramidal process of bone, connecting the head with the body, and forming with the latter a wide angle open- ing medialward. The angle is widest in infancy, and becomes lessened during growth, so that at puberty it forms a gentle curve from the axis of the body of the bone. In the adult, the neck forms an angle of about 125° with the body, but this varies in inverse proportion to the development of the pelvis and the stature. In- 346 OSTEOLOGY Ohluralor internus and Geiiielli Piriformis Tubercle Articular capsule Medial ^ ,1] epicondyle Fig. 384. — Right femur. Anterior surface. ^^'^fe' the female, in consequence of the increased width of the pelvis, the neck of the femur forms more nearly a right angle with the body than it does in the male. The angle decreases during the period of growth, but after full growth has been attained it does not usually undergo any change, even in old age; it varies considerably in differ- ent persons of the same age. It is smaller in short than in long bones, and when the pelvis is wide. In addition to projecting upward and medialward from the body of the femur, the neck also projects some- what forward; the amount of this forward projection is extremely variable, but on an average is from 12° to 14°. The neck is flattened from before backward, contracted in the middle, and broader laterally than medially. The vertical diameter of the lateral Ijalf is increased by the obliquity of the lower edge, which slopes down- ward to join the body at the level of the lesser trochanter, so that it measures one-third more than the antero-posterior diameter. The medial half is smaller and of a more circular shape. The anterior surface of the neck is perforated by numerous vascular foramina. Along the upper part of the line of junc- tion of the anterior surface with the head is a shallow groove, best marked in elderly subjects; this groove lodges the orbicular fibres of the capsule of the hip-joint. The posterior surface is smooth, and is broader and more concave than the anterior: the posterior part of the capsule of the hip-joint is attached to it about 1 cm. above the intertrochanteric crest. The superior border is short and thick, and ends laterally at the greater trochanter; its surface is perforated by large foramina. The inferior border, long and narrow, curves a little backward, to end at the lesser trochanter. The Trochanters. — The trochan- ters are prominent processes which THE FEMUR 347 att'ord leverage to the muscles that rotate the thiuh on its axis. They are two in number, the greater and the lesser. The Greater Trochanter {tro- chanter DKtjor: (jrcat trnvhtutcr) is a large, irregular, (juadrilateral eminence, situated at the junc- tion of the neck with the upper part of the body. It is directed a little laterahvard and backward, and, in the adult, is about 1 cm. lower than the head. It has two surfaces and four borders. The lateral surface, quadrilateral in form, is broad, rough, convex, and marked by a diagonal im- pression, which extends from the postero-superior to the antero-inferior angle, and serves for the insertion of the tendon of the Glutaeus mediiis. Above the impression is a triangular surface, sometimes rough for part of the tendon of the same muscle, sometimes smooth for the interposition of a bursa be- tween the tendon and the bone. Below and behind the diagonal impression is a smooth, trian- gular surface, over which the tendon of the Glutaeus maxi- mus plays, a bursa being inter- posed. The medial surface, of much less extent than the lateral, presents at its base a deep depression, the trochanteric fossa {digital fossa), for the in- sertion of the tendon of the Ob- turator externus, and above and in front of this an impression for the insertion of the Obtura- tor internus and Gemelli. The superior border is free ; it is thick and irregular, and marked near the centre by an impression for the insertion of the Piriformis. The inferior border corresponds to the line of junction of the base of the trochanter with the lateral surface of the body; it is marked by a rough, prominent, slightly curved ridge, which gives origin to the upper part of the Vastus lateralis. The anterior border is prominent and some- FiG. 385 Articular capsule Right femur. Posterior surface. 348 OSTEOLOGY what irregular; it affords insertion at its lateral part to the Glutaeus minimus. The posterior border is very prominent and appears as a free, rounded edge, which bounds the back part of the trochanteric fossa. The Lesser Trochanter (trochanter minor; small trochanter) is a conical eminence, which varies in size in different subjects; it projects from the lower and back part of the base of the neck. From its apex three well-marked borders extend; two of these are above — a medial continuous with the lower border of the neck, a lateral with the intertrochanteric crest; the inferior border is continuous with the middle division of the linea aspera. The summit of the trochanter is rough, and gives insertion to the tendon of the Psoas major. A prominence, of variable size, occurs at the junction of the upper part of the neck with the greater trochanter, and is called the tubercle of the femur; it is the point of meeting of five muscles: the Glutaeus minimus laterally, the Vastus lateralis below, and the tendon of the Obturator internus and two Gemelli above. Running obliquely downward and medialward from the tubercle is the intertro- chanteric line (spiral line of the femur) ; it winds around the medial side of the body of the bone, below the lesser trochanter, and ends about 5 cm. below this eminence in the linea aspera. Its upper half is rough, and affords attachment to the ilio- femoral ligament of the hip-joint; its lower half is less prominent, and gives origin to the upper part of the Vastus medialis. Running obliquely downward and medial- ward from the summit of the greater trochanter on the posterior surface of the neck is a prominent ridge, the intertrochanteric crest. Its upper half forms the pos- terior border of the greater trochanter, and its lower half runs downward and medialward to the lesser trochanter. A slight ridge is sometimes seen commencing about the middle of the intertrochanteric crest, and reaching vertically downward for about 5 cm. along the back part of the body: it is called the linea quadrata, and gives attachment to the Quadratus femoris and a few fibres of the Adductor magnus. Generally there is merely a slight thickening about the middle of the intertrochanteric crest, marking the attachment of the upper part of the Quadratus femoris. The Body or Shaft (corpus femoris) . — The body, almost cylindrical in form, is a little broader above than in the centre, broadest and somewhat flattened from before backward below^ It is slightly arched, so as to be convex in front, and con- cave behind, where it is strengthened by a prominent longitudinal ridge, the linea aspera. It presents for examination three borders, separating three surfaces. Of the three borders, one, the linea aspera, is posterior, one is medial, and the other, lateral. The linea aspera (Fig. 385) is a prominent longitudinal ridge or crest, on the middle third of the bone, presenting a medial and a lateral lip, and a narrow rough, intermediate line. Above, the linea aspera is prolonged by three ridges. The lateral ridge is very rough, and runs almost vertically upward to the base of the greater trochanter. It is termed the gluteal tuberosity, and gives attachment to part of the Glutaeus maximus: its upper part is often elongated into a roughened crest, on which a more or less well-marked, rounded tubercle, the third trochanter, is occasionally developed. The intermediate ridge or pectineal line is continued to the base of the lesser trochanter and gives attachment to the Pectineus; the medial ridge is lost in the intertrochanteric line; between these two a portion of the Iliacus is inserted. Below, the linea aspera is prolonged into two ridges, enclosing between them a triangular area, the popliteal surface, upon which the popliteal artery rests. Of these two ridges, the lateral is the more prominent, and descends to the summit of the lateral condyle. The medial is less marked, especially at its upper part, where it is crossed by the femoral artery. It ends below at the summit of the medial condyle, in a small tubercle, the adductor tubercle, which affords insertion to the tendon of the Adductor magnus. THE FEMUR 349 From the medial lip of the linea aspera and its proh:)ngations above and below, the Vastus niedialis arises; and from tlie lateral lip and its upward prokjngation, the Vastus lateraHs takes origin. The Ad(kictor magnus is inserted into the hnea aspera, and to its hiteral prolongation above, and its medial prolongation below. Between the Vastus lateralis and the Adductor magnus two muscles are attached — viz.. the Glutaeus maximus inserted above, and the short head of the Biceps femoris arising below. Betweeen the Adductor magnus and the Vastus medialis four muscles are inserted: the Iliacus and Pectineus above; the Adductor brevis and Adductor longus below. The linea aspera is perforated a little below its centre by the nutrient canal, which is directed obliquely upward. The other two borders of the femur are only slightly marked: the lateral border extends from the antero-inferior angle of the greater trochanter to the anterior extremity of the lateral cond}4e; the medial border from the intertrochanteric line, at a point opposite the lesser trochanter, to the anterior extremity of the medial condyle. The anterior surface includes that portion of the shaft which is situated between the lateral and medial borders. It is smooth, convex, broader above and below than in the centre. From the upper three-fourths of this surface the Vastus inter- medins arises; the lower fourth is separated from the muscle by the intervention of the synovial membrane of the knee-joint and a bursa; from the upper part of it the Articularis genu takes origin. The lateral surface includes the portion between the lateral border and the linea aspera ; it is continuous above with the correspond- ing surface of the greater trochanter, below with that of the lateral condyle : from its upper three-fourths the Vastus intermedins takes origin. The medial surface includes the portion between the medial border and the linea aspera; it is continu- ous above with the lower border of the neck, below with the medial side of the medial condvle: it is covered bv the Vastus medialis. Lateral groove — j Lateral epicondyle Media I groove Medial epicondyle ihHBH! Semilunar area Fig. 386. — Lower extremity of right femur viewed from below. The Lower Extremity (distal extremity, Fig. 386). — The lower extremity, larger than the upper, is somewhat cuboid in form, but its transverse diameter is greater than its antero-posterior; it consists of two oblong eminences known as the condyles. In front, the condyles are but slightly prominent, and are separated from one another by a smooth shallow articular depression called the patellar surface; behind, they project considerably, and the interval between them forms a deep notch, the intercondyloid fossa. The lateral condyle is the more prominent and is the broader both in its antero-posterior and transverse diameters, the medial condyle is the longer and, when the femur is held with its body perpendicular, projects to a lo\\'er level. When, however, the femur is in its natural oblique position the lower sur- faces of the two condyles lie practically in the same horizontal plane. The condyles are not quite parallel with one another; the long axis of the lateral is almost 350 OSTEOLOGY directly aiitero-posterior, but that of the medial runs backward and mediahvard. Their opposed surfaces are small, rough, and concave, and form the walls of the intercondyloid fossa. This fossa is limited above by a ridge, the intercondyloid line, and below by the central ])art of the ])osterior margin of the patellar surface. The posterior cruciate ligament of the knee-joint is attached to the lower and front part of the medial wall of the fossa and the anterior cruciate ligament to an ini])res- sion on the upper and back part of its lateral wall. Each condyle is surmounted by an elevation, the epicondyle. The medial epicondyle is a large convex eminence to which the tibial collateral ligament of the knee-joint is attached. At its upper part is the adductor tubercle, already referred to, and behind it is a rough impres- sion which gives origin to the medial head of the Gastrocnemius. The lateral epicondyle, smaller and less prominent than the medial, gives attachment to the fibular collateral ligament of the knee-joint. Directly below it is a small depression from which a smooth well-marked groo\e curves obliquely upward and backward to the posterior extremity of the condyle. This groove is separated from the articular surface of the condyle by a prominent lip across which a second, shallower groove runs vertically downward from the depression. In the recent state these grooves are covered with cartilage. The Popliteus arises from the depression; its tendon lies in the oblique groove when the knee is flexed and in the vertical groove when the knee is extended. Above and behind the lateral epicondyle is an area for the origin of the lateral head of the Gastrocnemius, above and to the medial side of which the Plantaris arises. The articular surface of the lower end of the femur occupies the anterior, inferior, and posterior surfaces of the condyles. Its front part is named the patellar surface and articulates with the patella; it presents a median groove which extends down- ward to the intercondyloid fossa and two convexities, the lateral of which is broader, more prominent, and extends farther upward than the medial. The lower and posterior parts of the articular surface constitute the tibial surfaces for articulation with the corresponding condyles of the tibia and menisci. These surfaces are separated from one another by the intercondyloid fossa and from the patellar surface by faint grooves w^hich extend obliquely across the condyles. The lateral groove is the better marked; it runs lateralward and forward from the front part of the intercondyloid fossa, and expands to form a triangular depression. When the knee-joint is fully extended, the triangular depression rests upon the anterior portion of the lateral meniscus, and the medial part of the groo\'e comes into con- tact with the medial margin of the lateral articular surface of the tibia in front of the lateral tubercle of the tibial intercondyloid eminence. The medial groove is less distinct than the lateral. It does not reach as far as the intercondyloid fossa and therefore exists only on the medial part of the condyle; it receives the anterior edge of the medial meniscus when the knee-joint is extended. Where the groove ceases laterally the patellar surface is seen to be continued backward as a semilunar area close to the anterior part of the intercondyloid fossa ; this semi- lunar area articulates with the medial vertical facet of the patella in forced flexion of the knee-joint. The tibial surfaces of the condyles are convex from side to side and from before backward. Each presents a double curve, its posterior segment being an arc of a circle, its anterior, part of a cycloid.^ Structure. — The body of the femur is a cylinder of compact tissue, hollowed by a large medullary canal. The wall of the cyUnder is of great thickness and density in the middle third of the body, where the bone is narrowest and the medullary canal best formed; but above and below this the wall becomes thinner, while the medullary canal is gradually filled up by cancellous tissue, so that the upper (Fig. 387j and lower ends of the body, and the articular extremities more especially, consist of cancellous tissue, invested by a thin compact layer. line 1 A cycloid is a cur^^e traced by a point in the circumference of a wheel when the wheel is rolled along in a straight rilE FEMUR 351 The cancelli in the ends of the femur are disposc'd along the Hnes of greatest pressure and tension. In the upper end (Fig. 388) the chief hunelhe are arranged in the following manner. A series of Ijony i)lanes at right angles to the articular smrncc of the head converge to a central fJpipliU-sail line Fig. 387. — Longitudinal section of head and neck of femur. dense wedge, which presents few and dense cancelli. The w^edge is supported by strong lamellae, which extend to the sides of the neck and are especially marked along its upper and lower borders. Any force therefore apphed to the head of the femur is transmitted directly to the central wedge and thence to the junction of the neck with the body. This junction is especially strengthened by a series of dense lamellae which extend from the lesser trochanter to the lateral end of the superior border of the neck; this arrangement will ob- viously oppose considerable resistance to either tensile or shearing force. A smaller bar stretching across the junction of the greater trochanter with the neck and body resists the shearing force of the muscles attached to this prominence. These two bars, one at the junction of body and neck, the other at the junction of body and greater trochanter, form the upper layers of a series of arches which extend across between the sides of the body and transmit to the body forces applied to the upper end of the bone. In the cancellous tissue of the neck is a thin vertical plate of bone, the calcar femorale, which springs from the compact wall of the body in the region of the linea aspera. Medially it is attached to the interior sur- face of the posterior wall of the neck of the bone; laterally it continues the plane of the posterior wall of the neck into the greater trochanter where it shades off into the general cancel- lous tissue. It is thus situated in a plane anterior to the inter- trochanteric crest and to the base of the lesser trochanter (Fig. 389). In the lower end, the cancelli spring on all sides from the inner surface of the cylinder, and descend in a perpendicular direction to the articular surface, the cancelli being strongest and having a more accurately perpendicular coiu'se above the condyles. In addition to this, there Fig. 388. — Scheme showing disposi- tion of principal cancellous lamellse in upper extremity of femur. 352 OSTEOLOGY are horizontal planes of cancellous tissue, so that the spongy tissue in this situation presents an appearance of being mapped out into a series of cubical areas. Articulations. — The femur articulates with three bones: the hip bone, tibia, and patella. Ossification (Figs. 390, 391, 392). — The femur is ossified from Jive centres: one for the body, one for the head, one for each trochanter, and one for the lower extremity. Of all the long bones, except the clavicle, it is the first to show traces of ossification; this commences in the middle of the body, at about the seventh week of fetal life, and rapidly extends upward and downward. The centres in the epiphyses appear in the following order: in the lower end of the bone, at the ninth month of fetal life (from this centre the condyles and epicondyles are formed) ; in the head, at the end of the first year after birth; in the greater trochanter, during the fourth year; and in the lesser trochanter, between the thirteenth and fourteenth years. The order in which the epiphyses are joined to the body is the reverse of that of their appearance; they are not united until after puberty, the lesser trochanter being first joined, then the greater, then the head, and, lastly, the inferior extremity, which is not united until the twentieth year. Appears at 4:th year ; joins body about ISth yr Caicar femorale Appears at 9th month of fceial life Appears at end of 1st yr. ; joins body about \%th yr. Appears IZth^-lUh year ; joins body about 18th year Joins body a 20th year Lower extremity Fig. 389. — Oblique section of upper extremity of femur showing caicar femorale. Fig. 390.- -Plan of ossification of tiie femur, five centres. From Applied Anatomy. — The lower end of the femur is the only epiphysis in which ossification has commenced at the time of birth. The presence of this ossific centre is, therefore, a proof, in a newly born child found dead, that the child has arrived at the full period of uterogestation, and is always reUed upon in medicolegal investigations. The position of the epiphysial plate should be carefully noted. It is on a level with the adductor tubercle, and the epiphysis does not, there- fore, form the whole of the cartilage-clad portion of the lower end of the bone. It is essential to bear this point in mind in performing excision of the knee, since growth in length of the femur takes place chiefly from the lower epiphysis, and any interference with the epiphysial cartilage in a young child would involve such ultimate shortening of the limb, from want of growth, as to render the limb almost useless. Separation of the lower epiphysis may take place up to the age THE FEMUR 358 of twenty, at which time it becomes comi)lctely joined to the body of tlie bone; but, as a mattei" of fact, few cases occur after the age of sixteen or seventeen. The epiphysis of the head of the femur is the seat of origin, in a large number of cases, of tuberculous disease of the hip-joint. In the majority of cases the disease begins in the highly vascular and growing tissue at the end of the body in the neighborhood of the epiphysial cartilage, and extends into the joint. The epiphysis for the head is entirely intracapsular. Fractures of the femur are divided, like those of the other long bones, into fractures of the upper end; of the body; and of the lower end. The fractures of the upper end may be classified into (1) fracture of the neck; (2) fracture at the junction of the neck with the greater trochanter: (3) fracture of the greater trochanter; and (4) separation of the epiphysis, either of the head or of the greater trochanter. The first of these, fi'acture of the neck, is usually termed intracapsular fracture, but this is scarcely a correct designation, as, owing to the attachment of the articular capsule, the fracture is partly within and partly without the capsule when the fracture occurs at the lower part of the neck. It generally takes place in old people, principally women, and , Fig. 391. — Epiphysial lines of femur in a young adult. Anterior aspect. The lines of attachment of the articular capsules are in blue. Fig. 392. — Epiphysial lines of femur in a young' adult. Posterior aspect. The hnes of attachment of the articular capsules are in blue. usually from a very slight degree of indirect violence. Probably the main cause of its occurrence in old people is the senile degenerative change which takes place in the bone. Merkel believes that it is mainly due to the absorption of the calcar femorale. As a rule the fragments become imited by fibrous tissue, but frequently no union takes place, and the opposed surfaces become smooth and eburnated. Fractures at the junction of the neck with the greater trochanter are usually termed extra- capsular, but this designation is also incorrect, as the fracture is partly within the capsule, owing to its attachment in front to the intertrochanteric line, which is situated below the Line of fracture. These fractures are produced by direct violence to the greater trochanter, as from a fall laterally on the hip. From the manner in which the accident is caused the neck of the bone is driven into the trochanter, where it may remain impacted, or the trochanter may be spHt into two or more fragments, disimpaction resulting. Fractures of the body may occur at any part, but the most usual situation is at or near .the centre of the bone. They may be caused by direct or indirect violence. Fractures of the upper third of the body ai-e almost always the result of indirect violence, while those of the lower third 23 354 OSTEOLOGY are the result, for the most part, of direct violence. Fractures of the body are generally oblique, but they may be transverse, longitudinal, or spiral. The transverse fracture occurs most fre- quently in children. The fractures of the lower end of the femur include transverse fracture above the condyles, the most common; and this may be complicated by a vertical fracture be- tween the condyles, constituting the T-shaped fracture. In these cases the popliteal artery is in danger of being wounded. Oblique fracture separating either the medial or lateral condjde, and a longitudinal incomplete fractm-e between the condyles, may also take place. The femur as well as the other bones of the leg is frequently the seat of acute osteomj^elitis in children. This is no doubt due to their greater exposure to injmy, which is often the exciting cause of this disease. Necrosis of portions of the diaphysis frequently ensues, especially in the region of the pophteal surface of the femur, and the disease may continue for years, great trouble being experienced with discharging sinuses which periodically close and reopen to allow of the exit of a piece of dead bone. Tumors are not infrequently found growing from the femur: the most common forms being sarcoma which may grow either from the periosteum or from the medullary tissue within the interior of the bone, and exostosis which commonly originates in the neighborhood of the epiphysial cartilage of the lower end. The periosteal sarcomata of the femur and most of the central growths are usually of a very high degree of malignancy, although the "myeloid" growth, which is of but low malignancy, may also be found. The region of the lower epiphysial line is by far the com- moner seat for all these tumors, and it should be noted that the lower epiphysis has the longest period of active growth, and that these tumors usually appear toward the end of the period of active growth of the bone. Sarcomata about the upper end of the femur are seen occasionally, but very rarely in comparison with those at the lower end. Secondary carcinoma also occurs in this bone, most commonly due to a primary focus in the breast, and spontaneous fracture of the bone may take place in these cases. The Patella (Knee Cap). The patella (Figs. 393, 394) is a flat, triangular bone, situated on the front of the knee-joint. It is usually regarded as a sesamoid bone, developed in the tendon of the Quadriceps femoris, and resembles these bones (1) in being developed in a tendon ; (2) in its centre of ossification presenting a knotty or tuberculated outline; (3) in being composed mainly of dense cancellous tissue. It serves to protect the front of the joint, and increases the leverage of the Quadriceps femoris by making it act at a greater angle. It has an anterior and a posterior surface three borders, and an apex. Surfaces.— The anterior surface is convex, perforated by small apertures for the passage of nutrient \'essels, and marked by numerous rough, longitudinal striae. This surface is covered, in the recent state, by an expansion from the tendon of the Quadriceps femoris, which is continuous below with the superficial fibres of the ligamentum patellae. It is separated from the integument by a bursa. The posterior surface presents above a smooth, oval, articular area, divided into two facets by a vertical ridge; the ridge corresponds to the groove on the patellar surface of the femur, and the facets to the medial and lateral parts of the same surface; the lateral facet is the broader and deeper. Below the articular surface is a rough, convex, non-articular area, the lower half of which gives attachment to the ligamentum patellae ; the upper half is separated from the head of the tibia by adipose tissue. Borders.— The base or superior border is thick, and sloped from behind, down- ward, and forward : it gives attachment to that portion of the Quadriceps femoris which is derived from the Rectus femoris and Vastus intermedins. The medial and lateral borders are thinner and converge below: they give attachment to those -'ii^ Fig. 393.— Right patella. Anterior surface. Fig. 394. — Right patella. Posterior surface. 77/ A' Tin I A •joo })orti()ns of the Qua(lri('e])s t'einoris which arc (hTi\('(l from the Vasti hiteraHs and inediaHs. Apex. — The a])ex is pointed, and <;i\'es atta<-hnient to the H^ainentnin patellae. Structure. — The p:itc>lla consists of ;i nearly uniform dense caneellous tissue, covered by a thin eonipact lamina. The cancH^lli immediately beneath the anterior surface are arranged parallel with it. In tlie rest of the bon(> tiiey radiate from tlie articular surface toward the other parts of the bone. Ossification. — -Tlie patella is ossified from a single centre, which usually makes its appearance in tlie second or third year, but may be delayed until the sixth year. More rarely, the bone is developed by two centres, placed side by side. Ossification is completed about the age of ]juberty. Articulation. — The patella articulates with the femur. Applied Anatomy. — The main surgical interest about the patella is in connection with fractures, which are of frequent occurrence. They are most often produced by muscular action — that is to say, by violent contraction of the quadriceps femoris while the limb is in a position of semi- flexion, so that the bone is snapped across the condyles of the femur and the fracture is transverse. Fracture of the patella is also produced by direct violence, such as falls on the knee, and here the fracture is usually stellate and the bone comminuted. Owing to the displacement of the fragments, and the difficulty there is in maintaining them in apposition, union takes place by fibrous tissue which may subsequently stretch, producing wide separation of the fragments and permanent lameness. Truly satisfactory results after this fracture are generally only to be obtained by opening the joint and wiring the fragments together, and this is especially so when there is marked separation of the fragments owing to laceration of the retinacula. It is an anatomical possibiUty, if the fracture involve only the lower and non-articular part of the bone, for this to take place without injury to the synovial membrane and without involving the cavity of the knee-joint. The Tibia (Shin Bone). The tibia (Figs. 396, 397) is situated at the medial side of the leg, and, excepting the femur, is the longest bone of the skeleton. It is prismoid in form, expanded above, where it enters into the knee-joint, contracted in the lower third, Tuhprosity and again enlarged but to a lesser extent below. In the male, its direction is vertical, and parallel with the bone of the opposite side; but in the female it has a slightly oblique direction downward andlateralward, to compensate for the greater oblicjuity of the femur. It has a body and two extremities. The Upper Extremity {proximal extremity). — The upper extremity is large, and expanded into two eminences, the medial and lateral condyles. The superior articular surface pre- sents tAVo smooth articular facets (Fig. 395). The medial facet, oval in shape, is slightly concave from side to side, and from before backward. The lateral, nearly circular, is concave from side to side, but slightly convex from before backward, especially at its posterior part, where it is prolonged on to the posterior surface for a short distance. The central portions of these facets articulate with the con- dyles of the femur, while their peripheral portions support the menisci of the knee-joint, which here intervene between the two bones. Between the artic- ular facets, but nearer the posterior than the anterior aspect of the bone, is the intercondyloid eminence (spine of tibia), surmounted on either side by a prominent tubercle, on to the sides of which the articular facets are prolonged; in front of and behind the intercondyloid eminence are rough depressions for the attachment of the anterior and posterior cruciate ligaments and the menisci. The anterior surfaces of the condyles are continuous with one another, forming a large somewhat Intercondyloid eminence Fig. 39.5. — Upper surface of right tibia. 356 OSTEOLOGY Articular capsule Styloid 2)rocess —y Fibular collateral ligament \ el " . il ICLLA-/ . "s^ v\ S Articular capsule Lateral malleolus Fig. 396.— Bones of the right leg Medial malleolus Anterior surface. flattened area; this area is trian- gular, broad al)ove, and perforated by large vascular foramina; narrow below where it ends in a large ob- long elevation, the tuberosity of the tibia, which gives attachment to the ligamentum patellae; a bursa intervenes between the deep surface of the ligament and the part of the bone immediately above the tuberosity'. Posteriorly, the condyles are separated from each other by a shallow depres- sion, the posterior intercondyloid fossa, which gives attachment to part of the posterior cruciate liga- ment of the knee-joint. The medial condyle presents posteriorly a deep transverse groove, for the insertion of the tendon of the Semimembranosus. Its medial surface is convex, rough, and prominent; it gives attachment to the tibial collateral ligament. The lateral condyle presents pos- teriorly a flat articular facet, nearly circular in form, directed down- ward, backward, and lateralward, for articulation with the head of the fibula. Its lateral surface is convex, rough, and prominent in front : on it is an eminence, situated on a level with the upper border of the tuberosity and at the junc- tion of its anterior and lateral surfaces, for the attachment of the iliotibial band. Just below this a part of the Extensor digi- torum longus takes origin and a slip from the tendon of the Biceps femoris is inserted. The Body or Shaft {corims tibiae). — The body has three borders and three surfaces. Borders. — The anterior crest or border, the most prominent of the three, commences above at the tuberosity, and ends below at the anterior margin of the medial malleolus. It is sinuous and prominent in the upper two-thirds of its extent, but smooth and rounded below; it gives attach- ment to the deep fascia of the les;. THE TJBIA 357 The medial border is smooth a in the centre; it begins at the posterior border of the medial malleohis; its upper part gives attachment to the tibial collat- eral ligament of the knee-joint to the extent of about 5 cm., and insertion to some fibres of the Popliteus; from its middle third some fibres of the Soleus and Flexor digitorum longus take origin. The interosseous crest or lat- eral border is thin and promi- nent, especially its central part, and gi\'es attachment to the interosseous membrane; it com- mences above in front of the fibular articular facet, and bifurcates below, to form the boundaries of a triangular rough surface, for the attachment of the interosseous ligament con- necting the tibia and fibula. Surfaces. — The medial surface is smooth, convex, and broader above than below; its upper third, directed forward and medialward, is covered by the aponeurosis derived from the tendon of the Sartorius, and by the tendons of the Gracilis and Semitendinosus, all of which are inserted nearly as far for- ward as the anterior crest; in the rest of its extent it is sub- cutaneous. The lateral surface is narrower than the medial; its upper two- thirds present a shallow^ groove for the origin of the Tibialis anterior; its lower third is smooth, convex, curves grad- ually forward to the anterior aspect of the bone, and is covered by the tendons of the Tibialis anterior. Extensor hal- lucis longus, and Extensor digi- torum longus, arranged in this order from the medial side. The posterior surface (Fig. 397) presents, at its upper part, a prominent ridge, the popliteal line, w^hich extends obliquely downward from the back part of nd rounded above and below, but more prominent back part of the medial condyle, and ends at the Articular capsule Y"^^ Articular ws\ capsule ■^'-■^ Stxjloid process Articulates with tams Articular capsule Fig. 397. — Bones of the right leg. Posterior surface. 358 OSTEOLOGY the articular facet for the fibula to the medial border, at the junction of its upper and middle thirds; it marks the lower limit of the insertion of the Popliteus, serves for the attachment of the fascia covering this muscle, and gives origin to part of the Soleus, Flexor digitorum longus, and Tibialis posterior. The triangular area, above this line, gives insertion to the Popliteus. The middle third of the posterior surface is divided by a vertical ridge into two parts; the ridge begins at the popliteal line and is well-marked above, but indistinct below; the medial and broader por- tion gives origin to the Flexor digitorum longus, the lateral and narrow^er to part of the Tibialis posterior. The remaining part of the posterior surface is smooth and covered by the Tibialis posterior, Flexor digitorum longus, and Flexor hallucis longus. Immediately below the popliteal line is the nutrient foramen, which is large and directed obliquely downward. The Lower Extremity {distal extremity). — The lower extremity, much smaller than the upper, presents five surfaces; it is prolonged downward on its medial side as a strong process, the medial malleolus. Surfaces. — The inferior articular surface is quadrilateral, and smooth for articu- lation with the talus. It is concave from before backward, broader in front than behind, and traversed from before backward by a slight elevation, separating two depressions. It is continuous with that on the medial malleolus. Upper extremity Appears before or shortly after birth Appea-'-s at 2mZ__ year Joins body 'about 20th year Joins body about \8th year Lower extremity Fig. 398. — Plan of ossification of the tibia, centres. From three Fig. 399. — Epiphysial lines of tibia and fibula in a young adult. Anterior aspect. The anterior surface of the lower extremity is smooth and rounded above, and covered by the tendons of the Extensor muscles ; its lower margin presents a rough transverse depression for the attachment of the articular capsule of the ankle- joint. The posterior surface is traversed by a shallow groove directed obliquely down- w-ard and medialward, continuous wdth a similar groove on the posterior surface of the talus and serving for the passage of the tendon of the Flexor hallucis longus. The lateral surface presents a triangular rough depression for the attachment of the inferior interosseous ligament connecting it with the fibula; the lower part THE FI/ULA 859 of this depression is siiiot)tli, coxered witli cartilage in tiie recent state, and articu- lates with the fibula. The surface is bounded by two prominent borders, con- tinuous above with the interosseous crest; they afford attachment to the anterior and posterior li,u;aments of the lateral malleolus. The medial surface is jjrolonged downward to form a strong pyramidal process, fiattened from without inward — the medial malleolus. The medial surface of this process is convex and subcutaneous; its lateral t)r articular surface is smooth and slightl>' concave, and articulates with the talus; its anterior border is rough, for the attachment of the anterior fibres of the deltoid ligament of the ankle-joint; its posterior border presents a broad groove, the malleolar sulcus, directed obliquely downward and medialward, and occasionally double; this sulcus lodges the tendons of the Tibialis posterior and Flexor digitorum longus. The summit of the medial malleolus is marked by a rough depression behind, for the attachment of the deltoid ligament. Structure. — The structure of the tibia is like that of the othei- long bones. The compact wall of the body is thickest at the junction of the middle and lower thirds of the bone. Ossification. — The tibia is ossified from three centres (Figs. 398, 399) : one for the bod}' and one for either extremity. Ossification begins in the centre of the body, about the seventh week of fetal life, and gradually extends toward the extremities. The centre for the upper epiphysis appears before or shortly after birth; it is flattened in form, and has a thin tongue-shaped process in front, which forms the tuberosity (Fig. 399) ; that for the lower epiphj^sis appears in the second year. The lower epiphysis joins the body at about the eighteenth, and the upper one joins about the twentieth year. Two additional centres occasionally exist, one for the tongue-shaped process of the upper epiphysis, which forms the tuberosity, and one for the medial malleolus. Articulations. — The tibia articulates with three bones: the femur, fibula, and talus. The Fibula (Calf Bone). The fibula (Figs. 396, 397) is placed on the lateral side of the tibia, with which it is connected above and below. It is the smaller of the two bones, and^ in proportion to its length, the most slender of all the long bones. Its upper extremity is small, placed toward the back of the head of the tibia, below the level of the knee-joint, and excluded from the formation of this joint. Its lower extremity inclines a little forward, so as to be on a plane anterior to that of the upper end; it projects below the tibia, and forms the lateral part of the ankle-joint. The bone has a body and two extremities. The Upper Extremity or Head {capitulum fibulae; proximal extremity). — The upper extremity is of an irregular quadrate form, presenting above a flattened articular surface, directed upward, forward, and medialward, for articulation with a corresponding surface on the lateral condyle of the tibia. On the lateral side is a thick and rough prominence continued behind into a pointed eminence, the apex (styloid process), which projects upward from the posterior part of the head. The prominence, at its upper and lateral part, gives attachment to the tendon of the Biceps femoris and to the fibular collateral ligament of the knee-joint, the liga- ment dividing the tendon into two parts. The remaining part of the circumference of the head is rough, for the attachment of muscles and ligaments. It presents in front a tubercle for the origin of the upper and anterior fibres of the Peronaeus longus, and a surface for the attachment of the anterior ligament of the head; and behind, another tubercle, for the attachment of the posterior ligament of the head and the origin of the upper fibres of the Soleus. The Body or Shaft (corpus fibulae). — The body presents four borders — the antero-lateral, the antero-medial, the postero-lateral, and the postero-medial ; and four surfaces — anterior, posterior, medial, and lateral. Borders. — The antero-lateral border begins above in front of the head, runs ver- tically downward to a little below the middle of the bone, and then curving some- what lateralward, bifurcates so as to embrace a triangular subcutaneous surface 360 OSTEOLOGY immediately above the lateral malleolus. This border gives attachment to an intermuscular septum, which separates the Extensor muscles on the anterior surface of the leg from the Peronaei longus and brevis on the lateral surface. The antero-medial border, or interosseous crest, is situated close to the medial side of the preceding, and runs nearly parallel Avith it in the upper third of its extent, but diverges from it in the lower two-thirds. It begins above just beneath the head of the bone (sometimes it is quite indistinct for about 2.5 cm. below the head), and ends at the apex of a rough triangular surface immediately above the articular facet of the lateral malleolus. It serves for the attachment of the inter- osseous membrane, which separates the Extensor muscles in front from the Flexor muscles behind. The postero-lateral border is prominent; it begins above at the apex, and ends below in the posterior border of the lateral malleolus. It is directed lateralward above, backward in the middle of its course, backward, and a little medialward below, and gives attachment to an aponeurosis which separates the Peronaei on the lateral surface from the Flexor muscles on the posterior surface. The postero-medial border, sometimes called the oblique line, begins above at the medial side of the head, and ends by becoming continuous with the interosseous crest at the lower fourth of the bone. It is well-marked and prominent at the upper and middle parts of the bone. It gives attachment to an aponeurosis which sep- arates the Tibialis posterior from the Soleus and Flexor hallucis longus. Surfaces. — The anterior surface is the interval between the antero-lateral and antero-medial borders. It is extremely narrow and flat in the upper third of its extent: broader and grooved longitudinallj^ in its lower third; it serves for the origin of three muscles: the Extensor digitorum longus, Extensor hallucis longus, and Peronaeus tertius. The posterior surface is the space included between the postero-lateral and the postero-medial borders; it is continuous below with the triangular area above the articular surface of the lateral malleolus; it is directed back^^ard above, back- ward and medialward at its middle, directly medialward below. Its upper third is rough, for the origin of the Soleus; its lower part presents a triangular surface, connected to the tibia by a strong interosseous ligament; the intervening part of the surface is covered by the fibres of origin of the Flexor hallucis longus. Near the middle of this surface is the nutrient foramen, which is directed downward. The medial surface is the interval included between the antero-medial and the postero-medial borders. It is grooved for the origin of the Tibialis posterior. The lateral surface is the space between the antero-lateral and postero-lateral borders. It is broad, and often deeply grooved; it is directed lateralward in the upper two-thirds of its course, backward in the lower third, where it is continuous with the posterior border of the lateral malleolus. This surface gives origin to the Peronaei longus and brevis. The Lower Extremity or Lateral Malleolus {malleolus lateralis; distal extremity; external malleolus) . — The lower extremity is of a pyramidal form, and somewhat flattened from side to side; it descends to a lower level than the medial malleolus. The lateral surface is convex, subcutaneous, and continuous with the triangular, subcutaneous sm-face on the lateral side of the body. The medial surface (Fig. 400) presents in front a smooth triangul'ar surface, convex from above dow^nward, which articulates with a corresponding surface on the lateral side of the talus. Behind and beneath the articular surface is a rough depression, which gives attach- ment to the posterior talofibular ligament. The anterior border is thick and rough, and marked below by a depression for the attachment of the anterior talofibular ligament. The posterior border is broad and presents the shallow malleolar sulcus, for the passage of the tendons of the Peronaei longus and brevis. The summit is rounded, and give attachment to the calcaneofibular ligament. THE FIBULA 361 Articulations. — The fibula articulates with two bones: the tibia and talus. Ossification. — The fibula is ossified from three centres (Fig. 401): one for the body, and one for either entl. Ossification begins in the body about the eighth week of fetal life, and extends toward the extremities. At birth the ends are cartilaginous. Ossification commences in the lower end in the second year, and in the upper about the fourth year. The lower epiphysis, the first to ossify, unites with the body about the twentieth year; the upper epiphysis joins about the twenty-fifth year. Applied Anatomy of the Tibia and Fibula. — In fractures of the bones of the leg, both bones are generally involved, but cither bone may be broken separately, the fibula more frequently than the tibia. Fracture of both bones may be caused by either direct or indirect violence. When it occiu-s from indirect force, the fracture in the tibia is at the junction of the middle and lower thirds of the bone. Many causes conduce to render this the weakest part of the bone. The fractm-e of the fibula is usually at a rather higher level. These fractiu'es present great variety, both as regards their direction and condition. Thej^ may be oblique, transverse, longitudinal, or spiral. When oblique, they are for the most part the result of indirect violence, and the direc- tion of the fracture is downward, forward, and medialw'ard in many cases, but maj' be down- ward and lateralward, or downward aiid backward. When transverse, the fracture is often at the upper part of the bone, and is the result of direct violence. The spiral fracttire of the tibia generally starts as a vertical fissure, involving the ankle-joint, and is associated with fracture of the fibula higher up. It is the result of torsion, from twisting of the body while the foot is fixed. Upper extremity Lntero-sseous crest Appears about ith year Unites about 25th year For talus For posterior talofibular ligt. Appears at MS 2nd year Unites about 20th year Fig. •iOO. — Lower extremitj of right fibula. INIedial aspect Lower extremity Fig. 4:01. — Plan of ossification of the fibula. From three centres. Fractures of the tibia alone are almost always the result of direct violence, except where the malleolus is broken off by twists of the foot. Fractures of the fibula alone may arise from indirect or direct force, those of the low^er end being usually the result of the former, and those higher up being caused by a direct blow on the part. The tibia is the bone which is most commonly and most extensively distorted in rickets. It bends at the junction of the middle and lower third, its weakest part, and presents a curve forward wdth generally some lateral displacement. The tibia is more often the seat of acute infective necrosis than any other bone in the body, and with the formation of the sequestrum, a large amount of new bony material is thrown out by the periosteima. The sequence of events in this disease can be very closely followed in the case of the tibia, and it is not xmcommon to find a patient from whom the whole diaphysis of the tibia has been removed, going about with a new bone entirely of periosteal formation. Chronic bone abscess is more frequently met with in the canceUotis tissue of the head or lower end -of the tibia than in any other bone in the body. These abscesses are very chronic, and in most cases the result of tuberculous osteitis, although they are sometimes due to the organisms of suppura- tion or even the Bacillus typhosus. 362 OSTEOLOaY THE FOOT. The skeleton of the foot (Figs. 403 and 404) consists of three parts: the tarsus, metatarsus, and phalanges. The Tarsus (Ossa Tarsi). The tarsal bones are se\'en in number, \iz., the calcaneus, talus, cuboid, navicular, and the first, second, and third cuneiforms. Groovzfor Ppronceus hrev Trochlear proca^ Groove for Peronceus longus tendo calcaneus Lateral process of tuberosity B For posterior facet of talus For middle facet of talus ^^*l^^^ -^°' ^' ter-ioi facet of talus Medial process of tuberosity j ' ^'°'' '^"^"'^^ Groove for Flexor Judlucis longus Sustentaculum tali Groove for inierosscus ligament Fig. 402.— The left calcaneus. .4. Postero-lateral view. B. Antero-medial view. The Calcaneus {as calcis) (Fig. 402).— The calcaneus is the largest of the tarsal bones. It is situated at the lower and back part of the foot, serving to transmit the weight of the body to the ground, and forming a strong lever for the muscle? of the calf. It is irregularly cuboidal in form, having its long axis directed forward and lateralward; it presents for examination six surfaces. Surf aces.— The superior surface extends behind on to that part of the bone which projects backward to form the heel. This varies in length in different individuals, THE TARDUS 363 Groove f 01 tendon of PER0NAEI"> LON(TT.b (iroovefor ten I >n if PKRONAEIs } I EM'5 PERONAEUS TI I TILS PERONAETS BRFMb Groove for tendon of Fr,EXOH HALLUCIS LONGUS Tarsus Metatarsus Ext. digitorum brevis Phcdanges Ext. HALLUCIS LONGUS Fig. 403. — Bones of the right foot. Dorsal surface. 3G4 OSTEOLOGY j\bductlr iiallucis Medial iikad of Flexor hallucis brevis Tubercle of navicular Tibialis anterior Two sesamoid hones Lateral wrkd of quapratus PLANTiE f'LEXOR BREA'IS ANi> Abductor DIGITI QUINTI Flexor digitorum BREVIS Flexor digitorum longus Fig. 404. — Bones of the right foot. Plantar surface. THE TARSUS 365 is convex from side to side, concave from before backward, and supports a mass of fat placed in front of the tendo calcaneus. Tn front of this area is a large usually somewhat oval-shaped facet, the posterior articular surface, which looks upward and forward; it is convex from behind forward, and articulates with the posterior calcaneal facet on the under surface of the talus. It is bounded anteriorly by a deep depression which is continued backward and medialward in the form of a groove, the calcaneal sulcus. In the articulated foot this sulcus lies below a similar one on the under surface of the talus, and the two form a canal (sinus tarsi) for the lodgement of the interosseous talocalcaneal ligament. In front and to the medial side of this groove is an elongated facet, concave from behind forward, and with its long axis directed forward and lateralward. This facet is frequently divided into two by a notch : of the two, the posterior, and larger is termed the middle articular surface; it is supported on a projecting process of bone, the sustentaculum tali, and articulates with the middle calcaneal facet on the under surface of the talus; the anterior articular surface is placed on the anterior part of the body, and articu- lates with the anterior calcaneal facet on the talus. The upper surface, anterior and lateral to the facets, is rough for the attachment of ligaments and for the origin of the Extensor digitorum brevis. The inferior or plantar surface is uneven, wider behind than in front, and convex from side to side; it is bounded posteriorly by a transverse elevation, the calcaneal tuberosity, which is depressed in the middle and prolonged at either end into a process; the lateral process, small, prominent, and rounded, gives origin to part of the Abductor digiti quinti ; the medial process, broader and larger, gives attach- ment, by its prominent medial margin, to the Abductor hallucis, and in front to the Flexor digitorum brevis and the plantar aponeurosis ; the depression between the processes gives origin to the Abductor digiti quinti. The rough surface in front of the processes gives attachment to the long plantar ligament, and to the lateral head of the Quadratus plantae; while to a prominent tubercle nearer the anterior part of this surface, as w^ell as to a transverse groove in front of the tubercle, is attached the plantar calcaneocuboid ligament. The lateral surface is broad behind and narrow in front, flat and almost sub- cutaneous; near its centre is a tubercle, for the attachment of the calcaneofibular ligament. At its upper and anterior part, this surface gives attachment to the lateral talocalcaneal ligament; and in front of the tubercle it presents a narrow surface marked by two oblique grooves. The grooves are separated by an elevated ridge, or tubercle, the trochlear process (peroneal tubercle),, which varies much in size in different bones. The superior groove transmits the tendon of the Peronaeus brevis; the inferior groove, that of the Peronaeus longus. The medial surface is deeply concave; it is directed obliquely downward and forward, and serves for the transmission of the plantar vessels and nerves into the sole of the foot; it affords origin to part of the Quadratus plantae. At its upper and forepart is a horizontal eminence, the sustentaculum tali, which gives attach- ment to a slip of the tendon of the Tibialis posterior. This eminence is concave above, and articulates with the middle calcaneal articular surface of the talus; below, it is grooved for the tendon of the Flexor hallucis longus ; its anterior margin gives attachment to the plantar calcaneonavicular ligament, and its medial, to a part of the deltoid ligament of the ankle-joint. The anterior or cuboid articular surface is of a somewhat triangular form. It is concave from above downward and lateralward, and convex in a direction at right angles to this. Its medial border gives attachment to the plantar calcaneonavicular ligament. The posterior surface is prominent, convex, wider below than above, and divisible into three areas. The lowest of these is rough, and covered by the fatty and fibrous tissue of the heel; the middle, also rough, gives insertion to the tendo calcaneus 566 OSTEOLOGY and Plantaris; wliile the hi.iijliest is smooth, and is c()\-ered by a bursa which inter- venes between it and the tendo calcaneus. Articulations. — The calcaneus articulates with two bones: the talus and cuboid. For navicular Neck A Trocldra for tibia ^ For transver>ie inferior tihio- / filnilrtr ligament lor process For lat. malleolus For med malleolus Trochlea foi tibia Groove for Flexor halluris longus For 'plantar calcaneo- navicular ligament Middle calcaneal articular surface Posterior calcaneal articular surface Groove for Flex, halluris longus For navicular For navicular Anterior calcaneal articular surface Groove for interosseous talocalcaneal ligament Fig. 405. — The left talus. --1. Supero-lateral view. B. Infero-medial view. C. Inferior view. The Talus (astragalus; ankle hone) (Fig. 405).— The talus is the second largest of the tarsal bones. It occupies the middle and upper part of the tarsus, support- ing the tibia above, resting upon the calcaneus below, articulating on either side with the malleoli, and in front with the navicular. It consists of a body, a neck, and a head. 77/ A' TARSUS 367 The Body (rorpii,'i fali). — The superior surface of the body presents, l)eliiii(l, a smooth troehU'ar surfaee, tlie trochlea, for artieuhition with the tibia. The trochlea is broader in front than behind, convex from before backward, slightly concave from side to side: in front it is continnons with the npper snrface of the neck of the bone. The inferior surface ])resents two articular areas, the posterior and middle cal- caneal surfaces, separated from one another by a deep groo\e, the sulcus tali. The gToove runs obliquely forward and lateralward, becoming gradually broader and deei)er in front: in the articulated foot it lies above a similar groove upon the upper surface of the calcaneus, and forms, with it, a canal (sinus tarsi) filled up in the recent state by the interosseous talocalcaneal ligament. The posterior calcaneal articular surface is large and of an oval or oblong form. It articulates with the corresi)onding facet on the upper surface of the calcaneus/ and is deeply concave in the direction of its long axis which runs forward and lateralward at an angle of about 45° with the median plane of the body. The middle calcaneal articular surface is small, oval in form and slightly convex; it articulates with the upper surface of the sustentaculum tali of the calcaneus. The medial surface presents at its upper part a pear-shaped articular facet for the medial malleolus, continuous above with the trochlea; below the articular surface is a rough depression for the attachment of the deep portion of the deltoid ligament of the ankle-joint. The lateral surface carries a large triangular facet, concave from above downward, for articulation with the lateral malleolus; its anterior half is continuous above with the trochlea ; and in front of it is a rough depression for the attachment of the ante- rior talofibular ligament. Between the posterior half of the lateral border of the trochlea and the posterior part of the base of the fibular articular surface is a tri- angular facet (Fawcett-) which comes into contact with the transverse inferior tibiofibular ligament during flexion of the ankle-joint; below the base of this facet is a groo^-e which aft'ords attachment to the posterior talofibular ligament. The posterior surface is narrow, and traversed by a groove running obliquely downward and mediahvard, and transmitting the tendon of the Flexor hallucis longus. Lateral to the groove is a prominent tubercle, the posterior process, to which the posterior talofibular ligament is attached; this process is sometimes separated from the rest of the talus, and is then known as the os trigonum. Medial to the groove is a second smaller tubercle. The Neck {collum tali). — The neck is directed forward and medialw^ard, and comprises the constricted portion of the bone between the body and the oval head. Its upper and medial surfaces are rough, for the attachment of ligaments; its lateral surface is concave and is continuous below with the deep groove for ,the inter- osseous talocalcaneal ligament. The Head {caput tali). — The head looks forward and mediahvard; its anterior articular or navicular surface is large, oval, and convex. Its inferior surface has two facets, which are best seen in the recent condition. The medial, situated in front of the middle calcaneal facet, is convex, triangular, or semi-oval in shape, and rests on the plantar calcaneonaA'icular ligament; the lateral, named the anterior calcaneal articular surface, is somewhat flattened, and articulates with the facet on the upper surface of the anterior part of the calcaneus. Articulations. — The talus articulates with four bones: tibia, fibula, calcaneus, and navicular. The Cuboid Bone {os ciiboideum) (Fig. -106). — The cuboid bone is placed on the lateral side of the foot, in front of the calcaneus, and behind the fourth and fifth metatarsal bones. It is of a pyramidal shape, its base being directed mediahvard. 1 Sewell (Journal of Anatomy and Physiology, vol. xxxviii) pointed out that in about 10 per cent, of bones a small triangular facet, continuous with the posterior calcaneal facet, is present at the junction of the lateral surface of the body with the posterior wall of the sulcus tali. - Edinburgh Medical Journal, 1895. 368 OSrEOLOCY Surfaces. — The dorsal surface, directed iijnvard and laterahvard, is rough, for the attachment of ligaments. The plantar surface presents in front a deep groove, the peroneal sulcus, which runs obliquely forward and mediahvard; it lodges the tendon of the Peronaeus longiis, and is bounded })ehind by a prominent ridge, to which the long plantar ligament is attached. The ridge ends laterally in an eminence, the tuberosity, the surface of which presents an oval facet; on this facet glides the sesamoid bone or cartilage frequently found in the tendon of the Pero- naeus longus. The surface of bone behind the groove is rough, for the attachment of the plantar calcaneocuboid ligament, a few fibres of the Flexor hallucis brevis, and a fasciculus from the tendon of the Tibialis posterior. The lateral surface presents a deep notch formed by the commencement of the peroneal sulcus. The For Srd cuneiform For 4(h metatarsal Occasional facet for navicular r. For 5th metatarsal ^^ .,„^™.„.„«. Pero?icEaZ Tuhtroady For calcaneus sulcus A B Fig. 406. — The left cuboid. .-1. Antero-medial view. B. Postero-lateral view. posterior surface is smooth, triangular, and concavo-convex, for articulation with the anterior surface of the calcaneus; its infero-medial angle projects backward as a process which underlies and supports the anterior end of the calcaneus. The anterior surface, of smaller size, but also irregularly triangular, is divided by a vertical ridge into two facets: the medial, quadrilateral in form, articulates with the fourth metatarsal; the lateral, larger and more triangular, articulates with the fifth. The medial surface is broad, irregularly c[uadrilateral, and presents at its middle and upper part a smooth oval facet, for articulation with the third cuneiform; and behind this (occasionally) a smaller facet, for articulation with the navicular ; it is rough in the rest of its extent, for the attachment of strong interosseous ligaments. Articulations. — The cuboid articulates with /owr bones: the calcaneus, third cuneiform, and fourth and fifth metatarsak; occasionally with a fifth, the navicular. For Ist cuneiform For 2nd cuneiform For 3rd cuneiform Occasional ^ facet for cuboid Fig. 407. — The left navicular. A. Antero-lateral view. B. For ialas Tuberosity Postero-medial view. The Navicular Bone {os naviculare pedis; scaphoid bone) (Fig. -107). — The navicular bone is situated at the medial side of the tarsus, between the talus behind and the cuneiform bones in front. THE TARSUS 369 Surfaces. — The anterior surface is convex from side to side, and subdivided by two ridges into three facets, for articuhition with the three cuneiform bones. The posterior surface is oval, concave, broader hiterally than medially, and articulates with the rounded head of the talus. The dorsal surface is convex from side to side, and rough for the attachment of ligaments. The plantar surface is irregular, and also rough for the attachment of ligaments. The medial surface presents a rounded tuberosity, the lower ])art of which gives attachment to part of the tendon of the Tibialis posterior. The lateral surface is rough and irregular for the attachment of ligaments, and occasionally presents a small facet for articulation with the cuboid bone. Articulations. ^The navicular articulates with/o«?- bones: occasionallv with a fifth, the cuboid. the talus and the three cuneiforms; The First Cuneiform Bone (os cuneiform, primum; interned cuneiform) (Fig. 408). — The first cuneiform bone is the largest of the three.cuneiforms. It is situated at the medial side of the foot, between For 1st metatarsal -J For 2nd metatarsal For 2nd cuneiform For tendon of Tibialis anterior For navicular Fig. 40S.- -The left first cuneiform. A. Antero-medial view. B. Postero-lateral view. the navicular behind and the base of the first metatarsal in front. Surfaces. — The medial surface is subcutaneous, broad, and quadrilateral; at its anterior plantar angle is a smooth oval impression, into which part of the tendon of the Tibialis ante- rior is inserted; in the rest of its extent it is rough for the attach- ment of ligaments. The lateral surface is concave, presenting, along its superior and posterior borders a narrow L-shaped sur- face, the vertical limb and pos- terior part of the horizontal limb of which articulate with the second cuneiform, while the anterior part of the horizontal limb articulates with the second metatarsal bone: the rest of this surface is rough for the attachment of ligaments and part of the tendon of the Peronaeus longus. The anterior surface, kidney-shaped and much larger than the posterior, articulates with the first metatarsal bone. The posterior surface is triangular, concave, and articulates with the most medial and largest of the three facets on the anterior surface of the navicular. The plantar surface is rough, and forms the base of the wedge; at its back part is a tuberosity for the insertion of part of the tendon of the Tibialis posterior. It also gives insertion in front to part of the tendon of the Tibialis anterior. The dorsal surface is the narrow end of the wedge, and is directed upward and lateralward; it is rough for the attachment of ligaments. Articulations. — -The first cuneiform articulates with, four bones: the navicular, second cunei- form, and first and second metatarsals. The Second Cuneiform Bone {os cuneiforme secundum; middle cuneiform) (Fig. 409). — The second cuneiform bone, the smallest of the three, is of very regular wedge-like form, the thin end being directed downward. It is situated between the other two cuneiforms, and articulates with the navicular behind, and the second metatarsal in front. Surfaces. — The anterior surface, triangular in form, and narrower than the pos- terior, articulates with the base of the second metatarsal bone. The posterior sur- face, also triangular, articulates with the intermediate facet on the anterior surface 24 370 OSTEOLOGY of the navicular. The medial surface carries an L-shai)e(l articular facet, running along the superior and posterior borders, for articulation Avitli the first cuneiform, and is rough in the rest of its extent for the attachment of ligaments. The lateral surface presents posteriorly a smooth For 1st nmcifonn For navicular facet for articulation with the third cuneiform bone. The dorsal surface forms the base of the wedge; it is quadrilateral and rough for the at- tachment of ligaments. The plantar surface, sharp and tuberculated, is also rough for the attachment of ligaments, and for the insertion of a slip from the tendon of the Tibialis posterior. For 2nd metatarsal For 3rd cuneiform Fig. 409. — The left second cuneiform. A. Antero-medial view. B. Postero-lateral view. Articulations. — The second cuneiform articulates with four bones: the navicular, first and third cuneiforms, and second metatarsal. The Third Cuneiform Bone (os ciineifonne tertium; external cuneiform) (Fig. 410). — The third cuneiform bone, intermediate in size between the two preceding, is wedge-shaped, the base being uppermost. It occupies the centre of the front row of the tarsal bones, between the second cuneiform medially, the cuboid laterally, the navicular behind, and the third metatarsal in front. Surfaces.^ — The anterior surface, triangular in form, articulates with the third metatarsal bone. The posterior surface articulates with the lateral facet on the anterior surface of the navicular, and is rough below for the attachment of liga- mentous fibres. The medial surface presents an anterior and a posterior articular facet, separated by a rough depression: the anterior, sometimes divided, articulates with the lateral side of the base of the second metatarsal bone; the posterior skirts For navicular For 2nd cuneiform Fo7- 4th metatarsal For cuboid For 2nd metatarsal For 3rd metatarsal Fig. 410. — The left third cuneiform. .4. Postero-medial view. B. Antero-lateral view. the posterior border, and articulates with the second cuneiform ; the rough depres- sion gives attachment to an interosseous ligament. The lateral surface also pre- sents two articular facets, separated by a rough non-articular area; the anterior facet, situated at the superior angle of the bone, is small and semi-oval in shape, and articulates with the medial side of the base of the fourth metatarsal bone; the posterior and larger one is triangular or oval, and articulates with the cuboid; the rough, non-articular area serves for the attachment of an interosseous ligament. The three facets for articulation with the three metatarsal bones are continuous with one another; those for articulation with the second cuneiform and navicular are also continuous, but that for articulation with the cuboid is usually separate. The dorsal surface is of an oblong form, its postero-lateral angle being prolonged backward. The plantar surface is a rounded margin, and serves for the attachment THE METATARSUS 371 of i)art of tlic tendon of the "rihialis ])ost('rior, i)art of the Flexor halhieis brevis, and lioaments. Articulations. — Thr tliiid cimciform articulates with six bones: the navicular, second cunei- form, cuboid, and second, (liird, and fourth metatarsals. The Metatarsus. The metatarsus consists of five bones which are numbered from the medial side (ossa meiatarsalia I.-V.); each presents for examination a body and two extremities. Common Characteristics of the Metatarsal Bones. — The body is prismoid in form, tapers gradually from the tarsal to the phalangeal extremity, and is curved longitudinally, so as to be concave below, slightly convex above. The base or posterior extremity is wedge-shaped, articulating proximally with the tarsal bones, and by its sides with the contiguous metatarsal bones: its dorsal and plantar surfaces are rough for the attachment of ligaments. The head or anterior extremity presents a convex articular surface, oblong from above downward, and extend- ing farther backward below than above. Its sides are flattened, and on each is a depression, surmounted by a tubercle, for ligamentous attachment. Its plantar surface is grooved antero-posteriorly for the passage of the Flexor tendons, and marked on either side by an articular eminence continuous with the terminal articular surface. For sesamoid hones For \st For Peronoeus cuneiform longus Fig. 411. — The first metatarsal. (Left.) Foi lit "^ \ cuneifoim For 2nd cuneiform Fig. 412 For 3rd ciLueiforvi The second metatarsal. (Left.) Characteristics of the Individual Metatarsal Bones. — The First Metatarsal Bone {os metatarsale I; metatarsal hone of the great toe) (Fig. 411). — The first metatarsal bone is remarkable for its great thickness, and is the shortest of the metatarsal bones. The body is strong, and of well-marked prismoid form. The base presents, as a rule, no articular facets on its sides, but occasionally on the lateral side there is an oval facet, by which it articulates with the second metatarsal. Its proximal articular surface is of large size and kidney-shaped; its 372 OSTEOLOGY circumference is grooved, for the tarsometatarsal ligaments, and mediall}' gives insertion to part of the tendon of the Tibialis anterior; its i)lantar angle presents a rough oval prominence for the insertion of the tendon of the Peronaeus longus. The head is large; on its plantar surface are two grooved facets, on which glide sesamoid bones; the facets are separated by a smooth elevation. The Second Metatarsal Bone {os metatarsale II) (Fig. 412).- — The second meta- tarsal bone is the longest of the metatarsal bones, being prolonged backward into the recess formed by the three cuneiform bones. Its base is broad above, narrow and rough below. It presents four articular surfaces: one behind, of a triangular form, for articulation with the second cuneiform ; one at the upper part of its medial surface, for articulation with the first cuneiform; and two on its lateral surface, an upper and lower, separated by a rough non-articular interval. Each of these lateral articular surfaces is divided into two by a vertical ridge; the two anterior facets articulate with the third metatarsal; the two posterior (sometimes continuous) with the third cuneiform. A fifth facet is occasionally present for articulation with the first metatarsal; it is oval in shape, and is situated on the medial side of the bodv near the base. For 2nd metatarsal For Zrd cuneiform 413. — The third metatarsal. For Uh metatarsal (Left.) For 37 a meiataibul Foi cuboid For 3rd cuneiform For 5th metatarsal Fig. 414. — The fourth metatarsal. (Left.) The Third Metatarsal Bone (os metatarsale III) (Fig. 413). — The third meta- tarsal bone articulates proximally, by means of a triangular smooth surface, with the third cuneiform; medially, by two facets, with the second metatarsal; and laterally, by a single facet, with the fourth metatarsal. This last facet is situated at the dorsal angle of the base. The Fourth Metatarsal Bone (os metatarsale IV) (Fig. 414). — The fourth meta- tarsal bone is smaller in size than the preceding; its base presents an oblique quadrilateral surface for articulation with the cuboid ; a smooth facet on the medial side, divided by a ridge into an anterior portion for articulation with the third metatarsal, and a posterior portion for articulation with the third cuneiform; on the lateral side a single facet, for articulation with the fifth metatarsal. The Fifth Metatarsal Bone (os metatarsale V) (Fig. 415). — The fifth metatarsal bone is recognized by a rough eminence, the tuberosity, on the lateral side of its THE PHALANGES OF THE FOOT 373 base. The base nrticiilates behind, by a trianguhir surt'aee cut obHquely in a trans- ^'e^se direction, with the cuboid; and medially, with the fourth metatarsal. On the medial part of its dorsal surface is inserted the tendon of the Peronaeus tertius and on the dorsal surface of the tuberosity that of the Peronaeus brevis. A strong band of the plantar aponeurosis connects the i)r()jecting part of the tuberosity with the lateral process of the tuberosity of the calcaneus. The plantar surface of the base is grooved for the tendon of the Abductor digiti quinti, and gives origin to the Flexor digiti quinti brevis. For ith metatarsal For cuboid Tuberosity Fig. 415. — The fifth metatarsal. (Left.) Articulations. — The base of each metatarsal bone articulates with one or more of the tarsal bones, and the head with one of the first row of phalanges. The first metatarsal articulates with the first cuneiform, the second with all three cuneiforms, the third with the third cuneiform, the fourth with the third cuneiform and the cuboid, and the fifth with the cuboid. The Phalanges of the Foot (Phalanges Digitorum Pedis). The phalanges of the foot correspond, in number and general arrangement, with those of the hand; there are two in the great toe, and three in each of the other toes. They differ from them, however, in their size, the bodies being much reduced in length, and, especially in the first row, laterally compressed. First Row. — The phalanges of the first row closely resemble those of the hand. The body of each is compressed from side to side, convex above, concave below. The base is concave; and the head presents a trochlear surface for articulation with the second phalanx. Second Row. — The phalanges of the second row are remarkably small and short, but rather broader than those of the first row. The ungual phalanges, in form, resemble those of the fingers; but they are smaller and are flattened from above downward ; each presents a broad base for articula- tion with the corresponding bone of the second row, and an expanded distal extremity for the support of the nail and end of the toe. Articulations. — In the second, third, fourth, and fifth toes the phalanges of the first row articu- late behind with the metatarsal bones, and in froAt with the second phalanges, which in their turn articulate with the first and third: the imgual phalanges articulate with the second. In 374 OSTEOLOGY the great toe the first phalanx articulates proximally with the metatarsal bone and distaUy with the ungual phalanx. Ossification of the Bones of the Foot (Fig. 416).— The tarsal bones are each ossified from a single centre, excepting the calcaneus, which has an epiphysis for its posterior extremity. The centres make their appearance in the following order: calcaneus at the sixth month of fetal life; talus, about the seventh month; cuboid, at the ninth month; third cuneiform, during the first year; first cuneiform, in the third year; second cuneiform and navicular, in the fourth year. The epiphysis for the posterior extremity of the calcaneus appears at the tenth year, and unites with the rest of the bone soon after puberty. The posterior process of the talus is sometimes ossified from a separate centre, and may remain distinct from the main mass of the bone, when it is named the os trigonum. TARSUS. One centre for each hone, except calcaneus OUTER FOUR METATARSALS. Two centres for each hone One for hody One for head PHALANGES. Two centres for each hone . One for hody One for metatarsal extremity Appears 10th year ; unites after piiberty Appears 3rd year ) Unite 18;h-20th year ^1 \;^''^ "^ %' P -'^l^l^ears 1th week Unite 18-20 yr. I Apps. 3rd yr. - ^^^^ AjJ2J- itii yr. Unite 17-lS yr. I ^^^ App. 2 4 mo. —X is::^ App. 6-7th yr. .^ , Unite 17-18 yr. I ^^^ A2>2}- 2-4 mo. -|\j1: C~"? App.&thyr._ \f Unite 17-18 yr. ?'^ J ^ App. 7th wk. -S^S; Fig. 416. — Plan of ossification of the foot. The metatarsal bones are each ossified from tivo centres: one for the body, and one for the head, of the second, thu-d, fourth, and fifth metatarsals; one for the body, and one for the base, of the first metatarsal.^ Ossification commences in the centre of the body about the ninth week, and extends toward either extremity. The centre for the base of the first metatarsal appears about the third year; the centres for the heads of the other bones between the fifth and eighth years; they join the bodies between the eighteenth and twentieth years. The phalanges are each ossified from tu-o centres: one for the body, and one for the base. The centre for the body appears about the tenth week, that for the base between the fourth and tenth years; it joins the body about the eighteenth year. 1 As was noted in the first metacarpal (see footnote, page 332), so in the first metatarsal, there is often a second epiphysis for its head. COMPARISON OF THE BOXES OF THE IIAXD AXD FOOT 375 Comparison of the Bones of the Hand and Foot. The haiiil and foot are constructed on somewhat siniihir i)rinciples, each con- sisting of a proximal part, the carpus or the tarsus, a middle portion, the meta- carpus, or the metatarsus, and a terminal portion, the phalanges. The proximal part consists of a series of more or less cubical bones which allow a slight amount of gliding on one another and are chiefly concerned in distributing forces transmitted to or from the bones of the arm or leg. The middle part is made up of slightly movable long bones which assist the carpus or tarsus in distributing forces and also give greater breadth for the reception of such forces. The separation of the indi\idual bones from one another allows of the attachments of the Interossei and protects the dorsi-palmar and dorsi-plantar vascular anastomoses. The terminal portion is the most movable, and its separate elements enjoy a varied range of movements, the chief of which are flexion and extension. The function of the hand and foot are, however, very different, and the general similarity between them is greatly modified to meet these requirements. Thus the foot forms a firm basis of support for the body in the erect posture, and is there- fore more solidly built up and its component parts are less movable on each other than those of the hand. In the case of the phalanges the dift'erence is readily noticeable; those of the foot are smaller and their movements are more limited than those of the hand. Very much more marked is the difference between the metacarpal bone of the thumb and the metatarsal bone of the great toe. The meta- carpal bone of the thumb is constructed to permit of great mobility, is directed at an acute angle from that of the index finger, and is capable of a considerable range of movements at its articulation w^ith the carpus. The metatarsal bone of the great toe assists in supporting the weight of the body, is constructed with great solidity, lies parallel with the other metatarsals, and has a very limited degree of mobility. The carpus is small in proportion to the rest of the hand, is placed in line with the forearm, and forms a transverse arch, the concavity of which constitutes a bed for the Flexor tendons and the palmar vessels and nerves. The tarsus forms a considerable part of the foot, and is placed at right angles to the leg, a position which is almost peculiar to man, and has relation to his erect pos- ture. In order to allow of their supporting the weight of the body with the least expenditure of material the tarsus and a part of the metatarsus are constructed in a series of arches (Figs. 417, 418), the disposition of which will be considered after the articulations of the foot have been described. Applied Anatomy. — Considering the injuries to which the foot is subjected, it is sui-prising how seldom the tarsal bones are fractured. This is no doubt due to the fact that the tarsus is composed of a number of bones, articulated by a considerable extent of sm-face, and joined together by verj'^ strong ligaments which serve to break the force of violence appUed to this part of the body. TMien fracture does occur, these bones being composed for the most part of a soft cancellous structm-e, covered only by a thin shell of compact tissue, are often extensively com- minuted, especially as most of the fractm-es are produced by direct violence; and, as there is only a verj' scanty amount of soft parts over the bones, the fractures are very often compound, and amputation is often necessary. TMien fracture occm-s in the anterior gi-oup of tarsal bones, it is almost invariabh' the result of direct violence; but fractm-es of the posterior group — that is, of the calcaneus and talus — are usually produced by falls from a height on to the feet. In club-foot (talipes), especially in congenital cases, the bones of the tarsus become altered in shape and size, and displaced from their proper positions. This is principally the case in con- genital tahpes equinovarus, in which the head of the talus becomes twisted and atrophied, and a similar condition maj- be present in the other bones, more especially the navicular. The tarsal bones are peculiarly hable to become the seat of tuberculous caries following comparativeh' trivial injuries, especiallj' as thej" are not maintained in a condition of rest to the same extent as some other parts of the body after similar injuries. Caries of the calcaneus or talus maj' remain Limited to the one bone for a long period, but when one of the other bones is affected, the remainder 376 OSTEOLOGY frequently become involved, since the disease spreads througii the lurfi;e and complicated synovial membrane which is more or less common to these bones. Amputation of the foot is often required either for injury or disease. The principal amputa- tions are as follows: (1) Syme's: amputation at the ankle-joint by a heel flap, with removal of Fig. 417. — Skeleton of foot. Medial aspect. the malleoli and sometimes a thin shce from the lower end of the tibia. (2) Pirogoff's: amputa- tion of the whole of the tarsal bones (except the posterior part of the calcaneus), and a^thin slice from the tibia and fibula, including the two malleoli. The sawn surface of the calcaneus is then turned up and united to the cut surface of the tibia. (3) Subastragalar: amputation of the^foot below the talus through the joint between it and the calcaneus. Fig. 418. — Skeleton of foot. Lateral aspect. The bones of the tarsus occasionally require removal individually. This is especially the case with the talus for tuberculous disease hmited to that bone; or the talus may require excision in cases of subastragalar dislocation, or in cases of inveterate talipes. The cuboid has been removed for the same reason. Fractures of the metatarsal bones and phalanges are nearly always the result of direct violence, and in the majority of cases the injury is caused by severe crushing accidents, necessitating amputation. The metatarsal bones, and especially that of the great toe, are frequently diseased, either in tuberculous subjects or in patients with perforating ulcer of the foot. The Sesamoid Bones (Ossa Sesamoidea). Sesamoid bones are small more or less rounded masses embedded in certain tendons and usually related to joint surfaces. Their functions probably are to modify pressure, to diminish friction, and occasionally to alter the direction of a muscle pull. That they are not developed to meet certain physical requirements in the adult is evidenced by the fact that they are present as cartilagionus nodules in the fetus, and in greater numbers than in the adult. They must be regarded, according to Thilenius, as integral parts of the skeleton phylogenetically inherited.^ Morpholog. Arbeiten, 1906, v, 309. 77//'; Sl<:SAMOlD BONES 377 Physical necessities probably come into play in selecting and in reoulating the degree of development of the original cartilaginons nodules. Nevertheless, irreg- ular nodules of bone may appear as the result of intermittent i)ressure in certain regions, c. g., the "rider's bone," which is occasionally (levek)ped in the Adductor muscles of the thigh. Sesamoid bones are invested by the fibrous tissue of the tendons, except on the surfaces in contact with the i)arts over which they glide, where they present smooth articular facets. In the upper extremity the sesamoid bones of the joints are found only on the palmar surface of the hand. Two, of which the medial is the the larger, are constant at the metacarpophalangeal joint of the thumb; one is frequently present in the corresponding joint of the little finger, and one (or two) in the same joint of the index finger. Sesamoid bones are also found occasionally at the metacarpophal- angeal joints of the middle and ring fingers, at the interphalangeal joint of the thumb and at the distal interphalangeal joint of the index finger. In the lower extremity the largest sesamoid bone of the joints is the patella, developed in the tendon of the Quadriceps femoris. On the plantar aspect of the foot, two, of which the medial is the larger, are always present at the metatar- sophalangeal joint of the great toe; one sometimes at the metatarsophalangeal joints of the second and fifth toes, one occasionally at the corresponding joint of the third and fourth toes, and one at the interphalangeal joint of the great toe. Sesamoid bones apart from joints are seldom found in the tendons of the upper limb; one is sometimes seen in the tendon of the Biceps brachii opposite the radial tuberosity. They are, however, present in several of the tendons of the lower limb, viz., one in the tendon of the Peronaeus longus, where it glides on the cuboid; one, appearing late in life, in the tendon of the Tibialis anterior, opposite the smooth facet of the first cuneiform bone; one in the tendon of the Tibialis posterior, oppo- site the medial side of the head of the talus; one in the lateral head of the Gastroc- nemius, behind the lateral condyle of the femur; and one in the tendon of the Psoas major, where it glides over the pubis. Sesamoid bones are found occasionally in the tendon of the Glutaeus maximus, as it passes over the greater trochanter, and in the tendons which wind around the medial and lateral malleoli. SYN1)ESM()1.()(JY rpHE bones of the skeleton are joined to one another at dift'erent parts of their J- surfaces, and such connections are termed Joints or Articulations. Where the joints are immovable, as in the articulations between practically all the bones of the skull, the adjacent margins of the bones are almost in contact, being separated merely by a thin layer of fibrous membrane, named the sutural ligament. In certain regions at the base of the skull this fibrous membrane is replaced by a layer of car- tilage. Where slight movement combined with great strength is required, the osseous surfaces are united by tough and elastic fibrocartilages, as in the joints between the vertebral bodies, and in the interpubic articulation. In the freely movable joints the surfaces are completely separated; the bones forming the articulation are ex- panded for greater convenience of mutual connection, covered by cartilage and enveloped by capsules of fibrous tissue. The cells lining the interior of the fibrous capsule form an imperfect membrane — the sjmovial membrane — which secretes a lubricating fluid. The joints are strengthened by strong fibrous bands called ligaments, which extend between the bones forming the joint. Bone. — Bone constitutes the fundamental element of all the joints. In the long bones, the extremities are the parts which form the articulations; they are generally somewhat enlarged; and consist of spongy cancellous tissue with a thin coating of compact substance. In the flat bones, the articulations usually take place at the edges; and in the short bones at various parts of their surfaces. The layer of compact bone which forms the joint surface, and to which the articular cartilage is attached, is called the articular lamella. It differs from ordinary bone tissue in that it contains no Haversian canals, and its lacunee are larger and have no canaliculi. The vessels of the cancellous tissue, as they approach the articular lamella, turn back in loops, and do not perforate it; this layer is con- sequently denser and firmer than ordinary bone, and is evidently designed to form an unyielding support for the articular cartilage. Articular Cartilage. — Articular cartilage, which covers the articular surfaces of bones, and fibrocartilages, which enters into the structure of some of the joints, are described in the section on Histology (pages 47 and 48). Ligaments. — Ligaments are composed mainly of bundles of white fibrous tissue placed parallel with, or closely interlaced with one another, and present a w^hite, shining, silvery appearance. They are pliant and flexible, so as to allow perfect freedom of movement, but strong, tough, and inextensible, so as not to yield readily to applied force. Some ligaments consist entirely of yellow elastic tissue, as the ligamenta flava which connect together the lamince of adjacent vertebrae, and the ligamentum nuchae in the lower animals. In these cases the elasticity of the ligament is intended to act as a substitute for muscular power. The Articular Capsules. — The articular capsules form complete envelopes for the freely movable joints. Each capsule consists of two strata — an external {stratum fibrosum) composed of white fibrous tissue, and an internal (stratum synoviale) which is a secreting layer, and is usually described separately as the synovial membrane. The fibrous capsule is attached to the whole circumference of the articular end of each bone entering into the joint, and thus entirely surrounds the articulation. 380 SYNDESMOLOGY The synovial membrane imests the inner surface of the fibrous capsule, and is reflected over any tendons i)assing through the joint cavity, as the tendon of the Popliteus in the knee, and the tendon of the Biceps brachii in the shoulder. It is composed of a thin, delicate, connective tissue, with branched connective-tissue corpuscles Its secretion is thick, viscid, and glairy, like the white of an egg, and is hence termed synovia. In the fetus this membrane is said, by Toynbee, to be continued over the surfaces of the cartilages; but in the adult such a continuation is wanting, excepting at the circumference of the cartilage, upon which it encroaches for a short distance and to which it is firmly attached. In some of the joints the synovial membrane is thrown into folds which pass across the cavity; they are especially distinct in the knee. In other joints there are flattened folds, subdivided at their margins into fringe-like processes which contain convoluted vessels. These folds generally project from the synovial membrane near the margin of the cartilage, and lie flat upon its surface. They consist of connective tissue, covered with endothelium, and contain fat cells in variable quantities, and, more rarely, isolated cartilage cells; the larger folds often contain considerable quantities of fat. Closely associated with synovial membrane, and therefore conveniently described in this section, are the mucous sheaths of tendons and the mucous bursse. Mucous sheaths (vaginae mucosae) serve to facilitate the gliding of tendons in fibroosseous canals. Each sheath is arranged in the form of an elongated closed sac, one layer of w^hich adheres to the wall of the canal, and the other is reflected upon the surface of the enclosed tendon. These sheaths are chiefly found surround- ing the tendons of the Flexor and Extensor muscles of the fingers and toes as they pass through fibroosseous canals in or near the hand and foot. Bursae mucosae are interposed between surfaces which glide upon each other. They consist of closed sacs containing a minute quantity of clear viscid fluid, and may be grouped, according to their situations, under the headings subcutaneous, submuscular, subfacial, and subtendinous. CLASSIFICATION OF JOINTS. The articulations are divided into three classes: synarthroses or immovable, amphiarthroses or slightly movable, and diarthroses or freely movable, joints. Synarthroses (immovable articulations). — Synarthroses include all those articu- lations in which the surfaces of the bones are in almost direct contact, fastened together by intervening connective tissue or hyaline cartilage, and in which there is no appreciable motion, as in the joints between the bones of the skull, excepting those of the mandible. There are four varieties of synarthrosis: sutura, schindylesis, gomphosis, and synchondrosis. Suturalligament .^^^\ / Cartilage Periosteum '.•■•■- -^rn w / Pericliondrii Periosteum Fig. 419. — Section across the sagittal suture. Fig. 420. — Section through occipitosphenoid synchon- drosis of an infant. Sutura. — Sutura is that form of articulation where the contiguous margins of the bones are united by a thin layer of fibrous tissue; it is met with only in the skull (Fig. 419). When the margins of the bones are connected by a series of processes, and indentations interlocked together, the articulation is termed a true suture CLASS! FIC AT JOX OF JOIXTS 381 (sntiira irra); aiul of this there are three \urieties: sutura dentata, serrata, and limbosa. The margins of the bones are not in direct contact, being separated by a thin hiyer of fibrous tissue, continuous externally with the pericranium, internally with the dura mater. The sutura dentata is so called from the tooth-like form of the projecting processes, as in the suture between the parietal bones. In the sutura serrata the edges of the bones are serrated like the teeth of a fine saw, as between the two portions of the frontal bone. In the sutura limbosa, there is besides the interlocking, a certain degree of bevelling of the articular surfaces, so that the bones overlap one another, as in the suture between the parietal and frontal bones. When the articulation is formed by roughened surfaces placed in apposition with one another, it is termed a false suture {siititm notlia), of which there are two kinds: the sutura squamosa, formed by the overlapping of contiguous bones by broad bevelled margins, as in the squamosal suture between the temporal and parietal, and the sutura harmonia, where there is simple apposition of contiguous rough surfaces, as in the articulation between the maxilla?, or between the horizontal parts of the palatine bones. Schindylesis. — Schindylesis is that form or articulation in which a thin plate of bone is received into a cleft or fissure formed by the separation of two lamina? in another bone, as in the articulation of the rostrum of the sphenoid and perpendicular plate of the ethmoid with the vomer, or in the reception of the latter in the fissure between the maxillte and between the palatine bones. Gomphosis. — Gomphosis is articulation by the insertion of a conical process into a socket; this is not illustrated by any articulation between bones, properly so called, but is seen in the articulations of the roots of the teeth with the alveoli of the mandible and maxillse. Synchondrosis. — Where the connecting medium is cartilage the joint is termed a synchondrosis (Fig. 420). This is a temporary form of joint, for the cartilage is converted into bone before adult life. Such joints are found between the epiphyses and bodies of long bones, between the occipital and the sphenoid at, and for some years after, birth, and between the petrous portion of the temporal and the jugular process of the occipital. Amphiarthroses [slightly movable articulations). — In these articulations the contiguous bony surfaces are either connected by broad flattened disks of fibro- cartilage, of a more or less complex struc- ture, as in the articulations between the bodies of the vertebrae; or are united by an Ligamenu interosseous ligament, as in the inferior '^'.''^ '^^ 7 ' tibiofibular articulation. The first form is a.,- 1°^^'^' !^r 1 ,.,„.,-,,, ^1 1 Articular cartilage. termed a symphysis (hig. 421), the second a syndesmosis. DiarthrOSeS (freely movable articulations). Fig. 421.— Diagrammatic section of a symphysis. — This class includes the greater number of the joints in the body. In a diarthrodial joint the contiguous bony surfaces are covered with articular cartilage, and connected by ligaments lined by synovial membrane (Fig. 422). The joint may be divided, completely or incompletely, by an articular disk or meniscus, the periphery of which is continuous with the fibrous capsule while its free surfaces are covered by synovial membrane (Fig. 423). The varieties of joints in this class have been determined by the kind of motion permitted in each. There are two varieties in which the movement is uniaxial, that is to say, all movements take place around one axis. In one form, the ginglymus, this axis is, practically speaking, transverse; in the other, the trochoid or pivot- joint, it is longitudinal. There are two varieties where the movement is biaxial, or around two horizontal axes at right angles to each other, or at any intervening 382 SYNDESMOLOGY axis between the two. These are the condyloid and X\\v saddle-joint. There is one form where the movement is polyaxial, the enarthrosis or ball-and-socket joint; and finally there are the arthrodia or gliding joints. Articular cartilage Synovial memhrane Fibrous capsule Fig. 422. — Diagrammatic section of a diarthrodial joint. Synovial memhrane Articular cartilage Articular disc Fibrous capsule Fig. 423. — Diagrammatic section of a diarthrodial joint, with an articular disk. Ginglymus or Hinge-joint.- — In this form the articular surfaces are moulded to each other in such a manner as to permit motion only in one plane, forward and backward, the extent of motion at the same time being considerable. The direction wdiich the distal bone takes in this motion is seldom in the same plane as that of the axis of the proximal bone; there is usually a certain amount of devia- tion from the straight line during flexion. The articular surfaces are connected together by strong collateral ligaments, which form their chief bond of union. The best examples of ginglymus are the interphalangeal joints and the joint between the humerus and ulna; the knee- and ankle-joints are less typical, as they allow a slight degree of rotation or of side-to-side movement in certain positions of the limb. Trochoid or Pivot-joint (articulatio trochoidea; rotary joint). — Where the movement is limited to rotation, the joint is formed by a pivot-like process turning within a ring, or a ring on a pivot, the ring being formed partly of bone, partly of ligament. In the proximal radioulnar articulation, the ring is formed by the radial notch of the ulna and the annular ligament; here, the head of the radius rotates w^ithin the ring. In the articulation of the odontoid process of the axis with the atlas the ring is formed in front by the anterior arch, and behind b}^ the transverse ligament of the atlas; here, the ring rotates around the odontoid process. Condyloid Articulation {articulatio ellipsoidea). — In this form of joint, an ovoid articular surface, or condyle, is received into an elliptical cavity in such a manner as to permit of flexion, extension, adduction, abduction, and circumduction, but no axial rotation. The wrist-joint is an example of this form of articulation. Articulation by Reciprocal Reception {articidatio sellaris; saddle-joint). — In this variety the opposing surfaces are reciprocally concavo-convex. The movements are the same as in the preceding form ; that is to say, flexion, extension, adduction, abduction, and circumduction are allowed; but no axial rotation. The best example of this form is the carpometacarpal joint of the thumb. Enarthrosis (ball-and-socket joints) . — Enarthrosis is a joint in which the distal bone is capable of motion around an indefinite number of axes, which have one common centre. It is formed by the reception of a globular head into a cup-like cavity, hence the name "ball-and-socket." Examples of this form of articulation are found in the hip and shoulder. Arthrodia {gliding joints) is a joint which admits of only gliding movement; it is formed by the apposition of plane surfaces, or one slightly concave, the other slightly convex, the amount of motion between them being limited by the ligaments THE KIXDS OF MOVEMENT ADMITTED IX ,101 XT S 383 or osseous processes surroiiiiding the articulation. It is the form present in the joints between the articuUir processes of the \'ertebr8e, the car])al joints, except that of the capitate with the navicular and lunate, and the tarsal joints with the exception of that between the talus and the navicular. THE KINDS OF MOVEMENT ADMITTED IN JOINTS. The movements admissible in joints may be divided into four kinds: gliding and angular movements, circumduction, and rotation. These movements are often, however, more or less combined in the various joints, so as to produce an infinite variety, and it is seldom that onh' one kind of motion is found in any particular joint. Gliding Movement. — Gliding movement is the simplest kind of motion that can take place in a joint, one surface gliding or moving over another without any angular or rotatory movement. It is common to all movable joints; but in some, as in most of the articulations of the carpus and tarsus, it is the only motion per- mitted. This movement is not confined to plane surfaces, but may exist between any two contiguous surfaces, of whatever form. Angular Movement. — Angular movement occurs only between the long bones, and by it the angle between the two bones is increased or diminished. It may take place: (1) forward and backward, constituting flexion and extension; or (2) toward and from the median plane of the body, or, in the case of the fingers or toes, from the middle line of the hand or foot, constituting adduction and abduction. The strictly ginglymoid or hinge-joints admit of flexion and extension only. Abduc- tion and adduction, combined with flexion and extension, are met with in the more movable joints; as in the hip, the shoulder, the wrist, and the carpometacarpal joint of the thumb. Circumduction.^ — Circumduction is that form of motion which takes place between the head of a bone and its articular cavity, when the bone is made to circumscribe a conical space; the base of the cone is described by the distal end of the bone, the apex is in the articular cavity ; this kind of motion is best seen in the shoulder- and hip-joints. Rotation.- — Rotation is a form of movement in which a bone moves around a central axis without undergoing any displacement from this axis ; the axis of rota- tion may lie in a separate bone, as in the case of the pivot formed by the odontoid process of the axis vertebrae around which the atlas turns; or a bone may rotate around its ownTongitudinal axis, as in the rotation of the humerus at the shoulder- joint; or the axis of rotation may not be quite parallel to the long axis of the bone, as in the movement of the radius on the ulna during pronation and supina- tion of the hand, where it is represented by a line connecting the centre of the head of the radius above with the centre of the head of the ulna below. Ligamentous Action of Muscles. — The movements of the different joints of a hmb are combined by means of the long muscles passing over more than one joint. These, when relaxed and stretched to their greatest extent, act as elastic hgaments in restraining certain movements of one joint, except when combined with corresponding movements of the other — the latter movements being usually in the opposite direction. Thus the shortness of the hamstring muscles prevents com- plete flexion of the hip, unless the knee-joint is also flexed so as to bring their attachments nearer together. The uses of this arrangement are threefold: (1) It coordinates the kinds of move- ments which are the most habitual and necessary, and enables them to be performed with the least expenditure of power. (2) It enables the short muscles which pass over only one joint to act upon more than one. (3) It provides the joints with ligaments which, while they are of very great power in resisting movements to an extent incompatible with the mechanism of the joint, at the same time spontaneously yield when necessary. Applied Anatomy. — W. W. Keen points out how important it is "that the svn-geon should remember this ligamentous action of muscles in making passive motion — for instance, at the wrist 384 SYXDESMOLOGY after Colles' fracture. If the fingers be extended, the wrist can be flexed to a right angle. If, however, they be first flexed as in 'making a fist,' flexion at the wrist is quickty Umited to from fort}' to fifty degrees in different persons, and is very painful Vjeyond that point. Hence passive motion here should be made with the fingers extended. In the leg, when flexing the hip, the knee should be flexed." The articulations ma>' be grou})e(l into those of the trunk, and those of the upper and hnver extremities. ARTICULATIONS OF THE TRUNK. These may be divided into the following groups, viz.: I. Of the Vertebral Column. ^T. Of the Cartilages of the Ribs with the II. Of the Atlas with the Axis. Sternum, and with Each Other. III. Of the Vertebral Column with VII. Of the Sternum. the Cranium. ^TII. Of the vertebral Column with the IV. Of the Mandible. Pelvis. V. Of the Ribs with the Vertebrse. IX. Of the Pelvis. I. Articulations of the Vertebral Column. The articulations of the vertebral column consist of (1) a series of amphi- arthrodial joints between the vertebral bodies, and (2) a series of diathrodial joints between the vertebral arches. 1. Articulations of Vertebral Bodies (intercentral ligaments). — The articulations between the bodies of the vertebrse are amphiarthrodial joints, and the individual vertebrae move only slightly on each other. When, however, this slight degree of movement between the pairs of bones takes place in all the joints of the vertebral column, the total range of movement is very considerable. The ligaments of these articulations are the following: The Anterior Longitudinal. The Posterior Longitudinal. The Intervertebral Fibrocartilages. The Anterior Longitudinal Ligament (ligamentum longitudinale anterius; anterior common ligament) (Figs. 424, 435). — The anterior longitudinal ligament is a broad and strong band of fibres, which extends along the anterior surfaces of the bodies of the vertebrae, from the axis to the sacrum. It is broader below than above, thicker in the thoracic than in the cervical and lumbar regions, and somewhat thicker opposite the bodies of the vertebrse than opposite the intervertebral fibro- cartilages. It is attached, above, to the body of the axis, where it is continuous with the anterior atlantoaxial ligament, and extends down as far as the upper part of the front of the sacrum. It consists of dense .longitudinal fibres, which are intimately adherent to the intervertebral fibrocartilages and the prominent margins of the vertebrae, but not to the middle parts of the bodies. In the latter situation the ligament is thick and serves to fill up the concavities on the anterior surfaces, and to make the front of the vertebral column more even. It is composed of several layers of fibres, which vary in length, but are closely interlaced with each other. The most superficial fibres are the longest and extend between four or five vertebrse. A second, subjacent set extends between two or three vertebrae; while a third set, the shortest and deepest, reaches from one vertebra to the next. At the sides of the bodies the ligament consists of a few short fibres which pass from one vertebra to the next, separated from the concavities of the vertebral bodies by oval apertures for the passage of vessels. Afx'TlCLLATIOXS OF THE VERTEBRAL COLUMX 385 The Posterior Longitudinal Ligament (li(/a)n('itfuni lougiiudhidJc posierius; posterior collision lu/atiif')ii) (Figs. 424, 4'2r)). — The posterior longitudinal ligament is situated within the vertebral canal, and extends along the posterior surfaces of the bodies Fig. 424. — Median sagittal section of two lumbar vertebrae and their ligaments. Pedicle (cut) Intervertebral fibrocariilage of the vertebra?, from the body of the axis, where it is continuous with the membrana tectoria, to the sacrum. It is broader above than below, and thicker in the thoracic than in the cervical and lumbar regions. In the situation of the intervertebral fibrocartilages and contiguous margins of the vertebrae, where the ligament is more intimately adherent, it is broad, and in the thoracic and lumbar regions presents a series of dentations with intervening concave margins ; but it is narrow and thick over the centres of the bodies, from which it is separated by the basivertebral veins. This ligament is com- posed of smooth, shining, longitudinal fibres, denser and more compact than those of the anterior ligament, and consists of superficial layers occupying the interval between three or four vertebrae, and deeper layers which ex- tend between adjacent vertebrae. The Intervertebral Fibrocartilages (fibrocariil- agines intervertebrales; intervertebral disks) (Figs. 424, 436). — The intervertebral fibrocartilages are interposed between the adjacent surfaces of the bodies of the vertebra?, from the axis to the sacrum, and form the chief bonds of connection between the vertebrae. They vary in shape, size, and thickness, in different parts of the verte- bral column. In shape and size they correspond with the surfaces of the bodies between which they are placed, except in the cervical region, where they are slightly smaller from side to side than the corresponding bodies. In thickness they vary Fig. 425.- -Posterior longitudinal ligament, in the thoracic region. 386 SYNDESMOLOGY not only in the different regions of the cokimn, but in different parts of the same fibrocartilage ; they are thicker in front than behind in the cervical and lumbar regions, and thus contribute to the anterior convexities of these parts of the column; while they are of nearly uniform thickness in the thoracic region, the anterior con- cavity of this part of the column being almost entirely owing to the shape of the vertebral bodies. The intervertebral fibrocartilages constitute about one-fourth of the length of the vertebral column, exclusive of the first two vertebrae; but this amount is not equally distributed between the various bones, the cervical and lumbar portions having, in proportion to their length, a much greater amount than the thoracic region, with the result that these parts possess greater pliancy and freedom of movement. The intervertebral fibrocartilages are adherent, by their surfaces, to thin layers of hyaline cartilage which cover the upper and under surfaces of the bodies of the vertebrae; in the lower cervical vertebrse, however, small joints lined by synovial membrane are occasionally present between the upper surfaces of the bodies and the margins of the fibrocartilages on either side. By their circumferences the intervertebral fibrocartilages are closely con- nected in front to the anterior, and behind to the posterior, longitudinal liga- ments. In the thoracic region they are joined laterally, by means of the inter- articular ligaments, to the heads of those ribs which articulate with two vertebrse. Structure of the Intervertebral Fibrocartilages. — Each is composed, at its circumference, of laminse of fibrous tissue and fibrocartilage, forming the annulus fibrosus; and, at its centre, of a soft, pulp 5^, highly elastic substance, of a yellowish color, which projects considerably above the surrounding level when the disk is divided horizontally. This pulpy substance {nucleus pulposus), especially well-developed in the lumbar region, is the remains of the notochord. The laminse are arranged concentrically; the outermost consist of ordinary fibrous tissue, the others of white fibrocartilage. The laminse are not quite vertical in their direction, those near the cir- cimxference being curved outward and closely approximated; while those nearest the centre curve in the opposite direction, and are somewhat more widely separated. The fibres of which each lamina is composed are directed, for the most part, obhquely from above downward, the fibres of adjacent laminse passing in opposite directions and varying in every layer; so that the fibres of one layer are directed across those of another, like the Umbs of the letter X. This laminar arrangement belongs to about the outer half of each fibrocartilage. The pulpy substance presents no such arrangement, and consists of a fine fibrous matrix, containing angular cells united to form a reticular structure. Applied Anatomy. — When an aneurism presses on the vertebral column, the vertebral bodies are often deeply eroded by the tumor, while the intervertebral fibrocartilages remain intact. The fibrocartilages are the first to be destroyed, however, in tuberculosis of the vertebral coliunn, where, as not infrequently happens, the disease begins in the fibrocartilages, and spreads thence to the bodies of the two adjoining vertebrse simultaneously. 2. Articulations of Vertebral Arches. — The joints between the articular pro- cesses of the vertebrse belong to the arthrodial variety and are enveloped by capsules lined by synovial membranes; while the laminae spinous and transverse processes are connected by the following ligaments: The Ligamenta Flava. The Ligamentum Nuchae. The Supraspinal. The Interspinal. The Intertransverse. The Articular Capsules (capsulae articulares; capsular ligaments) (Fig. 424). — The articular capsules are thin and loose, and are attached to the margins of the articular processes of adjacent vertebrae. They are longer and looser in the cervical than in the thoracic and lumbar regions. The Ligamenta Flava {ligmenta subflava (Fig. 426). — The ligamenta flava connect the laminae of adjacent vertebrae, from the axis to the first segment of the sacrum. They are best seen from the interior of the vertebral canal ; when looked at from the outer surface they appear short, being overlapped by the laminse. Each ligament ARTICULATIONS OF THE VERTEBRAL COLUMN 387 Pedicle {cut) Lamina Fig. 426. — Vertebral arches of three thoracic vertebrae ^'iewed from the front. consists of two lateral portions which commence one on either side of the roots of the articular processes, and extend backA\ard to the point where the laminae meet to form the spinous process ; the posterior margins of the two portions are in contact and to a certain extent united, slight intervals being left for the passage of small vessels. Each consists of yellow elastic tissue, the fibres of which, almost perpendicular in direction, are at- tached to the anterior surface of the lamina above, some distance from its inferior margin, and to the posterior surface and upper margin of the lamina below. In the cervical region the ligaments are thin, but broad and long; they are thicker in the thoracic region, and thickest in the lumbar region. Their marked elasticity serves to preserve the up- right posture, and to assist the vertebral column in resuming it after flexion. The Supraspinal Ligament (liga- mentum supraspinale; supraspinous ligament) (Fig. 424). — The supra- spinal ligament is a strong fibrous cord, which connects together the apices of the spinous processes from the seventh cervical vertebra to the sacrum; at the points of attachment to the tips of the spinous processes fibrocartilage is developed in the ligament. It is thicker and broader in the lumbar than in the thoracic region, and intimately blended, in both situations, with the neighboring fascia. The most superficial fibres of this ligament extend over three or four vertebrae; those more deeply seated pass between two or three vertebrae ; w^hile the deepest connect the spinous processes of neighboring vertebrae. Between the spinous processes it is continuous with the interspinal ligaments. It is continued upward to the external occipital protuberance and median nuchal line, as the ligamentum nuchae. The Ligamentum Nuchae.^ — The ligamentum nuchae is a fibrous membrane, which, in the neck, represents the supraspinal ligaments of the lower vertebrae. It extends from the external occipital protuberance and median nuchal line to the spinous process of the seventh cervical vertebra. From its anterior border a fibrous lamina is given oft', which is attached to the posterior tubercle of the atlas, and to the spinous processes of the cervical vertebrae, and forms a septum between the muscles on either side of the neck. In man it is merely the rudiment of an important elastic ligament, which, in some of the lower animals, serves to sustain the weight of the head. The Interspinal Ligaments (ligamenta inter spinalia; interspinous ligaments) (Fig. 424). — The interspinal ligaments thin and membranous, connect adjoining spinous processes and extend from the root to the apex of each process. They meet the ligamenta flava in front and the supraspinal ligament behind. They are narrow and elongated in the thoracic region; broader, thicker, and quadrilateral in form in the lumbar region; and only slightly developed in the neck. The Intertransverse Ligaments (ligamenta intertransversaria) . — The intertransverse ligaments are interposed between the transverse processes. In the cervical region they consist of a few irregular, scattered fibres; in the thoracic region they are rounded cords intimately connected with the deep muscles of the back; in the lumbar region they are thin and membranous. 388 SYNDESMOLOGY Movements. — The movements permitted in the vertebral cohunn are: flexion, extension, lateral moroneiU, circumduction, and rotation. In flexion, or movement forward, the anterior longitudinal ligament is relaxed, and the inter- vertebral fibrocartilages are cornpressed in front; while the posterior longitudinal ligament, the Ugamenta flava, and the inter- and supraspinal ligaments are stretched, as well as the posterior fibres of the intervertebral fibrocartilages. The interspaces between the lamina; are widened, and the inferior articular processes glide upward, upon the superior articular processes of the subjacent vertebrae. Flexion is the most extensive of all the movements of the vertebral column, and is freest in the lumbar region. In extension, or movement backward, an exactly opposite disposition of the parts takes place. This movement is Umited by the anterior longitudinal ligament, and by the approximation of the spinous processes. It is freest in the cervical region. In lateral movement, the sides of the intervertebral fibrocartilages are compressed, the extent of motion being limited by the resistance offered by the surrounding ligaments. This movement may take place in any part of the column, but is freest in the cervical and lumbar regions. Circumduction is verj^ limited, and is merely a succession of the preceding movements. Rotation is produced by the twisting of the intervertebral fibrocartilages; this, although only shght between any two vertebra;, allows of a considerable extent of movement when it takes place in the whole length of the column, the front of the upper part of the column being turned to one or other side. This movement occurs to a shght extent in the cervical region, is freer in the upper part of the thoracic region, and absent in the lumbar region. The extent and variety of the movements are influenced by the shape and direction of the articular surfaces. In the cervical region the upward incUnation of the superior articular surfaces allows of free flexion and extension. Extension can be carried farther than flexion; at the upper end of the region it is checked by the locking of the posterior edges of the superior atlantal facets in the condyloid fossae of the occipital bone; at the lower end it is limited bj^ a mechanism whereby the inferior articular processes of the seventh cervical vertebra slip into grooves behind and below the superior articular processes of the first thoracic. Flexion is arrested just beyond the point where the cervical convexity is straightened; the movement is checked by the apposition of the projecting lower Lips of the bodies of the vertebrae with the shelving surfaces on the bodies of the subjacent vertebrae. Lateral flexion and rotation are free in the cervical region; they are, however, always combined. The upward and medial inclinations of the superior articular surfaces impart a rotator}^ movement during lateral flexion, while pure rotation is prevented by the slight medial slope of these surfaces. In the thoracic region, notably in its upper part, all the movements are limited in order to reduce interference with respiration to a minimum. The ahnost complete absence of an upward incUnation of the superior articular surfaces prohibits any marked flexion, while extension is checked by the contact of the inferior articular margins with the laminae, and the contact of the spinous processes with one another. The mechanism between the seventh cervical and the first thoracic vertebrae, which limits extension of the cervical region, will also serve to limit flexion of the thoracic region when the neck is extended. Rotation is free in the thoracic region: the superior articular processes are segments of a cyUnder whose axis is in the mid-ventral line of the vertebral bodies. The direction of the articular facets would allow of free lateral flexion, but this movement is considerably limited in the upper part of the region by the resistance of the ribs and sternum. In the lumbar region flexion and extension are free. Flexion can be carried farther than exten- sion, and is possible to just beyond the straightening of the lumbar curve; it is, therefore, greatest at the lowest part where the curve is sharpest. The inferior articular facets are not in close appo- sition with the superior facets of the subjacent vertebrae, and on this account a considerable amoimt of lateral flexion is permitted. For the same reason a slight amount of rotation can be carried out, but this is so soon checked by the interlocking of the articular surfaces that it is negligible. The principal muscles which produce flexion are the Sternocleidomastoideus, Longus capitis, and Longus coUi; the Scaleni; the abdominal muscles and the Psoas major. Extension is produced by the intrinsic muscles of the back, assisted in the neck by the Splenius, Semispinales dorsi and cervicis, and the Mtdtifidus. Lateral motion is produced by the intrinsic muscles of the back by the Splenius, the Scaleni, the Quadratus lumborum, and the Psoas major, the muscles of one side only acting; and rotation by the action of the following muscles of one side only, viz., the Sternocleidomastoideus, the Longus capitis, the Scaleni, the IMultifidus, the Semispinalis capitis, and the abdominal muscles. n. Articulation of the Atlas with the Epistropheus or Axis (Articulatio Atlantoepistrophica) . The articulation of the atlas with the axis is of a complicated nature, com- prising no fewer than four distinct joints. There is a pivot articulation between ARTICULATIOX OF THE ATLAS WITH THE EPISTROPHEUS OR AXIS 389 the odontoid process of the axis and the rin^- formed by the anterior arch and the tranversc hgament of the athis (see Fig. 429); here there are two joints: one between the posterior surface of the anterior arch of the atlas and the front of the odontoid process; the other between the anterior surface of the ligament and the back of the process. Between the articular processes of the two bones there is on either side an arthrodial or gliding joint. The ligaments connecting these bones are: Two Articular Capsules. The Anterior Atlantoaxial. The Posterior Atlantoaxial. The Transverse. The Articular Capsules {capsidae articulares; cajjsular ligaments) . — The articular capsules are thin and loose, and connect the margins of the lateral masses of the atlas with those of the posterior articular surfaces of the axis. Each is strength- ened at its posterior and medial part by an accessory ligament, which is attached below to the body of the axis near the base of the odontoid process, and above to the lateral mass of the atlas near the transverse ligament. Atlanto- ocoipital f Articular capsule -[ and [^synovial membrane tlanto- al f Articular capsule and ysynovial membrane Fig. 427. — Anterior atlantoocoipital membrane and atlantoaxial ligament. The Anterior Atlantoaxial Ligament (Fig. 427). — This ligament is a strong mem- brane, fixed, above, to the lower border of the anterior arch of the atlas; below, to the front of the body of the axis. It is strengthened in the middle line by a rounded cord, which connects the tubercle on the anterior arch of the atlas to the body of the axis, and is a continuation upward of the anterior longitudinal liga- ment. The ligament is in relation, in front, with the Longi capitis. The Posterior Atlantoaxial Ligament (Fig. 428). — This ligament is a broad, thin membrane attached, above, to the lower border of the posterior arch of the atlas; below, to the upper edges of the laminae of the axis. It supplies the place of the ligamenta flava, and is in relation, behind, with the Obliqui capitis inferiores. The Transverse Ligament of the Atlas (ligamentum transversum atlantis) (Figs. 429, 430, 431).- — The transverse ligament of the atlas is a thick, strong band, which arches across the ring of the atlas, and retains the odontoid process in contact with the anterior arch. It is concave in front, convex behind, broader and thicker in 390 SYNBESMOLOGY the middle than at the ends, and firml}' attached on either side to a small tubercle on the medial surface of the lateral mass of the atlas. As it crosses the odontoid process, a small fasciculus {cms superius) is prolonged upward, and another {cms inferius) downward, from the superficial or posterior fibres of the ligament. The Arch for passage of vertebral artery and first cervical nerve Fig. 428. — Posterior atlantooccipital membrane and atlantoaxial ligament. former is attached to the basilar part of the occipital bone, in close relation with the membrana tectoria; the latter is fixed to the posterior surface of the body of the axis; hence, the whole ligament is named the cruciate ligament of the atlas. The transverse ligament divides the ring of the atlas into two unequal parts: of these, the posterior and larger serves for the transmission of the medulla spinalis Fig. 429. — Articulation between odontoid process and atlas. and its membranes and the accessory nerves; the anterior and smaller contains the odontoid process. The neck of the odontoid process is constricted where it is embraced posteriorly by the transverse ligament, so that this ligament suffices to retain the odontoid process in position after all the other ligaments have been divided. ARTICULATIOX OF THE ATLAS WITH THE EPISTROPHEUS OR AXIS 391 1 '— Anneal odontoid liijainent Atlanta, f Articular capsule _,.,- -f 7-! and ipitai. \^,^,pi„„i(i,i membrane C Articular capside Atlanto-j ^,,^,, ^ axi a i y synovial membrane Fig. 430. — Membrana tectoria, transverse, and alar ligaments. Anterior atlanto- occipital membrane Membrana tectoria Crus superius of transverse ligament Apical odont. lig. Ant. arch of atlas Odontoid process of axis Articular cavity Transverse ligament Anterior atlanto- axial ligament Intervertebral fhrocartilage Anterior longitudinal ligament S II pel fie ml layer of membrana tectoria Ganalis hypoglossi Posterior ailanto- cccipital membrane 'gVJ*\ Posterior arch ^""•^ ' of atlas Suboccipital nerve Posterior longitudinal ligament Fig. 431.— Median sagittal section through the occipital bone and first three cervical vertebra. (Spalteholz.) 392 SYNDESMOLOGY Synovial Membranes. — There is a synovial membrane for each of the torn- joints; the joint cavity bet^Yeen the odontoid process and the transverse ligament is often continuous with those of the atlantooccipital articulations. The opposed articular surfaces of the atlas and axis are not reciprocally curved; both surfaces are convex in their long axes. When, therefore, the upper facet glides forward on the lower it Movements.— This joint allows the rotation of the atlas (and, with it, the skull) upon the axis, the extent of rotation being hmited by the alar hgaments. also descends; the fibres of the articular capsule are relaxed in a vertical direction, and will then permit of movement in an antero-posterior direction. By this means a shorter capsule suffices and the strength of the joint is materially increased.^ The principal muscles by w^hich these movements are produced are the Sternocleidomastoideus and Semispinalis capitis of one side, acting with the Longus capitis, Splenius, Longissimus capitis, Rectus capitis posterior major, and Obliqui capitis superior and inferior of the other side. III. Articulations of the Vertebral Column with the Cranium. The ligaments connecting the vertebral column with the cranium may be divided into two sets: those uniting the atlas with the occipital bone, and those connecting the axis with the occipital bone. • Articulation of the Atlas with the Occipital Bone {articulatio atlantooccipitalis) . —The articulation between the atlas and the occipital bone consists of a pair of condyloid joints. The ligaments connecting the bones are : Two Articular Capsules. The Posterior Atlantooccipital The Anterior Atlantooccipital membrane. membrane. Two Lateral Atlantooccipital, The Articular Capsules {capsulae articulares; capsular ligaments). — The articular capsules surround the condyles of the occipital bone, and connect them with the articular processes of the atlas: they are thin and loose. The Anterior Atlantooccipital Membrane {memhrana atlantooccipitalis anterior; , anterior atlantodccipital ligament) (Fig. 427).— The anterior atlantooccipital mem- brane is broad and composed of densely woven fibres, which pass between the anterior margin of the foramen magnum above, and the upper border of the anterior arch of the atlas below; laterally, it is continuous with the articular capsules; in front, it is strengthened in the middle line by a strong, rounded cord, which connects the basilar part of the occipital bone to the tubercle on the anterior arch of the atlas. This membrane is in relation in front with the Recti capitis anteriores, behind with the alar ligaments. The Posterior Atlantooccipital Membrane {memhrana atlantooccipitalis posterior; posterior atlantooccipital ligament) (Fig. 428).— The posterior atlantooccipital mem- brane, broad but thin, is connected above, to the posterior margin of the foramen magnum; below, to the upper border of the posterior arch of the atlas. On either side this membrane is defective below, over the groove for the vertebral artery, and forms with this groove an opening for the entrance of the artery and the exit of the suboccipital nerve. The free border of the membrane, arching over the artery and nerve, is sometimes ossified. The membrane is in vdoXiow, behind, with the Recti capitis posteriores minores and Obliqui capitis superiores; \\\ front, with the dura mater of the vertebral canal, to which it is intimately adherent. The Lateral Ligaments.— The lateral ligaments are thickened portions of the articular capsules, reinforced by bundles of fibrous tissue, and are directed obliquely upward and medialward; they are attached above to the jugular processes of the occipital bone, and below, to the bases of the transverse processes of the atlas. 1 Corner ("The Phj^siology of the Atlanto-axial Joints," Journal of Anatomy and Physiology, vol. xli) states that the movements which take place at these articulations are of a complex nature. The first part of the movement is an eccentric or asymmetrical one; the atlanto-axial joint of the side to which the head is mpved is fixed, or practically fixed by the muscles of the neck, and forms the centre of the movement, while the opposite atlantal facet is carried downward and forward on the corresponding axial facet. The second part of the movement is centric and symmetrical, the odontoid process forming the axis of the movement. ARTICULATION OF THE MANDIBLE 393 Synovial Membranes. — There are two synovial inenibranes: one lining each of the articular capsules. The joints frequently communicate with that between the posterior surface of the odontoid process and the transverse hgament of the atlas. Movements. — The movements permitted in this joint are (a) flexion and extension, which give rise to the ordinary forward and backward nodding of the head, and (b) slight lateral motion to one or other side. Flexion is produced mainly by the action of the Longi capitis and Recti capitis anteriores; extension by the Recti capitis posteriores major and minor, the Obliquus su- perior, the Semispinalis capitis, Splenius capitis, Sternocleidomastoideus, and upper fibres of the Trapezius. The Recti laterales are concerned in the lateral movement, assisted by the Trapezius, Splenius capitis, Semispinalis capitis, and the Sternocleidomastoideus of the same side, all acting together. Ligaments Connecting the Axis with the Occipital Bone. — The Membrana Tectoria. Two Alar. The Apical Odontoid. The Membrana Tectoria {occipitoaxial ligament) (Figs. 430, 431).^ — The mem- brana tectoria is situated within the vertebral canal. It is a broad, strong band, which covers the odontoid process and its ligaments, and appears to be a prolon- gation upward of the posterior longitudinal ligament of the vertebral column. It is fixed, below, to the posterior surface of the body of the axis, and, expanding as it ascends, is attached to the basilar groove of the occipital bone, in front of the foramen magnum, where it blends with the cranial dura mater. Its anterior sur- face is in relation with the transverse ligament of the atlas, and its posterior surface with the dura mater. The Alar Ligaments (ligamenta alaria; odontoid ligaments) (Fig. 430). — The alar ligaments are strong, rounded cords, which arise one on either side of the upper part of the odontoid process, and, passing obliquely upward and lateralward, are inserted into the rough depressions on the medial sides of the condyles of the occipi- tal bone. In the triangular interval between these ligaments is another fibrous cord, the apical odontoid ligament (Fig. 431), which extends from the tip of the odon- toid process to the anterior margin of the foramen magnum, being intimately blended with the deep portion of the anterior atlantooccipital membrane and superior crus of the transverse ligament of the atlas. It is regarded as a rudimentary intervertebral fibrocartilage, and in it traces of the notochord may persist. The alar ligaments limit rotation of the cranium and therefore receive the name of check ligaments. In addition to the ligaments which unite the atlas and axis to the skull, the ligamentum nuchae (page 387) must be regarded as one of the ligaments connecting the vertebral column with the cranium. Applied Anatomy. — The ligaments which unite the component parts of the vertebral column, together are so strong, and the bones are so interlocked by the arrangement of their articulating processes, that dislocation is very uncommon, and, indeed, except in the upper part of the neck, rarely occurs unless accompanied by fracture. Dislocation of the occipital bone from the atlas has been recorded only in one or two cases; but dislocation of the atlas from the axis, with rupture of the transverse hgament, is much more common; it is the mode in which death is produced in many cases of execution by hanging. In the lower part of the neck — that is, below the third cervical vertebra — dislocation unattended by fracture occasionally takes place. IV. Articulation of the Mandible (Articulatio Mandibularis ; Temporo- mandibular Articulation). This is a ginglymo-arthrodial joint; the parts entering into its formation on either side are: the anterior part of the mandibular fossa of the temporal bone and the articular tubercle above; and the condyle of the mandible below. The ligaments of the joint are the following: The Articular Capsule. The Sphenomandibular. The Temporomandibular. The Articular Disk. The Stylomandibular. 394 SYNDESMOLOGY The Articular Capsule (capsida articularis; capsular ligament). — The articular capsule is a thin, loose envelope, attached above to the circumference of the mandibular fossa and the articular tubercle immediately in front; below, to the neck of the condvle of the mandible. Fig.' 432. — -Articulation of the mandible. Lateral aspect. The Temporomandibular Ligament (ligamentum temporomandibulare; external lateral ligament) (Fig. 432). — The temporomandibular ligament consists of two Fig. 433. — Articulation of the mandible. Medial aspect. Fig. 434.— Sagittal section of the articulation of the mandible. short, narrow fasciculi, one in front of the other, attached, above, to the lateral surface of the zygomatic arch and to the tubercle on its lower border; below, ARTICULATION OF THE MANDIBLE 395 to the lateral surface and posterior border of the neck of the mandible. It is broader above than below, and its fibres are directed obliquely downward and backward. It is covered by the ])ari)ti;anient sometimes completely obliterates the cavity, so as to convert the articulation into an amphiarthrosis. The Costoxiphoid Ligaments {ligamenta costoxiphoidea; chondroxiphoid ligaments) . — These ligaments connect the anterior and posterior surfaces of the seventh costal cartilage, and sometimes those of the sixth, to the front and back of the xiphoid process. They vary in length and breadth in different subjects; those on the back of the joint are less distinct than those in front. Synovial Membranes. — There is no synovial membrane between the first costal cartilage and the sternum, as this cartilage is directly continuous with the manubrium. There are two in the articulation of the second costal cartilage and generally one in each of the other joints; but those of the sixth and seventh sternocostal joints are sometimes absent; where an interarticular liga- ment is present, there are two synovial cavities. After middle life the articular surfaces lose their polish, become roughened, and the synovial membranes apparently disappear. In old age, the cartilages of most of the ribs become continuous with the sternum, and the joint cavities are consequently obhterated. Movements. — Shght gliding movements are permitted in the sternocostal articulations. Interchondral Articulations {articulationes interchondrales; articulations of the cartilages of the ribs with each other) (Fig. 438). — The contiguous borders of the sixth, seventh, and eighth, and sometimes those of the ninth and tenth, costal cartilages articulate with each other by small, smooth, oblong facets. Each articulation is enclosed in a thin articular capsule, lined by synovial membrane and strengthened laterally and medially by ligamentous fibres (interchondral ligaments) which pass from one cartilage to the other. Sometimes the fifth costal cartilages, more rarely the ninth and tenth, articulate by their low^er borders with the adjoining cartilages by small oval facets; more frequentl}^ the connection is by a few ligamentous fibres. Costochondral Articulations. — The lateral end of each costal cartilage is received into a depression in the sternal end of the rib, and the two are held together by the periosteum. VII. Articulation of the Manubrium and Body of the Sternum. The manubrium is united to the body of the sternum either by an amphiarthrodial joint^ — a piece of fibrocartilage connecting the segments — or by a diarthrodial joint, in which the articular surface of each bone is clothed with a lamina of car- tilage. In the latter case, the cartilage covering the body is continued without interruption on to the cartilages of the facets for the second ribs. Rivington found the diarthrodial form of joint in about one-third of the specimens examined by him, Maisonneuve more frequently. It appears to be rare in childhood, and is formed, in Rivington's opinion, from the amphiarthrodial form, by absorption. The diarthrodial joint seems to have no tendency to ossify, while the amphiar- throdial is more liable to do so, and has been found ossified as early as thirty-four years of age. The two segments are further connected by anterior and posterior intersternal ligaments consisting of longitudinal fibres. Mechanism of the Thorax. — Each rib possesses its own range and variety of movements, but the movements of all are combined in the respiratory excm'sions of the thorax. Each rib may be regarded as a lever the fulcrum of which is situated immediately outside the costotransverse articulation, so that when the body of the rib is elevated the neck is depressed and vice versa; from the disproportion in length of the arms of the lever a sUght movement at the vertebral end of the rib is greatly magnified at the anterior extremity. The anterior ends of the ribs lie on a lower plane than the posterior; when therefore the body of the rib is elevated the anterior extremity is thrust also forward. Again, the middle of the body of the rib hes in a plane below that passing through the two extremities, so that when the body is elevated relatively to its ends it is at the same time carried outward from the median plane of the thorax. Finther, each rib forms the segment of a ciu've which is greater than that of the rib immediately above, and therefore the elevation of a rib increases the transverse diameter of the thorax in the plane to which it is raised. The modifications of the rib movements at their vertebral ends have akeady been described (page 399). Fui'ther modifications result from the 26 402 SYNDESMOLOGY attachments of their anterior extremities, and it is convenient therefore to consider separately the movements of the ribs of the three groups — vertebrosternal, vertebrochondral, and vertebral. V erkhrosternal Ribs (P'igs. 439, 440).— The first rib differs from the others of this group in that its at- tachment to the sternum is a rigid one; this is counterbalanced to some extent by the fact that its head possesses no interarticular ligament, and is therefore more movable. The first pair of ribs with the manu- brium sterni move as a single piece, the anterior portion being elevated by rotatory movements at the vertebral extremities. In normal quiet respiration the movement of this arc is practically 7iil; when it does occur the anterior part is raised and carried forward, increas- ing the antero-posterior and trans- verse diameters of this region of the chest. The movement of the second rib is also slight in normal respira- tion, as its anterior extremity is fixed to the manubrium, and pre- vented therefore from moving up- ward. The sternocostal articulation, however, allows the middle of the body of the rib to be drawn up, and in this way the transverse thoracic diameter is increased. Elevation of the third, fourth, fifth, and sixth ribs raises and thrusts forward their anterior extremities, the greater part of the move- ment being effected by the rotation of the rib neck backward. The thrust of the anterior extremities carries forward and upward the body of the sternum, which moves on the joint Fig. 439. — Lateral view of first and seventh ribs in position, sliow- ing the movements of the sternum and ribs in A , ordinary expiration ; B, quiet inspiration; C, deep inspiration. Fig. 440. — Diagram showing the axes of movement (A B and C D) oi a vertebrosternal rib. The inter- rupted lines indicate the position of the rib in inspiration. Fig. 441. — Diagram showing the axis of movement (*4 B) of a vertebrochondral rib. The interrupted lines indicate the position of the rib in inspiration. between it and the manubrium, and thus the antero-posterior thoracic diameter is increased. This movement is, however, soon arrested, and the elevating force is then expended in raising the middle part of the body of the rib and everting its lower border; at the same time the ARTIVLLATIOS OF THE VERTEBRAL COLUMX WITH THE PELVIS 403 costochondnil unfile is opened out. By these latter movements a considerable inca-ease in the transverse diameter of the thorax is efTeeted. Vcrlebrochondral Ribs (Fig. 441). — The seventh rib is included with this group, as it conforms more closelj- to their type. While the movements of these ribs assist in enlarging the thorax for respiratory purposes, they are also concerned in increasing the upper abdominal space for viscera displaced by the action of the Diaphragma. The costal cartilages articulate with one another, so that (>ach pushes up that above it, the final thrust being directed to pushing forward and upward the lower end of the body of the sternum. The amount of elevation of the anterior extremities is limited on account of the very slight rotation of the rib neck. Elevation of the shaft is accompanied b}' an outward and backward movement; the outward movement everts the anterior end of the rib and opens up the subcostal angle, while the backward movement pulls back the anterior extremity and counteracts the forward thrust due to its elevation; this latter is most noticeable in the lower ribs, which are the shortest. The total result is a con.sider- able inci'ease in the transverse and a diminution in the median antero-posterior diameter of the upper part of the abdomen; at the same time, however, the lateral antero-posterior diameters of the abdomen are increased. Vertebral Ribs. — Since these ribs have free anterior extremities and only costocentral articula- "tions with no interarticular ligaments, they are capable of slight movements in all directions. WTien the other ribs are elevated these are depressed and fixed to form points of action for the Diaphragma. Aferture of communication with bursa under Psoas and Iliacus Fejtiur'm Fig. 442. — Articulations of pelvis and hip. Anterior view. VIII, Articulation of the Vertebral Column with the Pelvis. The ligaments connecting the fifth himbar vertebra witli the sacrum are similar to those which join the movable segments of the vertebral column with each other — viz.: 1. The continuation downward of the anterior and posterior longitudinal ligaments. 2. The intervertebral fibrocartilage, connecting the body of the fifth lumbar to that of the first sacral vertebra and forming an amphiarthrodial joint. 3. Ligamenta flava, uniting the laminae of the fifth lumbar vertebra with those of the first sacral. 4. Capsules connecting the articular processes and forming a double arthrodia. 5. Inter- and supraspinal ligaments. 404 SYNDESMOLOGY On either side an additional ligament, the iliolumbar, connects the pelvis with the A'ertebral column. The Iliolumbar Ligament (ligamentum iliolumbale) (Fig. 442). — The iliolumbar ligament is attached above to the lower and front part of the transverse process of the fifth lumbar vertebra. It radiates as it passes lateralward and is attached by two main bands to the pelvis. The lower bands run to the base of the sacrum, blending with the anterior sacroiliac ligament; the upper is attached to the crest of the ilium immediately in front of the sacroiliac articulation, and is continuous above with the lumbodorsal fascia. In front, it is in relation with the Psoas major; behind, with the muscles occupying the vertebral groove; above, with the Quadratus lumborum. IX. Articulations of the Pelvis. The ligaments connecting the bones of the pelvis with each other may be divided into four groups: 1. Those connecting the sacrum and ilium. 2. Those passing between the sacrum and ischium. 3. Those uniting the sacrum and coccyx. 4. Those between the two pubic bones. 1. Sacroiliac Articulation (articulatio sacroiliaca). — The sacroiliac articulation is an amphiarthrodial joint, formed between the auricular surfaces of the sacrum and the ilium. The articular surface of each bone is covered with a thin plate of cartilage, thicker on the sacrum than on the ilium. These cartilaginous plates are in close contact with each other, and to a certain extent are united together by irregular patches of softer fibrocartilage, and at their upper and posterior part by fine interosseous fibres. In a considerable part of their extent, especially in advanced life, they are separated by a space containing a synovia-like fluid, and hence the joint presents the characteristics of a diarthrosis. The ligaments of the joint are: The Anterior Sacroiliac. The Posterior Sacroiliac. The Interosseous. The Anterior Sacroiliac Ligament {ligamentum sacroiliacum anterius) (Fig. 442) .■ — The anterior sacroiliac ligament consists of numerous thin bands, which connect the anterior surface of the lateral part of the sacrum to the margin of the auricular surface of the ilium and to the preauricular sulcus. The Posterior Sacroiliac Ligament (ligamentum sacroiliacum posterius) (Fig. 443). — The posterior sacroiliac ligament is situated in a deep depression between the sacrum and ilium behind; it is strong and forms the chief bond of union between the bones. It consists of numerous fasciculi, which pass between the bones in various directions. The upper part (short posterior sacroiliac ligament) is nearly horizontal in direction, and passes from the first and second transverse tubercles on the back of the sacrum to the tuberosity of the ilium. The lower part (long posterior sacroiliac ligament) is oblique in direction; it is attached by one extremity to the third transverse tubercle of the back of the sacrum, and by the other to the posterior superior spine of the ilium. The Interosseous Sacroiliac Ligament (ligamentum sacroiliacum inter os s eum) . — This ligament lies deep to the posterior ligament, and consists of a series of short, strong fibres connecting the tuberosities of the sacrum and ilium. 2. Ligaments Connecting the Sacrum and Ischium (Fig. 443). The Sacrotuberous. The Sacrospinous. The Sacrotuberous Ligament (ligamentum sacrotuberosum; great or posterior sacrosciatic ligament). — The sacrotuberous ligament is situated at the lower and back part of the pelvis. It is flat, and triangular in form; narrower in the middle than at the ends; attached by its broad base to the posterior inferior spine of the ARTICULATIONS OF THE PELVIS 405 ilium, to the fourth and fifth transverse tuherek's of the sacrum, and to the lower part of the lateral margin of that bone and the coccyx. Passing obliquely downward, forward, and lateralward, it becomes narrow and thick, but at its insertion into the inner margin of the tuberosity of the ischium, it increases in breadth, and is prolonged forward along the inner margin of the ramus, as the falciform process, the free concave edge of which gives attachment to the obturator fascia; one of its surfaces is turned toward the perineum, the other toward the Obturator internus. The lower border of the ligament is directly continuous with the tendon of origin of the long head of the Biceps femoris, and b}' many is believed to be the proximal end of this tendon, cut off by the projection of the tuberosity of the ischium. Fig. 443. — Articulations of pelvis and hip. Posterior view. Relations. — The posterior surface of this hgament gives origin, by its whole extent, to the Glutaeus maximus. Its anterior surface is in part united to the sacrospinous Ugament. Its upper harder forms, above, the posterior boundary of the greater sciatic foramen, and, below, the pos- terior boundary of the lesser sciatic foramen. Its lower border forms part of the boundary of the perineum. It is pierced by the coccygeal nerve and the coccygeal branch of the inferior gluteal artery. The Sacrospinous Ligament {ligamentum sacrospinosum; small or anterior sacro- sciatic ligament). — The sacrospinous ligament is thin, and triangular in form; it is attached by its apex to the spine of the ischium, and medially, by its broad base, to the lateral margins of the sacrum and coccyx, in front of the sacrotuberous ligament with wdiich its fibres are intermingled. Relations. — ^It is in relation, anteriorly, with the Coccygeus muscle, to which it is closely con- nected; posteriorly, it is covered by the sacrotuberous ligament, and crossed by the internal pudendal vessels and nerve. Its upper border forms the lower boundary of the greater sciatic foramen; its lower border, part of the margin of the lesser sciatic foramen. 406 SYNDES}fr)LOGY These two ligaments convert the sciatic notches into foramina. The greater sciatic foramen is bounded, in front and above, by the posterior border of the hip bone; hcliind, \)\ the sacrotuberous Ugament; and below, by the sacrospinous hgament. It is partially filled up, in the recent state, by the Piriformis which leaves the pelvis through it. Above this muscle, the superior gluteal vessels and nerve emerge from the pelvis; and below it, the inferior gluteal vessels and nerve, the internal pudendal vessels and nerve, the sciatic and posterior femoral cutaneous nerves, and the nerves to the Obturator internus and Quadratus femoris make their exit from the pelvis. The lesser sciatic foramen is bounded, in front, by the tuberosity of the ischium; above, by the spine of the ischium and sacrospinous ligament; behind, by the sacrotuberous ligament. It trans- mits the tendon of the Obturator internus, its nerve, and the internal pudendal vessels and nerve 3. Sacrococcygeal Symphysis {.siimphysis sacrococcygea; articulation of the sacrvin and coccyx). — This articulation is an amphiarthroclial joint, formed between the oval surface at the apex of the sacrum, and the base of the coccyx. It is homol- ogous with the joints between the bodies of the vertebrte, and is connected by similar ligaments. They are: The Anterior Sacrococcygeal. The Lateral Sacrococcygeal. The Posterior Sacrococcygeal. The Interposed Fibrocartilage. The Interarticular. The Anterior Sacrococcygeal Ligament (ligamentum sacrococcygeum anterius). — This consists of a few irregular fibres, which descend from the anterior surface of the sacrum to the front of the coccyx, blending with the periosteum. The Posterior Sacrococcygeal Ligament (ligamentum sacrococcygeum posterius). — This is a flat band, which arises from the margin of the lower orifice of the sacral canal, and descends to be inserted into the posterior surface of the coccyx. This ligament completes the lower and back part of the sacral canal, and is divisible into a short deep portion and a longer superficial part. It is in relation, behind, with the Glutaeus maximus. The Lateral Sacrococcygeal Ligament {ligamentum sacrococcygeum laterale; inter- transverse ligament). — The lateral sacrococcygeal ligament exists on either side and connects the transverse process of the coccyx to the lower lateral angle of the sacrum; it completes the foramen for the fifth sacral nerve. A disk of fibrocartilage is interposed between the contiguous surfaces of the sacrum and coccyx; it differs from those between the bodies of the vertebrae in that it is thinner, and its central part is firmer in texture. It is somewhat thicker in front and behind than at the sides. Occasionally the coccyx is freely movable on the sacrum, most notably during pregnancy ; in such cases a synovial membrane is present. The Interarticular Ligaments are thin bands, which unite the cornua of the two bones. The different segments of the coccyx are connected together by the extension downw^ard of the anterior and posterior sacrococcygeal ligaments, thin annular disks of fibrocartilage being interposed between the segments. In the adult male, all the pieces become ossified together at a comparatively early period; but in the female, this does not commonly occur until a later period of life. At more advanced age the joint between the sacrum and coccyx is obliterated. Movements. — The movements which take place between the sacrum and coccyx, and between the different pieces of the latter bone, are forward and backward; they are very limited. Their extent increases during pregnancy. 4. The Pubic Symphysis {symphysis ossium yuhis; articulation of the imbic hones) (Fig. 444). — The articulation between the pubic bones is an amphiarthro- dial joint, formed between the two oval articular surfaces of the bones. The ligaments of this articulation are: The Anterior Pubic. The Superior Pubic. The Posterior Pubic. The Arcuate Pubic. The Interpubic Fibrocartilaginous Lamina. ARTIClLAriONS OF TJII'J J'KLVIS 407 The Anterior Pubic Ligament (Fiji;. 442). — The anterior pubic lioament consists of several sui)erinii)ose(l layers, which pass across the front of the articulation. The superficial fibres pass obliciuely from one bone to the other, decussating and forming an interlacement with the fibres of the aj'joneuroses of the Obliqui externi and the medial tendons of origin of the Recti abdominis. The deep fibres pass transversely across the symphysis, and arc blended with the fibrocartilaginous lamina. The Posterior Pubic Ligament. — The posterior pubic ligament consists of a few thin, scattered fibres, which unite the two pubic bones posteriorly. The Superior Pubic Ligament {Ugamentuin puhicum superius). — The superior pubic ligament connects together the two pubic bones superiorly, extending later- ally as far as the pubic tubercles. A)it. sup. iliac spine- ^: Inierpuhic fibro- cartilaginous lamina Transverse acetabular ligament Fig. 444. — Symphysis pubis expo-sed by a coronal section. The Arcuate Pubic Ligament {Ugamentuin arcuatum pubis; inferior pubic or subpubic ligament). — The arcuate pubic ligament is a thick, triangular arch of ligamentous fibres, connecting together the two pubic bones below, and forming the upper boundary of the pubic arch. Above, it is blended with the interpubic fibrocartilaginous lamina; laterally, it is attached to the inferior rami of the pubic bones; below, it is free, and is separated from the fascia of the urogenital diaphragm by an opening through which the deep dorsal vein of the penis passes into the pelvis. The Interpubic Fibrocartilaginous Lamina {lamina fibrocartilaginea interpiibica; interpubic disk). — The interpubic fibrocartilaginous lamina connects the opposed surfaces of the pubic bones. Each of these surfaces is covered by a thin layer of hyaline cartilage firmly joined to the bone by a series of nipple-like processes which accurately fit into corresponding depressions on the osseous surfaces. These opposed cartilaginous surfaces are connected together by an intermediate lamina of fibrocartilage which varies in thickness in dift'erent subjects. It often contains a cavity in its interior, probably formed by the softening and absorption of the fibrocartilage, since it rarely appears before the tenth year of life and is not lined 408 SYNDESMOLOGY by synovial membrane. This cavity is larger in the female than in the male, but it is very doubtful whether it enlarges, as was formerly supposed, during pregnancy. It is most frequently limited to the upper and back part of the joint; it occasion- ally reaches to the front, and may extend the entire length of the cartilage. It may be easily demonstrated when present by making a coronal section of the symphysis pubis near its posterior surface (Fig. 444). Fig. 445. — Coronal section of anterior sacral segment. Mechanism of the Pelvis. — The pelvic girdle supports and protects the contained viscera and affords surfaces for the attachments of the trunk and lower limb muscles. Its most important mechanical function, however, is to transmit the weight of the trunk and upper limbs to the lower extremities. It may be divided into two arches by a vertical plane passing through the acetabular cavities; the posterior of these arches is the one chiefly concerned in the function of transmitting the weight. Its essential parts are the upper three sacral vertebrae and two strong piUars of bone running from the sacroihac articulations to the acetabular cavities. For the reception and diffu- sion of the weight each acetabular cavity is strengthened by two additional bars rxmning toward Fig. 446. — Coronal section of middle sacral segment. the pubis and ischium. In order to lessen concussion in rapid changes of distribution of the weight, joints (sacroihac articulations) are interposed between the sacrum and the iliac bones; an accessory joint (pubic symphysis) exists in the middle of the anterior arch. The sacrum forms the summit of the posterior arch; the weight transmitted falls on it at the lumbosacral articula- tion and, theoretically, has a component in each of two directions. One component of the force is expended in driving the sacrum downward and backward between the ihac bones, while the other thrusts the upper end of the sacrum downward and forward toward the pelvic cavity. The movements of the sacrum are regulated by its form. Viewed as a whole, it presents the shape of a wedge with its base upward and forward. The first component of the force is there- fore acting against the resistance of the wedge, and its tendency to separate the ihac bones is resisted by the sacroiliac and iholumbar hgaments and by the Ugaments of the pubic symphysis. If a series of coronal sections of the sacroiliac joints be made, it will be foimd possible to divide STERNOCLAVICULAR ARTICULATION 409 the articular portion of the sacrum into three segments: anterior, middle, and posterior. In the anterior segment (Fig. 445), which involves the first sacral vertebra, the articular surfaces show sUght sinuosities and are almost parallel to one another; the distance between their dorsal nuu-gins is, however, slightly greater than that between their ventral margins. This segment therefore presents a shght wedge shape with the truncated apex down- ward. The middle segment (Fig. 446) is a narrowband across the centres of the articu- lations. Its dorsal width is distinctly greater than its ventral, so that the segment is more definitely wedge-shaped, the trun- cated apex being again directed downward. Each articular sm-face presents in the centre Fig. 447.— Coronal section of posterior sacral segment. a marked concavity from above downward, and into this a corresponding convexity of the iliac articular surface fits, forming an interlocking mechanism. In the posterior segment (Fig. 447) the ventral width is greater than the dorsal, so that the wedge form is the reverse of those of the other segments — i. e., the truncated apex is directed upward. The articular surfaces are only slightly concave. Dislocation downward and forward of the sacrum by the second component of the force applied to it is prevented therefore by the middle segment, which interposes the resistance of its wedge shape and that of the interlocking mechanism on its surfaces; a rotatory movement, however, is produced by which the anterior segment is tilted downward and the posterior upward ; the axis of this rotation passes through the dorsal part of the middle segment. The movement of the anterior segment is slightly limited by its wedge form, but chiefly by the posterior and inter- osseous sacroihac ligaments; that of the posterior segment is checked to a sUght extent by its wedge form, but the chief limiting factors are the sacrotuberous and sacrospinous hgaments. In all these movements the effect of the sacroihac and iUolumbar hgaments and the hgaments of the symphysis pubis in resisting the separation of the ihac bones must be recognized. During pregnancy the pelvic joints and ligaments are relaxed, and capable therefore of more extensive movements. When the fetus is being expelled the force is apphed to the front of the sacrmn. Upward dislocation is again prevented by the interlocking mechanism of the middle segment. As the fetal head passes the anterior segment the latter is carried upward, enlarging the antero-posterior diameter of the pelvic inlet; when the head reaches the posterior segment this also is pressed upward against the resistance of its wedge, the movement only being possible by the laxity of the joints and the stretching of the sacrotuberous and sacrospinous ligaments. ARTICULATIONS OF THE UPPER EXTREMITY. The articulations of the Upper Extremity may be arranged as follows: I. Sternoclavicular. VI. Wrist. II. Acromioclavicular. VII. Intercarpal. III. Shoulder. VIII. Carpometacarpal. IV. Elbow. IX. Intermetacarpal. V. Radioulnar. X. Metacarpophalangeal. XL Articulations of the Digits. I. Sternoclavicular Articulation (Articulatio Sternoclavicularis) (Fig. 448). The sternoclavicular articulation is a double arthrodial joint. The parts entering into its formation are the sternal end of the clavicle, the upper and lateral part of the manubrium sterni, and the cartilage of the first rib. The articular surface of the clavicle is much larger than that of the sternum, and is invested with a layer of cartilage,^ which is considerably thicker than that on the latter bone. The ligaments of this joint are: The Articular Capsule. The Interclavicidar. The Anterior Sternoclavicular. The Costoclavicular. The Posterior Sternoclavicular. The Articular Disk. 1 According to Bruch, the sternal end of the clavicle is covered by a tissue which is fibrous rather than cartilaginous in structure. 410 SYNDESMOLOGY The Articular Capsule {cap.siila arilcuJaris; cap.syJar ligament). — The articular capsule surrounds the articulation and varies in thickness and strength. In front and behind it is of considerable thickness, and forms the anterior and posterior sternoclavicular ligaments; but above, and especially below, it is thin and par- takes more of the character of areolar than of true fibrous tissue. The Anterior Sternoclavicular Ligament (ligamentum sternoclaviculare anterior).- — The anterior sternoclavicular ligament is a broad band of fibres, covering the anterior surface of the articulation ; it is attached above to the upper and front part of thesternal end of the clavicle, and, passing obliquely downward and medialward, is attached below to the front of the upper part of the manubrium sterni. This ligament is covered by the sternal portion of the Sternocleidomastoideus and the integument; behind, it is in relation with the capsule, the articular disk, and the two synovial membranes. Fig. 448. — Sternoclavicular articulation. Anterior view. The Posterior Sternoclavicular Ligament (ligamentum sternoclaviculare posteriiis). — The posterior sternoclavicular ligament is a similar band of fibres, covering the posterior surface of the articulation; it is attached above to the upper and back part of the sternal end of the clavicle, and, passing obliquely downward and medialward, is fixed below to the back of the upper part of the manubrium sterni. It is in relation, in front, with the articular disk and synovial membranes; behind, with the Sternohyoideus and Sternothyreoideus. The Interclavicular Ligament (ligamentum interclaviculare) . — This ligament is a flattened band, which varies considerably in form and size in difterent individuals, it passes in a curved direction from the upper part of the sternal end of one clavicle to that of the other, and is also attached to the upper margin of the sternum. It is in relation, in front, with the integument and Sternocleidomastoidei ; behind, with the Sternothyreoidei. The Costoclavicular Ligament (ligamentum costoclavicular e; rhomboid ligament). — This ligament is short, flat, strong, and rhomboid in form. Attached below to the upper and medial part of the cartilage of the first rib, it ascends obliquely backward and lateralward, and is fixed above to the costal tuberosity on the under surface of the clavicle. It is in relation, in front, with the tendon of origin of the Subclavius; behind, with the subclavian vein. The Articular Disk (discus articular is) . — The articular disk is flat and nearly circular, interposed between the articulating surfaces of the sternum and clavicle. It is attached, above, to the upper and posterior border of the articular surface of the clavicle; below, to the cartilage of the first rib, near its junction with the sternum; and bv its circumference to the interclavicular and anterior and posterior sterno- . I C ROM IOC LA 1 ICi LA H ART ICC LA TIOX 41 1 clavicular lis;aments. It is thicker at the circumference, especially its upper and back i)art. than at its centre. It divides the joint into two cavities, each of which is furnished with a syno\'ial nienihrane. Synovial Membranes. — Of the two synovial membranes found in this articulation, the lateral is rellorlcd from the sternal end of the clavicle, over the adjacent surface of the articular disk, and arountl the nuu-fiin of the facet on the cartilage of the first rib; the medial is attached to the margin of the articular surface of the sternum and clothes the adjacent surface of the articular disk; the latter is the larger of the two. Movements. — -This articulation admits of a limited amount of motion in nearly every direc- tion — upward, downward, backward, forwaixl, as well as circumduction. When these move- ments take place in the joint, the clavicle iia its motion carries the scapula with it, this bone gliding on the outer surface of the chest. This joint therefore forms the centre from which all movements of the supporting arch of the shoulder originate, and is the only point of articulation of the shoulder girdle with the trunk. The movements attendant on elevation and depression of the shoulder take place between the clavicle and the articular disk, the bone rotating upon the ligament on an axis drawn from before backward through its own articular facet; when the shoulder is moA'ed forward and backward, the clavicle, with the articular disk rolls to and fro on the articular surface of the sternum, revolving, with a sUding movement, around an axis drawn nearly vertically through the sternum; in the circumduction of the shoulder, which is compounded of these two movements, the clavicle revolves upon the articular disk and the latter, with the clavicle, rolls upon the sternum.^ Elevation of the shoulder is limited principally by the costoclavicular ligament; depression, by the interclavicular ligament and articular disk. The muscles which raise the shoulder are the upper fibres of the Trapezius, the Levator scapulae, and the clavicular head of the Sternocleidomastoideus, assisted to a certain extent by the Rhomboidei, which pull the vertebral border of the scapula backward and upward and so raise the shoulder. The depres- sion of the shoulder is principally effected by gravity assisted by the Subclavius, Pectoralis minor and lower fibres of the Trapezius. The shoulder is drawn backward by the Rhomboidei and the middle and lower fibres of the Trapezius, and forward by the Serratus anterior and PectoraUs minor. Applied Anatomy. — The strength of this joint mainly depends upon its ligaments, and it is owing to these, and to the fact that the force of the blow is usually transmitted along the long axis of the clavicle, that dislocation rarely occurs, and that the bone is broken rather than dis- placed. When dislocation does occur, the course which the displaced bone takes depends more upon the direction in which the violence is applied than upon the anatomical construction of the joint; it may be either forward, backward, or upward. Should it be displaced backward it may cause pressure on the trachea. The chief point worthy of note, as regards the construction of the joint, in connection with dislocation, is the fact that, owing to the shape of the articular surfaces, and the strength of the joint mainly depending upon the ligaments, the displacement when reduced is very liable to recur, and hence it is extremely difficult to keep the end of the bone in its proper place. II. Acromioclavicular Articulation (Articulatio Acromioclavicularis ; Scapulo- clavicular Articulation) (Fig. 449). The acromioclavicular articulation is an arthrodial joint between the acromial end of the clavicle and the medial margin of the acromion of the scapula. Its ligaments are: The Articular Capsule. The Articular Disk. The Superior Acromioclavicular. rpi p i " i [Trapezoid and The Inferior Acromioclavicular. I Conoid. The Articular Capsule (capsida articularis; capsular ligament). — The articular capsule completely surrounds the articular margins, and is strengthened above and below by the superior and inferior acromioclavicular ligaments. The Superior Acromioclavicular Ligament {ligamentum acromioclaviculare) . — This ligament is a quadrilateral band, covering the superior part of the articula- tion, and extending between the upper part of the acromial end of the clavicle and the adjoining part of the upper surface of the acromion. It is composed of parallel fibres, which interlace with the aponeuroses of the Trapezius and Deltoideus; below, it is in contact with the articular disk when this is present. 1 Humphrj', On the Human Skeleton, page 402. 412 SYNDESMOLOGY The Inferior Acromioclavicular Ligament. — This ligament is somewhat thinner than the preceding; it covers the untler part of the articulation, and is attached to the adjoining surfaces of the two bones. It is in relation, above, in rare cases with the articular disk; helow, with the tendon of the Supraspinatus. The Articular Disk (discus articular is) . — The articular disk is frequently absent in this articulation. When present, it generally only partially separates the artic- ular surfaces, and occupies the upper part of the articulation. More rarely, it completely divides the joint into two cavities. The Synovial Membrane. — There is usually only one synovial membrane in this articulation, but when a complete articular disk is present, there are two. Fig. 449. — -The left shoulder and acromioclavicular joints, and the proper ligaments of the scapula. The Coracoclavicular Ligament {licjamentum coracoclaviculare) (Fig. 449).^ — This ligament serves to connect the clavicle with the coracoid process of the scapula. It does not properly belong to this articulation, but is usually described with it, since it forms a most efficient means of retaining the clavicle in contact with the acromion. It consists of two fasciculi, called the trapezoid and conoid ligaments. The Trapezoid Ligament {ligamentum trapezoideum) , the anterior and lateral fas- ciculus, is broad, thin, and quadrilateral : it is placed obliquely between the cora- coid process and the clavicle. It is attached, below, to the upper surface of the coracoid process; above, to the oblique ridge on the under surface of the clavicle. Its anterior border is free; its posterior border is joined with the conoid ligament, the two forming, by their junction, an angle projecting backward. The Conoid Ligament (ligamentum conoideum), the posterior and medial fa&ciculus, is a dense band of fibres, conical in form, with its base directed upward. It is attached by its apex to a rough impression at the base of the coracoid process, medial to the trapezoid ligament; above, by its expanded base, to the coracoid THE LIGAMENTS OF THE SCAPULA 413 tuberosity on the under surface of the c-hivicle, and to a Hue proceeding medial- ward from it for 1.25 cm. These ligaments are in rehition, in front, with the Subclavius and Deltoideus; behind, with the Trapezius. Movements. — The movements of this articulation are of two kinds: (1) a gliding motion of the articular entl of the clavicle on the acromion; (2) rotation of the scapula forward and back- ward upon the clavicle. The extent of this rotation is limited by the two portions of the coraco- clavicular ligament, the trapezoid limiting rotation forward, and the conoid backward. The acromioclavicular joint has important functions in the movements of the upper extremity. It has been well pointed out by Humphry, that if there had been no joint between the clavicle and scapula, the circular movement of the scapula on the ribs (as in throwing the shoulders back- ward or forward) would have been attended with a greater alteration in the direction of the shoulder than is consistent with the free use of the arm in such positions, and it would have been impossible to give a blow straight foi'ward with the full force of the arm; that is to say, with the combined force of the scapula, arm, and forearm. "This joint," as he happily says, "is so adjusted as to enable either bone to turn in a hiiage-like manner upon a vertical axis drawn through the other, and it permits the surfaces of the scapula, like the baskets in a roundabout swing, to look the same way in every position, or nearly so." Again, when the whole arch formed by the clavicle and scapula rises and falls (in elevation or depression of the shoulder), the joint between these two bones enables the scapula still to maintain its lower part in contact with the ribs. Applied Anatomy. — The acromioclavicular joint owes its security mainly to the coracoclavicular ligament, which limits the amount of movement of the acromial end of the clavicle either upward, backward, or forward. Owing to the slanting shape of the articular surfaces of this joint, dis- location generally occurs upward; that is to say, the acromial end of the clavicle is displaced above the acromion of the scapula. The displacement is often incomplete, on account of the strong coracoclavicular ligaments, which remain untorn. The same difficulty exists, as in the sterno- clavicular dislocation, in maintaining the ends of the bone in position after reduction. THE LIGAMENTS OF THE SCAPULA. The ligaments of the scapula (Fig. 449) are : Coracoacromial, Superior and Inferior Transverse. The Coracoacromial Ligament {ligamentum coracoacromiale) . — This ligament is a strong triangular band, extending between the coracoid process and the acromion. It is attached, by its apex, to the summit of the acromion just in front of the articular surface for the clavicle ; and by its broad base to the w^hole length of the lateral border of the coracoid process. This ligament, together with the coracoid process and the acromion, forms a vault for the protection of the head of the humerus. It is in relation, above, with the clavicle and under surface of the Del- toideus; beloio, with the tendon of the Supraspinatus, a bursa being interposed. Its lateral border is continuous with a dense lamina that passes beneath the Del- toideus upon the tendons of the Supraspinatus and Infraspinatus. The ligament is sometimes described as consisting of two marginal bands and a thinner inter- vening portion, the two bands being attached respectively to the apex and the base of the coracoid process, and joining together at the acromion. When the Pectoralis minor is inserted, as occasionally is the case, into the capsule of the shoulder-joint instead of into the coracoid process, it passes between these two bands, and the intervening portion of the ligament is then deficient. The Superior Transverse Ligament {ligamentum transversum scapulae superius; transverse or suprascapular ligament). — This ligament converts the scapular notch into a foramen. It is a thin and flat fasciculus, narrower at the middle than at the extremities, attached by one end to the base of the coracoid process, and by the other to the medial end of the scapular notch. The suprascapular nerve runs through the foramen; the transverse scapular vessels cross over the ligament. The ligament is sometimes ossified. The Liferior Transverse Ligament {ligamentum transversum scapulae inferius; spinoglenoid ligament). — This ligament is a weak membranous band, situated 414 SYNDESMOLOGY behind the neck of the scapuhx and stretching from the hiteral border of the spine to the margin of the glenoid cavity. It forms an arch inider which the transverse scapular vessels and suprascapular nerve enter the infraspinatous fossa. III. Humeral Articulation or Shoulder-joint (Articulatio Humeri) (Fig. 449). The shoulder-joint is an enarthrodial or ball-and-socket joint. The bones entering into its formation are the hemispherical head of the humerus and the shallow glenoid cavity of the scapula, an arrangement Avhich permits of very considerable movement, while the joint itself is protected against displacement by the tendons which surround it. The ligaments do not maintain the joint sur- faces in apposition, because when they alone remain the humerus can be separated to a considerable extent from the glenoid cavity; their use, therefore, is to limit Suiter lor transverse ligament Transverse humeral ligament Prolongation of synovial m,etn- brane on tendon of Biceps hrachii Bursa under Subscapularis Fig. 450. — Capsule of shoulder-joint (distended). Anterior aspect. the amount of movement. The joint is protected above by an arch, formed by the coracoid process, the acromion, and the coracoacromial ligament. The artic- ular cartilage on the head of the humerus is thicker at the centre than at the cir- cumference, the reverse being the case with the articular cartilage of the glenoid cavity. The ligaments of the shoulder are: The Articular Capsule. The Coracohumeral. The Glenohumeral. The Transverse Humeral. The Glenoidal Labrum.^ The Articular Capsule {capsida articidaris; capsular ligament) (Fig. 450). — The articular capsule completely encircles the joint, being attached, above, to the circumference of the glenoid cavity beyond the glenoidal labrum; below, to the anatomical neck of the humerus, approaching nearer to the articular cartilage above than in the rest of its extent. It is thicker above and below than elsewhere, 1 The long tendon of origin of the biceps brachii also acts as one of the ligaments of this joint. See the observations on page 383, on the function of the muscles passing over more than one joint. HUMERAL ARTICULATIOX OR SHOULDER-JOLVf 415 and is so remarkably loose and lax, that it has no action in keeping the bones in contact, but allows them to be separated from each other more than 2.5 cm., an evident j^nnision for that extreme freedom of mox-ement which is peculiar to this articulation. It is strengthened, above, by the Sui)raspinatus; beloiv, by the long head of the Triceps brachii; behind, by the tendons of the Infraspinatus and Teres minor; and in front, by the tendon of the Subscapularis. There are usually three openings in the capsule. One anteriorly, below the coracoid process, establishes a communication between the joint and a bursa l)eneath the tendon of the Sub- scapularis.- The second, which is not constant, is at the posterior part, where an opening sometimes exists between the joint and a bursal sac under the tendon of the Infraspinatus. The third is between the tubercles of the humerus, for the passage of the long tendon of the Biceps brachii. The Coracohumeral Ligament {Ugamentum coracohumerale) . — This ligament is a broad band which strengthens the upper part of the capsule. It arises from the lateral border of the coracoid process, and passes obliciuely downward and lateral ward to the front of the greater tubercle of the humerus, blending with the tendon of the Supraspinatus. This ligament is intimately united to the capsule by its hinder and lower border; but its anterior and upper border presents a free edge, which overlaps the capsule. Glenohumeral Ligaments. — In addition to the coracohumeral ligament, three supplemental bands, which are named the glenohumeral ligaments, strengthen the capsule. These may be best seen by opening the capsule at the back of the joint and removing the head of the humerus. One on the medial side of the joint passes from the medial edge of the glenoid cavity to the lower part of the lesser tubercle of the humerus. A second at the lower part of the joint extends from the under edge of the glenoid cavity to the under part of the anatomical neck of the humerus. A third at the upper part of the joint is fixed above to the apex of the glenoid cavity close to the root of the coracoid process, and passing down- ward along the medial edge of the tendon of the Biceps brachii, is attached below to a small depression above the lesser tubercle of the humerus. In addition to these, the capsule is strengthened in front by two bands derived from the tendons of the Pectoralis major and Teres major respectively. The Transverse Humeral Ligament (Fig. 450) is a broad band passing from the lesser to the greater tubercle of the humerus, and always limited to that portion of the bone which lies above the epiphysial line. It converts the intertubercular groove into a canal, and is the homologue of the strong process of bone which connects the summits of the two tubercles in the musk ox. The Glenoidal Labrum {labrium glenoidale; glenoid ligament) is a fibrocartilaginous rim attached around the margin of the glenoid cavity. It is triangular on section, the base being fixed to the circumference of the cavity, while the free edge is thin and sharp. It is continuous above with the tendon of the long head of the Biceps brachii, which gives off two fasciculi to blend with the fibrous tissue of the labrum. It deepens the articular cavity, and protects the edges of the bone. Synovial Membrane. — The synovial membrane is reflected from the margin of the glenoid cavity over the labrum; it is then reflected over the inner surface of the capsule, and covers the lower part and sides of the anatomical neck of the humerus as far as the articular cartilage on the head of the bone. The tendon of the long head of the Biceps brachii passes through the capsule and is enclosed in a tubular sheath of synovial membrane, which is reflected upon it from the summit of the glenoid cavity and is continued around the tendon into the intertubercular groove as far as the surgical neck of the humerus (Fig. 450). The tendon thus traverses the articu- lation, but it is not contained within the sjmovial cavity. Bursae. — The bursse in the neighborhood of the shoulder-joint are the following: (1) A constant bm'sa is situated between the tendon of the Subscapularis muscle and the capsule; it communi- cates with the synovial cavity tln-ough an opening in the front of the capsule; (2) a bursa which occasionally communicates with the joint is sometimes found between the tendon of the Infra- spinatus and the capsule; (3) a large bm'sa exists between the under surface of the Deltoideus 416 . SYNDESMOLOGY and the capsule, but does not communicate with the joint; this bursa is prolonged under the acromion and coracoacromial ligament, and intervenes between these structures and the capsule; (■i) a large bursa is situated on the summit of the acromion; (5) a bursa is frequently found between the coracoid process and the capsule; (6) a bursa exists beneath the Coracobrachiahs; (7) one lies between the Teres major and the long head of the Triceps brachii; (8) one is placed in front of, and another behind, the tendon of the Latissimus dorsi. The muscles in relation with the joint are, above, the Supraspinatus; below, the long head of the Triceps bracliii; in front, the Subscapularis; behind, the Infraspinatus and Teres minor; within, the tendon of the long head of the Biceps brachii. The Deltoideus covers the articulation in front, behind, and laterally. The arteries supplying the joint are articular branches of the anterior and posterior humeral circumflex, and transverse scapular. The nerves are derived from the axillary and suprascapular. Movements. — The shoulder-joint is capable of every variety of movement, flexion, extension, abduction, adduction, circumduction, and rotation. The humerus is flexed (drawn forward) by the Pectorahs major, anterior fibres of the Deltoideus, Coracobrachiahs, and when the fore- arm is flexed, by the Biceps brachii; extended (drawn backward) by the Latissimus dorsi. Teres major, posterior fibres of the Deltoideus, and, when the forearm is extended, by the Triceps brachii; it is abducted by the Deltoideus and Supraspinatus; it is adducted by the Subscapularis, Pectorahs major, Latissimus dorsi, and Teres major, and by the weight of the hmb; it is rotated outward by the Infraspinatus and Teres minor; and it is rotated inward by the Subscapularis, Latissimus dorsi. Teres major, Pectorahs major, and the anterior fibres of the Deltoideus. The most striking peculiarities in this joint are: (1) The large size of the head of the humerus in comparison mth the depth of the glenoid cavity, even when this latter is supplemented by the glenoidal labrum. (2) The looseness of the capsule of the joint. (3) The intimate connection of the capsule with the muscles attached to the head of the humerus. (4) The pecuhar relation of the tendon of the long head of the Biceps brachii to the joint. It is in consequence of the relative sizes of the two articular surfaces, and the looseness of the articular capsule, that the joint enjoys such free movement in all directions. When these movements of the arm are arrested in the shoulder- joint by the contact of the bony surfaces, and by the tension of the fibres of the capsule, together with that of the muscles acting as accessor}' ligaments, the arm can be carried considerably farther by the movements of the scapula, involv- ing, of course, motion at the acromio- and sternoclavicular joints. These joints are therefore to be regarded as accessory structm-es to the shoulder-joint (see pages 411 and 413). The extent of the scapular movements is very considerable, especially in extreme elevation of the arm, a movement best accompHshed when the arm is thrown somewhat forward and outward, because the margin of the head of the humerus is by no means a true circle; its greatest diameter is from the intertubercular groove, downward, medialward, and backward, and the greatest elevation of the arm can be obtained by rolhng its articular surface in the direction of this measurement. The great width of the central portion of the humeral head also allows of very free horizontal movement when the arm is raised to a right angle, in which movement the arch formed by the acromion, the coracoid process and the coracoacromial hgament, constitutes a sort of supple- mental articular cavity for the head of the bone. The looseness of the capsule is so great that the arm will fall about 2.5 cm. from the scapula when the muscles are dissected from the capsule, and an opening made in it to counteract the atmospheric pressiire. The movements of the joint, therefore, are not regulated by the capsult so much as by the surroimding muscles and by the pressure of the atmosphere, an arrangemene which "renders the movements of the joint much more easy than they would otherwise haA'e been, and permits a swinging, pendulum-hke vibration of the Umb when the muscles are at rest" (Hiunphry). The fact, also, that in all ordinary positions of the joint the capsule is not put on the stretch, enables the arm to move freely in all directions. Extreme movements are checked by the tension of appropriate portions of the capsule, as well as by the interlocking of the bones. Thus it is said that "abduction is checked by the contact of the great tuberosity with the upper edge of the glenoid cavity; adduction by the tension of the coracohimaeral hgament" (Beaimis et Bouchard). Cleland^ maintains that the limitations of movement at the shoulder-joint are due to the structure of the joint itself, the glenoidal labrum fitting, in different positions of the elevated arm, into the anatomical neck of the humerus. The scapula is capable of being moved upward and downward, forward and backward, or, bj- a combination of these movements, circumducted on the wall of the chest. The muscles which raise the scapula are the upper fibres of the Trapezius, the Levator scapulae, and the Rhomboidei ; those which depress it are the lower fibres of the Trapezius, the Pectorahs minor, and, through the clavicle, the Subclavius. The scapula is drawn backward by the Rhomboidei and the middle and lower fibres of the Trapezius, and forward by the Serratus anterior and Pectorahs minor, assisted, when the arm is fixed, by the Pectorahs major. The mobihty of the scapula is very ' Journal of Anatomy and Physiologj', 1867, i, 8.5. HLMERAL ARTICULATIOX OR SHOi'LDER-JOINT 417 considerable, and greatly assists the movements of the arm at the shoulder-joint. Thus, in raising the arm from the side, the Deltoideus and Supraspinatus can only lift it to a right angle with the trunk, the further elevation of the limb being effected by the Trapezius and Serratus anterior moving the scapula on the wall of the chest. This mobihty is of special importance in ankjdosis of the shoulder-joint, the movements of this bone compensating to a veiy great extent for the immobility of the joint. Cathcart^ has pointed out that in abducting the arm and raising it above the head, the scapula rotates throughout the whole movement with the exception of a short space at the beginning and at the end; that the humerus moves on the scapula not only while passing from the hanging to the horizontal position, but also in travelling upward as it approaches the vertical above; that the clavicle moves not only during the second half of the movement but in the first as well, though to a less extent — i. e., the scapula and clavicle are concerned in the first stage as well as in the second; and that the humerus is partly involved in the second as well as chiefly in the first. The intimate union of the tendons of the Supraspinatus, Infraspinatus, Teres minor and Subscapularis with the capsule, converts these muscles into elastic and spontaneously acting ligaments of the joint. The peculiar relations of the tendon of the long head of the Biceps brachii to the shoulder- joint appear to subserve various purposes. In the first place, by its connection with both the shoulder and elbow the muscle harmonizes the action of the two joints, and acts as an elastic ligament in all positions, in the manner previously discussed (see page 383). It strengthens the upper part of the articular cavity, and prevents the head of the humerus from being pressed up against the acromion, when the Deltoideus contracts; it thus fixes the head of the humerus as the centre of motion in the glenoid cavity. By its passage along the intertubercular groove it assists in steadying the head of the humerus in the various movements of the arm. When the arm is raised from the side it assists the Supraspinatus and Infraspinatus in rotating the head of the humerus in the glenoid cavity. It also holds the head of the bone firmly in contact wnth the glenoid cavity, and prevents its slipping over its lower edge, or being displaced by the action of the Latissimus dorsi and Pectoralis major, as in climbing and many other movements. Applied Anatomy. — Owing to the construction of the shoulder-joint and the freedom of move- ment which it enjoys, as well as in consequence of its exposed situation, it is more frequently dislocated than any other joint. Dislocation occurs when the arm is abducted, and when, there- fore, the head of the humerus presses against the lower and front part of the capsule, which is the thinnest and least supported part of the hgament. The rent in the capsule almost invariably takes place in this situation, and through it the head of the bone escapes, so that the dislocation in most instances is primarily subglenoid. The head of the bone does not usually remain in this situation, between the tendons of the Subscapularis and the Triceps brachii, but generally assumes some other position, which varies according to the direction and amount of force producing the dislocation and the relative strength of the muscles in front of and behind the joint. As the muscles at the back are stronger than those in front, and especially since the long head of the Triceps brachii prevents the bone from passing backward, dislocation forward is much the more common. The most frequent position which the head of the humerus ultimately assumes is on the front of the neck of the scapula, beneath the coracoid process, and hence named subcoracoid. Occasionally, in consequence of a greater amoimt of force being brought to bear on the limb, the head is driven farther medialward, and rests on the upper part of the front of the chest, be- neath the clavicle (subclavicular) . Sometimes it remains in the position in which it was primarily displaced, resting on the axillary border of the scapula (subglenoid), and rarely it passes back- ward and remains in the infraspinatous fossa, beneath the spine (subspinous). The shoulder- joint may be the seat of any of those inflammatory affections, either acute or chronic, which attack joints, though perhaps less frequently than some other articulations of equal size and importance. Acute synovitis may result from injury, rheumatism, or pyemia, or may follow secondarily on acute epiphysitis in infants. It is attended with effusion into the joint, and when this occurs the capsule is evenly distended, and the contour of the joint rounded. Special projections may occur at the sites of the openings in the capsule. Thus a swelling may appear just medial to the lesser tubercle, from effusion into the bxu-sa beneath the Subscapularis; or, again, a swelUng which is sometimes bilobed may be seen in the interval between the Deltoideus and PectoraUs major, from effusion into the diverticulum which runs down the intertubercular groove with the tendon of the Biceps brachii. The effusion into the joint cavity can be best ascertained by examination from the axilla, where a soft, elastic, fluctuating swelling can usually be felt. In cases of septic synovitis, where incision is required, the opening should be made in front, over the most prominent point of the sweUing. After the pus has been evacuated a counter- opening should be made behind, so as to ensure efficient di-ainage. Tuberculous arthritis not infrequently attacks the shoulder-joint, and may lead to total destruc- tion of the articulation, when ankylosis may result, or long-protracted suppuration may necessitate 1 Journal of Anatomy and Physiology, 1884, vol. xviii. 27 418 SYXDESMOLOGY excision. This joint is also one of those which is most liable to be the seat of osteoarthritis, and may also be affected in gout and rheumatism; or in locomotor ataxia, when it becomes the seat of Charcot's disease. Ankylosis is occasionally met with in the shoulder-joint as the result of destructive changes. The ankylosis usually takes place with the arm in a dependent position, and any attempt to raise the arm is attended by a rotation of the scapula on the wall of the chest. Excision of the shoulder-joint may be required in cases of arthritis (especially the tuberculous form) which have gone on to destruction of the articulation; in compound dislocations and frac- tures, particularly those arising from gunshot injuries, in which there has been extensive injury to the head of the bone; in some cases of old unreduced dislocation, where there is much pain. The operation is best performed by making an incision from the middle of the coracoacromial ligament do-mi the arm for about 7 or 8 cm.; this will expose the intertubercular groove contain- ing the tendon of the Biceps brachii, which should be hooked out of the way. The capsule is freely opened, and the muscles attached to the greater and lesser tubercles of the humerus are stripped off mth the capsiile, without dividing their attachments to the latter. The head of the bone can then be thriist out of the wound and sawn off; or divided with a narrow saw in situ and subsequently removed. The section should be made, if possible, just below the articular surface, so as to leave the bone as long as possible. IV. Elbow-joint Articulatio Cubiti; (Tigs. 451, 452). The elbow-joint is a ginglymus or hinge-joint. The trochlea of the humerus is received into the semilunar notch of the ulna, and the capitulum of the humerus articulates ^\dth the fovea on the head of the radius. The articular surfaces are connected together by a capsule, which is thickened medially and laterally, and, to a less extent, in front and behind. These thickened portions are usually described as distinct ligaments under the following names : The Anterior. The Ulnar Collateral. The Posterior. The Radial Collateral. The Anterior Ligament (Fig. 451). — ^The anterior ligament is a broad and thin fibrous layer covering the anterior surface of the joint. It is attached to the front of the medial epicondyle and to the front of the humerus immediately above the coronoid and radial fossEe; heloic, to the anterior surface of the coronoid process of the ulna and to the annular ligament I'page 422j, being continuous on either side with the collateral ligaments. Its superficial fibres pass obliquely from the medial epicondyle of the humerus to the annular ligament. The middle fibres, vertical in direction, pass from the upper part of the coronoid depression and become partly blended with the preceding, but are inserted mainly into the anterior surface of the coronoid process. The deep or transA'erse set intersects these at right angles. This ligament is in relation, in front, with the Brachialis, except at its most lateral part. The Posterior Ligament 'Fig. 452 j. — This posterior ligament is thin and mem- branous, and consists of transverse and oblique fibres. Above, it is attached to the humerus immediately behind the capitulum and clo.se to the medial margin of tihe trochlea, to the margins of the olecranon fossa, and to the back of the lateral epicondyle some little distance from the trochlea. Below, it is fixed to the upper and lateral margins of the olecranon, to the posterior part of the annular ligament, and to the ulna behind the radial notch. The transverse fibres form a strong band which bridges across the olecranon fossa ; under cover of this band a pouch of synovial membrane and a pad of fat project into the upper part of the fossa when the joint is extended. In the fat are a few scattered fibrous bundles, which pass from the deep surface of the transverse band to the upper part of the fossa. This ligament is in relation, heJiind, with the tendon of the Triceps brachii and the Anconaeus. The Ulnar Collateral Ligament (Ugamentum collaterale ulnare; internal lateral ligament) (Fig. 451 j. — This ligament is a thick triangular band consisting of two ELBOW-JOINT 419 portions, an aiit(>ri()r and i)osterior nnitcd hy a thinner intermediate portion. The anterior portion, directed ol)li(iuel\- forward, is attached, ahow, h\ its apex, to the front part of the medial epicondyle of the humerus; and, below, hy its broad base to the me(Hal margin of the coronoid process. The posterior portion, also of trian- gular form, is attached, above, by its apex, to the lower and Inick jjart of the medial epicondyle; below, to the medial margin of the olecranon. Ik^tween these two bands a few intermediate fibres descend from the medial epicondyle to blend with a transverse band which bridges across the notch between the olecranon and the coronoid process. This ligament is in relation with the Triceps brachii and Flexor carpi ulnaris and the ulnar nerve, and gives origin to part of the Flexor digitorum sublimis. Fig. 451. — Left elbow-joint, showing anterior and ulnar collateral ligaments. Fig. 452. — ^Left elbow-joint, showing posterior and radial collateral ligaments. The Radial Collateral Ligament {ligamentum collaterale radiale; external lateral ligament) (Fig. 452). — This ligament is a short and narrow fibrous band, less dis- tinct than the ulnar collateral, attached, above, to a depression below the lateral epicondyle of the humerus; below, to the annular ligament, some of its most pos- terior fibres passing over that ligament, to be inserted into the lateral margin of the ulna. It is intimately blended with the tendon of origin of the Supinator. Sjrnovial Membrane (Figs. 453, 454). — The synovial membrane is very extensive. It extends from the margin of the articular sm-face of the humerus, and lines the coronoid, radial and olec- ranon fossae on that bone; it is reflected over the deep surface of the capsule and forms a pouch between the radial notch, the deep surface of the annular ligament, and the circumference of the head of the radius. Projecting between the radius and ulna into the cavity is a cresceiitic fold of 420 SYNDESMOLOGY synovial membrane, suggesting the division of the joint into two; one the humeroradial, the other the humeroulnar. Between the capsule and the synovial membrane are three masses of fat: the largest, over the olecranon fossa, is pressed into the fossa by the Triceps brachii during the flexion; the second, over the coronoid fossa, and the third, over the radial fossa, are pressed by the Brachialis into their respective fossae during extension. The muscles in relation with the joint are, in front, the Brachialis; behind, the Triceps brachii and Anconaeus; laterally, the Supinator, and the common tendon of origin of the Extensor muscles; medially, the common tendon of origin of the Flexor muscles, and the Flexor carpi ulnaris. The arteries supplying the joint are derived from the anastomosis between the profunda and the superior and inferior iiLnar collateral branches of the brachial, with the anterior, posterior, and interosseous recm-rent branches of the ulnar, and the recurrent branch of the radial. These vessels form a complete anastomotic network around the joint. Fig. 453. — Capsule of elbow-joint (distended). Anterior aspect. Fig. 454. — Capsule of elbow-joint (distended). Posterior aspect. The nerves of the joint are a twig from the ulnar, as it passes between the medial condyle and the olecranon; a filament from the musculocutaneous, and two from the median. Movements. — The elbow-joint comprises three different portions — viz., the joint between the ulna and humerus, that between the head of the radius and the humerus, and the proximal radioulnar articulation, described below. All these articular surfaces are enveloped by a common synovial membrane, and the movements of the whole joint should be studied together. The com- bination of the movements of flexion and extension of the forearm with those of pronation and supination of the hand, which is ensured by the two being performed at the same joint, is essential to the accuracy of the various minute movements of the hand. The portion of the joint between the ulna and humerus is a simple hinge-joint, and allows of movements of flexion and extension only. Owing to the obUquity of the trochlea of the humerus, this movement does not take place in the antero-posterior plane of the body of the humerus. ELBOW-JOINT 421 When the forearm is extended and supinated, the axes of the arm and forearm are not in the same line; the arm forms an obtuse angle with the forearm, the hand and forearm being directed lateral- ward. During flexion, however, the forearm and the hand tend to approach the middle hne of the body, and thus enable the hand to be easily carried to the face. The accurate adaptation of the trochlea of the humerus, with its prominences and depressions, to the semilunar notch of the ulna, prevents any lateral movement. Flexion is produced by the action of the Biceps brachii and Brachialis, assisted by the Brachioradiahs and the muscles arising from the medial condyle of the humerus; cxleusion, by the Triceps brachii and Anconaeus, assisted by the Extensors of the wrist, the Extensor digitoruni comnmnis, and the Extensor digiti quinti proprius. The joint between the head of the radius and the capitulum of the humerus is an arthrodial joint. The bony surfaces would of themselves constitute an enarthrosis and allow of movement in all directions, were it not for the annular Ugament, by which the head of the radius is bound to the radial notch of the ulna, and which prevents any separation of the two bones laterally. It is to the same ligament that the head of the radius owes its security from dislocation, which would otherwise tend to occur, from the shallowness of the cup-like surface on the head of the radius. In fact, but for this hgament, the tendon of the Biceps brachii would be hable to pull the head of the radius out of the joint. The head of the radius is not in complete contact with the capitulum of the humerus in all positions of the joint. The capitulum occupies only the anterior and inferior surfaces of the lower end of the humerus, so that in complete extension a part of the radial head can be plainly felt projecting at the back of the articulation. In full flexion the movement of the radial head is hampered by the compression of the surrounding soft parts, so that the freest rotatory movement of the radius on the humerus (pronation and supina- tion) takes place in semiflexion, in which position the two articular surfaces are in most intimate contact. Flexion and extension of the elbow-joint are limited by the tension of the structures on the front and back of the joint; the limitation of flexion is also aided by the soft structm-es of the arm and forearm coming into contact. In any position of flexion or extension, the radius, carrying the hand with it, can be rotated in the proximal radioulnar joint. The hand is directly articulated to the lower surface of the radius only, and the ulnar notch on the lower end of the radius travels aroimd the lower end of the ulna. The latter bone is excluded from the wrist-joint by the articular disk. Thus, rotation of the head of the radius around an axis passing through the centre of the radial head of the humerus imparts circular movement to the hand through a very considerable arc. Applied Anatomy. — From the great breadth of the joint, and the manner in which the articular surfaces are interlocked, and also on account of the strong collateral ligaments and the support which the joint derives from the mass of muscles attached to each epicondyle of the humerus, lateral displacement of the bones is very uncommon; whereas antero-posterior dislocation, on account of the shortness of the antero-posterior diameter, the weakness of the anterior and posterior hgaments, and the want of support of muscles, occurs much more frequently. Dislo- cation backward takes place when the forearm is in a position of extension, and forward when in a position of flexion. For, in the extended position, the coronoid process is not locked into the coronoid fossa, and loses its grip to a certain extent, whereas the olecranon is in the olecranon fossa, and entirely prevents displacement forward. On the other hand, during flexion, the coronoid process is in the coronoid fossa, and prevents dislocation backward, while the olecranon, having left the olecranon fossa, is not so efficient in preventing a forward displacement. When lateral dislocation does take place it is generally incomplete. Dislocation of the elbow-joint is of common occm'rence in children, far more common than dislocation of any other articiUation. As a rule, in yoimg persons, the appUcation of any severe violence to a joint is more likely to produce a fracture of bone than dislocation. In lesions of this joint there is often very great difficulty in ascertaining the exact natm-e of the injury. The elbow-joint is occasionally the seat of acute synovitis. The joint-cavity then becomes distended witla fluid, the bulging showing itself principally around the olecranon, in consequence of the laxness of the posterior hgament. Again, there is often some swelling just above the head of the radius, in the Ime of the radiohumeral joint, or the whole elbow may assume a fusiform appearance. There is not generally much swelhng at the front of the joint, though sometimes deep-seated fulness beneath the Brachiahs may be noted. W^hen suppm'ation occurs the abscess usually points at one or other border of the Triceps brachii; occasionaUy the pus discharges itself in front, near the insertion of the Brachiahs. In cases of suppm-ative sjTiovitis, incisions should be made into the joint on either side of the olecranon, care being taken to avoid woimding the uhiar nerve on the medial side. Chronic synovitis, usually of tuberculous origin, is of common occm-rence in the elbow-joint; in such cases the forearm tends to assume the position of semi- flexion, which is that of greatest ease and relaxation of hgaments. It should be borne in mind that if ankylosis occm* in this or the extended position, the limb will not be nearlj- so useful as if ankylosed in a position of rather less than a right angle. The elbow-joint is also sometimes affected with osteoarthi'itis, but less commonly than some of the larger joints. Excision of the elbow is principally requii-ed for one of three conditions — viz., tuberculous arthritis, injurj' and its results, or faultj^ ankylosis — but maj^ be necessary for some other rarer 422 SYNDESMOLOGY conditions, such as disorganizing arthritis after pyemia and unreduced dislocations. The results of the operation are, as a rule, more favorable than those of excision of any other joint, especially in any of the first three conditions mentioned above. The operation is best performed by a vertical incision down the back of the joint; a straight incision is made about 10 cm. long, the mid-point of which is on a level with and a little to the medial side of the tip of the olecranon. This incision is made down to the bone, through the substance of the Triceps brachii. The operator, guarding the soft parts with his thumb-nail, separates them from the bone with the point of his knife. In doing this there are two structures which he should carefully avoid: the ulnar nerve, which as it courses down between the medial epicondyle and the olecranon lies parallel but a little medial to his incision; and the prolongation of the Triceps brachii into the deep fascia of the forearm over the Anconaeus. Having cleared the bones and divided the col- lateral and posterior ligaments, the forearm is strongly flexed and the ends of the bones turned out and sawn off. The turning out of the ends of the bones is rendered easier by first cutting off the olecranon with a pair of cutting bone forceps. The section of the humerus should be through the base of the epicondyles, that of the ulna and radius should be just below the level of the radial notch of the ulna and the neck of the radius. In this operation the object is to obtain such imion as shall allow free motion of the bones of the forearm; and, therefore, passive move- ments must be commenced early — that is to say, about the tenth day. It is most important to maintain the continuity of the Triceps brachii with the deep fascia of the forearm, so as to obtain good power of extension in the new joint. V. Radioulnar Articulations (Articulatio Radioulnaris) . The articulation of the radius with the ulna is effected by ligaments which con- nect together the extremities as well as the bodies of these bones. The ligaments may, consequently, be subdivided into three sets : 1 , those of the proximal radio- ulnar articulation; 2, the middle radioulnar ligaments; 3, those of the distal radio- ulnar articulation. Proximal Radioulnar Articulation (articulatio radioulnaris proximalis; superior radioulnar joint). — This articulation is a trochoid or pivot-joint between the circumference of the head of the radius and the ring formed by the radial notch of the ulna and the annular ligament. Head of radius Quadrate {cut) ligament Semilunar notch Annular ligament Radial notch ' Olecranon [cut) Fig. 455. — Annular ligament of radius, from above. The head of the radius has been sawn ofi and the bone dislodged from the ligament. The Annular Ligament (ligamentum annulare radii; orbicular ligament) (Fig. 455). — This ligament is a strong band of fibres, which encircles the head of the radius, and retains it in contact with the radial notch of the ulna. It forms about four- fifths of the osseo-fibrous ring, and is attached to the anterior and posterior margins of the radial notch ; a few of its lower fibres are continued around below the cavity and form at this level a complete fibrous ring. Its upper border blends with the anterior and posterior ligaments of the elbow, while from its lower border a thin RADIOULNAR ARTICULATIONS 423 loose membrane passes to be attached to the neck of the radius; a thickened band "which extends from the inferior border of the annular liulo7i of Popliteu-s Lateral meniscus Fibular collateral ligament Ligament of Wrisherg Medial meniscu^i Tibial collateral ligament Fig. 469. — Left knee-joint from behind, phoning inteiior ligaments. The Posterior Cruciate Ligament (ligamentum cruciatum posterius; internal crucial ligament) (Fig. 469) is stronger, but shorter and less oblique in its direction, than the anterior. It is attached to the posterior intercondyloid fossa of the tibia, and to the posterior extremity of the lateral meniscus; and passes upward, forAvard, and medialward, to be fixed into the lateral and front part of the medial condyle of the femur. The Menisci [semilunar fihrocartilages) (Fig. 470). — The menisci are two crescentic lamella?, which serve to deepen the surfaces of the head of the tibia for articulation with the condyles of the femur. The peripheral border of each meniscus is thick, convex, and attached to the inside of the capsule of the joint; the opposite border is thin, concave, and free. The upper surfaces of the menisci are concave, and in contact with the condyles of the femur; their lower surfaces are flat, and rest upon the head of the tibia; both surfaces are smooth, and invested by synovial membrane. Each meniscus covers approximately the peripheral two-thirds of the corresponding articular surface of the tibia. 442 SYNDESMOLOGY The medial meniscus (meniscus medialis; internal semilunar fibrocartilage) is nearly semicircular in form, a little elongated from before backward, and broader behind than in front; its anterior end, thin and pointed, is attached to the anterior intercondyloid fossa of the tibia, in front of the anterior cruciate ligament; its posterior end is fixed to the posterior intercondyloid fossa of the tibia, between the attachments of the lateral meniscus and the posterior cruciate ligament. Anterior cruciate ligament Transverse ligament I Ligament of Wrishcrg Posterior cruciate ligament Fig. 470. — Head of right tibia seen from above, showing menisci and attachments of ligaments. The lateral meniscus (meniscus lateralis; external semilunar fibrocartilage) is nearly circular and covers a larger portion of the articular surface than the medial one. It i& grooved laterally for the tendon of the Popliteus, which separates it from the fibular collateral ligament. Its anterior end is attached in front of the intercon- dyloid eminence of the tibia, lateral to, and behind, the anterior cruciate ligament, with which it blends; the posterior end is attached behind the intercondyloid eminence of the tibia and in front of the posterior end of the medial meniscus. The anterior attachment of the lateral meniscus is twisted on itself so that its free margin looks backward and upward, its anterior end resting on a sloping shelf of bone on the front of the lateral process of the intercondyloid eminence. Close to its posterior attachment it sends off a strong fasciculus, the ligament of Wrisberg (Figs. 469, 470), w^hich passes upward and medialward, to be inserted into the medial condyle of the femur, immediately behind the attachment of the posterior cruciate ligament. Occasionally a small fasciculus passes forward to be inserted into the lateral part of the anterior cruciate ligament. The lateral meniscus gives off from its anterior convex margin a fasciculus which forms the transverse ligament. The Transverse Ligament (ligamentum transversuvi genu).- — The transverse liga- ment connects the anterior convex margin of the lateral meniscus to the anterior end of the medial meniscus; its thickness varies considerably in different subjects, and it is sometimes absent. The coronary ligaments are merely portions of the capsule, which connect the periphery of each meniscus with the margin of the head of the tibia. Synovial Membrane. — The synovial membrane of the knee-joint is the largest and most exten- sive in the body. Commencing at the upper border of the patella, it forms a large cul-de-sac beneath the Quadriceps femoris (Figs. 471, 472) on the lower part of the front of the femur, and frequently communicates with a bursa interposed between the tendon and the front of the femur. The pouch of synovial membrane between the Quadriceps and front of the femur is supported, during the movements of the knee, by a small muscle, the Articularis genu, which THE KXEE-JOIXT 443 is inserted into it. On either side of the patella, the synovial membrane extends beneath the aponem-oses of the \'asti, and more especially beneath that of the Va-stus medialLs. Below the patella it is separated from the ligamentum patellae by a considerable quantity of fat. known as the infrapatellar pad. From the medial and lateral borders of the articular surface of the patella, reduplications of the synovial momljrane project into the interior of the joint. These form two fringe-hke folds termed the alar folds; below, these folds converge and are continued as a single band, the patellar fold (ligamcnluin mucosum), to the front of the intercondyloid fossa of the femur. On either side of the joint, the s\'novial membrane passes downward from the femur, lining the capsule to its point of attachment to the menisci; it may then be traced over the upper surfaces of these to their free borders, and thence along their under surfaces to the tibia (Figs. 472, 473). Oblique poplitt ligament Medial meniscus k — Adipose tissue Bursa under Quadriceps fevioris Medial meniscus ^j^ Ligament urn paiellce Bursa between tibia and ligamentum patellae Fig. 471. — ^Sagittal section of right knee-joint. At the back part of the lateral meniscus it forms a cul-de-sac between the gi'oove on its surface and the tendon of the Popliteus; it is reflected across the front of the cruciate ligaments, which are therefore situated outside the SATiovial cavity. Bursae. — The bursae near the knee-joint are the following: In front there are four bm-sae: a large one is interposed between the patella and the skin, a small one between the upper part of the tibia and the ligamentum patellae, a thii-d between the lower part of the tuberosity of the tibia and the skin, and a fourth between the anterior sm-face of the lower part of the femur and the deep siirface of the Quadiiceps femoris, usually commimicating with the knee-joint. LateraUj- there are four bursae: (1) one (which sometimes coimaiunicates with the joint) between the lateral head of the Gastrocnemius and the capsule; (2) one between the fibular collateral ligament 444 SYNDESMOLOGY and the tendon of the Biceps; (3) one between the fil)ul:ir collaUTul Uganient and the tendon of the Pophteus (this is sometimes only an expansion from the next bursa); (4) one between the tendon of the Pophteus and the lateral condyle of the femur, usually an extension from the synovial membrane of the joint. Medially, there are five burste: (1) one between the medial head of the Gastrocnemius and the (;apsule; this sends a prolongation between the tendon of the medial head of the Gastrocnemius and the tendon of the Semimembranosus and often communi- cates with the joint; (2) one superficial to the tibial collateral ligament, between it and the tendons of the Sartorius, Gracilis, and Semitendinosus; (3) one deep to the tibial collateral ligament, between it and the tendon of the Semimembranosus (this is sometimes only an expansion from the next bursa) ; (4) one between the tendon of the Semimembranosus and the head of the tibia; (5) occasionally there is a bursa between the tendons of the Semimembranosus and Semitendinosus. Ouadi iccfs jemons Fibular collateral ligament Tendon of Popllteus Lateral meniscus n L'gamcntum I J patellae Fig. 472. — Capsule of right knee-joint (di.stended) . Lateral aspect. Structures Around the Joint. — In front, and at the sides, is the Quadriceps femoris; laterally the tendons of the Biceps femoris and Pophteus and the common peroneal nerve; medially, the Sartorius, Gracihs, Semitendinosus, and Semimembranosus; behind, the pophteal vessels, and the tibial nerve, Pophteus, Plant aris, and medial and lateral heads of the Gastrocnemius, some lymph glands, and fat. The arteries supplying the joint are the highest genicular (anastomotica magna), a branch of the femoral, the genicular branches of the popliteal, the recurrent branches of the anterior tibial, and the descending branch from the lateral femoral circumflex of the profunda femoris. The nerves are derived from the obturator, femoral, tibial, and common peroneal. Movements. — The movements which take place at the knee-joint are flexion and extension, and, in certain positions of the joint, internal and external rotation. The movements of flexion and extension at this joint differ from those in a typical hinge-joint, such as the elbow, in that (a) the axis around which motion takes place is not a fixed one, but shifts forward during extension and backward during flexion; (5) the commencement of flexion and the end of extension are accompanied by rotatory movements associated with the fixation of the limb in a position of THE KNKK-JOIJ^T 445 Icxion Id lull cxicMision may lIuTol'ore bo (Inscribed posterior parts ol I lu surfaces, and in tlii^ leinora.i condyle,^ position a slif^ht- I'cst on tlio corre amount, of sim])l( great stability. The movement from in throe phases: 1. In the fully flexed condition I he spondiiAf;- portions of the meniscol il)ial rolling movement is allowed. 2. During the passage of the limb from the flexed to the extended jjosition a gliding movement is superposeil on the rolling, so that the axis, which at the commencement is re])rcseiited by a line through the inner and outer condyles of the femur, gradually shifts forward. In this part of the movement, the posterior two-tliirds of the tibial arti(adar surfaces of the two femoral condyles are involved, and as these have similar curvatures and are parallel to one another, they move forward equally. Posterior cruciate ligcmieni Medial meniscus Tibial collateral lifjanieni Anterior cruciate ligctment Lateral meniscus fibular collateral ligament Fig. 473. — Capsule of riglit knee-joint (distended). Posterior aspect. 3. The lateral condyle of the femur is brought almost to rest by the tightening of the anterior cruciate Ugament; it moves, however, shghtly forward and medialward, pvishing before it the anterior part of the lateral meniscus. The tibial surface on the medial condyle is prolonged farther forward than that on the lateral, and this prolongation is directed lateralward. When, therefore, the movement forward of the condyles is checked by the anterior cruciate ligament, continued muscular action causes the medial condyle, dragging with it the meniscus, to travel backward and medialward, thus producing an internal rotation of the thigh on the leg. When the position of full extension is reached the lateral part of the groove on the lateral condyle is pressed against the anterior part of the corresponding meniscus, while the medial part of the groove rests on the articular margin in front of the lateral process of the tibial intercondyloid eminence. Into the groove on the medial condyle is fitted the anterior part of the medial meniscus, while the anterior cruciate ligament and the articular margin in front of the medial process of the tibial intercondyloid eminence are received into the forepart of the intercondyloid fossa of the femur. This third phase by which all these parts are brought into accurate apposition is known as the "screwing home," or locking movement of the joint. The complete movement of flexion is the converse of that described above, and is therefore preceded by an external rotation of the femur which unlocks the extended joint. The axes around which the movements of flexion and extension take place are not preciselj- at right angles to either bone; in flexion, the femur and tibia are in the same plane, but in exten- sion the one bone forms an angle, opening lateralward with the other. 446 SYNDESMOLOGY In addition to the rotatory movements associated with the comijlctioii of extension and the initiation of flexion, rotation inward or outward can be effected when the joint is partially flexed; these movements take place mainty between the tibia and the menisci, and are freest when the leg is bent at right angles with the thigh. Movements of Patella. — The articular surface of the patella is indistinctly divided into seven facets — upper, middle, and lower horizontal pairs, and a medial perpendicular facet (Fig. 474). When the knee is forcibly flexed, the medial perpendicular facet is in contact with the semilunar surface on the lateral part of the medial condyle; this semilunar surface is a pro- longation backward of the medial part of the patellar surface. As the leg is carried from the flexed to the extended position, first the highest pair, then the middle pair, and lastly the lowest pair of horizontal facets is successively brought into contact with the patellar sm'face of the femur. In the ex- tended position, when the Quadriceps femoris is relaxed, the patella Ues loosely on the front of the lower end of the femur. During flexion, the ligamentum patellae is put upon the stretch, and in extreme flexion the posterior cruciate „ . . . , ligament, the oblique popliteal, and collateral Ugaments, Fig. 474. — Posterior surface of the i, \- t ^ l ^ \^ j. ■ ■ j. i- j. right patella, showing diagrammatically and, to a shght extent, the anterior cruciate hgament, the areas of contact with the femur in are relaxed. Flexion is checked during life by the contact posi ions o e -nee. ^^ ^-^^ ^^^ ^.^j^ the thigh. When the knee-joint is fully extended the oblique pophteal and collateral ligaments, the anterior cruciate ligament, and the posterior cruciate ligament, are rendered tense; in the act of extending the knee, the ligamentum patellae is tightened by the Quadriceps femoris, but in full extension with the heel supported it is relaxed. Rotation inward is checked by the anterior cruciate ligament; rotation outward tends to xmcross and relax the cruciate liga- ments, but is checked by the tibial collateral ligament. The main function of the cruciate liga- ment is to act as a direct bond between the tibia and femur and to prevent the former bone from being carried too far backward or forward. They also assist the collateral Ugaments in resisting any bending of the joint to either side. The menisci are intended, as it seems, to adapt the surfaces of the tibia to the shape of the femoral condyles to a certain extent, so as to fill up the intervals which would otherwise be left in the varying positions of the joint, and to obviate the jars which would be so frequently transmitted up the hmb in jumping or by falls on the feet; also to permit of the two varieties of motion, flexion and extension, and rotation, as explained above. The patella is a great defence to the front of the knee-joint, and distributes upon a large and tolerably even surface, during kneeling, the pressure which would otherwise fall upon the prominent ridges of the condyles; it also affords leverage to the Quadriceps femoris. When standing erect in the attitude of "attention," the weight of the body falls in front of a line carried across the centres of the knee-joints, and therefore tends to produce overextension of the articulations; this, however, is prevented by the tension of the anterior cruciate, oblique popUteal, and collateral ligaments. Extension of the leg on the thigh is performed by the Quadriceps femoris; flexion by the Biceps femoris, Semitendinosus, and Semimembranosus, assisted by the GraciUs, Sartorius, Gastroc- nemius, Popliteus, and Plantaris. Rotation outward is effected by the Biceps femoris, and rota- tion inward by the Popliteus, Semitendinosus, and, to a shght extent, the Semimembranosus, the Sartorius, and the Gracihs. The Pophteus comes into action especially at the commencement of the movement of flexion of the knee; by its contraction the leg is rotated inward, or, if the tibia be fixed, the thigh is rotated outward, and the knee-joint is unlocked. Applied Anatomy. — From a consideration of the construction of the knee-joint, it would at first sight appear to be one of the least secure joints in the body. It is formed between the two longest bones, and therefore the amount of leverage which can be brought to bear upon it is con- siderable; the articular surfaces are but ill-adapted to each other, and the range of motion which it enjoys is great. All these circumstances tend to render the articulation insecure; never- theless on account of the powerful hgaments which bind the bones together, the joint is one of the strongest in the body, and dislocation from traumatism is a rare occurrence. When, on the other hand, the hgaments have been softened or destroyed by disease, partial displacement is Uable to occur, and is frequently brought about by the action of the muscles. One or other of the menisci may become displaced and nipped between the femur and tibia. The accident is produced by a twist of the leg when the knee is flexed, and is accompanied by a sudden pain and fixation of the knee in a flexed position. The meniscus may be displaced either medialward or lateralward; that is to say, either toward the tibial intercondyloid eminence, so that the cartilage becomes lodged in the intercondyloid fossa; or to one side, so that the cartilage projects beyond the margin of the two articular surfaces. The medial meniscus is much more commonly affected than the lateral. Acute synovitis, the result of traumatism, is of frequent occurrence in the knee, on account of ARTICULATIONS BKTWEEX THE TIBIA AXD FIBULA 447 the superficial position of the joint. When the cavity is distended with fluid, the swelling shows itself above and at the sides of the patella, reacihing about 2.5 cm., occasionally 5 cm. or more, above the patellar surface of the fenun-, and extending a little higher under the Vastus medialis than under the Vastus lateralis. The lower level of the synovial membrane is just at the level of the head of the tibia. Chronic synovitis shows itself principally in the form of pulpy degenera- tion of the sj'novial membrane, the result of tuberculous infection. Syphilitic disease with gum- matous infiltration of the synovial membrane may take place. The knee is one of the joints most commonly afTccted with osteoarthritis, and is more frequently the seat of this disease in women than in men. The occurrence of the so-called loose cartilages is almost confined to the knee, though thej' are occasionally met with in other joints. Many of them occur in cases of osteoarthritis, in which calcareous or cartilaginous material is formed in one of the synovial fringes and constitutes the foreign body, and may or may not become detached, only in the former case meriting the usual term, "loose" cartilage. In other cases they have their origin in the exudation of inflammatory lymph, and possibly, in some rare instances, a portion of the articular cartilage or one of the menisci becomes detached and constitutes the foreign body. In inflammatory affections of the knee-joint, the position of greatest ease, and therefore the one which is always assumed, is that of slight flexion. In this position there is the most complete relaxation of ligamentous structures, and, therefore, the greatest diminution in the tension caused bj' the effusion. If this flexed position be maintained for any length of time, it becomes perma- nent from fibrous adhesions taking place, and the utility of the limb is materially impaired. Attention should therefore be paid by the surgeon to the position of the limb; and by carefully appUed spUnts, with the leg in an extended position, this untoward result should be prevented. In cases of septic synovitis, incisions to evacuate the pus should be made vertically on either side of the patella, between it and the condyles of the femur. Genu valgum, or knock-knee, is a common deformity of childhood. In this condition, as the patient stands, the medial condyles of the two femora are in contact, but the two medial malleoli are more or less widely separated from each other. When, however, the knees are flexed to a right angle, the two legs are practically parallel with each other. At the commencement of the disease there is a yielding of the tibial collateral ligament and other fibrous structures on the medial side of the joint; as a result of this there is a constant undue pressure of the lateral condyle of the tibia against the lateral condyle of the femur. This pressure causes arrest of growth, and, possibly, wasting of the lateral condyle, and a consequent tendency for the tibia to become separated from the medial condyle of the femur. Irregular overgrowth from the medial portion of the epiphysial line takes place, giving rise to apparent enlargement of the medial condyle of the femur, the line of the epiphysis becoming oblique, with a direction downward and medialward, instead of at right angles to the axis of the bone. If the deformity be marked, an osteotomy of the femur is required to correct it. Excision of the knee-joint is most frequently required for tuberculous disease of this articula- tion, but is also practised in cases of disorganization of the knee from other causes. It is also occasionally called for in cases of injury, gmishot or otherwise. The operation is best performed by a horseshoe-shaped incision, starting from one femoral condyle, descending as low as the tuberosity of the tibia, and then carried upward to the other femoral condyle. The bone ends having been cleared, and in those cases where the operation is performed for tuberculous disease all pulpy tissue having been carefuUy removed, the section of the femur is first made. This should never include, in children, more than, at the most, two-thirds of the articular surface, otherwise the epiphysial cartilage will be involved, with disastrous results as regards the growth of the limb. Afterward a thin slice, not more than 1.25 cm., should be removed from the upper end of the tibia. If any diseased tissue still appears to be left in the bones, it should be removed with the gouge, rather than by a f mother section. The bursse about the knee-joint are sometimes the seat of enlargement. The bursa between the front of the patella and the skin is frequently affected in individuals who are in the habit of constantly kneeling, and the condition is then known as "housemaid's knee." The bm-sa be- neath the Semimembranosus tendon also occasionally becomes enlarged, and forms a fluctuating swelling at the back of the knee. During extension, the swelling is firm and tense; but during flexion it becomes soft, and, as the bursa often communicates with the sjiiovial cavity of the joint, the fluid it contains can be made to disappear by pressure when the knee is flexed. Exten- sion of septic processes within the joint is apt to occur along the tendon sheath of the PopUteus, and this may lead to deep-seated suppuration in the popliteal fossa, often associated with septic thrombosis of the popUteal vein; when this occurs amputation of the limb is necessary. III. Articulations between the Tibia and Fibula. The articulations between the tibia and fibula are effected by ligaments which connect the extremities and bodies of the bones. The ligaments may consequently 448 SYNDESMOLOGY be suhdividefl into three sets: (1) those of the Tihi(jfibiilar articuhition; (2) the interosseous membrane; (3) those of the Tibiofibular syndesmosis. Tibiofibular Articulation (ariicidatio iihiofibrihiris; superior tibiofibular articula- tion). — This articulation is an arthrodial joint between the lateral condyle of the tibia and the head of the fibula. The contiguous surfaces of the bones present flat, oval facets covered with cartilage and connected together by an articular capsule and by anterior and posterior ligaments. The Articular Capsule (capsula articularis; capsular ligament). — The articular capsule surrounds the articulation, being attached around the margins of the articular facets on the tibia and fibula; it is much thicker in front than behind. The Anterior Ligament (anterior superior ligament). — The anterior ligament of the head of the fibula (Fig. 468) consists of two or three broad and fiat bands, which pass obliquely upward from the front of the head of the fibula to the front of the lateral condyle of the tibia. The Posterior Ligament (posterior superior ligament). — The posterior ligament of the head of the fibula (Fig. 469) is a single thick and broad band, which pas.ses obliquely upward from the back of the head of the fibula to the back of the lateral condyle of the tibia. It is covered by the tendon of the Popliteus. Synovial Membrane. — A synovial membrane lines the capsule; it is continuous with that of the knee-joint in occasional cases when the two joints communicate. Interosseous Membrane (membrana interossea cruris; middle tibiofibular liga- ment). — An interosseous membrane extends between the interosseous crests of the tibia and fibula, and separates the muscles on the front from those on the back of the leg. It consists of a thin, aponeurotic lamina composed of oblique fibres, which for the most part run downward and lateralward; some few fibres, however, pass in the opposite direction. It is broader above than below. Its upper margin does not quite reach the tibiofibular joint, but presents a free concave border, above which is a large, oval aperture for the passage of the anterior tibial vessels to the front of the leg. In its lower part is an opening for the passage of the anterior peroneal vessels. It is continuous below with the interosseous ligament of the tibio- fibular syndesmosis, and presents numerous perforations for the passage of small vessels. It is in relation, in front, with the Tibialis anterior. Extensor digitorum longus, Extensor hallucis proprius, Peronaeus tertius, and the anterior tibial vessels and deep peroneal nerve; behind, with the Tibialis posterior and Flexor hallucis longus. Tibiofibular Syndesmosis (syndesmosis tibiofibidaris; inferior tibiofibular articu- lation). — This syndesmosis is formed by the rough, convex surface of the medial side of the lower end of the fibula, and a rough concave surface on the lateral side of the tibia. Below, to the extent of about 4 mm. these surfaces are smooth, and covered with cartilage, which is continuous with that of the ankle-joint. The ligaments are: anterior, posterior, inferior transverse, and interosseous. The Anterior Ligament (ligamentum malleoli lateralis anterius; anterior inferior ligament). — ^The anterior ligament of the lateral malleolus (Fig. 476) is a flat, triangular band of fibres, broader below than above, which extends obliquely downward and lateralward betvxeen the adjacent margins of the tibia and fibula, on the front aspect of the syndesmosis. It is in relation, m front, with the Peronaeus tertius, the aponeurosis of the leg, and the integument; behind, with the interosseous ligament; and lies in contact with the cartilage covering the talus. The Posterior Ligament (ligamentum malleoli lateralis posterius; po.sterior inferior ligament).- — The posterior ligament of the lateral malleolus (Fig." 476), smaller than the preceding, is disposed in a similar manner on the posterior surface of the syndesmosis. TALOCRURAL ARTICULATION OR ANKLE-JOINT 449 The Inferior Transverse Ligament. — The inferior transverse ligament lies in front of the posterior ligament, and is a strong, thick band, of yellowish fibres which passes transversely across the back of the joint, from the lateral malleolus to the posterior border of the articular surface of the tibia, almost as far as its malleolar process. This ligament projects below the margin of the bones, and forms part of the articulating surface for the talus. The Interosseous Ligament. — The interosseous ligament consists of numerous short, strong, fibrous bands, which pass between the contiguous rough surfaces of the tibia and fibula, and constitute the chief bond of union between the bones. It is continuous, above, with the interosseous membrane. Synovial Membrane. — The synovial membrane associated with the small arthrodial part of this joint is continuous with that of the ankle-joint. IV. Talocrural Articulation or Ankle-joint (Articulatio Talocruralis ; Tibiotarsal Articulation) . The ankle-joint is a ginglymus, or hinge-joint. The structures entering into its formation are the lower end of the tibia and its malleolus, the malleolus of the fibula, and the transverse ligament, which together form a mortise for the recep- tion of the upper convex surface of the talus and its medial and lateral facets. The bones are connected by the following ligaments: The Articular Capsule. The Deltoid. The Anterior Talofibular. The Posterior Talofibular. The Calcaneofibular. The Articular Capsule {cajjsida articularis; capsular ligament). — The articular cap- sule surrounds the joints, and is attached, above, to the borders of the articular surfaces of the tibia and malleoli ; and below, to the talus around its upper articular surface. Tarsometatarsal articulations Intertarsal Fig. 475. — Right talocrural intertarsal and tarsometatarsal articulations. Medial aspect. The anterior part of the capsule (anterior ligament) (Fig. 475) is a broad, thin, membranous layer, attached, above, to the anterior margin of the lower end of 29 450 SYNDESMOLOGY the tibia; below, to the takis, in front of its superior articular surface. It is in relation, in front, with the Extensor tendons of the toes, the tendons of the Tibialis anterior and Peronaeus tertius, and the anterior tibial vessels and deep peroneal nerve. The posterior part of the capsule {yosterior ligament) is very thin, and consists principally of transverse fibres. It is attached, above, to the margin of the articular surface of the tibia, blending Avith the transverse ligament; helou\ to the talus behind its superior articular facet. Laterally, it is somewhat thickened, and is attached to the hollow on the medial surface of the lateral malleolus. The Deltoid Ligament (ligamentum deltoideiim; internal lateral ligament) (Fig. 475). — The deltoid ligament is a strong, flat, triangular band, attached, above, to the apex and anterior and posterior borders of the medial malleolus. It consists of two sets of fibres, superficial and deep. Of the superficial fibres the most anterior (tibionavicular) pass forward to be inserted into the tuberosity of the navicular bone, and immediately behind this they blend with the medial margin of the plantar calcaneonavicular ligament; the middle (calcaneotibial) descend almost perpendicularly to be inserted into the whole length of the sustentaculum tali of the calcaneus; the posterior fibres (2)osterior talotibial) pass backward and lateralward to be attached to the inner side of the talus, and to the prominent tubercle on its posterior surface, medial to the groove for the tendon of the Flexor hallucis longus. The deep fibres (anterior talotibial) are attached, above, to the tip of the medial malleolus, and, below, to the medial surface of the talus. The deltoid ligament is covered by the tendons of the Tibialis posterior and Flexor digitorum longus. The anterior and posterior talofibular and the calcaneofibular ligaments were formerly described as the three fasciculi of the external lateral ligament of the ankle-joint. Fig. 476. — Right talocrural intertarsal and tarsometatarsal articulations. Lateral aspect. The Anterior Talofibular Ligament (ligamentum talofibular e anterius) (Fig. 476). — The anterior taliofibular ligament, the shortest of the three, passes from the anterior margin of the fibular malleolus, forward and medially, to the talus, in front of its lateral articular facet. TALOCRURAL ARTICULATION OR ANKLE-JOINT 451 The Posterior Talofibular Ligament {lU/uiitcidum talujibulare poaterius) (Fig. 476). — The posterior talofibular ligament, the strongest and most deeply seated, runs almost horizontally' from the depression at the medial and back part of the fibular malleolus to a prominent tubercle on the posterior surface of the talus immediately lateral to the groove for the tendon of the Flexor hallucis longus. The Calcaneofibular Ligament (ligamentum calccmeofibulare) (Fig. 470).- — ^The calcaneofibular ligament, the longest of the three, is a narrow, rounded cord, run- ning from the apex of the fibular malleolus downward and slightly backward' to a tubercle on the lateral surface of the calcaneus. It is covered by the tendons of the Peronaei longus and brevis. \ 1 Wm^)^ Anterior talofibular ligament rm^^^^ P^^^^'''"^''' talofibular ligament 'Illl^Sm Calvaneofihular ligament ,^ Lateral talocalcaneal ligament Anterior talocalcaneal ligament Fig. 477. — Capsule of left talocrural articulation (distended). Lateral aspect. Synovial Membrane (Fig. 477). — The synovial membrane invests the deep surfaces of the ligaments, and sends a small process upward between the lower ends of the tibia and fibula. Relations. — -The tendons, vessels, and nerves in connection with the joint are, in front, from the medial side, the TibiaUs anterior, Extensor haUucis proprius, anterior tibial vessels, deep peroneal nerve. Extensor digitorum longus, and Peronaeus tertius; behind, from the medial side, the TibiaUs posterior. Flexor digitorum longus, posterior tibial vessels, tibial nerve. Flexor hallucis longus; and, in the groove behind the fibular malleolus, the tendons of the Peronaei longus and brevis. The arteries supplying the joint are derived from the malleolar branches of the anterior tibial and the peroneal. The nerves are derived from the deep peroneal and tibial. Movements. — When the body is in the erect position, the foot is at right angles to the leg. The movements of the joint are those of dorsiflexion and extension; dorsiflexion consists in the approximation of the dorsum of the foot to the front of the leg, while in extension the heel is drawn up and the toes pointed downward. The malleoh tightly embrace the talus in aU positions of the joint, so that any slight degree of side-to-side movement which may exist is simply due to stretching of the Ugaments of the talofibular syndesmosis, and slight bending of the body of the fibula. The superior articular surface of the talus is broader in front than behind. In dorsi- flexion, therefore, greater space is required between the two malleoU. This is obtained by a slight outward rotatory movement of the lower end of the fibula and a stretching of the ligaments of the syndesmosis ; this lateral movement is facilitated by a slight gliding at the tibiofibular articula- tion, and possibly also by the bending of the body of the fibula. Of the Ugaments, the deltoid is of very great power — so much so, that it usually resists a force which fractures the process of bone to which it is attached. Its middle portion, together with the calcaneofibular Ugament, binds the bones of the leg firmly to the foot, and resists displacement in every direction. Its anterior and posterior fibres limit extension and flexion of the foot respectively, and the anterior fibres also Umit abduction. The posterior talofibular ligament assists the calcaneofibular in 452 SYNDESMOLOGY resisting the displacement of the foot backward, and deepens the cavity for the reception of the talus. The anterior talofibular is a security against the displacement of the foot forward,, and limits extension of the joint. The movements of inversion and eversion of the foot, together with the minute changes in form by which it is apphed to the ground or takes hold of an object in chmbing, etc., are mainly eflfected in the tarsal joints; the joint which enjoys the greatest amount of motion being that be- tween the talus and calcaneus behind and the navicular and cuboid in front. This is often called the transverse tarsal joint, and it can, with the subordinate joints of the tarsus, replace the ankle- joint in a great measure when the latter has become ankylosed. Extension of the foot upon the tibia and fibula is produced by the Gastrocnemius, Soleus, Plantai'is, Tibialis posterior, Peronaei longus and brevis, Flexor digitorum longus, and Flexor haUucis longus; dorsifiexion, by the Tibialis anterior, Peronaeus tertius. Extensor digitorum longus, and Extensor hallucis proprius.^ Applied Anatomy. — As the ankle-joint is a very strong and powerful articulation, displace- ment of the talus from the tibiofibular mortise is a rare accident, and great force is required to produce it. Nevertheless, dislocation does occasionally occur, either antero-posteriorly or to one or other side. In the latter, which is th? more common, fracture is a necessary accompani- ment of the injury. The dislocation in these cases is somewhat peculiar, and is not a displace- ment in a horizontal direction, such as usually occurs in dislocations of ginglymoid joints, but the talus undergoes a partial rotation around an antero-posterior axis drawn through its own centre, so that the superior surface, instead of being directed upward, is incUned more or less medialward or lateralward according to the variety of the displacement. The ankle-joint is more frequently sprained than any joint in the body, and this may lead to acute synovitis. In these cases, when the synovial sac is distended with fluid, the bulging appears principally in the front of the joint, beneath the anterior tendons, and on either side, between the Tibiahs anterior and the deltoid ligament on the medial side, and between the Peronaeus tertius and the anterior talofibular ligament laterally. In addition to this, bulging often occurs posteriorly, and a fluctuating swelling may be detected on either side of the tendo calcaneus. A large proportion of so-caUed "sprains" of the ankle have been proved by a;-ray examination to be some variety of fracture about the malleoli, with or without displacement. Chronic synovitis may result from frequent sprains, and when once this joint has been .sprained it is Liable to a recurrence of the injury; or the synovitis may be tuberculous in its origin, the disease usually beginning in the talus and extending to the joint, though it may commence in the synovial membrane, the result probably of some slight strain in a tuberculous subject. Excision of the ankle-joint is not often performed, since the foot after excision is often of very little use; far less useful, in fact, than it is after Syme's amputation, which is, therefore, a prefer- able operation in these cases. Further, disease of the ankle-joint is frequently associated with disease of the tarsal bones. V. Intertarsal Articulations (Articulationes Intertarseae ; Articulations of the Tarsus). Talocalcaneal Articulation (articulatio talocalcanea; articulation of the calcaneus and astragalus; calcaneo-astragaloid articulation). — The articulations between the calcaneus and talus are two in number — anterior and posterior. Of these, the anterior forms part of the talocalcaneonavicular joint, and will be described with that articulation. The posterior or talocalcaneal articulation is formed between the posterior calcaneal facet on the inferior surface of the talus, and the posterior facet on the superior surface of the calcaneus. It is an arthrodial joint, and the two bones are connected by an articular capsule and by anterior, posterior, lateral, medial, and interosseous talocalcaneal ligaments. The Articular Capsule (capsula articularis) . — The articular capsule envelops the joint, and consists for the most part of short fibres, which are split up into distinct slips; between these there is only a weak fibrous investment. The Anterior Talocalcaneal Ligament {ligamentum talocalcaneum anterius; anterior calcaneo-astragaloid ligament) (Figs. 477, 480). — The anterior talocalcaneal liga- ment extends from the front and lateral surface of the neck of the talus to the superior surface of the calcaneus. It forms the posterior boundary of the 1 The student must bear in mind that the Extensor digitorum longus and Extensor hallucis proprius are extensors of the toes, but flexors of the ankle; and that the Flexor digitorum longus and Flexor hallucis longus are flexors of the toes, but extensors of the ankle. IXTERTARSAL ARTICULATIONS 453 talocalcaneonavicular joint, and is sometimes described as the anterior interosseous ligament. The Posterior Talocalcaneal Ligament (Jigainoifuni talocalcaneum posterius; posicrior calcaitco-aMragdIoid ligaiiicnt) (Fig. 475). — The posterior talocalcaneal ligament connects the lateral tubercle of the talus with the upper and medial part of the calcaneus; it is a short band, and its fibres radiate from their narrow attach- ment to the talus. The Lateral Talocalcaneal Ligament iligamoifiim. talocalcaneum laterale; external calcanco-astragaluid ligament) (Figs. 477, 480). — The lateral talocalcaneal ligament is a short, strong fasciculus, passing from the lateral surface of the talus, imme- diately beneath its fibular facet to the lateral surface of the calcaneus. It is placed in front of, but on a deeper plane than, the calcaneofibular ligament, with the fibres of which it is parallel. The Medial Talocalcaneal Ligament (ligamentum talocalcaneum mediale; internal calcaneo-astragaloid ligament). — The medial talocalcaneal ligament connects the medial tubercle of the back of the talus with the back of the sustentaculum tali. Its fibres blend with those of the plantar calcaneonavicular ligament. Jledial malleolus Deltoid ligament Tibialis posterior- Flexor digitorum longus Flexor halliicis longus Med. plantar nerve and vessels Quadratus planice Abductor hallucis Lat. plantar nerve and vessels Flexor digitorum brevis Interosseous ligament of tibio- fibular syndesmosis Lateral malleolus rof,^^ — Calcaneofibular ligament ^^^, Interosseous talocalcaneal ligament Peronceus hrevis' PerojicBUS longus Abductor digiti quinii Fig. 478. — Coronal section through right talocrural and talocalcaneal joints. The Interosseous Talcocalcaneal Ligament (ligamentmn talocalcaneum interosseum) (Figs. 47S, 480). — The interosseous talocalcaneal ligament forms the chief bond of union between the bones. It is, in fact, a portion of the united capsules of the talocalcaneonavicular and the talocalcaneal joints, and consists of two partially united layers of fibres, one belonging to the former and the other to the latter joint. It is attached, above, to the groove between the articular facets of the under surface of the talus; below, to a corresponding depression on the upper surface of the cal- caneus. It is very thick and strong, being at least 2.5 cm. in breadth from -side to side, and serves to bind the calcaneus and talus firmly together. 454 SYNDESMOLOGY Synovial Membrane (Fig. 481). — The synovial membrane lines the capsule of the joint, and is distinct from the other synovial membranes of the tarsus. Movements. — The movements permitted between the talus and calcaneus are hmited to glid- ing of the one bone on the other backward and forward and from side to side. Talocalcaneonavicular Articulation {articulaiio talocalcaneonancularis) . — This articulation is an arthrodial joint: the rounded head of the tahis being received into the concavity formed by the posterior surface of the navicular, the anterior articular surface of the calcaneus, and the upper surface of the plantar calcaneo- navicular ligament. There are two ligaments in this joint: the articular capsule and the dorsal talonavicular. The Articular Capsule (capsida articular is) . — The articular capsule is imperfectly developed except posteriorly, where it is considerably thickened and forms, with a part of the capsule of the talocalcaneal joint, the strong interosseous ligament which fills in the canal formed by the opposing grooves on the calcaneus and talus, as above mentioned. The Dorsal Talonavicular Ligament (ligamentum talonavicular e dorsale; superior astragalonamcular ligament) (Fig. 475). — This ligament is a broad, thin band, which connects the neck of the talus to the dorsal surface of the navicular bone; it is covered by the Extensor tendons. The plantar calcaneonavicular supplies the place of a plantar ligament for this joint. Synovial Membrane. — The synovial membrane Unes aU parts of the capsule of the joint. Movements. — This articulation permits of a considerable range of gliding movements; its feeble construction allows occasionally of dislocation of the other bones of the tarsus from the talus. Calcaneocuboid Articulation (articulaiio calcaneocuboidea; articulation of the calcaneus ivith the cuboid). — The ligaments connecting the calcaneus with the cuboid are five in number, viz., the articular capsule, the dorsal calcaneocuboid, part of the bifurcated, the long plantar, and the plantar calcaneocuboid. The Articular Capsule {capsula articular is) . — The articular capsule is an imper- fectly developed investment, containing certain strengthened bands, which form the other ligaments of the joint. The Dorsal Calcaneocuboid Ligament (ligamentum calcaneocuboideum dorsale; supe- rior calcaneocuboid ligament) (Fig. 476).— The dorsal calcaneocuboid ligament is a thin but broad fasciculus, which passes between the contiguous surfaces of the calcaneus and cuboid, on the dorsal surface of the joint. The Bifurcated Ligament (ligamentum bifurcatum; internal calcaneocuboid; inter- osseous ligament) (Fig. 476, 480).— The bifurcated ligament is a strong band, attached behind to the deep hollow on the upper surface of the calcaneus and divid- ing in front in a Y-shaped manner into a calcaneocuboid and a calcaneonavicular part. The calcaneocuboid part is fixed to the medial side of the cuboid and forms one of the principal bonds between the first and second rows of the tarsal bones. The calcaneonavicular part is attached to the lateral side of the navicular. The Long Plantar Ligament {ligamentum plantare longum; long calcaneocuboid ligament; superficial long plantar ligament) (Fig. 479).— The long plantar ligament is the longest of all the ligaments of the tarsus: it is attached behind to the plantar surface of the calcaneus in front of the tuberosity, and in front to the tuberosity on the plantar surface of the cuboid bone, the more superficial fibres being con- tinued forward to the bases of the second, third, and fourth metatarsal bones. This ligament converts the groove on the plantar surface of the cuboid into a canal for the tendon of the Peronaeus longus. The Plantar Calcaneocuboid Ligament {ligamentum calcaneocuboideum plantare; short calcaneocuboid ligament; short plantar ligament) (Fig. 479).— The plantar calcaneocuboid ligament lies nearer to the bones than the preceding, from which it is separated by a little areolar tissue. It is a short but wide band of great strength, and extends from the tubercle and the depression in front of it, on the forepart INTERTARSAL ARTICULATIONS 455 of the plantar surface of the calcaneus, to the i)lantar surface of the cu})oid behind the peroneal groove. Synovial Membrane.— The synovial membrane lines the inner surface of the cajisule and is distinct from that of the other tarsal articulations (Fig. 481). Movements.— The movements permitted between the calcaneus and cuboid are limited to slight glidhig movements of the bones upon each other. The tnmst'erse tarsal joint is formed by the articulation of the calcaneus with the cuboid, and the articulation of the talus with the navicular. The movement which takes place in this Joint is more extensive than that in the other tarsal joints, and consists of a sort of rotation by means of which the foot may be sUghtly flexed or extended, the sole being at the same time carried medially (inverted) or laterally (everted). The Ligaments Connecting the Calcaneus and Navicular.— Though the calcaneus and navicular do not directly articulate, they are connected by two ligaments: the calcaneonavicular part of the bifurcated, and the plantar calcaneonavicular. The calcaneonavicular part of the bifurcated ligament is described on page 454. The Plantar Calcaneonavicular Ligament (liga- mentum calcaneonavicular e plant are; inferior or internal calcaneonavicular ligament; calcaneona- vicular ligament) (Fig. 480). — The plantar cal- caneonavicular ligament is a broad and thick band of fibres, which connects the anterior margin of the sustentaculum tali of the calca- Lateral talocalcaneal ligament Anterior talocalcaneal ligatnent Tibialis posterior Interosseous talocalcaneal ligairbent Fig. 479.- -Ligaments of plantar surface of the right foot. Fig. 480. — Talocalcaneal and talocalcaneonavicular articula- tions exposed from above by removing the talus. neus to the plantar surface of the navicular. This ligament not only serves to connect the calcaneus and navicular, but supports the head of the talus, forming part of the articular cavity in which it is received. The dorsal surface of the ligament presents a fibrocartilaginous facet, lined by the synovial membrane, and upon this a portion of the head of the talus rests. Its plantar surface is supported by the tendon of the Tibialis posterior ; its medial border is blended with the forepart of the deltoid ligament of the ankle-joint. 456 SYNDESMOLOGY Applied Anatomy. — The plantar calcaneonavicular ligament, by supporting the head of the talus, is principally concerned in maintaining the arch of the foot. When it yields, the head of the talus is pressed downward, medialward, and forward by the weight of the body, and the foot becomes flattened, expanded, and turned lateralward, and exhibits the condition known as flat-foot. This ligament contains a considerable amount of elastic fibres, so as to give elasticity to the arch and spring to the foot; hence it is sometimes called the "spring" ligament. It is supported, on its plantar surface, by the tendon of the Tibialis posterior, which spreads out at its insertion into a number of fasciculi, to be attached to most of the tarsal and metatarsal bones. This prevents undue stretching of the ligament, and is a protection against the occur- rence of flat-foot; hence muscular weakness is, in most cases, the primary cause of the deformity. Cuneonavicular Articulation (articidatio cuneonamcularis ; articulation of the navicular with the cuneiform hones). — The navicular is connected to the three cuneiform bones by dorsal and plantar ligaments. The Dorsal Ligaments (ligamenta navicular icuneif or mia dorsalia).- — The dorsal ligaments are three small bundles, one attached to each of the cuneiform bones. The bundle connecting the navicular with the first cuneiform is continuous around the medial side of the articulation with the plantar ligament which unites these two bones. The Plantar Ligaments (ligamenta navicular icuneif or mia ylantaria). — The plantar ligaments have a similar arrangement to the dorsal, and are strengthened by slips from the tendon of the Tibialis posterior. Deltoid ligament ■Ankle-joint Talofibular ligame^it Interosseous alocalcaneal ligament Mctata) sals. Fig. 481. — Oblique section of left intertarsal and tarsometatarsal articulations, showing the synovial cavities Synovial Membrane. — The synovial membrane of these joints is part of the great tarsal synovial membrane (Fig. 481). Movements. — Mere gliding movements are permitted between the navicular and cuneiform bones. TARSOMETATARSAL ARTICULATIONS 457 Cuboideonavicular Articulation. — The navicular bone is connected with the cuboid by dorsal, phnitar, and interosseous ligaments. The Dorsal Ligament [Ii(/a)iienfn))i ciiboideonavicvlare dorsale) .■ — The dorsal ligament extends obliciueiy forward and lateralward from the navicular to the cuboid bone. The Plantar Ligament {ligameiitum cuboideonauiculare ylantare). — The plantar ligament passes nearly transversely between these two bones. The Interosseous Ligament. — The interosseous ligament consists of strong trans- verse fibres, and connects the rough non-articular portions of the adjacent surfaces of the two bones. Synovial Membrane. — The synovial membrane of this joint is part of the great tarsal synovial membrane (Fig. -481). Movements. — The movements permitted between the navicular and cuboid bones are limited to a slight ghding upon each other. Intercuneiform and Cuneocuboid Articulations. — The three cuneiform bones and the cuboid are connected together by dorsal, plantar, and interosseous ligaments. The Dorsal Ligaments {ligamenta interciineiformia dorsalia). — The dorsal liga- ments consist of three transverse bands: one connects the first with the second cuneiform, another the second with the third cuneiform, and another the third cuneiform with the cuboid. The Plantar Ligaments {ligamenta intercuneiformia plantaria). — The plantar liga- ments have a similar arrangement to the dorsal, and are strengthened by slips from the tendon of the Tibialis posterior. The Interosseous Ligaments (ligamenta intercuneiformia interossea). — The inter- osseous ligaments consist of strong transverse fibres which pass between the rough non-articular portions of the adjacent surfaces of the bones. Synovial Membrane. — The synovial membrane of these joints is part of the great tarsal synovial membrane (Fig. 481). Movements. — The movements permitted between these bones are limited to a slight gliding upon each other. Applied Anatomy. — In spite of the great strength of the ligaments which connect the tarsal bones together, dislocation at some of the tarsal joints does occasionally occur. When this takes place, it is most commonly in connection with the talus; for not only may this bone be dislocated from the tibia and fibula at the ankle-joint, but the other bones may be dislocated from it, the bone remaining in situ in the tibiofibular mortise. This constitutes what is known as . the subtalar dislocation. Or, agaih, the talus may be dislocated from all its connections — from the tibia and fibula above, the calcaneous below, and the navicular in front — and may even undergo a rotation, on either a vertical or a horizontal axis. In the former case the long axis of the bone is directed across the joint, so that the head faces the articular surface on one or other malleolus; in the latter, the collateral sm-faces are directed upward and downward, so that the superior surface faces to one or the other side. Reduction in these cases is often very difficult or impossible, and the displaced talus may require removal by open operation. Dislocation may also occur at the transverse tarsal joint, the anterior tarsal bones being luxated from the talus and calcaneus. The other tarsal bones are occasionally, though rarely, dislocated from their connections. VI. Tarsometatarsal Articulations (Articulationes Tarsometatarseae) . These are arthrodial joints. The bones entering into their formation are the first, second, and third cuneiforms, and the cuboid, which articulate w^ith the bases of the metatarsal bones. The first metatarsal bone articulates with the first cunei- form; the second is deeply wedged in between the first and third cuneiforms articulating by its base with the second cuneiform; the third articulates with the third cuneiform; the fourth, with the cuboid and third cuneiform; and the fifth, with the cuboid. The bones are connected by dorsal, plantar, and interosseous ligaments. The Dorsal Ligaments {ligamenta tarsometatarsea dorsalia) . — The dorsal ligaments are strong, flat bands. The first metatarsal is joined to the first cuneiform by a broad, thin band; the second has three, one from each cuneiform bone; the third 458 SYNDESMOLOGY has one from the third cuneiform; tlie fourtli has one from the third cuneiform and one from the cuboid; and the fifth, one from the cuboid. The Plantar Ligaments iUgamenta tarsometatarsea ylantaria). — The plantar Hga- ments consist of k)ngitudinal and ohhque hands, (Hsposed with less regularity than the dorsal ligaments. Those for the first and second metatarsals are the strongest; the second and third metatarsals are joined by oblique bands to the first cuneiform; the fourth and fifth metatarsals are connected by a few fibres to the cuboid. The Interosseous Ligaments {ligamenta cimeometatarsea interussia). — The inter- osseous ligaments are three in number. The first is the strongest, and passes from the lateral surface of the first cuneiform to the adjacent angle of the second meta- tarsal. The second connects the third cuneiform with the adjacent angle of the second metatarsal. The third connects the lateral angle of the third cuneiform with the adjacent side of the base of the third metatarsal. Sjmovial Membrane (Fig. 481). — -The synovial membrane between the first cuneiform and the first metatarsal forms a distinct sac. The synovial membrane between the second and third cuneiforms behind, and the second and thud metatarsal bones in front, is part of the great tarsal synovial membrane. Two prolongations are sent forward from it, one between the adjacent sides of the second and third, and another between those of the third and fourth metatarsal bones. The synovial membrane between the cuboid and the fourth and fifth metatarsal bones forms a distinct sac. From it a prolongation is sent forward between the fourth and fifth metatarsal bones. Movements. — The movements permitted between the tarsal and metatarsal bones are limited to shght ghding of the bones upon each other. Nerve Supply. — The intertarsal and tarsometatarsal joints are supplied by the deep peroneal nerve. VII. Intermetatarsal Articulations (Articulationes Intermetatarseae) . The base of the first metatarsal is not connected with that of the second by any ligaments; in this respect the great toe resembles the thumb. The bases of the other four metatarsals are connected by the dorsal, plantar, and interosseous ligaments. The Dorsal Ligaments {ligamenta basiwn [oss. metatars.] dorsalia) pass transversely between the dorsal surfaces of the bases of the adjacent metatarsal bones. The Plantar Ligaments (ligamenta hasiiim [oss. metatars] plantaria). — The plantar ligaments have a similar arrangement to the dorsal. The Interosseous Ligaments {ligamenta hasium [oss. metatars.] interossea). — The interosseous ligaments consist of strong transverse fibres which connect the rough non-articular portions of the adjacent surfaces. Synovial Membranes (Fig. 481). — The synovial membranes between the second and third, and the third and fourth metatarsal bones are part of the great tarsal synovial membrane; that between the fourth and fifth is a prolongation of the synovial membrane of the cuboideometatarsal joint. Movements. — The movement permitted between the tarsal ends of the metatarsal bones is limited to a slight gUding of the articular surfaces upon one another. The heads of all the metatarsal bones are connected together by the transverse metatarsal ligament. The Transverse Metatarsal Ligament. — The transverse metatarsal ligament is a narrow band wdiich runs across and connects together the heads of all the meta- tarsal bones; it is blended anteriorly with the plantar (glenoid) ligaments of the metatarsophalangeal articulations. Its plantar surface is concave where the Flexor tendons run below it; above it the tendons of the Interossei pass to their insertions. It diflfers from the transverse metacarpal ligament in that it connects the metatarsal to the others. The Synovial Membranes in the Tarsal and Tarsometatarsal Joints (Fig. 481). — The synovial membranes found in the articulations of the tarsus and metatarsus are six in number: one for ARCHES OF Tflh: FOOT 459 the talocalcaueal articulation; a sccoiul i'or the talocalcanoonavicidar articulation; a third for the calcaneocuboid articulation; and a fourth for the cuneonavicnilar, intercuneiform, and cuneo- cuboid articulations, the articulations of the second and third cuneiforms with the bases of the second and third metatarsal bones, and the adjatient surfaces of the bases of the second, third, and fourth metatarsal bones; a fifth for the first cuneiform with the metatarsal bone of the great toe; and a sixth for the articulation of the cuboid with the fourth and fifth metatarsal bones. A small synovial cavity is sometimes found between the contiguous surfaces of the navicular and cuboid bones. VIII. Metatarsophalangeal Articulations (Articulationes Metatarsophalangeae) . The metatarsophalangeal articulations are of the condyloid kind, formed by the reception of the rounded heads of the metatarsal bones in shallow cavities on the ends of the first phalanges. The ligaments are the plantar and two collateral. The Plantar Ligaments {ligamenta accessoria j)lantaria; glenoid ligaments of Cru- veilhier). — The plantar ligaments are thick, dense, fibrous structures. They are placed on the plantar surfaces of the joints in the intervals between the collateral ligaments, to which they are connected; they are loosely united to the metatarsal bones, but very firmh' to the bases of the first phalanges. Their plantar surfaces are intimately blended with the transverse metatarsal ligament, and grooved for the passage of the Flexor tendons, the sheaths surrounding which are connected to the sides of the grooves. Their deep surfaces form part of the articular facets for the heads of the metatarsal bones, and are lined by synovial membrane. The Collateral Ligaments {ligamenta collateralia; lateral ligaments). — The collat- eral ligaments are strong, rounded cords, placed one on either side of each joint, and attached, by one end, to the posterior tubercle on the side of the head of the metatarsal bone, and, by the other, to the contiguous extremity of the phalanx. The place of dorsal ligaments is supplied by the Extensor tendons on the dorsal surfaces of the joints. Movements. — ^The movements permitted in the metatarsophalangeal articulations are flexion, extension, abduction, and adduction. IX. Articulations of the Digits (Articulationes Digitorum Pedis; Articulations of the Phalanges). The interphalangeal articulations are ginglymoid joints, and each has a plantar and two collateral ligaments. The arrangement of these ligaments is similar to that in the metatarsophalangeal articulations: the Extensor tendons supply the places of dorsal ligaments. Movements. — ^The only movements permitted in the joints of the digits are flexion and exten- sion; these movements are more extensive between the first and second phalanges than between the second and third. The amount of flexion is very considerable, but extension is limited by the plantar and collateral ligaments. Applied Anatomy. — Gout peculiarly affects the metatarsophalangeal joint of the big toe, be- ginning with the deposit of sodium and calcium urates in the articular cartilages, and slow necrosis of the surrounding tissue. Later the circumarticular fibrous tissue becomes the seat of these gouty deposits, and considerable thickening and deformity may result. The other chief joint affections, such as rheumatism, gonorrhoeal arthritis, tuberculosis, or syphilis, seldom attack the big toe-joint; but septic arthritis associated with perforating ulcer of the foot is not uncommon. Arches of the Foot. In order to allow it to support the weight of the body in the erect posture with the least expenditure of material, the foot is constructed of a series of arches formed by the tarsal and metatarsal bones, and strengthened by the ligaments and tendons of the foot. 460 SYNDESMOLOGY The main arches are the antero-posterior arches, which may, for descriptive purposes, be regarded as divisible into two types — a medial and a lateral. The medial arch (see Fig. 417, page 376) is made up by the calcaneus, the talus, the navicular, the three cuneiforms, and the first, second, and third metatarsals. Its summit is at the superior articular surface of the talus, and its two extremities or piers, on which it rests in standing, are the tuberosity on the plantar surface of the calcaneus posteriorly and the heads of the first, second, and third metatarsal bones anteriorly. The chief characteristic of this arch is its elasticity, due to its height and to the number of small joints between its component parts. Its weakest part, i. e., the part most liable to yield from overpressure, is the joint between the talus and navicular, but this portion is braced by the plantar calcaneonavicular ligament, which is elastic and is thus able to quickly restore the arch to its pristine condition when the disturbing force is removed. The ligament is strengthened medially by blending with the deltoid ligament of the ankle-joint, and is supported inferiorly by the tendon of the Tibialis posterior, which is spread out in a fan- shaped insertion and prevents undue tension of the ligament or such an amount of stretching as would permanently elongate it. The arch is further supported by the plantar aponeurosis, by the small muscles in the sole of the foot, by the tendons of the Tibialis anterior and posterior and Peronaeus longus, and by the ligaments of all the articulations involved. The lateral arch (see Fig. 418, page 376) is com- posed of the calcaneus, the cuboid, and the fourth and fifth metatarsals. Its summit is at the talocalcaneal articulation, and its chief joint is the calcaneocuboid, which possesses a special mechanism for locking, and allows only a limited move- ment. The most marked features of this arch are its solidity and its slight eleva- tion; two strong ligaments, the long plantar and the plantar calcaneocuboid, together with the Extensor tendons and the short muscles of the little toe, preserve its integrity. While these medial and lateral arches may be readily demonstrated as the component antero-posterior arches of the foot, yet the fundamental longitudinal arch is contributed to by both, and consists of the calcaneus, cuboid, third cunei- form, and third metatarsal : all the other bones of the foot may be removed without destroying this arch. In addition to the longitudinal arches the foot presents a series of transverse arches. At the posterior part of the metatarsus and the anterior part of the tarsus the arches are complete, but in the middle of the tarsus they present more the characters of half-domes the concavities of which are directed downward and medialward, so that when the medial borders of the feet are placed in apposition a complete tarsal dome is formed. The transverse arches are strengthened by the interosseous, plantar, and dorsal ligaments, by the short muscles of the first and fifth toes (especially the transverse head of the Adductor hallucis), and by the Peronaeus longus, whose tendon stretches across between the piers of the arches. MYOLOGY; rPHE Muscles are connected Avith the bones, cartilages, ligaments, and skin, -*- either directly, or through the intervention of fibrous structures called tendons or aponeuroses, ^yhe^e a muscle is attached to bone or cartilage, the fibres end in blunt extremities upon the periosteum or perichondrium, and do not come into direct relation with the osseous or cartilaginous tissue. Where muscles are con- nected with its skin, they lie as a flattened layer beneath it, and are connected with its areolar tissue by larger or smaller bundles of fibres, as in the muscles of the face. The muscles vary extremely in their form. In the limbs, they are of considerable length, especially the more superficial ones; they surround the bones, and constitute an important protection to the various joints. In the trunk, they are broad, flattened, and expanded, and assist in forming the walls of the trunk cavities. Hence the reason of the terms, long, broad, short, etc., used in the description of a muscle. There is considerable variation in the arrangement of the flbres of certain muscles with reference to the tendons to which they are attached. In some muscles the fibres are parallel and run directly from their origin to their insertion; these are quadrilateral muscles, such as the Thyreohyoideus. A modification of these is found in the fusiform muscles, in which the fibres are not quite parallel, but slightly curved, so that the muscle tapers at either end; in their actions, however, they resemble the quadrilateral muscles. Secondly, in other muscles the fibres are convergent; arising by a broad origin, they converge to a narrow or pointed inser- tion. This arrangement of fibres is found in the triangular muscles — e. g., the Temporalis. In some muscles, which otherwise would belong to the quadrilateral or triangular type, the origin and insertion are not in the same plane, but the plane of the line of origin intersects that of the line of insertion; such is the case in the Pectineus. Thirdly, in some muscles {e. g., the Peronei) the fibres are oblique and converge, like the plumes of a quill pen, to one side of a tendon which runs the entire length of the muscle; such muscles are termed unipennate. K modification of this condition is found where oblique fibres converge to both sides of a central tendon; these are called bipennate, and an example is afforded in the Rectus femoris. Finally, there are muscles in which the fibres are arranged in curved bundles in one or more planes, as in the Sphincters. The arrangement of the fibres is of con- siderable importance in respect to the relative strength and range of movement of the muscle. Those muscles where the fibres are long and few in number have great range, but diminished strength; where, on the other hand, the fibres are short and more numerous, there is great power, but lessened range. The names applied to the various muscles have been derived: (1) from their situation, as the Tibialis, Radialis, Ulnaris, Peronaeus; (2) from their direction, as the Rectus abdominis, Obliqui capitis, Transversus abdominis; (3) from their uses, as Flexors, Extensors, Abductors, etc.; (4) from their shape, as the Deltoideus, 1 The muscles and fasciae are described conjointly, in order that the student may consider the arrangement of the latter in his dissection of the former. It is rare for the student of anatomy in this country t9 have the opportunity of dissecting the fasciae separately; and it is for this reason, as well as from the close connection that exists between the muscles and their investing sheaths, that they are considered together. Some general observations are first made on the anatomy of the muscles and fasciae, the special descriptions being given in connection with the different regions. 462 MYOLOGY Rhomboideus; (5) from the number of their divisions, as the Biceps and Triceps; (6) from their points of attachment, as the Sternocleidomastoideus, Sternohyoideus, Sternothyreoideus. In the description of a muscle, the term origin is meant to imply its more fixed or central attachment; and the term insertion the movable point on which the force of the muscle is applied; but the origin is absolutely fixed in only a small number of muscles, such as those of the face which are attached by one extremity to immov- able bones, and by the other to the movable integument; in the greater number, the muscle can be made to act from either extremity. In the dissection of the muscles, attention should be directed to the exact origin, insertion, and actions of each, and to its more important relations with surrounding parts. While accurate knowledge of the points of attachment of the muscles is of great importance in the determination of their actions, it is not to be regarded as conclusive. The action of the muscle deduced from its attachments, or even by pulling on it in the dead subject, is not necessarily its action in the living. By pulling, for example, on the Brachioradialis in the cadaver the hand may be slightly supinated when in the prone position and slightly pronated when in the supine position, but there is no evidence that these actions are performed by the muscle during life. It is impossible for an individual to throw into action any one muscle; in other words, movements, not muscles, are represented in the central nervous system. To carry out a movement a definite combination of muscles is called into play, and the individual has no power either to leave out a muscle from this com- bination or to add one to it. One (or more) muscle of the combination is the chief moving force; when this muscle passes over more than one joint other muscles (syngeric muscles) come into play to inhibit the movements not required; a third set of muscles (fixation muscles) fix the limb — i. e., in the case of the limb-movements — and also prevent disturbances of the equilibrium of the body generally. As an example, the movement of the closing of the fist may be considered: (1) the prime movers are the Flexores digitorum. Flexor pollicis longus, and the small muscles of the thumb; (2) the synergic muscles are the Extensores carpi, which prevent flexion of the wrist; while (3) the fixation muscles are the Biceps and Triceps brachii, which steady the elbow^ and shoulder. A further point which must be borne in mind in considering the actions of muscles is that in certain positions a movement can be effected by gravity, and in such a case the muscles acting are the antagonists of those which might be supposed to be in action. Thus in flexing the trunk when no resistance is interposed the Sacrospinales contract to regulate the action of gravity, and the Recti abdominis are relaxed.^ By a consideration of the action of the muscles, the surgeon is able to explain the causes of displacement in various forms of fracture, and the causes which pro- duce distortion in various deformities, and, consequently, to adopt appropriate treatment in each case. The relations, also, of some of the muscles, especially those in immediate apposition with the larger bloodvessels, and the surface mark- ings they produce, should be remembered, as they form useful guides in the application of ligatures to those vessels. The minute anatomy of muscular tissue is described on pages 64 to 69. Applied Anatomy. — Degeneration of muscular tissue is important clinically, and is met with in two main conditions. In one, the degeneration is myopathic, or primary in the muscles them- selves; in the other it is neuropathic, or secondary to some lesion of the nervous system — a hemor- rhage into the brain, for example, or injury or inflammation of some part of the medulla spinalis or peripheral nerves. In either case more or less paralysis and atrophy of the affected muscles result. When the degeneration begins primarily in the muscles, however, it often happens that though the muscle fibres waste away, their place is taken by fibrous and fatty tissue to such an extent that the affected muscles increase in volmne, and actually appear to hypertrophy. 1 Consult in this connection the Croonian Lectures (190.3) on "Muscular Movements and Their Representation in the Central Nervous System," by Charles E. Beevor, M.D. TENDONS, APONEUROSPJS, AND FASCIA 463 Ossification of muscular tissue as a result of repeated strain or injury is not infrequent. It is oftenest found about the tendon of the Adductor longus and \'astus medialis in horsemen, or in the Pectoralis major and Deltoideus of soldiers. It may take the form of exostoses firmly fixed to the bone — e. g., "rider's bone" on the femur — or of layers or spicules of bone lying in the muscles or their fascias and tendons. Busse states tliat these bony deposits are preceded by a hemorrhagic myositis due to injury, the effused blood organizing and being finally converted into bone. In the rarer disease, progressive myositis ossificans, there is an unexplained tendency for practically any of the voluntary muscles to become converted into solid and brittle bony masses which are eompletelj^ rigid. TENDONS, APONEUROSES, AND FASCIA. Tendons are white, glistening, fibrous cords, varying in length and thickness, sometimes round, sometimes flattened, and devoid of elasticity. They consist almost entirely of white fibrous tissue, the fibrils of which have an undulating course parallel with each other and are firmly united together. They are ver}^ sparingly supplied with bloodvessels, the smaller tendons presenting in their interior no trace of them. Nerves supplying tendons have special modifications of their terminal fibres, named organs of Golgi. Aponeuroses are flattened or ribbon-shaped tendons, of a pearly white color, iridescent, glistening, and similar in structure to the tendons. They are only sparingly supplied with bloodvessels. The tendons and aponeuroses are connected, on the one hand, with the muscles, and, on the other hand, with the movable structures, as the bones, cartilages liga- ments, and fibrous membranes (for instance, the sclera) . Where the muscular fibres are in a direct line with those of the tendon or aponeurosis, the two are directly continuous. But where the muscular fibres join the tendon or aponeurosis at an oblique angk, they end, according to Kolliker, in rounded extremities which are received into corresponding depressions on the surface of the latter, the connective tissue between the muscular fibres being continuous wdth that of the tendon. The latter mode of attachment occurs in all the penniform and bipenniform muscles, and in those muscles the tendons of which commence in a membranous form, as the Gastrocnemius and Soleus. The fasciae are fibroareolar or aponeurotic laminae, of variable thickness and strength, found in all regions of the body, investing the softer and more delicate organs. During the process of development many of the cells of the mesoderm are difl'erentiated into bones, muscles, vessels, etc.; the cells of the mesoderm which are not so utilized form an investment for these structures and are differentiated into the true skin and the fasciee of the body. They have been subdivided, from the situations in which they occur, into superficial and deep. The superficial fascia is found immediately beneath the integument over almost the entire surface of the body. It connects the skin with the deep fascia, and consists of fibroareolar tissue, containing in its meshes pellicles of fat in varying quantity. It varies in thickness in different parts of the body; in the groin it is so thick that it may be subdivided into several laminae. Beneath the fatty layer there is generally another layer of superficial fascia, comparatively devoid of adipose tissue, in which the trunks of the subcutaneous vessels and nerves are found, as the superficial epigastric vessels in the abdominal region, the superficial veins in the forearm, the saphenous veins in the leg and thigh, and the superficial lymph glands. Certain cutaneous muscles also are situated in the superficial fascia, as the Platysma in the neck, and the Orbicularis oculi around the eyelids. This fascia is most dis- tinct at the lower part of the abdomen, perineum, and extremities; it is very thin in those regions where muscular fibres are inserted into the integument, as on the side of the neck, the face, and around the margin of the anus. It is very dense in the scalp, in the palms of the hands, and soles of the feet, forming a fibro-fatty layer, which binds the integument firmly to the underlying structures. 464 MYOLOGY The superficial fascia connects the skin to the subjacent parts, facilitates the movement of the skin, serves as a soft nidus for the passage of vessels and nerves to the integument, and retains the warmth of the body, since the fat contained in its areolae is a bad conductor of heat. The deep fascia is a dense, inelastic, fibrous membrane, forming sheaths for the muscles, and in some cases affording them broad surfaces for attachment. It consists of shining tendinous fibres, placed parallel with one another, and connected together by other fibres disposed in a rectilinear manner. It forms a strong invest- ment which not only binds down collectively the muscles in each region, but gives a separate sheath to each, as well as to the vessels and nerves. The fasciae are thick in unprotected situations, as on the lateral side of a limb, and thinner on the medial side. The deep fasciae assist the muscles in their actions, by the degree of tension and pressure they make upon their surfaces; and, in certain situations, where they are strengthened by the presence in them of degenerated muscular fibres which have become converted into fibrous sheets, the degree of tension and pressure is regulated by the associated muscles, as, for instance, by the Tensor fasciae latae and Glutaeus maximus in the thigh, by the Biceps in the upper and lower extremi- ties, and Palmaris longus in the hand. In the limbs, the fasciae not only invest the entire limb, but give off septa which separate the various muscles, and are attached to the periosteum: these prolongations of fasciae are usually spoken of as intermuscular septa. The Fasciae and Muscles may be arranged, according to the general division of the body, into those of the head and neck; of the trunk; of the upper extremity; and of the lower extremity. THE FASCIiE AND MUSCLES OF THE HEAD. I. THE MUSCLE OF THE SCALP. Epicranius. Dissection (Fig. 482). — The head being shaved, and a block placed beneath the back of the neck, make a vertical incision through the skin, commencing at the root of the nose in front, 1. Dissection of scalp. 2, 3, of auricular region. 4, 5, 6, of face. 7, 8, of neck. Fig. 482. — Dissection of the head, face, and neck. and terminating behind at the occipital protuberance; make a second incision in a horizontal direction along the forehead and around the side of the head, from the anterior to the posterior THE MUSCLE OF THE SCALP 465 extremity of the preceding. Raise the skin in front, from the subjacent muscle, from below upward; this must be done with extreme care, removing the integument from the outer surface of the vessels and the nerves which lie immediately beneath the skin. The Skin of the Scalp. — This is thicker than in any other part of the body. It is intimately ailherent to the superhcial fascia, which attaches it firmly to the imderlying aponeurosis and muscle. Movements of the muscle move the skin. The hair follitdes are very closely set together, and extend throughout the whole thickness of the skin. It also (iontains a number of sebaceous glands. Corrugatot Dilatator naiis ant. Dilatator naris jMst Nasalis Depressor septi '" Mentalia Fig. 483. — Muscles of the head, face, and neck. The superficial fascia in the cranial region is a firm, dense, fibro-fatty layer, intimately adherent to the integument, and to the Epicraniiis and its tendinous aponeurosis; it is continuous, behind, with the superficial fascia at the back of the neck; and, laterally, is continued over the temporal fascia. It contains between its layers the superficial vessels and nerves and much granular fat. The Epicranius (Occipitofrontalis) (Fig. 483) is a broad, musculofibrous layer, which covers the whole of one, side of the vertex of the skull, from the occipital 30 466 MYOLOGY bone to the eyebrow. It consists of two parts, the OccipitaHs and the Frontalis, connected by an intervening tendinous aponeurosis, the galea aponeurotica. The Occipitalis, thin and quadrilateral in form, arises by tendinous fibres from the lateral two-thirds of the superior nuchal line of the occipital bone, and from the mastoid part of the temporal. It ends in the galea aponeurotica. The Frontalis is thin, of a ciuadrilateral form, and intimately adherent to the superficial fascia. It is broader than the Occipitalis and its fibres are longer and paler in color. It has no bony attachments. Its medial fibres are continuous with those of the Procerus; its immediate fibres blend with the Corrugator and Orbicu- laris oculi; and its lateral fibres are also blended with the latter muscle over the zygomatic process of the frontal bone. From these attachments the fibres are directed upward, and join the galea aponeurotica below the coronal suture. The medial margins of the Frontales are joined together for some distance above the root of the nose; but between the Occipitales there is a considerable, though variable, interval, occupied by the galea aponeurotica. The galea aponeurotica (epicranial aponeurosis) covers the upper part of the cranium; behind, it is attached, in the interval between the Occipitales, to the external occipital protuberance and highest nuchal lines of the occipital bone; in front, it forms a short and narrow prolongation between the Frontales. On either side it gives origin to the Auriculares anterior and superior ; in this situation it loses its aponeurotic character, and is continued over the temporal fascia to the zygomatic arch as a layer of laminated areolar tissue. It is closely connected to the integument by the firm, dense, fibro-fatty layer which forms the superficial fascia of the scalp : it is attached to the pericranium by loose cellular tissue, which allows the aponeurosis, carrying with it the integument to move tlirough a consid- erable distance. Nerves. — The Frontalis is supplied by the temporal branches of the facial nerve, and the Occipitalis by the posterior auricular branch of the same nerve. Actions. — The Frontales raise the eyebrows and the skin over the root of the nose, and at the same time draw the scalp forward, throwing the integument of the forehead into transverse wrinkles. The Occipitales draw the scalp backward. By bringing alternately into action the Frontales and Occipitales the entire scalp may be moved forward and backward. In the ordinary action of the muscles, the eyebrows are elevated, and at the same time the aponeurosis is fixed by the Occipitales, thus giving to the face the expression of surprise; if the action be exaggerated, the eyebrows are still further raised, and the skin of the forehead thrown into transverse wrinkles, as in the expression of fright or horror. A thin muscular slip, the Transversus nuchae, is present in a considerable pro- portion (25 per cent.) of cases; it arises from the external occipital protuberance or from the superior nuchal line, either superficial or deep to the Trapezius; it is frequently inserted with the Auricularis posterior, but may join the posterior edge of the Sternocleidomastoideus. Applied Anatomy. — From an anatomical point of view, the scalp consists of five layers, viz., the skin, subcutaneous tissue, Epicranius and its aponeurosis, subaponeurotic connective tissue, and pericranium. But from a surgical standpoint it is better to regard the first three of these structures as a single layer, since they are all intimately fused together, and when torn off in an accident, or turned down as a flap in a surgical operation, remain firmly connected to each other. In consequence of the dense character of the subcutaneous tissue, the amount of sweUing which occurs as the result of inflammation is shght; and the edges of a wound which does not involve the Epicranius or its aponeurosis do not gape. The bloodvessels, also, which lie in this tissue, when wounded, do not contract and retract freely; and therefore the hemorrhage from scalp wounds is often very considerable, but can always be arrested by pressm-e — ^a matter of great importance, as it is often very difficult or impossible to pick up with forceps a wounded vessel in the scaljj. The subaponeurotic connective tissue is, from a surgical point of view, of considerable impor- tance. It is loose and lax, and is easily torn through; and hence, when the scalp is wounded, this is the tissue which is torn when the flap is separated from the parts beneath. The vessels are contained in the flap, and there is Httle risk of sloughing, unless the vitality of the part has been THE MUSCLES OE THE EYELIDS 467 uctuiiUy tlestroyed by the injury. In couyequencc of the loose nature of the sul)tii)oneurotic tissue, any septic infhiinniation is ai)t to assume a very dilTuse form and spread over the skull, and, unless relieved by timely incisions, may lead to serious c()m{)hcations. Owing to the attach- ments of the aponeiu-osis to the zj^gomatic arch and highest nuchal line, subaponeurot ic etTusions sag down in these situations, but do not extend bej'^ond to the infratemporal fossa or into the neck; anteriorly, however, where there is no definite attachment to bone, the effusion will pass down over the nose, and into the eyelids. When making incisions into the scalp, care should be taken to avoid the course of the main arteri(>s. The skin of the scalp is abimdantly sui)iilied with sebaceous and sudori])ar()us glands. The former are sometimes the seat of cystic enlargement, constituting the so-called sebaceous cysts or wens. II. THE MUSCLES OF THE EYELIDS. The muscles of the eyelids are: Levator palpebrae superioris. Orbicularis oculi. Corrugator. Dissection (Fig. 482). — ^In order to expose the muscles of the face, continue the longitudinal incision made in the dissection of the Epicranius down the median line of the face to the tip of the nose, and from this point onward to the upper lip; and carry another incision along the margin of the lip to the angle of the mouth, and transversely across the face to the angle of the mandible. Then make an incision in front of the external ear, from the angle of the mandible upward to join the transverse incision made in exposing the Epicranius. These incisions include a square-shaped flap, which should be removed in the direction marked in the figure, with care, as the muscles at some points are intimately adherent to the integument. The Levator palpebrae superioris is described with the Anatomy of the Eye. Probe in frontal sinus Probe in ant. eth- moidal cells Crista galli ^. — Lacrimal part of Orbicularis oculi Probe in lacrimal sac — f Probes from frontal \sinus and ant. eth- moidal cells Middle meatus Septum of nose Probe in nasolacrimal duct Infraorbital no ve and a) toy Fig. 4S4. — Left orbicularis oculi, seen from behind. The Orbicularis oculi (Orbicularis jxdpebrarum) (Fig. 484) arises from the nasal part of the frontal bone, from the frontal process of the maxilla in front of the lacrimal groove, and from the anterior surface and borders of a short fibrous band. 468 MYOLOGY the medial palpebral ligament. From this origin, the fibres are directed lateral- ward, forming a broad and thin layer, which occupies the eyelids or palpebrae, surrounds the circumference of the orbit, and spreads over the temple, and down- ward on the cheek. The palpebral portion of the muscle is thin and pale; it arises from the bifurcation of the medial palpebral ligament, forms a series of concentric curves, and is inserted into the lateral palpebral raphe. The orbital portion is thicker and of a reddish color; its fibres form a complete ellipse without interruption at the lateral palpebral commissure; the upper fibres of this portion blend with the Frontalis and Corrugator. The lacrimal part (Tensor tarsi) is a small, thin muscle, about 6 mm. in breadth and 12 mm. in length, situated behind the medial palpebral ligament and lacrimal sac (Fig. 484). It arises from the posterior crest and adjacent part of the orbital surface of the lacrimal bone, and passing behind the lacrimal sac, divides into two slips, upper and lower, which are inserted into the superior and inferior tarsi medial to the puncta lacrimalia; occasionally it is very indistinct. The medial palpebral ligament (tendo oculi), about 4 mm. in length and 2 mm. in breadth, is attached to the frontal process of the maxilla in front of the lacrimal groove. Crossing the lacrimal sac, it divides into two parts, upper and lower, each attached to the medial end of the corresponding tarsus. As the ligament crosses the lacrimal sac, a strong aponeurotic lamina is given off from its posterior surface; this expands over the sac, and is attached to the posterior lacrimal crest. The lateral palpebral raphe is a much weaker structure than the medial palpebral ligament. It is attached to the margin of the frontosphenoidal process of the zygomatic bone, and passes medialward to the lateral commissure of the eyelids, where it divides into two slips, which are attached to the margins of the respective tarsi. The Corrugator^ (Corrugator swpercilii) is a small, narrow, pyramidal muscle, placed at the medial end of tlie eyebrow, beneath the Frontalis and Obricularis oculi. It arises from the medial end of the superciliary arch; and its fibres pass upward and lateralward, between the palpebral and orbital portions of the Orbicu- laris oculi, and are inserted into the deep surface of the skin, above the middle of the orbital arch. Nerves. — The Orbicularis oculi and Corrugator are supplied by the facial nerve. Actions. — The Orbicularis oculi is the sphincter muscle of the eyeUds. The palpebral portion acts involuntarily, closing the hds gently, as in sleep or in blinking; the orbital portion is subject to the will. When the entire muscle is brought into action, the skin of the forehead, temple, and cheek is drawn toward the medial angle of the orbit, and the eyehds are firmly closed, as in photophobia. The skin thus drawn upon is thrown into folds, especially radiating from the lateral angle of the eyelids; these folds become permanent in old age, and form the so-called "crows' feet." The Levator palpebrae superioris is the direct antagonist of this muscle; it raises the upper eyelid and exposes the front of the bulb of the eye. Each time the eyeUds are closed through the action of the Orbicularis, the medial palpebral hgament is tightened, the wall of the lacrimal sac is thus drawn lateralward and forward, so that a vacuum is made in it, and the tears are sucked along the lacrimal canals into it. The lacrimal part of the Orbicularis oculi draws the eyehds and the ends of the lacrimal canals medialward and compresses them against the surface of the globe of the eye, thus placing them in the most favorable situation for receiving the tears; it also compresses the lacrimal sac. The Corrugator draws the ej'ebrow downward and medialward, producing the vertical wrinkles of the forehead. It is the "frowning" muscle, and may be regarded as the principal muscle in the expression of suffering. m. THE MUSCLES OF THE NOSE (Fig. 483). The muscles of the nose comprise: Procerus. Depressor septi. Nasalis. Dilatator naris posterior. Dilatator naris anterior. ' The corrugator is not recognized as a separate muscle in the Basle Nomenclature. THE MUSCLES OF THE MOUTH 469 The Procerus [Pyraniidalis nasi) is a small pyramidal slip ar.ising by tendinous fibres from the fascia covering the lower part of the nasal bone and upper part of the lateral nasal cartilage; it is inserted into the skin over the lower part of the forehead between the two eyebrows, its fibres decussating with those of the F'routalis. The Nasalis {('oni pressor naris) consists of two parts, transverse and alar. The transverse part arises from the maxilla, above and lateral to the incisive fossa; its fibres proceed upward and medialward, expanding into a thin aponeurosis which is continuous on the bridge of the nose with that of the muscle of the oppo- site side, and with the aponeurosis of the Procerus. The alar part is attached by one end to the greater alar cartilage, and by the other to the integument at the point of the nose. The Depressor septi (Depressor alae nasi) arises from the incisive fossa of the maxilla ; its fibres ascend to be inserted into the septum and back part of the ala of the nose. It lies between the mucous membrane and muscular structure of the lip. The Dilatator naris posterior is placed partly beneath the Quadratus labii superioris. It arises from the margin of the nasal notch of the maxilla, and from the lesser alar cartilages, and is inserted into the skin near the margin of the nostril. The Dilatator naris anterior is a delicate fasciculus, passing from the greater alar cartilage to the integument near the margin of the nostril; it is situated in front of the preceding. Nerves. — All the muscles of this group are supplied by the facial nerve. Actions. — The Procerus draws down the medial angle of the eyebrows and produces transverse wrinkles over the bridge of the nose. The two Dilatatores enlarge the aperture of the nares. Their action in ordinary breathing is to resist the tendencj^ of the nostrils to close from atmos- pheric pressure, but in difficult breathing, as well as in some emotions, such as anger, they con- tract strongly. The Depressor septi is a direct antagonist of the other muscles of the nose, drawing the ala of the nose do-miward, and thereby constricting the aperture of the nares. The Xasalis depresses the cartilaginous part of the nose and draws the ala toward the septum. IV. THE MUSCLES OF THE MOUTH. The muscles of the mouth are : Quadratus labii superioris. Quadratus labii inferioris. Caninus. Triangularis. Zygomaticus. Buccinator. Mentalis. Orbicularis oris. Risorius. Dissection. — The dissection of these muscles may be considerably facihtated bj' filling the cavit}- of the mouth with tow, so as to distend the cheeks and Hps; the mouth should then be closed by a few stitches and the integument carefulty removed from the surface. The Quadratus labii superioris is a broad sheet, the origin of which extends from the side of the nose to the zygomatic bone. Its medial fibres form the angular head, which arises by a pointed extremity from the upper part of the frontal process of the maxilla and passing obliquely downward and lateralward divides into two slips. One of these is inserted into the greater alar cartilage and skin of the nose; the other is prolonged into the lateral part of the upper lip, blending with the infraorbital head and with the Orbicularis oris. The intermediate portion or infraorbital head arises from the lower margin of the orbit immediately above the infraorbital foramen, some of its fibres being attached to the maxilla, others to the zygomatic bone. Its fibres converge, to be inserted into the muscular substance 470 MYOLOGY of the upper lip between the anguhir head and the Caninus. The lateral fibres, forming the zygomatic head, arise from the malar surface of the zygomatic bone immediately behind the zygomaticomaxillary suture and pass downward and medialward to the upper lip. The Caninus [Lcmfor anguli oris) arises from the canine fossa, immediately below the infraorbital foramen; its fibres are inserted into the angle of the mouth, intermingling with those of the Zygomaticus, Triangularis, and Orbicularis oris. The Zygomaticus {Zygomaticus major) arises from the zygomatic bone, in front of the zygomaticotemporal suture, and descending obliquely with a medial inclina- tion, is inserted into the angle of the mouth, wdiere it blends with the fibres of the Caninus, Orbicularis oris, and Triangularis. Nerves. — This group of muscles is supplied by the facial nerve. Actions. — The Quadratus labii superioris is the proper elevator of the upper lip, carrying it at the same time a httle forward. Its angular head acts as a dilator of the naris; the infraorbital and zygomatic heads assist in forming the nasolabial furrow, which passes from the side of the nose to the upper hp and gives to the face an expression of sadness. When the whole muscle is in action it gives to the countenance an expression of contempt and disdain. The Quadratus labii superioris raises the angle of the mouth and assists the Caninus in producing the nasolabial furrow. The zygomaticus draws the angle of the mouth backward and upward, as in laughing. The Mentalis (Levator menti) is a small conical fasciculus, situated at the side of the frenulum of the lower lip. It arises from the incisive fossa of the mandible, and descends to be inserted into the integument of the chin. The Quadratus labii inferioris {Depressor labii injerioris; Quadratus menti) is a small quadrilateral muscle. It arises from the oblique line of the mandible, between the symphysis and the mental foramen, and passes upward and medial- ward, to be inserted into the integument of the low^er lip, its fibres blending with the Orbicularis oris, and with those of its fellow of the opposite side. At its origin it is continuous with the fibres of the Platysma. Much yellow fat is intermingled with the fibres of this muscle. The Triangularis {Depressor anguli oris) arises from the oblique line of the mandible, wdience its fibres converge, to be inserted, by a narrow fasciculus, into the angle of the mouth. At its origin it is continuous with the Platysma, and at its insertion with the Orbicularis oris and Risorius; some of its fibres are directly continuous with those of the Caninus, and others are occasionally found crossing from the muscle of one side to that of the other; these latter fibres constitute the Transversus menti. Nerves. — This group of muscles is supplied by the facial nerve. Actions. — The Mentahs raises and protrudes the lower hp, and at the same time wrinkles the skin of the chin, expressing doubt or disdain. The Quadratus labii inferioris draws the lower lip directly downward and a httle lateralward, as in the expression of irony. The Triangularis depresses the angle of the mouth, being the antagonist of the Caninus and Zygomaticus; acting with the Caninus, it will draw the angle of the mouth medialward. The Buccinator (Fig. 485) is a thin quadrilateral muscle, occupying the interval between the maxilla and the mandible at the side of the face. It arises from the outer surfaces of the alveolar processes of the maxilla and mandible, corresponding to the three molar teeth; and behind, from the anterior border of the pterygoman- dibular raphe which separates it from the Constrictor pharyngis superior. The fibres converge toward the angle of the mouth, where the central fibres intersect each other, those from below being continuous with the upper segment of the Orbicularis oris, and those from above with the lower segment; the upper and lower fibres are continued forward into the corresponding lip without decussation. Relations. — The Buccinator is covered by the buccopharyngeal fascia, and is in relation by its superficial surface, behind, with a large mass of fat, which separates it from the ramus of the mandible, the Masseter, and a small portion of the Temporalis; this fat has been named the THE MUSCLES OF THE MOUTH 471 suctorial pad, because it is sui)i)osed to assist in the act of sucking. In front the superficial surface of the Buccinator is in relation with the Zygoniaticus, Risorius, Caninus, Triangularis, and the parotid duct which pierces it opposite the second molar tooth of the maxilla; the external maxillary artery antl anterior facial vein cross it from below upward; it is also crossed by the branches of the facial and buccinator nerves. The deep surjace is in relation with the buccal glands and mucous membrane of the mouth. The pterygomandibular raphe {pterycjomandibular ligament) is a tendinous band of the buccopharyngeal fascia, attached by one extremity to the hamulus of the medial pterygoid plate, and by the other to the posterior end of the mylohyoid line of the mandible. Its medial surjace is covered by the mucous membrane of the mouth. Its laferal surface is separated from the ramus of the mandible by a quantity of adipose tissue. Its posterior border gives attachment to the Constrictor pharyngis superior; its anterior border, to part of the Buccinator (Fig. 485). The Orbicularis oris (Fig. 486) is not a simple sphincter muscle like the Orbic- ularis oculi; it consists of numerous strata of muscular fibres surrounding the orifice of the mouth but having dift'erent direction. It consists partly of fibres de- rived from the other facial muscles which are inserted into the lips, and partly of fibres proper to the lips. Of the former, a considerable number are derived from the Buccinator and form the deeper stratum of the Orbicularis. Some of the Buccinator fibres — namely, those near the middle of the muscle^ — decussate at the angle of the mouth, those arising from the maxilla passing to the lower lip, BUCCINATOR Fig. 485. — Muscles of the pharynx and cheek. Fig. 486.- TRIANGULAFUS -Scheme showing arrangement of fibres of Orbicularis oris. and those from the mandible to the upper lip. The uppermost and lowermost fibres of the Buccinator pass across the lips from side to side without decussation. Superficial to this stratum is a second, formed on either side by the Caninus and Triangularis, which cross each other at the angle of the mouth; those from the Caninus passing to the lower lip, and those from the Triangularis to the upper lip, along which they run, to be inserted into the skin near the median line. In addi- tion to these there are fibres from the Quadratus labii superioris, the Zygomaticus, and the Quadratus labii inferioris; these intermingle with the transverse fibres aboA'e described, and have principally an oblique direction. The proper fibres of the lips are oblique, and pass from the under surface of the skin to the mucous membrane, through the thickness of the lip. Finally there are fibres by whicli the muscle is connected with the maxillse and the septum of the nose above and with 472 MYOLOGY the mandible below. In the upper lip these consist of two hands, lateral and mecHal, on either side of the middle line; the lateral band {m. incisivus labii superioris) arises from the alveolar border of the maxilla, opposite the lateral incisor tooth, and arching laterahvard is continuous with tKe other muscles at the angle of the mouth; the medial band (m. na.wJahiaUfi) connects the upper lip to the back of the septum of the nose. The interval between the two medial bands corresponds with the depression, called the philtrum, seen on the lip beneath the septum of the nose. The additional fibres for the lower lip constitute a slip (???. incisivus labii inferioris) on either side of the middle line; this arises from the mandible, lateral to the Mentalis, and intermingles with the other muscles at the angle of the mouth. The Risorius arises in the fascia over the Masseter and, passing horizontally forward, superficial to the Platysma, is inserted into the skin at the angle of the mouth (Fig. 483). It is a narrow bundle of fibres, broadest at its origin, but varies much in its size and form. Nerves. — The muscles in this group are all supplied by the facial nerve. Actions. — The Orbicularis oris in its ordinary action effects the direct closure of the lips; by its deep fibres, assisted by the obhque ones, it closely apphes the hps to the alveolar arch. The superficial part, consisting principally of the decussating fibres, brings the lips together and also protrudes them forward. The Buccinators compress the cheeks, so that, during the process of mastication, the food is kept under the immediate pressure of the teeth. When the cheeks have been previously distended with air, the Buccinator muscles expel it from between the lips, as in blowing a trumpet; hence the name (buccina, a trumpet). The Risorius retracts the angle of the mouth, and produces an unpleasant grinning expression. IV. THE MUSCLES OF MASTICATION. The chief muscles of mastication are: Masseter. Pterygoideus externus. Temporalis. Pterygoideus internus. Parotideomasseteric Fascia {masseteric fascia) . — Covering the Masseter, and firmly connected with it, is a strong layer of fascia derived from the deep cervical fascia. Above, this fascia is attached to the lower border of the zygomatic arch, and behind, it invests the parotid gland. The Masseter (Fig. 483) is a thick, somewhat quadrilateral muscle, consisting of two portions, superficial and deep. The superficial portion, the larger, arises by a thick, tendinous aponeurosis from the zygomatic process of the maxilla, and from the anterior two-thirds of the lower border of the zygomatic arch : its fibres pass downward and backward, to be inserted into the angle and lower half of the lateral surface of the ramus of the mandible. The deep portion is much smaller, and more muscular in texture; it arises from the posterior third of the lower border and from the whole of the medial surface of the zygomatic arch; its fibres pass downward and forward, to be inserted into the upper half of the ramus and the lateral surface of the coronoid process of the mandible. The deep portion of the muscle is partly concealed, in front, by the superficial portion; behind, it is covered by the parotid gland. The fibres of the two portions are continuous at their insertion. Relations. — The Masseter is in relation by its superficial surface with the integument, Platysma, Risorius, Zygomaticus, the parotid gland and its accessory portion; the parotid duct, the branches of the facial nerve and the transverse facial vessels cross it. By its deep surface, it is in relation with the insertion of the TemporaUs and the ramus of the mandible; a mass of fat separates it from the Buccinator and the buccinator nerve. The masseteric nerve and artery enter the muscle on its deep surface. Its posterior ■margin is overlapped by the parotid gland. Its anterior margin projects over the Buccinator and is crossed below bj' the anterior facial vein. THE MUSCLES OF MASTICATION 473 Temporal Fascia. — The temporal faseia covers the Temjioralis muscle, It is a stront;-, fibrous in\estmeut, covered, laterally, by the Auricularis anterior and supe- rior, by the galea aponeurotica, and by ])art of the Orbicularis oculi. The super- ficial temi)oral \essels and the auriculotemporal nerve cross it from below upward. Above, it is a single layer, attached to the entire extent of the superior temporal line; but bcloic, where it is fixed to the zygomatic arch, it consists of two layers, one of which is inserted into the lateral, and the other into the medial border of the arch. A small cpiantity of fat, the orbital branch of the superficial temporal artery, and a filament from the zygomatic branch of the maxillary nerve, are contained between these two layers. It affords attachment b>' its deep surface to the super- ficial fibres of the Temporalis. Dissection. — In order to expose the Temporalis, remove the temporal fascia, which may be eiTccted by separating it at its attachment along the upper border of the zygoma and dissecting it upward from the surface of the muscle. The zj^gomatic arch should then be divided in front at its junction with the zygomatic bone, and behind near the external auditor}^ meatus, and drawii downward with the Masseter, which should be detached from its insertion into the ramus and angle of the mandible. The whole extent of the Temporalis is then exposed. Fig. 4S7. — The Temporalis; the zygomatic arch and Masseter have been removed. The Temporalis {Temporal muscle) (Fig. 487) is a broad, radiating muscle, situated at the side of the head. It arises from the whole of the temporal fossa (except that portion of it which is formed by the zygomatic bone) and from the deep surface of the temporal fascia. Its fibres converge as they descend, and end in a tendon, which passes deep to the zygomatic arch and is inserted into the medial surface, apex, and anterior border of the coronoid process, and the anterior border of the ramus of the mandible nearly as far forward as the last molar tooth. Relations. — The Temporalis is in relation by its superficial surface with the integument, the Auriculares anterior and superior, the temporal fascia, the superficial temporal vessels, the auriculotemporal nerve, the temporal branches of the facial and zygomatic nerves, the galea aponeurotica, the zygomatic arch, and the Masseter. By its deep surface, it is in relation with the temporal fossa, the Pterygoideus externus and part of the Buccinator, the internal maxillary artery, and its deep temporal branches, the deep temporal nerves, and the buccinator vessels and nerve. Behind the tendon are the massetei'ic vessels and nerve. Its anterior border is sepa- rated from the zygomatic bone by a mass of fat. 474 MYOLOGY Dissection. — The Temporalis having been examined, saw through the base of the coronoid process and draw it upward, together with the TemporaUs, which should be detached from the surface of the temporal fossa. Divide the ramus of the mandible just below the condyle, and also, by a ti'ansverse incision extending across the middle, ju.^t above the dental foramen; remove the fragment, and the Pterygoidci will be exposed. The Pterygoideus externus {External pterygoid muscle) (Fig. 488) is a short, thick muscle, somewhat conical in form, which extends almost horizontally between the infratemporal fossa and the condyle of the mandible. It arises by two heads; an upper from the lower part of the lateral surface of the great wing of the sphenoid and from the infratemporal crest; a lower from the lateral surface of the lateral pterygoid plate. Its fibres pass horizontally backward and lateralward, to be inserted into a depression in front of the neck of the condyle of the mandible, and into the front margin of the articular disk of the temporomandibular articulation. Fig. 488. — The Pterygoidei ; the zygomatic arch and a portion of the ramus of the mandible have been removed. Relations. — Its superficial surface is in relation with the ramus of the mandible, the internal maxillary artery, which crosses it,i the tendon of the Temporahs, and the Masseter. Its deep surface rests against the upper part of the Pterygoideus internus, the sphenomandibular ligament, the middle meningeal artery, and the mandibular nerve; its upper border is in relation with the temporal and masseteric branches of the mandibular nerve; its lower border with the lingual and inferior alveolar nerves. The buccal nerve and the internal maxillary artery pass between the two portions of the muscle (Fig. 488) . The Pterygoideus internus (Internal pterygoid muscle) (Fig. 488) is a thick, quad- rilateral muscle. It arises from the medial surface of the lateral pterygoid plate and the grooved surface of the pyramidal process of the palatine bone; it has a second slip of origin from the lateral surfaces of the pyramidal process of the pala- tine and tuberosity of the maxilla. Its fibres pass downward, lateralward, and backward, and are inserted, by a strong tendinous lamina, into the lower and back part of the medial surface of the ramus and angle of the mandible, as high as the mandibular foramen. Relations. — Its lateral surface is in relation with the ramus of the mandible, from wliich it is separated, at its upper part, by the Pterygoideus externus, the sphenomandibular Mgament, the internal maxillary artery, the inferior alveolar vessels and nerve, the hngual nerve, and a process of the parotid gland. Its medial surface is in relation with the Tensor veli palatini, being separated from the Constrictor pharyngis superior by some areolar tissue. 1 In many cases the artery will be found under cover of the muscle. THE LATERAL CERVICAL MUSCLES 475 Nerves. — The muscles of mastication are supplied by the iiuuulibular nerve. Actions. — The Tempoi-alis, Masseter, and Pterygoideus internus raise the mandible against the maxilku with great force. The Pterygoideus cxtornus assists in opening the mouth, but its main action is to draw forward the condyle and articular disk so that the mandible is protruded and the inferior incisors projected in front of the u{)per; in this action it is assisted by the Ptery- goideus internus. The mandible is retracted by the posterior fibres of the Temporalis. If the Pterygoidei internus and externus of one side act, the corresponding side of the mandible is drawn forward while the opposite condyle remains comparatively fixed, and side-to-side move- ments, such as occur during the tritui-ation of food, take place. THE FASCI-ai AND MUSCLES OF THE ANTERO-LATERAL REGION OF THE NECK. The antero-lateral muscles of the neck may be arranged into the following groups : I. Superficial Cervical. III. Supra- and Infra-hyoid. II. Lateral Cervical. IV. Anterior Vertebral. V. Lateral Vertebral. I. THE SUPERFICIAL CERVICAL MUSCLE. Platysma. Dissection — A block having been placed at the back of the neck, and the face turned to the side opposite that to be dissected, so as to place the parts upon the stretch, make two trans- verse incisions, one from the chin, along the margin of the mandible, to the mastoid process, and the other along the upper border of the clavicle. Connect these by an oblique incision made in the com'se of the Sternocleidomastoideus, from the mastoid process to the sternum; the two flaps of integument having been removed in the direction shown in Fig. 482, the superficial fascia will be exposed. The Superficial Fascia of the neck is a thin lamina investing the Platysma, and is hardly demonstrable as a separate membrane. The Platysma (Fig. 483) is a broad sheet arising from the fascia covering the upper parts of the Pectoralis major and Deltoideus; its fibres cross the clavicle, and proceed obliquely upward and medial ward along the side of the neck. The anterior fibres interlace, below and behind the symphysis menti, with the fibres of the muscle of the opposite side; the posterior fibres cross the mandible, some being inserted into the bone below the oblique line, others into the skin and sub- cutaneous tissue of the lower part of the face, many of these fibres blending with the muscles about the angle and lower part of the mouth. Sometimes fibres can be traced to the zygomaticus, or to the margin of the Orbicularis oculi. Beneath the Platysma, the external jugular vein descends from the angle of the mandible to the clavicle. Actions. — When the entire Platysma is in action it produces a slight wi-inkling of the surface of the skin of the neck in an oblique direction. Its anterior portion, the thickest part of the muscle, depresses the low^er jaw; it also serves to draw down the lower lip and angle of the mouth in the expression of melancholy. Nerve. — The Platysma is supplied by the cervical branch of the facial nerve. n. THE LATERAL CERVICAL MUSCLES. The lateral muscles are : Trapezius and Sternocleidomastoideus. The Trapezius is described on page 522. 476 MYOLOGY The Fascia Colli {deep cervical fascia) (Fig. 4S9). — The fascia colli lies under cover of the Platysma, and invests the neck; it also forms sheaths for the carotid vessels, and for the structures situated in front of the vertebral column. OmoTiyoideus Tlnj) Old gland Common carotid anay Int. jugular vein \ y Sternccle idoinasto ideus Vagus nerve^~~ , Ext. jugular vein Scalenus anterior Scalenus mcdius' Sflenius colli Levator scapulae Trapeziub Ant. jugular vein ~- SternoJiyoidctis ' Sternoihyreoideus Trachea (( ^^^fe- Oeso2:)h agus ~~ ' oth cervical vertebra — Vertebral vessels Semisjnnalis colli Sem,is}:iinalis capitis Splenius capitis Fig. 489. — Section of the neck at about the level of the sixth cervical vertebra. Showing the arrangement of the fascia coli. The investing portion of the fascia is attached behind to the ligamentum nuchae and to the spinous process of the seventh cervical vertebra. It forms a thin in- vestment to the Trapezius, and at the anterior border of this muscle is continued forward as a rather loose areolar layer, covering the posterior triangle of the neck, to the posterior border of the Sternocleidomastoideus, where it begins to assume the appearance of a fascial membrane. Along the hinder edge of the Sterno- cleidomastoideus it divides to enclose the muscle, and at the anterior margin again forms a single lamella, which covers the anterior triangle of the neck, and reaches forward to the middle line, where it is continuous with the corresponding part from the opposite side of the neck. In the middle line of the neck it is attached to the symphysis menti and the body of the hyoid bone. THE LATERAL CERVICAL MUSCLES 477 Above, the fascia is attached to the sujierior nuchal Hne of the occipital, to the mastoid process of the temporal, and to the whole length of the inferior border of the l)0(ly of the mandible. ()i)])osite the angle of the mandible the fascia is very strong, and binds the anterior edge of the Sternoclcidomastoideus firmly to that bone. Between the mandible and the mastoid process it ensheathes the parotid gland — the layer which covers the gland extends upward under the name of the parotideomasseteric fascia and is fixed to the zygomatic arch. From the part which passes under the parotid gland a strong band extends upward to the styloid process, forming the stylomandibular ligament. Two other l)ands may be defined: the sphenomandibular (page 395) and the pterygospinous ligaments. The pterygospinous ligament stretches from the upper part of the posterior border of the lateral ptery- goid plate to the spinous process of the sphenoid. It occasionally ossifies, and in such cases, between its upper border and the base of the skull, a foramen is formed which transmits the branches of the mandibular nerve to the muscles of mastication. Below, the fascia is attached to the acromion, the clavicle, and the manubrium sterni. Some little distance above the last it splits into two layers, superficial and deep. The former is attached to the anterior border of the manubrium, the latter to its posterior border and to the interclavicular ligament. Between these two layers is a slit-like interval, the suprasternal space {space of Burns) ; it contains a small quantity of areolar tissue, the lower portions of the anterior jugular veins and their transverse connecting branch, the sternal heads of the Sternocleido- mastoidei, and sometimes a lymph gland. The fascia which lines the deep surface of the Sternocleidomastoideus gives off the following processes: (1) A process envelops the tendon at the Omohyoideus, and binds it down to the sternum and first costal cartilage. (2) A strong sheath, the carotid sheath, encloses the carotid artery, internal jugular vein, and vagus nerve. (3) The prevertebral fascia extends medialward behind the carotid vessels, where it assists in forming their sheath, and passes in front of the prevertebral muscles. It forms the posterior limit of a fibrous compartment, which contains the larynx and trachea, the thyroid gland, and the pharynx and oesophagus. The prevertebral fascia is fixed above to the base of the skull, and below is continued into the thorax in front of the Longus colli muscles. Parallel to the carotid sheath and along its medial aspect the prevertebral fascia gives off a thin lamina, the buccopharyngeal fascia, which closely invests the Constrictor muscles of the pharynx, and is continued forward from the Constrictor pharyngis superior on to the Buc- cinator. It is attached to the prevertebral layer by loose connective tissue only, and thus an easily distended space, the retropharyngeal space, is found between them. . This space is limited above by the base of the skull, while below it extends behind the oesophagus into the posterior mediastinal cavity of the thorax. The pre- vertebral fascia is prolonged downward and lateralward behind the carotid vessels and in front of the Scaleni, and forms a sheath for the brachial nerves and sub- clavian vessels in the posterior triangle of the neck; it is continued under the clavicle as the axillary sheath and is attached to the deep surface of the coracoclavicular fascia. Immediately above and behind the clavicle an areolar space exists between the investing layer and the sheath of the subclavian vessels, and in this space are found the low^er part of the external jugular vein, the descending clavicular nerves, the transverse scapular and transverse cervical vessels, and the inferior belly of the Omohyoideus muscle. This space is limited below by the fusion of the coraco- clavicular fascia with the anterior wall of the axillary sheath. (4) The pretrachial fascia extends medially in front of the carotid vessels, and assists in forming the carotid sheath. It is continued behind the depressor muscles of the hyoid bone, and, after enveloping the thyroid gland, is prolonged in front of the trachea to meet the corresponding layer of the opposite side. Above, it is fixed to the liyoid bone, while below it is carried downward in front of the trachea and large vessels 478 MYOLOGY at the root of the neck, and ultimately blends with the fibrous pericardium. Tliis layer is fused on either side with the prevertebral fascia, and with it completes the compartment containing the larynx and trachea, the thyroid gland, and the pharynx and oesophagus.^ Applied Anatomy. — The deep cervical fascia is of considerable importance from a surgical point of view. The investing layer opposes the extension of abscesses toward the surface, and pus forming beneath it has a tendency to extend laterally. If the pus be contained in the anterior triangle, it may find its way into the anterior mediastinal cavity, in front of the layer of fascia which passes down into the thorax to blend with the pericardium; but owing to the less density and thickness of the fascia in this situation it more frequently finds its way to the surface and points above the sternum. Pus forming beneath the pretracheal layer would in all probability find its way into the posterior mediastinal cavity. Pus forming behind the prevertebral layer, in cases, for instance, of caries of the bodies of the cervical vertebrae, may extend toward the lateral part of the neck and point in the posterior triangle, or may perforate this layer of fascia and the buccopharyngeal fascia and point into the pharynx {retropharyngeal abscess). In cases of cut throat, when the wound involves only the investing layer the injury is usually trivial, the special danger being injury to the external jugular vein, and the special complication, diffuse cellulitis. But where the second of the two layers is opened up, important structures may be injured, and serious results follow. The sternal head of origin of the Sternocleidomastoideus is contained in the suprasternal space, so that this space is opened in division of this tendon. The lower part of the anterior jugular vein is also contained in the same space. The Sternocleidomastoideus {Sternomastoid muscle) (Fig. 490) passes obliquely across the side of the neck. It is thick and narrow at its central part, but broader and thinner at either end. It arises from the sternum and clavicle by two heads. The medial or sternal head is a rounded fasciculus, tendinous in front, fleshy behind, which arises from the upper part of the anterior surface of the manubrium sterni, and is directed upward, lateralward, and backward. The lateral or clavicular head, composed of fleshy and aponeurotic fibres, arises from the superior border and anterior surface of the medial third of the clavicle; it is directed almost vertically upward. The two heads are separated from one another at their origins by a triangular interval, but gradually blend, below the middle of the neck, into a thick, rounded muscle which is inserted, by a strong tendon, into the lateral surface of the mastoid process, from its apex to its superior border, and by a thin aponeurosis into the lateral half of the superior nuchal line of the occipital bone. The Sternocleidomastoideus varies much in its extent of origin from the clavicle : in some cases the clavicular may be as narrow as the sternal head; in others, as much as 7.5 cm. in breadth. When the clavicular origin' is broad, it is occasionally subdivided into several slips, separated by narrow intervals. More rarely, the adjoining margins of the Sternocleidomastoideus and Trapezius have been found in contact. Triangles of the Neck. — This muscle divides the quadrilateral area of the side of the neck into two triangles, an anterior and a posterior. The boundaries of the anterior triangle are, in front, the median line of the neck; above, the lower border of the body of the mandible, and an imaginary line drawn from the angle of the mandible to the Sternocleidomastoideus; behind, the anterior border of the Sternocleidomastoideus. The apex of the triangle is at the upper border of the sternum. The boundaries of the posterior triangle are, in fro7it, the posterior border of the Sternocleidomastoideus; below, the middle third of the clavicle; behind, the anterior margin of the Trapezius. The apex corresponds with the meeting of the Sternocleidomastoideus and Trapezius on the occipital bone. The anatomy of these triangles will be more fully described with that of the vessels of the neck (p. 642). Relations. — The superficial surface of the Sternocleidomastoideus is in relation with the integu- ment and Platysma, from which it is separated by the external jugular vein, several of the superficial branches of the cervical plexus, and the investing layer of the deep cervical fascia. The deep surface of the muscle is in relation with the sternoclavicular articulation, the pro- cess of the deep cervical fascia which binds the inferior belly of the Omohyoideus to the sternum and clavicle, the Sternohyoideus, Sternothyreoideus, Omohyoideus, posterior belly of 1 F. G. Parsons (Journal of Anatomy and Physiology, vol. xliv) regards the carotid sheath and the fascial planes in the neck as structures which are artificially produced by dissection. THE LATERAL CERVICAL MUSCLES 479 the Digastricus, Levator scapulae, Spleuius and Scaleni muscles, the common carotid artery, the internal and anterior jugular veins, the origins of the internal and external carotid arteries, the occipital, subclaviaii, transverse cervical, and transverse scapular arteries and veins, the phrenic, vagus, hypoglossal, descendens and communicantes hypoglossi nerves, the accessory nerve which pierces its upper third, the cervical plexus, the upper part of the brachial plexus, parts of the thyroid and parotid glands and their vessels, and the deep cervical lymi)h glands. Actions. — -When only one Sternocleidomastoideus acts, it draws the head toward the shoulder of the same side, assisted by the Splenius and the Obliquus capitis inferior of the opposite side. At the same time it rotates the head so as to carry the face toward the opposite side. Acting together from their sternoclavicular attachments the muscles will flex the cervical part of the vertebral column. If the head be fixed, the two muscles assist in elevating the thorax in forced inspiration. Fig. 490. — Muscles of the neck. Lateral view. Nerves. — The Sternocleidomastoideus is supplied by the accessory nerve and branches from the anterior divisions of the second and third cervical nerves. Applied Anatomy. — The surgical anatomy of the Sternocleidomastoideus is of importance in connection with the deformity known as wry-neck, which is due to a contracted condition of this muscle. The wry-neck may be -temporary, as the result of direct irritation of the muscle or of the nerves supplying it, and may occur in acute glandular enlargement, cellulitis of the neck, myositis of the muscle, or cervical caries. It may, however, be permanent, and is then most often due to injm-y to the muscle during birth, especially in breech presentations, rupture of the fibres and subsequent cicatricial contraction taking place. In these cases, division of the muscle is often necessary to effect a cure, and this may be done either subcutaneously or through an open wound. The subcutaneous method is thus performed; the external jugular and anterior jugular veins having been, if possible, defined, a tenotomy knife is introduced close to the margin of one tendon of origin of the muscle, about 1.25 cm. above the clavicle, and the tenotome passed flat behind the tendon and then turned forward, and the tendon divided from behind forward while the muscle is put well upon the stretch by an assistant. The other tendon is then divided in a similar manner. In dividing the clavicular origin, it is always desirable to introduce the tenotome along the posterior border, in order to avoid the external jugular vein. The open method is, however, much to be preferred, as being the more effectual and the less dangerous, if precau- tions are taken to keep the wound aseptic. The tendons of origin are freely exposed by a. hori- zontal incision across the root of the neck and carefully divided; any tense bands of fascia which 480 MYOLOGY exist should also be divided. The wound is now sutured and dressed, and the head fixed in as straight a position as possible. There is also a condition coming on in adult life (spasinodic torlicollis) which is a very distress- ing form of functional nervous disease. It begins with tonic or clonic spasm of one of the Sterno- cleidomastoidei, which is soon followed by spasm of the Trapezius, particularly its clavicular portion. The Splenius of the opposite side, the Scaleni, Semispinales capitis, and Longissimi capitis may all become involved in turn, with secondary contracture of the deep cervical fascia. Operation in these cases often fails to give satisfactory results. Tenotomy of the affected muscles or section of the nerves supplying them may afford temporary relief, but the .spasm often returns when the cut nerves or muscles rejoin. III. THE SUPRA- AND INFRAHYOID MUSCLES (Figs. 490, 491). The suprahyoid muscles are : Digastricus. Mylohyoideus. Stylohyoideus. Geniohyoideus. Dissection. — To dissect these muscles a block should be placed beneath the back of the neck, and the head drawn backward and retained in that position. On the removal of the deep fascia the muscles are at once exposed. Sternum Fig. 491. — Muscles of the neck. Anterior view. The Digastricus (Digastric muscle) consists of two fleshy belhes united by an intermediate rounded tendon. It lies below the body of the mandible, and extends, in a curved form, from the mastoid process to the symphysis menti. The posterior belly, longer than the anterior; arises from the mastoid notch of the temporal bone and passes downward and forward. The anterior belly arises from a depression on the inner side of the lower border of the mandible, close to the symphysis, and passes downward and backward. The two bellies end in an intermediate tendon which perforates the Stylohyoideus muscle, and is held in connection with the side of the body and the greater cornu of the hyoid bone by a fibrous loop, which is sometimes lined bv a mucous sheath. A broad aponeurotic layer is given off THE SUPRA- AND INFRAHYOID MUSCLES 481 from the tendon of the Digastricus on either side, to he attached to the hody and greater cornu of the hyoid bone; this is termed the suprahyoid aponeurosis. The Digastricus divides the anterior triangle of the neck into three smaller triangle (1) the submaxillary triangle, bounded above by the lower border of the body of the mandible, and a line drawn from its angle to the Sternocleidomastoideus, below by the posterior belly of the Digastricus and the Stylohyoideus, in front by the anterior belly of the Digastricus; (2) the carotid triangle, bounded above by the posterior belly of the Digastricus and Stylohyoideus, behind by the Sternocleidomastoideus, below by the Omohyoideus; (3) the suprahyoid or sub- mental triangle, boiftidcd laterally by the anterior belly of the Digastricus, medially by the middle line of the neck from the hyoid bone to the symphysis menti, and interiorly by the body of the hyoid bone. Relations. — The Digastricus is in relation by its superficial surface with the Platysma, Sterno- cleidomastoideus, part of the Splenius, Longissimus capitis, mastoid process, Stylohyoideus, and the parotid gland. The deep surface of the anterior belly lies on the Mylohyoideus; that of the posterior bellj'^ on the Styloglossus, Stylopharyiigeus, and Hyoglossus muscles, the external carotid artery and its occipital, lingual, external maxillary, and ascending pharyngeal branches, the internal carotid artery, internal jugular -s^ein, and hypoglossal nerve. The stylohyoideus (Stylohyoid muscle) is a slender muscle, lying in front of, and above, the posterior belly of the Digastricus. It arises from the back and lateral surface of the styloid process, near the base; and, passing downward and forward, is inserted into the body of the hyoid bone, at its junction with the greater cornu, and just above the Omohyoideus. It is perforated, near its insertion, by the tendon of the Digastricus. The Stylohyoid Ligament (ligavientum stylohyoideus). — In connection with the Stylohyoideus muscle a ligamentous band, the stylohyoid ligament, may be described. It is a fibrous cord, which is attached to the tip of the styloid process of the temporal and the lesser cornu of the hyoid bone. It frequently contains a little cartilage in its centre, is often partially ossified, and in many animals forms a distinct bone, the epihyal. The Mylohyoideus (Mylohyoid muscle), flat and triangular, is situated imme- diately above the anterior belly of the Digastricus, and forms, with its fellow of the opposite side, a muscular floor for the cavity of the mouth. It arises from the whole length of the mylohyoid line of the mandible, extending from the symphysis in front to the last molar tooth behind. The posterior fibres pass medialward and slightly downward, to be inserted into the body of the hyoid bone. The middle and anterior fibres are inserted into a median fibrous raphe extending from the sym- physis menti to the hyoid bone, where they join at an angle with the fibres of the opposite muscle. This median raphe is sometimes wanting; the fibres of the two muscles are then continuous. Relations. — The Mylohyoideus is in relation by its superficial or under surface with the Platys- ma, the anterior belly of the Digastricus, the suprahyoid aponeurosis, the superficial part of the submaxillary gland, the external maxillary and submental vessels, and the mylohyoid vessels and nerve. By its deep or superior surface it is in relation with the Geniohyoideus, part of the Hyoglossus, and the Styloglossus muscles, the hypoglossal and Ungual nerves, the submaxillary ganglion, the subUngual gland, the deep portion of the submaxillary gland and the submaxillary duct, the lingual and subUngual vessels, and the buccal mucous membrane. Dissection. — The Mylohyoideus should now be removed, in order to expose the muscles which lie beneath; this is effected by reflecting it from its atta^ments to the hyoid bone and mandible, and separating it by a vertical incision from its fellow of the opposite side. The Geniohyoideus (Geniohyoid muscle) is a narrow muscle, situated above the medial border of the Mylohyoideus. It arises from the inferior mental spine on the back of the symphysis menti, and runs backward and slightly downward, to be inserted into the anterior surface of the body of the hyoid bone; it lies in con- tact with its fellow of the opposite side. * Nerves. — -The Mylohyoideus and anterior belly of the Digastricus are suppUed by the mylo- hyoid branch of the inferior alveolar; the Stylohyoideus and posterior belly of the Digastricus, by the facial; the Geniohyoideus, by the hypoglossal. 31 482 MYOLOGY Actions. — ^These muscles perform two very important actions. During the act of deglutition they raise the hyoid bone, and with it the base of the tongue; when the hyoid bone is fixed by its depressors and those of the larynx, they depress the mandible. During the first act of degluti- tion, when the mass of food is being driven from the mouth into the pharynx, the hyoid bone and with it the tongue, is carried upward and forward by the anterior bellies of the Digastrici, the Mylohyoidei, and Geniohyoidei. In the second act, when the mass is passing through the pharynx, the direct elevation of the hyoid bone takes place by the combined action of all the muscles; and after the food has passed, the hyoid bone is carried upward and backward by the posterior bellies of the Digastrici and the Stylohyoidei, which assist in preventing the return of the food into the mouth. The infrahyoid muscles are : Sternohyoideiis. Thyreohyoideus. Sternothyreoideiis. Omohyoideus. Dissection. — The muscles in this region may be exposed by removing the deep fascia from the front of the neck. In order to see the entire extent of the Omohyoideus it is necessary to divide the Sternocleidomastoideus at its centre, and turn its ends aside, and to detach the Trape- zius from the clavicle and scapula. This, however, should not be done until the Trapezius has been dissected. The Sternohyoideus {Sternohyoid muscle) is a thin, narrow muscle, which arises from the posterior surface of the medial end of the clavicle, the posterior sterno- clavicular ligament, and the upper and posterior part of the manubrium sterni. Passing upward and medialward, it is inserted, by short, tendinous fibres, into the lower border of the body of the hyoid bone. Below, this muscle is separated from its fellow by a considerable interval; but the two muscles come into contact with one another in the middle of their course, and from this upward, lie side by side. It sometimes presents, immediately above its origin, a transverse tendinous inscription. The Sternothyreoideus (Sternothyroid muscle) is shorter and wider than the preceding muscle, beneath which it is situated. It arises from the posterior surface of the manubrium sterni, below the origin of the Sternohyoideus, and from the edge of the cartilage of the first rib, and sometimes that of the second rib, it is inserted into the oblique line on the lamina of the thyroid cartilage. This muscle is in close contact with its fellow at the lower part of the neck, but diverges somewhat as it ascends; it is occasionally traversed by a transverse or oblique tendinous inscription. The Thyreohyoideus {Thyrohyoid muscle) is a small, quadrilateral muscle appearing like an upward continuation of the Sternothyreoideus. It arises from the oblique line on the lamina of the thyroid cartilage, and is inserted into the lower border of the greater cornu of the hyoid bone. The Omohyoideus {Omohyoid muscle) consists of two fleshy bellies united by a central tendon. It arises from the upper border of the scapula, and occasionally from the superior transverse ligament which crosses the scapular notch, its extent of attachment to the scapula varying from a few millimetres to 2.5 cm. From this origin, the inferior belly forms a flat, narrow fasciculus, which inclines forward and slightly upward across the lower part of the neck, being bound down to the clavicle by a fibrous expansion; it then passes behind the Sternocleidomastoideus, becomes tendinous and changes its direction, forming an obtuse angle. It ends in the superior belly, which passes almost vertically upward, close to the lateral border of the Sternohyoideus, to be inserted into the lower border of the body of the hyoid bone, lateral to the insertion of the Sternohyoideus. The central tendon of this muscle varies much iif length and form, and is held in position by a process of the deep cervical fascia, which sheaths it, and is prolonged down to be attached to the clavicle and first rib; it is by this means that the angular form of the muscle is maintained. THE ANTERIOR VERTEBRAL MUSCLES 483 Th(> iut'crit)!- hcUy of tlic OinoliyoicUai.s tlividcs the poslcrior triniitilc of the neck into an upper or occipital triangle aiul ;i lown- or subclavian triangle, w liilc its suix'iior })elly divides the anterior triangk' into an uj)])or or carotid triangle aiul a lower or muscular triangle. Nerves. — The 'riiyreohyoidcus is .supi)lied by a branch from t he hypoglossal nerve; the superior belly of the Omohyoideus by the tleseendens hypoglossi; the Btcrnohyoidcus, Sternothyreoideus, ami inferior lielly of the Omohyoideus are sui:)phed by branches from the loop between the des- cendeiis hyj^oglossi and descendens eervicalis. Actions. — These muscles depress the larynx and hyoid bone, after they have been drawn up with the pharynx in the act of deglutition. The Omohyoidei not only depress the hyoid bone, but carry it backward and to one or the other side. They are concerned especially in prolonged inspiratory efforts; for by rendering the lower part of the cervical fascia tense they lessen the inward suction of the soft parts, which would otherwise compress the great vessels and the apices of the lungs. The Thyreohyoideus may act as an elevator of the thyroid cartilage, when the hyoid bone ascends, drawing the thyroid cartilage up behind the hyoid bone. The Sterno- thyreoideus acts as a depressor of the thyroid cartilage. IV. THE ANTERIOR VERTEBRAL MUSCLES (Fig. 492). The anterior vertebral muscles are: Longiis colli. Longus capitis. Rectus capitis anterior. Rectus capitis lateralis. Fig. 492. — The anterior vertebral muscles. The Longus colli is situated on the anterior surface of the vertebral column, between the atlas and the third thoracic vertebra. It is broad in the middle, narrow and pointed at either end, and consists of three portions, a superior oblique. 484 MYOLOGY an inferior oblique, and a vertical. The superior oblique portion arises from the anterior tubercles of the transverse processes of the third, fourth, and fifth cervical vertebrte; and, ascending obliquely with a medial inclination, is inserted by a narrow tendon into the tubercle on the anterior arch of the atlas. The inferior oblique portion, the smallest part of the muscle, arises from the front of the bodies of the first two or three thoracic vertebrse; and, ascending obliquely in a lateral direction, is inserted into the anterior tubercles of the transverse processes of the fifth and sixth cervical vertebrse. The vertical portion arises, below, from the front of the bodies of the upper three thoracic and lower three cervical vertebrse, and is in- serted into the front of the bodies of the second, third, and fourth cervical vertebrae. The Longus capitis (Rectus capitis anticus major), broad and thick above, narrow below, arises by four tendinous slips, from the anterior tubercles of the transverse processes of the third, fourth, fifth, and sixth cervical vertebrse, and ascends, converging toward its fellow of the opposite side, to be inserted into the inferior surface of the basilar part of the occipital bone. The Rectus capitis anterior (Rectus capitis anticus minor) is a short, flat muscle, situated immediately behind the upper part of the Longus capitis. It arises from the anterior surface of the lateral mass of the atlas, and from the root of its transverse process, and passing obliquely upward and medialward, is inserted into the inferior surface of the basilar part of the occipital bone immediately in front of the foramen magnum. The Rectus capitis lateralis, a short, flat muscle, arises from the upper surface of the transverse process of the atlas, and is inserted into the under surface of the jugular process of the occipital bone. Nerves. — -The Rectus capitis anterior and the Rectus capitis lateralis are supplied from the loop between the first and second cervical nerves; the Longus capitis, by branches from the first, second, and third cervical; the Longus colh, by branches from the second to the seventh cervical nerves. Actions. — The Longus capitis and Rectus capitis anterior are the direct antagonists of the muscles at the back of the neck, serving to restore the head to its natural position after it has been di-awn backward. These muscles also flex the head, and from their obhquity, rotate it, so as to turn the face to one or the other side. The Rectus lateraUs, acting on one side, bends the head laterally. The Longus colli flexes and shghtly rotates the cervical portion of the vertebral column. V. THE LATERAL VERTEBRAL MUSCLES (Fig. 492). The lateral vertebral muscles are : Scalenus anterior. Scalenus medius. Scalenus posterior. The Scalenus anterior (Scalenus anticus) lies deeply at the side of the neck, behind the Sternocleidomastoideus. It arises from the anterior tubercles of the transverse processes of the third, fourth, fifth, and sixth cervical vertebrse, and descending, almost vertically, is inserted by a narrow, flat tendon into the scalene tubercle on the inner border of the first rib, and into the ridge on the upper surface of the rib in front of the subclavian groove. Relations. — In front of the Scalenus anterior are the clavicle, the Subclavius, Sternocleido- mastoideus, and Omohyoideus muscles, the transverse cervical, the transverse scapular, and ascending cervical arteries, the subclavian vein, and the plu-enic nerve. By its posterior surface, it is in relation with the cords of the brachial plexus, the subclavian artery, and the pleura, which separate it from the Scalenus medius. Below, it is separated from the Longus colh by the vertebral artery, and above, from the Longus capitis, by the ascending cervical branch of the inferior thjToid arterj^ The Scalenus medius, the largest and longest of the three Scaleni, arises from the posterior tubercles of the transverse processes of the lower six cervical THE DEEP MUSCLES OF THE BACK 485 vertebra', and descending along the side of the vertebral column, is inserted by a broad attachment into the upper surface of the first ril), between the tubercle and the subclavian groove. Relations. — The Scalenus niedius is in relation by its anterior surface with the Sternocleido- mastoidcus; it is crossed by the clavicle and the Omohyoidcus; the subclavian artery and the cervical nerves separate it from the Scalenus anterior. Lateral to it are the Levator scapulae and the Scalenus jiostcrior. The long thoracic nerve is formed in the substance of the Scalenus medius and emerges from it; the dorsal scapular nerve also pierces it. The Scalenus posterior {Scalenus posticus), the smallest and most deeply seated of the three Scaleni, arises, by two or three separate tendons, from the posterior tubercles of the transverse processes of the lower two or three cervical vertebrae, and is inserted by a thin tendon into the outer surface of the second rib, behind the attachment of the Serratus anterior. It is occasionally blended Avith the Scalenus medius. Nerves. — The Scaleni are supplied by branches from the second to the seventh cervical nei'ves. Actions. — When the Scaleni act from above, they elevate the first and second ribs, and are, therefore, inspiratory muscles. Acting from below, they bend the vertebral column to one or other side; if the muscles of both sides act, the vertebral column is shghtly flexed. THE FASCI.ZE AND MUSCLES OF THE TRUNK. The muscles of the trunk may be arranged in six groups: I. Deep Muscles of the Back. IV. Muscles of the Abdomen. II. Suboccipital Muscles. V. Muscles of the Pelvis. III. Muscles of the Thorax. VI. Muscles of the Perineum. I. THE DEEP MUSCLES OF THE BACK (Fig. 494). The deep or intrinsic muscles of the back consist of a complex group of muscles extending from the pelvis to the skull. They are: Splenius capitis. Multifidus. Splenius cervicis. Rotatores. Sacrospinalis. Interspinales. Semispinalis. Intertransversarii. Dissection of the Muscles of the Back by Layers (Fig. 493). — Fiist Layer. — Place the body in a prone position, with the arms extended over the sides of the table, and the thorax and abdomen supported by several blocks, so as to render the muscles tense. Then make an inci- sion along the middle line of the back from the occipital protuberance to the coccyx. Make a transverse incision from the upper end of this to the mastoid process, and a third incision from its lower end, along the crest of the ilium to about its middle. This large intervening space should, for convenience of dissection, be subdivided by a fom-th incision, extending obUquely from the spinous process of the last thoracic vertebra, upward and outward to the acromion process. This incision corresponds with the lower border of the Trapezius muscle. The flaps of integument are then to be removed in the direction shown in the figure. Second Layer. — The Trapezius must be removed, in order to expose the second layer; to effect this, detach the muscle from its attachment to the clavicle and spine of the scapula, and tm-n it back toward the vertebral coliman. Third Layer. — To bring into view the third layer of muscles, remove the whole of the second, together with the Latissimus dorsi, by cutting through the Levator scapulae and Rhomboidei muscles near their origin, and reflecting them downward, and by dividing the Latissimus dorsi in the middle by a vertical incision carried from its upper to its lower part, and reflecting the two halves of the muscle. Fourth Layer. — To expose the muscles of the fourth layer, remove entirely the Serrati and the vertebral and lumbar fasciae. Then detach the Splenius by separating its attachment to the spinous processes and reflecting it outward. 486 MYOLOGY Fifth Layer. — Remove the muscles of the preceding layer by dividing and turning aside the Semispinalis capitis; then detach the Spinalis and Longissimus dorsi from their attachments, divide the Sacrospinalis at its connection below to the sacral lumbar vertebrae and turn it out- ward. The muscles filling up the interval between the spinous and transverse processes are then exposed. The Lumbodorsal Fascia (fasciti hni/hodorsalis; linnbar (ijxmeiirosi.s and vertebral fascia). — The lumbodorsal fascia is a deep investing membrane which co\-ers the deep muscles of the back of the trunk. Above, it passes in front of the Serratus posterior superior and is continuous with a similar investing layer on the back of the neck — the nuchal fascia. In the thoracic region the lumbodorsal fascia is a thin fibrous lamina which serves to bind down the Extensor muscles of the vertebral column and to separate them from the muscles connecting the vertebral column to the upper extremity. It contains both longitudinal and transverse fibres, and is attached, medially, to the spinous processes of the thoracic vertebrae; laterally to the angles of the ribs. In the lumbar region the fascia (lumbar apon- eurosis) is in two layers, anterior and posterior (Fig. 494). The posterior layer is attached to the spinous processes of the lumbar and sacral vertebrae and to the supraspinal ligament; the anterior is attached, medially, to the tips of the transverse processes of the lumbar vertebrae and to the intertransverse ligaments, below, to the iliolumbar ligament, and above, to the lumbo- costal ligament. The tw^o layers unite at the lateral margin of the Sacrospinalis, to form the tendon of origin of the Transversus abdominis. The Splenius capitis (Fig. 516) arises from the lower half of the ligamentum nuchae, from the spinous process of the seventh cervical vertebra, and from the spinous processes of the upper three or four thoracic vertebrae. The fibres of the muscle are directed upw^ard and lateralward and Ohliquus externus Fig. 493. — Dissection of the muscles of the back. Lumbodorsal \ fascia Fasciaon Quad. Luwb. Anterior layer \ Posterior layer Fig. 494. — Diagram of a transverse .section of the posterior abdominal wall, to show the disposition of the lumbodorsal fascia. are inserted, under cover of the Sternocleidomastoideus, into the mastoid process of the temporal bone, and into the rough surface on the occipital bone just below the lateral third of the superior nuchal line. THE DEEP MUSCLES OF THE BACK 487 The Splenius cervicis {Spleniu, colli) (Fig. rAC,) arises by a narrow tendinous l)an(l In.ni tin- spinous processes of the third to the sixth thoracic vertebrje; it is Occipital bone Multindus First thoracic vertebra First lumbar vertebra Vv-> First sacral vertebra Fig. 495. — Deep muscles of the back. 488 MYOLOGY inserted, by tendinous fasciculi, into the posterior tubercles of the transverse processes of the upper two or three cervical vertebrae. Sl Nerves. — The Splenii are supplied by the lateral branches of the posterior divisions of the middle and lower cervical nerves. Actions. — The Splenii of the two sides, acting together, draw the head directly backward, assisting the Trapezius and Semispinahs capitis; acting separately, they draw the head to one side, and slightly rotate it, turning the face to the same side. They also assist in supporting the head in the erect position. The Sacrospinalis {Erector spinae) (Fig. 495), and its prolongations in the thoracic and cervical regions, lie in the groove on the side of the vertebral column. They are covered in the lumbar and thoracic regions by the lumbodorsal fascia, and in the cervical region by the nuchal fascia. This large muscular and tendinous mass varies in size and structure at different parts of the vertebral column. In the sacral region it is narrow and pointed, and at its origin chiefly tendinous in structure. In the lumbar region it is larger, and forms a thick fleshy mass which, on being followed upward, is subdivided into three columns; these gradually diminish in size as they ascend to be inserted into the vertebrae and ribs. The Sacrospinalis arises from the anterior surface of a broad and thick tendon, which is attached to the medial crest of the sacrum, to the spinous processes of the lumbar and the eleventh and twelfth thoracic vertebrae, and the supraspinal ligament, to the back part of the inner lip of the iliac crests and to the lateral crests of the sacrum, where it blends with the sacrotuberous and posterior sacro- iliac ligaments. Some of its fibres are continuous with the fibres of origin of the Glutaeus maximus. The muscular fibres form a large fieshy mass which splits, in the upper lumbar region into three columns, viz., a lateral, the Iliocostalis, an intermediate, the Longissimus, and a medial, the Spinalis. Each of these consists from below upward, of three parts, as follows: Lateral Colwiui. Intermediate Column. Medial Column. Iliocostalis. Longissimus. Spinalis. (a) I. lumborum. (a) L. dorsi. {a) S. dorsi. (h) I. dorsi. (6) L. cervicis. (6) S. cervicis. (c) I. cervicis. (c) L. capitis. (c) S. capitis. The Iliocostalis lumborum (Iliocostalis muscle; Sacrolumhalis muscle) is inserted, by six or seven flattened tendons, into the inferior borders of the angles of the lower six or seven ribs. The Iliocostalis dorsi (Musculus accessorius) arises by flattened tendons from the upper borders of the angles of the lower six ribs medial to the tendons of insertion of the Iliocostalis lumborum; these become muscular, and are inserted into the upper borders of the angles of the upper six ribs and into the back of the transverse process of the seventh cervical vertebra. The Iliocostalis cervicis {Cervicalis ascendens) arises from the angles of the third, fourth, fifth, and sixth ribs, and is inserted into the posterior tubercles of the trans- verse processes of the fourth, fifth, and sixth cervical vertebrae. The Longissimus dorsi is the intermediate and largest of the continuations of the Sacrospinalis. In the lumbar region, where it is as yet blended with the Ilio- costalis lumborum, some of its fibres are attached to the whole length of the pos- terior surfaces of the transverse processes and the accessory processes of the lumbar vertebrae, and to the anterior layer of the lumbodorsal fascia. In the thoracic region it is inserted, by rounded tendons, into the tips of the transverse processes of all the thoracic vertebrae, and by fleshy processes into the lower nine or ten ribs between their tubercles and angles. The Longissimus cervicis (TransversaUs cervicis), situated medial to the Longis- simus dorsi, arises by long thin tendons from the summits of the transverse pro- cesses of the upper four or five thoracic vertebrae, and is inserted by similar tendons THE DEEP MUSCLES OF THE BACK 489 into the posterior tubercles of the transverse processes of the cervical vertebree from the second to the sixth inclusive. The Longissimus capitis (Trachelomastoid muscle) lies medial to the Longissimus cervicis, between it and the Semispinalis capitis. It arises by tendons from the the transverse processes of the upper four or five thoracic vertebrae, and the artic- ular processes of the lower three or four cervical vertebrae, and is inserted into the posterior margin of the mastoid process, beneath the Splenius capitis and Sterno- cleidomastoideus. It is almost always crossed by a tendinous intersection near its insertion. The Spinalis dorsi, the medial continuation of the Sacrospinalis, is scarcely separable as a distinct muscle. It is situated at the medial side of the Longissimus dorsi, and is intimately blended with it; it arises by three or four tendons from the spinous processes of the first two lumbar and the last two thoracic vertebrae : these, uniting, form a small muscle w^hich is inserted by separate tendons into the spinous processes of the upper thoracic vertebra?, the number varying from four to eight. It is intimately united with the Semispinalis dorsi, situated beneath it. The Spinalis cervicis (Spinalis colli) is an inconstant muscle, which arises from the lower part of the ligamentum nuchae, the spinous process of the seventh cer- vical, and sometimes from the spinous processes of the first and second thoracic vertebrae, and is inserted into the spinous process of the axis, and occasionally into the spinous processes of the two vertebrae below it. The Spinalis capitis (Biventer cervicis) is usually inseparably connected with the Semispinalis capitis (see below) . The Semispinalis dorsi consists of thin, narrow, fleshy fasciculi, interposed between tendons of considerable length. It arises by a series of small tendons from the transverse processes of the sixth to the tenth thoracic vertebrae, and is inserted, by tendons, into the spinous processes of the upper four thoracic and lower two cervical vertebrae. The Semispinalis cervicis {Semispinalis colli), thicker than the preceding, arises by a series of tendinous and fleshy fibres from the transverse processes of the upper five or six thoracic vertebrae, and is inserted into the cervical spinous processes, from the axis to the fifth inclusive. The fasciculus connected with the axis is the largest, and is chiefly muscular in structure. The Semispinalis capitis {Complexus) is situated at the upper and back part' of the neck, beneath the Splenius, and medial to the Longissimus cervicis and capitis. It arises by a series of tendons from the tips of the transverse processes of the upper six or seven thoracic and the seventh cervical vertebrae, and from the articular processes of the three cervical above this. The tendons, uniting, form a broad muscle, which passes upward, and is inserted between the superior and inferior nuchal lines of the occipital bone. The medial part, usually more or less distinct from the remainder of the muscle, is frequently termed the Spinalis capitis ; it is also named the Biventer cervicis since it is traversed by an imperfect tendinous inscription. The Multifidus (Midtifidiis spinae) consists of a number of fleshy and tendinous fasciculi, which fill up the groove on either side of the spinous processes of the ver- tebrae, from the sacrum to the axis. In the sacral region, these fasciculi arise from the back of the sacrum, as low^ as the fourth sacral foramen, from the aponeu- rosis of origin of the Sacrospinalis, from the medial surface of the posterior superior iliac spine, and from the posterior sacroiliac ligaments; in the lumbar region, from all the mamillary processes; in the thoracic region, from all the transverse processes; and in the cervical region, from the articular processes of the lower four vertebrae. Each fasciculus, passing obliquely upward and medialward, is inserted into the whole length of the spinous process of one of the vertebrae above. These fasciculi vary in length: the most superficial, the longest, pass from one 490 MYOLOGY vertebra to the third or fourth above; those next in order run from one vertebra to the second or third above; while the deepest connect two contif^uous vertebra?. The Rotatores (Roiatores spinae) he beneath the jNIultifidus and are found only in the thoracic region; they are eleven in number on either side. Each muscle is small and somewhat quadrilateral in form; it arises from the upper and back part of the transverse process, and is inserted into the lower border and lateral surface of the lamina of the vertebra above, the fibres extending as far as the root of the spinous process. The first is found between the first and second thoracic vertebrae; the last, between the eleventh and twelfth. Sometimes the number of these muscles is diminished by the absence of one or more from the upper or lower end. The Interspinales are short muscular fasciculi, placed in pairs between the spinous processes of the contiguous vertebrae, one on either side of the interspinal ligament. In the cervical region they are most distinct, and consist of six pairs, the first being situated between the axis and third vertebra, and the last between the seventh cervical and the first thoracic. They are small narrow bundles, attached, above and below, to the apices of the spinous processes. In the thoracic region, they are found between the first and second vertebrae, and sometimes be- tween the second and third, and between the eleventh and twelfth. In the lumbar region there are four pairs in the intervals between the five lumbar vertebrae. There is also occasionally one between the last thoracic and first lumbar, and one between the fifth lumbar and the sacrum. The Extensor coccygis is a slender muscular fasciculus, which is not always present; it extends over the lower part of the posterior surface of the sacrum and coccyx. It arises by tendinous fibres from the last segment of the sacrum, or first piece of the coccyx, and passes downward to be inserted into the lower part of the coccyx. It is a rudiment of the Extensor muscle of the caudal vertebrae of the lower animals. The Intertransversarii {Intertransversales) are small muscles placed between the transverse processes of the vertebrae. In the cervical region they are best developed, consisting of rounded muscular and tendinous fasciculi, and are placed in pairs, passing between the anterior and the posterior tubercles respectively of the transverse processes of two contiguous vertebrae, and separated from one another by an anterior primary division of the cervical nerve, which lies in the groove between them. The muscles connecting the anterior tubercles are termed the Intertransversarii anteriores; those between the posterior tubercles, the Inter- transversarii posteriores; both sets are supplied by the anterior divisions of the spinal nerves (Lickley^). There are seven pairs of these muscles, the first pair being between the atlas and axis, and the last pair between the seventh cervical and first thoracic vertebrae. In the thoracic region they are present between the transverse processes of the lower three thoracic vertebrae, and between the trans- verse processes of the last thoracic and the first lumbar. In the lumbar region they are arranged in pairs, on either side of the vertebral column, one set occupy- ing the entire interspace between the transverse processes of the lumbar vertebrae, the Intertransversarii laterales; the other set, Intertransversarii mediales, passing from the accessory process of one vertebra to the mamillary of the vertebra below. The Intertransversarii laterales are supplied by the anterior divisions, and the Intertransversarii mediales by the posterior divisions of the spinal nerves (Lichley, oy. cit.). II. THE SUBOCCIPITAL MUSCLES (Fig. 495). The suboccipital group comprises: Rectus capitis posterior major. Obliquus capitis inferior. Rectus capitis posterior minor. Obliquus capitis superior. I Journal of Anatomy and Physiology, 1904, vol. xxxix. THE SIBOCCIPITAL MUSCLES 491 The Rectus capitis posterior major {Rectus capitib- ijo.s-ticus- major) aris-es b}- a pointed tendon from the spinous process of the axis, and, becoming broader as it ascends, is inserted into the lateral part of the inferior nuchal line of the occipital bone and the surface of the bone immediately below the line. Aii the muscles of the two sides pass upward and lateralward, they leave between them a triangular space, in which the Recti cai)itis ])osteriores minores are seen. The Rectus capitis posterior minor (Rectus capitis posticus minor) arises by a narrow pointed tendon from the tubercle on the posterior arch of the atlas, and, widenino- as it ascends, is inserted into the medial part of the inferior nuchal line of the occipital !)()ne and the surface between it and the foramen magnum. The Obliquus capitis inferior (Obliq^ms inferior), the larger of the two Oblique muscles, arises from the apex of the spinous process of the axis, and passes lateral- ward and slightly upward, to be inserted into the lower and back part of the transverse process of the atlas. The Obliquus capitis superior (Obliquus superior), narrow below, wide and expanded above, arises by tendinous fibres from the upper surface of the transverse process of the atlas, joining with the insertion of the preceding. It passes upward and medialward, and is inserted into the occipital bone, between the superior and inferior nuchal lines, lateral to the Semispinalis capitis. The Suboccipital Triangle. — Between the Obliqui and the Rectus capitis posterior major is the suboccipital triangle. It is bounded, above and medially, by the Rectus capitis posterior major; aboDe and laterally, by the Obliquus capitis superior; below and laterally, by the Obliquus capitis inferior. It is covered by a layer of dense fibro-fatty tissue, situated beneath the Semi- spinalis capitis. The floor is formed by the posterior occipitoatlantal membrane, and the posterior arch of the atlas. In the deep groove on the upper surface of the posterior arch of the atlas are the vertebral artery and the first cervical or suboccipital nerve. Nerves. — The deep muscles of the back and the suboccipital muscles are supplied by the posterior primary divisions of the spinal nerves. Actions. — The Sacrospinalis and its upward continuations and the Spinales serve to main- tain the vertebral column in the erect posture; they also serve to bend the trunk backward when it is required to counterbalance the influence of any weight at the front of the body — as, for instance, when a heavy weight is suspended from the neck, or when there is any great abdominal distension, as in pregnancy or dropsy; the peculiar gait under such circumstances depends upon the vertebral column being drawn backward, by the counterbalancing action of the Sacrospinales. The muscles which form the continuation of the Sacrospinales on to the head and neck steady those parts and fix them in the upright position. If the Iliocostalis lumborum and Longissimus dorsi of one side act, they serve to draw down the chest and vertebral column to the correspond- ing side. The IHocostales cervicis, taking their fixed points from the cervical vertebrae, elevate those ribs to which they are attached; taking their fixed points from the ribs, both muscles help to extend the neck; while one muscle bends the neck to its own side. When both Longissimi cervicis act from below, they bend the neck backward. When both Longissimi capitis act from below, they bend the head backward; while, if only one muscle acts, the face is turned to the side on which the muscle is acting, and then the head is bent to the shoulder. The two Recti draw the head backward. The Rectus capitis posterior major, owing to its obliquity, rotates the skull, with the atlas, around the odontoid process, turning the face to the same side. The Multifidus acts successively upon the different parts of the column; thus, the sacrum furnishes a fixed point from which the fasciculi of this muscle acts upon the lumbar region; which in turn becomes the fixed point for the fascicuU moving the thoracic region, and so on throughout the entire length of the column. The Multifidus also serves to rotate the column, so that the front of the trunk is turned to the side opposite to that from which the muscle acts, this muscle being assisted in its action by the Obliquus externus abdominis. The Obliquus capitis superior draws the head backward and to its own side. The Obliquus inferior rotates the atlas, and with it the skull, around the odontoid process, turning the face to the same side. When the Semispinals of the two sides act together, they help to extend the vertebral column; when the muscles of only one side act, they rotate the thoracic and cervical parts of the column, turning the body to the opposite side. The Semispinales capitis draw the head directly backward; if one muscle acts, it draws the head to one side, and rotates it so that the face is turned to the opposite side. The Interspinales by approximating the spinous processes help to extend the column. The Inter- transversarii approximate the transverse processes, and help to bend the column to one side. The Rotatores assist the Multifidus to rotate the vertebral column, so that the front of the trunk is turned to the side opposite to that from which the muscles act. 492 MYOLOGY Applied Anatomy. — In cases of tuberculous caries of the vertebral bodies, and in other diseases affecting the vertebral column, rigidity of the spinal muscles is one of the earliest and most con- ' stant sj^mptoms. A child with commencing spinal disease always maintains the affected portion of the column in a state of absolute rigidity, to prevent the inflamed structures from being moved against each other; this is one of the best examples of nature's method of producing rest of the affected part. III. THE MUSCLES OF THE THORAX. The muscles belonging to this group are the Intereostales externi. Levatores costarum. Intercostales interni. Serratus posterior superior. Subcostales. Serratus posterior inferior. Transversus thoracis. Diaphragma. Intercostal Fascias. — In each intercostal space thin but firm layers of fascia cover the outer surface of the Intercostalis externus and the inner surface of the Intercostalis internus; and a third, more delicate layer, is interposed between the two planes of muscular fibres. They are best marked in those situations where the muscular fibres are deficient, as between the Intercostales externi and sternum in front, and between the Intercostales interni and vertebral column behind. The Intercostales (Intercostal muscles) (Fig. 520) are two thin planes of muscular and tendinous fibres occupying each of the intercostal spaces. They are named external and internal from their surface relations — the external being superficial to the internal. The Intercostales externi (External intercostals) are eleven in number on either side. They extend from the tubercles of the ribs behind, to the cartilages of the ribs in front, where they end in thin membranes, the anterior intercostal membranes, which are continued forward to the sternum. Each arises from the lower border of a rib, and is inserted into the upper border of the rib below. In the two lower spaces they extend to the ends of the cartilages, and in the upper two or three spaces they do not quite reach the ends of the ribs. They are thicker than the Intercostales interni, and their fibres are directed obliquely downward and lateral- ward on the back of the thorax, and downward, forward, and medialward on the front. The Intercostales interni (Internal intercostals) are also eleven in number on either side. They commence anteriorly at the sternum, in the interspaces between the cartilages of the true ribs, and at the anterior extremities of the cartilages of the false ribs, and extend backward as far as the angles of the ribs, whence they are continued to the vertebral column by thin aponeuroses, the posterior intercostal membranes. Each arises from the ridge on the inner surface of a rib, as well as from the corresponding costal cartilage, and is inserted into the upper border of the rib below. Their fibres are also directed obliquely, but pass in a direction opposite to those of the Intercostales externi. The Subcostales (Infracostales) consist of muscular and aponeurotic fasciculi, which are usually well-developed only in the lower part of the thorax; each a,rises from the inner surface of one rib near its angle, and is inserted into the inner surface of the second or third rib below. Their fibres run in the same direction as those of the Intercostales interni. The Transversus thoracis (Triangularis sterni) is a thin plane of muscular and tendinous fibres, situated upon the inner surface of the front wall of the chest (Fig. 496). It arises on either side from the lower third of the posterior surface of the body of the sternum, from the posterior surface of the xiphoid process, and from the sternal ends of the costal cartilages of the lower three or four true ribs. Its fibres diverge upward and lateralward,' to be inserted by slips into the THE MUSCLES OF THE THORAX 493 lower borders and inner surfaces of the costal cartilages of the second, third, fourth, fifth, and sixth ribs. The lowest fibres of this muscle are horizontal in their direc- tion, and are continuous with those of the Transversus abdominis; the intermediate fibres are oblique, while the highest arc almost vertical. This muscle varies in its attachments, not only in different sub- jects, but on opposite sides of the same subject. The Levatores costarum (Fig. 495), twelve in number on either side, are small tendinous and fleshy bundles, which arise from the ends of the transverse processes of the seventh cervical and upper eleven thoracic vertebrae; they pass obliquely downward and lateral- ward, like the fibres of the Intercostales externi, and each is inserted into the outer surface of the rib immediately below the vertebra from which it takes origin, between the tubercle and the angle (Levatores costarum breves) . Each of the four lower muscles divides into two fasciculi, one of which is inserted as above described; the other passes down to the second rib below its origin (Levatores costarum longi) . The Serratus posterior superior (Ser- ratus ijosticns suiJerior) is a thin, quad- rilateral muscle, situated at the upper and back part of the thorax. It arises by a thin and broad aponeurosis from the lower part of the ligamentum nu- ehae, from the spinous processes of the seventh cervical and upper two or three thoracic vertebrae and from the supra- spinal ligament. Inclining downward and lateralward it becomes muscular, and is inserted, by four fleshy digitations, into the upper borders of the second, third, fourth, and fifth ribs, a little beyond their angles. The Serratus posterior inferior (Serratus posticus inferior) (Fig. 516) is situated at the junction of the thoracic and lumbar regions: it is of an irregularly quadri- lateral form, broader than the preceding, and separated from it by a wide interval. It arises by a thin aponeurosis from the spinous processes of the lower two thoracic and upper two or three lumbar vertebra?, and from the supraspinal ligament. Passing obliquely upward and lateralward, it becomes fleshy, and divides into four flat digitations, which are inserted into the inferior borders of the lower four ribs, a little beyond their angles. The thin aponeurosis of origin is intimately blended with the lumbodorsal fascia. Nerves. — The muscles of this group are supplied by the intercostal nerves. The Diaphragma (Diaphragm) (Figs. 497, 498) is a dome-shaped musculo- fibrous septum which separates the thoracic from the abdominal cavity, its convex upper surface forming the floor of the former, and its concave under surface the roof of the latter. Its peripheral part consists of muscular fibres which take origin from the circumference of the thoracic outlet and converge to be inserted into a central tendon. Stetnal o> igin of Diaphragma Fig. 496. — Posterior surface of sternum and costal cartilages, showing Transversus thoracis. 494 MYOLOGY The muscular fibres may be grouped according to their origins into three parts -sternal, costal, and lumbar. The sternal part r/n'.vf.s- b\- two fleshy slips from Vena caved foramen (Esophageal Aortic hiatus Fig. 497. — Posterior half of Diaphragma. (Modified from model by His.) Xiphoid process Opening for Lesser Splanchnic Nerve Fig. 498. — The Diaphragma. Under surface THE MUSCLES OF THE THORAX 495 the back of the xiphoid process; the costal part from the inner surfaces of the car- tilages and adjacent portions of the lower six ribs on either side, interdigitating with the Transversus abdominis; and the lumbar part from aponeurotic arches, named the lumbocostal arches, and from the lumbar \'ertebra? by two pillars or crura. There are two lumbocostal arches, a medial and a lateral, on either side. The Medial Lumbocostal Arch (circus lumhocostalis mediaUs [Ilalleri]; internal arcuate llgiuncitt) is a tendinous arch in the fascia covering the upper part of the Psoas major; medially, it is continuous with the lateral tendinous margin of the corresponding crus, and is attached to the side of the body of the first or second lumbar vertebra ; laterally, it is fixed to the front of the transverse process of the first and, sometimes also, to that of the second lumbar vertebra. The Lateral Lumbocostal Arch (arcus lumhocostalis lateralis [Halleri]; external arcuate ligament) arches across the upper part of the Quadratus lumborum, and is attached, medially, to the front of the transverse process of the first lumbar vertebra, and, laterally, to the tip and lower margin of the twelfth rib. The Crura. — At their origins the crura are tendinous in structure, and blend with the anterior longitudinal ligament of the vertebral column. The right crus, larger and longer than the left, arises from the anterior surfaces of the bodies and intervertebral fibrocartilages of the upper three lumbar vertebrae, while the left crus arises from the corresponding parts of the upper two only. The medial ten- dinous margins of the crura pass forward and medialward, and meet in the middle line to form an arch across the front of the aorta; this arch is often poorly defined. From this series of origins the fibres of the Diaphragma converge to be inserted into the central tendon. The fibres arising from the xiphoid process are very short, and occasionally aponeurotic; those from the medial and lateral lumbocostal arches, and more especially those from the ribs and their cartilages, are longer, and describe marked curves as they ascend and converge to their insertion. The fibres of the crura diverge as they ascend, the most lateral being directed upward and lateralward to the central tendon. The medial fibres of the right crus ascend on the left side of the oesophageal hiatus, and occasionally a fasciculus of the left crus crosses the aorta and runs obliquely through the fibres of the right crus tow^ard the vena caval foramen (Low^). The Central Tendon. — The central tendon of the Diaphragma is a thin but strong aponeurosis situated near the centre of the vault formed by the muscle, but some- what closer to the front than to the back of the thorax, so that the posterior muscu- lar fibres are the longer. It is situated immediately below the pericardium, with which it is partially blended. It is shaped somewhat like a trefoil leaf, consisting of three divisions or leaflets separated from one another by slight indentations. The right leaflet is the largest, the middle, directed toward the xiphoid process, the next in size, and the left the smallest. In structure the tendon is composed of several planes of fibres, which intersect one another at various angles and unite into straight or curved bundles — an arrangement which gives it additional strength. Openings in the Diaphragma. — The Diaphragma is pierced by a series of apertures to permit of the passage of structures between the thorax and abdomen. Three large openings — the aortic, the oesophageal, and the vena caval — and a series of smaller ones are described. The aortic hiatus is the lowest and most posterior of the large apertures; it lies at the level of the twelfth thoracic vertebra. Strictly speaking, it is not an aperture in the Diaphragma but an osseoaponeurotic opening between it and the vertebral column, and therefore behind the Diaphragma; occasionally some tendinous fibres prolonged across the bodies of the vertebrae from the medial parts of the lower ends of the crura pass behind the aorta, and thus convert the hiatus into a fibrous ring. 1 Journal of Anatomj' and Physiology, vol. xlii. 496 MYOLOGY The hiatus is situated slightly to the left of the middle line, and is bounded in front by the crura, and behind by the body of the first lumbar vertebra. Through it pass the aorta, the azygos vein, and the thoracic duct; occasionally the azygos vein is transmitted through the right crus. The oesophageal hiatus is situated in the muscular part of the Diaphragma at the level of the tenth thoracic vertebra, and is elliptical in shape. It is placed above, in front, and a little to the left of the aortic hiatus, and transmits the oesophagus, the vagus nerves, and some small oesophageal arteries. Thr vena caval foramen is the highest of the three, and is situated about the level of the fibrocartilage between the eighth and ninth thoracic vertebrae. It is quad- rilateral in form, and is placed at the junction of the right and middle leaflets of the central tendon, so that its margins are tendinous. It transmits the inferior vena cava, the wall of which is adherent to the margins of the opening, and some branches of the right phrenic nerve. Of the lesser apertures, two in the right crus transmit the greater and lesser right splanchnic nerves ; three in the left crus give passage to the greater and lesser left splanchnic nerves and the hemiazygos vein. The gangliated trunks of the sympathetic usually enter the abdominal cavity behind the Diaphragma, under the medial lumbocostal arches. The structures piercing the crura are sometimes utilized to divide each crus into three parts — medial, intermediate, and lateral. Between the medial and intermediate crura pass the hemiazygos vein and the splanchnic nerves; between the intermediate crus and the lateral crus (which consists of the fibres rising from the medial lumbocostal arch) the gangliated trunks pass. On either side two small intervals exist at which the muscular fibres of the Diaphragma are deficient and are replaced by areolar tissue. One between the sternal and costal parts transmits the superior epigastric branch of the internal mammary artery and some lymphatics from the abdominal wall and convex surface of the liver. The other, between the fibres springing from the medial and lateral lumbocostal arches, is less constant; when this interval exists, the upper and back part of the kidney is separated from the pleura by areolar tissue only. Relations. — The upper surface of the Diaphragma is in relation with three serous membranes, viz., on either side the pleura, which separates it from the base of the corresponding lung, and on the middle leaflet of the central tendon the pericardium, which intervenes between it and the heart. The central portion hes on a shghtly lower level than the summits of the lateral portions. The greater part of the under sm-face is covered by the peritoneum. The right side is accurately moulded over the convex surface of the right lobe of the Uver, the right kidney, and right supra- renal gland; the left over the left lobe of the hver, the fundus of the stomach, the spleen, the left kidnej^, and left suprarenal gland. Nerves. — The Diaphragma is supphed by the phrenic and lower intercostal nerves. Actions.^The Diaphragma is the principal muscle of inspiration, and presents the form of a dome concave toward the abdomen. The central part of the dome is tendinous, and the peri- cardium is attached to its upper surface; the circumference is muscular. Dm-ing inspuation the lowest ribs are fixed, and from these and the crura the muscular fibres contract and draw do^m- ward and forward the central tendon with the attached pericardium. In this movement the curvature of the Diaphragma is scarcely altered, the dome moving downward nearly parallel to its original position and pushing before it the abdominal viscera. The descent of the abdominal viscera is permitted by the elasticity of the abdominal wall, but the Umit of this is soon reached. The central tendon apphed to the abdominal viscera then becomes a fixed point for the action of the Diaphragma, the effect of which is to elevate the lower ribs and through them to push forward the body of the stermun and the upper ribs. The right cupola of the Diaphragma, lying on the hver, has a greater resistance to overcome than the left, which lies over the stomach, but to compensate for this the right crus and the fibres of the right side generally are stronger than those of the left. In all expulsive acts the Diaphragma is called into action to give additional power to each expulsive effort. Thus, before sneezing, coughing, laughing, crying, or vomitmg, and previous to the expulsion of m-ine or feces, or of the fetus from the uterus, a deep inspiration takes place. The height of the Diaphragma is constantly varying dm-ing respiration; it also varies with the THE MUSCLES OF THE THORAX 497 degree of distcMision of the stonuicli aiul intoslincs ;iml with the size of the hver. After a forced expu'ation the right cupohi is on a level in front with th(> fourth costal cartilage, at the side with the fifth, sixth, and seventh ribs, and behind with the eighth rib; the left cupola is a little lower than the right. Halls Dally' stat(\s that the absolute range of movement between deep inspira- tion and deep expiration averages in the male and female 30 mm. on the right side and 28 mm. on tlie left; in quiet respiration the average movement is 1^.5 mm. on the right side and 12 mm. on the left. Skiagraphy shows that the height of the Diaphragma in the thorax varies considerably with the position of the body. It stands highest when the body is horizontal and the patient on his back, and in this jiosition it performs the largest respiratory excursions with normal breathing. When the body is erect the dome of the Diaphragma falls, and its respiratory movements become smaller. The dome falls still lower when the sitting posture is assumed, and in this position its respiratory excursions are sm.allest. These facts may, perhaps, explain why it is that patients suffering from severe dyspncea are most comfortable and least short of breath when they sit up. When the body is horizontal and the patient on his side, the two halves of the Diaphragma do not behave alike. The uppermost half sinks to a level lower even than when the patient sits, and moves little with respiration; the lower half rises higher in the thorax than it does when the patient is supine, and its respiratory excursions are much increased. In vmilateral disease of the plem'a or lungs analogous interference with the position or movement of the diaphragma can generally be observed skiagraphically. It appears that the position of the Diaphragma in the thorax depends upon three main factors, viz.: (1) the elastic retraction of the lung tissue, tending to pull it upward; (2) the pressure exerted on its under surface by the viscera; this naturally tends to be a negative pressure, or down- ward suction, when the patient sits or stands, and positive, or an upward pressure, when he lies (3) the intra-abdominal tension due to the abdominal muscles. These are in a state of contrac- tion in the standing position and not in the sitting; hence the Diaphragma, when the patient stands, is pushed up higher than when he sits. The Intercostales interni and externi have probably no action in moving the ribs. They con- tract simultaneously and form strong elastic supports which prevent the intercostal spaces being pushed out or drawn in dming respiration. The anterior portions of the Intercostales interni probably have an additional function in keeping the sternocostal and interchondral joint sur- faces in apposition, the posterior parts of the Intercostales externi performing a similar function for the costovertebral articulations. The Levatores costarum being inserted near the fulcra of the ribs can have little action on the ribs; they act as rotators and lateral flexors of the vertebral column. The Transversus thoracis draws down the costal cartilages, and is therefore a muscle of expiration. The Serrati are respiratory muscles. The Serratus posterior superior elevates the ribs and is therefore an inspiratory muscle. The Serratus posterior inferior draws the lower ribs dowoi- ward and backward, and thus elongates the thorax; it also fixes the lower ribs, thus assisting the inspiratory action of the Diaphragma and resisting the tendency it has to draw the lower ribs upw^ard and forward. It must therefore be regarded as a muscle of inspiration. Mechanism of Respiration. — ^The respiratory movements must be examined during (a) quiet respiration, and (5) deep respiration. Quiet Respiration. — The first and second pairs of ribs are fixed by the resistance of the cervical structm-es; the last pair, and through it the eleventh, by the Quadratus lumborum. The other ribs are elevated, so that the first two intercostal spaces are diminished while the others are increased in width. It has aheady been shown (p. 401) that elevation of the third, fourth, fifth, and sixth ribs leads to an increase in the antero-posterior and transverse diameters of the thorax; the vertical diameter is increased by the descent of the diaphragmatic dome so that the lungs are expanded in all directions except backward and upward. Elevation of the eighth, ninth, and tenth ribs is accompanied by a lateral and backward movement, leading to an increase in the transverse diameter of the upper part of the abdomen; the elasticity of the anterior abdominal wall allows a slight increase in the antero-posterior diameter of this part, and in this way the decrease in the vertical diameter of the abdomen is compensated and space provided for its displaced viscera. Exphation is effected by the elastic recoil of its walls and by the action of the abdominal muscles, which push back the viscera displaced downward by the Diaphragma. Deep Respiration. — All the movements of quiet respiration are here carried out, but to a greater extent. In deep inspiration the shoulders and the vertebral borders of the scapulae are fixed and the limb muscles. Trapezius, Serratus anterior, Pectorales, and Latissimus dorsi, are called into play. The Scaleni are in strong action, and the Sternocleidomastoidei also assist when the head is fixed by drawing up the sternum and by fixing the clavicles. The first rib is therefore no longer stationary, but, with the sternum, is raised; with it all the other ribs except the last are raised to a higher level. In conjunction wdth the increased descent of the Diaphragma this provides for a considerable augmentation of all the thoracic diameters. The anterior abdomi- 1 Journal of Anatomy and Physiology, 1908, vol. xliii. 32 498 MYOLOGY nal muscles come into action so that the umbihcus is drawn upward and backward, but this allows the Diaphragma to exert a more powerful influence on the lower ribs; the transverse diam- eter of the upper part of the abdomen is greatly increased and the subcostal angle opened out. The deeper muscles of the back, e. g., the Serrati posteriores superiores and the Sacrospinales and their continuations, are also brought into action; the thoracic curve of the vertebral column is partially straightened, and the whole column, above the lower lumbar vertebrae, drawn back- ward. This increases the antero-posterior diameters of the thorax and upper part of the abdomen and ^\adens the intercostal spaces. Deep expiration is effected by the recoil of the walls and by the contraction of the antero-lateral muscles of the abdominal wall, and the Serrati posteriores inferiores and Transversus thoracis. Halls Dally {op. cit.) gives the following figures as representing the average changes which occur during deepest possible respiration. The manubrium stemi moves 30 mm. in an upward and 14 mm. in a forward direction; the width of the subcostal angle, at a level of 30 mm. below the articulation between, the body of the sternmn and the xiphoid process, is increased by 26 mm.; the umbihcus is retracted and drawn upward for a distance of 13 mm. IV. THE MUSCLES AND FASCI.ffi OF THE ABDOMEN. The miisclcs of the abdomen may be divided into two groups: (1) the antero- lateral muscles; (2) the posterior muscles. 1. The Antero-lateral Muscles of the Abdomen. The muscles of this group are: Obliquus externus. Obliquus internus. Transversus. Rectus. Pyramidalis. Dissection (Fig. 499). — To dissect the abdominal muscles, make a vertical incision from the ensiform cartilage to the symphysis pubis; a second incision from the umbilicus obliquely upward and outward to the outer surface of the thorax, as high as the lower border of the fifth or sixth rib; and a third, commencing midway between the umbihcus and pubes, transversely outward to the anterior superior iliac spine, and along the crest of the ihxmi as far as its posterior third. Then reflect the three flaps included be- tween these incisions from within outward, in the lines of direction of the muscle fibres. If necessary, the abdomi- nal muscles may be made tense by inflating the peritoneal cavity through the umbihcus. The Superficial Fascia. — The superficial fascia of the abdomen consists, over the greater part of the abdominal wall, of a single layer containing a variable amount of fat; but near the groin it is easily divisible into two layers, between which are found the superficial vessels and nerves and the superficial inguinal lymph glands. The superficial layer (jascia of Camjjer) is thick, areolar in texture, and contains in its meshes a varying quantity of adipose tissue. Below, it passes over the inguinal ligament, and is continu- ous with the superficial fascia of the thigh. In the male, Camper's fascia is continued over the penis and outer surface of the spermatic cord to the scrotum, where it helps to form the dartos. As it passes to the scrotum it changes its characteristics, becoming thin, destitute of adipose tissue, and of a pale reddish color, and in the scrotum it acquires some involuntary muscular fibres. From the scrotum it may be traced backward into continuity with the superficial fascia of the Fig. 499. — Dissection of abdomen. THE AXTERO-LATERAL MUSCLES OF THE ABDOMEX 499 perineum. In the female, Camper's fascia is continued from the abdomen into the hibia majora. The deep layer (fascici of Scarpa) is tliimier and more memhranous in character than tlie superficial, and contains a considerable quantity of yellow elastic fibres. It is loosely connected by areolar tissue to the aponeurosis of the Obliquus externus abdominis, but in the middle line it is more intimately adherent to the linea alba and to the symphysis pubis, and is prolonjied on to the dorsum of the penis, form- ing the fundiform lio-ament; above, it is continuous with the superficial fascia over the rest of the trunk; below and laterally, it blends with the fascia lata of the thigh a little below the inguinal ligament; medially and below, it is continued over the penis and spermatic cord to the scrotum, where it helps to form the dartos. From the scrotum it may be traced backward into continuity with the deep layer of the superficial fascia of the perineum (fascia of CoUes). In the female, it is con- tinued into the labia majora and thence to the fascia of Colles. The Obliquus externus abdominis {External or descending oblique muscle) (Fig. 500), situated on the lateral and anterior parts of the abdomen, is the largest and the most superficial of the three flat muscles in this region. It is broad, thin, and irregularly quadrilateral, its muscular portion occupying the side, its aponeurosis the anterior wall of the abdomen. It arises, by eight fleshy digitations, from the external surfaces and inferior borders of the lower eight ribs; these digitations are arranged in an oblique line which runs downward and backward, the upper ones being attaclied close to the cartilages of the corresponding ribs, the lowest to the apex of the cartilage of the last rib, the intermediate ones to the ribs at some distance from their cartilages. The five superior serrations increase in size from above downward, and are received between corresponding processes of the Serratus anterior; the three lower ones diminish in size from above downward and receive between them corresponding processes from the Latissimus dorsi. From tliese attachments the fleshy fibres proceed in various directions. Those from the lowest ribs pass nearly vertically downward, and are inserted into the anterior half of the outer lip of the iliac crest; the middle and upper fibres, directed downward and forward, end in an aponeurosis, opposite a line drawn from the prominence of the ninth costal cartilage to the anterior superior iliac spine. The aponeurosis of the Obliquus externus abdominis is a thin but strong mem- branous structure, the fibres of which are directed downward and medialward. It is joined with that of the opposite muscle along the middle line, and covers the whole of the front of the abdomen; above, it is covered by and gives origin to the lower fibres of the Pectoralis major; heloic, its fibres are closely aggregated together, and extend obliquely across from the anterior superior iliac spine to the pubic tubercle and the pectineal line. In the middle line, it interlaces with the aponeurosis of the opposite muscle, forming the linea alba, which extends from the xiphoid process to the symphysis pubis. That portion of the aponeurosis which extends between the anterior superior iliac spine and the pubic tubercle is a thick band, folded inward, and continuous below witli the fascia lata; it is called the inguinal ligament. The portion which is reflected from the inguinal ligament at the pubic tubercle is attached to the pectineal line and is called the lacunar ligament. From the point of attachment of the latter to the pectineal line, a few fibres pass upward and medialward, behind the medial crus of the subcutaneous inguinal ring, to the linea alba; they diverge as they ascend, and form a thin triangular fibrous band wliicli is called the reflected inguinal ligament. In the aponeurosis of the Obliquus externus, immediately above the crest of the pubis, is a triangular opening, the subcutaneous inguinal ring, formed by a separation of the fibres of the aponeurosis in this situation. The following structures require further description, viz., the subcutaneous 500 MYOLOGY inguinal ring, the intercrural fibres and fascia, and the inguinal, lacunar, and reflected inguinal ligaments. The Subcutaneous Inguinal Ring {annuluii InguinuiL'; subcutancus; external abdominal ring) (Fig. 501). — The subcutaneous inguinal ring is an interval in the aponeurosis of the Obhquus externus, just above and hiteral to the crest of the pubis. The aperture is obHque in direction, somewhat trianguhir in form, and corresponds with the course of the fibres of the aponeurosis. It usually measures Fig. 500. — The Obliquus externus abdominis. from base to apex about 2.5 cm., and transversely about 1.25 cm. It is bounded helow by the crest of the pubis; on either side by the margins of the opening in the aponeurosis, which are called the crura of the ring; and above, by a series of curved intercrural fibres. The inferior crus {external lyillar) is the stronger and is formed by that portion of the inguinal ligament which is inserted into the pubic tubercle; it is curved so as to form a kind of groove, upon which, in the male, the spermatic cord rests. The superior crus {iriternal pillar) is a broad, thin, flat band, attached to the front of the symphysis pubis and interlacing with its fellow of the opposite side. THE AXTERO-LATERAL MLSCLES OF THE ABDOMEN 501 The subcutaneous in«uinal ring gives passage to the spermatic cord and iho- inguinal nerve in the male, and to the round Hgament of the uterus and the ilioinguinal nerve in the female; it is much larger in men than in women, on account of the large size of the spermatic cord. The Intercrural Fibres ( fibrae intercrurales; intercolunmar fibres).— The mtercrural fibres are a series of curved tendinous fibres, which arch across the lower part of the aponeurosis of the Obliquus externus, describing curves with the convexities downward. The\- have received their name from stretching across between the two crura of the subcutaneous inguinal ring, and they are much thicker and stronger Superficial iliac circumflex vein r 11 Subcutaneous inguinal ring ' Fig. -501. — The subcutaneous inguinal ring. at the inferior crus, where they are connected to the inguinal ligament, than supe- riorly, where they are inserted into the linea alba. The intercrural fibres increase the strength of the lower part of the aponeurosis, and prevent the divergence of the crura from one another; they are more strongly developed in the male than m the female. As they pass across the subcutaneous inguinal ring, the\' are connected together by delicate fibrous tissue, forming a fascia, called the intercrural fascia. This inter- crural fascia is continued down as a tubular prolongation around tke spermatic cord and testis, and encloses them in a sheath; hence it is also called the external spermatic fascia. The subcutaneous inguinal ring is seen as a distinct aperture only after the intercrural fascia has been removed. The Inguinal Ligament (ligamentum inguinale [Pouparti] ; Pouparfs ligament) (Fig. 502).— The inguinal ligament is the lower border of the aponeurosis of the 502 MYOLOGY Obliquus externus, and extends from the anterior superior iliae spine to the pubic tubercle. From this latter point it is reflected backward and lateralward to be attached to the pectineal line for about 1.25 cm., forming the lacunar ligament. Its general direction is convex downward toward the thigh, where it is continuous with the fascia lata. Its lateral half is rounded, and oblique in direction; its medial half gradually widens at its attachment to the pubis, is more horizontal in direction, and lies beneath the spermatic cord. The Lacunar Ligament (ligamentum lacunar e [Gimbernati] ; Gimbernat's ligament) (Fig. 502). — The lacunar ligament is that part of the aponeurosis of the Obliquus externus w^hich is reflected backward and lateralward, and is attached to the pecti- neal line. It is about 1.25 cm. long, larger in the male than in the female, almost horizontal in direction in the erect posture, and of a triangular form with the base Symphysis pubis TransvPTse acetabular ligament Fig. 502. — The inguinal and lacunar ligaments. directed lateralward. Its base is concave, thin, and sharp, and forms the medial boundary of the femoral ring. Its apex corresponds to the pubic tubercle. Its posterior margin is attached to the pectineal line, and is continuous with the pectineal fascia. Its anterior margin is attached to the inguinal ligament. Its surfaces are directed upward and downward. The Reflected Inguinal Ligament {ligamentum inguinale refiexum [Collesi] ; trian- gular fascia) . — The reflected inguinal ligament is a layer of tendinous fibres of a triangular shape, formed by an expansion from the lacunar ligament and the inferior crus of the subcutaneous inguinal ring. It passes medialward behind the spermatic cord, and expands into a somewhat fan-shaped band, lying behind the superior crus of the subcutaneous inguinal ring, and in front of the inguinal aponeurotic falx, and interlaces with the ligament of the other side of the linea alba. Ligament of Cooper. — ^This is a strong fibrous band, which was first described by Sir Astley Cooper. It extends lateralward from the base of the lacunar ligament (Fig. 502) along the pectineal Une. to which it is attached. It is strengthened by the pectineal fascia, and by a lateral expansion from the lower attachment of the hnea alba {adminiculum lineae albae). THE ANTERO-LATKliAL MUSCLES OF THE ABDOMEN 503 Dissection.— Detach the Obhquus cxternus abdominis by dividing it across, just in front of its attachment to the ribs, as far as its posterior border, and separate it below from the crest of the ihum as far as the anterior superior spine; then separate the muscle carefully from the Obhquus internus abdominis, which lies beneath, and turn it toward the opposite side. The Obliquus internus abdominis {Intertial or ascending oblique muscle) (Fig. 503), thinner and smaller than the Obliquus externus, beneath which it lies, is of an irregularly quadrilateral form, and situated at the lateral and anterior parts of the abdomen. It arises, by fleshy fibres, from the lateral half of the grooved upper surface of the inguinal ligament, from the anterior two-thirds of the middle lip of the iliac crest, and from the posterior lamella of the lumbodorsal fascia. From this origin the fibres diverge; those from the inguinal ligament, few in number Inguinal apon- eurotic falx Cremaster Fig. 503. — The Obliquus internus abdominis. and paler in color than the rest, arch downward and medialward across the sper- matic cord in the male and the round ligament of the uterus in the female, and, becoming tendinous, are inserted, conjointly with those of the Transversus, into the crest of the pubis and medial part of the pectineal line behind the lacunar ligament, forming what is known as the inguinal aponeurotic falx. Those from the anterior third of the iliac origin are horizontal in their direction, and, becoming tendinous along the lower fourth of the linea semilunaris, pass in front of the Rectus abdominis to be inserted into the linea alba. Those arising from the middle third of the iliac origin run obliquely upward and medialward, and end in an aponeurosis; this divides at the lateral border of the Rectus into two lamellae, which are con- tinued forward, one in front of and the other behind this muscle, to the linea alba: 504 MYOLOGY the posterior lamella has an attachment to the cartilages of the seventh, eighth, and ninth ribs. The most posterior fibres pass almost vertically upward, to be inserted into the inferior borders of the cartilages of the three lower ribs, being continuous with the Intercostales interni. The Cremaster (Fig. 504) is a thin muscular layer, composed of a number of fasciculi which arise from the middle of the inguinal ligament where its fibres are continuous with those of the Obliquus internus and also occasion- ally with the Transversus. It passes along the lateral side of the spermatic cord, descends with it through the sub- cutaneous inguinal ring upon the front and sides of the cord, and forms a series of loops which dift'er in thickness and length in different subjects. x\t the upper part of the cord the loops are short, but they become in succession longer and longer, the longest reaching down as low as the testis, where a few- are inserted into the tunica vaginalis. These loops are united together by areolar tissue, and form a thin cover- ing over the cord and testis, the cremas- teric fascia. The fibres ascend along the medial side of the cord, and are inserted by a small pointed tendon into the tubercle and crest of the pubis and into the front of the sheath of the Rectus abdominis. >^^ Fig. 504. — The Cremaster. Dissection. — Detach the Obhquus internus abdominis in order to expose the Transversus abdominis beneath. This may be effected by dividing the muscle, above, at its attachment to the ribs; below, at its connection with the inguinal ligament and the crest of the iUum; and behind, by a vertical incision extending from the last rib to the crest of the ihum. The muscle should previously be made tense by drawing upon it with the fingers of the left hand, and if its division be carefully effected, the cellular interval between it and the Transversus abdominis, as well as the direction of the fibres of the latter muscle, will afford a clear guide to their separation; along the crest of the ilium the circumflex ihac vessels are interposed be- tween them, and form an important guide in separating them. The muscle should then be thrown inward toward the hnea alba. The Transversus abdominis {Transversals muscle) (Fig. 505), so called from the direction of its fibres, is the most internal of the flat muscles of the abdomen, being placed immediately beneath the Obliquus internus. It arises, by fleshy fibres, from the lateral third of the inguinal ligament, from the anterior three-fourths of the inner lip of the iliac crest, from the inner surfaces of the cartilages of the lower six ribs, interdigitating with the Diaphragma, and from the lumbodorsal fascia. The muscle ends in front in a broad aponeurosis, the lower fibres of which curve downward and medialward, and are inserted, together with those of the Obliquus internus, into the crest of the pubis and pectineal line, forming the ingui- nal aponeurotic falx. Throughout the rest of its extent the aponeurosis passes horizontally to the middle line, and is inserted into the linea alba; its upper three fourths lie behind the Rectus and blend with the posterior lamella of the aponeur- osis of the Obliquus internus; its lower fourth is in front of the Rectus. THE AXTERO-LATERAL MUSCLES OF THE ABDOMEN 505 The inguinal aponeurotic falx (fair aponeurotica mcjuinaUs; conjoined tendon of Internal oblique a)td Trausirrscdils muscle) of the ObHqims interims and Trans- versus is mainlv formed by the lower part of the tendon of the Transversiis and is inserted into the crest of the pubis and pectineal line immediately behind the subcutaneous inguinal ring, serving to protect what would otherwise be a weak point in tlic abdominal wall. Lateral to the falx is a ligamentous band con- Linea alba PiQ 505.— The Transversus abdominis, Rectus abdominis, and Pyramidalis. nected with the lower margin of the Transversus and extending down behind the inferior epigastric arterv to the superior ramus of the pubis; it is termed the inter- foveolar ligament of Hesselbach (Fig. 506) and sometimes contains a few muscular fibres. Dissection.— To expose the Rectus abdominis muscle, open its sheath by a vertical incision extending from the costal arch to the pubis, and then reflect the two portions from the sur- face of the muscle, which is easily done, excepting at the lineae transversae, where so dose an adhesion exists that the greatest care is requisite in separating them. Now raise the outer edge 506 MYOLOGY of the muscle, in order to examine the posterior layer of the sheath. By dividing the muscle in the centre, and turning its lower part downward, the point where the posterior wall of the sheath terminates in a thin curved margin will be seen. The Rectus abdominis (Fig. 505) is a long flat muscle, which extends along the whole length of the front of the abdomen, and is separated from its fellow of the opposite side by the linea alba. It is much broader, but thinner, above than below, and arises by two tendons; the lateral or larger is attached to the crest of the pubis, the medial interlaces with its fellow of the opposite side, and is con- nected w^ith the ligaments covering the front of the symphysis pubis. The muscle is inserted by three portions of unequal size into the cartilages of the fifth, sixth, and seventh ribs. The upper portion, attached principally to the cartilage of the fifth rib, usually has some fibres of insertion into the anterior extremity of the rib itself. Some fibres are occasionally connected with the costoxiphoid ligaments, and the side of the xiphoid process. Linea semicircularis Transversus Rectus L abdomijiis \ \ \ \' \i\ Inferior epigastric artery ami vein Obliquus internus Inguinal aponeuiotic falx Inieijoveolar ligament Fig. 506. — The interfoveolar ligament, seen from in front. (Modified from Braune. The Rectus is crossed by .fibrous bands, three in number, which are named the tendinous inscriptions; one is usually situated opposite the umbilicus, one at the extremity of the xiphoid process, and the third about midway between the xiphoid process and the umbilicus. These inscriptions pass transversely or obliquely across the muscle in a zigzag course; they rarely extend completely through its substance and may pass only halfway across it; they are intimately adherent in front to the sheath of the muscle. Sometimes one or two additional inscriptions, generally incomplete, are present below the umbilicus. The Rectus is enclosed in a sheath (Fig. 507) formed by the aponeuroses of the Obliqui and Transversus, which are arranged in the following manner. At the lateral margin of the Rectus, the aponeurosis of the Obliquus internus divides into two lamellae, one of which passes in front of the Rectus, blending with the aponeurosis of the Obliquus externus, the other, behind it, blending with the aponeurosis of the Transversus, and these, joining again at the medial border of the Rectus, are inserted into the linea alba. This arrangement of the aponeurosis exists from the costal margin to midway between the umbilicus and symphysis pubis, where THE ANTERO-LATERAL MUSCLES OF THE ABDOMEN 507 the posterior wall of the sheath ends in a thin curved margin, the linea semicircu- laris, the concavity of which is directed downward : below this level the aponeuroses of all three muscles pass in front of the Rectus. The Rectus, in the situation where its sheath is deficient below, is separated from the peritoneum by the transversalis fascia (Fig. 508). Since the tendons of the Obliquus internus and Transversus only reach as high as the costal margin, it follows that above this level the sheath of the Rectus is deficient behind, the muscle resting directly on the cartilages of the ribs, and being covered merely by the tendon of the Obliquus externus. Linea alba Obliquus internus / Transversus Fig. 507. — Diagram of sheath of Rectus. The Pyramidalis (Fig. 505) is a small triangular muscle, placed at the lower part of the abdomen, in front of the Rectus, and contained in the sheath of that muscle. It arises by tendinous fibres from the front of the pubis and the anterior pubic ligament; the fleshy portion of the muscle passes upward, diminishing in size as it ascends, and ends by a pointed extremity which is inserted into the linea alba, midway between the umbilicus and pubis. This muscle may be wanting on one or both sides; the lower end of the Rectus then becomes proportionately increased in size. Occasionally it is double on one side, and the muscles of the two sides are sometimes of unequal size. It may extend higher than the level stated. Obliquus internus - Transversus^ Fig. 508. — Diagram of a transverse section through the anterior abdominal wall, below the linea semicircularis. Besides the Rectus and Pyramidalis, the sheath of the Rectus contains the superior and inferior epigastric arteries, and the lower intercostal nerves. Nerves. — The abdominal muscles are supphed by the lower intercostal nerves. The Obhquus internus and Transversus also receive filaments from the anterior branch of the iliohypogastric and sometimes from the ilioinguinal. The Cremaster is supphed by the external spermatic branch of the genitofemoral and the Pyramidahs usually by the tweKth thoracic. The Linea Alba. — ^The hnea alba is a tendinous raphe in the middle line of the abdomen, stretching between the xiphoid process and the symphysis pubis. It is placed between the medial borders of the Recti, and is formed by the blending of the aponem-oses of the ObUqui and Trans- versa It is narrow below, corresponding to the hnear interval existing between the Recti; but broader above, where these muscles diverge from one another. At its lower end the hnea alba has a double attachment — its superficial fibres passing in front of the medial heads of the Recti to the symphysis pubis, while its deeper fibres form a triangular lamella, attached behind the Recti to the posterior lip of the crest of the pubis, and named the adminiculum Uneae albae. It presents apertures for the passage of vessels and nerves; the vunbihcus, which in the fetus exists as an aperture and transmits the umbihcal vessels, is closed in the adult. The Lineae Semilunares. — The lineae semilunares are two curved tendinous hues placed one on either side of the linea alba. Each corresponds with the lateral border of the Rectus, extends from the cartilage of the ninth rib to the pubic tubercle, and is formed by the aponeurosis of the Obhquus internus at its line of division to enclose the Rectus, reinforced in front by that of the Obliquus externus, and behind by that of the Transversus. 508 MYOLOGY Actions. — When the pelvis and thorax are fixed, the abdominal muscles compress the abdominal viscera by constricting the cavity of the abdomen, in which action they are materially assisted by the descent of the Diaphragma. By these means assistance is given in expelling the feces from the rectum, the m-ine from the bladder, the fetus from the uterus, and the contents of the stomach in vomiting. If the pelvis and vertebral column be fixed, these muscles compress the lower part of the thorax, materially assisting expiration. If the pelvis alone be fixed, the thorax is bent directly forward, when the muscles of both sides act; when the muscles of only one side contract, the trunk is bent toward that side and rotated toward the opposite side. If the thorax be fixed, the muscles, acting together, draw the pelvis upward, as in climbing; or, acting singly, they draw^ the pelvis upward, and bend the vertebral column to one side or the other. The Recti, acting from below, depress the thorax, and consequently flex the vertebral column ; when acting from above, they flex the pelvis upon the vertebral column. The PjTamidales are tensors of the linea alba. The Transversalis Fascia. — The transversalis fascia is a thin aponeurotic membrane which Hes between the inner surface of the Transversus and the extraperitoneal fat. It forms part of the general layer of fascia lining the abdominal parietes, and is directly continuous with the iliac and pelvic fasciae. In the inguinal region, the transversalis fascia is thick and dense in structure and is joined by fibres from the aponeurosis of the Transversus, but it becomes thin as it ascends to the Dia- phragma, and blends with the fascia covering the under surface of this muscle. Behind, it is lost in the fat which covers the posterior surfaces of the kidneys. Below, it has the following attachments : posteriorly, to the whole length of the iliac crest, between the attachments of the Transversus and Iliacus; between the ante- rior superior iliac spine and the femoral vessels it is connected to the posterior margin of the inguinal ligament, and is there continuous with the iliac fascia. Medial to the femoral vessels it is thin and attached to the pubis and pectineal line, behind the inguinal aponeurotic falx, with which it is united; it descends in front of the femoral vessels to form the anterior wall of the femoral sheath. Beneath the inguinal ligament it is strengthened by a band of fibrous tissue, which is only loosely connected to the ligament, and is specialized as the deep crural arch. The spermatic cord in the male and the round ligament of the uterus in the female pass through the transversalis fascia at a spot called the abdominal inguinal ring. This opening is not visible externally, since the transversalis fascia is prolonged on these structures as the infundibuliform fascia. The Abdominal Inguinal Ring {annulus inguinalis abdominis; internal or deep abdominal ring).— The abdominal inguinal ring is situated in the transversalis fascia, midway between the anterior superior iliac spine and the symphysis pubis, and about 1.25 cm. above the inguinal ligament (Fig. 509). It is of an oval form, the long axis of the oval being vertical; it varies in size in different subjects, and is much larger in the male than in the female. It is bounded, above and laterally, by the arched lower margin of the Transversus; below and medially, by the inferior epigastric vessels. It transmits the spermatic cord in the male and the round ligament of the uterus in the female. From its circumference a thin funnel-shaped membrane, the infundibuliform fascia, is continued around the cord and testis, enclosing them in a distinct covering. The Inguinal Canal {canalis inguinalis; spermatic canal). — The inguinal canal contains the spermatic cord and the ilioinguinal nerve in the male, and the round ligament of the uterus and the ilioinguinal nerve in the female. It is an oblique canal about 4 cm. long, slanting downward and medialward, and placed parallel with and a little above the inguinal ligament; it extends from the abdominal inguinal ring to the subcutaneous inguinal ring. It is bounded, in front, by the integument and superficial fascia, by the aponeurosis of the Obliquus externus throughout its whole length, and by the Obliquus internus in its lateral third; behind, by the reflected inguinal ligament, the inguinal aponeurotic falx, the trans- versalis fascia, the extraperitoneal connective tissue and the peritoneum; above, THE ANTERO-LATERAL MUSCLES OF THE ABDOMEN 509 by the arched fibres of Oblic^uus interims and Transversus abdominis; beloiv, by the union of the transversalis fascia witii the ini^ninal Hgament, and at its medial end by the Lacunar ligament. Extraperitoneal Connective Tissue. — Between the inner surface of the general layer of the fascia which lines the interior of the abdominal and pelvic cavities, and the peritoneum, there is a considerable amount of connective tissue, termed the extraperitoneal or subperitoneal connective tissue. The parietal portion lines the cavity in varying quantities in difl'erent situations. It is especially abundant on the posterior wall of the abdomen, and, particularly around the kidneys, where it contains much fat. On the anterior wall of the abdo- men, except in the pubic region, and on the lateral wall above the iliac crest, it is scanty, and here the transversalis fascia is more closely connected with the peritoneum. There is a considerable amount of extraperitoneal connective tissue in the pelvis. Abdominal inguinal ring Inf. epigastric arter Fig. 509. — The abdominal inguinal ring. The visceral portion follows the course of the branches of the abdominal aorta between the layers of the mesenteries and other folds of peritoneum which connect the various viscera to the abdominal wall. The two portions are directly con- tinuous with each other. The Deep Crural Arch. — Curving over the external iliac vessels, at the spot where they become femoral, on the abdominal side of the inguinal ligaments and loosely connected with it, is a thickened band of fibres called the deep crural arch. It is apparently a thickening of the transversalis fascia joined laterally to the centre of the lower margin of the inguinal ligament, and arching across the front of the femoral sheath to be inserted by a broad attachment into the pubic tubercle and pectineal line, behind the inguinal aponeurotic falx. In some subjects this structure is not very prominently marked, and not infrequently it is altogether wanting. 510 MYOLOGY 2. The Posterior Muscles of the Abdomen. Psoas major. Iliacus. Psoas minor. Quadratus lumborum. The Psoas major, the Psoas minor, and the Iliacus, with the fascite covering them, will be described with the muscles of the lower extremity (see page 559). The Fascia Covering the Quadratus Lumborum. — This is a thin layer attached, medially, to the bases of the transverse processes of the lumbar vertebra; beloiv, to the iliolumbar ligament; above, to the apex and lower border of the last rib. The upper margin of this fascia, which extends from the transverse process of the first lumbar vertebra to the apex and lower border of the last rib, constitutes the lateral lumbocostal arch (page 495). Laterally, it blends with the lumbodorsal fascia, the anterior layer of which intervenes between the Quadratus lumborum and the Sacrospinalis. The Quadratus lumborum (Fig. 495, page 487) is irregularly quadrilateral in shape, and broader below than above. It arises by aponeurotic fibres from the iliolumbar ligament and the adjacent portion of the iliac crest for about 5 cm., and is inserted into the lower border of the last rib for about half its length, and by four small tendons into the apices of the transverse processes of the upper four lumbar vertebrae. Occasionally a second portion of this muscle is found in front of the preceding. It arises from the upper borders of the transverse processes of the lower three or four lumbar vertebrae, and is inserted into the lower margin of the last rib. In front of the Qaudratus lumborum are the colon, the kidney, the Psoas major and minor, and the Diaphragma; between the fascia and the muscle are the twelfth thoracic, ilioinguinal, and iliohypogastric nerves. Nerve Supply. — The tweKth thoracic and first and second lumbar nerves supplj^ this muscle. Actions. — The Quadratus lumborum draws down the last rib, and acts as a muscle of inspira- tion by helping to fix the origin of the Diaphragma. If the thorax and vertebral column are fixed, it may act upon the pelvis, raising it toward its own side when only one muscle is put in action; and when both muscles act together, either from below or above, they flex the trunk. V. THE MUSCLES AND FASCLffi OF THE PELVIS. Obturator internus. Levator ani. Piriformis. Coccygeus. The muscles within the pelvis may be divided into two groups : (1) the Obturator internus and the Piriformis, which are muscles of the lower extremity, and will be described with these (pages 571 and 572) ; (2) the Levator ani and the Coccygeus, which together form the pelvic diaphragm and are associated with the pelvic viscera. The classification of the two groups under a common heading is convenient in connection with the fasciae investing the muscles. These fasciae are closely related to one another and to the deep fascia of the perineum, and in addition have special connections with the fibrous coverings of the pelvic viscera ; it is customary there- fore to describe them together under the term pelvic fascia. Pelvic Fascia. — ^The fascia of the pelvis may be resolved into: (a) the facial sheaths of the Obturator internus. Piriformis, and pelvic diaphragm; (6) the fascia associated with the pelvic viscera. The fascia of the Obturator internus covers the pelvic surface of, and is attached around the margin of the origin of, the muscle. Above, it is loosely connected to the back part of the arcuate line, and here it is continuous with the iliac fascia. In front of this, as it follows the line of origin of the Obturator internus, it gradually separates from the iliac fascia and the continuity between the two is retained only through the periosteum. It arches beneath the obturator vessels and nerve, com- pleting the obturator canal, and at the front of the pelvis is attached to the back THE }fUSCLES AXD FASCLE OF THE PELVIS 511 of the superior ramus of the pubis. Below, the obturator fascia is attached to the falciform process of the sacrotuberous ligament and to the pubic arch, where it becomes continuous with the superior fascia of the urogenital diaphragm. Behind, it is prolonged into the gluteal region. The internal pudendal vessels and pudendal nerve cross the pelvic surface of the Obturator internus and are enclosed in a special canal — Alcock's canal — formed by the obturator fascia. The fascia of the Piriformis is very thin and is attached to the front of the sacrum and the sides of the greater sciatic foramen; it is prolonged on the muscle into the gluteal region. At its sacral attachment around the margins of the anterior sacral foramina it comes into intimate association with and ensheathes the nerves emerging from these foramina. Hence the sacral nerves are frequently described as lying behind the fascia. The internal iliac vessels and their branches, on the other hand, lie in the subperitoneal tissue in front of the fascia, and the branches to the gluteal region emerge in special sheaths of this tissue, above and below the Piriformis muscle. [ Svperior Diaphragmatw layer part of pelvic J fascia Inferior \ layer Tendinous arch Fascia endopelvina Vesicula seminalis Dtictus deferens Rectovesical layer Fig. 510. — Coronal section of pelvis, showing arrangement of fasciae. Viewed from behind. (Diagrrfinmatic.) The diaphragmatic part of the pelvic fascia (Fig. 510) covers both surfaces of the Levatores ani. The inferior layer is known as the anal fascia; it is attached above to the obturator fascia along the line of origin of the Levator ani, while below it is continuous with the superior fascia of the urogenital diaphragm, and with the fascia on the Sphincter ani internus. The layer covering the upper surface of the pelvic diaphragm follows, above, the line of origin of the Levator ani and is there- fore somewhat variable. In front it is attached to the back of the symphysis pubis about 2 cm. above its lower border. It can then be traced laterally across the back of the superior ramus of the pubis for a distance of about 1.25 cm., when it reaches the obturator fascia. It is attached to this fascia along a line which pursues a somewhat irregular course to the spine of the ischium. The irregularity of this line is due to the fact that the origin of the Levator ani, which in lower forms is from the pelvic brim, is in man lower down, on the obturator fascia. Tendinous fibres of origin of the muscle are therefore often found extending up toward, and in some cases reaching, the pelvic brim, and on these the fascia is carried. 512 MYOLOGY It will be evident that the fascia covering that part of the Obturator internus which Hes above the origin of the Levator ani is a composite fascia and includes the following: (a) the obturator fascia; (6) the fascia of the Levator ani; (c) degenerated fibres of origin of the Levator ani. The lower margin of the fascia covering the upper surface of the pelvic diaphragm is attached along the line of insertion of the Levator ani. At the level of a line extending from the lower part of the symphysis pubis to the spine of the ischium is a thickened whitish band in this upper la>er of the diaphragmatic part of the pelvic fascia. It is termed the tendinous arch or white line of the pelvic fascia, and marks the line of attachment of the special fascia (^pars endopch'ina fasciae pelvis) which is associated with the pelvic viscera. Peritoncuin Veaical laye urogemtal- jj^^..^^ diaphragm y ^^^^^ Rectovesical layer CajJsnle of prostate Rectal layer Transversus perinoei sujierfieialis Colles' fascia Urogenital diaphragm Fig. 5H. — Median sagittal section of pelvis, showing arrangement of fasciae. The endopelvic part of the pelvic fascia is continued over the various pelvic viscera (Fig. 511) to form for them fibrous coverings which will be described later (see section on Splanchnology). It is attached to the diaphragmatic part of the pelvic fascia along the tendinous arch, and has been subdivided in accordance with the viscera to which it is related. Thus its anterior part, known as the vesical layer, forms the anterior and lateral ligaments of the bladder. Its middle part crosses the floor of the pelvis between the rectum and vesiculae seminales as the rectovesical layer; in the female this is perforated by the vagina. Its posterior THE MUSCLES AXD FASCLE OF THE PELVIS 513 portion passes to the side of the rectum; it forms a loose sheath for the rectum, but is firmly attached around the anal canal; this i)ortion is known as the rectal layer. The Levator ani i^Fig. 512) is a broad, thin muscle, situated on the side of the pelvis. It is attached to the inner surface of the side of the lesser pelvis, and unites with its fellow of the opposite side to form the greater part of the floor of the pelvic cavity. It supports the viscera in this cavity, and surrounds the various structures which pass through it. It arises, in front, from the posterior surface of the superior ramus of the pubis lateral to the symphysis; behind, from the inner surface of the spine of the ischium; and between these two points, from the obturator fascia. /A-vV'. Superior glutoeal vessels Obturator nerve and vessels Left lobe of prostate (cut) Anococcygeal raphe Fig. 512. — Left Levator ani from -witliin. Posteriorly, this fascial origin corresponds, more or less closely, with the tendinous arch of the pelvic fascia, but in front, the muscle arises from the fascia at a vary- ing distance above the arch, in some cases reaching nearly as high as the canal for the obturator vessels and nerve. The fibres pass downward and backw^ard to the middle line of the floor of the pelvis; the most posterior are inserted into the side of the last two segments of the cocc^'x; those placed more anteriorly unite with the muscle of the opposite side, in a median fibrous raphe (anococcygeal 33 514 MYOLOGY raphe), which extends between the coccyx and the margin of the anus. The middle fibres are inserted into the side of the rectum, blciuUng with the fibres of the Sphincter muscles; lastly, the anterior fibres descend upon the side of the prostate to unite beneath it with the muscle of the opposite side, joining with the fibres of the Spliincter ani externus and Transversus perinaei, at the central tendinous point of the perineum. The anterior portion is occasionally separated from the rest of the muscle by connective tissue. From this circumstance, as well as from its peculiar relation with the prostate, which it supports as in a sling, it has been described as a distinct muscle, under the name of Levator prostatas. In the female the anterior fibres of the Levator ani descend upon the side of the vagina. Relations. — By its upper or pelvic surface, with the diaphragmatic part of the pelvic fascia which separates it from tfie bladder, prostate, rectum, and peritoneum. By its lower or perineal surface, it forms the medial boundary of the ischiorectal fossa, and is covered by the inferior layer of the diaphi'agmatic part of the pelvic fascia (anal fascia) . Its posterior border is free and sepa- rated from the Coccygeus by areolar tissue. Its anterior border is separated from the muscle of the opposite side by a triangular space, through which the urethra, and in the female the vagina, pass from the pelvis. The Levator ani may be divided into ihococcygeal and pubococcygeal parts. The Iliococcygeus arises from the ischial spine and from the posterior part of the tendinous arch of the pelvic fascia, and is attached to the coccyx and anococcygeal raph^; it is usually thin, and may fail entirely, or be largely replaced by fibrous tissue. An accessory slip at its posterior part is sometimes named the Iliosacralis. The Pubococcygeus arises from the back of the pubis and from the anterior part of the obturator fascia, and "is directed backward almost horizontally along the side of the anal canal toward the coccyx and sacrum, to which it finds attachment. Between the termination of the vertebral column and the anus, the two Pubococcygei muscles come together and form a thick, fibromuscular layer lying on the raphe formed by the lUococcygei" (Peter Thompson). The greater part of this muscle is inserted into the coccyx and into the last one or two pieces of the sacrum. This insertion into the vertebral column is, however, not- admitted by all observers. The fibres which form a sling for the rectum are named the Pubo- rectalis or Sphincter recti. They arise from the lower part of the symphysis pubis, and from the superior fascia of the urogenital diaphragm. They meet with the corresponding fibres of the opposite side around the lower part of the rectum, and form for it a strong sHng. Nerve Supply. — The Levator ani is suppUed by a branch from the fourth sacral nerve and by a branch which is sometimes derived from the perineal, sometimes from the inferior hemor- rhoidal division of the pudendal nerve. The Coccygeus (Fig. 512) is situated behind the preceding. It is a triangular plane of muscular and tendinous fibres, arising by its apex from the spine of the ischium and sacrospinous ligament, and inserted by its base into the margin of the coccyx and into the side of the lowest piece of the sacrum. It assists the Levator ani and Piriformis in closing in the back part of the outlet of the pelvis. Nerve Supply. — The Coccygeus is supphed by a branch from the fourth and fifth sacral nerves. Actions. — The Levatores ani constrict the lower end of the rectum and vagina. They elevate and invert the lower end of the rectum after it has been protruded and everted during the expul- sion of the feces. They are also muscles of forced expiration. The Coccygei puU forward and support the coccyx, after it has been pressed backward during defecation or parturition. The Levatores ani and Coccygei together form a muscular diaphragm which supports the pelvic viscera. VI. THE MUSCLES AND FASCIA OF THE PERINEUM. The perineum corresponds to the outlet of the pelvis. Its deep boundaries are — in front, the pubic arch and the arcuate ligament of the pubis ; behind, the tip of the coccyx; and on either side the inferior rami of the pubis and ischium, and the sacrotuberous ligament. The space is somewhat lozenge-shaped and is limited on the surface of the body by the scrotum in front, by the buttocks behind, and laterally by the medial side of the thigh. A line drawn transversely across in front of the ischial tuberosities divides the space into two portions. The pos- terior contains the termination of the anal canal and is known as the anal region; THE MUSCLES OF THE AXAL REGION 515 the anterior, which contjiins the external urogenital organs, is termed the urogenital region. The muscles of the perineum may therefore be divided into two groups: 1. Those of the anal region. 2. Those of the urogenital region: a, In the male; b, In the female. 1. The Muscles of the Anal Region. Corrugator cutis ani. Sphincter ani externus. Sphincter ani internus. The Superficial Fascia.— The superficial fascia is very thick, areolar in texture, and contains much fat in its meshes. On either side a pad of fatty tissue extends deeply between the Levator ani and Obturator internus into a space known as the iscluorectal fossa. . „ The Deep Fascia.— The deep fascia forms the limng of the ischiorectal fossa; it comprises the anal fascia, and the portion of obturator fascia below the origin of]Levator ani. Fig. 513. — The perineum. The integument and superficial layer of superficial fascia reflected. Ischiorectal Fossa (fossa isckioredalis) (Fig. 513).— The fossa is somew'hat pris- matic in shape, with its base directed to the surface of the perineum, and its apex at the line of meeting of the obturator and anal fascife. It is bounded medially by the Sphincter ani externus and the anal fascia; lateraUij, by the tuberosity_ of the ischium and the obturator fascia; anteriorly, by the fascia of Colles covering the Transversus perinaei superficialis, and by the inferior fascia of the urogenital diaphragm; posteriorly, bv the Glutaeus maximus and the sacrotuberous ligament. Crossing the space transversely are the inferior hemorrhoidal vessels and nerves; at the back part are the perineal and perforating cutaneous branches of the pudendal plexus; while from the forepart the posterior scrotal (or labial) vessels and nerves emerge. The internal pudendal vessels and pudendal nerve lie m 516 MYOLOGY Alcock's canal on the lateral wall. The fossa is filled with fatty tissue across which numerous fibrous bands extend from side to side. Applied Anatomy. — Abscess in the ischiorectal fossa commonly occurs; it is most often the result of infection from the bowel, and is especially prone to occur in tuberculous subjects; occa- sionally it follows perforation by a foreign body which has been swallowed, such as a fish bone. The abscess may bulge at the side of the anus, at the border of Glutaeus maximus, or against the rectal wall. There is great pain on defecation. On examining the bowel, fulness on the side of the abscess may be detected. If left to itself the pus will find exit through the skin, or into the rectum between the two Sphincters; and the condition will degenerate into one of the varieties of fistula, owing to the constant pull of the Sphincter ani externus preventing closure of the walls of the cavity. These abscesses should be opened at the earliest possible moment, as they tend to track and burrow widely into the soft fat in the fossa, and also in the subcutaneous tissues. An incision should be made tangential to the anus over the region of the ischiorectal fossa, and should then be converted into a T, by making a second incision laterally at right angles to it, so that the wound may be kept open and may heal up from the bottom. Frequently, however, in spite of care, a fistula ensues which requires division of the Sphincter ani externus for its cure. The Corrugator Cutis Ani. — Around the anus is a thin stratum of involuntary- muscular fibre, which radiates from the orifice. Medially the fibres fade off into the submucous tissue, while laterally they blend with the true skin. By its contrac- tion it raises the skin into ridges around the margin of the anus. The Sphincter ani externus {External spJwicter ani) (Fig 513) is a flat plane of muscular fibres, elliptical in shape and intimately adherent to the integument surrounding the margin of the anus. It measures about 8 to 10 cm. in length, from its anterior to its posterior extremity, and is about 2.5 cm. broad opposite the anus. It consists of two strata, superficial and deep. The superficial, constituting the main portion of the muscle, arises from a narrow tendinous band, the anococcy- geal raphe, which stretches from the tip of the coccyx to the posterior margin of the anus; it forms two flattened planes of muscular tissue, which encircle the anus and meet in front to be inserted into the central tendinous point of the perineum, joining with the Transversus perinaei superficialis, the Levator ani, and the Bul- bocavernosus. The deeper portion forms a complete sphincter to the anal canal. Its fibres surround the canal, closely applied to the Sphincter ani internus, and in front blend with the other muscles at the central point of the perineum. In a considerable proportion of cases the fibres decussate in front of the anus, and are continuous with the Transversi perinaei superficiales. Posteriorly, they are not attached to the coccj-x, but are continuous with those of the opposite side behind the anal canal. The upper edge of the muscle is ill-defined, since fibres are given off from it to join the Levator ani. Nerve Supply. — A branch from the fourth sacral and twigs from the inferior hemorrhoidal branch of the pudendal supply the muscle. Actions. — The action of this muscle is peculiar. (1) It is, like other muscles, always in a state of tonic contraction, and having no antagonistic muscle it keeps the anal canal and orifice closed. (2) It can be put into a condition of greater contraction under the influence of the wiU, so as more firmly to occlude the anal aperture, in expiratory efforts unconnected with defecation. (3) Taking its fixed point at the coccyx, it helps to fix the central point of the perineum, so that the Bulbocavernosus may act from this fixed point. The Sphincter ani internus {Internal sphincter ani) is a muscular ring which surrounds about 2.5 cm. of the anal canal; its inferior border is in contact with, but quite separate from, the Sphincter ani externus. It is about 5 mm. thick, and is formed by an aggregation of the involuntary circular fibres of the intestine. Its lower border is about 6 mm. from the orifice of the anus. Actions. — Its action is entirely involuntary. It helps the Sphincter ani externus to occlude the anal aperture and aids in the expulsion of the feces. THE MUSCLES OF THE UROGEXITAL REGIOX IN THE MALE 517 2. A. The Muscles of the Urogenital Region in the Male (Fig. 514). Transversus perinaei superficialis. Ischiocaveriiosus. Biilbocavernosus. Transversus perinaei protundus. Si)luncter urethrae membranaceae. Superficial Fascia.^The superficial fascia of this region consists of two layers, superficial and deep. Fig. 514. — Muscles of male perineum. The superficial layer is thick, loose, areolar in texture, and contains in its meshes much adipose tissue, the amount of which varies m different subjects. In frmt, i?is continuous with the dartos tunic of the scrotum; feeAmd, w-.th the subcuta- neous areolar tissue surrounding the anus; and, on either srde^jith the same fascia «n the inner sides of the thighs. In the middle Km, it is adherent to the skm on the raph^ and to the deep layer of the superficial fascia. The deep layer ot superficial fascia (fascia of Colle.,) (Fig. 513) is thin, aponeurot^ in structure, and of considerable strength, serving to bind down the muscles of the root of the penis. It is continuous, in front, with the dartos tunic the deep fascia of the penis, the fascia of the spermatic cord, and Scarpa s fascia upon the 518 MYOLOGY anterior -wall of the abdomen; on either side it is firmly attached to the margins of the rami of the pubis and ischium, hiteral to the crus penis and as far back as the tuberosity of the ischium; posteriorly, it curves around the Transversi perinaei superficiales to join the lower margin of the inferior fascia of the' urogenital dia- phragm. In the middle line, it is connected with the superficial fascia and with the median septum of the Bulbocavernosus. This fascia not only co^•ers the muscles in this region, but at its back part sends upward a vertical septum from its deep surface, Avhich separates the posterior portion of the subjacent space into two. The Central Tendinous Point of the Perineum. — ^This is a fibrous point in the middle line of the perineum, between the urethra and anus, and about 1.25 cm. in front of the latter. At this point six muscles converge and are attached: viz., the Sphincter ani externus, the Bulbocavernosus, the two Transversi perinaei super- ficiales, and the anterior fibres of the Levatores ani. The Transversus perinaei superficialis {Transversus perinaei; Superficial transverse perineal muscle) is a narrow muscular slip, which passes more or less transversely across the perineal space in front of the anus. It arises by tendinous fibres from the inner and forepart of the tuberosity of the ischium, and, running medialward, is inserted into the central tendinous point of the perineum, joining in this situa- tion with the muscle of the opposite side, with the Sphincter ani externus behind, and with the Bulbocavernosus in front. In some cases, the fibres of the deeper layer of the Sphincter ani externus decussate in front of the anus and are con- tinued into this muscle. Occasionally it gives off fibres, which join with the Bulbocavernosus of the same side. Actions. — The simultaneous contraction of the two muscles serves to fix the central tendinous point of the perineum. The Bulbocavernosus {Ejaculator urinae; Accelerator urinae) is placed in the middle line of the perineum, in front of the anus. It consists of tAvo symmetrical parts, united along the median line by a tendinous raphe. It arises from the cen- tral tendinous point of the perineum and from the median raphe in front. Its fibres diverge like the barbs of a quill-pen; the most posterior form a thin layer, which is lost on the inferior fascia of the urogenital diaphragm; the middle fibres encircle the bulb and adjacent parts, of the corpus cavernosum urethrae, and join with the fibres of the opposite side, on the upper part of the corpus cavernosum urethrae, in a strong aponeurosis; the anterior fibres, spread out over the side of the corpus cavernosum penis, to be inserted partly into that body, anterior to the Ischiocavernosus, occasionally extending to the pubis, and partly ending in a tendinous expansion which covers the dorsal vessels of the penis. The latter fibres are best seen by dividing the muscle longitudinally, and reflecting it from the surface of the corpus cavernosum urethrae. Actions. — This muscle serves to empty the canal of the urethra, after the bladder has expelled its contents; during the greater part of the act of micturition its fibres are relaxed, and it only comes into action at the end of the process. The middle fibres are supposed by Ivrause to assist in the erection of the corpus cavernosum urethi'ae, by compressing the erectile tissue of the bulb. The anterior fibres, according to T;yTrel, also contribute to the erection of the penis by compressing the deep dorsal vein of the penis as they are inserted into, and continuous with, the fascia of the penis. The Ischiocavernosus (Erector penis) covers the crus penis. It is an elongated muscle, broader in the middle than at either end, and situated on the lateral bound- ary of the perineum. It arises by tendinous and fleshy fibres from the inner sur- face of the tuberosity of the ischium, behind the crus penis; and from the rami of the pubis and ischium on either side of the crus. From these points fleshy fibres succeed, and end in an aponeurosis which is inserted into the sides and under surface of the crus penis. THE MUSCLES OF THE UROGENITAL REGION IN THE MALE 519 Action. — Tlie Ischiocavernosus compresses the cms penis, and retards the return of tlie blood through the veins, and thus serves to maintain the organ erect. Between the muscles just examined a triangular space exists, bounded medially by the Bulbo- cavernosus, laterally by the Ischiocavernosus, and behinrl by the Transversus perinaei super- ficialis; the floor is formed by the inferior fascia of the urogenital diaphragm. Running from behind forward in the space are the posterior scrotal vessels and nerves, and the perineal branch of the posterior femoral cutaneous nerve; the transverse perineal artery courses along its posterior boundary on the Transversus perinaei superficialis. The Deep Fascia. — The deep fascia of the urogenital region forms an investment for the Transversus perinaei profundus and the Sphincter urethrae membranaceae, but within it lie also the deep vessels and nerves of this part, the whole forming a transverse septum which is known as the urogenital diaphragm. From its shape it is usually termed the triangular ligament, and is stretched almost horizontally across the pubic arch, so as to close in the front part of the outlet of the pelvis. It consists of two dense membranous laminae (Fig. 515), which are united along their posterior borders, but are separated in front by intervening structures. The superficial of these two layers, the inferior fascia of the urogenital diaphragm, is tri- angular in shape, and about 4 cm. in depth. Its apex is directed forward, and is urogenital-, j f^ diaphragm I ,- ferior Bulbocavernosus Fig. 515. — Coronal section of anterior part of pelvis, through the pubio arch. Seen from in front. (Diagrammatic.) separated from the arcuate pubic ligament by an oval opening for the transmission of the deep dorsal vein of the penis. Its lateral margins are attached on either side to the inferior rami of the pubis and ischium, above the crus penis. Its base is directed toward the rectum, and connected to the central tendinous point of the perineum. It is continuous with the deep layer of the superficial fascia behind the Transversus perinaei superficialis, and with the inferior layer of the diaphragmatic part of the pelvic fascia. It is perforated, about 2.5 cm. below the symphysis pubis, by the urethra, the aperture for which is circular and about 6 mm. in diameter by the arteries to the bulb and the ducts of the bulbourethral glands close to the urethral orifice; by the deep arteries of the penis, one on either side close to the pubic arch and about halfway along the attached margin of the fascia ; by the dorsal arteries and nerves of the penis near the apex of the fascia. Its base is also perfor- ated by the perineal vessels and nerves, while between its apex and the arcuate pubic ligament the deep dorsal vein of the penis passes upward into the pelvis. 520 MYOLOGY If the inferior fascia of the urogenital diaphragm be detached on either side, the following structures will be seen between it and the superior fascia: the deep dorsal vein of the penis; the membranous portion of the urethra; the Transversus perinaei profundus and Sphincter urethrae membranaceae muscles; the bulbo- urethral glands and their ducts; the pudendal vessels and dorsal nerves of the penis; the arteries and nerves of the urethral bulb, and a plexus of veins. The superior fascia of the urogenital diaphragm is continuous with the obturator fascia and stretches across the pubic arch. If the obturator fascia be traced medially after leaving the Obturator internus muscle, it will be found attached by some of its deeper or anterior fibres to the inner margin of the pubic arch, while its super- ficial or posterior fibres pass over this attachment to become continuous with the superior fascia of the urogenital diaphragm. Behind, this layer of the fascia is continuous with the inferior fascia and .with the fascia of Colles ; in front it is con- tinuous with the fascial sheath of the prostate, and is fused with the inferior fascia to form the transverse ligament of the pelvis. The Transversus perinaei profundus arises from the inferior rami of the ischium and runs to the median line, where it interlaces in a tendinous raphe with its fellow of the opposite side. It lies in the same plane as the Sphincter urethrae membran- aceae; formerly the two muscles were described together as the Constrictor urethrae. The Sphincter urethrae membranaceae surrounds the whole length of the mem- branous portion of the urethra, and is enclosed in the fasciae of the urogenital dia- phragm. Its external fibres arise from the junction of the inferior rami of the pubis and ischium to the extent of 1.25 to 2 cm., and from the neighboring fasciae. They arch across the front of the urethra and bulbourethral glands, pass around the urethra, and behind it unite with the muscle of the opposite side, by means of a tendinous raphe. Its innermost fibres form a continuous circular investment for the membranous urethra. Actions. — The muscles of both sides act together as a sphincter, compressing the membranous portion of the urethra. During the transmission of fluids they, like the Bulbocavernosus, are relaxed, and only come into action at the end of the process to eject the last drops of the fluid. Nerve Supply. — The perineal branch of the pudendal nerve supplies this group of muscles. 2. B. The Muscles of the Urogenital Region in the Female (Fig. 515). Transversus perinaei superficialis. Ischiocavernosus. Bulbocavernosus. Transversus perinaei profundus. Sphincter urethrae membranaceae. The Transversus perinaei superficialis {Transversus yerinaei; Superficial trans- verse perineal muscle) in the female is a narrow muscular slip, M'hich arises by a small tendon from the inner and forepart of the tuberosity of the ischium, and is inserted into the central tendinous point of the perineum, joining in this situa- tion with the muscle of the opposite side, the Sphincter ani externus behind, and the Bulbocavernosus in front. Action. — The simultaneous contraction of the two muscles serves to fix the central tendinous point of the perineum. The Bulbocavernosus (Sphincter vaginae) surrounds the orifice of the vagina. It covers the lateral parts of the vestibular bulbs, and is attached posteriorly to the central tendinous point of the perineum, where it blends with the Sphincter ani externus. Its fibres pass forward on either side of the vagina to be inserted into the corpora cavernosa clitoridis, a fasciculus crossing over the body of the organ so as to compress the deep dorsal vein. Actions. — The Bulbocavernosus diminishes the orifice of the vagina. The anterior fibres contribute to the erection of the clitoris, as they are inserted into and are continuous with the fascia of the clitoris, compressing the deep dorsal vein during the contraction of the muscle. THE MUSCLES OF THE UROGENITAL REGION IN THE FEMALE 521 The Ischiocavernosus {Erector clltoridis) is smaller than the corresponding muscle in the male. It covers the unattached surface of the crus clitoridis. It is an elongated muscle, broader at the middle than at either end, and situated on the side of the lateral boundary of the perineum. It arises by tendinous and fleshy fibres from the inner surface of the tuberosity of the ischium, behind the crus clitoridis; from the surface of the crus; and from the adjacent portion of the ramus of the ischium. From these points fleshy fibres succeed, and end in an aponeurosis, which is inserted into the sides and under surface of the crus clitoridis. Clitoris Urethra Vagina Sphincter ani externus Fig. 516. — -Muscles of the female perineum. (Modified from a drawing by Peter Thompson.) Actions.— The Ischiocavernosus compresses the crus cKtoridis and retards the return of blood through the veins, and thus serves to maintain the organ erect. The fascia of the urogenital diaphragm in the female is not so strong as in the male. It is attached to the pubic arch, its apex being connected with the arcuate pubic ligament. It is divided in the middle line by the aperture of the vagina, with the external coat of which it becomes blended, and in front of this is perfor- ated by the urethra. Its posterior border is continuous, as in the male, with the deep layer of the superficial fascia around the Transversus perinaei superficialis. Like the corresponding fascia in the male, it consists of two layers, between which are to be found the following structures: the deep dorsal vein of the clitoris, a portion of the urethra and the Constrictor urethra muscle, the larger vestibular glands and their ducts; the internal pudendal vessels and the dorsal nerves of the clitoris; the arteries and nerves of the bulbi vestibuli, and a plexus of veins. The Transversus perinaei profundus arises from the inferior rami of the ischium and runs across to the side of the vagina. The Sphincter urethrae membranaceae {Constrictor urethrae), like the corresponding muscle on the male, consists of external and internal fibres. The external fibres arise on either side from the margin of the 522 MYOLOGY inferior ramus of the pubis. They are directed across the public arch in front of the urethra, and pass around it to blend with the muscular fil)res of the opposite side, between the urethra and vagina. The irmervwst fibres encircle the lower end of the urethra. Nerve Supply. — The muscles of this group are supplied by the perineal branch of the pudendal- THE MUSCLES AND FASCI-ffl OF THE UPPER EXTREMITY. The muscles of the upper extremity are divisible into groups, corresponding with the different regions of the limb. I. Muscles Connecting the Upper Extremity to the Vertebral Column. II. Muscles Connecting the Upper Extremity to the Anterior and Lateral Thoracic Walls. III. Muscles of the Shoulder. V. Muscles of the Forearm. IV. Muscles of the Arm. VI. Muscles of the Hand. I. THE MUSCLES CONNECTING THE UPPER EXTREMITY TO THE VERTEBRAL COLUMN. The muscles of this group are : Trapezius. Rhomboideus major. Latissimus dorsi. ' Rhomboideus minor. Levator scapulae. Superficial Fascia.^ — The superficial "fascia of the back forms a layer of con- siderable thickness and strength, and contains a quantity of granular fat. It is continuous with the general superficial fascia. Deep Fascia. — The deep fascia is a dense fibrous layer, attached above to the superior nuchal line of the occipital bone; in the middle line it is attached to the ligamentum nuchae and supraspinal ligament, and to the spinous processes of all the vertebrae below the seventh cervical ; laterally, in the neck it is continuous with the deep cervical fascia; over the shoulder it is attached to the spine of the scapula and to the acromion, and is continued downward over the Deltoideus to the arm; on the thorax it is continuous with the deep fascia of the axilla and chest, and on the abdomen with that covering the abdominal muscles; below, it is attached to the crest of the ilium. The Trapezius (Fig. 517) is. a flat, triangular muscle, covering the upper and back part of the neck and shoulders. It arises from the external occipital protu- berance and the medial third of the superior nuchal line of the occipital bone, from the ligamentum nuchae, the spinous process of the seventh cervical, and the spinous processes of all the thoracic vertebrae, and from the corresponding portion of the supraspinal ligament. From this origin, the superior fibres proceed downward and lateralward, the inferior upward and lateralward, and the middle horizontally; the superior fibres are inserted into the posterior border of the lateral third of the clavicle; the middle fibres into the medial margin of the acromion, and into the supe- rior lip of the posterior border of the spine of the scapula; the inferior fibres con- verge near the scapula, and end in an aponeurosis, which glides over the smooth triangular surface on the medial end of the spine, to be inserted into a tubercle at the apex of this smooth triangular surface. At its occipital origin, the Trapezius is connected to the bone by a thin fibrous lamina, firmly adherent to the skin. At the middle it is connected to the spinous processes by a broad semi-elliptical aponeurosis, which reaches from the sixth cervical to the third thoracic vertebrae, and forms, w^ith that of the opposite muscle, a tendinous ellipse. The rest of the MUSCLES OF THE UPPER EXTREMITY 523 Lumbar triangle Fig. 517.— Muscles connecting the upper extremity to the vertebral column. 524 MYOLOGY muscle arises by numerous short tendinous fibres. The two Trapezius muscles together resemble a trapezium, or diamond-shaped quadrangle: two angles corre- sponding to the shoulders; a third to the occipital protuberance; and the fourth to the spinous process of the twelfth thoracic vertebra. The clavicular insertion of this muscle varies in extent; it sometimes reaches as far as the middle of the clavicle, and occasionally may blend with the posterior edge of the Sternocleidomastoideus, or overlap it. The Latissimus dorsi (Fig. 517) is a triangular, flat muscle, which covers the lumbar region and the lower half of the thoracic region, and is gradually con- tracted into a narrow fasciculus at its insertion into the humerus. It arises by tendinous fibres from the spinous processes of the lower six thoracic vertebrae and from the posterior layer of the lumbodorsal fascia (see page 486), by which it is attached to the spines of the lumbar and sacral vertebrae, to the supraspinal ligament, and to the posterior part of the crest of the ilium. It also arises by muscular fibres from the external lip of the crest of the ilium lateral to the margin of the Sacrospinalis, and from the three or four lower ribs by fleshy digitations, which are interposed between similar processes of the Obliquus abdominis externus (Fig. 500, page 500). From this extensive origin the fibres pass in dift'erent direc- tions, the upper ones horizontally, the middle obliquely upward, and the lower vertically upward, so as to converge and form a thick fasciculus, which crosses the inferior angle of the scapula, and usually receives a few fibres from it. The muscle curves around the lower border of the Teres major, and is twisted upon itself, so that the superior fibres become at first posterior and then inferior, and the vertical fibres at first anterior and then superior. It ends in a quadrilateral tendon, about 7 cm. long, which passes in front of the tendon of the Teres major, and is inserted into the bottom of the intertubercular groove of the humerus ; its insertion extends higher on the humerus than that of the tendon of the Pectoralis major. The lower border of its tendon is united with that of the Teres major, the surfaces of the two being separated near their insertions by a bursa ; another bursa is sometimes inter- posed between the muscle and the inferior angle of the scapula. The tendon of the muscle gives off an expansion to the deep fascia of the arm. A muscular slip, the axillary arch, varjdng from 7 to 10 cm. in length, and from 5 to 15 mm. in breadth, occasionally springs from the upper edge of the Latissimus dorsi about the middle of the posterior fold of the axilla, and crosses the axilla in front of the axillary vessels and nerves, to join the under surface of the tendon of the Pectorahs major, the Coracobrachiahs, or the fascia over the Biceps brachii. This axillary arch crosses the axillary artery, just above the spot usually selected for the application of a hgature, and may mislead the surgeon duriag the operation. It is present in about 7 per cent, of subjects and may be easily recognized by the transverse direction of its fibres. A fibrous sHp usually passes from the lower border of the tendon of the Latissimus dorsi, near its insertion, to the long head of the Triceps brachii. This is occasionally muscular, and is the representative of the Dorsoepitrochlearis brachii of apes. The lateral margin of the Latissimus dorsi is separated below from the Obliquus externus abdominis by a small triangular interval, the lumbar triangle of Petit, the base of which is formed by the iliac crest, and its floor by the Obliquus internus abdominis. Another triangle is situated behind the scapula. It is bounded above by the Trapezius, below by the Latissimus dorsi, and laterally by the vertebral border of the scapula; the floor is partly formed by the Rhomboideus major. If the scapula be drawn forward by folding the arms across the chest, and the trunk bent forward, parts of the sixth and seventh ribs and the interspace between them become subcutaneous and available for auscultation. The space is there- fore known as the triangle of auscultation. Nerves. — The Trapezius is supplied by the accessory nerve, and by branches from the third and fourth cervical nerves; the Latissimus dorsi by the sixth, seventh, and eighth cervical nerves through the thoracodorsal (long subscapular) nerve. MUSCLES OF THE UPPER EXTREMITY 525 The Rhomboideus major (Fig. 517) arises by tendinous fibres from the spinous processes of the second, third, fourth, and fifth thoracic vertebrae and the supra- spinal Hgament, and is inserted into a narrow tendinous arch, attached above to the lower part of the triangular surface at the root of the spine of the scapula; below to the inferior angle, the arch being connected to the vertebral border by a thin membrane. When the arch extends, as it occasionally does, only a short distance, the muscular fibres are inserted directly into the scapula. The Rhomboideus minor (Fig. 517) arises from the lower part of the ligamentum nucliae and from the spinous processes of the seventh cervical and first thoracic vertebrae. It is inserted into the base of the triangular smooth surface at the root of the spine of the scapula, and is usually separated from the Rhomboideus major by a slight interval, but the adjacent margins of the two muscles are occasionally united. The Levator scapulae {Levator anguli scapulae) (Fig. 517) is situated at the back and side of the neck. It arises by tendinous slips from the transverse pro- cesses of the atlas and axis and from the posterior tubercles of the transverse processes of the third and fourth cervical vertebrae. It is inserted into the verte- bral border of the scapula, between the medial angle and the triangular smooth surface at the root of the spine. Nerves. — The Rhomboidei are supplied by the dorsal scapular nen-e from the fifth cervical; the Levator scapulae by the third and fourth cervical nerves, and frequently by a branch from the dorsal scapular. Actions. — The movements effected by the preceding muscles are nimaerous, as may be con- ceived from their extensive attachments. "Wlien the whole Trapezius is in action it retracts the scapula and braces back the shoulder; If the head be fixed, the upper part of the muscle wiU elevate the point of the shoulder, as in supporting weights; when the lower fibres contract they assist in depressing the scapula. The middle and lower fibres of the muscle rotate the scapula, causing elevation of the acromion. If the shoulders be fixed, the Trapezii, acting together, will draw the head dii-ectly backward; or if only one act, the head is drawn to the corresponding side. When the Latissimus dorsi acts upon the humerus, it depresses and di-aws it backward, and at the same time rotates it inward. It is the muscle which is principal!}- employed in giving a downward blow, as iu felling a tree or in sabre practice. If the arm be fixed, the muscle may act in various ways upon the trunk; thus, it may raise the lower ribs and assist in forcible inspira- tion; or, if both arms be fixed, the two muscles may assist the abdominal muscles and Pectorales in suspending and drawing the trunk forward, as in climbing. If the head be fixed, the Levator scapulae raises the medial angle of the scapula; if the shoulder be fixed, the muscle inclines the neck to the corresponding side and rotates it in the same direc- tion. The Rhomboidei carry the inferior angle backward and upward, thus producing a shght rotation of the scapvda upon the side of the chest, the Rhomboideus major acting especially on the inferior angle of the scapula, through the tendinous arch bj" which it is inserted. The Rhom- boidei, acting together with the middle and inferior fibres of the Trapezius, will retract the scapula. n. THE MUSCLES CONNECTING THE UPPER EXTREMITY TO THE ANTERIOR AND LATERAL THORACIC WALLS. The muscles of the anterior and lateral thoracic regions are: Pectoralis major. Subclavius. Pectoralis minor. Serratus anterior. Dissection of Pectoral Region and Axilla (Fig. 518). — The arm being drawTi away from the side nearly at right angles with the trunk and rotated outward, make a vertical incision through the integument in the median fine of the thorax, from the upper to the lower part of the sternum; a second incision along the lower border of the Pectorahs major muscle, from the ensiform cartilage to the inner side of the axiUa; a third, from the sternum along the clavicle, as far as its centre; and a fourth, from the middle of the clavicle obliquely downward, along the interspace between the Pectorahs major and Deltoideus muscles, as low as the fold of the axilla. The flap of integu- ment is then to be dissected off in the direction indicated in the figm-e. but not entire!}- removed, 526 MYOLOGY Dissection of idder and Arm. Bend 0/ Elbow. as it should be replaced on completing the dissection. If a transverse incision is now made from the lower end of the sternum to the side of the thorax, as far as the posterior fold of the axilla, and the integument reflected outward, the axillarj' space will be more completely exposed. Superficial Fascia. — The superficial fascia of the anterior thoracic region is con- tinuous with that of the neck and upper extremity above, and of the abflomen below. It encloses the mamma and gives off numerous septa which pass into the gland, supporting its various lobes. From the fascia over the front of the mamma, fibrous processes pass forward to the integument and papilla; these were called by Sir A. Cooper the ligamenta suspensoria. Pectoral Fascia. — The pectoral fascia is a thin lamina, covering the surface of the Pectoralis major, and sending numerous prolongations be- tween its fasciculi: it is attached, in the middle line, to the front of the sternum; above, to the clavicle; laterally and below it is contintious with the fascia of the shoulder, axilla, and thorax. It is very thin over the upper part of the Pectoralis major, but thicker in the interval between it and the Latissimus dorsi, w^here it closes in the axillary space and forms the axillary fascia; it divides at the lateral margin of the Latis- simus dorsi into two layers, one of which passes in front of, and the other behind it; these proceed as far as the spinous processes of the thoracic vertebrae, to which they are attached. As the fascia leaves the lower edge of the Pectoralis major to cross the floor of the axilla it sends a layer upward under cover of the muscle; this lamina splits to envelop the Pectoralis minor, at the upper edge of which it is continuous with the coracoclavicular fascia. The hollow of the armpit, seen when the arm is abducted, is produced mainly by the traction of this fascia on the axillary floor, and hence the lamina is sometimes named the suspensory ligament of the axilla. At the lower part of the thoracic region the deep fascia is well-developed, and is continuous with the fibrous sheaths of the Recti abdominis. Applied Anatomy. — In cases of suppuration in the axilla, the axillary fascia prevents the exten- sion of the pus in a downward direction, and so it has a tendency to spread upward, beneath the Pectoral muscles, toward the root of the neck. Early evacuation is therefore necessary. The incision should be made midway between the anterior and posterior axillary folds, so as to avoid the lateral thoracic and subscapular vessels, and the edge of the knife should be directed away from the axillary vessels. The Pectoralis major (Fig. 519) is a thick, triangular muscle, situated at the upper and forepart of the chest. It arises from the anterior surface of the sternal half of the clavicle; from half the breadth of the anterior surface of the sternum, as low down as the attachment of the cartilage of the sixth or seventh rib ; from the cartilages of all the true ribs, with the exception, frequently, of the first or seventh, or both, and from the aponeurosis of the Obliquus exiternus abdominis. From this Palm of Hand. Fig. 518. — Dissection of the upper extremity. MUSCLES OF THE UPPER EXTREMITY 527 extensive origin the filires converge toward their insertion; those arising from the clavicle pass ol)lit|uely downward and hiterahvard, and are usually separated from the rest by a slight interval; those from the lower part of the sternum, and the cartilages of the lower true ribs, run upward and lateralward; while the middle fibres pass horizontally. They all end in a flat tendon, about 5 cm. broad, which is inserted into the crest of the greater tubercle of the humerus. This tendon con- sists of two laminte, placed one in front of the other, and usually blended together below. The anterior lamina, the thicker, receives the clavicular and the uppermost Fig. 519. — Superficial muscles of the chest and front of the arm. Sternal fibres; they are inserted in the same order as that in which they arise: that is to say, the most lateral of the clavicular fibres are inserted at the upper part of the anterior lamina; the uppermost sternal fibres pass down to the lower part of the lamina which extends as low as the tendon of the Deltoideus and joms with it. The posterior lamina of the tendon receives the attachment of the greater part of the sternal portion and the deep fibres, i. e., those from the costal cartilages. These deep fibres, and particularly those from the lower costal cartilages, ascend the higher, turning backward successively behind the superficial and upper ones, 528 MYOLOGY so that the tendon appears to be twisted. The posterior lamina reaches higher on the humerus than the anterior one, and from it an expansion is given oft" which covers the intertubercular groove and blends with the capsule of the shoulder- joint. From the deepest fibres of this lamina at its insertion an expansion is given off which lines the intertubercular groove, while from the lower border of the tendon a third expansion passes downward to the fascia of the arm. Relations. — The Pectoralis major is in relation by its anterior surface with the integument, the superficial fascia, the Platysma, the anterior and middle supraclavicular nerves, the mamma, and the deep fascia; by its posterior surface, with the sternum, the ribs and costal cartilages, the coracoclavicular fascia, the Subclavius, PectoraUs minor, Serratus anterior, and the Intercostales; it forms the anterior wall of the axillary space, and covers the axillary vessels and nerv^es and the Biceps brachii and Coracobrachialis. Its upper border hes parallel with the Deltoideus, from which it is separated by a sKght interspace in which he the cephaUc vein and deltoid branch of the thoracoacromial artery. Its lower border forms the anterior fold of the axilla, being separated medially from the Latissimus dorsi by a considerable interval; but the two muscles gradually converge toward the lateral part of the space. Dissection. — Detach the Pectoralis major by dividing the muscle along its attachment to the clavicle, and by making a vertical incision through its substance a httle external to its line of attachment to the sternum and costal cartilages. The muscle should then be reflected outward, and its tendon carefully examined. The Pectorahs minor is now exposed, and immediately above it, in the interval between its upper border and the clavicle, a strong fascia, the coraco- clavicular fascia. Coracoclavicular Fascia {fascia coracociavicularis; costocoracoid membrane; clavi- yectoral fascia).- — The coracoclavicular fascia is a strong fascia situated under cover of the clavicular portion of the Pectoralis major. It occupies the interval between the Pectoralis minor and Subclavius, and protects the axillary vessels and nerves. Traced upward, it splits to enclose the Subclavius, and its two layers are attached to the clavicle, one in front of and the other behind the muscle; the latter layer fuses with the deep cervical fascia and wdth the sheath of the axillary vessels. Medially, it blends with the fascia covering the first two intercostal spaces, and is attached also to the first rib medial to the origin of the Subclavius. Laterally, it is very thick and dense, and is attached to the coracoid process. The portion extending from the first rib to the coracoid process is often whiter and denser than the rest, and is sometimes called the costocoracoid ligament. Below this it is thin, and at the upper border of the Pectoralis minor it splits into two layers to invest the muscle; from the lower border of the Pectoralis minor it is continued downward to join the axillary fascia, and lateralward to join the fascia over the short head of the Biceps brachii. The coracoclavicular fascia is pierced by the cephalic vein, thoracoacromial artery and vein, and external anterior thoracic nerve. The Pectoralis minor (Fig. 520) is a thin, triangular muscle, situated at the upper part of the thorax, beneath the Pectoralis major. It arises from the upper margins and outer surfaces of the third, fourth, and fifth ribs, near their cartilage and from the aponeuroses covering the Intercostalis; the fibres pass upward and lateralward and converge to form a flat tendon, which is inserted into the medial border and upper surface of the coracoid process of the scapula. Relations. — By its anterior surface it is in relation with the Pectoralis major, the lateral anterior thoracic ner^'e, and the pectoral branch of the thoracoacromial artery; by its posterior surface, with the ribs, Intercostales, Serratus anterior, the axillary space, and the axillary vessels and brachial plexus of nerves. Its upper border is separated from the clavicle by a narrow tri- angular interval occupied by the coracoclavicular fascia, behind which are the axillary vessels and nerves. Running parallel to the lower border of the muscle is the lateral thoracic artery, and piercing the muscle is the medial anterior thoracic nerve. The Subclavius (Fig. 520) is a small triangular muscle, placed between the clavicle and the first rib. It arises by a short, thick tendon from the first rib and its cartilage at their junction, in front of the costoclavicular ligament; the fleshy MrSCLES OF THE CPPEIi EXTREMITY 529 fibres proceed obliquely ii])war(l and laterahvard, to be inserted into the groove on the under surface of the clavicle between the costoclavicular and conoid ligaments. Relations. — Its deep surface is separated from the first rib by the subclavian vessels and brachial plexus of nerves. Its anterior surface is separated from the Pectoralis major by the coraco- clavicular fascia, which, with the clavicle, forms an osseofibrous sheath for the muscle. The Serratus anterior {Serratus magnus) (Fig. 520) is a thin muscular sheet, situated between the ribs and the scapula at the upper and lateral part of the chest. It arises by fleshy digitations from the outer surfaces and superior borders of the upper eight or nine ribs, and from the aponeuroses covering the intervening Intercostales. Each digitation (except the first) arises from the Radius Fig. 520. — Deep muscles of the chest and front of the arm, with the boundaries of the axilla. corresponding rib ; the first springs from the first and second ribs ; and from the fascia covering the first intercostal space. From this extensive attachment the fibres pass backward, closely applied to the chest-wall, and reach the vertebral border of the scapula, and are inserted into its ventral surface in the following manner. The first digitation is inserted into a triangular area on the ventral surface of the medial angle. The next two digitations spread out to form a thin, triangular sheet, the base of which is directed backward and is inserted into nearly the whole length of the ventral surface of the vertebral border. The lower five or six digita- tions converge to form a fan-shaped mass, the apex of which is inserted, by muscular and tendinous fibres, into a triangular impression on the ventral surface of the inferior angle. The lower four slips interdigitate at their origins with the upper five slips of the Obliquus externus abdominis. 34 530 MYOLOGY Relations.— This muscle is partly covered, in front, by the Pectorales and by the mamma; behind, by the Subscapularis. The axillary vessels and nerves he upon its upper part, while its deep surface rests upon the ribs and Intercostales. Nerves. — The PectoraUs major is supplied by the medial and lateral anterior thoracic nerves; through these ners-es the muscle receives filaments from all the spinal nerves entering into the formation of the brachial plexus; the Pectorahs minor receives its fibres from the eighth cervical and first thoracic nerves through the medial anterior thoracic nerve. The Subclavius is supUed by a filament from the fifth and sixth cervical nerves; the Serratus anterior is supplied by the long thoracic, which is derived from the fifth, sixth, and seventh cervical nerves. Actions. — If the arm has been raised by the Deltoideus, the Pectorahs major will, conjointly with the Latissimus dorsi and Teres major, depress it to the side of the chest. If acting alone, it adducts and draws forward the arm, bringing it across the front of the chest, and at the same time rotates it inward. The Pectoralis minor depresses the point of the shoulder, dra\\Tng the scapula downward and medialward toward the thorax, and throwng the inferior angle back- ward. The Subclavius depresses the shoulder, carrj^mg it downward and fom^ard. When the arms are fixed, all three of these muscles act upon the ribs; drawing them upward and expand- ing the chest, and thus becoming very important agents in forced inspiration. The Serratus anterior, as a whole, carries the scapula forward, and at the same time raises the vertebral border of the bone. It is therefore concerned in the action of pushing. Its lower and stronger fibres move forward the lower angle and assist the Trapezius in rotating the bone at the sternoclavicular joint, and thus assist this muscle in raising the acromion and supporting weights upon the shoulder. It is also an assistant to the Deltoideus in raising the arm, inasmuch as during the action of this latter muscle it fixes the scapula and so steadies the glenoid cavity on which the head of the humerus rotates. After the Deltoideus has raised the arm to a right angle with the trunk, the Serratus anterior and the Trapezius, by rotating the scapula, raise the arm into an almost vertical position. It is possible that when the shoulders are fixed the lower fibres of the Serratus anterior may assist in raising and everting the ribs; but it is not the important inspiratory muscle it was formerly believed to be. Applied Anatomy. — When the Serratus anterior is paralyzed, the vertebral border, and especially the lower angle of the scapula, leave the ribs and stand out prominently on the surface, giving a pecuhar "winged" appearance to the back (p. 309). The patient is unable to raise the arm, and an attempt to do so is followed by a further projection of the lower angle of the scapula from the back of the thorax. m. THE MUSCLES AND FASCLffi OF THE SHOULDER. In this group are included: Deltoideus. Infraspinatus. Subscapularis. Teres minor. Supraspinatus. Teres major. Dissection. — ^After completing the dissection of the axilla, if the muscles of the back have been dissected, the upper extremity should be separated from the trunk. Saw through the clavicle at its centre, and then cut through the muscles which connect the scapula and arm with the trunk — viz., the Pectoralis minor in front, Serratus anterior at the side, and the Levator anguli, the Pvhomboideus, Trapezius, and Latissimus dorsi behind. These muscles should be cleaned and traced to their respective insertions. Then make an incision through the integu- ment, commencing at the outer third of the clavicle, and extending along the margin of that bone, the acromion process, and spine of the scapula; the integument should be dissected from above downward and outward, when the fascia covering the Deltoideus will be exposed (Fig. 518, No. 3). Deep Fascia. — The deep fascia covering the Deltoideus invests the muscle, and sends numerous septa between its fasciculi. In front it is continuous with the fascia covering the Pectoralis major; behind, where it is thick and strong, with that covering the Infraspinatus; above, it is attached to the clavicle, the acromion, and the spine of the scapula; below, it is continuous with the deep fascia of the arm. The Deltoideus {Deltoid muscle) (Fig. 519) is a large, thick, triangular muscle, which covers the shoulder- joint in front, behind, and laterally. It arises from the anterior border and upper surface of the lateral third of the clavicle; from the lateral margin THE MUSCLES AXD FASCLE OF THE SHOULDER 531 and upper surface of the acromion, and from the knver lip of the posterior border of the spine of the scapula, as far back as the triangular surface at its medial end. From this extensive origin the fibres converge toward their insertion, the middle passing vertically, the anterior obliquely backward and lateralward, the posterior obliquely forward and lateralward; they unite in a thick tendon, which is inserted into the deltoid prominence on the middle of the lateral side of the body of the humerus. At its insertion the muscle gives off an expansion to the deep fascia of the arm. This muscle is remarkably coarse in texture, and the arrangement of its fibres is somewhat peculiar; the central portion of the muscle— that is to say, the part arising from the acromion — consists of oblique fibres; these arise in a bipenniform manner from the sides of the tendinous intersections, generally four in number, which are attached above to the acromion and pass downward parallel to one another in the substance of the muscle. The oblique fibres thus formed are inserted into similar tendinous intersections, generally three in number, which pass upward from the insertion of the muscle and alternate with the descending septa. The portions of the muscle arising from the clavicle and spine of the scapula are not arranged in this manner, but are inserted into the margins of the inferior tendon. Relations. — The Deltoideus is in relation by its superficial surface with the integument, the superficial and deep fasciae, Platysma, and posterior supraclavicular nerves. Its deep surface is separated from the capsule of the shoulder-joint by a large bursa, and covers the coracoid process, coracoacromial hgament, Pectoralis minor, Coracobrachialis, both heads of the Biceps brachii, the tendon of the Pectorahs major, the insertions of the Supraspinatus, Infraspmatus, and Teres minor, the long and lateral heads of the Triceps brachii, the humeral circvunflex vessels, the axillary nerve, and the upper part of the body of the hmnerus. Its anterior border is separated at its upper part from the Pectorahs major by a narrow interval, which lodges the cephahc vein and deltoid branch of the thoracoacromial artery; lower down the two muscles are in close contact. Its posterior border rests on the Infraspinatus and Triceps. Nerves. — The Deltoideus is supphed by the fifth and sixth cervical through the axiUary nerve. Actions. — The Deltoideus raises the arm from the side, so as to bring it at right angles with the trunk. Its anterior fibres, assisted by the Pectorahs major, draw the arm forward; and its posterior fibres, aided by the Teres major and Latissimus dorsi, draw it backward. Applied Anatomy.^The Deltoideus is very hable to atroph}-, and ua this condition dislocation of the shoulder-joints is simulated, as there is flattening of the shoulder and apparent prominence of the acromion; the distance also between the acromion and the head of the bone is mcreased, and the tips of the fingers can be mserted between them. Atrophy of the Deltoideus may be due to disuse, such as follows chronic arthritis or permanent injm-y of the shoulder-jomt. It also frequently results from degenerations occurring in the medulla spmahs, or injury to the axiUary nerve ("crutch palsy"). The Deltoideus, Supraspinatus, and Infraspinatus often escape in myopathic atrophies affectmg the other muscles of the upper arm or shoulder in yoimg persons. Dissection. — Divide the Deltoideus across, near its upper part, by an incision carried along the margin of the clavicle, the acromion process and spine of the scapula, and reflect it do^Tiward, when the structm-es under cover of it will be seen. Subscapular Fascia (fascia subscapularis) . — The subscapular fascia is a thin membrane attached to the entire circumference of the subscapular fossa, ^and affording attachment by its deep surface to some of the fibres of the Sub- scapularis. The Subscapularis (Fig. 520) is a large triangular muscle which fills the sub- scapular fossa, and arises from its medial two-thirds and from the lower two- thirds of the groove on the axillary border of the bone. Some fibres arise from tendinous laminae which intersect the muscle and are attached to ridges on the bone; others from an aponeurosis, which separates the muscle from the Teres major and the long head of the Triceps brachii. The fibres pass lateralward, and, gradually converging, end in a tendon which is inserted into the lesser tubercle of the humerus and the front of the capsule of the shoulder-joint. The tendon of the muscle is separated from the neck of the scapula by a large bursa, which communicates with the cavity of the shoulder-joint through an aperture in the capsule. 532 MYOLOGY Relations. — The milerlor surface of this inusclu forms a considerable part of the posterior wall of the axilla, and is in relation with the Serratus anterior, Coracobrachialis, and Biceps brachii, the axillary vessels and brachial plexus of nerves, and the subscapular vessels and nerves. Its posterior surface is in relation with the scapula and the capsule of the shoulder-joint. Its lower border is in contact with the Teres major and Latissimus dorsi. Nerves. — The Subscapularis is supplied by the fifth and sixth cervical nerves througli the upper and lower subscapular nerves. Actions. — The Subscapularis rotates the head of the humerus inward; when the arm is raised, it draws the humerus forward and downward. It is a powerful defence to the front of the shoulder- joint, preventing displacement of the head of the humerus. Dissection. — To expose these muscles, and to examine their insertion into the humerus, detach the Deltoideus and Trapezius from their attachment to the spine of the scapula and acromion process. Remove the clavicle by dividing the ligaments connecting it with the coracoid process, and separate it at its articulation with the scapula; divide the acromion process near its root with a saw. The fragments being removed, the tendons of the posterior Scapular muscles will be fully exposed. A block should be placed beneath the shoulder-joint, so as to make the muscles tense. Fig. 521. — Muscles on the dorsum of the scapula, and the Triceps brachii. Supraspinatous Fascia (fascia supraspinata) . — The supraspinatous fascia com- pletes the osseofibrous case in which the Supraspinatus muscle is contained; it affords attachment, by its deep surface, to some of the fibres of the muscle. It is thick medially, but thinner laterally under the coracoacromial ligament. ]]3The Supraspinatus (Fig. 521) occupies the whole of the supraspinatous fossa, arising from its medial two-thirds, and from the strong supraspinatous fascia. The muscular fibres converge to a tendon, which crosses the upper part of the shoulder-joint, and is inserted into the highest of the three impressions on the greater tubercle of the humerus ; the tendon is intimately adherent to the capsule of the shoulder-joint. THE MUSCLES AND FASCI.E OF THE ARM 533 Infraspinatous Fascia { fascia, 'nifrasphiaia). — The int'raspinatous fascia is a dense fibrous iiu'inhraiu', coNering the Infraspinatous niuscU' and fixed to the circumfer- ence of the infras])inatous fossa; it affords attachment, by its deep surface, to some fibres of that muscle. It is intimately attached to the deltoid fascia along the over- lapping border of the Deltoideus. The Infraspinatus (Fig. 021) is a thick triangular muscle, which occupies the chief part of the infraspinatous fossa; it arises by fleshy fibres from its medial two- thirds, and by tendinous fibres from the ridges on its surface; it also arises from the infraspinatous fascia which covers it, and separates it from the Teretes major and minor. The fibres converge to a tendon, which glides over the lateral border of the spine of the scapula, and, passing across the posterior part of the capsule of the shoulder-joint, is inserted into the middle impression on the greater tubercle of the humerus. The tendon of this muscle is sometimes separated from the capsule of the shoulder-joint by a bursa, which may communicate with the joint cavity. The Teres minor (Fig. 521) is a narrow, elongated muscle, which arises from the dorsal surface of the axillary border of the scapula for the upper two-thirds of its extent, and from two aponeurotic laminae, one of which separates it from the Infraspinatus, the other from the Teres major. Its fibres run obliquely upward and lateralward; the upper ones end in a tendon which is inserted into the lowest of the three impressions on the greater tubercle of the humerus; the lowest fibres are inserted directly into the humerus immediately below this impression. The tendon of this muscle passes across, and is united with, the posterior part of the capsule of the shoulder-joint. The Teres major (Fig. 521) is a thick but somewhat flattened muscle, which arises from the oval area on the dorsal surface of the inferior angle of the scapula, and from the fibrous septa interposed between the muscle and the Teres minor and Infraspinatus; the fibres are directed upward and lateralward, and end in a flat tendon, about 5 cm. long, which is inserted into the crest of the lesser tubercle of the humerus. The tendon, at its insertion, lies behind that of the Latissimus dorsi, from which it is separated by a bursa, the two tendons being, however, united along their lower borders for a short distance. Nerves. — The Supraspinatus and Infraspinatus are supplied by the fifth and sixth cervical nerves through the suprascapular nerve; the Tei'es minor, by the fifth cervical, through the axillary; and the Teres major, by the fifth and sixth cervical, through the lowest subscapular. Actions. — The Supraspinatus assists the Deltoideus in raising the arm from the side of the trunk and fixes the head of the humerus in the glenoid cavity. The Infraspinatus and Teres minor rotate the head of the humerus outward; they also assist in carrying the arm backward. One of the most important uses of these three muscles is to protect the shoulder-joint, the Supra- spinatus supporting it above, and the Infraspinatus and Teres minor behind. The Teres major assists the Latissimus dorsi in drawing the previously raised humerus downward and backward, and in rotating it inward ; when the arm is fixed it may assist the Pectorales and the Latissimus dorsi in drawing the trunk forward. IV. THE MUSCLES AND FASCIA OF THE ARM. The muscles of the arm are : Coracobrachialis. Brachialis. Biceps brachii. Triceps brachii. Dissection. — The arm being placed on the table, with the front surface uppermost, make a vertical incision through the integument along the middle hue, from the clavicle to about two inches below the elbow-joint, where it should be joined bj^ a transverse incision, extending from the inner to the outer side of the forearm; the two flaps being reflected on either side, the fascia should be examined (Fig. 518). 534 MYOLOGY Brachial Fascia (fascia brachil; deep fascia of the arm). — The brachial fascia is continuous with that covering the Deltoideus and the Pectoralis major, by means of which it is attached, above, to the clavicle, acromion, and spine of the scapula; it forms a thin, loose, membranous sheath for the muscles of the arm, and sends septa between them; it is composed of fibres disposed in a. circular or spiral direc- tion, and connected together by vertical and oblique fibres. It differs in thickness at different parts, being thin over the Biceps brachii, but thicker where it covers the Triceps brachii, and over the epicondyles of the humerus: it is strengthened by fibrous aponeuroses, derived from the Pectoralis major and Latissimus dorsi medially, and from the Deltoideus laterally. On either side it gives oif a strong intermuscular septum, which is attached to the corresponding supracondylar ridge and epicondyle of the humerus. The lateral intermuscular septum extends from the lower part of the crest of the greater tubercle, along the lateral supra- condylar ridge, to the lateral epicondyle; it is blended with the tendon of the Del- toideus, gives attachment to the Triceps brachii behind, to the Brachialis, Brachio- radialis, and Extensor carpi radialis longus in front, and is perforated by the radial nerve and profunda branch of the brachial artery. The medial intermuscular septum, thicker than the preceding, extends from the lower part of the crest of the lesser tubercle of the humerus below the Teres major, along the medial supra- condylar ridge to the medial epicondyle; it is blended with the tendon of the Coracobrachialis, and affords attachment to the Triceps brachii behind and the Brachialis in front. It is perforated by the ulnar nerve, the superior ulnar collateral artery, and the posterior branch of the inferior ulnar collateral artery. At the elbow, the deep fascia is attached to the epicondyles of the humerus and the olecranon of the ulna, and is continuous with the deep fascia of the forearm. Just below the middle of the arm, on its medial side, is an oval opening in the deep fascia, which transmits the basilic vein and some lymphatic vessels. The Coracobrachialis (Fig. 520), the smallest of the three muscles in this region, is situated at the upper and medial part of the arm. It arises from the apex of the coracoid process, in common with the short head of the Biceps brachii, and from the intermuscular septum between the two muscles; it is inserted by means of a flat tendon into an impression at the middle of the medial surface and border of the body of the humerus between the origins of the Triceps brachii and Brachialis. It is perforated by the musculocutaneous nerve. Relations. — The Coracobrachialis is in relation, in front, with the Pectoralis major above, and at its insertion with the brachial vessels and median nerve which cross it; behind, with the tendons of the Subscapularis, Latissimus dorsi, and Teres major, the medial head of the Triceps brachii, the hmnerus, and the anterior humeral circumflex vessels; by its medial border, with the third part of the axillary and upper part of the brachial artery and the median and musculo- cutaneous nerves; by its lateral border, with the short head of the Biceps brachii and Brachialis. The Biceps brachii (Biceps; Biceps flexor cuhiti) (Fig. 520) is a long fusiform muscle, placed on the front of the arm, and arising by two heads, from which circumstance it has received its name. The short head arises by a thick flattened tendon from the apex of the coracoid process, in common with the Coracobrachialis. The long head arises from the supraglenoid tuberosity at the upper margin of the glenoid cavity, and is continuous with the glenoidal labrum. This tendon, enclosed in a special sheath of the synovial membrane of the shoulder-joint, arches over the head of the humerus; it emerges from the capsule through an opening close to the humeral attachment of the ligament, and descends in the intertubercular groove; it is retained in the groove by the transverse humeral ligament and by a fibrous prolongation from the tendon of the Pectoralis major. Each tendon is succeeded by an elongated muscular belly, and the two bellies, although closelj'' applied to each other, can readily be separated until within about 7.5 cm, of the elbow-joint. Here they end in a flattened tendon, which is inserted into the rough THE MUSCLES AXD FASCLE OF THE ARM 535 posterior portion of the tuberosity of the radius, a bursa being interposed between the tendon and the front part of the tuberosity. As the tendon of the muscle approaches the radius it is twisted upon itself, so that its anterior surface becomes lateral and is applied to the tuberosity of the radius at its insertion. Opposite the bend of the elbow the tendon gives off, from its medial side, a broad aponeu- rosis, the lacertus fibrosus (bicipital fascia) which passes obliquely downward and medialward across the brachial artery, and is continuous with the deep fascia covering the origins of the Flexor muscles of the forearm (Fig. 519). A third head to the Biceps brachii is occasionally found, arising at the upper and medial part of the Brachialis, with the fibres of which it is continuous, and inserted into the lacertus fibrosus and medial side of the tendon of the muscle. In most cases this additional slip hes behind the brachial arterj"- in its course down the arm. In some instances the third head consists of two slips, which pass down, one in front of and the other behind the arterj^ concealing the vessel in the lower half of the arm. Relations. — The Biceps brachii is overlapped above bj' the Pectorahs major and Deltoideus; in the rest of its extent it is covered by the superficial and deep fasciae and the integument. It rests above on the shoulder-joint and upper part of the humei'us; below, it lies on the Brachiahs, the musculocutaneous nerve, and the Supinator. Its medial border is in relation with the Coraco- brachialis, and overlaps the brachial vessels and median nerve; its lateral border, with the Del- toideus and Brachioradialis. The Brachialis (Brachialis anficus) (Fig. 520) covers the front of the elbow-joint and the lower half of the humerus. It arises from the lower half of the front of the humerus, commencing above at the insertion of the Deltoideus, which it embraces by two angular processes. Its origin extends below to within 2.5 cm. of the margin of the articular surface. It also arises from the intermuscular septa, but more extensively from the medial than the lateral; it is separated from the lateral below by the Brachioradialis and Extensor carpi radialis longus. Its fibres converge to a thick tendon, which is inserted into the tuberosity of the ulna and the rough depression on the anterior surface of the coronoid process. Relations. — The Brachiahs is in relation, in front, with the Biceps brachii, the brachial vessels, musculocutaneous and median nerves; behind, with the humerus and front of the elbow-joint; by its medial border, with the Triceps brachii, ulnar nerve, and Pronator' teres, from which it is separated by the intermuscular septum: by its lateral border, with the radial nerve, radial recurrent artery, the Brachioradialis and Extensor carpi radiahs longus. Nerves. — -The Coracobrachiahs, Biceps brachii and Brachiahs are supphed by the musculo- cutaneous nerve; the Brachiahs usually receives an additional filament from the radial. The Coracobrachiahs receives its supply primarily from the seventh cervical, the Biceps brachii and Brachialis from the fifth and sixth cervical nerves. Actions. — The Coracobrachiahs draws the himierus forward and medialward, and at the same time assists in retaining the head of the bone in contact- with the glenoid ca^^ty. The Biceps brachii is a flexor of the elbow and, to a less extent, of the shoulder; it is also a powerful supinator, and serves to render tense the deep fascia of the forearm by means of the lacertus fibrosus given off from its tendon. The Brachialis is a flexor of the forearm, and forms an impor- tant defence to the elbow-joint. T\Tien the forearm is fixed, the Biceps brachii and Brachiahs flex the arm upon the forearm, as in efforts of climbing. Applied Anatomy. — The long tendon of the Biceps brachii is sometimes dislocated from the intertubercular groove. ^Tien this has taken place, the arm is fixed in a position of abduction, but the head of the humerus can be felt in its proper position. It can general!}' be replaced by flexing the forearm on the arm and rotatiag the hmb. Rupture of the long tendon of the Biceps brachii may also take place. The Triceps brachii (Triceps; Triceps extensor cubiti) (Fig. 521) is situated on the back of the arm, extending the entire length of the dorsal surface of the humerus. It is of large size, and arises by three heads (long, lateral, and medial), hence its name. The long head arises by a flattened tendon from the infraglenoid tuberosity of the scapula, being blended at its upper part with the capsule of the shoulder- joint; the muscular fibres pass downward between the two other heads of the muscle, and join with them in the tendon of insertion. 536 MYOLOGY The lateral head arhes from the posterior surface of the body of the humerus, between the insertion of the Teres minor and the upper part of the groove for the radial nerve, and from the lateral border of the humerus and the lateral intermus- cular septum; the fibres from this origin converge toward the tendon of insertion. The medial head arises from the posterior surface of the body of the humerus, below the groove for the radial nerve; it is narrow and pointed above, and extends from the insertion of the Teres major to within 2.5 em. of the trochlea: it also arises from the medial border of the humerus and from the back of the whole length of the medial intermuscular septum. Some of the fibres are directed downward to the olecranon, while others converge to the tendon of insertion. The tendon of the Triceps brachii begins about the middle of the muscle: it con- sists of two aponeurotic laminae, one of which is subcutaneous and covers the back of the lower half of the muscle; the other is more deeply seated in the substance of the muscle. After receiving the attachment of the muscular fibres, the two lamellae join together above the elbow, and are inserted, for the most part, into the posterior portion of the upper surface of the olecranon; a band of fibres is, however, continued downward, on the lateral side, over the Anconaeus, to blend with the deep fascia of the forearm. The long head of the Triceps brachii descends between the Teres minor and Teres major, dividing the triangular space between these two muscles and the humerus into two smaller spaces, one triangular, the other quadrangular (Fig. 521). The triangular space contains the scapular circumflex vessels; it is bounded by the Teres minor above, the Teres major below, and the scapular head of the Triceps laterally. The quadrangular space transmits the posterior humeral circumflex vessels and the axillary nerve; it is bounded by the Teres minor and capsule of the shoulder-joint above, the Teres major below, the long head of the Triceps brachii medially, and the humerus laterally. The Subanconaeus is the name given to a few fibres which spring from the deep surface of the lower part of the Triceps brachii, and are inserted into the posterior ligament and synovial membrane of the elbow-joint. Nerves. — The Triceps brachii is supplied by the seventh and eighth cervical nerves through the radial nerve. Actions. — The Triceps brachii is the great extensor muscle of the forearm, and is the direct antagonist of the Biceps brachii and Brachiahs. When the arm is extended, the long head of the muscle may assist the Teres major and Latissimus dorsi in drawing the humerus backward and in adducting it to the thorax. The long head supports the under part of the shoulder-joint. The Subanconaeus draws up the synovial membrane of the elbow-joint during extension of the forearm. Applied Anatomy. — The continuity of the insertion of the Triceps brachii with the deep fascia of the forearm is of importance in the operation of excision of the elbow; it should always be carefuUy preserved from injury. By means of these fibres the patient is enabled to extend the forearm, a movement which would otherwise be accomphshed mainly by gravity — that is to say, by allowing the forearm to drop by its own weight. V. THE MUSCLES AND FASCI.ffi OF THE FOREARM. Dissection. — To dissect the forearm, place the hmb in the position indicated in Fig. 518, make a vertical incision along the middle line from the elbow to the wrist, and a transverse incision at the extremity of this; the superficial structures being removed, the deep fascia of the forearm is exposed. Antibrachial Fascia {fascia antibrachii; deep fascia of the forearm). — The anti- brachial fascia continuous above with the brachial fascia, is a dense, membranous investment, which forms a general sheath for the muscles in this region; it is at- tached, behind, to the olecranon and dorsal border of the ulna, and gives off from its deep surface numerous intermuscular septa, which enclose each muscle separately. Over the Flexor tendons as they approach the wrist it is especially thickened, and forms the volar carpal ligament. This is continuous with the transverse carpal liga- ment, and forms a sheath for the tendon of the Palmaris longus which passes over the transverse carpal ligament to be inserted into the palmar aponeurosis. Behind, THE VOLAR AST I BRACHIAL MUSCLES 537 near the wrist-joint, it is thickened by the addition of many transverse fibres, and forms the dorsal carpal ligament. It is mnch thicker on the dorsal than on the volar snrface, and at the lower than at the nj)per i)art of the forearm, and is strengthened above by tendinons hbres derived from the Biceps brachii in front, and from the Triceps brachii behind. It gives origin to muscular fibres, especially at the upper part of the medial and lateral sides of the forearm, and forms the boundaries of a series of cone-shaped cavities, in which the muscles are contained. Besides the vertical septa separating the indi\idiial muscles, transverse septa are given off both on the volar and dorsal surfaces of the forearm, separating the deep from the superficial layers of muscles. Apertures exist in the fascia for the passage of vessels and nerves; one of these apertures of large size, situated at the front of the elbow, serves for the passage of a communicating branch between the superficial and deep veins. The antibrachial or forearm muscles may be divided into a volar and a dorsal group. 1. The Volar Antibrachial Muscles. These muscles are divided for convenience of description into two groups, superficial and deep. The Superficial Group (Fig. 522). Pronator teres. Palmaris longus. Flexor carpi radialis. Flexor carpi ulnaris. Flexor digitorum sublimis. The muscles of this group take origin from the medial epicondyle of the humerus by a common tendon; they receive additional fibres from the deep fascia of the fore- arm near the elbow, and from the septa which pass from this fascia between the individual muscles. The Pronator teres has two heads of origin — humeral and ulnar. The humeral head, the larger and more superficial, arises immediately above the medial epi- condyle, and from the tendon common to the origin of the other muscles; also from the intermuscular septum between it and the Flexor carpi radialis and from the antibrachial fascia. The ulnar head is a thin fasciculus, w^hich arises from the medial side of the coronoid process of the ulna, and joins the preceding at an acute angle. The median nerve enters the forearm between the two heads of the muscle, and is separated from the ulnar artery by the ulnar head. The muscle passes ob- liquely across the forearm, and ends in a flat tendon, which is inserted into a rough impression at the middle of the lateral surface of the body of the radius. The lateral border of the muscle forms the medial boundary of a triangular hollow situated in front of the elbow-joint and containing the brachial artery, median nerve, and tendon of the Biceps brachii. Applied Anatomy. — This muscle, when suddenly brought into active use, as in the game of lawn tennis, is apt to be strained, producing shght swelling, tenderness, and pain on putting the muscle, into action. This is known as "lawn-tennis arm." The Flexor carpi radialis lies on the medial side of the preceding muscle. It arises from the medial epicondyle by the common tendon; from the fascia of the forearm; and from the intermuscular septa between it and the Pronator teres laterally, the Palmaris longus medially, and the Flexor digitorum sublimis beneath. Slender and aponeurotic in structure at its commencement, it increases in size, and ends in a tendon which forms rather more than the lower half of its length. This tendon passes through a canal in the lateral part of the transverse carpal ligament and runs through a groove on the greater multangular bone; the groove is converted into a canal by fibrous tissue, and lined by a mucous sheath. The ten- don is inserted into the base of the second metacarpal bone, and sends, a slip to 538 MYOLOGY the base of the third metacarpal bone. The radial artery, in the lower part of the forearm, lies between the tendon of this muscle and the Brachioradialis. The Palmaris longus is a slender, fusiform muscle, lying on the medial side of the preceding. It arises from the medial epicondyle of the humerus by the common tendon, from the inter- muscular septa between it and the adjacent muscles, and from the anti- brachial fascia. It ends in a slender, Fig. 522. — Front of the left forearm, muscles. Superficial Fig. 523.— Front of the left forearm. Deep muscles. THE VOLAR AXTIBRACHIAL MUSCLES 539 flattened tendon, which passes over the upper part of the transverse carpal liga- ment, and is iri'^oied into the central part of the transverse carpal ligament and lower part of the palmar aponeurosis, frequently sending a tendinous slip to the short muscles of the thmnb. This muscle is often absent, and is subject to very considerable variations; it may be tendinous above and muscular below; or it may be muscular in the centre with a tendon above and below; or it may present two muscular bundles with a central tendon; or finally it may consist solely of a tendinous band. Just above the wrist, the median nerve lies close to the tendon, on its lateral and dorsal aspects. The Flexor carpi ulnaris lies along the ulnar side of the forearm. It arises by two heads, humeral and ulnar, connected by a tendinous arch, beneath which the ulnar nerve and posterior ulnar recurrent artery pass. The humeral head arises from the medial epicondyle of the humerus by the common tendon; the ulnar head arises from the medial margin of the olecranon and from the upper two-thirds of the dorsal border of the ulna by an aponeurosis, common to it and the Extensor carpi ulnaris and Flexor digitorum profundus ; and from the intermuscular septum between it and the Flexor digitorum sublimis. The fibres end in a tendon, which occupies the anterior part of the lower half of the muscle and is inserted into the pisiform bone, and is prolonged from this to the hamate and fifth metacarpal bones by the pisohamate and pisometacarpal ligaments; it is also attached by a few fibres to the transverse carpal ligament. The ulnar vessels and nerve lie on the lateral side of the tendon of this muscle, in the lower two-thirds of the forearm. The Flexor digitorum sublimis is placed beneath the previous muscle; it is the largest of the muscles of the superficial group, and arises by three heads — • humeral, ulnar, and radial. The humeral head arises from the medial epicondyle of the humerus by the common tendon, from the ulnar collateral ligament of the elbow-joint, and from the intermuscular septa between it and the preceding muscles. The ulnar head arises from the medial side of the coronoid process, above the ulnar origin of the Pronator teres (see Fig. 353, page 316). The radial head arises from the oblique line of the radius, extending from the radial tuberosity to the insertion of the Pronator teres. The muscle speedily separates into two planes of muscular fibres, superficial and deep: the superficial plane divides into two parts which end in tendons for the middle and ring fingers; the deep plane gives off a muscular slip to join the portion of the superficial plane which is asso- ciated with the tendon of the ring finger, and then divides into two parts, which end in tendons for the index and little fingers. As the four tendons thus formed pass beneath the transverse carpal ligament into the palm of the hand, they are arranged in pairs, the superficial pair going to the middle and ring fingers, the deep pair to the index and little fingers. The tendons diverge from one another in the palm and form dorsal relations to the superficial volar arch and digital branches of the median and ulnar nerves. Opposite the bases of the first phalanges each tendon divides into two slips to allow of the passage of the corresponding tendon of the Flexor digitorum profundus ; the two slips then reunite and form a grooved channel for the reception of the accompanying tendon of the Flexor digitorum profundus. Finally the tendon divides and is inserted into the sides of the second phalanx about its middle. The Deep Group (Fig. 523). Flexor digitorum profundus. Flexor pollicis longus. Pronator quadratus. Dissection. — Divide each of the superficial muscles at its centre, and turn either end aside; the deep layer of muscles, together with the median nerve and ulnar vessels, will then be exposed. 540 MYOLOGY The Flexor digitorum profundus is situated on the uhiar side of the forearm, immediately beneath the superficial Flexors. It arises from the upper three- fourths of the volar and medial surfaces of the body of the ulna, embracing the insertion of the Brachialis above, and extending below to within a short distance of the Pronator quadratus. It also arises from a depression on the medial side of the coronoid process; by an aponeurosis from the upper three-fourths of the dorsal border of the ulna, in common with the Flexor and Extensor carpi ulnaris; and from the ulnar half of the interosseous membrane. The muscle ends in four tendons which run under the transverse carpal ligament dorsal to the tendons of the Flexor digitorum sublimis. Opposite the first phalanges the tendons pass through the openings in the tendons of the Flexor digitorum sublimis, and are finally inserted into the bases of the last phalanges. The portion of the muscle for the index finger is usually distinct throughout, but the tendons for the middle, ring, and little fingers are connected together by areolar tissue and tendinous slips, as far as the palm of the hand. Fibrous Sheaths of the Flexor Tendons. — After leaving the palm, the tendons of the Flexores digitorum sublimis and profundus lie in osseo-aponeurotic canals (Fig. 534), formed behind by the phalanges and in front by strong fibrous bands, which arch across the tendons, and are attached on either side to the margins of the phalanges. Opposite the middle of the proximal and second phalanges the bands (digital vaginal ligaments) are very strong, and the fibres are transverse; but opposite the joints they are much thinner, and consist of annular and cruciate ligamentous fibres. Each canal contains a mucous sheath, which is reflected on the contained tendons. Within each canal the tendons of the Flexores digitorum sublimis and profundus are connected to each other, and to the phalanges, by slender, tendinous bands, called vincula tendina (Fig. 524). There are two sets of these; {a) the vincula brevia, which are two in number in each finger, and consist of triangular bands of fibres, one connecting the tendon of the Flexor digitorum sublimis to the front of the first interphalangeal joint and head of the first phalanx, and the other the tendon of the Flexor digitorum profundus to the front of the second interphalan- geal joint and head of the second phalanx; (6) the vincula longa, which connect the under surfaces of the tendons of the Flexor digitorum profundus to those of the subjacent Flexor sublimis after the tendons of the former have passed through the latter. Four small muscles, the Lumbricales, are connected with the tendons of the Flexor profundus in the palm. They will be described with the muscles of the hand (page 555). The Flexor poUicis longus is situated on the radial side of the forearm, lying in the same plane as the preceding. It arises from the grooved volar surface of the body of the radius, extending from immediately below the tuberosity and oblique line to within a short distance of the Pronator quadratus. It arises also from the adjacent part of the interosseous membrane, and generally by a fleshy slip from the medial border of the coronoid process, or from the medial epicondyle of the humerus. The fibres end in a fiattened tendon, which passes beneath the transverse carpal ligament, is then lodged between the lateral head of the Flexor pollicis brevis and the oblique part of the Adductor pollicis, and, entering an osseo- aponeurotic canal similar to those for the Flexor tendons of the fingers, is inserted into the base of the distal phalanx of the thumb. The volar interosseous nerve and vessels pass downward on the front of the interosseous membrane between the Flexor pollicis longus and Flexor digitorum profundus. The Pronator quadratus is a small, flat, quadrilateral muscle, extending across the front of the lower parts of the radius and ulna. It arises from the pronator ridge on the lower part of the volar surface of the body of the ulna; from the medial THE VOLAR AXTIBRACIIIAL MUSCLES 541 part of the volar surface of the h)\ver fourtli of the ulna; and from a strong apon- eurosis which covers the medial third of the muscle. The fibres pass laterahvard and slightly downward, to be inserted into the lower fourth of the lateral border and the volar surface of the body of the radius. The deeper fibres of the muscle are inserted into the triangular area above the ulnar notch of the radius — an attachment comparable with the origin of the Supinator from the triangular area below the radial notch of the ulna. Tendon of Exi. carpi nid. longus Tendon of Ext. digitormn communis Tendon of Extensor indici pro prills First Lumbrical Tendon of Abditctor poll ids longus Greater midtetngideir hone Radial artery 1 Tendon of Ext. pollicis hrevis , W4 I t ///// Li I i,\ -H — Tendon of Ext. pollicis longus '/// Vincula brevia / V \ ^ 1 [p. -% /J~r~\ \ Flexor d, digitorum sublimis Flexor digitorum profundus Vincula longa Fig. 524. — Tendons of forefinger and vincula tendina Nerves. — All the muscles of the superficial layer are suppHed by the median nerve, excepting the Flexor carpi ulnaris, which is supphed by the ulnar. The Pronator teres, the Flexor carpi radiahs, and the Palmaris longus derive their supply primarily from the sixth cervical nerve; the Flexor digitorum sublimis from the seventh and eighth cervical and first thoracic nerves, and the Flexor carpi ulnaris from the eighth cervical and first thoracic. Of the deep layer, the Flexor digitorum profundus is supplied by the eighth cervical and first thoracic through the ulnar, and the volar interosseous branch of the median. The Flexor pollicis longus and Pronator quadratus are supplied by the eighth cervical and first thoracic through the volar interosseous branch of the median. Actions. — These muscles act upon the forearm, the wi'ist, and hand. The Pronator teres rotates the radius upon the ulna, rendering the hand prone; when the radius is fixed, it assists in flexing the forearm. The Flexor carpi radiahs is a flexor and abductor of the wrist; it also assists in pronating the hand, and in bending the elbow. The Flexor carpi ulnaris is a flexor and adductor of the wrist; it also assists in bending the elbow. The Palmaris longus is a flexor of the wrist-joint; it also assists in flexing the elbow. The Flexor digitorum subhmis flexes first the middle and then the proximal phalanges; it also assists in flexing the wrist and elbow. The Flexor digitorum profundus is one of the flexors of the phalanges. After the Flexor sublimis has bent the second phalanx, the Flexor profundus flexes the terminal one; but it cannot do so until after the contraction of the superficial muscle. It also assists in flexing the wrist. The 542 MYOLOGY Flexor pollicis longus is a flexor of the phalanges of the thumb; when the thumb is fixed, it assists in flexing the wrist. The Pronator quadratus rotates the radius upon the ulna, rendering the hand prone. 2. The Dorsal Antibrachial Muscles. These muscles are divided for convenience of description into two groups, superficial and deep. The Superficial Group (Fig. 525). Brachioradialis. Extensor digitorum communis. Extensor carpi radialis longus. Extensor digiti quinti proprius. Extensor carpi radialis brevis. Extensor carpi ulnaris. Anconaeus. Dissection. — Divide the integument in the same manner as in the dissection of the volar anti- brachial region, and, after having examined the cutaneous vessels and nerves and deep fascia, remove all those structures. The muscles will then be exposed. The removal of the fascia will be considerably facilitated by detaching it from below upward. Great care should be taken to avoid cutting across the tendons of the muscles of the thumb, which cross obhquely the larger tendons running down the back of the radius. The Brachioradialis {Supinator longus) is the most superficial muscle on the radial side of the forearm. It arises from the upper two-thirds of the lateral supracondylar ridge of the humerus, and from the lateral intermuscular septum, being limited above by the groove for the radial neri^e. Interposed between it and the Brachialis are the radial nerve and the anastomosis between the anterior branch of the profunda artery and the radial recurrent. The fibres end above the middle of the forearm in a flat tendon, which is inserted into the lateral side of the base of the styloid process of the radius. The tendon is crossed near its insertion by the tendons of the Abductor pollicis longus and Extensor pollicis brevis; on its ulnar side is the radial artery. The Extensor carpi radialis longus {Extensor carpi radialis longior) is placed partlj- beneath the Brachioradialis. It arises from the lower third of the lateral supracon- dylar ridge of the humerus, from the lateral intermuscular septum, and by a few filDres from the common tendon of origin of the Extensor muscles of the forearm. The fibres end at the upper third of the forearm in a fiat tendon, which runs along the lateral border of the radius, beneath the Abductor pollicis longus and Extensor pollicis brevis; it then passes beneath the dorsal carpal ligament, where it lies in a groove on the back of the radius common to it and the Extensor carpi radialis brevis, immediately behind the styloid process. It is inserted into the dorsal surface of the base of the second metacarpal bone, on its radial side. The Extensor carpi radialis brevis {Extensor carpi radialis brevior) is shorter and thicker than the preceding muscle, beneath which it is placed. It arises from the lateral epicondyle of the humerus, by a tendon common to it and the three following muscles; from the radial collateral ligament of the elbow-joint; from a strong aponeurosis which covers its surface; and from the intermuscular septa between it and the adjacent muscles. The fibres end about the middle of the forearm in a flat tendon, which is closely connected with that of the preceding muscle, and accompanies it to the wrist; it passes beneath the Abductor pollicis longus and Extensor pollicis brevis, then beneath the dorsal carpal ligament, and is inserted into the dorsal surface of the base of the third metacarpal bone on its radial side. Under the dorsal carpal ligament the tendon lies on the back of the radius in a shallow groove, to the ulnar side of that which lodges the tendon of the Extensor carpi radialis, longus, and separated from it by a faint ridge. The tendons of the two preceding muscles pass through the same compartment of the dorsal carpal ligament in a single mucous sheath. THE DORSAL ANT I BRACHIAL MUSCLES 543 Abductor pollicis longus Ext. poinds brevis Ext. poinds loiKJllS Fig. 525. — Posterior surface of the forearm. Superficial muscles. Fig. 526. — Posterior surface of the forearm. Deep muscles. 544 MYOLOGY The Extensor digitorum communis uriscs from the hiteral epieoiid^le of the humerus, by the common tendon; from the intermuscular septa between it and the adjacent muscles, and from the antibrachial fascia. It divides below into four tendons, which pass, together with that of the Extensor indicis proprius, through a separate compartment of the dorsal carpal ligament, within a mucous sheath. The tendons then diverge on the back of the hand, and are inserted into the second and third phalanges of the fingers in the following manner. Opposite the meta- carpophalangeal articulation each tendon is bound by fasciculi to the collateral ligaments and serves as the dorsal ligament of this joint; after having crossed the joint, it spreads out into a broad aponeurosis, which covers the dorsal surface of the first phalanx and is reinforced, in this situation, by the tendons of the Inter- ossei and Lumbricalis. Opposite the first interphalangeal joint this aponeurosis divides into three slips; an intermediate and two collateral: the former is inserted into the base of the second phalanx; and the two collateral, which are continued onward along the sides of the second phalanx, unite by their contiguous margins, and are inserted into the dorsal surface of the last phalanx. As the tendons cross the interphalangeal joints, they furnish them with dorsal ligaments. The tendon to the index finger is accompanied by the Extensor indicis proprius, which lies on its ulnar side. On the back of the hand, the tendons to the middle, ring, and little fingers are connected by two obliquely placed bands, one from the third tendon passing downward and lateralward to the second tendon, and the other passing from the same tendon downward and medialward to the fourth. Occa- sionally the first tendon is connected to the second by a thin transverse band. The Extensor digit! quinti proprius (Extensor minimi digiti) is a slender muscle placed on the medial side of the Extensor digitorum communis, wdth which it is generally connected. It arises from the common Extensor tendon by a thin tendinous slip, from the intermuscular septa between' it and the adjacent muscles. Its tendon runs through a compartment of the dorsal carpal ligament behind the distal radio-ulnar joint, then divides into two as it crosses the hand, and finally joins the expansion of the Extensor digitorum communis tendon on the dorsum of the first phalanx of the little finger. The Extensor carpi ulnaris lies on the ulnar side of the forearm. It arises from the lateral epicondyle of the humerus, by the common tendon; by an aponeu- rosis from the dorsal border of the ulna in common with the Flexor carpi ulnaris and the Flexor digitorum profundus; and from the deep fascia of the forearm. It ends in a tendon, which runs in a groove between the head and the styloid process of the ulna, passing through a separate compartment of the dorsal carpal ligament, and is inserted into the prominent tubercle on the ulnar side of the base of the fifth metacarpal bone. The Anconaeus is a small triangular muscle which is placed on the back of the elbow-joint, and appears to be a continuation of the Triceps brachii. It arises by a separate tendon from the back part of the lateral epicondyle of the humerus ; its fibres diverge and are inserted into the side of the olecranon, and upper fourth of the dorsal surface of the body of the ulna. The Deep Group (Fig. 526). Supinator. Extensor pollicis brevis. Abductor pollicis longus. Extensor pollicis longus. Extensor indicis proprius. The Supinator {Supinator brevis) (Fig. 527) is a broad muscle, curved around the upper third of the radius. It consists of two planes of fibres, between which the deep branch of the radial nerve lies. The two planes arise in common^the superficial one by tendinous and the deeper by muscular fibres — from the lateral THE DORSAL AST 1 BRACHIAL MLSCLES 545 epicoiidyle of tlic Iuuiktus; from tlie radial collateral ligament of the elbow-joint, and the annular liuanient; from the ridge on the ulna, whieh runs obliquely down- ward from the dorsal end of the radial notch; from the triangular depression })elow the notch; and from a tendinous expansion which covers the surface of the muscle. The superficial fibres surround the upper part of the radius, and are inserted into the lateral edge of the radial tuberosity and the oblique line of the radius, as low down as the insertion of the Pronator teres. The upper fibres of the deeper plane form a sling-like fasciculus, which encircles the neck of the radius above the tuber- osity and is attached to the back part of its medial surface; the greater part of this portion of the muscle is inserted into the dorsal and lateral surfaces of the body of the radius, midway between the oblique line and the head of the bone. The Abductor pollicis longus (Ex- tensor OSS. nietacarpi poUicis) lies im- mediately below the Supinator and is sometimes united with it. Is arises from the lateral part of the dorsal surface of the body of the ulna below the insertion of the Anco- naeus, from the interosseous mem- brane, and from the middle third of the dorsal surface of the body of the radius. Passing obliquely downward and lateralward, it ends in a tendon, which runs through a groove on the lateral side of the lower end of the radius, accompanied by the tendon of the Extensor pollicis brevis, and is inserted into the radial side of the base of the first metacarpal bone. It occasionally gives ofi^ two slips near its insertion: one to the greater multangular bone and the other to . blend with the origin of the Abduc- tor pollicis brevis. The Extensor pollicis brevis (Ex- tensor primi internodii pollicis) lies on the medial side of, and is- closely connected with, the Abductor pollicis longus. It arises from the dorsal surface of the body of the radius below that muscle, and from the interosseous membrane. Its direction is similar to that of the Abductor pollicis longus, its tendon passing through the same groove on the lateral side of the lower end of the radius, to be inserted into the base of the first phalanx of the thumb. The Extensor pollicis longus {Extensor secundi internodii pjollicis) is much larger than the preceding muscle, the origin of which it partly covers. It arises from the lateral part of the middle third of' the dorsal surface of the body of the ulna below the origin of the Abductor pollicis longus, and from the interosseous mem- brane. It ends in a tendon, which passes through a separate compartment in the dorsal carpal ligament, lying in a narrow, oblique groove on the back of the lower end of the radius. It then crosses obliquely the tendons of the Extensores carpi radialis longus and brevis, and is separated from the Extensor brevis pollicis by a 35 Lateral epicondyle Radial collateral Itg. Annular ligament Deep branch of radial nerve Intewsseous recurrent art. Deep branch of radial nerve Dorsal interosseous art. Fig. 527. — The Supinator. 546 MYOLOGY triangular interval, in which the radial artery is found; and is finally inserted into the base of the last phalanx of the thumb. The radial artery is crossed by the tendons of the Abductor pollicis longus and of the Extensores pollicis longus and brevis. The Extensor indicis proprius (Extensor hidicls) is a narrow, elongated muscle, placed medial to, and parallel with, the preceding. It arises, from the dorsal sur- face of the body of the ulna below the origin of the Extensor pollicis longus, and from the interosseous membrane. Its tendon passes under the dorsal carpal ligament in the same compartment as that which transmits the tendons of the Extensor digitorum communis, and opposite the head of the second metacarpal bone, joins the ulnar side of the tendon of the Extensor digitorum communis which belongs to the index finger. Nerves. — The Brachioradialis is supplied by the fifth and sixth, the Extensores carpi radialis longus and brevis by the sixth and seventh, and the Aijconaeus by the seventh and eighth cervical nerves, through the radial nerve; the remaining muscles are innervated through the deep radial nerve, the Supinator being supplied by the sixth, and aU the other muscles by the seventh cervical. Actions. — The muscles of the lateral and dorsal aspects of the forearm, which comprise all the Extensor muscles and the Supinator, act upon the forearm, wrist, and hand; they are the du'ect antagonists of the Pronator and Flexor muscles. The Anconaeus assists the Triceps in extending the forearm. The Brachioradiahs is a flexor of the elbow-joint, but only acts as such when the movement of flexion has been initiated by the Biceps brachii and Brachiahs. The action of the Supinator is suggested by its name; it assists the Biceps in bringing the hand into the supine position. The Extensor carpi radialis longus extends the wrist and abducts the hand. It may also assist in bending the elbow-joint; at all events it serves to fix or steady this articula- tion. The Extensor carpi radialis brevis extends, the wrist, and may also act sHghtly as an abductor of the hand. The Extensor carpi ulnaris extends the wrist, but when acting alone inclines the hand toward the ulnar side; by its continued action it extends the elbow-joint. The Extensor digitorima communis extends the phalanges, then the wrist, and finally the elbow. It acts prin- cipally on the proximal phalanges, the middle and terminal phalanges being extended mainly by the Interossei and Lumbricales. It tends to separate the fingers as it extends them. The Extensor digiti quinti proprius extends the Little finger, and by its continued action assists in extending the wrist. It is owing to this muscle that the little finger can be extended or pointed while the others are flexed. The chief action of the Abductor poUicis longus is to carry the thumb laterally from the palm of the hand. By its continued action it helps to extend and abduct the wrist. The Extensor poUicis brevis extends the proximal phalanx, and the Extensor poUicis longus the terminal phalanx of the thumb; by their continued action they help to extend and abduct the wrist. The Extensor indicis proprius extends the index finger, and by its continued action assists in extending the wrist. Applied Anatomy. — The tendons of the Abductor longus and Extensors of the thxmib are hable to become strained, and their sheaths inflamed {tenosynovitis) after excessive exercise, producing a sausage-shaped swelling along the course of the tendons and giving a pecuhar grating sensation to the touch when the muscles are put in action. Paralysis of the Extensor muscles of the wrists and fingers, with its resulting "wrist drop," is common in acute or chronic lead poisoning. The Brachioradiahs usually escapes in these cases, unless the muscles of the upper arm are paralyzed also. Usually the different Extensor muscles are unequally affected; thus the thumb, or index or httle finger, may be but slightly impUcated, and may recover rapidly while the Extensors of the other fingers or the wrist remain powerless. Some paresis is often shown by the Flexors of the fingers also, these muscles being thrown into a state of tremor whenever extension of the fingers is attempted. Atrophy often foUows paralysis in lead poisoning. VI. THE MUSCLES AND FASCIA OF THE HAND. The muscles of the hand are subdivided into three groups: (1) those of the thumb, which occupy the radial side and produce the thenar eminence ; (2) those of the little finger, which occupy the ulnar side and give rise to the hypothenar eminence; (3) those in the middle of the palm and between the metacarpal bones. Dissection (Fig. 518). — Make a transverse incision across the front of the wrist, and a second across the heads of the metacarpal bones; connect the two by a vertical incision in the middle Mne, and continue it through the centre of the middle finger. The volar, transverse, and dorsal carpal hgaments and the palmar aponeurosis should then be dissected. THE MUSCLES AND FASCI/E OF THE HAND 547 Volar Carpal Ligament (Ugamcntinu carpi volare). — The volar carpal ligament is the thickeiu'd hand of antihraehial fascia which extends from the radius to the ulna over the Flexor tendons as thev enter the wrist. Median nerve Palmaris longus Flex. foil. long. Flex. carp. rod. Radial artery Ahd. jmU. long. Ext. poll brev. Ext. carp. rnd. long. Flexor dig. sublimit Ulnar artery I Ulnar nerve Fle.T. carp. idn. Flex. dig. profundus E.vt. carp. rad. hiev ~ j 1 1 "V \ ^^^- ca»'P- uln. Ext poll long \ \ \ Distal ladio-ulnar artic. E.vt. indicia, prop. 1 Ext. dig. quinti prop. Ext. dig. commun. Fig. 528. — Transverse section across distal ends of radius and ulna. Transverse Carpal Ligament {ligamentum carpi transversum; anterior annular ligament) (Figs. 528, 529). — The transverse carpal ligament is a strong, fibrous band, which arches over the carpus, converting the deep groove on the front of the carpal bones into a tunnel, through which the Flexor tendons of the digits and the median nerve pass. It is attached, medially, to the pisiform and the Median nerve Transverse carpal ligament Flex. poll. long. \ \ Palmaris longus Flex, carpi rad. \ \ \ Flex. dig. sublimis Muscles of tliuml \ \\\\ // Ulnar art. a7id nerve _^^^_ ^ ^ ^ 11-- ^ ,t Muscles of little finger Abd. poll. long. ^ * \ \ i i z^-i /-» Ext. poll. brev. Flex. dig. profundus Ext. carp. rad. long. ^ \, Radial artery Ext. carp. rad. brev. Ext. poll. long. Ext. carp. uln. Ext. dig. quinti prop. Ext. dig. communis Ext. indicis prop. Fig. 529. — Transverse section across the wrist and digits. hamulus of the hamate bone; laterally, to the tuberosity of the navicular, and to the medial part of the volar surface and the ridge of the greater multangular. It is continuous, above, with the volar carpal ligament; and below, with the palmar aponeurosis. It is crossed by the ulnar vessels and nerve, and the cutaneous branches of the median and ulnar nerves. At its lateral end is the tendon of the 548 MYOLOGY Flexor carpi radialis, which Hcs in the groove on the greater multangular between the attachments of the ligament to the bone. On its volar surface the tendons of the Palmaris longus and Flexor carpi ulnaris are. partly inserted: below, it gives origin to the short muscles of the thumb and little finger Sheaths of terminal parts of Flexores digitorum Muscles of the eminence Sheath of Flexor poUicis longus Sheath of Flexor carpi radialis JIuscles of hypo- ihenar erainence Coiiunon sheath of / Flexo) es digitorum subli/iiis and piofuiidus Uxor carpi ulnaris Fig. 530. — The mucous sheaths of the tendons on the front of the wrist and digits. The Mucous Sheaths of the Tendons on the Front of the Wrist. — Two sheaths envelop the tendons as they pass beneath the transverse carpal ligament, one for the Flexores digitorum sublimis and profundus, the other for the Flexor pollicis longus (Fig. 530). They extend into the forearm for about 2.5 cm. above the transverse carpal ligament, and occasionally communicate with each other under THE MUSCLES AXD EASCLE OF THE HAXD 549 the ligament. The sheath which surrounds the Flexores digitorum extends down- ward about half-way along the metacarpal bones, where it ends in blind diverticula around the tendons to the index, middle, and ring fingers. It is prolonged on the tendons to the little finger and usually communicates with the mucous 7 AM. poll. long. J. — Ext. carp. rod. long. T Ejrt. carp. rad. brev. Fig. 531. — The mucous sheaths of the tendons on the back of the wriii. sheath of these tendons. The sheath of the tendon of the Flexor pollicis longus is continued along the thumb as far as the insertion of the tendon. The mucous sheaths enveloping the terminal parts of the tendons of the Flexores digitorum have been described on page oAi). 550 MYOLOGY Dorsal Carpal Ligament {ligamentum carpi dorsale; posterior annular ligament) (Figs. 528, 529).— The dorsal carpal ligament is a strong, fibrous band, extending obliquely downward and medialward across the back of the wrist, and consisting of part of the deep fascia of the back of the forearm, strengthened by the addition of some transverse fibres. It is attached, medially, to the styloid process of the ulna and to the triangular and pisiform bones; laterally, to the lateral margin of the radius; and, in its passage across the wrist, to the ridges on the dorsal surface of the radius. The Mucous Sheaths of the Tendons on the Back of the Wrist. — Between the dorsal carpal ligament and the bones six compartments are formed for the passage of tendons, each compartment having a separate mucous sheath. One is found in each of the following positions (Fig. 531) : (1) on the lateral side of the styloid pro- cess, for the tendons of the Abductor pollicis longus and Extensor pollicis brevis; (2) behind the styloid process, for the tendons of the Extensores carpi radialis longus and brevis; (3) about the middle of the dorsal surface of the radius, for the tendon of the Extensor pollicis longus; (4) to the medial side of the latter, for the tendons of the Extensor digitorum communis and Extensor indicis proprius; (5) opposite the interval between the radius and ulna, for the Extensor digiti quinti proprius; (6) between the head and styloid process of the ulna, for the tendon of the Extensor carpi idnaris. The sheaths lining these compartments extend from above the dorsal carpal ligament ; those for the tendons of Abductor pollicis longus, Extensor brevis pollicis, Extensores carpi radialis, and Extensor carpi ulnaris stop immediately proximal to the bases of the metacarpal bones, while the sheaths for Extensor communis digitorum, Extensor indicis proprius, and Extensor digiti quinti proprius are prolonged to the junction of the proximal and intermediate thirds of the metacarpus. Palmar Aponeurosis {aponeurosis palmaris; palmar fascia) (Fig. 532).^ — The palmar aponeurosis invests the muscles of the palm, and consists of central, lateral, and medial portions. The central portion occupies the middle of the palm, is triangular in shape, and of great strength and thickness. Its apex is continuous with the lower margin of the transverse carpal ligament, and receives the expanded tendon of the Pal- maris longus. Its base divides below into four slips, one for each finger. Each slip gives off superficial fibres to the skin of the palm and finger, those to the palm joining the skin at the furrow corresponding to the metacarpophalangeal articula- tions, and those to the fingers passing into the skin at the transverse fold at the bases of the fingers. The deeper part of each slip subdivides into two processes, which are inserted into the fibrous sheaths of the Flexor tendons. From the sides of these processes offsets are attached to the transverse metacarpal ligament. By this arrangement short channels are formed on the front of the heads of the metacarpal bones; through these the Flexor tendons pass. The intervals between the four slips transmit the digital vessels and nerves, and the tendons of the Lum- bricales. At the points of division into the slips mentioned, numerous strong, transverse fasciculi bind the separate processes together. The central part of the palmar aponeurosis is intimately bound to the integument by detise fibroareolar tissue forming the superficial palmar fascia, and gives origin by its medial margin to the Palmaris brevis. It covers the superficial volar arch, the tendons of the Flexor muscles, and the branches of the median and ulnar nerves; and on either side it gives off a septum, which is continuous with the interosseous aponeurosis, and separates the intermediate from the collateral groups of muscles. The lateral and medial portions of the palmar aponeurosis are thin, fibrous layers, which cover, on the radial side, the muscles of the ball of the thumb, and, on the ulnar side, the muscles of the little finger; they are continuous with the central portion and with the fascia on the dorsum of the hand. THE MUSCLES AND FA SOLE OF THE HAND 551 The Superficial Transverse Ligament of the Fingers is a thin bund of transverse fascicuH (Fig. 5;)2) ; it stretches across the roots of the four fingers, and is closely attached to the skin of the ck>fts, and mechally to the fifth metacarpal bone, forming a sort of rudimentary web. Beneath it the (hgital vessels and nerves pass to their destinations. Proper digital artery and nerve Uhmr artery and nerve Fig. 532. — The palmar aponeurosis. Applied Anatomy.— The palmar aponeurosis is liable to undergo contraction, producmg a very inconvenient deformity, known as Duptiytren's contraction. The ring and little fingers are most frequently imphcated, but the others may also be involved. The proximal phalanx is flexed and cannot be straightened, and the two distal phalanges become similarly flexed as the Owing to their constant exposure to injury and septic influences, the fingers are very hable to become the seat of serious inflammatory mischief. To this inflammation the term -paronychia or whitloiu is given, and the affection may assume various degrees of seventy. In the mildest cases the disease is confined to the superficial layer of the skin, and suppm-ation takes place beneath it. This is known as subcuticular paronychia, and is a comparatively simple condition, for an incision through the epidermis wiU at once reheve it. The only comphcation is that the pus may burrow under the nail, causing increased pain. A more severe condition is the paronychia cellulosa, in which the pulp of the end of the finger is involved. This is attended with intense thi'obbing pain, owing to the fact that the inflamed area is covered by thick and often horny epitheUum, especially when the disease occurs in the laboring classes, as it so frequently does. In these cases, unless a timely incision is made, the inflammation is hable to involve the. perios- teum coA-ering the phalanx, and subperiosteal paronychia is set up, which is followed by necrosis 552 MYOLOGY of a part or the whole of the ungual phalanx. In other cases, the inflammation maj' involve the theca of the Flexor tendons, and a thecal paronychia may result. The inflammation then rapidly spreads up the sheath; but the extent will depend upon the particular digit involved. From the description of the Flexor sheaths given above, it will be evident that inflammation of the mucous sheaths of the thumb and little finger may prove a far more formidable affection than that of the other three digits, because the sheaths of these two digits communicate with the large mucous sheath which surrounds the Flexor tendons (p. 548), and the inflammation may extend into the palm of the hand and beneath the transverse carpal ligament into the forearm. In order to relieve these conditions, free and early incisions are necessary, and must be made with discrimination, in order to avoid wounding important structures. In the pulp of the finger — i. e., over the distal phalanx — the incision should be made in the middle hne and down to the bone. In the rest of the finger, the incision should be made in the middle line over the phalanges, and not over the interphalangeal joints. In the palm of the hand, incisions may be made either on the distal or proximal side of the superficial volar arch. On the distal side the incisions should be made over the metacarpal bones, preferably those of the index and middle finger. On the proximal side, the safest line of incision is along the radial side of the hypothenar eminence, between the ulnar artery and nerve medially, and the median nerve laterally. When suppura- tion has extended under the transverse carpal ligament, and incisions are required in the fore- arm, the positions in which they should be made are over the tendons of the Flexor digitorum sublimis, between the median nerve and the ulnar artery, and over the tendon of the Flexor poUicis longus, between the radial artery and the tendon of the Flexor carpi radiahs. Chronic inflammation of the common flexor sheath is occasionally met with, constituting a disease known as compound palmar ganglion; it presents an hour-glass outline, with a swelling in front of the wrist and another in the palm of the hand, and a constriction, corresponding to the transverse carpal Ugament, between the two. The fluid can be forced from the one swelling to the other under the ligament, and when this is done, a creaking sensation is sometimes per- ceived, from the presence of "melon-seed" bodies in the interior of the gangUon. 1. The Lateral Volar Muscles (Figs. 533, 534). Abductor pollicis brevis. Flexor pollicis brevis. Opponens pollicis. Adductor pollicis (obliquus) . Adductor pollicis (transversus). Pisomefacarpal liq. Fig. 533. — The muscles of the thumb. The Abductor pollicis brevis {Abductor pollicis) is a thin, flat muscle, placed immediately beneath the integument. It arises from the transverse carpal liga- ment, the tuberosity of the navicular, and the ridge of the greater multangular, THE LATERAL VOLAR MUSCLES 553 frequently by two distinct slips. Runnino- laterahvard and downward, it is inserted by a thin, flat tendon into the racHal side of the base of the first phalanx of the thumb and the capsule of the metacari)ophalanf2;eal articulation. The Opponens pollicis is a small, triangular muscle, placed beneath the pre- ceding. It arises from the ridge on the greater multangular and from the trans- verse carpal ligament, passes downward and laterahvard, and is inserted into the whole length of the metacarpal bone of the thumb on its radial side. Fig. 534. — The muscles of the left hand. Palmar surface. The Flexor pollicis brevis consists of two portions, lateral and medial. The lateral and more superficial portion arises from the lower border of the transverse 554 MYOLOGY carpal ligament and the lower part of the ridge on the greater multangular bone; it passes along the radial side of the tendon of the Flexor pollicis longus, and, becoming tendinous, is inserted into the radial side of the base of the first phalanx of the thumb; in its tendon of insertion there is a sesamoid bone. The medial and deeper portion of the muscle is very small, and arises from the Ulnar side of the first metacarpal bone between the Adductor pollicis (obliquus) and the lateral head of the first Interosseous dorsalis, and is inserted into the ulnar side of the base of the first phalanx with the Adductor pollicis (obliquus). The medial part of the Flexor brevis pollicis is sometimes described as the first Interosseous volaris. The Adductor pollicis (obliquus) {Adductor obliquus iJolUcis) arises by several slips from the capitate bone, the bases of the second and third metacarpals, the intercarpal ligaments, and the sheath of the tendon of the Flexor carpi radialis. From this origin the greater number of fibres pass obliquely downward and con- verge to a tendon, which, uniting with the tendons of the medial portion of the Flexor pollicis brevis and the transverse part of the Adductor, is inserted into the ulnar side of the base of the first phalanx of the thumb, a sesamoid bone being present in the tendon. A considerable fasciculus, however, passes more obliquely beneath the tendon of the Flexor pollicis longus to join the lateral portion of the Flexor brevis and the Abductor pollicis brevis. The Adductor pollicis (transversus) {Adductor transversus jjollicis) (Fig. 533) is the most deeply seated of this group of muscles. It is of a triangular form arising by a broad base from the lower two-thirds of the volar surface of the third metacarpal bone; the fibres converge, to be inserted with the medial part of the Flexor pollicis brevis and the Adductor pollicis (obliquus) into the ulnar side of the base of the first phalanx of the thumb. Nerves. — The Abductor brevis, Opponens, and lateral head of the Flexor poUicis brevis are supphed by the sixth and seventh cervical nerves through the median nerve; the medial head of the Flexor brevis, and the Adductor, by the eighth cervical through the ulnar nerve. Actions. — The Abductor poUicis brevis draws the thumb forward in a plane at right angles to that of the pahn of the hand. The Abductor poUicis is the opponent of this muscle, and approxi- mates the thumb to the palm. The Opponens poUicis flexes the metacarpal bone, i. e., draws it medialward over the palm; the Flexor poUicis brevis flexes and adducts the proximal phalanx. 2. The Medial Volar Muscles (Figs. 533, 534). Palmaris brevis. Flexor digiti quinti brevis. Abductor digiti quinti. Opponens digiti quinti. The Palmaris brevis is a thin, quadrilateral muscle, placed beneath the integu- ment of the ulnar side of the hand. It arises by tendinous fasciculi from the transverse carpal ligament and palmar aponeurosis; the fleshy fibres are inserted into the skin on the ulnar border of the palm of the hand. The Abductor digiti quinti {Abductor minimi digiti) is situated on the ulnar border of the palm of the hand. It arises from the pisiform bone and from the tendon of the Flexor carpi ulnaris, and ends in a flat tendon, which divides into two slips; one is inserted into the ulnar side of the base of the first phalanx of the little finger; the other into the ulnar border of the aponeurosis of the Extensor digiti quinti proprius. » The Flexor digiti quinti brevis {Flexor brevis minimi digiti) lies on the same plane as the preceding muscle, on its radial side. It arises from the convex surface of the hamulus of the hamate bone, and the volar surface of the transverse carpal ligament, and is inserted into the ulnar side of the base of the first phalanx of the little finger. It is separated from the Abductor, at its origin, by the deep branches of the, ulnar artery and nerve. This muscle is sometimes wanting; the Abductor is then, usually, of large size. THE IXTEUMEDIATE MUSCLES 555 Tlie Opponens digiti quinti (Opponens minimi digiti) (Fig. 533) is of a tri- angular t'orin, aiul i)lace(l iinmediately beneath the preceding muscles. It arises from the convexity of the hamulus of the hamate bone, and contiguous portion of the transverse carpal ligament; it is inserted into the whole length of the meta- carpal bone of the little finger, along its ulnar margin. Nerves. — All the muscles of this group are supplied by the eighth cervical nerve through the ulnar nerve. Actions. — The Abductor and Flexor digiti quinti brevis abduct the little finger from the ring finger and assist in flexing the proximal phalanx. The Opponens digiti quinti draws forward the fifth metacarpal bone, so as to deepen the hollow of the palm. The Palmaris brevis corrugates the skin on the ulnar side of the palm. 3. The Intermediate Muscles. Lumbricales. Interossei. The Lumbricales (Fig. 534) are four small fleshy fasciculi, associated with the tendons of the Flexor digitorum profundus. The first and second arise from the radial sides and volar surfaces of the tendons of the index and middle fingers respectively; the third, from the contiguous sides of the tendons of the middle and ring fingers; and the fourth, from the contiguous sides of the tendons of the ring and little fingers. Each passes to the radial side of the corresponding finger, and opposite the metacarpophalangeal articulation is inserted into the tendinous expansion of the Extensor digitorum communis covering the dorsal aspect of the finger. Fig. 535. — The Interossei dorsales of left hand. Fig. 536. — The Interossei volares of left hand The Interossei (Figs. 535, 536) are so named from occupying the intervals between the metacarpal bones, and are divided into two sets, a dorsal and a volar. The Interossei dorsales (Dorsal interossei) are four in number, and occupy the intervals between the metacarpal bones. They are bipenniform muscles, each arising by two heads from the adjacent sides of the metacarpal bones, but more exten- sively from the metacarpal bone of the finger into which the muscle is inserted. They are inserted into the bases of the first phalanges and into the aponeuroses 556 MYOLOGY of the tendons of the Extensor digitonim comnuinis. Between the double origin of each of these muscles is a narrow triangular interval; through the first of these the radial artery passes; through each of the other three a i)erf()rating branch from the deep volar arch is transmitted. The first or Abductor indicis is larger than the others. It is flat, triangular in form, and arises by two heads, separated by a fibrous arch for the passage of the radial artery from the dorsum to the palm of the hand. The lateral head arises from the proximal half of the ulnar border of the first metacarpal bone; the medial head, from almost the entire length of the radial border of the second metacarpal bone; the tendon is inserted into the radial side of the index finger. The second and third are inserted into the middle finger, the former into its radial, the latter into its ulnar side. The fourth is inserted into the ulnar side of the ring finger. The Interossei volares (Palmar inter ossei), three in number, are smaller than the Interossei dorsales, and placed upon the volar surfaces of the metacarpal bones, rather than betw^een them. Each arises from the entire length of the metacarpal bone of one finger, and is inserted into the side of the base of the first phalanx and aponeurotic expansion of the Extensor communis tendon to the same finger. The first arises from the ulnar side of the second metacarpal bone, and is inserted into the same side of the first phalanx of the index finger. The second arises from the radial side of the fourth metacarpal bone, and is inserted into the same side of the ring finger. The third arises from the radial side of the fifth metacarpal bone, and is inserted into the same side of the little finger. From this account it may be seen that each finger is provided with two Interossei, with the exception of the little finger, in which the Abductor takes the place of one of the pair. As already mentioned (p. 554), the medial head of the Flexor pollicis brevis is sometimes described as the Interosseus volaris primus. Nerves. — The two lateral Lumbricales are supplied by the sixth and seventh cervical nerves, through the third and fourth digital branches of the median nerve; the two medial Lumbricales and all the Interossei are suppUed by the eighth cervical nerve, through the deep palmar branch of the ulnar nerve. The third Lumbricahs frequently receives a twig from the median. Actions. — The Interossei volares adduct the fingers to an imaginary line drawn longitudinally through the centre of the middle finger; and the Interossei dorsales abduct the fingers from that line. In addition to this the Interossei, in conjunction with the Lumbricales, flex the first phalanges at the metacarpophalangeal joints, and extend the second and third phalanges in consequence of their insertions into the expansions of the Extensor tendons. The Extensor digitorum communis is beheved to act almost entirely on the first phalanges. Applied Anatomy. — In considering the actions of the various muscles upon fractures of the upper extremity, the most common forms of injury have been selected both for illustration and description. Fracture of the middle of the clavicle (Fig. 537) is usually attended with considerable displace- ment of the lateral fragment, which is drawn downward and medialward, and at the same time rotated, so that its lateral end is carried forward and its medial end backward. The displacement is produced as follows: the lateral fragment is drawn downward by the weight of the arm, the Trapezius not being able to support this. It is drawn medialioard by the Subclavius and Pectoralis minor, possibly assisted by the Pectoralis major and Latissimus dorsi; and is rotated on an axis drawn through its own centre by the Serratus anterior, which causes the scapula to rotate on the wall of the chest, and carries the acromion and the end of the lateral fragment of the clavicle forward, and so carries the medial end of the lateral portion backward. The causes of displacement having been ascertained, it is easy to apply the appropriate treat- ment. The lateral fragment is to be drawn lateralward, and, together with the scapula, raised to a level with the medial fragment, and retained in that position. In fracture of the acromial end of the clavicle, between the conoid and trapezoid hgaments, only slight displacement occurs, as these ligaments, from their oblique insertion, serve to hold both portions of the bone in apposition. Fracture, also, of the sternal end, medial to the costo- clavicular hgament, is attended with only slight displacement, this hgament serving to retain the fragments in close apposition. Fracture of the acromion is usually caused by violence appUed to the upper and lateral part of the shoulder. There is great displacement; the lateral fragment being drawn downward by the weight of the arm, and rotated forward and medialward, so that it forms a right angle with the rest of the bone. THE INTERMEDIATE ^MUSCLES 557 Fracture of the surgical neck of the humerus (Fig. 538) is very common. It is attended with considerable displacement, and its ai)poarances correspond somewhat with those of dislocation of the head of the humerus into the axilla. The upper fragment remains in its place under the coracoacromial ligament; the lower is drawn medialward by the Pectoralis major, Latissimus dorsi, and Teres major; and the humerus is thrown obliquely from the side of the chest by the Deltoideus, and occasionally elevated so as to cause the upper end of the lower fragment to project beneath and in front of the coracoid process. The deformity is reduced by fixing the shoulder, and drawing the arm lateralward and downward. To counteract the opposing muscles, and to keep the fragments in position, a cone-shaped pad should be placed in the axilla, and the arm bandaged to the side bj^ a broad roller passed around the chest in such a manner that the elbow is carried slightly forward, so as to throw the upper end of the lower fragment backward and lateralward toward the head of the bone. The whole is then covered with a carefully moulded gutta-percha or poroplastic shoulder cap. Fig. 5.37. — Fracture of the middle of the clavicle. Fig. 538.- -Fracture of the surgical neck of the humerus. In fracture of the body of the humerus below the insertion of the Pectoralis major, Latissimus dorsi, and Teres major, and above the insertion of the Deltoideus, there is also considerable deformity, the upper fragment being drawn medialward by the first-mentioned muscles, and the lower fragment upward and lateralward by the Deltoideus. Shortening of the Umb results, with a considerable prominence at the seat of fracture, from the fractured ends of the bone riding over one another, especially if the fracture take place in an oblique direction. The fragments may be brought into apposition by extension from the elbow, and retained in that position by adopting the same means as in the preceding injury. In fracture of the body of the kmnerus immediately below the insertion of the Deltoideus the amount of deformity depends greatly upon the direction of the fracture. If it occur in a trans- verse direction, only shght displacement takes place, the upper fragment being drawn a httle forward; but in obUque fracture, the combined actions of the Biceps brachii and BrachiaUs in front and the Triceps brachii behind draw upward the lower fragment, causing it to ghde over the upper, either backward or forward, according to the direction of the fracture. Simple exten- sion reduces the deformity, and the apphcation of a shoulder cap and splints to the arm wiU retain the fragments in apposition. Fracture of the humerus (Fig. 539) immediately above the condyles deserves very attentive consideration, as the general appearances correspond somewhat with those produced by separa- tion of the epiphysis of the humerus, and with those of dislocation of the radius and ulna back- ward. If the direction of the fracture is obhque, from above, downward and forward, the lower fragment is drawn upward by the BrachiaUs and Biceps brachii in front, and the Triceps brachii behind; and at the same time is drawn backward behind the upper fragment by the Triceps brachii. This fracture may be diagnosticated from dislocation, by the increased mobility, the existence of crepitus, and the fact that the deformity is remedied by extension, but is reproduced on the 558 MYOLOGY discontinuance of it. The age of the patient is of importance in distinguishing this form of injurj' from separation of the epiphysis. In some cases where the injury has been produced by falls on the elbow, the lower fragment is drawTi upward and forward, causing a considerable prominence in front, the upper fragment projecting backward beneath the tendon of the Triceps brachii. In fracture of the olecranon (Fig. 540) the detached fragment is displaced upward, by the action of the Triceps brachii, from 1 to 5 cm.; the prominence of the elbow is consecjuently lost, and a deep hollow is felt at the back part of the joint, which is much increased on flexing the limb. The patient at the same time loses, more or less, the power of extending the forearm. The treatment consists in wiring the fragments together; but if for some reason this operation is not desirable, they should be approximated by strapping or a figure-of-eight bandage, and the arm put up in an extended position in order to relax the Triceps brachii. Massage and passive movements must be employed early, for fear of ankylosis. Union, when wiring is not resorted to, is usually fibrous. Fig. 539. — Fracture of the humerus above the condyles. Fig. 540. — Fracture of the olecranon. In fracture of the radius below the insertion of the Biceps brachii, but above the insertion of the Pronator teres, the upper fragment is strongly supinated by the Biceps brachii and Supi- nator, and at the same time drawn forward and flexed by the Biceps brachii; the lower fragment is pronated and drawn toward the ulna by both Pronators. Thus there is extreme displacement with very little deformity. In treating such a fracture the arm must be put up in a position of supination, otherwise union will take place with great impairment of the movements of the hand. In fractm-es of the radius below the insertion of the Pronator teres (Fig. 541), the upper fragment is drawn upward by the Biceps brachii and medialward by the Pronator teres, into a position midway between pronation and supina- tion, and a degree of fulness in the upper half of the forearm is thus produced. The lower fragment is drawn downward toward the ulna and pronated by the Pronator quadratus; at the same time, the Brachioradialis, by elevating the styloid process, into which it is inserted, wiU serve to depress the upper end of the lower frag- ment still more toward the ulna. In order to relax the opposing muscles the forearm should be bent, and the hmb placed in a position midway between pronation and supination; the fractiire is then easily reduced by extension from the wrist and elbow. WeU-padded splints should be applied on both sides of the forearm from the elbow to the wrist. In fracture of the body of the ulna the upper fragment retains its usual position, but the lower is drawn toward the radius by the Pronator quadratus, producing a well-marked depression at the seat of fracture, and some fulness on the dorsal and volar smiaces of the forearm. The frac- ture is easily reduced by extension from the wrist and elbow. The forearm should be flexed, and placed in a position midway between pronation and supination, and well-padded sphnts apphed from the elbow to the ends of the fingers. Fig. 541. — Fracture of the body of the radius. THE MUSCLES AND FASCLE OF THE ILIAC REGION 559 In fracture of tlie bodies of the racUtis and ulna loqelher, the lower fragments are drawn upward, sometimes forward, sometimes backward, according to the direction of the fracture, by the combined actions of the Flexor and Extensor muscles, producing a degree of fulness on either the dorsal or volar surface of the forearm. At the same time the lower fragments are drawn into contact by the Pronator quadratus, the radius being in a state of pronation. The upper frag- ment of the radius is drawn upward and medialward by the Biceps brachii and Pronator teres to a higher level than the ulna; the upper portion of the ulna is slightly elevated by the Brachialis. The fracture may be reduced by extension from the wrist and elbow, and the forearm should be placed in the same jiosition as in fracture of the ulna. Fig. 542. — Fracture of the lower end of the radius. In fracture of the lower end of the radius (Fig. 542) the displacement produced is very con- siderable, and bears some resemblance to dislocation of the carpus backward, from which it should be carefully distinguished. The lower fragment is displaced backward and upward, but this displacement is due to the force of the blow driving the portion of the bone into this position, and not to any muscular influence. The upper fragment projects forward, often lacerat- ing the substance of the Pronator quadratus, and is drawn by this muscle into close contact with the lower end of the ulna, causing a projection on the volar surface of the forearm, immediately above the carpus, from the Flexor tendons being thrust forward. This fracture may be distin- guished from dislocation by the relative positions of the styloid processes of the radius and ulna (the former of which is displaced upward in fracture) and by the deformity being removed on making sufficient extension, when crepitus may be occasionally detected. The age of the patient will assist in determining whether the injury is fracture or separation of the epiphysis. The treatment consists in flexing the forearm, and making powerful extension from the wrist and elbow, depressing at the same time the radial side of the hand, and retaining the parts in a posi- tion of adduction toward the ulnar side. THE MUSCLES AND FASCIA OF THE LOWER EXTREMITY. The muscles of the lower extremity are subdivided into groups corresponding with the different re2;ions of the limb. I. Muscles of the Iliac Region. II. Muscles of the Thigh. III. Muscles of the Leg. IV. Muscles of the Foot. I. THE MUSCLES AND FASCIA OF THE ILIAC REGION (Fig. 543). Psoas major. Psoas minor. Iliacus. Dissection. — No detailed description is required for the dissection of these muscles. On the removal of the viscera from the abdomen they are exposed, covered by the peritoneum and a thin layer of fascia, the iliac fascia. The Fascia Covering the Psoas and Iliacus is thin above, and becomes gradually thicker below as it approaches the inguinal ligament. The portion covering the Psoas is thickened above to form the medial lumbo- costal arch, which stretches from the transverse process of the first lumbar vertebra to the body of the second. Medially, it is attached by a series of arched processes 560 MYOLOGY t ^ ^SisJ.?' uw^^ W'li ' , I 3,2^1 ^ VI 'f//^ rrou Fig. 543. ' / -Muscles of the iliac and anterior femoral regions. to the intervertebral fihrocartilages, and promi- nent margins of the bodies of the vertebrae, and to the ui)])or i)art of the sacrum; the inter- vals left, oi)})osite the constricted portions of the bodies, transmit the lumbar arteries and veins and filaments of the sympathetic trunk. Laterally, above the crest of the ilium, it is continuous with the fascia co\'ering the front of the Quadratus lumborum (see page 510), while below the crest of the ilium it is con- tinuous with the fascia covering the Iliacus, The portions investing the Iliacus {fascia iliaca; iliac fascia) is connected, laterally to the M'hole length of the inner lip of the iliac crest; and medially, to the linea terminalis of the lesser pelvis, where it is continuous with the peri- osteum. At the iliopectineal eminence it re- ceives the tendon of insertion of the Psoas minor, when that muscle exists. Lateral to the femoral vessels it is intimately connected to the posterior margin of the inguinal ligament, and is continuous with the transversalis fascia. Immediately lateral to the femoral vessels the iliac fascia is prolonged backward and medial- ward from the inguinal ligament as a band, the iliopectineal fascia, which is attached to the iliopectineal eminence. This fascia divides the space between the inguinal ligament and the hip bone into two lacunae or compart- ments, the medial of which transmits the femoral vessels, the lateral the Psoas major and Iliacus and the femoral nerve. Medial to the vessels the iliac fascia is attached to the pectineal line behind the inguinal apon- eurotic falx, where it is again continuous with the transversalis fascia. On the thigh the fascise of the Iliacus and Psoas form a single sheet termed the iliopectineal fascia. Where the external iliac vessels pass into the thigh, the fascia descends behind them, forming the pos- terior wall of the femoral sheath. The portion of the iliopectineal fascia which passes behind the femoral vessels is also attached to the pectineal line beyond the limits of the attach- ment of the inguinal aponeurotic falx; at this part it is continuous with the pectineal fascia. The external iliac vessels lie in front of the iliac fascia, but all the branches of the lumbar plexus are behind it; it is separated from the peritoneum by a quantity of loose areolar tissue. The Psoas major (Psoas viagnus) (Fig. 543) is a long fusiform muscle placed on the side of the lumbar region of the vertebral column and brim of the lesser pelvis. It arises (1) THE MUSCLES AND FASCIA OF THE ILIAC REGION 561 from the anterior surfaces of the liases and lower liorders of the transverse processes of all the lumbar vertebrae; (2) from the sides of the bodies and the corresponding intervertebral fibrocartilages of the last thoracic and all the lumbar vertebrse by five slips, each of which is attached to the adjacent upper and lower margins of two vertebne, and to the intervertebral fibrocartilage; (3) from a series of tendinous arches which extend across the constricted parts of the bodies of the lumbar vertebne between the previous slips; the lumbar arteries and veins, and filaments from the sympathetic trunk pass beneath these tendinous arches. The muscle proceeds downward across the brim of the lesser pelvis, and diminishing gradually in size, passes beneath the inguinal ligament and in front of the capsule of the hip-joint and ends in a tendon; the tendon receives nearly the whole of the fibres of the Iliacus and is inserted into the lesser trochanter of the femur. A large bursa Mdiich may communicate with the cavity of the hip-joint, separates the tendon from the pubis and the capsule of the joint. Relations. — In the abdomen the Psoas major is in relation by its anterior surface with the medial lumbocostal arch, the fascia covering the muscle, the extraperitoneal fat and peritoneum, the kidney, Psoas minor, renal vessels, ureter, spermatic vessels, and genitofemoral nerve. In front of the right Psoas is the inferior vena cava and the terminal portion of the ileum, and in front of the left the iUac colon. By its posterior surface it is in relation with the transverse processes of the lumbar vertebrae, and the Quadratus lumborum. The lumbar plexus is situated in the posterior part of the substance of the muscle. By its medial side, the muscle is in relation with the bodies of the lumbar vertebraj, the lumbar arteries, the ganghated trunk of the sympa- thetic, and the lumbar lymph glands; with the inferior vena cava on the right, and the aorta on , the left side, and along the brim of the pelvis with the external iliac artery. In the thigh it is in relation, in front, with the fascia lata; behind, with the capsule of the hip- joint, from which it is separated by a bursa; by its medial border, with the Pectineus and medial circumflex femoral artery, and also with the femoral artery, which sUghtly overlaps it; by its lateral border, with the femoral nerve and Iliacus. The Psoas minor (Psoas parvus) is a long slender muscle, placed in front of the Psoas major. It arises from the sides of the bodies of the tw^elfth thoracic and first lumbar vertebrae and from the fibrocartilage between them. It ends in a long flat tendon which is inserted into the pectineal line and iliopectineal eminence, and, by its lateral border, into the iliac fascia. This muscle is often absent. The Iliacus is a flat, triangular muscle, w^hich fills the iliac fossa. It arises from the upper two-thirds of this fossa, and from the inner lip of the iliac crest; behind, from the anterior sacroiliac and the iliolumbar ligaments, and base of the sacrum; in front, it reaches as far as the anterior superior and anterior inferior iliac spines, and the notch between them. The fibres converge to be inserted into the lateral side of the tendon of the Psoas major, some of them being prolonged on to the body of the femur for about 2.5 cm. below and in front of the lesser trochanter.^ Relations. — Within the abdomen the lUacus is in relation by its anterior surface with the ihac fascia, which separates the muscle from the extraperitoneal fat and peritoneum, and with the lateral femoral cutaneous nerve; on the right side, with the cecimi; on the left side, with the ihac colon; by its posterior surface, with the iliac fossa; by its medial border, with the Psoas major and femoral nerve. In the thigh, it is in relation, by its anterior surface, with the fascia lata. Rectus femoris, Sar- torius, and profunda femoris artery; behind, with the capsule of the hip-joint, a bursa common to it and the Psoas major being interposed. Nerves. — The Psoas major is suppUed by branches of the second and third lumbar nerve; the Psoas minor by a branch of the first lumbar nerve; and the Ihacus by branches of the second and third lumbar nerves through the femoral nerve. Actions. — The Psoas major, acting from above, flexes the thigh upon the pelvis, being assisted by the Iliacus; acting from below, with the femur fixed, it bends the lumbar portion of the verte- bral column forward and to its own side, and then, in conjunction with the Iliacus, tilts the pelvis forward. When the muscles of both sides are acting from below, they serve to maintain the 1 The Psoas major and iliacus are sometimes regarded as a single muscle named the Iliopsoas. 36 562 MYOLOGY erect posture by supporting the vertebral column and pelvis upon the femora, or in continued action bend the trunk and pelvis forward, as in raising the trunk from the recumbent posture. The Psoas minor is a tensor of the iliac fascia. Applied Anatomy. — There is no definite septum between the portions of fascia covering the Psoas and Iliacus respectively, and the fascia is only connected to the subjacent muscles by a quantity of loose connective tissue. When an abscess forms beneath this fascia, as it is very apt to do, the matter is contained in an osseofibrous cavity which is closed on all sides within the abdomen, and is open only at its lower part, where the fascia is prolonged over the muscles into the thigh. Abscess within the sheath of the Psoas major (psoas abscess) is generally due to tuberculous caries of the bodies of the lower thoracic or the lumbar vertebraj. When the disease is in the thoracic region, the matter tracks down the posterior mediastinal cavity in front of the bodies of the vertebrte, and, passing beneath the medial lumbocostal arch, enters the sheath of the Psoas, down which it travels as far as the pelvic brim; it then gets beneath the iliac portion of the fascia, and fills up the iliac fossa. In consequence of the attachment of the fascia to the arcuate Une, it rarely finds its way into the lesser pelvis, but passes by a narrow opening under the inguinal hgament into the thigh, lateral to the femoral vessels. It thus follows that a psoas abscess may be described as consisting of four parts: (1) a somewhat narrow channel at its upper part, in the psoas sheath; (2) a dilated sac in the iliac fossa; (3) a constricted neck under the inguinal ligament, and (4) a dilated sac in the upper part of the thigh. When the lumbar vertebraj are the seat of the disease, the matter finds its w^ay directly into the substance of the Psoas. The muscular fibres are destroyed, and the nerves contained in the abscess are isolated and exposed in its interior; the iliac vessels which he in front of the fascia remain intact, and the peritoneum seldom becomes imphcated. All psoas abscesses do not, however, pursue this course; the matter may leave the sheath of the muscle above the crest of the ilium, and tracking backward may point in the loin {lumbar abscess); or it may point above the inguinal hgament in the inguinal region; or it may foUow the course of the branches of the hypogastric vessels into the lesser pelvis, and, passing through the greater sciatic foramen, discharge itself on the back of the thigh. n. THE MUSCLES AND FASCIA OF THE THIGH. 1. The Anterior Femoral Muscles (Fig. 543). Tensor fasciae latae. Quadriceps Sartorius. femoris. Articularis genu. Rectus femoris. Vastus lateralis. Vastus medialis. Vastus intermedins. Dissection. — To expose the muscles and fasciae in this region, make an incision along the inguinal ligament, from the anterior superior spine of the ilium to the spine of the pubis; a vertical incision from the centre of this, along the middle of the thigh to below the knee-joint; and a transverse incision from the inner to the outer side of the leg, at the lower end of the vertical incision. The flaps of integument having been removed, the superficial and deep fasciae should be examined. The more advanced student should commence the study of this region by an examination of the anatomy of femoral hernia and femoral triangle, the incisions for the dissection of which are marked out in Fig. 544. Superficial Fascia. — The superficial fascia forms a continuous layer over the whole of the thigh; it consists of areolar tissue containing in its meshes much fat, and may be separated into two or more layers, between which are found the superficial vessels and nerves. It varies in thickness in different parts of the limb; in the groin it is thick, and the two layers are separated from one another by the superficial inguinal lymph glands, the great saphenous vein, and several smaller vessels. The superficial layer is continuous above with the superficial fascia of the abdomen. The deep layer of the superficial fascia is a very thin, fibrous stratum, best marked on the medial side of the great saphenous vein and below the inguinal ligament. It is placed beneath the subcutaneous vessels and nerves and upon the surface of the fascia lata. It is intimately adherent to the fascia lata a little below the inguinal ligament. It covers the fossa ovalis (saphenous opening), being closely united to its circumference, and is connected to the sheath of the femoral vessels. The THE ANTERIOR FEMORAL MUSCLES 563 /. Dissection of femoral hernia, I and femoral or Scarpa's tri- angle. ^ \3. Front of thigh. portion of fascia {'o^■erino• this fossa is perforated by the great saphenous vein and hy numerous blood and lyin])hati(' ^•essels, lience it has been termed the fascia cribrosa, the oi)enini>;s for these \'essels ha\ini;- been Hkened to the lioles in a sieve. A hirge subcutaneous bursa is found in the sui)erficial fascia over the patella. Deep Fascia. — The deep fascia of the thigh is named, from its great extent, the fascia lata; it constitutes an investment for the whole of this region of the limb, but \ aries in thic-kness in diti'erent j)arts. Thus, it is thicker in the ui)i)er and lateral part of the thigh, where it receives a fibrous exi)ansion from the Glutaeus maximus, and where the Tensor fasciae latae is inserted between its layers.; it is very thin behind and at the upper and medial part, where it covers the Adductor muscles, antl again becomes stronger around the knee, receiving fibrous expansions from the tendon of the Biceps femoris laterally, from the Sarto- rius medially, and from the Quadriceps femoris in front. The fascia lata is attached, above and behind, to the back of the sacrum and coccyx; laterally, to the iliac crest; in front, to the inguinal ligament, and to the superior ramus of the pubis ; and medially, to the inferior ramus of the pubis, to the inferior ramus and tuberosity of the ischium, and to the lower border of the sacrotuberous ligament. From its attachment to the iliac crest it passes down over the Glu- taeus medius to the upper border of the Glutaeus maximus, where it splits into two layers, one passing superficial to and the other beneath this muscle ; at the lower border of the muscle the two layers reunite. Laterally, the fascia lata receives the greater part of the tendon of inser- tion of the Glutaeus maximus, and becomes proportionately thickened. The portion of the fascia lata attached to the front part of the iliac crest, and corresponding to the origin of the Tensor fasciae latae, extends down the lateral side of the thigh as two layers, one superficial to and the other beneath this muscle; at the lower end of the muscle these two layers unite and form a strong band, having first received the insertion of the muscle. This band is continued downward, under the name of the iliotibial band {tractus iliotibialis) and is attached to the lateral condyle of the tibia. The part of the iliotibial band which lies beneath the Tensor fasciae latae is prolonged upward to join the lateral part of the capsule of the hip-joint. Below, the fasciae lata is attached to all the promi- nent points around the knee-joint, viz., the condyles of the femur and tibia, and the head of the fibula. On either side of the patella it is strengthened by transverse fibres from the lower parts of the Vasti, which are attached to and support this bone. Of these the lateral are the stronger, and are continuous with the iliotibial band. The deep surface of the fascia lata gives off two strong intermuscular septa, which are attached to the whole length of the linea aspera and its prolon- gations above and below; the lateral and stronger one, which extends from the insertion of the Glutaeus maximus to the lateral condyle, separates the Vastus lateralis in front from the short head of the Biceps femoris behind, and gives 3. Front of leg. 4- Dorsum of foot. Fig. 544. — Dissection of lower extremity. Front view. 564 MYOLOGY partial origin to these muscles; the medial and thinner one separates the Vastus medialis from the Adductores and Pectineus. Besides these there are numerous smaller septa, separating the individual muscles, and enclosing each in a distinct sheath. The Fossa Ovalis (saphenous opening) (Fig. 545). — At the upper and medial part of the thigh, a little below the medial end of the inguinal ligament, is a large oval-shaped aperture in the fascia lata; it transmits the great saphenous vein, and other, smaller vessels, and is termed the fossa ovalis. The fascia cribrosa, which is pierced by the structures passing through the opening, closes the aperture and must be removed to expose it. The fascia lata in this part of the thigh is described as consisting of a superficial and a deep portion. Fig. 545. — The fossa ovalis. The superficial portion of the fascia lata is the part on the lateral side of the fossa ovalis. It is attached, laterally, to the crest and anterior superior spine of the ilium, to the whole length of the inguinal ligament, and to the pectineal line in con- junction with the lacunar ligament. From the tubercle of the pubis it is reflected downward and lateralward, as an arched margin, the falciform margin, forming the lateral boundary of the fossa ovalis; this margin overlies and is adherent to the anterior layer of the sheath of the femoral vessels: to its edge is attached the fascia cribrosa. The upward and medial prolongation of the falciform margin is named the superior cornu; its downward and medial prolongation, the inferior cornu. The latter is well-defined, and is continuous behind the great saphenous vein with the pectineal fascia. THE ANTEIilOR FK MORAL MUSCLES 565 The deep portion is situated on the medial side of the fossa ovalis, and at the lower margin of the fossa is eontinuous with the su])erfieial portion; traeed upward, it covers the Fectineus, Ad(hictor longus, and Gracilis, and, passing behind the sheath of the femoral vessels, to which it is closely united, is continuous with the iliopectineal fascia, and is attached to the pectineal line. From this descrij)tion it may be observed that the superficial portion of the fascia lata lies in front of the femoral vessels, and the deep portion behind them, so that an apparent aperture exists between the two, through which the great saphenous passes to join the femoral vein. The Tensor fasciae latae (Tensor fasciae femoris) arises from the anterior part of the outer lip of the iliac crest; from the outer surface of the anterior superior iliac spine, and part of the outer border of the notch below it, between the Glutaeus medius and Sartorius; and from the deep surface of the fascia lata. It is inserted between the two layers of the iliotibial band of the fascia lata about the junction of the middle and upper thirds of the thigh. The Sartorius, the longest muscle in the body, is narrow and ribbon-like; it arises by tendinous fibres from the anterior superior iliac spine and the upper half of the notch below it. It passes obliquely across the upper and anterior part of the thigh, from the lateral to the medial side of the limb, then descends vertically, as far as the medial side of the knee, passing behind the medial condyle of the femur to end in a tendon. This curves obliquely forward and expands into a broad apon- eurosis, which is inserted, in front of the Gracilis and Semitendinous, into the upper part of the medial surface of the body of the tibia, nearly as far forward as the anterior crest. The upper part of the aponeurosis is curved backward over the upper edge of the tendon of the Gracilis so as to be inserted behind it. An offset, from its upper margin, blends with the capsule of the knee-joint, and another from its lower border, with the fascia on the medial side of the leg. Relations. — The relations of this muscle to the femoral artery are important, as it constitutes the chief guide in tying the vessel. In the upper third of the thigh it forms the lateral side of a triangular space, the femoral (Scarpa's) triangle, the medial side of which is formed by the medial border of the Adductor longus, and the base, directed upward, by the inguinal hgament; the femoral artery passes perpendicularly through the middle of this space from its base to its apex. In the middle third of the thigh the femoral artery is contained in the adductor ( Hunter's) canal, on the roof of which the Sartorius lies. The Quadriceps femoris (Quadriceps extensor) includes the four remaining muscles on the front of the thigh. It is the great extensor muscle of the leg, forming a large flesh}^ mass which covers the front and sides of the femur. It is subdi^•ided into separate portions, which have received distinctive names. One occupying the middle of the thigh, and connected above w^ith the ilium, is called from its straight course the Rectus femoris. The other three lie in immediate connection with the body of the femur, which they cover from the trochanters to the condyles. The portion on the lateral side of the femur is termed the Vastus lateralis; that covering the medial side, the Vastus medialis ; and that in front, the Vastus intermedius. The Rectus femoris is situated in the middle of the front of the thigh ; it is fusi- form in shape, and its superficial fibres are arranged in a bipenniform manner, the deep fibres running straight down to the deep aponeurosis. It arises by two tendons: one, the anterior or straight, from the anterior inferior iliac spine; the other, the posterior or reflected, from a groove above the brim of the acetabulum. The two unite at an acute angle, and spread into an aponeurosis which is prolonged downward on the anterior surface of the muscle, and from this the muscular fibres arise. The muscle ends in a broad and thick aponeurosis which occupies the lower two-thirds of its posterior surface, and, gradually becoming narrowed into a flat- tened tendon, is inserted into the base of the patella. 566 MYOLOdY The Vastus lateralis (yastus externus) is the largest part of the Quadriceps femoris. It arises by a broad aponeurosis, which is attached to the upper part of the intertrochanteric line, to the anterior and inferior borders of the greater tro- chanter, to the lateral lip of the gluteal tuberosity, and to the upper half of the lateral lip of the linea aspera; this aponeurosis covers the upper three-fourths of the muscle, and from its deep surface many fibres take origin. A few additional fibres arise from the tendon of the Glutaeus maximus, and from the lateral inter- muscular septum between the Vastus lateralis and short head of the Biceps femoris. The fibres form a large fleshy mass, which is attached to a strong aponeurosis, placed on the deep surface of the lowTr part of the muscle : this aponeurosis becomes contracted and thickened into a flat tendon inserted into the lateral border of the patella, blending with the Quadriceps femoris tendon, and giving an expansion to the capsule of the knee-joint. The Vastus medialis and Vastus intermedius appear to be inseparably united, but when the Rectus femoris has been reflected a narrow interval will be observed extending upward from the medial border of the patella between the two muscles, and the separation may be continued as far as the lower part of the intertrochan- teric line, where, however, the two muscles are frequently continuous. The Vastus medialis {Vastus internus) arises from the lower half of the inter- trochanteric line, the medial lip of the linea aspera, the upper part of the medial supracondylar line, the tendons of the Adductor longus and the Adductor magnus and the medial intermuscular septum. Its fibres are directed downward and for- ward, and are chiefly attached to an aponeurosis which lies on the deep surface of the muscle and is inserted into the medial border of the patella and the Quad- riceps femoris tendon, an expansion being sent to the capsule of the knee-joint. The Vastus intermedius (Crureus) arises from the front and lateral surfaces of the body of the femur in its upper two-thirds and from the lower part of the lateral intermuscular septum. Its fibres end in a superficial aponeurosis, which forms the deep part of the Quadriceps femoris tendon. The tendons of the different portions of the Quadriceps unite at the lower part of the thigh, so as to form a single strong tendon, which is inserted into the base of the patella, some few fibres passing over it to blend with the Ugamentum patelte. More properly, the patella may be regarded as a sesamoid bone, developed in the tendon of the Quadriceps; and the ligamentum patellae, which is continued from the apex of the patella to the tuberosity of the tibia, as the proper tendon of insertion of the muscle, the medial and lateral patellar retinacula (see p. 439) being expan- sions from its borders. A bursa, which usually communicates with the cavity of the knee-joint, is situated between the femur and the portion of the Quadriceps tendon above the patella; another is interposed between the tendon and the upper part of the front of the tibia; and a third, the prepatellar bursa, is placed over the patella itself. The Articularis genu (Suhcrureus) is a small muscle, usually distinct from the Vastus intermedius, but occasionally blended with it; it arises from the anterior surface of the lower part of the body of the femur, and is inserted into the upper part of the synovial membrane of the knee-joint. It sometimes consists of several separate muscular bundles. Nerves. — The Tensor fasciae latae is supphed by the fourth and fifth lumbar and first sacral nerves through the superior gluteal nerve; the other muscles of this region, by the second, third, and fourth lumbar nerves, through the femoral nerve. Actions. — The Tensor fasciae latae is a tensor of the fascia lata; continuing its action, the obhque direction of its fibres enables it to abduct the thigh and to rotate it inward. In the erect posture, acting from below, it will serve to steady the pelvis upon the head of the femur; and by means of the ihotibial band it steadies the condyles of the femur on the articular surfaces of the tibia, and assists the Glutaeus maximus in supporting the knee in the extended position. The Sartorius flexes the leg upon the thigh, and, continuing to act, flexes the thigh upon the, pelvis; it next abducts and rotates the thigh outward. When the knee is bent, the Sartorius assists the Semitendinosus, Semimembranosus, and PopUteus in rotating the tibia inward. Tak- ing its fixed point from the leg, it flexes the pelvis upon the thigh, and, if one muscle acts, assists THE MKniAL FliMORAL MiSCLES 5()7 in rotating the pelvis. The Quach-iceps fenioris extends the leg upon the thigh. The Rectus femoris assists the Psoas major and Iliacus in supporting the pelvis and trunk upon the femur. It also assists in flexing the thigh on the i)elvis, or if the thigh be fixed it will flex the pelvis. The Vastus nu'dialis draws the patella medialward as well as upward. Applied Anatomy. — A few fibres of the Rectus femoris are occasionally ruptured from severe strain. This accident is especially hable to occur daring the games of football and baseball. The patient exi)eriences a sudden i)ain in the pai"t, as if he had been struck, and the Rectus stands out as is felt to be tense and rigid. The accident is often followed by considerable swelling from, inflammatory effusion. Occasionally the Quadriceps femoris may be torn away from its inser- tion into the patella; or the hgamentu^^ i)atellae may be ruptured about 2.5 cm. above the bone. This accident is caused in the .same manner as fracture of the patella by muscular action, viz., by a violent muscular effort to prevent falling while the knee is in a position of semiflexion. A distinct gap can be felt above the patella, and, owing to the retraction of the muscular fibres, imion may fail to take place. 2. The Medial Femoral Muscles. Gracilis. Adductor longus. Adductor magnus. Pectineus. Adductor brevis. Dissection. — These muscles are at once exposed by removing the fascia from the forepart and inner side of the thigh. The Hmb should be abducted, so as to render the muscles tense and easier of dissection. The Gracilis (Fig. 543) is the most superficial muscle on the medial side of the thigh. It is thin and flattened, broad above, narrow and tapering below. It arises by a thin aponeurosis from the anterior margins of the lower half of the symphysis pubis and the upper half of the pubic arch. The fibres run vertically downward, and end in a rounded tendon, which passes behind the medial condyle of the femur, curves around the medial condyle of the tibia, where it becomes flat- tened, and is inserted into the upper part of the medial surface of the body of the tibia, below the condyle. A few of the fibres of the lower part of the tendon are prolonged into the deep fascia of the leg. At its insertion the tendon is situated immediately above that of the Semitendinosus, and its upper edge is overlapped by the tendon of the Sartorius, with which it is in part blended. It is separated from the tibial collateral ligament of the knee-joint, by a bursa common to it and the tendon of the Semitendinosus. The Pectineus (Fig. 543) is a flat, quadrangular muscle, situated at the anterior part of the upper and medial aspect of the thigh. It arises from the pectineal line, and to a slight extent from the surface of bone in front of it, between the iliopectineal eminence and tubercle of the pubis, and from the fascia covering the anterior surface of the muscle; the fibres pass downward, backward, and lateral- ward, to be inserted into a rough line leading from the lesser trochanter to the linea aspera. Relations. — It is in relation by its anterior surface with the fascia lata, which separates it from the femoral vessels and great saphenous vein; by its posterior surface, with the capsule of the hip-joint, the Adductor brevis, Obtm-ator externus, and the anterior branch of the obturator nerve; by its lateral border, with the Psoas major and the medial femoral circumflex vessels; by its medial border, with the margin of the Adductor longus. The Adductor longus (Fig. 546), the most superficial of the three Adductores, is a triangular muscle, lying in the same plane as the Pectineus. It arises by a flat, narrow tendon, from the front of the pubis, at the angle of junction of the crest with the symphysis; and soon expands into a broad fleshy belly. This passes downward, backward, and lateralward, and is inserted, by an aponeurosis, into the linea aspera, between the Vastus medialis and the Adductor magnus, with both of which it is usually blended. Relations. — It is in relation by its anterior surface with the fascia lata, the Sartorius, and, near its insertion, with the femoral artery and vein; by its posterior surface, with the 568 MYOLOGY Adductores brevis and magnus, the anterior branch of the obturator nerve, and near its insertion with the profunda femoris artery and vein; by its lateral border, with the Pectineus; by its medial border, with the Gracihs. The Adductor brevis (Fig. 540) is situ- ated immediately l)ehiiid the two precethng muscles. It is somewhat triangular in form, and arises by a narrow origin from the outer surfaces of the superior and inferior rami of the pubis, between the Gracilis and Obturator externus. Its fibres, passing backward, lateralward, and downward, are inserted, by an aponeurosis, into the line leading from the lesser trochanter to the linea aspera and into the upper part of the linea aspera, immediately behind the Pectin- eus and upper part of the Adductor longus. Relations. — It is in relation by its anterior surface with the Pectineus, Adductor longus, profunda femoris artery, and anterior branch of the obturator nerve; by its posterior surface, with the Adductor magnus, and posterior branch of the obturator nerve; by its lateral border, with the medial femoral circum- flex artery, the Obturator externus, and conjoined teiidon of the Psoas major and Iliacus; by its medial border, with the Gracilis and Adductor magnus. It is pierced near its insertion by the second, or first and second, perforating branches of the profunda femoris artery. The Adductor magnus (Tig. 546) is a large triangular muscle, situated on the medial side of the thigh. It arises from a small part of the inferior ramus of the pubis, from the inferior ramus of the ischium, and from the outer margin of the inferior part of the tuberosity of the ischium. Those fibres which arise from the ramus of the pubis are short, horizontal in direction, and are inserted into the rough line leading from the greater trochanter to the linea aspera, medial to the Glutaeus maximus;^ those from the ramus of the ischium are directed downward and lat- eralward with different degrees of obliquity, to be iiiserted, by means of a broad aponeu- rosis, into the linea aspera and the upper part of its medial prolongation below. The medial portion of the muscle, composed principally of the fibres arising from the tuberosity of the ischium, forms a thick fleshy mass consisting of coarse bundles which descend almost vertically, and end about the lower third of the thigh in a rounded tendon which is inserted into the adductor tubercle on the medial condyle of Fig. 546.- -Deep muscles of the medial femoral region. 1 These uppermost fibres are sometimes described as a separate muscle — the Adductor minimus — Trhich is situated somewhat anterior to the other parts of the muscle. THE MUSCLES OF THE GLUTEAL REGION 569 the femur, aiul is connected by a fibrous expansion to the line leading upward frt)ni tile tubercle to the linea asi)era. At the insertion of the muscle, there is a series of osseoa])oneurotic ojieninos, formed by tendinous arches attached to the bone. The upper four openings are small, and give passage to the perforating branches of the profunda femoris artery. The lowest is of large size, and transmits the femoral vessels to the popliteal fossa. * su Relations. — It is in relation by its anterior surface with the Pectineus, Adductores brevis and longus, llio femoral and profunda vessels, and the posterior branch of the obturator nerve; by its posterior surface, with the sciatic nerve, the Glutaeus maximus. Biceps femoris, Semitendinosus, and Semimembranosus. Its superior border lies parallel with the Quadratus femoris, the medial femoral circumflex artery passing between them. Its medial border is in relation with the Gracilis, Sartorius, and fascia lata. Nerves. — The three Adductores and the Gracilis are supplied by the third and fourth lumbar nerves through the obturator nerve; the Adductor magnus receiving an additional branch from the sacral plexus through the sciatic. The Pectineus is supplied by the second, third, and fourth lumbar nerves through the femoral nerve, and by the third lumbar through the accessory obturator when this latter exists. Occasionally it receives a branch from the obturator nerve. ^ Actions. — -The Pectineus and three Adductores adduct the thigh powerfully; they are especially used in horse exercise, the sides of the saddle being grasped between the knees by the contraction of these muscles. In consequence of the obliquity of their insertions into the linea aspera, they rotate the thigh outward, assisting the external Rotators, and when the limb has been abducted, they draw it medialward, carrying the thigh across that of the opposite side. The Pectineus and Adductores brevis and longus assist the Psoas major and Ihacus in flexing the thigh upon the pelvis. In progression, all these muscles assist in drawing forward the lower limb. The Gracilis assists the Sartorius in flexing the leg and rotating it inward ; it is also an adductor of the thigh. If the lower extremities be fixed, these muscles, taking their fixed points below, may act upon the pelvis, serving to maintain the body in an erect posture; or, if their action be continued, flex the pelvis forward upon the femur. Applied Anatomy. — The Adductor longus is hable to be severely strained in those who ride much on horseback, or its tendon may be ruptured by suddenly gripping the saddle. Occasionally, especially in cavalry soldiers, the tendon becomes ossifled, constituting the rider's hone. 3. The Muscles of the Gluteal Region (Fig. 548). Glutaeus maximus. Obturator internus. Glutaeus medius. Gemellus superior. Glutaeus minimus. Gemellus inferior. Piriformis. Quadratus femoris. Obturator externus. Dissection (Fig. 547). — The subject should be turned on its face, a block placed beneath the pelvis to make the buttocks tense, and the limbs allowed to hang over the end of the table, with the foot inverted and the thigh abducted. Make an incision through the integument along the crest of the ihum to the middle of the sacrum, and thence downward to the tip of the coccyx, and carry a second incision from that point obliquely downward and outward to the outer side of the thigh, four inches below the great trochanter. The portion of integument included between these incisions is to be removed in the direction shown in the figure. The Glutaeus maximus, the most superficial muscle in the gluteal region, is a broad and thick fleshy mass of a quadrilateral shape, and forms the prominence of the nates. Its large size is one of the most characteristic features of the muscular system in man, connected as it is with the power he has of maintaining the trunk in the erect posture. The muscle is remarkably coarse in structure, being made up of fasciculi lying parallel with one another and collected together into large bundles separated by fibrous septa. It arises from the posterior gluteal line of the ilium, and the rough portion of bone including the crest, immediately above and behind it ; from the posterior surface of the lower part of the sacrum and the ■ ' The Pectineus may consist of two incompletely separated strata; the lateral or dorsal stratum, which is constant, is supplied bj' a branch from the femoral nerve, or in the absence of this branch by the accessory obturator nerve, the medial or ventral stratum, when present, is supplied by the obturator nerve. — A. M. Paterson, Journal of Anatomy and Physiology, xxvi, 43. 570 MYOLOGY side of the coccyx; from the aponeurosis of tlie Sacrospinalis, the sacrotuberous ligament, and the fascia (gluteal aponeurosis) covering the Glutaeus medius. The fibres are directed obliquely down^vard and laterahvard; those forming the upper and larger portion of the muscle, together Avith the superficial fibres of the lower portion, end in a thick tendinous lamina, which passes across the greater trochanter, and is inserted into the iliotibial band of the fascia lata; the deeper fibres of the lower portion of the muscle are inserted into the gluteal tuberosity between the Vastus lateralis and Adductor magnus. Bursse. of these, 1 1. Dmection of gluteal region. S — Three bursas ai'e usually found in relation with the deep surface of this muscle. One of large size, and generally multilocular, separates it from the greater trochanter; a second, often wanting, is situated on the tuberosity of the ischium; a third is found between the tendon of the muscle and that of the Vastus laterahs. Relations. — The Glutaeus maximus is in relation by its superficial surface with a thin fascia which separates it from the subcutaneous tissue; by its deep surface, from above downward, with the iUum, sacrum, coccy^x, and sacrotuberous hgament, part of the Glutaeus medius, Piriformis, Gemelli, Obturator internus, Quadratus femoris, the tuberosity of the ischium, greater trochanter, the origins of the Biceps femoris, Semitendinosus, Semi- membranosus, and the Adductor magnus. The super- ficial part of the superior gluteal artery reaches the deep sm-face of the muscle by passing between the Piriformis and the Glutaeus medius; the inferior gluteal and in- ternal pudendal vessels and the sciatic, pudendal, and lateral femoral cutaneous nerves, and muscular branches from the sacral plexus, issue from the pelvis below the Piriformis. The first perforating artery and the ter- minal branches of the medial circumflex femoral artery are also found under cover of the lower part of the muscle. Its upper border is thin, and connected with the Glutaeus medius by the gluteal aponeurosis. Its lower border is free and prominent, and is crossed by the fold of the nates. Dissection. — Divide the Glutaeus maximus near its origin by a vertical incision carried from its upper to its lower border; a cellular interval wiU be exposed, separating it from the Glutaeus medius and Rotator muscles beneath. The upper portion of the muscle is to be altogether detached, and the lower portion tm-ned outward; the loose areolar tissue filling up the inter- space between the trochanter major and tuberosity of the ischium being removed, the parts already enumer- ated as exposed by the removal of this muscle will be 3. Back of thigh. [3 \ 2. Popliteal space. 4/4- Back of leg. g \ 5. Sole of foot. Fig. 547. — Dissection of lower extremity. Posterior view. The Glutaeus medius is a broad, thick, radi- ating muscle, situated on the outer surface of the pelvis. Its posterior third is covered by the Glutaeus maximus, its anterior two-thirds by the gluteal aponeurosis, which separates it from the superficial fascia and in- tegument. It arises from the outer surface of the ilium between the iliac crest and posterior gluteal line above, and the anterior gluteal line below; it also arises from the gluteal aponeurosis covering its outer surface. The fibres converge to a strong flattened tendon, which is inserted into the oblique ridge which runs down- ward and forward on the lateral surface of the greater trochanter. A bursa separates the tendon of the muscle from the surface of the trochanter over which it glides. The Glutaeus minimus, the smallest of the three Glutaei, is placed immediately beneath the preceding. It is fan-shaped, arising from the outer surface of the ilium. THE MUSCLES OF THE (i Li TEAL REGION 571 between the anterior and inferior ghiteal lines, and l)ehind, from the margin of the greater sciatic notch. The fibres converge to the deep surface of a radiated aponeurosis, and this ends in a tension which is inserted into an impression on the anterior border of the greater trochanter, and gives an expansion to the capsule of the hip-joint. A bursa is interposed between the tendon and the greater trochanter. Be- tween the Glutaeus medius and Glutaeus minimus are the deep branches of the superior gluteal vessels and the superior gluteal nerve. The deep surface of the Glutaeus minimus is in relation with the reflected tendon of the Rectus femoris and the capsule of the hip-joint. The Piriformis is a flat muscle, pyramidal in shape, lying almost parallel with the posterior margin of the Glutaeus medius. It is situated partly within the pelvis against its posterior wall, and partly at the back of the hip- joint. It arises from the front of the sacrum by three fleshy digi- tations, attached to the portions of bone between the first, second, third, and fourth anterior sacral foramina, and to the grooves leading from the foramina : a few fibres also arise from the margin of the greater sciatic foramen, and from the anterior surface of the sacrotuberous ligament. The muscle passes out of the pelvis through the greater sciatic fora- men, the upper part of which it fills, and is inserted by a rounded tendon into the upper border of the greater trochanter behind, but often partly blended with, the common tendon of the Ob- turator internus and Gemelli. Relations. — Within the ■pelvis the Piriformis is in relation by its anterior surface with the rectum (especially on the left side), the sacral plexus of nerves, and branches of the hjrpogastric vessels; and by its posterior surface Medial hamstring tendojis Sartor ins Gracilis Semitendinosus Serni- membranosus Lateral liamsiring tendon Biceps femoris FiQ. 548. — Muscles of the gluteal and posterior femoral regions. 572 MYOLOGY with the sacrum. Outside the pelvis, its anterior surface is in contact with the posterior surface of the ischium and capsule of the hip-joint; and its posterior surface, with the Glutaeus maxi- mus; its upper border is in relation with the Glutaeus medius, and the superior gluteal vessels and nerve; its lower border, with the Gemellus superior and Coccygeus, the inferior gluteal and internal pudendal vessels, and the sciatic, posterior femoral cutaneous, and pudendal nerves, and muscular branches from the sacral plexus, passing from the pelvis in the interval between the two muscles. The muscle is frequently pierced by the common peroneal nerve. Obturator Membrane (Fig. 549) . — The obturator membrane is a thin fibrous sheet, which almost completely closes the obturator foramen. Its fibres are arranged in interlacing bundles mainly transverse in direction; the uppermost bundle is attached to the obturator tubercles and completes the obturator canal for the pas- sage of the obturator vessels and nerve. The membrane is attached to the sharp margin of the obturator foramen except at its lower lateral angle, where it is fixed to the pelvic surface of the inferior ramus of the ischium, i. e., within the margin. Both obturator muscles are connected with this membrane. Ant, sup. iliac spi'it- Obturator canal Lacunar ligament Pubic tubercle Symphysis pubis Tiansverse acetabular ligament Fig. 549. — The obturator membrane. Dissection. — The next muscle, as well as the origin of the Piriformis, can only be seen when the pelvis is divided and the viscera removed. The Obturator internus is situated partly within the lesser pelvis, and partly at the back of the hip-joint. It arises from the inner surface of the antero-lateral wall of the pelvis, where it surrounds the greater part of the obturator foramen, being attached to the inferior rami of the pubis and ischium, and at the side to the inner surface of the hip bone below and behind the pelvic brim, reaching from the upper part of the greater sciatic foramen above and behind to the obturator fora- men below and in front. It also arises from the pelvic surface of the obturator membrane except in the posterior part, from the tendinous arch which completes the canal for the passage of the obturator vessels and nerve, and to a slight extent from the obturator fascia, which covers the muscle. The fibres converge rapidly toward the lesser sciatic foramen, and end in four or five tendinous bands, which are found THE MUSCLES OF THE GLUTEAL REGIOX 573 on the deep surface of the muscle; these bands are reflected at a right angle over the grooved surface of the ischium between its spine and tuberosity. This bony surface is covered by smooth cartihige, which is separated from the tendon by a bursa, and presents one or more ridges corresponding with the furrows between the tendinous bands. These bands leave the pelvis through the lesser sciatic fora- men and unite into a single flattened tendon, which passes horizontally across the capsule of the hiji-joint, and, after receiving the attachments of the Gemelli, is inserted into the forepart of the medial surface of the greater trochanter above the trochanteric fossa. A bursa, narrow and elongated in form, is usually found between the tendon and the capsule of the hip-joint; it occasionally communicates with the bursa between the tendon and the ischium. Relations. — Within the pelvis, this muscle is in relation, bj' its antero-lateral surface, with the obturator membrane and inner sm'face of the anterior waU of the pelvis; by its pelvic surface, with the obturator fascia, and the origin of the Levator ani, and with the internal pudendal vessels and pudendal nerve which cross it. This surface forms the lateral boundary of the ischiorectal fossa. Outside the pelvis, the muscle is covered by the Glutaeus maximus, crossed by the sciatic nerve, and rests on the back part of the hip-joint. When the tendon of the Obturator internus emerges from the lesser sciatic foramen it is overlapped both in front and behind by the two Gemelh which form a muscular canal for it; near its. insertion the GemelU pass in front of the tendon and form a groove in which it hes. The Gemelli are two small muscular fasciculi, accessories to the tendon of the Obturator internus which is received into a groove between them. The Gemellus superior, the smaller of the two, arises from the outer surface of the spine of the ischium, blends with the upper part of the tendon of the Obturator internus, and is inserted with it into the medial surface of the greater trochanter. It is sometimes wanting. The Gemellus inferior arises from the upper part of the tuberosity of the ischium, immediately below the groove for the Obturator internus tendon. It blends with the lower part of the tendon of the Obturator internus, and is inserted with it it into the medial surface of the greater trochanter. The Quadratus femoris is a flat, quadrilateral muscle, between the Gemellus inferior and the upper margin of the Adductor magnus; it is separated from the latter by the terminal branches of the medial femoral circumflex vessels. It arises from the upper part of the external border of the tuberosity of the ischium, and is inserted into the upper part of the linea quadrata — that is, the line which extends vertically downward from the intertrochanteric crest. A bursa is often found between the front of this muscle and the lesser trochanter. The Obturator externus (Fig. 550) is a flat, triangular muscle, which covers the outer surface of the anterior wall of the pelvis. It arises from the margin of bone immediately around the medial side of the obturator foramen, viz., from the rami of the pubis, and the inferior ramus of the ischium; it also arises from the medial two-thirds of the outer surface of the obturator membrane, and from the tendinous arch which completes the canal for the passage of the obturator vessels and nerves. The fibres springing from the pubic arch extend on to the inner sur- face of the bone, where they obtain a narrow origin between the margin of the foramen and the attachment of the obturator membrane. The fibres converge and pass backward, lateralward, and upward, and end in a tendon which runs across the back of the neck of the femur and lower part of the capsule of the hip- joint and is inserted into the trochanteric fossa of the femur. The obturator vessels lie between the muscle and the obturator membrane; the anterior branch of the obturator nerve reaches the thigh by passing in front of the muscle, and the posterior branch by piercing it. Nerves. — The Glutaeus maximus is supphed by the fifth lumbar and first and second sacral nerves through the inferior gluteal nerve; the Glutaei medius and minimus by the fourth and 574 MYOLOGY fifth lumbar and first sacral nerves through the superior gluteal; the Piriformis is supplied by the first and second sacral nerves; the Gemellus inferior and Quadratus femoris by the last lumbar and first sacral nerves; the Gemellus superior and Obturator internus by the first, second, and third sacral nerves, and the Obturator externus by the third and fourth lumbar nerves through the obturator. Head of femur Obturator nerve A)tl. inf. iliac spine Fig. .5.50. — The Obturator externus. Actions. — When the Glutaeus maximus takes its fixed point from the pelvis, it extends the femur and brings the bent thigh into a line with the body. Taking its fixed point from below, it acts upon the pelvis, supporting it and the trunk upon the head of the femur; this is especially obvious in standing on one leg. Its most powerful action is to cause the bod}' to regain the erect position after stooping, by drawing the pelvis backward, being assisted in this action by the Biceps femoris, Semitendinosus, and Semimembranosus. The Glutaeus maximus is a tensor of the fascia lata, and by its connection with the ihotibial band steadies the femiu: on the articular surfaces of the tibia diu-ing standing, when the Extensor muscles are relaxed. The lower part of the muscle also acts as an adductor and external rotator of the limb. The Glutaei medius and minimus abduct the thigh, when the limb is extended, and are principally called into action in supporting the body on one Umb, in conjunction with the Tensor fasciae latae. Their anterior fibres, by drawing the greater trochanter forward, rotate the thigh inward, in which action the}' are also assisted by the Tensor fasciae latae. The remaining muscles are powerful external rotators of the thigh. In the sitting posture, when the thigh is flexed upon the pelvis, their action as rotators ceases, and they become abductors, with the exception of the Obturator externus, which still rotates the femur outward. 4. The Posterior Femoral Muscles fHamstring Muscles) (Fig. 548). Biceps femoris. Semitendinosus. Semimembrano.sus. Dissection (Fig. 547j. — Make a vertical incision along the middle of the back of the thigh, from the lower fold of the buttock to about three inches below the back of the knee-joint, and there connect it with a transverse incision, carried from the inner to the outer side of the leg. Make a third incision transversely at the junction of the middle with the lower third of the thigh. The integimient having been removed from the back of the knee, and the boundaries of the popliteal fossa having been examined, the removal of the integument from the remaining part of the thigh .should be continued, when the fascia and muscles of this region will be exjjosed. The Biceps femoris (Biceps) is situated on the posterior and lateral aspect of the thigh. It has two heads of origin; one, the long head, arises from the lower and inner impression on the back part of the tuberosity of the ischium, by a tendon common to it and the Semitendinosus, and from the lower part of the sacrotuberous liga- ment; the other, the short head, arises from the lateral lip of the linea aspera, THE POSTERIOR FEMORAL MUSCLES r^T^) between the Adductor maf2;nus and Vastus lateralis, extending up almost as hir the (•()rr(\siionding condyle; and one is occasionally found in the tendon of the medial head. The Soleus is a broad flat muscle situated iininediately in front of the Gastroc- nemius. It arises by tendhious fibres from the back of the head of the fibula, and from the upper third of the posterior surface of the body of the bone; from the popliteal line, and the middle third of the medial border of the tibia; some fibres also arise from a tendinous arch placed between the tibial and fibular origins of the muscle, in front of which the popliteal vessels and tibial nerve run. The fibres end in an aponeurosis which covers the posterior surface of the muscle, and, gradually becoming thicker and narrower, joins with the tendon of the Gastroc- nemius, and forms with it the tendo calcaneus. Relations. — By its superficial surface it is in relation with the Gastrocnemius and Plantaris; by its deep surface, with the Flexor digitorum longus, Flexor hallucis longus, Tibialis posterior, and posterior tibial vessels and nerve, from which it is separated by the deep transverse fascia of the leg. The Gastrocnemius and Soleus together form a muscular mass which is occa- sionally described as the Triceps surae; its tendon of insertion is the tendo calcaneus. Tendo Calcaneus (tendo AchiUis). — The tendo calcaneus, the common tendon of the Gastrocnemius and Soleus, is the thickest and strongest in the body. It is about 15 cm. long, and begins near the middle of the leg, but receives fleshy fibres on its anterior surface, almost to its lower end. Gradually becoming contracted below, it is inserted into the middle part of the posterior surface of the calcaneus, a bursa being interposed between the tendon and the upper part of this surface. The ten- don spreads out somewhat at its lower end, so that its narrowest part is about 4 cm. above its insertion. It is covered by the fascia and the integument, and is separated from the deep muscles and vessels by a considerable interval filled up with areolar and adipose tissue. Along its lateral side, but superficial to it, is the small saphenous vein. The Plantaris is placed between the Gastrocnemius and Soleus. It arises from the lower part of the lateral prolongation of the linea aspera, and from the oblique popliteal ligament of the knee-joint. It forms a small fusiform belly, from 7 to 10 cm. long, ending in a long slender tendon which crosses obliquely between the two muscles of the calf, and runs along the medial border of the tendo calcaneus, to be inserted with it into the posterior part of the calcaneus. This muscle is some- times double, and at other times wanting. Occasionally, its tendon is lost in the laciniate ligament, or in the fascia of the leg. Nerves. — The Gastrocnemius and Soleus are supplied by the first and second sacral nerves, and the Plantaris by the fourth and fifth lumbar and first sacral nerves, through the tibial nerve. Actions. — The muscles of the calf are the chief extensors of the foot at the ankle-joint. They possess considerable power, and are constantly called into use in standing, walking, dancing, and leaping; hence the large size they usuallj^ present. In walking, these muscles raise the heel from the ground; the body being thus supported on the raised foot, the opposite limb can be carried forward. In standing, the Soleus, taking its fixed point from below, steadies the leg upon the foot and prevents the body from falling forward. The Gastrocnemius, acting from below, serves to flex the femur upon the tibia, assisted by the PopUteus. The Plantaris is the rudiment of a large muscle which in some of the lower animals is continued over the, calcaneus to be inserted into the plantar aponeurosis. In man it is an accessory to the Gastrocnemius, extending the ankle if the foot be free, or bending the knee if the foot be fixed. The Deep Group (Fig. 553). Popliteus. Flexor digitorum longus. Flexor hallucis longus. Tibialis posterior. Dissection. — Detach the Soleus from its attachment to the fibula and tibia, and turn it down- ward, when the deep layer of muscles is exposed, covered by the deep transverse fascia of the leg. 580 MYOLOGY Deep Transverse Fascia.— The deep transverse fascia of the leg is a transversely placed, intermuscular septum, between the superficial and deep muscles of the S^5 =>< } Jt hal W/Iahml ,; / '' f I il ICALCPKEUSI m I'iH Tendons of ~ Peronae longus et brevis FemuA \ > -^ .i~ y/, Fig. 552. — Aluscles of the back of the Superficial layer. Fig. 553. — Muscles of the back of the leg. Deep layer. back of the leg. At the sides it is connected to the margms of the tibia and fibula. Above, where it covers the Popliteus, it is thick and dense, and receives an expansion from the tendon of the Semimembranosus; it is thinner m the middle THE POSTERIOR CRURAL MUSCLES 581 of the leg; but below, where it covers the tendons passhig behind the malleoli, it is thickened and continuous with the laciniate ligament. Dissection. — This fascia should now be removed, commencing from bcdow opposite the tendons, and detaching it from the muscles in the direction of their fibres. The Popliteus is a thin, flat, triangular muscle, which forms the lower part of the floor of the popliteal fossa. It arises by a strong tendon about 2.5 cm. long, from a depression at the anterior part of the groove on the lateral' condyle of the femur, and to a small extent from the oblique popliteal ligament of the knee-joint; and is inserted into the medial two-thirds of the triangular surface above the pop- liteal line on the posterior surface of the body of the tibia, and into the tendinous expansion covering the surface of the muscle. Relations. — The tendon of the muscle is covered by that of the Biceps femoris and by the fibular collateral ligament of the knee-joint; it grooves the posterior border of the lateral meniscus, and is invested by the synovial membrane of the knee-joint. The fascia covering the muscle separates it from the Gastrocnemius, Plantaris, popliteal vessels, and tibial nerve. The deep sm-face of the muscle is in contact with the obhque popliteal Ugament of the knee-joint and the back of the tibia. The Flexor hallucis longus is situated on the fibular side of the leg. It arises from the inferior two-thirds of the posterior surface of the body of the fibula, with the exception of 2.5 cm. at its lowest part; from the lower part of the interosseous membrane; from an intermuscular septum between it and the Peronaei, laterally, and from the fascia covering the Tibialis posterior, medially. The fibres pass obliquely downward and backward, and end in a tendon which occupies nearly the whole length of the posterior surface of the muscle. This tendon lies in a groove which crosses the posterior surface of the lower end of the tibia, the posterior surface of the talus, and the under surface of the sustentaculum tali of the calca- neus ; in the sole of the foot it runs forward between the two heads of the Flexor hallucis brevis, and is inserted into the base of the last phalanx of the great toe. The grooves on the talus and calcaneus, which contain the tendon of the muscle, are converted by tendinous fibres into distinct canals, lined by a mucous sheath. As the tendon passes forward in the sole of the foot, it is situated above, and crosses from the lateral to the medial side of the tendon of the Flexor digitorum longus, to which it is connected by a fibrous slip. Relations. — The Flexor hallucis longus is in relation by its superficial surface with the Soleus and tendo calcaneus, from which it is separated by the deep transverse fascia; by its deep surface, with the fibula, Tibialis posterior, the peroneal vessels, the lower part of the interosseous mem- brane, and the ankle-joint; by its lateral border, with the Peronaei; by its medial border, with the Tibialis posterior and posterior tibial vessels and tibial nerve. The Flexor digitorum longus is situated on the tibial side of the leg. At its origin it is thin and pointed, but it gradually increases in size as it descends. It arises from the posterior surface of the body of the tibia, from immediately below the popliteal line to within 7 or 8 cm. of its lower extremity, medial to the tibial origin of the Tibialis posterior; it also arises from the fascia covering the Tibialis posterior. The fibres end in a tendon, which runs nearly the whole length of the posterior surface of the muscle. This tendon passes behind the medial malleolus, in a groove, common to it and the Tibialis posterior, but separated from the latter by a fibrous septum, each tendon being contained in a special compartment lined by a separate mucous sheath. It passes obliquely forward and lateralward, super- ficial to the deltoid ligament of the ankle-joint, into the sole of the foot (Fig. 557), where it crosses below the tendon of the Flexor hallucis longus, and receives from it a 'strong tendinous slip. It then expands and is joined by the Quadratus plantae, and finally divides into four tendons, which are inserted into the bases of the last phalanges of the second, third, fourth, and fifth toes, each tendon passing through 582 MYOLOGY an opening in the corresponding tendon of the Flexor digitorum brevis opposite the base of the first phalanx. Relations. — In the leg this muscle is in relation by its superficial surface with the posterior tibial vessels and tibial nerve, and the deep transverse fascia which separates it from the Soleus; by its deep surface, with the tibia and TibiaUs posterior. In the foot, it is covered by the Abductor hallucis and Flexor digitorum brevis, and crosses superficial to the Flexor hallucis longus. The Tibialis posterior ( Tibialis posticus) lies between the two preceding muscles, and is the most deeply seated of the muscles on the back of the leg. It begins above by two pointed processes, separated by an angular interval through which the anterior tibial vessels pass forward to the front of the leg. It arises from the whole of the posterior surface of the interosseous membrane, excepting its lowest part; from the lateral portion of the posterior surface of the body of the tibia, between the commencement of the popliteal line above and the junction of the middle and lower thirds of the body below; and from the upper two-thirds of the medial surface of the fibula; some fibres also arise from the deep transverse fascia, and from the intermuscular septa separating it from the adjacent muscles. In the lower fourth of the leg its tendon passes in front of that of the Flexor digitorum longus and lies with it in a groove behind the medial malleolus, but enclosed in a separate sheath; it next passes under the laciniate and over the deltoid ligament into the foot, and then beneath the plantar calcaneonavicular ligament. The tendon contains a sesamoid fibrocartilage, as it runs under the plantar calcaneo- navicular ligament. It is inserted into the tuberosity of the navicular bone, and gives off fibrous expansions, one of which passes backward to the sustentaculum tali of the calcaneus, others forward and lateralward to the three cuneiforms, the cuboid, and the bases of the second, third, and fourth metatarsal bones. Relations. — The Tibiahs posterior is in relation by its superficial surface with the Soleus, from which it is separated by the deep transverse fascia, the Flexor digitorum longus, the posterior tibial vessels and tibial nerve, and the peroneal vessels; by its deep surface, with the interosseous membrane, the tibia, fibula, and ankle-joint. Nerves. — The Popliteus is supplied by the fourth and fifth lumbar and first sacral nerves, the Flexor digitorum longus and Tibialis posterior by the fifth lumbar and first sacral, and the Flexor hallucis longus by the fifth lumbar and the first and second sacral nerves, through the tibial nerve. Actions. — The Popliteus assists in flexing the leg upon the thigh; when the leg is flexed, it will rotate the tibia inward. It is especially called into action at the beginning of the act of bending the knee, inasmuch as it produces the slight inward rotation of the tibia which is essential in the early stage of this movement. The Tibiahs posterior is a direct extensor of the foot at the ankle- joint; acting in conjunction with the Tibiahs anterior, it turns the sole of the foot upward and medialward, i. e., inverts the foot, antagonizing the Peronaei, which turn it upward and lateral- ward (evert it). In the sole of the foot the tendon of the Tibiahs posterior hes directly below the plantar calcaneonavicular hgament, and is therefore an important factor in maintaining the arch of the foot. The Flexor digitorum longus and Flexor hallucis longus are the direct flexors of the phalanges, and, continuing their action, extend the foot upon the leg; they assist the Gastroc- nemius and Soleus in extending the foot, as in the act of walking, or in standing on tiptoe. In consequence of the obhque direction of its tendons the Flexor digitorum longus would draw the toes medialward, were it not for the Quadratus plantae, which is inserted into the lateral side of the tendon, and draws it to the middle line of the foot. Taking their fixed point from the foot, these muscles serve to maintain the upright posture by steadying the tibia and fibula perpendicularly upon the talus. 3. The Lateral Crural Muscles (Fig. 553). Peronaeus longus. Peronaeus brevis. Dissection. — The muscles are readily exposed by removing the fascia covering their surface, from below upward, in the fine of direction of their fibres. The Peronaeus longus is situated at the upper part of the lateral side of the leg, and is the more superficial of the two muscles. It arises from the head and THE LATERAL CRURAL MUSCLES 583 ui)l)er two-thirds of the hitcral surface of thi- Ixxly of the fihiila, from the deep surfaee of the fascia, and from tlie intermuscuhir septa l)et\veeii it and the muscles on the front and back of the k'j;-; occasionally also by a few fibres from the lateral condyle of the tibia. Between its attachments to the head and to the body of the fibula there is a fi;ap through which the common peroneal nerve passes to the front of the leg. It ends in a long tendon, which runs behind the lateral malleolus, in a groove common to it and the tendon of the Peronaeus brevis, behind which it lies; the groove is converted into a canal by the superior peroneal retinaculum, and the tendons in it are contained in a common mucous sheath. The tendon then extends obliquely forward across the lateral side of the calcaneus, beloAv the troch- lear process, and the tendon of the Peronaeus brevis, and under cover of the inferior peroneal retinaculum. It crosses the lateral side of the cuboid, and then runs on the under surface of that bone in a groove which is converted into a canal by the long plantar ligament; the tendon then crosses the sole of the foot obliquely, and. is inserted into the lateral side of the base of the first metatarsal bone and the lateral side of the first cuneiform. Occasionally it sends a slip to the base of the second metatarsal bone. The tendon changes its direction at two points: first, behind the lateral malleolus; secondly, on the cuboid bone; in both of these situations the ten- don is thickened, and, in the latter, a sesamoid fibrocartilage (sometimes a bone), is usually developed in its substance. The Peronaeus brevis lies under cover of the Peronaeus longus, and is a shorter and smaller muscle. It arises from the low^r tw^o-thirds of the lateral surface of the body of the fibula; medial to the Peronaeus longus; and from the intermuscular septa separating it from the adjacent muscles on the front and back of the leg. The fibres pass vertically downw^ard, and end in a tendon w^hich runs behind the lateral malleolus along w-ith but in front of that of the preceding muscle, the two tendons being enclosed in the same compartment, and lubricated by a common mucous sheath. It then runs forw^ard on the lateral side of the calcaneus, above the trochlear process and the tendon of the Peronaeus longus, and is inserted into the tuberosity at the base of the fifth metatarsal bone, on its lateral side. On the lateral surface of the calcaneus the tendons of the Peronaei longus and brevis occupy separate osseoaponeurotic canals formed by the calcaneus and the perineal retinacula; each tendon is enveloped by a forw^ard prolongation of the common mucous sheath. Nerves. — The Peronaei longus and brevis are supplied by the fourth and fifth lumbar and first sacral nerves through the superficial peroneal nerve. Actions. — The Peronaei longus and brevis extend the foot upon the leg, in conjunction with the Tibiahs posterior, antagonizing the Tibiahs anterior and Peronaeus tertius, which are flexors of the foot. The Peronaeus longus also everts the sole of the foot, and from the oblique direction of the tendon across the sole of the foot is an important agent in the maintenance of the trans- verse arch. Taking their fixed points below, the Peronaei serve to steady the leg upon the foot. This is especially the case in standing upon one leg, when the tendency of the superincumbent weight is to thi'ow the leg medialward; the Peronaeus longus overcomes this tendenc}^ by drawing on the lateral side of the leg. Applied Anatomy. — The student should now consider the positions of the tendons of the various muscles of the leg, their relation with the ankle-joint and surroimding bloodvessels, and especially theu- actions upon the foot, as their rigidity and contraction give rise to one or other of the kinds of deformity known as club-foot. The most simple and common deformity, and one that is rarely, if ever, congenital, is talipes equinus, the heel being raised by the rigidity and contraction of the Gastrocnemius so that the patient walks upon the ball of the foot. In talipes varus the foot is forcibly adducted and the medial side of the sole raised, sometimes to a right angle with the ground, by the action of the Tibiales anterior and posterior. In talipes valgus the lateral edge of the foot is raised by the Peronaei, and the patient walks on the medial side of the foot. In talipes calcaneus the toes are raised by the Extensor muscles, the heel is depressed and the patient walks upon it. Other varieties of deformity are met with, as talipes equinovarus, equinovalgus, and calcaneovalgiis, whose names sufficiently indicate their natm-e. Of these, tahpes equinovarus is the most common congenital form; the heel is raised bj^ the tendo calcaneus, the medial border of the foot dra^m upward by the Tibiahs anterior, the anterior two-thirds twisted medialward 584 MYOLOGY by the Tibialis posterior, and the arch increased by the contraction of the plantar aponeurosis, so that the patient walks on the middle of the lateral border of the foot. Each of these deformities may sometimes be successfully relieved by division of the opposing tendons and fascia; by this means the foot regains its proper position, and the tendons heal by the organization of lymph thrown out between the divided ends. The operation is easily performed by putting the con- tracted tendon upon the stretch, and dividing it by means of a narrow, shaip-pointed knife inserted beneath it. Rupture of a few of the fibres of the Gastrocneraius, or rupture of the Plantaris tendon, not uncommonl}' occurs, especially in men somewhat advanced in life, from some sudden exertion, and frequently occurs during the game of lawn tennis, and is hence known as lawn-tennis leg. The accident is accompanied by a sudden pain, and produces a sensation as if the individual had been struck a violent blow on the part. The tendo calcaneus is also sometimes ruptured. It is stated that John Hunter ruptured his tendo calcaneus while dancing, at the age of forty. The bursa between the tendo calcaneus and the posterior surface of the calcaneus sometimes becomes inflamed, especially in pedestrians and "long-distance" walkers. It causes great and disabling pain, and entirely prevents the sufferer from continuing his walk. THE FASCIA AROUND THE ANKLE. Fibrous bands, or thickened portions of the fascia, bind down the tendons in front of and behind the ankle in their passage to the foot. They comprise three ligaments, viz., the transverse crural, the cruciate crural, and the laciniate; and the superior and inferior peroneal retinacula. Tibialis anterior Extensor dig. longus Ext. hall. long. Ext. dig. hrevis Tendo calcaneus Peronaeus longus Pp.ronaeus hrevis Peronaeus tertius Fig. 554. — The mucous sheaths of the tendons around the ankle. Lateral aspect. Transverse Crural Ligament (ligamentum transversum cruris; upper part of anterior annular ligament) (Fig. 554). — The transverse crural ligament binds down the tendons of Extensor digitorum longus. Extensor hallucis longus, Peronaeus tertius, and Tibialis anterior as they descend on the front of the tibia and fibula; under it are found also the anterior tibial vessels and deep peroneal nerve. It is attached laterally to the lower end of the fibula, and medially to the tibia; above it is con- tinuous with the fascia of the leg. Cruciate Crural Ligament (ligamentum cruciatum cruris; lower part of anterior annular ligament) (Figs. 554, 555). — The cruciate crural ligament is a Y-shaped band placed in front of the ankle-joint, the stem of the Y being attached laterally THE FASCIA AROUND THE AXKLE 58;! to the upper surface of the calcaneus, in front of the depression for the interosseous talocalcancan ligament; it is directed mediahvard as a double layer, one lamina passing in front of, and the other behind, the tendons of the Peronaeus tertius and Extensor digitorum longus. At the medial l)order of the latter tendon these two layers join together, forming a compartment in which the tendons are enclosed. From the medial extremity of this sheath the two limbs of the Y diverge : one is directed upward and mediahvard, to be attached to the tibial malleolus, passing over the Extensor hallucis longus and the vessels and nerves, but enclosing the Tibialis anterior by a splitting of its fibres. The other limb extends downward and mediahvard, to be attached to the border of the plantar aponeurosis, and passes over the tendons of the Extensor hallucis longus and Tibialis anterior and also the vessels and ner^•es. Tibialis anterior J'ii: Tibialis posterior Ext. hall. lonq. Flexor Jiallucis longus B T endocalcaneus Fig. 555. — The mucous sheaths of the tendons around the ankle. Medial aspect. Laciniate Ligament (ligamentum lancinatinn; internal annular ligament). — The laciniate ligament is a strong fibrous band, extending from the tibial malleolus above to the margin of the calcaneus below, converting a series of bony grooves in this situation into canals for the passage of the tendons of the Flexor muscles and the posterior tibial vessels and tibial nerve into the sole of the foot. It is continuous by its upper border with the deep fascia of the leg, and by its lower border with the plantar aponeurosis and the fibres of origin of the Abductor hallucis muscle, Enumerated from the medial side, the four canals which it forms transmit the tendon of the Tibialis posterior; the tendon of the Flexor digitorum longus; the posterior tibial vessels and tibial nerve, which run through a broad space beneath the ligament; and lastly, in a canal formed partly by the talus, the tendon of the Flexor hallucis longus. Peroneal Retinacula. — The peroneal retinacula are fibrous bands which bind down the tendons of the Peronaei longus and brevis as they run across the lateral side of the ankle. The fibres of the superior retinaculum {external annular ligament) are attached ahoxe to the lateral malleolus and below to the lateral surface of the calcaneus. The fibres of the inferior retinaculum are continuous in front with those of the cruciate crural ligament; behind they are attached to the lateral surface of the calcaneus; some of the fibres are fixed to the peroneal trochlea, forming a septum between the tendons of the Peronaei longus and brevis. 586 MYOLOGY The Mucous Sheaths of the Tendons Around the Ankle.^ — All the tendons crossing the ankle-joint are enclosed for part of their lengtii in mucous sheaths which have an almost uniform length of about 8 cm. each. On the fro7it of the ankle (Fig. 554) the sheath for the Tibialis anterior extends from the upper margin of the trans- verse crural ligament to the interval between the diverging limbs of the cruciate ligament; those for the Extensor digitorum longus and Extensor hallucis longus reach upward to just above the level of the tips of the malleoli, the former being the higher. The sheath of the Extensor hallucis longus is prolonged on to the base of the first metatarsal bone, while that of the Extensor digitorum longus reaches only to the level of the base of the fifth metatarsal. On the medial side of the ankle (Fig. 555) the sheath for the Tibialis posterior extends highest up — to about 4 cm. above the tip of the malleolus — while below it stops just short of the tuber- osity of the navicular. The sheath for Flexor hallucis longus reaches up to the level of the tip of the malleolus, while that for the Flexor digitorum longus is slightly higher; the former is continued to the base of the first metatarsal, but the latter stops opposite the first cuneiform bone. On the lateral side of the ankle (Fig. 554) a sheath which is single for the greater part of its extent encloses the Peronaei longus and brevis. It extends upw^ard for about 4 cm. above the tip of the malleolus and downward and forward for about the same distance. IV. THE MUSCLES AND FASCIA OF THE FOOT. 1. The Dorsal Muscle of the Foot. Extensor digitorum brevis. The fascia on the dorsum of the foot is a thin membranous layer, continuous above with the transverse and cruciate crural ligaments; on either side it blends with the plantar aponeurosis; anteriorly it forms a sheath for the tendons on the dorsum of the foot. The Extensor digitorum brevis (Fig. 554) is a broad, thin muscle, which arises from the forepart of the upper and lateral surfaces of the calcaneus, in front of the groove for the Peronaeus brevis; from the lateral talocalcanean ligament; and from the common limb of the cruciate crural ligament. It passes obliquely across the dorsum of the foot, and ends in four tendons. The most medial, which is the largest, is inserted into the dorsal surface of the base of the first phalanx of the great toe, crossing the dorsalis pedis artery; it is frequently described as a separate muscle — the Extensor hallucis brevis. The other three are inserted into the lateral sides of the tendons of the Extensor digitorum longus of the second, third, and fourth toes. Nerves. — It is supplied by the deep peroneal nerve. Actions. — The Extensor digitorum brevis extends the phalanges of the four toes into which it is inserted, but in the great toe acts only on the first phalanx. The obliquity of its direction counteracts the oblique movement given to the toes by the long Extensor, so that when both muscles act, the toes are evenly extended. 2. The Plantar Muscles of the Foot. Plantar Aponeurosis {aijoneurosis p lantaris; plantar fascia) . — The plantar apon- eurosis is of great strength, and consists of pearly white glistening fibres, disposed, for the most part, longitudinally: it is divided into central, lateral, and medial portions. The central portion, the thickest, is narrow behind and attached to the medial process of the tuberosity of the calcaneus, posterior to the origin of the Flexor rJlE PLANTAR MUSCLES OF THE FOOT 587 digitoriim brevis; and becoming broader and thinner in front, divides near the heads of the metatarsal bones into five processes, one for each of the toes. Each of these processes divides opposite the metatarsoi)hahingeal articulation into two strata, su])erficial and dccj). The superficial stratum is inserted into the skin of the transverse sulcus which separates the toes from the sole. The deeper stratum divides into two slips which embrace the side of the Flexor tendons of the toes, and blend with the sheaths of the tendons, and with the transverse metatarsal ligament, thus forming a series of arches through which the tendons of the short and long Fh^xors pass to the toes. The intervals left between the five processes allow the digital vessels and nerves and the tendons of the Lumbricales to become superficial. At the point of division of the aponeurosis, numerous transverse fasciculi are superadded; these serve to increase the strength of the aponeurosis at this part by binding the processes together, and connecting them with the integu- ment. The central portion of the plantar aponeurosis is continuous with the lateral and medial portions and sends upward into the foot, at the lines of junction, two strong vertical intermuscular septa, broader in front than behind, which separate the intermediate from the lateral and medial plantar groups of muscles; from these again are derived thinner transverse septa which separate the various layers of muscles in this region. The upper surface of this aponeurosis gives origin behind to the Flexor digitorum brevis. The lateral and medial portions of the plantar aponeurosis are thinner than the central piece, and cover the sides of the sole of the foot. The lateral portion covers the under surface of the Abductor digiti quinti; it is thin in front and thick behind, where it forms a strong band between the lateral process of the tuberosity of the calcaneus and the base of the fifth metatarsal bone; it is continuous medially with the central portion of the plantar aponeurosis, and laterally with the dorsal fascia. The medial portion is thin, and covers the under surface of the Abductor hallucis ; it is attached behind to the laciniate ligament, and is continuous around the side of the foot with the dorsal fascia, and laterally wdth the central portion of the plantar aponeurosis. The muscles in the plantar region of the foot may be divided into three groups, in a similar manner to those in the hand. Those of the medial plantar region are connected with the great toe, and corrrespond with those of the thumb; those of the lateral plantar region are connected with the little toe, and correspond with those of the little finger; and those of the intermediate plantar region are connected with the tendons intervening between the two former groups. But in order to facilitate the description of these muscles, it is more convenient to divide them into four layers, in the order in which they are successively exposed. The First Layer (Fig. 556). x\bductor hallucis. Flexor digitorum brevis. Abductor digiti quinti. Dissection. — Remove the fascia on the inner and outer sides of the foot, commencing in front over the tendons and proceeding backward. The central portion should be divided transversely in the middle of the foot, and the two flaps dissected forward and backward. The Abductor hallucis lies along the medial border of the foot and covers the origins of the plantar vessels and nerves. It arises from the medial process of the tuberosity of the calcaneus, from the laciniate ligament, from the plantar aponeu- rosis, and from the intermuscular septum between it and the Flexor digitorum brevis. The fibres end in a tendon, which is inserted, together with the medial tendon of the Flexor hallucis brevis, into the tibial side of the base of the first phalanx of the great toe. 588 MYOLOGY The Flexor digitorum brevis lies in the middle of the sole of the foot, imme- diately above the central part of the plantar aponeurosis, with which it is firmly united. Its deep surface is separated from the lateral plantar vessels and nerves by a thin layer of fascia. It arises by a narrow tendon, from the medial process of the tuberosity of the calcaneus, from the central part of the plantar aponeurosis, and from the intermuscular septa between it and the adjacent muscles. It passes forward, and divides into four tendons, one for each of the four lesser toes. Oppo- site the bases of the first phalanges, each tendon divides into two slips, to allow of the passage of the corresponding tendon of the Flexor digi- torum longus; the two portions of the tendon then unite and form a grooved channel for the reception of the accompanying long Flexor tendon. Finally, it divides a second time, and is inserted into the sides of the second phalanx about its middle. The mode of division of the tendons of the Flexor digitorum brevis, and of their insertion into the phalanges, is analogous to that of the tendons of the Flexor digitorum sublimis in the hand. Fibrous Sheaths of the Flexor Tendons. — The terminal portions of the tendons of the long and short Flexor muscles are contained in osseoaponeurotic canals similar in their ar- rangement to those in the fingers. These canals are formed above by the phalanges and below by fibrous bands, which arch across the tendons, and are attached on either side to the margins of the phalanges. Opposite the bodies of the proximal and second pha- langes the fibrous bands are strong, and the fibres are transverse; but opposite the joints they are much thinner, and the fibres are directed obliquely. Each canal contains a mucous sheath, which is reflected on the con- tained tendons. The Abductor digiti quinti (Abductor minimi digiti) lies along the lateral border of the foot, and is in relation by its medial margin with the lateral plantar vessels and nerves. It arises, by a broad origin, from the lateral process of the tuberosity of the calcaneus, from the under surface of the calcaneus between the two pro- cesses of the tuberosity, from the forepart of the medial process, from the plantar aponeu- rosis, and from the intermuscular septum between it and the Flexor digitorum brevis. Its tendon, after gliding over a smooth facet on the under surface of the base of the fifth metatarsal bone, is inserted, with the Flexor digiti quinti brevis, into the fibular side of the base of the first phalanx of the fifth toe. Dissection. — The muscles of the superficial layer should be divided at their origin by inserting the knife beneath each, and cutting obliquely backward, so as to detach them from the bone; they should then be drawn forward, in order to expose the second layer, but not cut away at their insertion. The two layers are separated by a thin membrane, the deep plantar aponeurosis, on the removal of which is seen the tendon of the Flexor digitorum longus, the Quadratus plantae. Fig. 556.- -Muscles of the sole of the foot. First layer. THE PLAXTAR .}[USrLES OF THE FOOT 589 the tendon of the Flexor halkicis longus, and the Lumbricales. The long Flexor tendons diverge from each other at an acute an^le; the Flexor liallucis longus runs along the inner side of the foot, on a plane superior to that of the Flexor digitoruin longus, the dirciction of the latter being obliquely outward. The Second Layer (Fig. 557). Qiiadratiis plantae. Lumbricales. The Quadratus plantae (Flexor accessorius) is separated from the muscles of the first layer by the lateral plantar vessels and nerve. It arises by two heads, which are separated from each other by the long plantar ligament: the medial or larger head is muscular, and is attached to the medial concave surface of the calcaneus, below the groove which lodges the tendon of the Flexor hallucis longus ; the lateral head, flat and tendinous, arises from the lateral border of the inferior surface of the calcaneus, in front of the lateral process of its tuberosity, and from the long plantar ligament. The two portions join at an acute angle, and end in a flattened band which is inserted into the lateral margin and upper and under sur- faces of the tendon of the Flexor digitorum longus, forming a kind of groove, in which the tendon is lodged. It usually sends slips to those tendons of the Flexor digitorum longus which pass to the second, third, and fourth toes. The Lumbricales are four small muscles, accessory to the tendons of the Flexor digitorum longus and numbered from the medial side of the foot; they arise from these tendons, as far back as their angles of division, each springing from two tendons, except the first. The muscles end in tendons, which pass forward on the medial sides of the four lesser toes, and are inserted into the expansions of the tendons of the Extensor digitorum longus on the dorsal surfaces of the first phalanges. Dissection. — The Flexor tendons should be divided at the back part of the foot, and the Quadratus plantae at its origin, and drawn forward, in order to expose the third layer. The Third Layer (Fig. 558). Flexor hallucis brevis. Adductor hallucis. Flexor digiti qiiinti brevis. The Flexor hallucis brevis arises, by a pointed tendinous process, from the medial part of the under surface of the cuboid bone, from the contiguous portion of the third cuneiform, and from the prolongation of the tendon of the Tibialis posterior w^hich is attached to that bone. It divides in front into tw^o portions, which are inserted into the medial and lateral sides of the base of the first phalanx of the great toe, a sesamoid bone being present in each tendon at its insertion. The medial portion is blended with the Abductor hallucis previous to its insertion; the lateral portion with the Adductor hallucis; the tendon of the Flexor hallucis longus lies in a groove between them; the lateral portion is sometimes described as the first Interosseous plantaris. The Adductor hallucis {Adductor obliquus hallucis) arises by two heads — oblique and transverse. The oblique head is a large, thick, fleshy mass, crossing the foot obliquely and occupying the hollow space inider the first, second, third, and fourth metatarsal bones. It arises from the bases of the second, third, and fourth meta- tarsal bones, and from the sheath of the tendon of the Peronaeus longus, and is inserted, together with the lateral portion of the Flexor hallucis brevis, into the lateral side of the base of the first phalanx of the great toe. The transverse head ( Transversus pedis) is a narrow, flat fasciculus which arises from the plantar meta- tarsophalangeal ligaments of the third, fourth, and fifth toes (sometimes only from the third and fourth), and from the transverse ligament of the metatarsus. It is inserted into the lateral side of the base of the first phalanx of the great toe, its fibres blending with the tendon of insertion of the oblique head. 590 MYOLOGY The Abductor, Flexor brevis, and iVdductor of the ureat toe, hke the similar muscles of the thumb, give off, at their insertions, fibrous expansions to blend with the tendons of the Extensor digitorum longus. Fig. 557. — Muscles of the sole of the foot. Second layer. Fig. 558. — Muscles of the sole of the foot. Third layer. The Flexor digiti quinti brevis {Flexor brevis minimi digiii) lies under the metatarsal bone of the little toe, and resembles one of the Interossei. It arises from the base of the fifth metatarsal bone, and from the sheath of the Peronaeus longus; its tendon is inserted into the lateral side of the base of the first phalanx of the fifth toe. Occasionally a few of the deeper fibres are inserted into the lateral part of the distal half of the fifth metatarsal bone; these are described by some as a distinct muscle, the Opponens digiti quinti. The Fourth Layer. Interossei. The Interossei in the foot are similar to those in the hand, with this exception, that they are grouped arovnid the middle line of the second digit, instead of that THE PLAXTAli MUSCLES OF THE FOOT 591 of the //;//•(/. Thoy are seven in lumiber, and consist of two ^ronps, dorsal and plantar. The Interossei dorsales {Dorsal inti'rossci) (Fig. 559),/o(//- in nnmber, are situated between the metatarsal l)ones. They are bipenniform muscles, each arising by two heads from the adjacent sides of the metatarsal bones between which it is placed; their tendons are iuscried into the bases of the first phalanges, and into the aponeurosis of the tendons of the Extensor digitorum longus. In the angular interval left between the heads of each of the three lateral muscles, one of the perforating arteries passes to the dorsum of the foot; through the space between the heads of the first muscle the deep plantar branch of the dorsalis pedis artery enters the sole of the foot. The first is inserted into the medial side of the second toe; the other three are inserted into the lateral sides of the second, third, and fourth toes. Fig. 559. — The Interossei dorsales. Left foot. Fig. 560. — The Interossei plantares. Left foot. The Interossei plantares {Plantar interossei) (Fig. 560), three in number, lie beneath rather than between the metatarsal bones, and each is connected with but one metatarsal bone. They arise from the bases and medial sides of the bodies of the third, fourth, and fifth metatarsal bones, and are inserted into the medial sides of the bases of the first phalanges of the same toes, and into the aponeuroses of the tendons of the Extensor digitorum longus. Nerves. — The Flexor digitorum brevis, the Flexor haUucis brevis, the Abductor hallucis, and the first Lumbricahs are supphed by the medial plantar nerve; all the other muscles in the sole of the foot by the lateral plantar. The first Interosseous dorsalis frequently receives an extra filament from the medial branch of the deep peroneal nerve on the dorsum of the foot, and the second Interosseous dorsalis a twig from the lateral branch of the same nerve. Actions. — All the muscles of the foot act upon the toes, and may be grouped as abductors, adductors, flexors, or extensors. The abductors are the Interossei dorsales, the Abductor hallucis, and the Abductor digiti quinti. The Interossei dorsales are abductors from an imaginary line passing through the axis of the second toe, so that the first muscle draws the second toe medial- ward, toward the great toe, the second muscle draws the same toe lateralward, and the third and fourth di'aw the third and fourth toes in the same direction. Like the Interossei in the hand, each assists in flexing the first phalanx and extending the second and third phalanges. The Abductor haUucis abducts the great toe from the second, and also flexes its proximal phalanx. 592 MYOLOGY In the same way the action of the Abductor digiti fjuinli is twofold, as an abductor of this toe from the fourth, and also as a flexor of its proximal phalanx. The adductors are the Interossei plantares and the Adductor hallucis. The Interossei plantares adduct the third, fourth, and fifth toes toward the imaginary hne passing through the second toe, and by means of their inser- tions into the aponeuroses of the Extensor tendons they assist in flexing the proximal phalanges and extending the middle and terminal phalanges. The obhque head of the Adductor hallucis is chiefly concerned in adducting the great toe toward the second one, but also assists in flexing this toe; the transverse head approximates all the toes and thus increases the cm-ve of the trans- verse arch of the metatarsus. The flexors are the Flexor digitorum brevis, the Quadratus plantae, the Flexor hallucis brevis, the Flexor digiti quinti brevis, and the Lumbricales. The Flexor digitorum brevis flexes the second phalanges upon the first, and, continuing its action, flexes the first phalanges also, and brings the toes together. The Quadratus plantae assists the Flexor digi- torum longus and converts the obhque pull of the tendons of that muscle into a direct backward puU upon the toes. The Flexor digiti quinti brevis flexes the httle toe and draws its metatarsal bone downward and medialward. The Lumbricales, like the corresponding muscles in the hand, assist in flexing the proximal phalanges, and by their insertions into the tendons of the Extensor digitorum longus aid that muscle in straightening the middle and terminal phalanges. The Extensor digitorum brevis extends the first phalanx of the great toe and assists the long Extensor in extending the next three toes, and at the same time gives to the toes a. lateral direction when they are extended. Piriformis Gemellus superior Obturator internum Gemellus inferior Obturator externns Quadratus femoris Fig. 561. — Fracture of the neck of the femur within the articular capsule. Applied Anatomy. — The student should now consider the effects produced by the action of the various muscles in fractures of the bones of the lower extremity. The more common forms of fracture are selected for illustration and description. In fracture of the neck of the femur inside the articular capsule (Fig. 561), the characteristic signs are shght shortening of the limb, and eversion of the foot, neither of which may appear until some time after the injury. The eversion is caused by the w^eight of the hmb rotating it outward. The shortening is produced by the contractions of all the muscles about the joint. In fracture of the femur just below the trochanters (Fig. 562), the upper fragment is tilted forward almost at right angles with the pelvis, by the Psoas major and Ihacus; and, at the same time, everted and drawn laterally by the external rotator muscles and Glutaei, causing a marked prominence at the upper and lateral side of the thigh, and much pain from the bruising and lacera- tion of the muscles. The hmb is shortened, because the lower fragment is drawn upward by the Rectus femoris in front, and the Biceps"femoris, Semimembranosus, and Semitendinosus behind; it is, at the same time, everted. This fractm-e may be reduced by relaxation of all the muscles involved, to effect which the hmb should be put up with the thigh flexed on the pelvis and the leg on the thigh. THE PLANTAR MUSCLES OF THE FOOT 593 Oblique fracture of the femur immediately above the condyles (Fis- 563) is a formidable injury, and attended with consitlerable displacement. On examination of the limb, the lower fragment may be felt deep in the popliteal fossa, being drawn backward by the Gastrocnemius, and upward by the Hamstrings and li(>ctus femoris. The pointed end of the upper fragment is drawn medial- ward by the Pectineus and Adductores, and tilted forward by the Psoas major and Iliacus, piercing the Rectus, and occasionally the integument. Relaxation of these muscles, and direct approxima- tion of the broken fragments, are effected by traction with the limb fully flexed. The greatest care is requisite in keei)ing the pointed extremity of the upper fragment in proper position; otherwise, after union of the fracture, the power of extension of the limb is partially destroyed, the Rectus femoris being held down by the fractured end of the bone. j - ''..' ■ ■' - Semimeinhranosus ' ' ' 'i . Semitendinosus Fig. 562. -Fracture of the femur below the trochanters. Fig. 563. — Fracture of the femur above the condyles. In transverse fracture of the patella (Fig. 564) the fragments are separated by the action of the Quadriceps femoris and by the effusion which takes place into the joint; the extent of separa- tion of the two fragments depending upon the degree of laceration of the hgamentous structures around the bone. In obHque fracture of the body of the tibia (Fig. 565), if the fractm-e has taken place obhquely from above, downward and forward, the fragments ride over one another, the lower fragment being drawn backward and upward by the powerful action of the muscles of the calf; the pointed extremity of the upper fragment projects forward immediately beneath the integument, often protruding through it, and rendering the fracture compound. If the direction of the fractui'e is the reverse of that shown in the figm-e, the pointed extremity of the lower fragment projects forward, rising up on the lower end of the upper one. By bending the knee, which relaxes the opposing muscles, and making extension from the ankle and counter-extension at the knee, the fragments may be brought into apposition. It is sometimes necessary, however, in compound fractm'e to remove a portion of the projecting bone with the saw before complete adaptation can be effected. Fracture of the fibula with dislocation of the foot lateralivard, commonly known as Pott's fracture, is one of the most frequent injuries in the region of the ankle-joint. The fibula is fractured about 7 or 8 cm. above the ankle; in addition to this the medial malleolus is broken off, or the deltoid ligament torn through, and the talus displaced from the corresponding smiace of the tibia. The 38 594 MYOLOGY foot is markedly everted, and the sharp edge of the upper end of the fractured malleolus presses strongly against the skin; at the same time, the heel is drawn up by the muscles of the calf. This injury can generally be reduced by flexing the leg at right angles with the thigh, which relaxes Fig. 564. — Fracture of the patella. Fig. 565. — Oblique fracture of the body of the tibia. all the opposing muscles, and by making extension from the ankle and coimter-extension at the knee. There is later a great tendency for the foot to fall backward at the ankle-joint, and constant supervision is required to counteract this. ANGlOLUaY. rpPIE vascular system is divided for descriptive purposes into (a) the blood -*- vascular system, which comprises the heart and bloodvessels for the circula- tion of the blood; and (6) the lymph vascular system, consisting of lymph glands and lymphatic vessels, through which a colorless fluid, the lymph, circulates. It must be noted, however, that the two systems communicate with each other and are intimately associated developmentally. The heart is the central organ of the blood vascular system, and consists of a hollow muscle; by its contraction the blood is pumped to all parts of the body through a complicated series of tubes, termed arteries. The arteries undergo enormous ramification in their course throughout the body, and end in minute vessels, called arterioles, which in their turn open into a close-meshed network of microscopic vessels, termed capillaries. After the blood has passed through the capillaries it is collected into a series of larger vessels, called veins, by which it is returned to the heart. The passage of the blood through the heart and blood- vessels constitutes what is termed the circulation of the blood, of which the following is an outline.^ The human heart is divided by septa into right and left halves, and each half is further divided into two cavities, an upper termed the atrium and a lower the ventricle. The heart therefore consists of four chambers, two, the right atrium and right ventricle, forming the right half, and two, the left atrium and left ventricle the left half. The right half of the heart contains venous or impure blood; the left, arterial or pure blood. The atria are receiving chambers, and the ventricles dis- tributing ones. From the cavity of the left ventricle the pure blood is carried into a large artery, the aorta, through the numerous branches of which it is distributed to all parts of the body, with the exception of the lungs. In its passage through the capillaries of the body the blood gives up to the tissues the materials necessary for their growth and nourishment, and at the same time receives from the tissues the waste products resulting from their metabolism. In doing so it is changed from arterial into venous blood, which is collected by the veins and through them returned to the right atrium of the heart. From this cavity the impure blood passes into the right ventricle, and is thence conveyed through the pulmonary arteries to the lungs. In the capillaries of the lungs it again becomes arterialized, and is then carried to the left atrium by the pulmonary veins. From the left atrium " it passes into the left ventricle, from which the cycle once more begins. The course of the blood from the left ventricle through the body generally to the right side of the heart constitutes the greater or systemic circulation, while its passage from the right ventricle through the lungs to the left side of the heart is termed the lesser or pulmonary circulation. It is necessary, however, to state that the blood which circulates through the spleen, pancreas, stomach, small intestine, and the greater part of the large intes- tine is not returned directly from these organs to the heart, but is conveyed by the portal vein to the liver. In the liver this vein divides, like an artery, and ultimately ends in capillary-like vessels (sinusoids), from which the rootlets of a series of veins, called the hepatic veins, arise; these carry the blood into the inferior vena cava, 1 The composition of the blood is described on pp. 61 to 64. 596 ANGIOLOGY whence it is conveyed to the right atrium. From this it will be seen that the blood contained in the portal vein passes through two sets of vessels: (1) the capillaries in the spleen, pancreas, stomach, etc., and (2) the sinusoids in the liver. Speaking generally, the arteries may be said to contain pure and the veins impure blood. This is true of the systemic, but not of the pulmonary vessels, since it has been seen that the impure blood is conveyed from the heart to the lungs by the pulmonary arteries, and the pure blood returned from the lungs to the heart by the pulmonary veins. Arteries, therefore, must be defined as vessels which convey blood from the heart, and veins as vessels which return blood to the heart. Structure of Arteries (Fig. 566). — The arteries are composed of three coats: an internal or endotheUal coat {tunica intima of Kolliker); a middle or muscular coat {tunica media); and an external or connective-tissue coat {tunica adventitia). The two inner coats together are very easily separated from the external, as by the ordinary operation of tying a Ugatm-e around an artery. If a fine string be tied forcibly upon an artery and then taken off, the external coat will be found undivided, but the two inner coats are divided in the track of the hgature and can easily be further dissected from the outer coat. The inner coat {tunica intima) can be separated from the middle by a httle maceration, or it maj'^ be stripped off in small pieces; but, on account of its friabiUty, it cannot be separated as a complete mem- brane. It is a fine, transparent, colorless structure which is highly elastic, and, after death, is commonly corrugated into longitudinal wrinkles. The inner coat consists of: (1) A layer of pavement endothehum, the cells of which are polygonal, oval, or fusiform, and have very distinct round or oval nuclei. This endothelium is brought into view most distinctly by staining with nitrate of silver. (2) A subendotheUal layer, consisting of delicate connective tissue with branched cells lying in the interspaces of the tissue; in arteries of less than 2 mm. in diameter the sub- endothehal layer consists of a single stratum of stel- late cells, and the connective tissue is only largely developed in vessels of a considerable size. (3) An elastic or fenestrated layer, which consists of a mem- brane containing a net-work of elastic fibres, having principally a longitudinal direction, and in which, under the microscope, smaU elongated apertures or perforations may be seen, giving it a fenestrated ap- pearance. It was therefore called by Henle the fenes- trated membrane. This membrane forms the chief thickness of the inner coat, and can be separated into several layers, some of which present the appearance of a net-work of longitudinal elastic fibres, and others a more membranous character, marked by pale fines having a longitudinal direction. In minute arteries the fenestrated membrane is a very thin layer; but in the larger arteries, and especially in the aorta, it has a very considerable thickness. The middle coat {tunica media) is distinguished from the inner by its color and by the trans- verse arrangement of its fibres. In the smaller arteries it consists principally of plain muscle fibres in fine bundles, arranged in lamellae and disposed circularly around the vessel. These lamellae vary in number according to the size of the vessel; the smallest arteries having only a single layer (Fig. 567), and those sHghtly larger three or four layers. It is to this coat that the thickness of the wafi of the artery is mainly due (Fig. 566A, m). In the larger arteries, as the iliac, femoral, and carotid, elastic fibres unite to form lamellae which alternate with the layers of muscular fibres; these lamellae are united to one another by elastic fibres which pass between the muscular bundles, and are connected with the fenestrated membrane of the inner coat (Fig. 568). In the largest arteries, as the aorta and innominate, the amount of elastic tissue is very considerable; in these vessels a few bundles of white connective tissue also have been found in Fig. 566. — Transverse section through a small artery and vein of the mucous membrane of the epiglottis of a child. X 350. (Klein and Noble Smith.) A. Artery, showing the nucleated endo- thelium, e, which lines it; the vessel being con- tracted, the endothelial cells appear very thick. Underneath the endothelium is the wavy elastic lamina. The chief part of the wall of the vessel is occupied by the circular muscle coat m; the rod-shaped nuclei of the muscle cells are well seen. Outside this is a, part of the adventitia. This is composed of bundles of connective tissue fibres, shown in section, with the nuclei of the connec- tive tissue corpuscles. The adventitia gradually merges into the surrounding connective tissue. V. Vein showing a thin endothelial membrane, e, raised accidentally from the intima, which on account of its delicacy is seen as a mere line on the media m. This latter is composed of a few circular unstriped muscle cells a. The adventitia, similar in structure to that of an artery. STRUCTURE OF ARTERIES 597 the middle coat. The muscle fibre cells are about 50;u in length and contain well-marked, rod- shaped nuclei, which are often sUghtly curved. The external coat (tunica adventitia) consists mainly of fine and closely felted bundles of white connective tissue, but also contains clastic fibres in all but the smallest arteries. The elastic tissue is much more abundant next the tunica media, and it is sometimes described as forming here, between the adventitia and media, a special layer, the tunica elastica externa of Henle. This layer is most marked in arteries of medium size. In the largest vessels the external coat is relatively thin; but in small arteries it is of greater proportionate thickness. In the smaller arteries it consists of a single layer of white connec- tive tissue and elastic fibres; while in the smallest arteries, just above the capillaries, the elastic fibres are wanting, and the connective tissue of which the coat is composed becomes more nearly homogeneous the nearer it approaches the capillaries, and is grad- ually reduced to a thin membranous envelope, which finally disappears. Some arteries have extremely thin walls in propor- tion to their size; this is especially the case in those situated in the cavity of the cranium and vertebral canal, the difference depending on the thinness of the external and middle coats. The arteries, in their distribution throughout the body, are included in thin fibro-areolar investments, which form their sheaths. The vessel is loosely con- nected with its sheath by delicate areolar tissue; and the sheath usually encloses the accompanying veins, and sometimes a nerve. Some arteries, as those in the cranium, are not included in sheaths. All the larger arteries, like the other organs of the body, are supphed with bloodvessels. These Endothelial and suh- endothelial layer of inner coat — Elastic layer Innermost layers of middle coat Fig. 567. — Small artery and vein, pia mater of sheep. X 250. Surface view above the inter- rupted line; longitudinal section below. Artery in red; vein in blue. Outermost layers of — middle coat Innermost fart of Older coat Outermost part of outer coat Fig. 56S. — Section of a medium-sized artery. (After Griinstein.) nutrient vessels, called the vasa vasorum, arise from a branch of the artery, or from a neighbor- ing vessel, at some considerable distance from the point at which they are distributed; they 598 ANGIOLOGY ramify in the loose areolar tissue connecting the artery with its sheath, and are distributed to the external coat, but do not, in man, penetrate the other coats; in some of the larger mammals a few vessels have been traced into the middle coat. Minute veins return the blood from these vessels; they empty themselves into the vein or veins accompanying the artery. Lymphatic vessels are also present in the outer coat. Arteries are also supplied with nerves, which are derived from the sympathetic, but may pass through the cerebrospinal nerves. They form intricate plexuses upon the surfacics of the larger trunks, and run along the smaller arteries as single filaments, or bundles of filaments which twist around the vessel and unite with each other in a plexiform manner. The branches derived from these plexuses penetrate the external coat and are distributed principally to the muscular tissue of the middle coat, and thus regulate, by causing the contraction and relaxation of this tissue the amount of blood sent to any part. The Capillaries. — The smaller arterial branches (excepting those of the cavernous structure of the sexual organs, of the splenic puliD, and of the placenta) terminate in net-works of vessels which pervade nearly every tissue of the body. These vessels, from their minute size, are termed capillaries. They are interposed between the smallest branches of the arteries and the commenc- ing veins, constituting a net -work, the branches of which maintain the same diameter throughout; the meshes of the net-work are more uniform in shape and size than those formed by the anasto- moses of the small arteries and veins. The diameters of the capillaries vary in the different tissues of the body, the usual size being about 8ju. The smallest are those of the brain and the mucous membrane of the intestines; and the largest those of the skin and the marrow of bone, where they are stated to be as large as 20^ in diameter. The form of the capillary net varies in the different tissues, the meshes being generally roimded or elongated. The rounded form of mesh is most common, and prevails where there is a dense network, as in the lungs, in most glands and mucous membranes, and in the cutis; the meshes are not of an absolutely circular outUne, but more or less angular, sometimes nearly quadrangular, or polygonal, or more often irregular. Elongated meshes are observed in the muscles and nerves, the meshes resembhng parallelograms in form, the long axis of the mesh running parallel with the long axis of the nerve or muscle. Sometimes the capillaries have a looped arrangement; a single vessel projecting from the common net-work and returning after forming one or more loops, as in the papillse of the tongue and skin. The number of the capillaries and the size of the meshes determine the degree of vascularity of a part. The closest network and the smallest interspaces are found in the lungs and in the choroid coat of the eye. In these situations the interspaces are smaller than the capillary vessels themselves. In the intertubular plexus of the kidney, in the conjunctiva, and in the cutis, the interspaces are from three to four times as large as the capillaries which form them; and in the brain from eight to ten times as large as the capillaries in their long diameters, and from four to six times as large in their transverse diameters. In the adventitia of arteries the width of the meshes is ten times that of the capillary vessels. As a general rule, the more active the func- tion of the organ, the closer is its capillary net and the larger its supply of blood; the meshes of the network are very narrow in all growing parts, in the glands, and in the mucous membranes, wider in bones and Ugaments which are comparatively inactive; bloodvessels are nearly alto- gether absent in tendons, in which very httle organic change occurs after their formation. In the liver the capillaries take a more or less radial course toward the intralobular vein, and their walls are incomplete, so that the blood comes into direct contact with the hver cells. These vessels in the liver are not true capillaries but "sinusoids;" they are developed by the growth of columns of hver cells into the blood spaces of the embryonic organ. Structure. — The wall of a capillary consists of a fine transparent endothehal layer, composed of cells joined edge to edge by an interstitial cement substance, and continuous with the endo- thelial cells which line the arteries and veins. When stained with nitrate of silver the edges which bound the epithehal cells are brought into view (Fig. 569). These cells are of large size and of an irregular polygonal or lanceolate shape, each containing an oval nucleus which may be dis- played by carmine or hematoxyUn. Between their edges, at various points of their meeting, roundish dark spots are sometimes seen, which have been described as stomata, though they are closed by intercellular substance. They have been beheved to be the situations through which the colorless corpuscles of the blood, when migrating from the bloodvessels, emerge; but this view, though probable, is not universally accepted. Kolossow describes these cells as having a rather more complex structure. He states that each consists of two parts: of hyaline groxmd plates, and of a protoplasmic granular part, in which is imbedded the nucleus, on the outside of the ground plates. The hyahne internal coat of the capillaries does not form a complete membrane, but consists of "plates" which are inelastic, and though in contact with each other are not continuous; when therefore the capillaries are sub- jected to intravascular pressure, the plates become separated from each other; the protoplasmic portions of the cells, on the other hand, are united together. In some organs, e. g., the glomeruli STRUCTURE OF VEINS 599 Fig. 569. — Capillaries from the mesen- tery of a guinea-pig, after treatment with solution of nitrate of silver, a. Cells. b. Their nuclei. of the kidneys, intercellular cement (iaiuiol l)c dcnionstrated in the capillary wall and the cells are believed to form a syncytium. In many situations a delicate sheath or envelope of branched nucleated connective tissue cells is found around the simple capillary tube, particularly in the larger ones; and in other places, especially in the glands, the cajiillarics are invested with retiform connective tissue. Sinusoids. — In certain organs, viz., the heart, the liver, the suprarenal and parathyroid glands, the glomus caroti(uun and glomus coccygeum, the smallest bloodvessels present various differences from true capillaries. They are wider, with an irregular lumen, and have no connective tissue covering, their endothelial cells being in direct contact with the cells of the organ. Moreover, they are either arterial or venous and not intermediate as are the true capillaries. These vessels have been called sinusoids by Minot. They are formed by coluums of cells or trabecular pushing their way into a large bloodvessel or blood space and carrying its endothe- lium before them; at the same time the wall of the vessel or space grows out between the cell columns. Structure of Veins. — ^The veins, like the arteries, are com- posed of three coats: internal, middle, and external; and these coats are, with the necessary modifications, analogous to the coats of the arteries; the internal being the endo- thelial, the middle the muscular, and the external the connective tissue or areolar (Fig. 570). The main differ- ence between the veins and the arteries is in the compara- tive weakness of the middle coat in the former. In the smallest veins the three coats are hardly to be dis- tinguished (Fig. 567). The endothelium is supported on a membrane separable into two layers, the outer of which is the thicker, and consists of a delicate, nucleated mem- brane {adventitia) , while the inner is composed of a network of longitudinal elastic fibres {media). In the veins next above these in size (0.4 mm. in diameter), according to KoUiker, a connective tissue layer containing numerous muscle fibres circular^ disposed can be traced, forming the middle coat, while the elastic and connective tissue elements of the outer coat become more distinctly perceptible. In the middle-sized veins the typical structure of these vessels becomes clear. The endothelium is of the same character as in the arteries, but its cells are more oval and less fusiform. It is supported by a connective tissue layer, consisting of a delicate net-work of branched cells, and external to this is a layer of elastic fibres disposed in the form of a net-work in place of the definite fenestrated membrane seen in the arteries. This constitutes the internal coat. The middle coat is composed of a thick layer of con- nective tissue with elastic fibres, intermixed, in some veins, with a transverse layer of muscular tissue. The white fibrous element is in considerable excess, and the elastic fibres are in much smaller proportion in the veins than in the arteries. The outer coat consists, as in the arteries, o^ areolar tissue, with longitudinal elastic fibres. In the largest veins the outer coat is from two to five times thicker than the middle coat, and contains a large number of longitudinal muscular fibres. These are most distinct in the inferior vena cava, especially at the termination of this vein in the heart, in the trunks of the hepatic veins, in all the large trunks of the portal vein, and in the external ihac, renal, and azygos veins. In the renal and portal veins they extend through the whole thickness of the outer coat, but in the other veins mentioned a layer of con- nective and elastic tissue is found external to the muscular fibres. All the large veins which open into the heart are covered for a short distance with a layer of striped muscular tissue continued on to them from the heart. Muscular tissue is wanting: (1) in the veins of the maternal part of the placenta; (2) in the venous sinuses of the dura mater and the veins of the pia mater of the brain and meduUa spinaUs; (3) in the veins of the retina; (4) in the veins of the cancellous tissue of bones; (5) in the venous spaces of the corpora cavernosa. The veins of the above-men- tioned parts consist of an internal endotheUal lining supported on one or more layers of areolar tissue. Most veins are provided with valves which serve to prevent the reflux of the blood. Each valve is formed by a reduphcation of the inner coat, strengthened by connective tissue and elastic fibres, and is covered on both surfaces with endothehum, the arrangement of which differs on the two surfaces. On the surface of the valve next the wall of the vein the cells are arranged transversely; while on the other surface, over which the current of blood flows, the cells are arranged longitudinally in the direction of the current. Most commonly two such valves are found placed opposite one another, more especially in the smaller veins or in the larger trunks at the point where they are joined by smaller branches; occasionally there are three and some- 600 ANGIOLOGY times only one. The valves are semilunar. They are attached by their convex edges to the wall of the vein; the concave margins are free, directed in the course of the venous current, and lie in close apposition with the wall of the vein as long as the current of blood takes its natural course; if, however, any regurgitation takes place, the valves become distended, their opposed edges are brought into contact, and the current is interrupted. The wall of the vein on the cardiac side of the point of attachment of each valve is expanded into a pouch or sinus, which gives to the vessel, when injected or distended with blood, a knotted appearance. The valves are very numerous in the veins of the extremities, especially of the lower extremities, these vessels Endothelium •■ ~ . Elastic layer y-^' Middle coat ; — ■ Outer coat . Fig. 570. — Section of a medium-sized vein. having to conduct the blood against the force of gravity. They are absent in the very small veins, i. e., those less than 2 mm. in diameter, also in the venae cavse, hepatic, renal, uterine, and ovarian veins. A few valves are found in each spermatic vein, and one also at its point of jxmc- tion with the renal vein or inferior vena cava respectively. The cerebral and spinal veins, the veins of the cancellated tissue of bone, the pulmonary veins, and the umbilical vein and its branches, are also destitute of valves. A few valves are occasionally found in the azygos and intercostal veins. Rudimentary valves are found in the tributaries of the portal venous system. The veins, like the arteries, are supphed with nutrient vessels, vasa vasorum. Nerves also are distributed to them in the same manner as to the arteries, but in much less abundance. THE THORACIC CAVITY. The heart and lungs are situated in the thorax, the walls of which afford them protection. The heart lies between the two lungs, and is enclosed within a fibrous bag, the pericardium, while each lung is invested by a serous membrane, the pleura. The skeleton of the thorax, and the shape and boundaries of the cavity, have already been described (page 216). The Cavity of the Thorax. — The capacity of the cavity of the thorax does not correspond with its apparent size externally, because (1) the space enclosed by the lower ribs is occupied by some of the abdominal viscera; and (2) the cavity THE PERICARDIUM 601 extends above the anterior parts of the first ribs into the neck. The size of the thoracic cavity is constantly varying during life with the movements of the ribs and Diai^hragma, and ^^•itll the degree of distention of the abdominal viscera. From the collapsed state of the lungs as seen when the thorax is opened in the dead body, it would appear as if the viscera only partly filled the cavity, but during life there is no vacant space, that which is seen after death being filled up by the ex])anded lungs. The Upper Opening of the Thorax. — The parts which pass through the upper opening of the thorax are, from before backward, in or near the middle line, the Sternohyoideus and Sternothyreoideus muscles, the remains- of the thymus, the inferior thyroid veins, the trachea, oesophagus, thoracic duct, and the Longus colli muscles; at the sides, the innominate artery, the left common carotid, left subclavian and internal mammary arteries and the costocervical trunks, the innominate veins, the vagus, cardiac, phrenic, and sympathetic nerves, the greater parts of the anterior divisions of the first thoracic nerves, and the recurrent nerve of the left side. The apex of each lung, covered by the pleura, also projects through this aperture, a little above the level of the sternal end of the first rib. The Lower Opening of the Thorax.T— The lower opening of the thorax is wider transversely than from before backward. It §lopes obliquely downward and back- ward, so that the thoracic cavity is much deeper behind than in front. The Dia- phragma (see page 493) closes the opening and forms the floor of the thorax. The floor is flatter at the centre than at the sides, and higher on the right side than on the left; in the dead body the right side reaches the level of the upper border of the fifth costal cartilage, while the left extends only to the corresponding part of the sixth costal cartilage. From the highest point on each side the floor slopes suddenly downward to the costal and vertebral attachments of the Diaphragma; this slope is more marked behind than in front, so that only a narrow space is left between the Diaphragma and the posterior wall of the thorax. THE PERICARDIUM. The pericardium (Fig. 571) is a conical fibro-serous sac, in which the heart and the roots of the great vessels are contained. It is placed behind the sternum and the cartilages of the third, fourth, fifth, sixth, and seventh ribs of the left side, in the mediastinal cavity. In front, it is separated from the anterior wall of the thorax, in the greater part of its extent, by the lungs and pleurae ; but a small area, somewhat variable in size, and usually corresponding with the left half of the lower portion of the body of the sternum and the medial ends of the cartilages of the fourth and fifth ribs of the left side, comes into direct relationship with the chest wall. The lower extrem- ity^ of the thymus, in the child, is in contact with the front of the upper part of the pericardium. Behind, it rests upon the bronchi, the oesophagus, the descending thoracic aorta, and the posterior part of the mediastinal surface of each lung. Laterally, it is covered by the pleurae, and is in relation with the mediastinal sur- faces of the lungs; the phrenic nerve, with its accompanying vessels, descends between the pericardium and pleura on either side. Structure of the Pericardium. — Although the pericardium is usually described as a single sac, an examination of its structm-e shows that it consists essentially of two sacs intimately connected with one another, but totally different m structm'e. The outer sac, kno^Ti as the fibrous peri- cardium, consists of fibrous tissue. The inner sac, or serous pericardium, is a dehcate mem- brane which hes within the fibrous sac and lines its walls; it is composed of a single layer of flattened cells resting on loose connective tissue. The heart invaginates the wall of the serous sac from above and behind, and practically obliterates its cavity, the space being a potential one, except in front, where a small interspace exists below the apex of the heart. 602 AN GIG LOGY The fibrous pericardium forms a flask-shaped baK, the neck of which is closed by its fusion with the external coats of the si'cat vessels, while its base is attached to the central tendon and to the muscular fibres of the left side of the Diaphragma. In some of the lower mammals the base is either completely separated from the Diapln-agma or joined to it by some loose areolar tissue; in man much of its diaphragmatic attachment consists of loose fibrous tissue which can be readily broken down, but over a small area the central tendon of the Diaphragma and the pericardium are completely fused. Above, the fibrous pericardium not only blends with the external coats of the great vessels, but is continuous with the pretracheal layer of the deep cervical fascia. By means of these upper and lower connections it is securely anchored within the thoracic cavity. It is also attached to the posterior surface of the sternum by the superior and inferior stemopericardiac ligaments ; the upper passing to the manubrium, and the lower to the xiphoid process. On either side , of the ascending aorta it sends upward a diverticulum; that on the left R. common carotid a. R. subclavian a ^-—r^/ L. coinmon carotid a. L. subclavian a. Sup. vena cava R. 'pulmonary veiiib Cut edges of serous pericardium, ':ix-p^ ^- pulmomtry veins Fig. .571. -Posterior wall of the pericardial sac, showing the lines of reflection of the serous pericardium on the great vessels. side, somewhat conical in shape, passes between the arch of the aorta and the pulmonary artery, toward the ligamentum arteriosum, where it ends in a cecal extremity which is attached by loose connective tissue to the hgament ; that on the right side passes between the ascending aorta and superior vena cava, and also ends in a blind extremity. The vessels receiving fibrous prolongations from this membrane are: the aorta, the superior vena cava, the right and left pulmonary arteries, and the four pulmonary veins. The mferior vena cava enters the pericardium through the central tendon of the Diaphragma, and receives no covering from the fibrous layer. THE PERICARDIUM 603 The serous pericardium is, as already stated, a closed sac which linos the fil)rous pericardium and is invaginated l)y the heart; it therefore consists of a visceral and a parietal portion. The visceral portion, or epicardium, covers the heart and the great vessels, and from the latter is continuous with the i)arietal layer which lines the fibrous pericardium. The portion which covers the vessels is arranged in tlie form of two tubes. The aorta and pulmonary artery are enclosed in one tube, the arterial mesocardium. The superior and inferior venaj cava? and the four pulmonar\' veins are enclosed in a second tube, the venous mesocardium, the attachment of wliich to the parietal layer j^resents the shape of an inverted U. The cid-iJe-sdc enclosed between the limbs of the H lies behind the left atrium and is known as the oblique sinus, while the passage between the venous and arterial mesocardia — i. e., between the aorta and pubiionary artery in front and the atria behind — is termed the transverse sinus. The Ligament of the Left Vena Cava. — Between the left pulmonary artery and subjacent pidmonary \ein is a triangular fold of the serous pericardium; it is knowoi as the ligament of the left vena cava {rcsligial fold of Marshall). It is formed by the dupUcature of the serous layer over the remnant of the lower part of the left superior vena cava {dud ofCuvier), which becomes obliterated during fetal life, and remains as a fibrous band stretching from the highest left inter- costal vein to the left atrium, where it is continuous with a small vein, the vein of the left atrium (oblique rein of Marshall), which opens into the coronary sinus. The arteries of the pericardium are derived from the internal mammarj^ and its musculo- phrenic branch, and from the descending thoracic aorta. The nerves of the percardium are derived from the vagus and phrenic nerves, and the sj^mpa- thetic trunks. Apphed Anatomy. — Effusion of fluid into the pericardial sac often occurs in acute rheumatism or pneumonia, or in patients with chronic vascular and renal disease, embarrassing the heart's action and giving rise to signs of cardiac distress, such as pallor, a rapid and feeble pulse, dyspnoea, and restlessness. On examination, the apical cardiac impulse is absent, or replaced by a more extensive indefinite and wavering pulsation; it may appear to be in the second, third, or fourth left space, and is then not an apex impulse, as Potain has stated, but due to the impact of some portion of the heart wall nearer its base. In cliildren the precordial intercostal spaces may bulge outward. The most striking sign, however, is the great increase in all directions of the precordial dulness on percussion. This becomes pear-shaped, the stalk of the pear reaching up to about the left sternoclavicular articulation; the dulness also extends some distance to the right of the sternum, particular^ in the fifth interspace (Rotch). The fluid collects mainly on either side of the heart, and below it, especially on the left side, where the Diaphi-agma can yield more readilj' to pressiu-e than it can on the right. Ewart has drawn attention to the presence of a square patch of dulness over the base of the left lung behind, reaching up to the level of the ninth or tenth rib, and extending laterally as far as the inferior angle of the scapula; the imder- IjTug lung tissue gives the physical signs of compression or collapse. Paracentesis of the pericardium is often required to reheve the m'gent cardiac or respiratorj^ distress in these cases, and should be performed -ndthout hesitation and before the patient is in extremis. It may also be required when the pericardium is filled with blood or pus, and as it is advisable to perform this operation without transfixing the pleura, the puncture should be made either in the fifth or sixth intercostal space on the left side and close to the sternum, sO as to avoid wounding the internal mammary artery, which descends about 1.25 cm. from the sternal margin; or the needle may be entered at the left costoxiphoid angle and made to pass upward and backward behind the lower end of the body of the sternum into the pericardial sac. Cursch- mann,^ however, argues that the heart itself necessarih* hes almost in contact with the anterior wall of the thorax even in cases of the largest pericardial effusion, so that there is risk of piercing it if the puncture is made in the fourth or fifth left intercostal space within even so much as 5 to 8 cm. of the sternal margin. He therefore advises that in moderately large pericardial effusions the trocar should be inserted in the left mamillary hne, or lateral to it if the effusion is very large, in the fifth or sixth interspace. In consequence of the uncertain and varying position of the anterior reflexion of the pleura, transfixion of the plem-al sac cannot always be a^'oided. Peri- cardiotomy is required when the effusion is of a pm-ulent nature. In this operation a portion of the fifth or sixth costal cartilage is excised. An incision is made along the left border of the sternum from the upper border of the fomih cartilage to the seventh. The fifth costal cartilage is now separated from the sternima by means of a gouge, great care being taken not to let the instrmnent shp and penetrate too deeph'. The cartilage is then seized with Hon forceps and raised, the tissues beneath it being peeled off, so as to avoid wounding the internal mammarj' artery or the pleura. The Transversus thoracis is now scratched through, with a director or the nail of the index finger, close to the sternum, and the pericardium felt for and opened, the finger guarding the pleura and left internal mammarj- artery. ' Therapie der Gegenwart, 1905. 604 AXaiOLOGY THE HEART (COR). The heart is a hollow muscular organ of a somewhat conical form; it lies between the hmgs in the middle mediastinum and is enclosed in the pericardium (Fig. 572). It is placed obliquely in the chest behind the body of the sternum and adjoining parts of the rib castilages, and projects farther into the left than into the right half of the thoracic cavity, so that about one-third of it is situated on the right and two-thirds on the left of the median plane. Size. — The heart, in the adult, measures about 12 cm. in length, 8 to 9 cm. in breadth at the broadest part, and 6 cm. in thickness. Its weight, in the male, varies from 280 to 340 grams; in the female, from 230 to 280 grams. The heart continues to increase in weight and size up to an advanced period of life; this increase is more marked in men than in women. Cut edge of pa icardium Fig. 572. — Front view of heart and lungs. Component Parts. — As has already been stated (page 595), the heart is sub- divided by septa into right and left halves, and a constriction subdivides each half of the organ into two cavities, the upper cavity being called the atrium, the lower the ventricle. The heart therefore consists of four chambers, viz., right and left atria, and right and left ventricles. The division of the heart into four cavities is indicated on its surface by grooves. The atria are separated from the ventricles by the coronary sulcus {auriculo- ventricular groove); this contains the trunks of the nutrient vessels of the heart, and is deficient in front, where it is crossed by the root of the pulmonary artery. The interatrial groove, separating the two atria, is scarcely marked on the posterior THE HEART 005 surface, while anteriorly it is hidden by the pulmonary artery and aorta. The ventricles are separated by two grooves, one of which, the anterior longitudinal sulcus, is situated on the sternocostal surface of the heart, dose to its left margin, the other posterior longitudinal sulcus, on the diaphragmatic surface near the right margin; these grooxcs extend from the base of the \-entricular i)ortion to a notch, the incisura apicis cordis, on the acute margin of the heart just to the right of the apex. The base {basis cordis) (Fig. 578), directed upward, backward, and to the right, is separated from the fifth, sixtli, seventh, and eighth thoracic vertebra by the oesophagus, aorta, and thoracic duct. It is formed mainly by the left atrium, and, to a small extent, by the back part of the right atrium. Somewhat quadri- lateral in form, it is in relation above with the bifurcation of the pulmonary artery, Azijgos vein Left jyulmonary vehis Ohlique vein of left atrium Great cardiac vein Left marginal vein Rigid ptdm-onary veins ^^^ Small cardiac vein Posterior vein of left ventricle Middle cardiac vein Fig. 573. — Base and diaphragmatic surface of heart. and is bounded below by the posterior part of the coronary sulcus, containing the coronary sinus. On the right it is limited by the sulcus terminalis of the right atrium, and on the left by the ligament of the left vena cava and the oblique vein of the left atrium. The four pulmonary veins, two on either side, open into the left atrium, while the superior vena cava opens into the upper, and the anterior vena cava into the lower, part of the right atrium. The Apex {apex cordis). — The apex is directed downward, forward, and to the left, and is overlapped by the left lung and pleura: it lies behind the fifth left intercostal space, 8 to 9 cm. from the mid-sternal line, or about 4 cm. below and 2 mm. to the medial side of the left mammary papilla. The sternocostal surface (Fig. 574) is directed forward, upward, and to the left. Its lower part is convex, formed chiefly by the right ventricle, and traversed near its left margin by the anterior longitudinal sulcus. Its upper part is separated from 606 ANGIOLOGY the lower by the coronary sulcus, and is formed by the atria; it presents a deep concavity (Fig. 576), occupied by the ascending aorta and the pulmonary artery. The diaphragmatic surface (Fig. 573), directed downward and slightly backward, is formed hx the ventricles, and rests upon the central tendon and a small part of the left muscular portion of the Diaphragma. It is separated from the base by the posterior part of the coronary sulcus, and is traversed obliquely by the posterior longitudinal sulcus. The right margin of the heart is long, and is formed by the right atrium above and the right ventricle below. The atrial portion is rounded and almost vertical; it is situated behind the third, fourth, and fifth right costal cartilages about 1.25 cm. from the margin of the sternum. The ventricular portion, thin and sharp, is named the acute margin; it is nearly horizontal, and extends from the sternal end of the sixth right costal cartilage to the apex of the heart. The left or obtuse margin is shorter, full, and rounded: it is formed mainly by the left ventricle, but to a slight extent, above, by the left atrium. It extends from a point in the second left intercostal space, about 2.5 mm. from the sternal margin, obliquely downward, with a convexity to the left, to the apex of the heart. Ant. desc. branch of left coronary artery RigJit corona' Fig. 574. — Sternocostal surface of heart. Right Atrium {atrium dextrum; right auricle). — The right atrium is larger than the left, but its walls are somewhat thinner, measuring about 2 mm.; its cavity is capable of containing about 57 c.c. It consists of two parts: a principal cavity, or sinus venarum, situated posteriorly, and an anterior, smaller portion, the auricula. Sinus Venarum {siiius venosus). — The sinus venarum is the large quadrangular cavity placed between the two vense cavse. Its walls, which are extremely thin, are connected below with the right ventricle, and medially with the left atrium, but are free in the rest of their extent. Auricula {auricula dextra; right auricidar appendix). — The auricula is a small conical muscular pouch, the margins of which present a dentated edge. It projects from the upper and front part of the sinus forward and toward the left side, over- lapping the root of the aorta. THE HEART 607 The separation of the aiiriciihi from the sinus venarum is indieated externally by a groove, the terminal sulcus, whieh extends from the front of the superior vena cava to the front of the inferior vena cava, and represents the line of union of the sinus venosus of the embryo with the primitive atrium. On the inner wall of the atrium the separation is marked by a vertical, smooth, muscular ridge, the terminal crest. Behind the crest the internal surface of the atrium is smooth, while in front of it the muscular fibres of the wall are raised into parallel ridges resembling the teeth of a comb, and hence named the musculi pectinati. Dissection. — To examine the interior of the auricula, an incision should be made along its right border from the entrance of the superior vena cava to that of the inferior vena cava. A second cut is to be made fi-om the centre of the first incision to the tip of the auricula dextra, and the flap raised. Pulmonary valve Opening of sup. vena cava Crista tertninalis Atrial septum Limbiis fossce ovalis Opening of coronary sinus Opening of inf. vena cava Ant. cusp of triciispid lulve Chordce taidinece Papillary '^Vi A* W^ "^ muscles Valve of inf. vena cava Valve of coronal y sinus Fig 575 — Interior of right side ol heart Its interior (Fig. 575) presents the following parts for examination; Superior vena cava. Openings Inferior vena cava. Coronary sinus. Foramina venarum minimarum. _ Atrioventricular. Valves f Valve of the inferior vena cava. I Valve of the coronary sinus. Fossa ovalis. Limbus fossae ovalis. Intervenous tubercle. JNIusculi pectinati. Crista terminalis. The superior vena cava returns the blood from the upper half of the body, and opens into the upper and back part of the atrium, the direction of its orifice being downward and forward. Its opening has no valve. The inferior vena cava, larger than the superior, returns the blood from the lower half of the body, and opens into the lowest part of the atrium, near the atrial septum, its orifice being directed upward and backward, and guarded by 608 ANGIOLOGY a rudimentary valve, the valve of the inferior vena cava {Eustachian valve). The blood entering the atrium through the superior vena cava is directed downward and forward, i. e., toward the atrioventricular orifice, while that entering through the inferior vena cava is directed upward and backward, toward tiie atrial septum. This is the normal direction of the two currents in fetal life. The coronary sinus opens into the atrium, between the orifice of the inferior vena cava and the atrioventricular opening. It returns blood from the substance of the heart and is protected by a semicircular valve, the valve of the coronary sinus {valve of Thebesius). The foramina venarum minimarum {foramina Thebesii) are the orifices of minute veins {venae cordis minimae), which return blood directly from the muscular sub- stance of the heart. The atrioventricular opening {tricuspid orifice) is the large oval aperture of com- munication between the atrium and the ventricle; it will be described with the right ventricle. The valve of the inferior vena cava {valvula venae cavae infer ioris [Eustachii]; Eustachian valve) is situated in front of the orifice of the inferior vena cava. It is semilunar in form, its convex margin being attached to the anterior margin of the orifice; its concave margin, which is free, ends in two cornua, of which the left is continuous with the anterior edge of the limbus fossae ovalis while the right is lost on the wall of the atrium. The valve is formed by a duplicature of the lining membrane of the atrium, containing a few muscular fibres. In the fetus this valve is of large size, and serves to direct the blood from the inferior vena cava, through the foramen ovale, into the left atrium. In the adult it occa- sionally persists, and may assist in preventing the reflux of blood into the inferior vena cava ; more commonly it is small, and may present a cribriform or filamentous appearance; sometimes it is altogether wanting. The valve of the coronary sinus {valvula sinus coronarii [Thebesii]; Thebesian valve) is a semicircular fold of the lining membrane of the atrium, at the orifice of the coronary sinus. It prevents the regurgitation of blood into the sinus during the contraction of the atrium. This valve may be double or it may be cribriform. The fossa ovalis is an oval depression on the septal wall of the atrium, and corre- sponds to the situation of the foramen ovale in the fetus. It is situated at the lower part of the septum, above and to the left of the orifice of the inferior vena cava. The limbus fossae ovalis {annulus ovalis) is the prominent oval margin of the fossa ovalis. It is most distinct above and at the sides of the fossa; below, it is deficient. A small slit-like valvular opening is occasionally found, at the upper margin of the fossa, leading upward beneath the limbus, into the left atrium; it is the remains of the fetal aperture between the two atria. The intervenous tubercle {tuberculum intervenosum; tubercle of Loiver) is a small projection on the posterior wall of the atrium, above the fossa ovalis. It is distinct in the hearts of quadrupeds, but in man is scarcely visible. It was supposed by Lower to direct the blood from the superior vena cava toward the atrio- ventricular opening. Right Ventricle {veniriculus dexter). — The right ventricle is triangular in form, and extends from the right atrium to near the apex of the heart. Its antero- superior surface is rounded and convex, and forms the larger part of the sterno- costal surface of the heart. Its under surface is flattened, rests upon the Dia- phragma, and forms a small part of the diaphragmatic surface of the heart. Its posterior wall is formed by the ventricular septum, which bulges into the right ventricle, so that a transverse section of the cavity presents a semilunar outline. Its upper and left angle forms a conical pouch, the conus arteriosus, from which the pulmonary artery arises. A tendinous band, which may be named the tendon of the conns arteriosus, extends upward from the right atrioventricular fibrous THE HEART 609 ring and connects tlie posterior surface of the conus arteriosus to the aorta. The wall of the right ventricle is thinner than that of the left, the proportion between them being as 1 to 3; it is thickest at the base, and gradually becomes thinner toward the apex. The cavity equals in size that of the left ventricle, and is capable of containing about 85 c.c. Dissection. — To examine the interior of the right ventricle, its anterior wall should be turned downward and to the right in the form of a triangular flap. This is accomplished by making two incisions: (1) From the pulmonary artery to the apex of the ventricle parallel to, but a little to the right of, the anterior interatrial groove; (2) another, starting from the upper extremity, of the first and carried outward parallel to, but a little below, the atrioventricular groove, care being taken not to injure the atrioventricular opening. Its interior (Fig. 575) presents the following parts for examination ^ . J Right atrioventricular. ,. , (Tricuspid. Upenmgs 1 t^ , , v'alves i tj i ^ ^ ^rulmonary artery. Irulmonary Trabeculae carneae. Chordae tendineae. The right atrioventricular orifice is the large oval aperture of communication between the right atrium and ventricle. Situated at the base of the ventricle, it measures about 4 cm. in diameter and is surrounded by a fibrous ring, covered by the lining membrane of the heart ; it is considerably larger than the correspond- ing aperture on the left side, being sufficient to admit the ends of four fingers It is guarded by the tricuspid valve. Right uuncula i light atrium Left auricula Left 'pidinonary veins Fig. 576. — Heart seen from above. Rigid 'pulmonary veins Fig. 577. — Base of ventricles exposed by removal of the atria. The opening of the pulmonary artery is circular in form, and situated at the summit of the conus arteriosus, close to the ventricular septum. It is placed above and to the left of the atrioventricular opening, and is guarded by the pulmonary semilunar valves. The tricuspid valve {valvula tricuspidalis) (Figs. 575, 577) consists of three some- what triangular cusps or segments. The largest cusp is interposed between the atrioventricular orifice and the conus arteriosus and is termed the anterior or infundib- ular cusp. A second, the posterior or marginal cusp, is in relation to the right margin of the ventricle, and a third, the medial or septal cusp, to the ventricular septum. They are formed by duplicatures of the lining membrane of the heart, strengthened 39 610 ANGIOLOGY by intervening layers of fibrous tissue: their central parts are thick and strong, their marginal portions thin and translucent, and in the angles between the latter small intermediate segments are sometimes seen. Their bases are attached to a fibrous ring surrounding the atrioventricular orifice and are also joined to each other so as to form a continuous annular membrane, while their apices project into the ventricular cavity. Their atrial surfaces, directed toward the blood current from the atrium, are smooth; their ventricular surfaces, directed toward the wall of the ventricle, are rough and irregular, and, together with the apices and margii^.s of the cusps, give attachment to a number of delicate tendinous cords, the chordae tendineae. The trabeculae carneae {columnae carneae) are rounded or irregular muscular columns which project from the whole of the inner surface of the ventricle, with the exception of the conus arteriosus. They are of three kinds : some are attached along their entire length on one side and merely form prominent ridges, others are fixed at their extremities but free in the middle, while a third set (musculi papillares) are continuous by their bases with the wall of the ventricle, while their apices give origin to the chordae tendineae w^hich pass to be attached to the seg- ments of the tricuspid valve. There are two papillary muscles, anterior and pos- terior : of these, the anterior is the larger, and its chordae tendineae are connected with the anterior and posterior cusps of the valve: the posterior papillary muscle sometimes consists of two or three parts; its chordae tendineae are connected wdth the posterior and medial cusps. In addition to these, some chordae tendineae spring directly from the ventricular septum, or from small papillary eminences on it, and pass to the anterior and medial cusps. A muscular band, well-marked in sheep and some other animals, frequently extends from the base of the anterior papillary muscle to the ventricular septum. From its attachments it may assist in preventing overdistension of the ventricle, and so has been named the moderator band. The pulmonary semilunar valves (Fig. 576) are three in number, two in front and one behind, formed by duplicatures of the lining membrane, strengthened by fibrous tissue. They are attached, by their convex margins, to the wall of the artery, at its junction wdth the ventricle, their free borders being directed upward into the lumen of the vessel. The free and attached margins of each are strength- ened by tendinous fibres, and the former presents, at its middle, a thickened nodule {corpus Arantii). From this nodule tendinous fibres radiate through the segment to its attached margin, but are absent from two narrow crescentic portions, the lunulae, placed one on either side of the nodule immediately adjoining the free margin. Between the semilunar valves and the wall of the pulmonary artery are three pouches or sinuses {sinuses of Valsalva). Dissection. — In order to examine the interior of the left atrium, make an incision on the pos- terior surface of the atrium from the puhnonary veins on one side to those on the other, the incision being carried a Uttle way into the vessels. Make another incision from the middle of the horizontal one to the auricula sinistra. Left Atrium {atrium sinistum; left auricle). — The left atrium is rather smaller than the right, but its walls are thicker, measuring about 3 mm. ; it consists, like the right, of two parts, a principal cavity and an auricula. The principal cavity is cuboidal in form, and concealed, in front, by the pul- monary artery and aorta; in front and to the right it is separated from the right atrium by the atrial septum; opening into it on either side are the two pulmonary veins. Auricula {auricula sinistra; left auricular appendix). — The auricula is somewhat constricted at its junction with the principal cavity; it is longer, narrower, and more curved than that of the right side, and its margins are more deeply indented. It is directed forward and toward the right and overlaps the root of the pulmonary artery. rilE HEART 611 The interior of the left atriiiin (Fig. 578) presents the following parts for examination: Openings of the fonr pulmonary veins. Left atrioventricular opening. Musculi pectinati. The pulmonary veins, four in number, open into the uj)per part of the posterior surface of the left atrium — two on either side of its middle line: they are not provided Avith valves. The two left veins frequently end by a common opening. The left atrioventricular opening is the aperture between the left atrium and ventricle, and is rather smaller than the corresponding opening on the right side. The musculi pectinati, fe\ver and smaller than in the right auricula, are confined to the inner surface of the auricula. On the atrial septum may be seen a lunated impression, bounded below by a crescentic ridge, the concavity of which is turned upward. The depression is just above the fossa ovalis of the right atrium. Fig. 578. — Interior of left side of heart. Dissection. — To examine the interior of the left ventricle, make an incision a little to thejleft of the anterior interatrial groove from the base to the apex of the heart, and carry it up from thence, a little to the left of the posterior interatrial groove, nearly as far as the atrioventricular groove. Left Ventricle {ventriculus sinister) . — The left ventricle is longer and more conical in shape than the right, and on transverse section its concavity presents an oval or nearly circular outline. It forms a small part of the sternocostal surface and a considerable part of the diaphragmatic surface of the heart; it also forms the apex of the heart. Its walls are about three times as thick as those of the right ventricle. Its interior (Fig. 578) presents the following parts for examination: r\ • [Left atrioventricular. Openmgs |^^^^^.^ ^ Trabeculae carneae. XT T (Bicuspid or Mitral, valves |^Qj.^j^ Chordae tendineae. 612 AXGIOWGY The left atrioventricular opening {mitral orifice) is placed below and to the left of the aortic orifice. It is a little smaller than the corresponding aperture of the opposite side, admitting only two fingers. It is surrounded by a dense fibrous ring, covered by the lining membrane of the heart, and is guarded by the bicuspid or mitral valve. The aortic opening is a circular aperture, in front and to the right of the atrio- ventricular, from which it is separated by the anterior cusp of the bicuspid valve. Its orifice is guarded by the aortic semilunar valves. The portion of the ventricle immediately below the aortic orifice is termed the aortic vestibule, and possesses fibrous instead of muscular walls. The bicuspid or mitral valve (valvula hicusjAdalis [metralis]) (Figs. 577, 578) is attached to the circumference of the left atrioventricular orifice in the same way that the tricuspid valve is on the opposite side. It consists of two triangular cusps, formed by duplicatures of the lining membrane, strengthened by fibrous tissue, and containing a few muscular fibres. The cusps are of unequal size, and are larger, thicker, and stronger than those of the tricuspid valve. The larger cusp is placed in front and to the right between the atrioventricular and aortic orifices, and is known as the anterior or aortic cusp; the smaller or posterior cusp is placed behind and to the left of the opening. Two smaller cusps are usually found at the angles of junction of the larger. The cusps of the bicuspid valve are furnished with chordae tendineae, which are attached in a manner similar to those on the right side; they are, however, thicker, stronger, and less numerous. Aortic sinus Left post. Noduhcs ^-^^^^ Lunula Oriains of coronary arteries Uiglit fast, valve Ant. valve Fig. 579. — Aorta laid open to show the semilunar valves. The aortic semilunar valves (Figs. 576, 579) are three in number, and surround the orifice of the aorta; two are posterior (right and left) and one anterior. They are similar in structure, and in their mode of attachment, to the pulmonary semi- lunar valves, but are larger, thicker, and stronger; the lunulae are more distinct, and the noduli or corpora Arantii thicker and more prominent. Opposite the valves the aorta presents slight dilatations, the aortic sinuses {sinuses of Valsalva), which are larger than those at the origin of the pulmonary artery. The trabeculae cameae are of three kinds, like those upon the right side, but they are more numerous, and present a dense interlacement, especially at the apex, and upon the posterior wall of the ventricle. The musculi papillares are two in number, one being connected to the anterior, the other to the posterior wall; they are of large size, and end in rounded extremities from which the chordae tendineae arise. The chordae tendineae from each papillary muscle are connected to both cusps of the bicuspid valve. THE HEART 013 Ventricular Septum [scpimn rciitriciilnniin : infcrrriifricuhd' .s-rjduui) (Fi^". 580). — The ventricular septum is directed ()l)li(iucly backward and to the right, and is curved with the convexity toward the right ventricle: its margins correspond with the anterior and posterior longitudinal sulci. The greater portion of it is thick and muscular and constitutes the muscular ventricular septum, but its upper and posterior part, which separates the aortic vestibule from the lower part of the right atrium and ui)per i)art of the right ventricle, is thin and fibrous, and is termed the membranous ventricular septum. An abnormal communication may exist between the ventricles at this part owing to defective de\-elopment of the membranous septum. Structure. — The heart consists of muscular fibres, and of fibrous rings which serve for their attachment. It is covered by the visceral layer of the serous pericardium (epicardiumj , and lined by the endocardium. Between these two membranes is the muscular wall or myocardium. The endocardium is a thin, smooth membrane which lines and gives the glistening appear- ance to the inner surface of the heart; it assists in forming the valves by its reduplications, and is continuous with the lining membrane of the large bloodvessels. It consists of connective tissue and elastic fibres, and is attached to the muscular structure by loose elastic tissue which contains bloodvessels and nerves; its free surface is covered by endothelial cells. Left auunda Inferior vena cava Membranoub sephwi Muscuh pectinati Aortic valve ^_^^^_^ Papillai y TI)3^V' -muscles Anterior papillary muscle Fig. 580. — Section of the heart showing the ventricular septum. The fibrous rings surround the atrioventricular and arterial orifices, and are stronger upon the l6ft than on the right side of the heart. The atrioA'entricular rings serve for the attachment of the muscular fibres of the atria and ventricles, and for the attachment of the bicuspid and tricuspid valves. The left atrioventricular ring is closely connected, by its right margin, with the aortic arterial ring; between these and the right atrioventricular ring is a triangular mass of fibrous tissue, the trigonum fibrosum, which represents the as cordis seen in the heart of some of the larger animals, as the ox and elephant. Lastly, there is the tendinous band, already referred to (p. 608), on the posterior surface of the conus arteriosus. The fibrous rings surrounding the arterial orifices serve for the attachment of the great vessels and semilunar valves. Each ring receives, by its ventricular margin, the attachment of some of the muscular fibres of the ventricles; its opposite margin presents three deep semicircular notches, to which the middle coat of the artery is firmly fixed. The attachment of the artery to its fibrous ring is strengthened by the extei'nal coat and serous membrane externally, and 614 ANGIOLOGY by the endocardium internally. From the margins of the semicircular notches the fibrous structure of the ring is continued into the segments of the valves. The middle coat of the artery in this situation is thin, and the vessel is filiated to form the sinuses of the aorta and pulmonary artery. The muscular structure of the heart consists of bands of fibres, which present an exceedingly intricate interlacement. They comprise (a) the fibres of the atria, (6) the fibres of the ventricles, and (c) the atrioventricular bundle of His. The fibres of the atria are arranged in two laj^ers — a superficial, common to both cavities, and a deep, proper to each. The superficial fibres are most distinct on the front of the atria, across the bases of which they run in a transverse dire(!tion, forming a thin and incomplete layer. Some of these fibres run into the atrial septum. The deep fibres consist of looped and annular fibres. The looped fibres pass upward over each atrium, being attached by their two extremities to the corresponding atrioventricular ring, in front and behind. The annular fibres sm-round the auricula;, and form annular bands around the terminations of the veins and around the fossa ovahs. The fibres of the ventricles are arranged in a complex manner, and various accounts have been given of their course and connections; the following description is based on the work of McCallum.i They consist of superficial and deep layers, all of which, with the exception of two, are inserted into the papillary muscles of the ventricles. The superficial layers consist of the following: (a) Fibres which spring from the tendon of the conus arteriosus and sweep down- ward and toward the left across the anterior longitudinal sulcus and around the apex of the heart, where they pass upward and inward to terminate in the papillary muscles of the left ventricle; those arising from the upper half of the tendon of the conus arteriosus pass to the anterior papillary muscle, those from the lower half to the posterior papillary muscle and the papillary muscles of the septum. (6) Fibres which arise from the right atrioventricular ring and run diagonally across the diaphragmatic surface of the right ventricle and around its right border on to its costosternal surface, where they dip beneath the fibres just described, and, crossing the anterior longitudinal sulcus, wdnd around the apex of the heart and end in the posterior papillary muscle of the left ventricle, (c) Fibres which spring from the left atrioventricular ring, and, crossing the posterior longitudinal sulcus, pass successively into the right ventricle and end in its papillary muscles. The deep layers are three in number; they arise in the papillary muscles of one ventricle and, curving in an S-shaped manner, turn in at the longitudinal sulcus and end in the papillary muscles of the other ventricle. The layer w^hich is most superficial in the right ventricle lies next the lumen of the left, and vice versa. Those of the first layer almost encircle the right ventricle and, crossing in the septum to the left, unite with the superficial fibres from the right atrioventricular ring to form the posterior papillary muscle. Those of the second layer have a less extensive com-se in the wall of the right ventricle, and a correspondingly greater course in the left, where they join with the superficial fibres from the anterior half of the tendon of the conus arteriosus to form the papillary muscles of the septum. Those of the third layer pass almost entirely around the left ventricle and unite with the superficial fibres from the lower half of the tendon of the conus arteriosus to form the anterior papillary muscle. Besides the layers just described there are two bands which do not end in papillary muscles. One springs from the right atrioventricular ring and crosses in the atrioventricular septum; it then encircles the deep layers of the left ventricle and ends in the left atrioventricular ring. The second band is apparently confined to the left ventricle; it is attached to the left atrioventricular ring, and encircles the portion of the ventricle adjacent to the aortic orifice. The atrioventricular bundle of His is the only direct muscular connection known to exist between the atria and the ventricles. It arises in connection with two small collections of spindle- shaped cells, the sinoatrial and atrioventricular nodes. The sinoatrial node is situated on the anterior border of the opening of the superior vena cava; from it strands of fusiform fibres run imder the endocardium of the wall of the atrium to the atrioventricular node. The atrioventricular node Hes near the orifice of the coronary sinus in the annular and septal fibres of the right atrium; from it the atrioventricular bundle passes forward in the lower part of the membranous septum, and divides into right and left fascicuh. These rim down in the right and left ventricles, one on either side of the ventricular septum, covered by endocardiiun. In the lower parts of the ventricles they break up into numerous strands which end in the papillary muscles and in the ventricular muscle generally. The greater portion of the atrioventricular bundle consists of narrow, somewhat fusiform fibres, but its terminal strands are composed of Purkinje fibres. Dr. A. Morison^ has showm that in the sheep and pig the atrioventricular bundle "is a great avenue for the transmission of nerves from the auricular to the ventricular heart; large and numerous nerve trunks entering the bundle and com-sing with it." From these, branches pass off and form plexuses around groups of Purkinje cells, and from these plexuses fine fibrils go to innervate individual cells. Applied Anatomy. — Chnical and experimental evidence go to prove that this bundle conveys the impulse to systohc contraction from the atrial septum to the ventricles, and much attention has recently been paid to it, because it appears to become fibrosed and to lose much of its ^ Johns Hopkins Hospital Reports, vol. ix. 2 Journal of Anatomy and Physiology, vol. xWi. THE HEART 615 conducting power (lieart-block) in many cases of Stokes-Adams' disease. This condition is characterized by a slow pulse, a tendency to syncopal or epileptiform seizures, and the fact that while th(> cardiac atria heal at a normal rate, the ventricles contract much less frequently. Vessels and Nerves. — The arteries sup])lying the heart are the right and left coronarj^ from the aoria: tlic veins end in the right airium. The lymphatics end in the thoracic and right lymphatic ducts. The nerves arc derived from the cardiac jilexus, which are formed partly from the vagi, and parti}' from the sympathetic trunks. They are freely distributed both on the surface and in the substance of the heart, the separate nerve filaments being furnished with small gangha. The Cardiac Cycle and the Actions of the Valves. — By the contractions of the heart the blood is pumped through the arteries to all parts of the body. These contractions occur regularly and at the rate of about seventy per minute. Each wave of contraction or yeriod of activity is followed by a yeriod of rest, the two periods constituting what is known as a cardiac cycle. Each cardiac cycle consists of three phases, which succeed each other as follows: (1) a short simultaneous contraction of both atria, termed the atrial systole, fol- lowed, after a slight pause, by (2) a simultaneous, but more prolonged, contraction of both ventricles, named the ventricular systole, and (3) a period of rest, during which the whole heart is relaxed. The atrial contraction commences around the venous openings, and sweeping over the atria forces their contents through the atrio- ventricular openings into the ventricles, regurgitation into the veins being pre- vented by the contraction of their muscular coats. When the ventricles contract, the tricuspid and bicuspid valves are closed, and prevent the passage of the blood back into the atria; the musculi papillares at the same time are shortened, and, pulling on the chordae tendineae, prevent the inversion of the valves into the atria. As soon as the pressure in the ventricles exceeds that in the pulmonary artery and aorta, the valves guarding the orifices of these vessels are opened and the blood is driven from the right ventricle into the pulmonary artery and from the left into the aorta. The moment the systole of the ventricles ceases, the pressure of the blood in the pulmonary artery and aorta closes the pulmonary and aortic semilunar valves to prevent regurgitation of blood into the ventricles, the valves remaining shut until reopened by the next ventricular systole. During the period of rest the tension of the tricuspid and bicuspid valves is relaxed, and blood is flowing from the veins into the atria, being aspirated by negative intrathoracic pressure, and slightly also from the atria into the ventricles. The average duration of a cardiac cycle is about j-^ of a second, made up as follows : Atrial systole, yV- Atrial diastole, -jo- Ventricular systole, 3%. Ventricular diastole, y^. Total systole, y\-. Complete diastole, ^. The rhythmical action of the heart is muscular in origin — that is to say, the heart muscle itself possesses the inherent property of contraction apart from any nervous stimulation. The more embryonic the muscle the better is it able to initiate and propagate the contraction wave; this explains why the normal systole of the heart starts at the entrance of the veins, for there the muscle is most embryonic in nature. At the atrioventricular junction there is a slight pause in the wave of muscular contraction. To obviate this as far as possible a peculiar band of marked embryonic type passes across the junction and so carries on the contraction wave to the ventricles. This band, composed of special fibres, is the atrioventricular bundle of His (p. 614). The nerves, although not concerned in originating the contractions of the heart muscle, play an important role in regidating their force and frequency in order to subserve the physiological needs of the organism. Applied Anatomy. — Wounds of the heart are often immediately fatal, but not necessarily so. They may be non-penetrating, when death may occur from hemorrhage if one of the coronary vessels has been wounded, or subsequently from pericarditis. Even a penetrating wound is not necessarity fatal, as a considerable mmiber of cases have been recorded in which the wound has been sutured successfully. 616 ■ ANGIOLOGY PECULIARITIES IN THE VASCULAR SYSTEM OF THE FETUS. The development of the heart and vascular system is described on pages 141 to 162. ■ . ' The chief peculiarities of the fetal heart are the direct communication between the atria through the foramen ovale, and the large size of the ^'alve of the inferior vena cava. Among other peculiarities the following may be noted. (1) In early fetal life the heart lies immediately below the mandibular arch, and as develop- ment proceeds it is gradually drawn within the thorax. (2) For a time the atrial portion exceeds the ventricular in size, and the walls of the ventricles are of equal thickness: toward the end of fetal life the ventricular portion becomes the larger and the wall of the left ventricle exceeds that of the right in thickness. (3) Its size is large as compared with that of the rest of the body, the proportion at the second month being 1 to 50, and at birth, 1 to 120, while in the adult the average is about 1 to 160. The foramen ovale, situated at the lower part' of the atrial septum, forms a free communication between the atria until the end of fetal life. A septum (septum secunduvi) grows down from the upper wall of the atrium to the right of the primary septum in which the foramen ovale is situated; shortly after birth it fuses with the primary septum and the foramen ovale is obliterated. The valve of the inferior vena cava serves to direct the blood from that vessel through the foramen ovale into the left atrium. The peculiarities in the arterial system of the fetus are the communication between the pulmonary artery and the aorta by means of the ductus arteriosus, and the continuation of the hypogastric arteries as the umbilical arteries to the placenta. The ductus arteriosus is a short tube, about 1.25 cm. in length at birth, and of the diameter of a goose-quill. In the early condition it forms the continuation of the pulmonary artery, and opens into the aorta, just beyond the origin of the left subclavian artery; and so conducts the greater amount of the blood from the right ventricle into the aorta. When the branches of the pulmonary artery have become larger relatively to the ductus arteriosus, the latter is chieflj^ connected to the left pulmonary artery. The hypogastric arteries run along the sides of the bladder and thence upward on the back of the anterior abdominal wall to the umbilicus; here they pass out of the abdomen and are continued as the umbilical arteries in the umbilical cord to the placenta. They convey the fetal blood to the placenta. The peculiarities in the venous system of the fetus are the communications established between the placenta and the liver and portal vein, through the umbil- ical vein; and between the umbilical vein and the inferior vena cava through the ductus venosus. Fetal Circulation (Fig. 581). — The fetal blood is returned from the placenta to the fetus by the umbilical vein. This vein enters the abdomen at the umbilicus, and passes upward along the free margin of the falciform ligament of the liver to the under surface of that organ, where it gives off two or three branches, one of large size to the left lobe, and others to the lobus quadratus and lobus caudatus. At the porta hepatis (transverse fissure of the liver) it divides into two branches : of these, the larger is joined by the portal vein, and enters the right lobe; the smaller is continued upward, under the name of the ductus venosus, and joins the inferior vena cava. The blood, therefore, which traverses the umbilical vein, passes to the inferior vena cava in three different ways. A considerable quantity circulates through the liver with the portal venous blood, before entering the inferior vena cava by the hepatic veins; some enters the liver directly, and is PECULIARITIES IX THE VASCULAR SYSTEM OF THE FETUS 017 carried to the inferior cava by the hepatic veins; the remainder passes directly into the inferior vena cava through the ductus venosus. In the inferior vena cava, the blood carried by the ductus venosus and hepatic veins becomes mixed with that returning from the lower extremities and abdominal Fig. 581.— Plan of the fetal circulation. In this plan the figured arrows represent the kind of blood, as well as the direction which it takes in the vessles. Thus— arterial blood is figured > >; venous blood, > >; misea (arterial and venous) blood, >• ■^. wall. It enters the right atrium, and, guided by the valve of the inferior vena cava, passes through the foramen ovale into the left atrium, where it mixes w-ith a small quantity of blood returned from the lungs by the pulmonary veins. From the left atrium "it passes into the left ventricle; and from the left ventricle mto the aorta, by means of which it is distributed almost entirely to the head and upper 618 ANGIOLOGY extremities, a small quantity being probably carried into the descending aorta. From the head and upper extremities the blood is returned by the superior vena cava to the right atrium, where it mixes with a small portion of the blood from the inferior vena cava. From the right atrium it descends into the right ventricle, and thence passes into the pulmonary artery. The lungs of the fetus being inactive, only a small quantity of the blood of the pulmonary artery is distributed to them by the right and left pulmonary arteries, and returned b\^ the pulmonary veins to the left atrium: the greater part passes through the ductus arteriosus into the aorta, where it mixes with a small quantity of the blood transmitted b}^ the left ventricle into the aorta. Through this vessel it descends, and is in part distributed to the lower extremities and the viscera of the abdomen and pelvis, but the greater amount is conveyed by the umbilical arteries to the placenta. From the preceding account of the circulation of the blood in the fetus the fol- lowing facts will be evident: (1) The placenta serves the purposes of nutrition and excretion, receiving the impure blood from the fetus, and returning it purified and charged with additional nutritive material. (2) Nearly the whole of the blood of the umbilical vein traverses the liver before entering the inferior vena cava; hence the large size of the liver, especially at an early period of fetal life. (3) The right atrium is the point of meeting of a double current, the blood in the inferior vena cava being guided by the valve of this vessel into the left atrium, while that in the superior vena cava descends into the right ventricle. At an early period of fetal life it is highly probable that the two streams are quite distinct; for the inferior vena cava opens almost directly into the left atrium, and the valve of the inferior vena cava would exclude the current from the right ventricle. At a later period, as the separation between the two atria becomes more distinct, it seems probable that some mixture of the two streams must take place. (4) The pure blood carried from the placenta to the fetus by the umbilical vein, mixed with the blood from the portal vein and inferior vena cava, passes almost directly to the arch of the aorta, and is distributed by the branches of that vessel to the head and upper extremities. (5) The blood contained in the descending aorta, chiefly derived from that which has already circulated through the head and limbs, together with a small quantity from the left ventricle, is distributed to the abdomen and lower extremities. Changes in the Vascular System at Birth. — At birth, when respiration is estab- lished, an increased amount of blood from the pulmonary artery passes through the lungs, and the placental circulation is cut off. The foramen ovale is closed by about the tenth day after birth : the valvular fold above mentioned adheres to the margin of the foramen for the greater part of its circumference, but a slit-like opening is left between the two atria above, and this sometimes persists. The ductus arteriosus begins to contract immediately after respiration is estab- lished, and is completely closed from the fourth to the tenth day; it ultimately degenerates into an impervious cord, the ligamentum arteriosum, which connects the left pulmonary artery to the arch of the aorta. Of the hypogastric arteries, the parts extending from the sides of the bladder to the umbilicus become obliterated between the second and fifth days after birth, and project as fibrous cords, the lateral umbilical ligaments, toward the abdominal cavity, carrying on them folds of peritoneum. The umbilical vein and ductus venosus are completely obliterated between the second and fifth days after birth; the former becomes the ligamentum teres, the latter the ligamentum venosum, of the liver. TIIK AKTFJIIRS. T^HE tlistrihution of the systematic arteries is like a highly ramified tree, the -^ common trunk of which, formed by the aorta, commences at the left ventricle, while the smallest ramifications extend to the peripheral parts of the body and the contained organs. Arteries are found in all parts of the body, except in the hairs, nails, epidermis, cartilages, and cornea ; the larger trunks usually occupy the most protected situations, running, in the limbs, along the flexor surface, where they are less exposed to injury. There is considerable variation in the mode of division of the arteries: occasion- ally a short trunk subdivides into several branches at the same point, as may be observed in the cceliac artery and the thyrocervical trunk: the vessel may give off several branches in succession, and still continue as the main trunk, as is seen in the arteries of the limbs; or the division may be dichotomous, as, for instance, when the aorta divides into the two common iliacs. A branch of an artery is smaller than the trunk from which it arises; but if an artery divides into two branches, the combined sectional area of the two vessels is, in nearly every instance, somewhat greater than that of the trunk; and the combined sectional area of all the arterial branches greatly exceeds that of the aorta; so that the arteries collectively may be regarded as a cone, the apex of which corresponds to the aorta, and the base to the capillary system. The arteries, in their distribution, communicate with one another, forming what are called anastomoses, and these communications are very free between the large as well as between the smaller branches. The anastomosis between trunks of equal size is found where great activity of the circulation is requisite, as in the brain; here the two vertebral arteries unite to form the basilar, and the two ante- rior cerebral arteries are connected by a short communicating trunk; it is also found in the abdomen, where the intestinal arteries have very ample anastomoses between their larger branches. In the limbs the anastomoses are most numerous and of largest size around the joints, the branches of an artery above uniting with branches from the vessels below. These anastomoses are of considerable in- terest to the surgeon, as it is by their enlargement that a collateral circulation is established after the application of a ligature to an artery. The smaller branches of arteries anastomose more frequently than the larger; and between the smallest twigs these anastomoses become so numerous as to constitute a close network that pervades nearly every tissue of the body. Throughout the body generally the larger arterial branches pursue a fairly straight course, but in certain situations they are tortuous. Thus the external maxillary artery in its course over the face, and the arteries of the lips, are extremely tortuous to accommodate themselves to the movements of the parts. The uterine arteries are also tortuous, to accommodate themselves to the increase of size which the uterus undergoes during pregnancy. Applied Anatomy. — All the arteries, and most of all the aorta, are Uable to a degenerative process known as atheroma, arteriosclerosis, or, more recentlj", atherosclerosis (Alarchand), that is of the greatest clinical importance. It is essentially a senile change, although it ma}- begin at any age and is predisposed to by renal disease, gout, diabetes meUitus, lead poisonilig, and a number of other morbid states, and results in the replacement of the arterial elastic tissue by 620 ANGIOLOGY fibrous tissue. Its chief ill effects are two. In the first place, it is associated with a permanent and often considerable rise in the arterial blood pressure, entailing a corresponding liyjiertrophy of the heart; in the second, it weakens tke ve.ssel walls, rendering them more liable to rupture, while at the same time it is apt to lessen the calibre of the affected vessels. The arteries are also frequently attacked by syphihs, which gives rise to inflammation and degeneration of their middle coats. Recent researches' go to prove that arterial aneurisms, other than those due to direct injury, occur almost solely in syphihtic patients. 1 'ransnersus thoracis Internal mnmman/ vennel Left phrenic nerve Fuhnojuiry pleura eura Sympathetic trunk / \J \ -^-V^o-^ ^'e"*' Thoracic duct Vagus nerves Fig. 582. — Transverse section of thorax, showing relations of pulmonary artery. The Pulmonary Artery (A. Pulmonalis) (Fig. 582). The pulmonary artery conveys the venous blood from the right ventricle of the heart to the lungs. It is a short, wide vessel, about 5 cm. in length and 3 cm. in diameter, arising from the conus arteriosus of the right ventricle. It extends obliquely upward and backward, passing at first in front and then to the left of the ascending aorta, as far as the under surface of the aortic arch, where it divides, about the level of the fibrocartilage between the fifth and sixth thoracic vertebra?, into right and left branches of nearly equal size. Relations. — The whole of this vessel is contained within the pericardium. It is enclosed with the ascending aorta in a single tube of the visceral layer of the serous pericardium, which is con- tinued upward upon them from the base of the heart. The fibrous layer of the pericardium is gradually lost upon the external coats of the two branches of the artery. In front, the pulmonary artery is separated from the anterior end of the second left intercostal space by the pleura and left lung, in addition to the pericardium; it rests at first upon the ascending aorta, and higher up lies in front of the left atrium on a plane posterior to the ascending aorta. On either side of its origin is the auricula of the corresponding atrium and a coronary artery, the left coronary artery passing, in the first part of its course, behind the vessel. The superficial part of the cardiac plexus hes above its bifm-cation, between it and the arch of the aorta. The right branch of the pulmonary artery {ramus dexter a. pulmonalis), longer and larger than the left, runs horizontally to the right, behind the ascending aorta and superior vena cava and in front of the right bronchus, to the root of the right 1 C. U. Aitchison, Archives of the Pathological Institute of the London Hospital, 190S, ii, 1. THE ASCENDING AORTA 621 lung, where it divides into two branches. The lower and larger of these goes to the middle and lower lobes of the lung; the upper and smaller is distributed to the upper lobe. The left branch of the pulmonary artery (raniiis- dninter a. pidiiionalis), shorter and somewhat smaller than the right, passes horizontally in front of the descending aorta and left bronchus to the root of the left lung, where it divides into two branches, one for each lobe of the lung. Above, it is connected to the concavity of the aortic arch by the ligamentum arteriosum, on the left of which is the left recurrent nerve, and on the right the superficial part of the cardiac plexus. Below, it is joined to the upper left pul- monary vein by the ligament of the left vena cava (page 159). The terminal branches of the pulmonary arteries will be described with the anatomy of the lungs. Applied Anatomy. — Stenosis of the pulmonary artery, either with, or, more rarely, without defective formation of the ventricular septum, is one of the commonest congenital defects of the heart. It may be due either to fetal endocarditis, or to maldevelopment of the bulbus cordis (p. 149). 1 As in most forms of congenital heart disease, the child is cyanosed (morbus caeruleus), especially when excited or on exertion, and rarely Hves to grow up, commonly dying of heart failure in infancy, or of pulmonary tuberculosis or intercm-rent disease in childhood. The chief signs of the condition are the loud, harsh systoUc cardiac miu'mur best heard over the second left costal cartilage, cyanosis, clubbing of the finger tips, and the presence of an excess of red corpuscles in the blood. EmboUsm of the pulmonary artery by a clot of blood coming from the right side of the heart in patients with heart disease, or from a thrombosed vein in cases, for example, of influenza, enteric fever, puerperal sepsis, or fractured hmbs, is a common cause of sudden or rapid death. The patient may cry out with sudden excruciating pain in the precordia when the detached embolus lodges, and after a brief period of intense dyspnoea, pallor, and anguish, die. THE AORTA. The aorta is the main trunk of a series of vessels which convey the oxygenated blood to the tissues of the body for their nutrition. It commences at the upper part of the left ventricle, where it is about 3 cm. in diameter, and after ascending for a short distance, arches backward and to the left side, over the root of the left lung; it then descends within the thorax on the left side of the vertebral column, passes into the abdominal cavity through the aortic hiatus in the Diaphragma, and ends, considerably diminished in size (about 1.75 cm. in diameter), opposite the lower border of the fourth lumbar vertebra, by dividing into the right and left common iliac arteries. Hence it is described in several portions, viz., the ascending aorta, the arch of the aorta, and the descending aorta, which last is again divided into the thoracic and abdominal aortse. THE ASCENDING AORTA (AORTA ASCENDENS) (Fig. 583). The ascending aorta is about 5 cm. in length. It commences at the upper part of the base of the left ventricle, on a level with the lower border of the third costal cartilage behind the left half of the sternum; it passes obliquely upward, forward, and to the right, in the direction of the heart's axis, as high as the upper border of the second right costal cartilage, describing a slight curve in its course, and being situated, about 6 cm. behind the posterior surface of the sternum. At its origin it presents, opposite the segments of the aortic valve, three small dilatations called the aortic sinuses. At the union of the ascending aorta with the aortic arch 1 Keith (Studies in Pathologj-, Aberdeen University, 1906) believes that the great majority of cases which are classified as congenital stenosis of the pulmonary or of the aortic orifices are, in reality, due to an arrest of development or mal- formation of the bulbus cordis. 622 ANGIOLOGY the calibre of the vessel is increased, owing to a bulging of its right wall. This dilatation is termed the bulb of the aorta, and on transverse section presents a some- what oval figure. The ascending aorta is contained within the pericardium, and is enclosed in a tube of the serous pericardium, common to it and the pulmonary artery. Relations. — The ascending aorta is covered at its commencement by the trunk of the pul- monary artery and the right auricula, and, higher up, is separated from the sternum by the pericardium, the right pleura, the anterior margin of the right lung, some loose areolar tissue, and the remains of the thymus; posteriorhj, it rests upon the left atrium and right pulmonary artery. On the right side, it is in relation with the superior vena cava and right atrium, the former lying partly behind it; on the left side, with the pulmonary artery. Left vagus Left phrenic — Thoracic duct Fig. 583. — The arch of the aorta, and its branches. Branches.— The only branches of the ascending aorta are the two coronary arteries which supply the heart; they arise near the commencement of the aorta immediately above the attached margins of the semilunar valves. The Coronary Arteries.— The Right Coronary Artery (a. coronaria [cordis] dextra) arises from the anterior aortic sinus. It passes at first between the conus arteriosus and the right auricula and then runs in the right portion of the coronary sulcus, coursing at first from the left to right and then on the diaphragmatic surface THE ARCH OF THE AORTA 623 of the heart from right to left as far as the posterior longitudinal sulcus, down which it is continued to the apex of the heart as the posterior descending branch. It gives off a large marginal branch which follows the acute margin of the heart and supplies branches to both surfaces of the right ventricle. It also gives twigs to the right atrium and to the part of the left ventricle which adjoins the posterior longitudinal sulcus. The Left Coronary Artery (a. coronaria [cordis] sinistra), larger than the right, arises from the left posterior aortic sinus and divides into an anterior descending and a circumflex branch. The anterior descending branch passes at first behind the pulmonary artery and then comes forward between that vessel and the left auricula to reach the anterior longitudinal sulcus, along which it descends to the incisura apicis cordis; it gives branches to both ventricles. The circumflex branch follows the left part of the coronary sulcus, running first to the left and then to the right, reaching nearly as far as the posterior longitudinal sulcus; it gives branches to the left atrium and ventricle. There is a free anastomosis between the minute branches of the two coronar}" arteries in the substance of the heart. Peculiarities. — These vessels occasionally arise bj^ a common trunk, or their number may be increased to three, the additional branch being of small size. ]More rarely, there are two addi- tional branches. Applied Anatomy. — The sudden blocking of a coronary arterj^ by an embolus, or its more gradual obstruction by arterial disease or thrombosis, is a common cause of sudden death in persons past middle age. If the obstruction to the passage of blood is incomplete, true angina pectoris maj^ occiu". In this condition the patient is suddenly seized with a spasm of agonizing pain in the precordial region and down the left arm, together with an indescribable sense of anguish. He may die in such an attack, or succmnb a few hom's or days later from heart failure, or sm'vive a number of attacks. THE ARCH OF THE AORTA (ARCUS AORTAE; TRANSVERSE AORTA) (Fig. 5S3). The arch of the aorta begins at the level of the upper border of the second sterno- costal articulation of the right side, and runs at first upward, backward, and to the left in front of the trachea ; it is then directed backward on the left side of the trachea and finally passes downward on the left side of the body of the fourth thoracic vertebra, at the lower border of which it becomes continuous with the descending aorta. It thus forms two curvatures: one wath its convexity upward, the other with its convexity forward and to the left. Its upper border is usually about 2.5 em. below the superior border to the manubrium sterni. Relations. — The arch of the aorta is covered anteriorly by the pleurse and anterior margins of the lungs, and b}^ the remains of the thj^mus. As the vessel runs backward its left side is in contact with the left lung and pleura. Passing do^miward on the left side of this part of the arch are four nerves; in order from before backward these are, the left phrenic, the lower of the superior cardiac branches of the left vagus, the superior cardiac branch of the left sjTiipathetic, and the trunk of the left vagus. As the last nerve crosses the arch it gives off its recurrent branch, which hooks around below the vessel and then passes upward on its right side. The highest left inter- costal vein runs obliquely upward and forward on the left side of the arch, between the pkrenic and vagus nerves. On the right are the deep part of the cardiac plexus, the left recm'rent nerve, the oesophagus, and the thoracic duct; the trachea hes behind and to the right of the vessel. Above are the innominate, left common carotid, and left subclavian arteries, which arise from the convexitj' of the arch and are crossed close to their origins by the left innominate vein. Below are the bifm-cation of the pulmonary arterj^, the left bronchus, the ligamentum arteriosum, the superficial part of the cardiac plexus, and the left recm-rent nerve. As ah'eady stated, the hga- mentum arteriosum connects the commencement of the left pulmonary artery to the aortic arch. Between the origin of the left subclavian artery and the attachment of the ductus arteriosus the lumen of the fetal aorta is considerably narrowed, forming what is termed the aortic isthmus, while immediately beyond the ductus arteriosus the vessel presents a fusiform dilation which His has named the aortic spindle — the 624 AXGIOLOGY point of junction of the two parts being marked in the concavity of the arch by an indentation or angle. These conditions persist, to some extent, in the adult, where His found that the average diameter of the spindle exceeded that of the isthmus by 3 mm. Distinct from this diffuse and moderate stenosis at the isthmus is the condition known as coarctation of the aorta, or marked stenosis often amounting to complete obUteration of its lumen, seen in adults and occurring at or near, oftenest a little below, the insertion of the ligamentum arteriosum into the aorta. According to Bonnet^ this coarctation is never found in the fetus or at birth, and is due to an abnormal extension of the peculiar tissue of the ductus into the aortic wall, which gives rise to a simultaneous stenosis of both vessels as it contracts after birth — the ductus is usually obhterated in these cases. An extensive collateral circulation is set up, by the costocervicals, internal mammaries, and the descending branches of the transverse cervical above the stenosis, and below it by the first four aortic intercostals, the pericardiaco-phrenics, and the superior and inferior epigastrics. Peculiarities. — The height to which the aorta rises in the thorax is usually about 2.5 cm. below the upper border of the sternum; but it may ascend nearly to the top of the bone. Occa- sionally it is found 4 cm., more rarely from 5 to 8 cm. below this point. Sometimes the aorta arches over the root of the right lung (right aortic arch) instead of over that of the left, and passes down on the right side of the vertebral column, a condition which is found in birds. In such cases all the thoracic and abdominal viscera are transposed. Less frequently the aorta, after arching over the root of the right lung, is directed to its usual position on the left side of the vertebral column; this peculiarity is not accompanied by transposition of the viscera. The aorta occa- sionally divides, as in some quadrupeds, into an ascending and a descending trunk, the former of which is directed vertically upward, and subdivides into three branches, to supply the head and upper extremities. Sometimes the aorta subdivides near its origin into two branches, which soon reimite. In one of these cases the oesophagus and trachea were found to pass through the interval between the two branches; this is the normal condition of the vessel in the reptiUa. Applied Anatomy. — Of all the vessels of the arterial system, the aorta, and more especially its arch, is most frequently the seat of disease; hence it is important to consider some of the consequences that may ensue from aneurism of this part. Aneurism of the ascending aorta, in the situation of the aortic sinuses, in the great majority of cases, affects the anterior sinus; this is mainly owing to the fact that the regurgitation of blood upon the sinuses takes place chiefly on the anterior aspect of the vessel. As the aneurismal sac enlarges, it may compress any or all of the structm'es in immediate proximity with it, but chiefly projects toward the right anterior side; and, consequently, interferes mainly with those structm-es that have a corresponding relation with the vessel. If it project forward, it may destroy the sternum and the cartilages of the ribs, usually on the right side, and appear as a pulsating tumor on the front of the chest, just below the manubrium; or it may burst into the pericardium, or may compress, or open into the right lung, the trachea, bronchi, or oesophagus. In the majority of cases it bursts into the cavity of the pericardium, the patient suddenly drops down dead, and, upon a postmortem examination, the pericardial sac is found full of blood; or it may compress the right atrium, or the pulmonary artery, and adjoining part of the right ventricle, and open into one or the other of these parts. It may press upon the .superior vena cava or the innominate veins, causing great venous engorgement. The face becomes livid and swollen, the right arm and anterior thoracic wall oedematous, and the congestion of the brain gives rise to headache and vertigo. An aneurism has occasionally perforated into the superior vena cava, setting up an arteriovenous aneurism. When this happens the patient suddenly becomes very short of breath, intensely congested and oedematous in the face and upper part of the body, and develops a palpable thrill and a continuous humming murmur, loudest during systole, over the sternum. Death follows a few days or weeks after such a perforation; and somewhat similar symptoms are occasioned when an aortic anem'ism erodes and bm'sts into the pulmonary artery. Regarding the arch of the aorta, the student is reminded that the vessel lies against the trachea, oesophagus, and thoracic duct; that the recmTent nerve winds around it; and that from its upper part are given off three large trunks, which supply the head, neck, and upper extremities. An aneui'ismal tumor taking origin from the posterior part of the vessel, its most usual site, may press upon the trachea and give rise to the sign known as tracheal tugging, impede the breathing, or produce cough, dyspnoea, bronchiectasis, hemoptysis, or stridulous breathing, or it may ulti- mately burst into that tube, producing fatal hemorrhage. Again, its pressure on the left recm-rent nerve may give rise to symptoms of laryngeal paralysis; or it may press upon the thoracic duct and destroy life by inanition; or it may involve the oesophagus, producing dysphagia, and has not infrequently been mistaken for oesophageal stricture; or it may burst into the oesophagus, when fatal hemorrhage will occur. Compression or stretching of the sympathetic filaments 1 Rev. de Med., Paris, 1903. THE INNOM-INATE ARTERY 625 may, in the former ease, produce dilatation of tlic pupil; in the latter, contraction, if the con- ducting jiower is abolisheil, on the affected side. This has proved to be an important diagnostic sign in this disease. Again, the innominate artery, or the subclavian, or left carotid, may be so obstructed by clots as to produce a weakness, or even a disappearance, of the pulse in one or the other wrist, or in the left superficial temporal artery; or the tumor may present itself at or above the manul)rium, generallj' cither in the median line, or to the right of the sternum, and may sim- ulate an aneurism of one of the arteries of the neck. Many of the physical signs of an aortic aneurism may be simulated with extraordinary fidelity by the preternatural pulsation or throbbing of a distended and elastic aorta, when no true aneu- rismal dilatation exists. This condition may be met with in young persons with aortic reflux and greatlj' hypertrophied hearts, in patients who are of a neurotic or hysterical temperament, and in cases of Graves' disease or of marked anemia. The condition is known as dynamic dilata- tion of the aorta, and in no way threatens life. Branches (Figs. 583, 584). — The branches given off from the arch of the aorta are three in number: the innominate, the left common carotid, and the left subclavian. Peculiarities. — Position of the Branches. — The branches, instead of arising from the highest part of the arch, may spring from the commencement of the arch or upper part of the ascending aorta; or the distance between them at their origins may be increased or diminished, the most frequent change in this respect being the approximation of the left carotid toward the innominate artery. The number of the primary branches may be reduced to one, or more commonly two; the left carotid arising from the innominate artery; or (more rarely) the carotid and subclavian arteries of the left side arising from a left innominate artery. But the number may be increased to four, from the right carotid and subclavian arteries arising directly from the aorta, the innominate being absent. In most of these latter cases the right subclavian has been found to arise from the left end of the arch; in other cases it is the second or third branch given off, instead of the first. Another common form in which there are four primary branches is that in which the left vertebral arterj'' arises from the arch of the aorta between the left carotid and subclavian arteries. Lastly, the number of trunks from the arch may be increased to five or six; in these instances, the external and internal carotids arise separately from the arch, the common carotid being absent on one or both sides. In some few cases six branches have been found, and this condition is associated with the origin of both vertebral arteries from the arch. Number Usual, Arrangement Different. — When the aorta arches over to the right side, the three branches have an arrangement the reverse of what is usual; the innominate artery is a left one, and the right carotid and subclavian arise separately. In other cases, where the aorta takes its usual course, the two carotids may be joined in a common trunk, and the subclavians arise separatel}^ from the arch, the right subclavian generally arising from the left end of the arch. In some instances other arteries spring from .the arch of the aorta. Of these the most common are the bronchial, one or both, and the thyreoidea ima; but the internal mammary and the inferior thyroid have been seen to arise from this vessel. The Innominate Artery (A. Anonyma; Brachiocephalic Artery) (Fig. 583). The innominate artery is the largest branch of the arch of the aorta, and is from 4 to 5 cm. in length. It arises, on a level with the upper border of the second right costal cartilage, from the commencement of the arch of the aorta, on a plane anterior to the origin of the left carotid; it ascends obliquely upward, backward, and to the right to the level of the upper border of the right sternoclavicular articulation, where it divides into the right common carotid and right subclavian arteries. Relations. — Anteriorly, it is separated from the manubrium sterni by the Sternohyoideus and Sternothjreoideus, the remains of the thymus, the left innominate and right inferior thyroid veins which cross its root, and sometimes the superior cardiac branches of the right vagus. Posterior to it is the trachea, which it crosses obhquely. On the right side are the right innominate vein, the superior vena cava, the right phrenic nerve, and the pleura; and on the left side, the remains of the thjTnus, the origin of the left common carotid artery, the inferior thyroid veins, and the trachea. Branches. — The innominate artery usually gives off no branches; but occasion- ally a small branch, the thyreoidea ima, arises from it. Sometimes it gives oft' a thymic or bronchial branch. 40 626 ANGIOLOGY The thyreoidea ima (a. fhijreoidea ima) ascends in front of the trachea to the lower part of the thyroid gland, which it supplies. It varies greatly in size, and appears to compensate for deficiency or absence of one of the other thyroid vessels. It occasionally arises from the aorta, the right common carotid, the subclavian or the internal mammary. Point of Division. — The innominate artery sometimes divides above the level of the sterno- clavicular joint, less frequently below it. Position. — When the aortic arch is on the right side, the innominate is directed to the left side of the neck. Collateral Circulation. — Allan Burns demonstrated, on the dead subject, the possibihtj' of the establishment of the collateral circulation after hgature of the innominate artery, bj- tying and dividing that artery. He then found that "Even coar.se injection, impelled into the aorta, pas.sed freeh' by the anastomosing branches into the arteries of the right arm, filling them and all the vessels of the head completely."^ The branches bj' which this circulation would be carried on are very numerous; thus, all the communications across the- middle line between the branches of the carotid arteries of opposite sides would be available for the supplj' of blood to the right side of the head and neck; while the anastomosis between the costocervical of the subclavian and the first aortic intercostal fsee infra on the collateral circulation after obhteration of the thoracic aorta) would bring the blood, by a free and direct course, into the right subclavian. The numerous connections, also, between the intercostal arteries and the branches of the axillary and internal mammary arteries would, doubtless, assist in the supply of blood to the right arm, while the inferior epigastric from the external ihac would, bj' means of its anastomo.sis with the internal mammarj^, compensate for any deficiency in the vascularity of the wall of the chest. Applied Anatomy. — Aneurism of the innominate artery not infrequently occurs as an accom- paniment to aneurism of the arch of the aorta. It caases bulging of the right sternoclavicular articulation, pushing forward the Sternocleidomastoideus muscle and filling up the jugular notch. It produces serious pressure symptoms; from pressure on the innominate veins it may cause oedema of the upper extremities, and of the head and neck; from pressure on the trachea it produces dyspnoea; and from pressure on the right recurrent nerve, hoarseness and larjmgeal cough. Although the operation of tying the innominate arterj- has been performed by several surgeons, not many successes have been recorded. The chief danger of the operation appears to be the frequency of secondary hemorrhage; but in the present day, with the practice of aseptic surgery and our greater knowledge of the use of the ligature, more favorable results may be anticipated. The main obstacles to the operation are, the deep situation of the artery behind the sternum, and the number of important structures which surround it. In order to apply a hgature to this vessel, the patient is to be placed upon his back ^dth the thorax slightly raised, the head bent a little backward, and the right shoulder strongly depressed, so as to draw out the artery from behind the sternum into the neck. An incision 7 cm. or more in length is then made along the anterior border of the Sternocleidomastoideus, terminating at the sternal end of the cla\acle. From this point, a second incision is carried about the same length along the upper border of the clavicle. The skin is then dissected back, and the Platysma divided; the sternal end of the Sternocleidomastoideus is now brought into view, and a director being passed beneath it, and close to its deep surface so as to avoid any small vessels, it is to be divided; in like manner the cla\acular origin is to be divided throughout the whole or greater part of its attachment. By pressing aside any loose cellular tissue or vessels "that may now appear, the Stemohyoideus and StemothjTeoideus muscles wiU be exposed, and must be divided. The inferior thjToid veins may come into view, and must be carefuUj" drawn either upward or down- ward, by means of a blunt hook, or tied with double hgatures and divided. After tearing through a strong fibrocellular lamina, the right common carotid is brought into view, and being traced do^Tiward, the innominate artery is reached. The left innominate vein should now be depressed; the right innominate vein, the internal jugular vein, and the vagus nerve drawn to the right side; and a curved aneurysm needle maj' then be passed around the vessel, close to its surface, and in a direction from below upward and medially; care being taken to avoid the right pleural sac, the trachea, and cardiac nerA'es. The hgature should be appUed to the artery as high as possible, in order to allow room between it and the aorta for the formation of the coagulum. The importance of avoiding the th3Toid plexus of veins during the primary steps of the operation, and the pleural sac while including the vessel in the ligature, should be most carefullj' borne in mind. ' Surgical Anatomy of the Head and Neck, p. 62. THE COMMOX CAROTID ARTERY 627 THE ARTERIES OF THE HEAD AND NECK. The principal arteries of supply to the head and neck are the two common carotids; thoy ascend in the neck and each divides into two branches, viz., (1) the external carotid, sujjplying the exterior of the head, the face, and the greater part of the neck; (2) the internal carotid, supplying to a great extent the parts within the cranial and orbital cavities. THE COMMON CAROTID ARTERY (A. CAROTIS COMMUNIS). The common carotid arteries differ in length and in their mode of origin. The right begins at the bifurcation of the innominate artery behind the sternoclavicular joint and is confined to the neck. The left springs from the highest part of the arch of the aorta to the left of, and on a plane posterior to the innominate artery, and therefore consists of a thoracic and a cervical portion. The thoracic portion of the left common carotid artery ascends from the arch of the aorta through the superior mediastinal cavity to the level of the left sterno- clavicular joint, where it is continuous with the cervical portion. Relations. — In front, it is separated from the manubrium sterni by the Sternoh3^oideus and SternothjTeoideus, the anterior portions of the left pleura and lung, the left innominate vein, and the remains of the thj'mus; behind, it lies on the trachea, oesophagus, left recurrent nerve, and thoracic duct. To its right side below is the innominate artery, and above, the trachea, the inferior thjToid veins, and the remains of the thymus; to its left side are the left vagus and phrenic nerves, left plem-a, and lung. The left subclavian arterj^ is posterior and slightly lateral to it. The cervical portions of the common carotids resemble each other so closely that one description will apply to both (Fig. 585). Each vessel passes obliquely upward, from behind the sternoclavicular articulation, to the level of the upper border of the thyroid cartilage, where it divides into the external and internal carotid arteries. At the lower part of the neck the two common carotid arteries are separated from each other by a very narrow interval which contains the trachea; but at the upper part, the thyroid gland, the larynx and pharynx project forward between the two vessels. The common carotid artery is contained in a sheath, which is derived from the deep cervical fascia and encloses also the internal jugular vein and vagus nerve, the vein lying lateral to the artery, and the nerve between the artery and vein, on a plane posterior to both. On opening the sheath, each of these three structures is seen to have a separate fibrous investment. Relations. — At the lower part of the neck the common carotid artery is very deeply seated, being covered by the integument, superficial fascia, Platj'sma, and deep cervical fascia, the Sterno- cleidomastoideus, Sternohyoideus, SternothjTeoideus, and Omohyoideus; in the upper part of its course it is more superficial, being covered merely by the integument, the superficial fascia, Platysma, deep cervical fascia, and medial margin of the Sternocleidomastoideus. When the latter muscle is drawn backward, the artery is seen to be contained in a triangular space, the carotid triangle, bounded behind by the Sternocleidomastoideus, above by the Stylohj'oideus and posterior belly of the Digastricus, and below by the superior belly of the Omohyoideus. This part of the artery is crossed obhquely, from its medial to its lateral side, by the sterno- cleidomastoid branch of the superior thjToid artery; it is also crossed bj^ the superior and middle thjToid veins which end in the internal jugular; descending in front of its sheath is the descending branch of the hj'poglossal nerve, this filament being joined by one or two branches from the cervical nerves, which cross the vessel obUquel3^ Sometimes the descending branch of the hj-po- glossal nerve is contained within the sheath. The superior thjToid vein crosses the arterj- near its termination, and the middle thyroid vein a httle below the level of the cricoid cartilage; the anterior jugular vein crosses the artery just above the clavicle, but is separated from it by the Sternohyoideus and SternothjTeoideus. Behind, the artery is separated from the transverse processes of the cervical vertebr£e by the Longus coUi and Longus capitis, the sj^mpathetic trunk being interposed between it and the muscles. The inferior thjToid artery crosses behind the lower part of the vessel. Medially, it is in relation with the oesophagus, trachea, and thjToid gland (which overlaps it), the inferior thjT-'oid arterj- and recm-rent nerve being interposed; higher 628 A NG 10 LOGY up, with the larynx and pharynx. Lateral to the artery are tlie internal jugular vein and vagus nerve. At the lower part of the neck, the right recurrent nerve crosses obliquely behind the artery; the right internal jugular vein diverges from the artery, but the left approaches and often over- laps the lower part of the artery. Behind the angle of bifurcation of the common carotid artery is a reddish-brown o\'al body, known as the glomus caroticum (carotid bodij) . It is similar in structure to the glomus coccygeum {coccygeal body) which is situated on the middle sacral artery. Fig. 585. — Superficial dissection of the right side of the neck, showing the carotid and subclavian arteries. Peculiarities as to Origin. — The right common carotid may arise above the level of the upper border of the sternoclavicular articulation; this variation occurs in about 12 per cent, of cases. In other cases the artery may arise as a separate branch from the arch of the aorta, or in con- junction with the left carotid. The left common carotid varies in its origin more than the right. In the majority of abnormal cases it arises with the innominate artery; if that artery is absent, the two carotids arise usually by a single trunk. It is rarely joined with the left subclavian, except in cases of transposition of the aortic arch. Peculiarities as to Point of Division. — In the majority of abnormal cases this occurs higher than usual, the artery dividing opposite or even above the hyoid bone; more rarely, it occurs THE COMMON CAROTID ARTERY ()29 below, opposite the middle of the larynx, or the lower border of the cricoid cartilage; one case is related by Morgagni, where the artery was only 4 cm. in length and divided at the root of the neck. Veiy rarely, the conmion carotid ascends in the neck without any subdivision, either the external or the internal carotid being wanting; and in a few cases the common carotid has been found to be absent, the external and internal carotids arising directly from the arch of the aorta. This peculiarity existed on both sides in some instances, on one side in others. Occasional Branches. — The common carotid usually gives off no branch previous to its bifurca- tion, but it occasionally gives origin to the superior thyroid or its laryngeal branch, the ascend- ing pharyngeal, the inferior thyroid, or, more rarely, the vertebral artery. Applied Anatomy. — Aneurisms are not commonly met with on the common carotid; when they do occm- thej^ are usually situated low dowii at the root of the neck, or just below the point of bifurcation of the vessel. They do not frequently assume a large size, and are more commonly found on the right side. As they increase in size they displace the trachea and larynx, and there- fore dyspnoea becomes a prominent symptom. Dysphagia also may be present from pressure on the a^sophagus, especially if the aneurism is on the left side; and pressure on the recurrent nerve may produce hoarseness and laryngeal cough. Pressure on the sympathetic will cause pupillary changes — dilatation of the pupil when the sympathetic is irritated, contraction when it has become pai'al3'zed — and may also give rise to unilateral sweating. Pressure on the super- ficial branches of the cervical plexus may give rise to pain in the head, face, and neck; pressure on the vagus to iri-egular action of the heart and to asthmatic attacks. It is important to bear in mind that an enlarged lymph gland in the superior carotid triangle, receiving a transmitted pulsation from the carotid artery, may simulate aneurism of that vessel, but may be distinguished from it by the character of the pulsation, which is not distensile. EmboUsm of the left common carotid has been known to produce aphasia by interference with the blood supply of the brain. Digital compression of the common carotid is sometimes required, and is best effected by compressing the vessel with the thumb against the anterior tubercle of the transverse process of the sixth cervical vertebra (see p. 199). Ligature of the common carotid artery may be necessary in a case of woimd of that vessel or its branches, in aneurism, or in a case of pulsating tumor of the orbit or skuU. If the wound involves the trunk of the common carotid, it will be necessary to tie the artery above and below the wounded part. In cases of aneurism, the whole of the artery is accessible, and any part of it may be tied. When the case is such as to allow of a choice being made, the upper part of the carotid should be selected as the spot upon which to place a hgature, for the lower part of the vessel is placed very deeply in the neck, and is covered by three layers of muscles; moreover, on the left side, the internal jugular vein, in the great majority of cases, passes obhquely in front of it. The part of the vessel which is-most favorable for the operation is that opposite the level of the cricoid cartilage. It occasionally happens that the carotid artery bifurcates below its usual position; if the artery be exposed at its point of bifurcation, both divisions of the vessel should be tied near their origin, in preference to tying the trunk of the artery near its termina- tion; and if, in consequence of the entire absence of the common carotid, or from its early divi- sion, two arteries, the external and internal carotids, are met with, the Hgature should be placed on that vessel which is found on compression to be connected with the diseased area. In this operation, the direction of the vessel and the anterior margin of the Sternocleido- mastoideus are the chief guides to its performance. The patient, should be placed on his back with the head extended and turned slightly to the opposite side; an incision is to be made, 7 or 8 cm. long, in the direction of the anterior border of the Sternocleidomastoideus, so that the centre corresponds to the level of the cricoid cartilage. After dividing the integument, super- ficial fascia, Platysma, and deep fascia, the margins of the wound are held asunder by retractors, and the ramus descendens hypoglossi is now exposed, and must be avoided. The sheath of the vessel is to be raised by forceps, and opened to a small extent over the artery at its medial side. The internal jugular vein may present itself alternately distended and relaxed, and must be carefully avoided. The aneurism needle is passed from the lateral aspect, care being taken to keep the needle in close contact with the artery, and thus avoid the risk of injuring the internal jugular vein, or including the vagus nerve. Before the ligature is tied, it should be ascertained that nothing but the artery is included in it. Ligature of the common carotid near the root of the neck is sometimes required in cases of aneurism of the upper part of the carotid, especially if the sac is of large size. It is best performed by dividing the sternal origin of the Sternocleidomastoideus, but may be done in some cases, if the anem'ism is not of very large size, by an incision along the anterior border of the muscle, extending down to the sternoclavicular articulation, and by then retracting the muscle. The easiest and best plan, however, is to make an incision 5 to 7 cm. long down the lower part of the anterior border of the Sternocleidomastoideus to the sternoclavicular joint, and a second inci- sion, starting from the termination of the first, along the upper border of the clavicle for about 5 cm. This incision is made through the superficial and deep fasciae and the sternal origin of the muscle is exposed. This is to be divided on a director and turned up, with the superficial struc- 630 A NG 10 LOGY tures, as a triangular flap. Some loose connective tissue is to be divided or torn through, and the lateral border of the Sternohyoideus exposed. In doing this, care must be taken not to wound the anterior jugular vein, which crosses this muscle to reach the external jugular or subclavian vein. The 8ternohyoidcus and Sternothyrcoideus are to be drawn mediahvard by means of a retractor, and the sheath of the vessel exposed. This must be opened on its medial or tracheal side, so as to avoid the internal jugular vein. Special care is necessary on the left side, where the artery is commonly overlapped by the vein; on the right side there is usually an interval between the artery and the vein, and the risk of wounding tlie latter is less. The common carotid artery, being a long vessel without any branches, is particularly suit- able for the performance of Brasdor's operation for the cure of an aneurism of the lower part of the vessel. Brasdor's procedure consists in ligaturing the artery on the distal side of the aneu- rism, and in the case of the common carotid there are no branches given off from the vessel between the aneurism and the site of the Ugature; hence the flow of blood through the sac of the aneurism is diminished, and cure takes place in the usual way by the deposit of laminated fibrin. Collateral Circulation. — After hgature of the common carotid, the collateral circulation can be perfectly established, by the free communication which exists between the carotid arteries of opposite sides, both withdut and within the cranium, and by enlargement of the branches of the subclavian artery on the side corresponding to that on which the vessel has been tied. The chief communications outside the skull take place between the superior and inferior thyroid arteries, and the profunda cervicis and ramus descendens of the occipital; the vertebral takes the place of the internal carotid within the cranium. The External Carotid Artery (A. Carotis Externa) (Fig. 585). The external carotid artery begins opposite the upper border of the thyroid cartilage, and, taking a slightly curved course, passes upward and forward, and then inclines backward to the space behind the neck of the mandible, where it divides into the superficial temporal and internal maxillary arteries. It rapidly diminishes in size in its course up the neck, owing to the number and large size of the branches given off from it. In the child, it is somewhat smaller than the internal carotid; but in the adult, the two vessels are of nearly equal size. At its origin, this artery is more superficial, and placed nearer the middle line than the internal carotid, and is contained within the carotid triangle. Relations. — The external carotid artery is covered by the skin, superficial fascia, Platysma, deep fascia, and anterior margin of the Sternocleidomastoideus; it is crossed by the hypoglossal nerve, by the lingual, ranine, common facial, and superior thyroid veins; and by the Digastricus and Stylohyoideus; higher up it passes deeply into the substance of the parotid gland, where it hes deep to the facial nerve and the junction of the temporal and internal maxillary veins. Medial to it are the hyoid bone, the wall of the pharynx, the superior laryngeal nerve, and a portion of the parotid gland. Lateral to it, in the lower part of its course, is the internal carotid artery. Posterior to it, near its origin, is the superior laryngeal nerve; and higher up, it is sepa- rated from the internal carotid by the Styloglossus and Stylopharyngeus, the glossopharyngeal nerve, the pharyngeal branch t)f the vagus, and part of the parotid gland. Applied Anatomy, — Ligature of the external carotid may be required in cases of wound of this vessel or of its branches when these cannot be tied, and in some cases of pulsating tumors of the scalp or face. It is also done as a preliminary measure to excision of the maxilla. The seat of election for Ugature is between the origins of its superior thyroid and lingual branches, about a finger's breadth below the tip of the greater cornu of the hyoid bone. To tie the vessel, an inci- sion is made from the angle of the mandible to the upper border of the thjroid cartilage, and the superficial tissues and the deep fascia divided. The anterior border of the Sternocleido- mastoideus must be retracted and the lower border of the parotid gland raised, so as to expose the tendon of the Digastricus and the hypoglossal nerve, which cross the artery. The great difficulty in doing this is due to the plexus of veins derived from the superior thwoid and Ungual veins, which overlie the artery. If necessary, these must be ligatured and divided. Care must be taken not to mistake the hngual and external maxillary, when they arise by a common trunk, as they sometimes do, for the external carotid. The -needle is to be passed from the lateral to the medial side of the vessel, carefully avoiding the superior laryngeal nerve, which lies in close proximity to the artery. The circulation is at once reestablished by the free communication between most of the large branches of the artery (external maxillary, hngual, superior thjToid, occipital) and the corresponding arteries of the opposite side, and by the anastomosis of its branches with those of the internal carotid, and of the occipital with branches of the subclavian, etc. Branches. — The branches of the external carotid artery may be divided into four sets. rilE EXTERNAL CAROTID ARTERY 631 Auferior. Posterior. Ascending. Terminal. Superior Thyroid. Occipital. Ascendin by the lower border of the body of the mandible, and an imaginary line extending from the angle of the mandible to the mastoid process; helow, by the upper border of the clavicle; in front, by the middle line of the neck; behind, by the anterior margin of the Trapezius. This space is subdivided into two large triangles by the Sternocleidomastoideus, which passes obliquely across the neck, from the sternum and clavicle below, to the mastoid process and occipital bone above. The triangular space in front of this muscle is called the anterior triangle ; and that behind it, the posterior triangle. Anterior Triangle. — The anterior triangle is bounded, in front, by the middle line of the neck; behind, by the anterior margin of the Sternocleidomastoideus; its base, directed upward, is formed by the lower border of the body of the mandible. THE TRIANGLES OF TIIE NECK 643 and a line extending from the angle of the mandible to the mastoid process; its apex is below, at the sternum. This space is subdivided into four smaller triangles by the Digastricus above, and the superior belly of the Omohyoideus below. These smaller triangles are named the inferior carotid, the superior carotid, the submaxillary, and the suprahyoid. Suprahyoid triangle Submaxillarij triangle Superior carotid triangle Inferior carotid triangle Occipital triangle Subclavian triangle Fig. 5S9. — The triangles of the neck. The Inferior Carotid, or Muscular Triangle, is bounded, in front, by the median line of the neck from the hyoid bone to the sternum; behind, by the anterior margin of the Sternocleidomastoideus; above, by the superior belly of the Omohyoideus. It is covered by the integument, superficial fascia, Platysma, and deep fascia, ramifying in which are some of the branches of the supraclavicular nerves. Be- neath these superficial structures are the Sternohyoideus and Sternothyreoideus, which, together with the anterior margin of the Sternocleidomastoideus, conceal the lower part of the common carotid artery.^ This vessel is enclosed within its sheath, together with the internal jugular vein and vagus nerve; the vein lies lateral to the artery on the right side of the neck, but overlaps it below on the left side; the nerve lies betw^een the artery and vein, on a plane posterior to both. In front of the sheath are a few descending filaments from the ansa hypoglossi; behind the sheath are the inferior thyroid artery, the recurrent nerve, and the sym- pathetic trunk; and on its medial side, the oesophagus, the trachea, the thyroid gland, and the lower part of the larynx. By cutting into the upper part of this space, and slightly displacing the Sternocleidomastoideus, the common carotid artery may be tied below the Omohyoideus. The Superior Carotid, or Carotid Triangle, is bounded, hehind by the Sternocleido- mastoideus; below, by the superior belly of the Omohyoideus; and above, by the Stylohyoideus and the posterior belly of the Digastricus. It is covered by the integu- ment, superficial fascia, Platysma and deep fascia; ramifying in which are branches of the facial and cutaneous cervical nerves. Its floor is formed by parts of the Thyro- hyoideus, Hyoglossus, and the Constrictores pharyngis medius and inferior. This 1 Therefore the common carotid artery and internal jugular vein are not, strictly speaking, contained in this tri- angle, since they are covered by the Sternocleidomastoideus; that is to say, they lie under that muscle, which forms the posterior border of the triangle. But as thej' he very close to the structures which are really contained in the triangle, and whose position it is essential to remember in operating on this part of the artery, it is expedient to study the relations of all these parts together. 644 ANGIOLOGY space when dissected is seen to contain the upper part of the common carotid artery, which bifurcates opposite the upper border of the thyroid cartilage into the external and internal carotid. These vessels are somewhat concealed from veiw by the anterior margin of the Sternocleidomastoideus, which overlaps them. The external and internal carotids lie side by side, the external being the more anterior of the two. The following branches of the external carotid are also met with in this space: the superior thyroid, running forward and downward; the lingual, directly forward; the external maxillary, forward and upward; the occipital, backward; and the ascending pharyngeal, directly upward on the medial side of the internal carotid. The veins met with are: the internal jugular, which lies on 'the lateral side of the common and internal carotid arteries; and veins corresponding to the above-mentioned branches of the external carotid — viz., the superior thyroid, the lingual, common facial, ascending pharyngeal, and sometimes the occipital- all of which end in the internal jugular. The nerves in this space are the following. In front of the sheath of the common carotid is the ramus descendens hypoglossi. The hypoglossal nerve crosses both the internal and external carotids above, curving around the origin of the occipital artery. Within the sheath, between the artery and vein, and behind both, is the vagus nerve; behind the sheath, the sym- pathetic trunk. On the lateral side of the vessels, the accessory nerve runs for a short distance before it pierces the Sternocleidomastoideus; and on the medial side of the external carotid, just below the hyoid bone, may be seen the internal branch of the superior laryngeal nerve; and, still more inferiorly, the external branch of the same nerve. The upper portion of the larynx and lower portion of the pharynx are also found in the front part of this space. The Submaxillary or Digastric Triangle corresponds to the region of the neck immediately beneath the body of the mandible. It is bounded, above, by the lower border of the body of the mandible, and a line drawn from its angle to the mastoid process; heloiv, by the posterior belly of the Digastricus and the Stylohyoideus; in front, by the anterior belly of the Digastricus. It is covered by the integument, superficial fascia, Platysma, and deep fascia, ramifying in which are branches of the facial nerve and ascending filaments of the cutaneous cervical nerve. Its floor is formed by the Mylohyoideus, Hyoglossus, and Constrictor pharyngis superior. It is divided into an anterior and a posterior part by the stylomandibular ligament. The anterior part contains the submaxillary gland, superficial to which is the anterior facial vein, while imbedded in the gland is the external maxillary artery and its glandular branches; beneath the gland, on the surface of the Mylo- hyoideus, are the submental artery and the mylohyoid artery and nerve. The posterior part of this triangle contains the external carotid artery, ascending deeply in the substance of the parotid gland; this vessel lies here in front of, and super- ficial to, the internal carotid, being crossed by the facial nerve, and gives off in its course the posterior auricular, superficial temporal, and internal maxillary branches: more deeply are the internal carotid, the internal jugular vein, and the vagus nerve, separated from the external carotid by the Styloglossus and Stylo- pharyngeus, and the glossopharyngeal nerve.^ The Suprahyoid Triangle is limited hehind by the anterior belly of the Digastricus, in front by the middle line of the neck between the mandible and the hyoid bone ; below, by the body of the hyoid bone; its floor is formed by the Mylohyoideus. It contains one or two lymph glands and some small veins; the latter unite to form the anterior jugular vein. Posterior Triangle.— The posterior triangle is bounded, in front, by the Sterno- cleidomastoideus; behind, by the anterior margin of the Trapezius; its base is formed 1 The remark made about the inferior carotid triangle applies also to this one. The structures enumerated as con- tained in its posterior part Ue, strictly speaking, beneath the muscles wjiich form the posterior boundary of the tri- angle; but as it is very important to bear in mind .their close relation to the parotid gland, all these parts are spoken of together. THE IXTERXAL CAROTID ARTERY 645 by the middle third of the clavicle; its a))ex, by the occipital bone. The space is crossed, about 2.5 cm. above the clavicle, by the inferior belly of the Omo- hyoideus, which divides it into two triangles, an upper or occipital, and a lower or subclavian. The Occipital Triangle, the larger division of the posterior triangle, is bounded, in front, by the Sternocleidomastoideiis; heJiind, by the Trapezius; below, by the Omohyoideus. Its fioor is formed from abo^'e downward b\' the Splenius capitis, Levator scapulae, and the Scaleni medius and posterior. It is covered by the skin, the superficial and deep fasciae, and by the Platysma below. The accessory nerve is directed obliquely across the space from the Sternocleidomastoideus, which it pierces, to the under surface of the Trapezius; below, the supraclavicular nerves and the transverse cervical vessels and the upper part of the brachial plexus cross thcLspace. A chain of lymph glands is also found running along the posterior border of the Sternocleidomastoideus, from the mastoid process to the root of the neck. The Subclavian Triangle, the smaller division of the posterior triangle, is bouixled, above, by the inferior bellv of the Omohyoideus; below, by the clavicle; its base is formed by the posterior border of the Sternocleidomastoideus. Its floor is formed by the first rib with the first digitation of the Serratus anterior. The size of the subclavian triangle varies with the extent of attachment of the clavicular portions of the Sternocleidomastoideus and Trapezius, and also with the height at which the Omohyoideus crosses the neck. Its height also varies according to the position of the arm, being diminished by raising the limb, on account of the ascent of the clavicle, and increased by drawing the arm donwward, when that bone is depressed. This space is covered by the integument, the superficial and deep fascise and the Platysma, and crossed by the supraclavicular nerves. Just above the level of the clavicle, the third portion of the subclavian artery curves lateralward and downward from the lateral margin of the Scalenus anterior, across the first rib, to the axilla, and this is the situation most commonly chosen for ligaturing the vessel. Some- times this vessel rises as high as 4 cm. above the clavicle; occasionally, it passes in front of the Scalenus anterior, or pierces the fibres of that muscle. The sub- clavian vein lies behind the clavicle, and is not usually seen in this space; but in some cases it rises as high as the artery, and has even been seen to pass with that vessel behind the Scalenus anterior. The brachial plexus of nerves lies above the artery, and in close contact with it. Passing transversely behind the clavicle are the transverse scapular vessels; and traversing its upper angle in the same direction, the transverse cervical artery and vein. The external jugular vein runs vertically downward behind the posterior border of the Sternocleidomastoideus, to terminate in the subclavian vein; it receives the transverse cervical and trans- verse scapular veins, which form a plexus in front of the artery, and occasionally a small vein which crosses the clavicle from the cephalic. The small nerve to the Subclavius also crosses this triangle about its middle, and some lymph glands are usually found in the space. The Internal Carotid Artery (A. Carotis Interna) (Fig. 590). The internal carotid artery supplies the anterior part of the brain, the eye and its appendages, and sends branches to the forehead and nose. Its size, in the adult, is equal to that of the external carotid, though, in the child, it is larger than that vessel. It is remarkable for the number of curvatures that it presents in different parts of its course. It occasionally has one or two flexures near the base of the skull, while in its passage through the carotid canal and along the side of the body of the sphenoid bone it describes a double curvature and resembles the italic letter S. Course and Relations. — In considering the course and relations of this vessel it may be divided into four portions: cervical, petrous, cavernous, and cerebral. ()4(3 ANGIOLOGY Cervical Portion.— This portion of the internal carotid beo;ins at the bifurca- tion of the common carotid, opposite the ui)per border of the thyroid cartilage, and runs perijendicularly upward, in front of the transverse processes of the upper three cervical vertebroe, to the carotid canal in the petrous portion of the temporal bone. It is comparatively superficial at its commencement, where it is contained First aortic intercostal Fig. 590. — The internal carotid and vertebral arteries. Right side. in the carotid triangle, and lies behind and lateral to the external carotid, over- lapped by the Sternocleidomastoideus, and covered by the deep fascia, Platysma, and integument: it then passes beneath the parotid gland, being crossed by the hypoglossal nerve, the Digastricus and Stylohyoideus, and the occipital and pos- terior auricular arteries. Higher up, it is separated from the external carotid by the Styloglossus and Stylopharyngeus, the tip of the styloid process and the stylo- THE INTERNAL CAROTID ARTERY 647 liyoid ligament, the glossopharyngeal nerve and the pharyngeal branch of the \'agus. It is in relation, behind, with the Longus capitis, tlie superior cer\ical ganglion of the sympathetic trunk, and the superior laryngeal nerve; laterally, with the internal jugular vein and vagus nerve, the nerve lying on a plane posterior to the artery; medially, with the pharynx, superior laryngeal nerve, and ascending pharyngeal artery. At the base of the skull the glossopharyngeal, vagus, accessory, and hypo- glossal nerves lie between the artery and the internal jugular vein. Petrous Portion. — When the internal carotid artery enters the canal in the petrous portion of the temporal bone, it first ascends a short distance, then curves forward and medialw^ard, and again ascends as it leaves the canal to enter the cavity of the skull between the lingula and petrosal process of the sphenoid. The artery lies at first in front of the cochlea and tympanic cavity; from the latter cavity it is separated by a thin, bony lamella, which is cribriform in the young subject, and often partly absorbed in old age, Farther forward it is separated from the semilunar ganglion by a thin plate of bone, which forms the floor of the fossa for the ganglion and the roof of the horizontal portion of the canal. Fre- quently this bony plate is more or less deficient, and then the ganglion is separated from the artery by fibrous membrane. The artery is separated from the bony wall of the carotid canal by a prolongation of dura mater, and is surrounded by a number of small veins and by filaments of the carotid plexus, derived from the ascending branch of the superior cervical ganglion of the sympathetic trunk. Cavernous Portion. — In this part of its course, the artery is situated between the layers of the dura mater forming the cavernous sinus, but covered by the lining membrane of the sinus. It at first ascends toward the posterior clinoid process, then passes forward by the side of the body of the sphenoid bone, and again curves upward on the medial side of the anterior clinoid process, and perforates the dura mater forming the roof of the sinus. This portion of the artery is surrounded by filaments of the sympathetic nerve, and on its lateral side is the abducent nerve. Cerebral Portion. — Having perforated the dura mater on the medial side of the anterior clinoid process, the internal carotid passes between the optic and oculo- motor nerves to the anterior perforated substance at the medial extremity of the lateral cerebral fissure, where it gives ofi' its terminal or cerebral branches. Peculiarities. — The length of the internal carotid varies according to the length of the neck, and also according to the point of bifurcation of the common carotid. It arises sometimes from the arch of the aorta; in such rare instances, this vessel has been found to be placed nearer the middle line of the neck than the external carotid, as far upward as the larynx, when the latter vessel crossed the internal carotid. The course of the artery, instead of being straight, may be very tortuous. A few instances are recorded in which this vessel was altogether absent; in one of these the common carotid passed up the neck, and gave off the usual branches of the external carotid; the cranial portion of the internal carotid was replaced by two branches of the internal maxillary, which entered the skull through the foramen rotundum and foramen ovale, and joined to form a single vessel. Applied Anatomy. — The cervical part of the internal carotid is very rarely wounded. It is, however, sometimes injured by a stab or gunshot wound in the neck, or even occasionally by a stab from within the mouth, as when a person receives a thrust from the end of a parasol, or falls down with a tobacco pipe in his mouth. Although the internal carotid lies about 2 cm. behind and lateral to the tonsil, instances have occurred in which the artery has been wounded during the operation of excision of the tonsil, and fatal hemorrhage has supervened. The incision for ligature of the cervical portion of the internal carotid should be made along the anterior border of the Sternocleidomastoideus, from the angle of the mandible to the upper border of the thyroid cartilage. The superficial structures being divided, and the Sternocleidomastoideus defined and drawn lateralward, the areolar tissue must be carefully separated and the posterior belly of the Digastricus and the hypoglossal nerve sought for as guides to the vessel. When the artery is found, the external carotid should be drawn medialward and the Digastricus upward, and the anem-ism needle passed from the lateral to the medial side. Obstruction of the internal carotid by embolism or thrombosis may give rise to symptoms of cerebral anemia and softening if the collateral circulation is ill-developed. The patient suffers from giddiness, with failure of the mental powers; and convulsions, coma, or hemiplegia on the opposite side of the body, may be observed. 648 ANGIOLOGY Branches.-^The cervical portion of the internal carotid gives off no branches. Those from the other portions are: , _, „ ^. (Caroticotympanic. From the Petrous Portion ^^^^^^^ ^^ ^^^ Pterygoid Canal. From the Cavernous Portion From the Cerebral Portion Cavernous. Hypophyseal. Semilunar. Anterior Meningeal. Ophthalmic. Anterior Cerebral. Middle Cerebral. Posterior Communicating. Choroidal. 1. The caroticotympanic branch {ramus caroticotymyanicus; tympanic branch) is small; it enters the tympanic cavity through a minute foramen in the carotid canal, and anastomoses with the anterior tympanic branch of the internal maxillary, and with the stylomastoid artery. 2. The artery of the pterygoid canal (a. canilis pterygoidei [Vidii]; Vidian artery) is a small, inconstant branch which passes into the pterygoid canal and anas- tomoses with a branch of the internal maxillary artery. 3. The cavernous branches are numerous small vessels which supply the hypo- physis, the semilunar ganglion, and the walls of the cavernous and inferior petrosal sinuses. Some of them anastomose with branches of the middle meningeal. 4. The hypophyseal branches are one or two minute vessels supplying the hypophysis. 5. The semilunar branches are small vessels to the semilunar ganglion. 6. The anterior meningeal branch (a. meningea anterior) is a small branch which passes over the small wing of the sphenoid to supply the dura mater of the anterior cranial fossa; it anastomoses with the meningeal branch from the posterior eth- moidal artery. 7. The ophthalmic artery (a. ophthalmica) (Fig. 591) arises from the interrial carotid, just as that vessel is emerging from the cavernous sinus, on the medial side of the anterior clinoid process, and enters the orbital cavity through the optic foramen, below and lateral to the optic nerve. It then passes over the nerve to reach the medial wall of the orbit, and thence horizontally forward, beneath the lower border of the Obliquus superior, and divides it into two terminal branches, the frontal and dorsal nasal. As the artery crosses the optic nerve it is accompanied by the nasociliary nerve, and is separated from the frontal nerve by the Rectus superior and Levator palpebrae superioris. Branches.— The branches of the ophthalmic artery may be divided into an orbital group, distributed to the orbit and surrounding parts; and an ocular group, to the muscles and bulb of the eye. Orbital Group. Ocular Group. Lacrimal. Central Artery of the Retina. Supraorbital. Short Posterior Ciliary. Posterior Ethmoidal. Long Posterior Ciliary. Anterior Ethmoidal. Anterior Ciliary. Medial Palpebral. Muscular. Frontal. Dorsal Nasal. THE INTERNAL CAROTID ARTERY 649 The Lacrimal Artery {a. lacriinulLs) arises close to the optic foramen, and is one of the largest branches derived from the ophthalmic: not infrequently it is given off before the artery enters the orbit. It accompanies the lacrimal nerve along the upper border of the Rectus lateralis, and supplies the lacrimal gland. Its terminal branches, escaping from the gland, are distributed to the eyelids and con- junctiva: of those supplying the eyelids, two are of considerable size and are named the lateral palpebral arteries; they run medialward in the upper and lower lids respectively and anastomose with the medial palpebral arteries, forming an arterial circle in this situation. The lacrimal artery give off one or two zygomatic branches, one of which passes through the zygomatico-temporal foramen, to reach the tem- poral fossa, and anastomoses with the deep temporal arteries; another appears on the cheek through the zygomatico-facial foramen, and anastomoses with the transverse facial. A recurrent branch passes backward through the lateral part of the superior orbital fissure to the dura mater, and anastomoses with a branch of the middle meningeal artery. The lacrimal artery is sometimes derived from one of the anterior branches of the middle meningeal artery. Dorsal nasal Medial palpebral H.i Frontal . Supraorbital Anterior ethmoidal Posterior ethmoidal _ Muscular I Zygomntic branches J^ of lacrimal Arteria centralis retince Lacrimal Ophthalmic Internal carotid Fig. 591. — The ophthalmic artery and its branches. The Supraorbital Artery (a. swpraorhitalis) springs from the ophthalmic as that vessel is crossing over the optic nerve. It passes upward on the medial borders of the Rectus superior and Levator palpebrae, and meeting the supraorbital nerve accompanies it between the periosteum and Levator palpebrae to the supraorbital foramen; passing through this it divides into a superficial and a deep branch, which supply the integument, the muscles, and the pericranium of the forehead, anastomosing with the frontal, the frontal branch of the superficial temporal, and the artery of the opposite side. This artery in the orbit supplies the Rectus superior and the Levator palpebrae, and sends a branch across the pulley of the Obliquus superior, to supply the parts at the medial palpebral commissure. At the supra- orbital foramen it frequently transmits a branch to the diploe. 650 AXGIOLOGY The Ethmoidal Arteries are two in number: posterior and anterior. The posterior ethmoidal artery, the smaller, passes through the postericjr ethmoidal canal, supplies the posterior ethmoidal cells, and, entering the cranium, gives off a meningeal branch to the dura mater, and nasal branches which descend into the nasal cavity through apertures in the cribriform plate, anastomosing with branches of the sphenopalatine. The anterior ethmoidal artery accompanies the nasociliary nerve through the anterior ethmoidal canal, supplies the anterior and middle ethmoidal cells and frontal sinus, and, entering the cranium, gives off a meningeal branch to the dura mater, and nasal branches; these latter descend into the nasal cavity through the slit by the side of the crista galli, and, running along the groove on the inner surface of the nasal bone, supply branches to the lateral wall and septum of the nose, and a terminal branch which appears on the dorsum of the nose between the nasal bone and the lateral cartilage. The Medial Palpebral Arteries iaa. palpebrales mediales; internal imlpehral arteries), two in number, superior and inferior, arise from the ophthalmic, opposite the pulley of the Obliquus superior; they leave the orbit to encircle the eyelids near their free margins, forming a superior and an inferior arch, which lie between the Orbicularis oculi and the tarsi. The superior palpebral anastomoses, at the lateral angle of the orbit, with the zygomaticoorbital branch of the temporal artery and with the upper of the two lateral palpebral branches from the lacrimal arterj-; the inferior palpebral anastomoses, at the lateral angle of the orbit, with the lower of the two lateral palpebral branches from the lacrimal and with the transverse facial artery, and, at the medial part of the lid, with a branch from the angular artery. From this last anastomoses a branch passes to the nasolacrimal duct, ramifying in its mucous membrane, as far as the inferior meatus of the nasal cavity. The Frontal Artery (a. frontalis), one of the terminal branches of the ophthalmic, leaves the orbit at its medial angle with the supratrochlear nerve, and, ascending on the forehead, supplies the integument, muscles, and pericranium, anastomosing with the supraorbital artery, and with the artery of the opposite side. The Dorsal Nasal Artery (a. dorsalis nasi; nasal artery), the other terminal branch of the ophthalmic, emerges from the orbit above the medial palpebral ligament, and, after giving a twig to the upper part of the lacrimal sac, divides into two branches, one of which crosses the root of the nose, and anastomoses with the angular artery, the other runs along the dorsum of the nose, supplies its outer surface; and anastomoses with the artery of the opposite side, and with the lateral nasal branch of the external maxillary. The Central Artery of the Retina (a. centralis retinae) is the first and one of the smallest branches of the ophthalmic artery. It runs for a short distance within the dural sheath of the optic nerve, but about 1.25 cm. behind the eyeball it pierces the nerve obliquely, and runs forward in the centre of its substance to the retina. Its mode of distribution will be described with the anatomy of the eye. The Ciliary Arteries (aa. ciliares) are divisible into three groups, the long and short, posterior, and the anterior. The short posterior ciliary arteries from six to twelve in number, arise from the ophthalmic, or its branches; they pass forward around the optic nerve to the posterior part of the eyeball, pierce the sclera around the entrance of the nerve, and supply the choroid and ciliary processes. The long posterior ciliary arteries, two in number, pierce the posterior part of the sclera at some little distance from the optic nerve, and run forward, along either side of the eyeball, between the sclera and choroid, to the ciliary muscle, where they divide into two branches; these form an arterial circle, the circulus arteriosus major, around the circumference of the iris, from which numerous converging branches run, in the substance of the iris, to its pupillary margin, where they form a second arterial circle, the circulus arteriosus minor. The anterior ciliary arteries are derived from THE INTERNAL CAROTID ARTERY 651 the muscular hraufhes; they ruu to the front of the eyeball in company with the tendons of the Recti, form a vascular zone beneath the conjunctiva, and then pierce the sclera a short distance from the cornea and end in the circulus arteriosus major. The Muscular Branches, {rami muscularcs) , two in number, superior and inferior, frequently s})ring from a common trunk. The superior, often wanting, supplies the Levator palpebrae superioris, Rectus superior, and Obliquus superior. The inferior, more constantly present, passes forward between the optic nerve and Rectus inferior, and is distributed to the Recti lateralis, medialis, and inferior, and the Obliquus inferior. This vessel gives off most of the anterior ciliary arteries. Addi- tional muscular branches are given off from the lacrimal and supraorbital arteries, or from the trunk of the ophthalmic. Fig. 592. — The arteries of the base of the brain. The temporal pole of the cerebrum and a portion of the cerebellar hemisphere have been removed on the right side. 8.. The anterior cerebral artery (a. cerebri anterior) (Figs. 592, 593, 594) arises from the internal carotid, at the medial extremity of the lateral cerebral fissure. It passes forward and medialw^ard across the anterior perforated substance, above the optic nerve, to the commencement of the longitudinal fissure. Here it comes into close relationship with the opposite artery, to which it is connected by a short trunk, the anterior communicating artery. From this point the two vessels run side by side in the longitudinal fissure, curve around the genu of the corpus callosum, and turning backward continue along the upper surface of the corpus callosum to its posterior part, where they end by anastomosing with the posterior cerebral arteries. G52 Branches, branches : ANGIOLOGY -In its course the anterior cerebral artery gives off tlie following Antero-medial Ganglionic. Inferior. Anterior. Middle. Posterior. The Antero-medial Ganglionic Branches are a group of small arteries which arise at the commencement of the anterior cerebral artery; they pierce the anterior perforated substance and lamina terminalis, and supply the rostrum of the corpus Fig. 593. — Outer surface of cerebral hemisphere, showing areas supplied by cerebral arteries. callosum, the septum pellucidum, and the head of the caudate nucleus. The inferior branches, two or three in number, are distributed to the orbital surface of the frontal lobe, wdiere they supply the olfactory lobe, gyrus rectus, and internal orbital gyrus. The anterior branches supply a part of the superior frontal gyrus, and send twigs over the edge of the hemisphere to the superior and middle frontal gyri and upper part of the anterior central gyrus. The middle branches supply the corpus callosum, the cingulate gyrus, the medial surface of the superior frontal gyrus, and the upper part of the anterior central gyrus. The posterior branches supply the precuneus and adjacent lateral surface of the hemisphere. Fig. 594. — Medial surface of cerebral hemisphere, showing areas supplied by cerebral arteries. The Anterior Communicating Artery (a. coiiwiunicans anterior) connects the two anterior cerebral arteries across the commencement of the longitudinal fissure. Sometimes this vessel is wanting, the two arteries joining together to form a single trunk, which afterward divides; or it may be wholly, or partially, divided into two. Its length averages about 4 mm., but varies greatly. It gives off some of the antero-medial ganglionic vessels, but these are principally derived from the anterior cerebral. 9. The middle cerebral artery {a. cerebri media) (Figs. 592, 593), the largest branch of the internal carotid, runs at first lateralward in the lateral cerebral or THE ARTERIES OF THE BRAIN 653 Sylvian fissure and then backward and upward on the surface of the insula, where it divides into a number of branches which are distributed to the lateral surface of the cerebral hemisphere. Branches. — The branches of this vessel are the: Antero-lateral Ganglionic. Ascending Parietal. Inferior Lateral Frontal. Parietotemporal. Ascending Frontal. Temporal. The Antero-lateral Ganglionic Branches, a group of small arteries which arise at the commencement of the middle cerebral artery, are arranged in two sets: one, the internal striate, passes upward through the inner segments of the lentiform nucleus, and supplies it, the caudate nucleus, and the internal capsule; the other, the external striate, ascends through the outer segment of the lentiform nucleus, and supplies the caudate nucleus and the thalamus. One artery of this group is of larger size than the rest^ and is of special importance, as being the artery in the brain most frequently ruptured; it has been termed by Charcot the artery of cerebral hemorrhage. It ascends between the lentiform nucleus and the external capsule, and ends in the caudate nucleus. The inferior lateral frontal supplies the inferior frontal gyrus (Brocas convolution) and the lateral part of the orbital surface of the frontal lobe. The ascending frontal supplies the anterior central gyrus. The ascending parietal is distributed to the posterior central gyrus and the lower part of the superior parietal lobule. The parietotemporal supplies the supra- marginal and angular gyri, and the posterior parts of the superior and middle temporal gyri. The temporal branches, two or three in number, are distributed to the lateral surface of the temporal lobe. 10. The posterior communicating artery (a. communicans iMsterior) (Fig. 592) runs backward from the internal carotid, and anastomoses with the posterior cerebral, a branch of the basilar. It varies in size, being sometimes small, and occa- sionally so large that the posterior cerebral may be considered as arising from the internal carotid rather than from the basilar. It is frequently larger on one side than on the other. From its posterior half are given off a number of small branches, the postero-medial ganglionic branches, which, with similar vessels from the posterior cerebral, pierce the posterior perforated substance and supply the medial surface of the thalami and the walls of the third ventricle. 11. The anterior choroidal (a. chorioidea; choroid artery) is a small but constant branch, which arises from the internal carotid, near the posterior communicating artery. Passing backward and lateralward between the temporal lobe and the cerebral peduncle, it enters the inferior horn of the lateral ventricle through the choroidal fissure and ends in the choroid plexus. It is distributed to the hippo- campus, fimbria, tela chorioidea of the third ventricle, and choroid plexus. THE ARTERIES OF THE BRAIN. Since the mode of distribution of the vessels of the brain has an important bearing upon a considerable number of the pathological lesions which may occur in this part of the nervous system, it is important to consider a little more in detail the manner in which the vessels are distributed. The cerebral arteries are derived from the internal carotid and vertebral, which at the base of the brain form a remarkable anastomosis known as the arterial circle of Willis. It is formed in front by the anterior cerebral arteries, branches of the internal carotid, which are connected together by the anterior communicating; behind by the two posterior cerebral arteries; branches of the basilar, which are connected on either side w^ith the internal carotid by the posterior communicating 654 ANGIOLOGY 4.7it. communicating Ant. cerebral Post com- municating (Figs. 592, 595). The parts of the brain induded within this arterial circle are the lamina terminalis, the optic chiasma, the infundil^ulum, the tuber cinereum, the corpora mamillaria, and the posterior perforated su})stance. The three trunks which together supply each cerebral hemisphere arise from the arterial circle of Willis. From its anterior part proceed the two anterior cerebrals, from its antero-lateral parts the middle cerebrals, and from its posterior part the posterior cerebrals. Each of these principal arteries gives origin to two difi'erent systems of secondary vessels. One of these is named the ganglionic system, and the vessels belonging to it supply the thalami and corpora striata; the other is the cortical system, and its vessels ramify in the pia mater and supply the cortex and subjacent brain substance. These two systems do not communicate at any point of their peripheral distribution, but are entirely independent of each other, and there is between the parts supplied by the two sys- tems a borderland of diminished nutritive activity, where, it is said, softening is especi- ally liable to occur in the brains of old people. The Ganglionic System. — All the vessels of this system are given off from the arterial circle of Willis, or from the vessels close to it. They form six principal groups: (I) the antero-medial group, derived from the anterior cerebrals and anterior communicating; (II) the postero-medial group, from the posterior cerebrals and posterior communicating; (III and IV) the right and left antero-lateral groups, from the middle cerebrals; and (V and VI) the right and left postero-lateral groups, from the posterior cerebrals, after they have wound around the cerebral pedun- cles. The vessels of this system are larger than those of the cortical system, and are what Cohnheim designated terminal arteries — that is to say, vessels which from their origin to their termination neither supply nor receive any anastomotic branch, so that, through any one of the vessels only a limited area of the thalamus or corpus striatum can be injected, and the injection cannot be driven beyond the area of the part supplied by the particular vessel which is the subject of the experiment. The Cortical Arterial System. — The vessels forming this system are the terminal branches of the anterior, middle, and posterior cerebral arteries. They divide and ramify in the substance of the pia mater, and give off branches which penetrate the brain cortex, perpendicularly. These branches are divisible into two classes, long and short. The long, or medullary arteries, pass through the gray substance and penetrate the subjacent white substance to the depth of 3 or 4 cm., without intercommunicating otherwise than by very fine capillaries, and thus constitute so many independent small systems. The short vessels are confined to the cortex, where they form with the long vessels a compact net-work in the middle zone of the gray substance, the outer and inner zones being sparingly supplied with blood. The vessels of the cortical arterial system are not so strictly "terminal" as those of the ganglionic system, 'but they approach this type very closely, so that injection of one area "from the vessel of another area, though possible, is Posterior inferior cerebellar Fig. 595. — Diagram of the arterial circulation at the base of the brain. A.L. Antero-lateral. A.M. Antero-medial. P.L. Postero-lateral. P.M. Postero- medial ganglionic branches. THE SUBCLAVIAN ARTERY 655 freciuently very difficult, and is only effected through vessels of small calibre. As a result of this, obstruction of one of the main branches, or its divisions, may have the effect of ])roducing' softening in a limited area of the cortex. THE ARTERIES OF THE UPPER EXTREMITY. The artery which supplies the upper extremity continues as a single trunk from its commencement down to the elbow; but different portions of it have received different names, according to the regions through which they pass. That part of the vessel which extends from its origin to the outer border of the first rib is termed the subclavian; beyond this point to the lower border of the axilla it is named the axillary; and from the lower margin of the axillary space to the bend of the elbow it is termed brachial; here the trunk ends by dividing into two branches the radial and ulnar. THE SUBCLAVIAN ARTERY (A. SUBCLAVIA) (Fig. 596). On the right side the subclavian artery arises from the innominate artery behind the right sternoclavicular articulation; on the left side it springs from the arch of the aorta. The two vessels, therefore, in the first part of their course, differ in length, direction, and relation with neighboring structures. In order to facilitate the description, each subclavian artery is divided into three parts. The first portion extends from the origin of the vessel to the medial border of the Scalenus anterior; the second lies behind this muscle; and the third extends from the lateral margin of the muscle to the outer border of the first rib, where it becomes the axillary artery. The first portions of the two vessels require separate descriptions; the second and third parts of the two arteries are practically alike. First Part of the Right Subclavian Artery (Figs. 583, 596). — The first part of the right subclavian artery arises from the innominate artery, behind the upper part of the right sternoclavicular articulation, and passes upward and lateralward to the medial margin of the Scalenus anterior. It ascends a little above the clavicle, the extent to which it does so varying in dift'erent cases. Relations. — It is covered, in Jront, by the integument, superficial fascia, Platysma, deep fascia, the clavicular origin of the Sternocleidomastoideus, the Sternohyoideus, and Sternothyreoideus, and another layer of the deep fascia. It is crossed by the internal jugular and vertebral veins, by the vagus nerve and the cardiac branches of the vagus and sympathetic, and by the sub- clavian loop of the sympathetic trunk which forms a ring around the vessel. The anterior jugular vein is directed lateralward in front of the artery, but is separated from it by the Sternohj-oideus and Sternothyreoideus. Below and behind the artery is the pleura, which separates it from the apex of the lung; behind is the sympathetic trunk, the Longus coUi and the first thoracic vertebra. The right recurrent nerve winds around the lower and back part of the vessel. First Part of the Left Subclavian Artery (Fig. 583).— The first part of the left subclavian artery arises from the arch of the aorta, behind the left common carotid, and at the level of the fourth thoracic vertebra; it ascends in the superior medias- tinal cavity to the root of the neck and then arches lateralward to the medial border of the Scalenus anterior. Relations. — It is in relation, in front, with the vagus, cardiac, and phrenic nerves, which he parallel with it, the left common carotid artery, left internal jugular and vertebral veins, and the commencement of the left innominate vein, and is covered by the Sternothj-reoideus, Sterno- hj^oideus, and Sternocleidomastoideus; behind, it is in relation with the oesophagus, thoracic duct, left recurrent nerve, inferior cervical ganglion of the sympathetic trunk, and Longus colli; higher up, however, the oesophagus and thoracic duct he to its right side; the latter ultimately arching over the vessel to join the angle of union between the subclavian and internal jugular veins. Medial to it are the oesophagus, trachea, thoracic duct, and left recurrent nerve; lateral to it, the left pleura and lung. / 650 A XG 10 LOGY Second and Third Parts of the Subclavian Artery (Fig. 590). — The second portion of the subclavian artery lies behind the Scalenus anterior; it is very short, anrl forms the highest part of the arch described by the vessel. Fig. 596. — Superficial dissection of the right side of the neck, showing the carotid and subcla-vian arteries. Relations. — It is covered, in front, by the skin, superficial fascia, Platysma, deep cervical fascia, Stemocleidomastoideus, and Scalenus anterior. On the right side of the neck the phrenic nerv'e is separated from the second part of the artery by the Scalenus anterior, while on the left side it crosses the first part cf the arterj' close to the medial edge of the muscle. Behind the vessel are the pleura and the Scalenus medius; above, the brachial plexus of nerves; below, the pleura. The subclavian vein hes below and in front of the artery, separated from it by the Scalenus anterior. The third portion of the subclavian artery runs downward and lateralward from the lateral margin of the Scalenus anterior to the outer border of the first rib, where it becomes the axillary artery. This is the most superficial portion of the vessel, and is contained in the subclavian triangle (see page 645). THE SL'BCLAVIAX ARTERY 657 Relations. — It i.s covered, in front, by the skin, the sujjerficial fascia, the Platysma, the supra- clavicular nerves, and the deep cervical fascia. The external jugular vein crosses its medial part and receives the transverse scapular, transverse cervical, and anterior jugular veins, which frequently form a i>lexus in front of the arter}^ Behind the veins, the nerve to the Bubclavius descends in front of the artery. The terminal part of the artery lies behind the clavicle and the Subclavius and is crossed by the transverse scapular vessels. The subclavian vein is in front of and at a slight Ij' lower level than the arter3\ Behind, it lies on the lowest trunk of the brachial plexus, which intervenes between it and the Scalenus medius. Above and to its lateral side are the upper trunks of the brachial plexus and the Omohyoideus. Below, it rests on the upper surface of tli(> first rib. Peculiarities. — The subclavian arteries vary in their origin, their course, and the height to which they rise in the neck. The origin of the right subclavian from the innominate takes place, in some cases, above the sternoclavicular articulation, and occasionally, but less frequently, below that joint. The artery may arise as a separate trunk from the arch of the aorta, and in such cases it may be either the first, second, third, or even the last branch derived from that vessel; in the majority, however, it is the first or last, rarety the second or third. When it is the first branch, it occupies the ordinary position of the innominate artery; when the second or third, it gains its usual position by passing behind the right carotid; and when the last branch, it arises from the left extremity of the arch, and passes obhquely toward the right side, usually behind the trachea, oesophagus, and right carotid, sometimes between the oesophagus and trachea, to the upper border of the first rib, whence it follows its ordinary course. In very rare instances, this ves.sel arises from the thoracic aorta, as low dowm as the fourth thoracic vertebra. Occasionally, it perforates the Scalenus anterior; more rarety it passes in front of that muscle. Sometimes the subclavian vein passes with the arterj^ behind the Scalenus anterior. The artery may ascend as high as 4 cm. above the clavicle, or any intermediate point between this and the upper border of the bone, the right subclavian usually ascending higher than the left. The left subclavian is occasionally joined at its origin with the left carotid. The left subclavian artery is more deeplj^ placed than the right in the first part of its course, and, as a rule, does not reach quite as high a level in the neck. The posterior border of the Sterno- cleidomastoideus corresponds pretty closely to the lateral border of the Scalenus anterior, so that the thii-d portion of the artery, the part most accessible for operation, lies immediately lateral to the posterior border of the Sternocleidomastoideus. Applied Anatomy. — An aneurism may form on any part of the subclavian artery, except the intrathoracic portion of the left vessel, which is said never to be the seat of anemism. The most common site is, however, the third portion, especially on the right side, on account of the greater exposm-e to injmy and the greater amovmt of use of the right upper extremity. In this situation it may cause pressure on the brachial plexus, producing pain and numbness in the arm and fingers, with loss of power or paralysis of the muscles of these parts. (Edema of the arm may result from pressure on the subclavian vein. The external jugular vein may become distended and varicose. The treatment is unsatisfactory, since proximal ligature cannot be undertaken with much chance of success. If constitutional treatment and direct pressm-e on the aneurismal sac fail, the best treatment is excision of the sac, if it be small. In aneurisms of the first portion of this artery there is oedema of the head and face, with lividity, congestion of the brain, and semi- consciousness from pressure on the internal jugular vein; and spasmodic action of the Diaphragma from pressure on the phrenic nerve. The collateral circulation is so good that blocking of the subclavian artery by embohsm or thi-ombosis often fails to give rise to any str ikin g signs or sjTnptoms, beyond occasional pains in the neck and shoulder and some degree of weakness and wasting in the muscles of the arm. Compression of the subclavian artery may be requii'ed to control hemorrhage, and there is only one situation in which it can be effectually apphed, viz., where the artery passes across the upper sm-face of the first rib. In order to compress the vessel in this situation, the shoulder should be depressed, and the surgeon grasping the side of the neck should press with his thumb in the angle formed by the posterior border of the Sternocleidomastoideus with the upper border of the clavicle, downward, backward, and inward against the rib; if from any cause the shoulder cannot be sufficiently depressed, pressure may be made from before backward, so as to compress the artery against the Scalenus medius and transverse process of the seventh cervical vertebra. In appropriate cases, a preliminary incision may be" made thi'ough the cervical fascia, and the finger may be pressed do^-n directly upon the artery. Ligature of the subclavian, artery may be required in cases of wounds, or of aneurism in the axilla, or in cases of anem-ism on the cardiac side of the point of hgatm-e; and the third part of the arterj' is that which is most favorable for an operation, on account of its being comparatively superficial, and most remote from the origin of the large branches. In those cases where the clavicle is not displaced, this operation may be performed with comparative facihty; but where the clavicle is pushed up by a large anemismal tumor in the axilla, the artery lies at a great depth from the surface, and this materialh' increases the difficulty of the operation. Under these 42 658 ANGIOLOGY circumstances, it becomes a matter of importance to consider the height to which this vessel reaches above the bone. In ordinary cases, its arch is about 1.25 cm. above the clavicle, occasionally as high as 4 cm., and sometimes so low as to be on a level with its upper border. If the clavicle be displaced, these variations wiU necessarily make the operation more or less difficult, accord- ing as the vessel is less or more accessible. The vessel is also hgatured as a preUminary measure to the complete interscapulothoracic amputation of the upper extremity, in which case the transverse scapular and transverse cervical arteries may, if found, be ligatured at the same time, making the "fore-quarter" amputation an almost bloodless procedure. The procedure in the operation of tying the third portion of the subclavian artery is as follows: The patient being placed on a table in the supine position, with the head drawn over to the oppo- site side, and the shoulder depressed as much as possible, the integument should be pulled down- ward over the clavicle, and an incision made through it, upon that bone, from the anterior border of the Trapezius to the posterior border of the Sternocleidomastoideus. The object in drawing the skin downward is to avoid any risk of wounding the external jugular vein, for as it perforates the deep fascia above the clavicle, it cannot be drawn downward with the skin. The soft parts should now be allowed to ghde up, and the cervical fascia divided upon a director, and if the interval between the Trapezius and Sternocleidomastoideus be insufficient for the performance of the operation, a portion of one or both may be divided. The external jugular vein will now be seen toward the medial side of the wound; this and the transverse scapular and transverse cervical veins which end in it should be held aside. If the external jugular vein be at all in the way and exposed to injxiry, it should be tied in two places and divided. The transverse scapular artery should be avoided, and the Omohyoideus held aside if necessary. In the space beneath this muscle, careful search must be made for the vessel; a deep layer of fascia and some connec- tive tissue having been divided carefully, the lateral margin of the Scalenus anterior muscle must be felt for, and the finger being guided by it to the first rib, the pulsation of the subclavian artery will be felt as it passes over the rib. The sheath of the vessels having been opened, the aneurism needle may then be passed around the artery from above downward and medialward so as to avoid including any of the branches of the brachial plexus. If the clavicle be so raised by the tumor that the application of the ligature cannot be effected in this situation, the artery may be tied above the first rib, or even behind the Scalenus anterior; the difficulties of the opera- tion in such a case will be materially increased, on account of the greater depth of the artery, and the alteration in position of the surrounding parts. The second part of the subclavian artery, the portion which rises highest in the neck, has been considered favorable for the apphcation of the hgature when it is difficult to tie the artery in the third part of its course. There are, however, many objections to the operation in this situation. It is necessary to divide the Scalenus anterior, upon which hes the phrenic nerve, and at the medial side of which is situated the internal jugular vein; and a wound of either of these struc- tures might lead to the most dangerous consequences. Again, the artery is in contact, below, with the plem-a, which must also be avoided; and, lastly, the proximity of so many of its large branches arising medially to this point must be a stiU further objection to the operation. In cases, however, where the sac of an axillary aneurism encroaches on the neck, it may be necessary to divide the lateral half or two-thirds of the Scalenus anterior, so as to place the ligature on the vessel at a greater distance from the sac. The operation is performed exactly in the same way as ligature of the third portion, until the Scalenus anterior is exposed, when it is to be divided on a director (never to a greater extent than its lateral two-thirds), and it immediately retracts. The operation is therefore merely an extension of the operation for hgature of the third portion of the vessel. In those cases of aneurism of the axillary or subclavian artery which encroach upon the lateral portion of the Scalenus anterior to such an extent that a hgature cannot be appHed in that situation, it may be deemed advisable, as a last resource, to tie the first portion of the sub- clavian artery. On the left side, this operation is almost impracticable; the great depth of the artery from the surface, its intimate relation with the pleura, and its close proximity to the thoracic duct and to so many important veins and nerves, present a series of difficidties which it is next to impossible to overcome. ^ On the right side, the operation is practicable, and has been performed on several occasions. The main objection to the operation in this situation is the smaUness of the interval which usually exists between the commencement of the vessel and the origin of the nearest branch. The operation may be performed in the following manner: The patient being placed on the table in the supine position, with the neck extended, an incision should be made along the upper border of the medial part of the clavicle, and a second along the medial border of the Sternocleidomastoideus, meeting the former at an angle. The attach- ments of both heads of the Sternocleidomastoideus must be divided on a director, and turned lateralward; a few small arteries and veins, and occasionally the anterior jugular, must be avoided, or, if necessary, hgatured in two places and divided, and the Sternohyoideus and Sternothyreoideus divided in the same manner as the preceding muscle. After tearing through the deep fascia, the ' The operation has, however, been performed by J. K. Rodgers, by Halsted, and by Schumpert. THE SUBCLAVIAN ARTERY 659 internal jugular vein will be seen crossing the subclavian artery; this should be pressed aside, and the artery secured by passing the needle from below upward, by which the pleura is more effectually avoided. The exact position of the vagus, recurrent, and phrenic nerves and the sympathetic trunk should be borne in mind, and the ligature should be appUed near the origin of the vertebral, in order to afford as much room as possible for the formation of a coagulum between the ligature and the origin of the vessel. It should be remembered that the right sub- clavian artery is occasionally deeply placed in the first part of its course, when it arises from the left side of the aortic arch, and passes in such cases behind the oesophagus, or between it and the trachea. Collateral Circulation. — After ligature of the third part of the subclavian artery, the collateral circulation is established mainly by three sets of vessels, thus described in a dissection : 1. A posterior set, consisting of the transverse scapular and the descending ramus of the trans- verse cervical branches of the subclavian, anastomosing with the subscapular from the axillary. 2. A medial set, produced by the connection of the internal mammary on the one hand, with the highest intercostal and lateral thoracic arteries, and the branches from the subscapular on the other. 3. A middle or axillary set, consisting of a number of small vessels derived from branches of the subclavian, above, and, passing through the axilla, terminating either in the main trunk, or some of the branches of the axillary below. This last set presented most con.spicuously the pecuhar character of newly formed or, rather, dilated arteries, being excessively tortuous, and forming a complete plexus. The chief agent in the restoration of the axillary artery below the tumor was the subscapular artery, which communicated most freely with the internal mammary, transverse scapular and descending ramus of the transverse cervical branches of the subclavian, from all of which it received so great an influx of blood as to dilate it to three times its natural size.^ When a hgature is applied to the first part of the subclavian artery, the collateral circulation is carried on by : (1) the anastomosis between the superior and inferior thyroids; (2) the anastomosis of the two vertebrals; (3) the anastomosis of the internal mammary with the inferior epigastric and the aortic intercostals; (4) the costocervical anastomosing with the aortic intercostals; (5) the profunda cervicis anastomosing with the descending branch of the occipital; (6) the scapular branches of the thjTocervical trunk anastomosing with the branches of the axillary, and (7) the thoracic branches of the axillary anastomosing with the aortic intercostals. Branches. — The branches of the subclavian artery are: Vertebral. Internal mammary. Thyrocervical. Costocervical. On the left side all four branches generally arise from the first portion of the vessel; but on the right side (Fig. 596) the costocervical trunk usually springs from the second portion of the vessel. On both sides of the neck, the first three branches arise close together at the medial border of the Scalenus anterior; in the majority of cases, a free interval of from 1.25 to 2,5 cm. exists between the commencement of the artery and the origin of the nearest branch. 1. The vertebral artery (a. mrtebralis) (Fig. 590), is the first branch of the sub- clavian, and arises from the upper and back part of the first portion of the vessel. It is surrounded by a plexus of nerve fibres derived from the inferior cervical ganglion of the sympathetic trunk, and ascends through the foramina in the transverse processes of the upper six cervical vertebrae ;2 it then winds behind the superior articular process of the atlas and, entering the skull through the foramen magnum, unites, at the lower border of the pons, with the vessel of the opposite side to form the basilar artery. Relations. — The vertebral artery may be divided into four parts: The first part rmis upward and backward between the Longus colli and the Scalenus anterior. In front of it are the internal jugular and vertebral veins, and it is crossed by the inferior thyroid artery; the left vertebral is crossed by the thoracic duct also. Behind it are the transverse process of the seventh cervical vertebra, the sympathetic trimk and its inferior cervical ganghon. The second part runs upward through the foramina in the transverse processes of the upper six cervical vertebrae, and is sur- rounded by branches from the inferior cervical sympathetic ganghon and by a plexus of veins 1 Guy's Hospital Reports, vol. i, 1S36. Case of axillary aneurism, in which Aston Key had tied the subclavian artery on the lateral edge of the Scalenus anterior, twelve years previously. - The vertebral artery sometimes enters the foramen in the transverse process of the fifth vertebra, and has been seen entering that of the seventh vertebra. 660 ANGIOLOGY which unite to form the vertebral w'm at the lower part of the neck. It is situated in front of the trunks of the cervical nerves, and pursues an almost vertical course as far as the transverse process of the atlas, above which it runs upward and lateralward to the foramen in the trans- verse process of the atlas. The third part issues from the latter foramen on the medial side of the Rectus capitis lateralis, and cur^'cs backward behind the superior articular process of the atlas, the anterior ramus of the first cervical nerve being on its medial side; it then lies in the groove on the upper surface of the posterior arch of the atlas, and enters the vertebral canal by passing beneath the posterior atlantooccipital membrane. This j)art of the artery is covered by the Semispinalis capitis and is contained in the suboccipital triangle — a triangular space bounded by the Rectus capitis posterior major, the Obhquus superior, and the Obliquus inferior. The first cervical or suboccipital nerve lies between the artery and the posterior arch of the atlas. The fourth part pierces the dura mater and inchnes medialward to the front of the medulla oblongata; it is placed between the hypoglossal nerve and the anterior root of the first cervical nerve and beneath the first digitation of the ligamentum denticulatum. At the lower border of the pons it unites with the vessel of the opposite side to form the basilar artery. Branches. — The branches of the vertebral artery may be divided into two sets: those given off in the neck, and those within the cranium. Cervical Branches. ' Cranial Branches. SpinaL Meningeal. Muscular. Posterior Spinal. Anterior Spinal. Posterior Inferior Cerebellar. Medullary. Spinal Branches {rami spinales) enter the vertebral canal through the interverte- bral foramina, and each divides into two branches. Of these, one passes along the roots of the nerves to supply the medulla spinalis and its membranes, anasto- mosing with the other arteries of the medulla spinalis; the other divides into an ascending and a descending branch, which unite with similar branches from the arteries above and below, so that two lateral anastomotic chains are formed on the posterior surfaces of the bodies of the vertebrae, near the attachment of the pedicles. From these anastomotic chains branches are supplied to the periosteum and the bodies of the vertebrae, and others form communications with similar branches from the opposite side; from these communications small twigs arise which join similar branches above and below, to form a central anastomotic chain on the posterior surface of the bodies of the vertebrae. Muscular Branches are given off to the deep muscles of the neck, where the vertebral artery curves around the articular process of the atlas. They anastomose with the occipital, and with the ascending and deep cervical arteries. The Meningeal Branch (ramus meningeus; posterior meningeal branch) springs from the vertebral opposite the foramen magnum, ramifies between the bone and dura mater in the cerebellar fossa, and supplies the falx cerebelli. It is fre- quently represented by one or two small branches. The Posterior Spinal Artery {a. spinalis posterior; dorsal spinal artery) arises from the vertebral, at the side of the medulla oblongata; passing backward, it descends on this structure, lying in front of the posterior roots of the spinal nerves, and is reinforced by a succession of small branches, which enter the vertebral canal through the intervertebral foramina; by means of these it is continued to the lower part of the medulla spinalis, and to the cauda equina. Branches from the posterior spinal arteries form a free anastomosis around the posterior roots of the spinal nerves, and communicate, by means of very tortuous transverse branches, with the vessels of the opposite side. Close to its origin each gives off an ascending branch, which ends at the side of the fourth ventricle. The Anterior Spinal Artery (a. spinalis anterior; ventral spinal artery) is a small branch, which arises near the termination of the vertebral, and, descending in front of the medulla oblongata, unites with its fellow of the opposite side at the THE Si'BCL.WIAX ARTERY G61 level of the foramen magnuni. One of these vessels is usually larger than the other, but oeeasionally they are about equal in size. The siiieii referred to in the description of the humerus (p. 312). As Regards its Division. — Occasionally, the artery is divided for a short distance at its upper l)art into two trunks, which are united below. Frequently the artery divides at a higher level than usual, and the vessels con(!erned in this high division are three, viz., radial, ulnar, and interosseous. Most frequently the radial is giv(;n off high up, the other limb of the bifurcation consisting of the ulnar and interosseous; in some instances the ulnar arises above the ordinary level, and the radial antl interosseous form the other limb of the division; occa- sionally the interosseous arises high up. Sometimes, long slender vessels, vasa abcrranlia, connect the brachial or the axillary artery with one of the arteries of the forearm, or branches from them. These vessels usually join the radial. Varieties in Muscular Relations. — The brachial artery is occasionally concealed, in some part of its course, by muscular or tendinous slips derived from the Cora- cobrachialis. Biceps brachii, Brachialis, or Pronator teres. Applied Anatomy. — In spite of the fact that the brachial artery is very superficial and but little protected by surrounding tissues, it is seldom wounded. This, no doubt, is due to its situation on the medial side of the arm, which is little exposed to injury. Compression of the brachial artery is required in cases of amputation and some other operations in the arm and forearm, and may be effected in almost any part of the course of the artery. If pressure be made in the upper part of the limb, it should be directed lateral- ward; if in the lower part, backward, as the artery lies on the medial side of the humerus above, and in front of it below. The most favorable situation is about the middle of the arm, where the artery lies on the tendon of the Coracobrachialis on the medial surface of the humerus. The application of a ligature to the brachial artery may be required in cases of wound of the vessel, and in some cases of wound of the volar arch. It is also sometimes necessary in cases of aneurism of the brachial, radial, ulnar, or interosseous arteries. The artery may be secured in any part of its course. The chief guides in determining its posi- tion are the surface markings produced by the medial margins of the Coraco- brachiahs and Biceps brachii, and the known course of the vessel; its pulsation should be carefully felt for before any operation is performed, as the vessel occasionally deviates from its usual position. It is essential in applying a ligature to this vessel that the arm should be held away from the side, and supported only from the elbow, for if the arm be allowed to rest on any firm structure the Triceps brachii is pressed forward and overlaps the vessel, thus making the operation much more difficult. In the upper third of the arm the artery may be exposed in the following manner. The patient being placed supine upon a table, the affected hmb should be raised from the side, and the hand supinated. An incision about 5 cm. in length is made on the medial side of the Coracobrachialis, and the subjacent fascia cautiously divided, so as to avoid wounding the medial antibrachial cutaneous nerve or basihc vein, as the latter sometimes runs on the surface of the artery as high as the axilla. The fascia having been divided, it should be remembered that the ulnar nerve and the medial antibrachial cutaneous nerve lie on the medial side of the artery, the median nerve 43 ulnar collateral artery ulnar collateral artery Fig. 601.— The brachial artery, 674 AXGIOLOGY on the lateral side but occasionally superficial to the artery in this situation, and that the venae eomitantes are also in relation with the vessel, one on either side. These being carefully sepa- rated, the aneurism needle should be passed around the artery from the medial side. In the case of a high division, the two arteries are usually placed side by side; and if they are exposed in an operation, the surgeon should endeavor to ascertain, by alternately pressing on each vessel, which is connected with the wound or aneurism, when a hgature may be applied accordingly; if pulsation or hemorrhage ceases only when both vessels are compressed, both must be tied. In the middle of the arm the brachial artery may be exposed by making an incision along the medial margin of the Biceps brachii. The forearm being bent so as to relax the muscle, it should be drawn sHghtly aside, and the fascia carefully divided, when the median nerve will be exposed lying upon (sometimes behind) the artery; the nerve being drawn medialward and the muscle lateralward, the artery should be separated from its accompanying veins and secured. In this situation the superior ulnar collateral {inferior profunda^) may be mistaken for the main trunk, especially if enlarged from the collateral circulation having become estabh.shed; this may be avoided by directing the incision toward the Biceps brachii, rather than toward the Triceps brachii. The loirer part of the brachial artery is of interest from a surgical point of view, on account of the relation which it bears to the veins most commonly opened in venesection. Of these vessels, the vena mediana cubiti (median ba.silic vein) is the largest and most prominent, and, conse- quently, the one usually selected for the operation. This vein runs parallel with the brachial artery, from which it is separated by the lacertus fibrosus (bicipital fascia), and care should be taken, in opening the vein, not to carry the incision too deep, so as to endanger the artery. Collateral Circulation. — After the apphcation of a ligature to the brachial artery in the upper third of the arm, the circulation is carried on by branches from the humeral circumflex and sub- scapular arteries anastomosing with ascending branches from the profunda brachii. If the artery be tied belovj the origin of the profunda brachii and superior ulnar collateral, the circula- tion is maintained by the branches of these two arteries anastomosing with the inferior ulnar collateral, the radial and ulnar recurrents, and the dorsal interosseous. Branches. — The branches of the brachial artery are: Profunda Brachii. Superior Ulnar Collateral. Nutrient. Inferior Ulnar Collateral. Muscular. 1 . The arteria profunda brachii (superior profunda artery) is sl large vessel which arises from the medial and back part of the brachial, just below the lower border of the Teres major. It follows closely the radial nerve, running at first backward between the medial and lateral heads of the Triceps brachii, then along the groove for the radial nerve, where it is covered by the lateral head of the Triceps brachii, to the lateral side of the arm; there it pierces the lateral intermuscular septum, and, descending between the Brachioradialis and the Brachialis to the front of the lateral epicondyle of the humerus, ends by anastomosing with the radial recur- rent artery. It gives branches to the Deltoideus and to the muscles between which it lies; it supplies an occasional nutrient artery which enters the humerus behind the deltoid tuberosity. A branch ascends between the long and lateral heads of the Triceps brachii to anastomose with the posterior humeral circumflex artery; a middle collateral branch descends in the middle head of the Triceps brachii and assists in forming the anastomosis above the olecranon; and, lastly, a radial collateral branch runs down behind the lateral intermuscular septum to the back of the lateral epicondyle of the humerus, where it anastomoses with the interosseous recurrent and the inferior ulnar collateral arteries. 2. The nutrient artery (a. mdricia humeri) of the body of the humerus ari.ses about the middle of the arm and enters the nutrient canal near the insertion of the Cora cobra chialis. 3. The superior ulnar collateral artery (a. collateralis uhiaris superior; inferior profunda artery), of small size, arises from the brachial a little below the middle of the arm; it frequently springs from the upper part of the a. profunda brachii. It pierces the medial intermuscular septum, and descends on the surface of the medial head of the Triceps brachii to the space between the medial epicondyle and THE BRACHIAL ARTERY 6' olecranon, accompanied by the ulnar nerve, and ends under the Flexor carpi ulnaris by anastomosing with the posterior ulnar recurrent, and inferior ulnar collateral. It sometimes sends a branch in front of the medial epicondyle, to anastomose with the anterior ulnar recurrent. 4. The inferior ulnar collateral artery {a. coUateralis ulnaris inferior; anastomotica magna artery) arises about 5 cm. abo\'e the elbow. It passes medialward upon the Brachialis, and piercing the medial intermuscular septum, winds around the back of the humerus between the Triceps brachii and the bone, forming, by its junction with the profunda brachii, an arch above the olecranon fossa. As the vessel lies on the Brachialis, it gives off branches which ascend to join the superior ulnar collateral: others descend in front of the medial epicondyle, to anastomose with the anterior ulnar recurrent. Behind the medial epicondyle a branch anastomoses with the superior ulnar collateral and posterior ulnar recurrent arteries. 5. The muscular branches {rami muscidares) three or four in number, are dis- tributed to the Coracobrachialis, Biceps brachii, and Brachialis. Anterior branch of 'profunda Radial collateral branch of profunda Radial recurrent Interosseous recurrent Radial A. profunda brachii Sup. ulnar collateral Brachial Inf. ulnar collateral Anterior idnar recurrent Posterior ulnar recurrent Interosseous Dorsal interosseous Ulnar Volar interosseous Fig. 602. — Diagram of the anastomosis around the elbow-joint. The Anastomosis Around the Elbow-joint (Fig. 602). — The vessels engaged in this anastomosis may be conveniently divided into those situated in front of and those behind the medial and lateral epicondyles of the humerus. The branches anastomosing in front of the medial epicondyle are : the anterior branch of the inferior ulnar collateral, the anterior ulnar recurrent, and the anterior branch of the superior ulnar collateral. Those behind the medial epicondyle are: the inferior ulnar collateral, the posterior ulnar recurrent, and the posterior branch of the supe- rior ulnar collateral. The branches anastomosing in front of the lateral epicondyle are: the radial recurrent and the terminal part of the profunda brachii. Those behind the lateral epicondyle (perhaps more properly described as being situated 676 AXGIOLOGY between the lateral epicondyle and the olecranon) are: the inferior ulnar collateral, the interosseous recurrent, and the radial collateral branch of the profunda brachii. There is also an arch of anastomosis above the olecranon, formed by the interosseous recurrent joining with the inferior ulnar collateral and posterior ulnar recurrent (Fig. 605). The Radial Artery (A. Radialis) (Fig. 603). The radial artery appears, from its direction, to be the continuation of the brachial, but it is smaller in calibre than the ulnar. It commences at the bifurcation of the brachial, just below the bend of the elbow, and passes along the radial side of the forearm to the wrist. It then winds backward, around the lateral side of the carpus, beneath the tendons of the Abductor pollicis longus and Extensores pollicis longus and brevis to the upper end of the space between the metacarpal bones of the thumb and index finger. Finally it passes forward between the two heads of the first Interosseous dorsalis, into the palm of the hand, where it crosses the metacarpal bones and at the ulnar side of the hand unites with the deep volar branch of the ulnar artery to form the deep volar arch. The radial artery therefore consists of three portions, one in the forearm, a second at the back of the wrist, and a third in the hand. Relations. — (a) In the forearm the artery extends from the neck of the radius to the forepart of the styloid process, being placed to the medial side of the body of the bone above, and in front of it below. Its upper part is overlapped by the fleshy beUy of the Brachioradiahs; the rest of the artery is superficial, being covered by the integument and the superficial and deep fasciae. In its course downward, it hes upon the tendon of the Biceps brachii, the Supinator, the Pronator teres, the radial origin of the Flexor digitorum subhmis, the Flexor poUicis longus, the Pronator quadratus, and the lower end of the radius. In the upper third of its course it hes between the Brachioradiahs and the Pronator teres; in the lower two-thirds, between the tendons of the Brachioradiahs and Flexor carpi radiahs. The superficial branch of the radial nerve is close to the lateral side of the artery in the middle third of its course; and some filaments of the lateral antibrachial cutaneous nerve run along the lower part of the artery as it winds around the wrist. The vessel is accompanied by a pair of venae comitantes throughout its whole course. (6) At the wrist the artery reaches the back of the carpus by passing between the radial collateral hgament of the wrist and the tendons of the Abductor polhcis longus and Extensor poUicis brevis. It then descends on the navicular and greater multangular bones, and before disappearing be- tween the heads of the first Interosseus dorsalis is crossed by the tendon of the Extensor pollicis longus. In the interval between the two Extensores polhcis it is crossed by the digital rami of the superficial branch of the radial nerve which go to the thumb and index finger. (c) In the hand, it passes from the upper end of the first interosseous space, between the heads of the first Interosseus dorsahs, transversely across the pahn between the Adductor polhcis obhquus and Adductor polhcis transversus, but sometimes piercing the latter muscle, to the base of the metacarpal bone of the httle finger, where it anastomoses with the deep volar branch from the uhiar artery, completing the deep volar arch (Fig. 604). Peculiarities. — The origin of the radial artery is, ua nearly one case in eight, higher than usual; more often it arises from the axillary or upper part of the brachial than from the lower part of the latter vessel. In the forearm it deviates less frequently from its normal position than the ulnar. It has been found lying on the deep fascia instead of beneath it. It has also been observed on the surface of the Brachioradiahs, instead of under its medial border; and in turning around the wrist, it has been seen lying on, instead of beneath, the Exten.sor tendons of the thumb. Applied Anatomy. — The radial artery is much exposed to injury in its lower third, and is fre- quently wounded by the hand being driven through a pane of glass, by the shpping of a knife or chisel held in the other hand, etc. The injury may be followed by a traumatic aneurism, for which the operation of laying open the sac and secm-ing the vessel above and below is necessary. The operation of tying the radial artery is required in cases of wounds either of its trimk, or of some of its branches, or for anemism; and the vessel may be exposed in any part of its course through the forearm without the division of any muscular fibres. The operation in the middle or distal third of the forearm is easily performed; but in the proximal thu-d, near the elbow, it is attended with some diflSculty, from the greater depth of the vessel, and from its being over- lapped by the Brachioradiahs. To tie the artery in the proximal third, an incision 7 or 8 cm. in length should be made through the integmnent, in a fine drawm from the centre of the bend of the elbow to the front of the styloid process of the radius, avoiding the branches of the median vein; the fascia of the arm being divided. THE RADIAL ARTERY 677 and the lirarhioradialis drawn aside, the artery will be exposed. The venae comitantes should be carefully separated from the vessel and the ligature passed from the radial to the ulnar side. Badial recurrent Badial recurrent Dorsal interosseous Muscular Deep volar Volar radial carpa branch Superficial volar of ulnar Inferior ulnar collateral Anterior ulnar recurrent Posterior ulnar recurrent Muscular r uhuir carpal Deep volar hrancli of ulnar Fig. 603. — The radial and ulnar arteries. Fig. 604. — Ulnar and radial arteries. Deep view. In the middle third of the forearm the artery may be exposed by making an incision of similar length on the medial border of the BrachioradiaKs. In this situation, the superficial part of the 678 ANGIOLOGY radial nerve lies in close relation with the lateral side of the artery, and should, as well as the veins, be carefull}' avoided. In the distal third, the arterj^ is easily secured by dividing the integument and fascia in the interval between the tendons of the Brachioradialis and Flexor carpi radialis. Branches. — The branches of the radial artery may be divided into three groups, corresponding with the three regions in which the vessel is situated. Ill the Forearm. At the Wrist. In the Hand. Radial Recurrent. Dorsal Carpal. Princeps Pollicis. ^Muscular. First Dorsal Metacarpal. Volaris Indicis Radialis. Volar Carpal. \'olar Metacarpal. Superficial Volar. Perforating. Recurrent. The radial recurrent artery (a. recur reus radialis) arises immediately below the elbow. It ascends between the branches of the radial nerve, lying on the Supinator and then between the Brachioradialis and Brachialis, supplying these muscles and the elbow-joint, and anastomosing with the terminal part of the profunda brachii. The muscular branches (rami muscidares) are distributed to the muscles on the radial side of the forearm. The volar carpal branch (ramus carpeus volaris; anterior radial carpal artery) is a small vessel which arises near the lower border of the Pronator quadratus, and, running across the front of the carpus, anastomoses with the volar carpal branch of the ulnar artery. This anastomosis is joined by a branch from the volar interosseous above, and by recurrent branches from the deep volar arch below, thus forming a volar carpal net-work which supplies the articulations of the wrist and carpus. The superficial volar branch (ramus volaris superficialis ; supjerficialis volae artery) arises from the radial artery, just where this vessel is about to wind around the lateral side of the wrist. Running forward, it passes through, occasionally over, the muscles of the ball of the thumb, which it supplies, and sometimes anastomoses with the terminal portion of the ulnar artery, completing the superficial volar arch. This vessel varies considerably in size: usually it is very small, and ends in the muscles of the thumb; sometimes it is as large as the continuation of the radial. The dorsal carpal branch (ramus carpeus dorsalis; posterior radial carpal artery) is a small vessel which arises beneath the Extensor tendons of the thumb; crossing the carpus transversely toward the medial border of the hand, it anastomoses with the dorsal carpal branch of the ulnar and wdth the volar and dorsal interosseous arteries to form a dorsal carpal network. From this network are given off three slender dorsal metacarpal arteries, which run downward on the second, third, and fourth Interossei dorsales and bifurcate into the dorsal digital branches for the supply of the adjacent sides of the middle, ring, and little fingers respectively, communicating wdth the proper volar digital branches of the superficial volar arch. Near their origins they anastomose with the deep volar arch by the superior perforating arteries, and near their points of bifurcation with the common volar digital vessels of the superficial volar arch by the inferior perforating arteries. The first dorsal metacarpal arises just before the radial arter\' passes between the two heads of the first Interosseous dorsalis and divides almost immediately into two branches which supply the adjacent sides of the thumb and index finger; the radial side of the thumb receives a branch directly from the radial artery. The arteria princeps pollicis arises from the radial just as it turns medialward to the deep part of the hand; it descends between the first Interosseus dorsalis and Adductor pollicis obliquus, along the ulnar side of the metacarpal bone of the thumb to the base of the first phalanx, where it lies beneath the tendon of the THE ULNAR ARTERY 679 Flexor })()llicis loiigus and (li\"idcs into two branches. These make their appear- ance between the medial and lateral insertions of the Adductor pollicis obliquus, and run along the sides of the thumb, forming on the volar surface of the last phalanx an arch, from which branches are distril^uted to the integument and subcutaneous tissue of the thumb. The arteria volaris indicis radialis {mdialis indicis artery) arises close to the pre- cetling, descends between the first Interosseus dorsalis and Adductor pollicis trans- versus, and runs along the radial side of the index finger to its extremity, where it anastomoses with the proper digital artery, supplying the ulnar side of the finger. At the lower border of the Adductor pollicis transversus this vessel anastomoses with the princeps pollicis, and gives a communicating branch to the superficial volar arch. The a. princeps pollicis and a. volaris indicis radialis may spring from a common trunk termed the first volar metacarpal artery. The deep volar arch {arcus rolaris profundus; deep palmar arch) (Fig. 604) is formed by the anastomosis of the terminal part of the radial artery with the deep volar branch of the ulnar. It lies upon the carpal extremities of the metacarpal bones and on the Interossei, being covered by the Adductor pollicis obliquus, the Flexor tendons of the fingers, and the Lumbricales. Alongside of it, but running in the opposite direction — that is to say, toward the radial side of the hand — is the deep branch of the ulnar nerve. The volar metacarpal arteries {aa. metacarpeae volares; palmar interosseous arteries), three or four in number, arise from the convexity of the deep volar arch; they run distally upon the Interossei, and anastomose at the clefts of the fingers with the common digital branches of the superficial volar arch. The perforating branches {rami perforantes) , three in number, pass backward from the deep volar arch, through the second, third, and fourth interosseous spaces and between the heads of the corresponding Interossei dorsalis, to anastomose with the dorsal metacarpal arteries. The recurrent branches arise from the concavity of the deep volar arch. They ascend in front of the wrist, supply the intercarpal articulations, and end in the volar carpal network. The Ulnar Artery (A. Ulnaris) (Fig. 604). The ulnar artery, the larger of the two terminal branches of the brachial, begins a little below the bend of the elbow, and, passing obliquely dow^nward, reaches the ulnar side of the forearm at a point about midway between the elbo^\' and the wrist. It then runs along the ulnar border to the wrist, crosses the transverse carpal ligament on the radial side of the pisiform bone, and immediately beyond this bone divides into two branches, which enter into the formation of the superficial and deep volar arches. Relations. — (a) In the forearm. — In its xipper half, it is deeply seated, being covered by the Pronator teres, Flexor carpi radialis, PaLmaris longus, and Flexor digitorum sublimis; it lies upon the Brachialis and Flexor digitorum profundus. The median nerve is in relation with the medial side of the arterj' for about 2.5 cm. and then crosses the vessel, being separated from it bj^ the ulnar head of the Pronator teres. In the lower half of the forearm it lies upon the Flexor digitorum profundus, being covered by the integument and the superficial and deep fasciae, and placed between the Flexor carpi uhiaris and Flexor digitorum subhmis. It is accompanied by two venae comit antes, and is overlapped in its middle third by the Flexor carpi uhiaris; the uhiar nerve Ues on the medial side of the lower two-thuds of the artery, and the palmar cutaneous branch of the nerve descends on the lower part of the vessel to the pahn of the hand. (6) At the ivrist (Fig. 603) the ulnar artery is covered bj^ the iategument and the volar carpal ligament, and hes upon the transverse carpal ligament. On its medial side is the pisiform bone, and, somewhat behind the artery, the uhiar nerve. Peculiarities. — The uhiar arteiy varies in its origin in the proportion of about one in thuteen cases; it may arise about 5 to 7 cm. below the elbow, but more frequently higher, the brachial In the Forearm 680 AXGIOLOGY being more often the source of origin than the axillary. Variations in the position of this \-essel are more common than in the radial. When its origin is normal, the course of the vessel is rarely changed. When it arises high up, it is almost invariably superficial to the Flexor muscles in the forearm, lying commonly beneath the fascia, more rarely between the fascia and integument. In a few cases, its position was subcutaneous in the upper part of the forearm, and subaponeurotic in the lower part. Applied Anatomy. — The application of a ligature to this vessel is required in cases of wound of the arterj^, or of its branches, or in consequence of aneurism. In the upper half of the forearm the artery is deeply seated beneath the superficial Flexor muscles, and the application of a liga- ture in this situation is attended with some difficulty. An incision is to be made in the course of a Une drawn from the front of the medial epicondyle of the humerus to the lateral side of the pisiform bone, so that the centre of the incision is three fingers' breadth below the medial epi- condyle. The skin and superficial fascia having been divided, and the deep fascia exposed, the white line which separates the Flexor carpi ulnaris from the other Flexor muscles is to be sought for, and the fascia incised in this Une. The Flexor carpi ulnaris is now to be carefully separated from the other muscles, when the ulnar nerve will be exposed lying on the Flexor digitorum profundus, and must be drawn aside. The artery will be found accompanied by its venae comi- tantes, and may be ligatured as it lies to the lateral side of the nerve. In the middle and lower thirds of the forearm, this vessel may be easily secured by making an incision on the radial side of the tendon of the Flexor carpi ulnaris; when the deep fascia is divided, and the tendon sepa- rated from the Flexor subUmis, the vessel will be exposed, accompanied by its venae comitantes, the ulnar nerve lying on its medial side. Branches. — The branches of the uhiar artery may be arranged in the following groups : Anterior Recurrent. 4///, w 'f / ^olar Carpal. Posterior Recurrent. " [ Dorsal Carpal. Common Interosseous, j^ ^j^^ Hand ^ ^^^P Volar. Muscular. i Superficial Volar Arch. The anterior ulnar recurrent artery (a. recurrentes ulnaris anterior) arises imme- diately below the elbow-joint, runs upward between the Brachialis and Pronator teres, supplies twigs to those muscles, and, in front of the medial epicondyle, anasto- moses with the superior and inferior ulnar collateral arteries. The posterior ulnar recurrent artery (a. recurrentes ulnaris posterior) is much larger, and arises somewhat lower than the preceding. It passes backward and medialward on the Flexor digitorum profundus, behind the Flexor digitorum sub- limis, and ascends behind the medial epicondyle of the humerus. In the interval between this process and the olecranon, it lies beneath the Flexor carpi ulnaris, and ascending between the heads of that muscle, in relation with the ulnar nerve, it supplies the neighboring muscles and the elbow-joint, and anastomoses with the superior and inferior ulnar collateral and the interosseous recurrent arteries (Fig. 605). The common interosseous artery {a. interossea communis) (Fig. 604), about 1 cm. in length, arises immediately below the tuberosity of the radius, and, passing backward to the upper border of the interosseous membrane, divides into two branches, the volar and dorsal interosseous arteries. The Volar Interosseous Artery {a. interossea volaris; anterior interosseous artery) (Fig. 604) , passes down the forearm on the volar surface of the interosseous mem- brane. It is accompanied by the volar interosseous branch of the median nerve, and overlapped by the contiguous margins of the Flexor digitorum profundus and Flexor poUicis longus, giving off in this situation muscular branches, and the nutrient arteries of the radius and ulna. At the upper border of the Pronator quadratus it pierces the interosseous membrane and reaches the back of the forearm, where it anastomoses with the dorsal interosseous artery (Fig. 605). It then descends, in company with the terminal portion of the dorsal interosseous nerve, to the back of the wrist to join the dorsal carpal net-work. The volar interosseous artery gives off a slender branch, the arteria mediana, which accompanies the median nerve, and gives offsets to its substance; this artery is sometimes much enlarged, and runs THE ULNAR ARTERY 681 with the nerve into the palm of the hand. Before it pierces the interosseous membrane the volar interosseous sends a branch downward behind the Pronator qundratns to join the volar carpal network. profunda brachii Inf. ulnar collateral Posterior ulnar recurrent Dorsal interosseous Dorsal ulnar carpal Termination of volar interosseous Dorsal radial carpal Fig. 605. — Arteries of the back of the forearm and hand. The Dorsal Interosseous^ Artery (a. interossea dorsalis; "posterior interosseous artery) (Fig. 605) passes backward between the oblique cord and the upper border of the interosseous membrane. ^ It appears between the contiguous borders of the Supinator and the Abductor pollicis longus, and runs down the back of the forearm between 682 ANGIOLOGY the superficial and deep layers of muscles, to both of which it distributes branches. Where it lies upon the Abductor pollicis longus and the Extensor pollicis brevis, it is accompanied by the dorsal interosseous nerve. At the lower part of the fore- arm it anastomoses with the termination of the volar interosseous artery, and Avith the dorsal carpal network. It gives off, near its origin, the interosseous recurrent artery, which ascends to the interval between the lateral epicondyle and olecranon, on or through the fibres of the Supinator, but beneath the Anconaeus, and anasto- moses with the radial collateral branch of the profunda brachii, the posterior ulnar recurrent and the inferior ulnar collateral. The muscular branches (rami muscular es) are distributed to the muscles along the ulnar side of the forearm. The volar carpal branch [ramus carpeus volares; anterior ulnar carpal artery) is a small vessel which crosses the front of the carpus beneath the tendons of the Flexor digitorum profundus, and anastomoses with the corresponding branch of the radial arte^3^ The dorsal carpal branch (ramifs carpeus clorsalis; posterior ulnar carpal artery) arises immediately above the pisiform bone, and winds backward beneath the tendon of the Flexor carpi ulnaris; it passes across the dorsal surface of the carpus beneath the Extensor tendons, to anastomose wath a corresponding branch of the radial artery. Immediately after its origin, it gives off a small branch, which runs along the ulnar side of the fifth metacarpal bone, and supplies the ulnar side of the dorsal surface of the little finger. The deep volar branch (ramus wlaris profundus; profunda branch) (Fig. 604) passes between the Abductor digiti quinti and Flexor digiti quinti brevis and through the origin of the Opponens digiti quinti; it anastomoses with the radial artery, and completes the deep volar arch. The superficial volar arch (arcus volar is siqyerficialis; superficial pjalmar arch) (Fig. 603) is formed by the ulnar artery, and is usually completed by a branch from the a. volaris indicis radialis, but sometimes by the superficial volar or by a branch from the a. princeps pollicis of the radial artery. The arch passes across the palm, describing a curve, wdth its convexity downward. Relations.— The superficial volar arch is covered by the skin, the Palmaris brevis, and the pahnar aponem'osis. It Ues upon the transverse carpal hgament, the Flexor digiti quinti brevis and Opponens digiti quinti, the tendons of the Flexor digitorum subhmis, the Lumbricales, and the divisions of the median and ulnar nerves. Three Common Volar Digital Arteries (cm. digitales volares communes; palmar digital arteries) (Fig. 603) arise from the convexity of the arch and proceed downward on the second, third, and fourth Lumbricales. Each receives the corresponding volar metacarpal artery and then divides into a pair of proper volar digital arteries (aa. digitales volares propriae; collatercd digital arteries) which run along the con- tiguous sides of the index, middle, ring, and little fingers, behind the corresponding digital nerves ; they anastomose freely in the subcutaneous tissue of the finger tips and by smaller branches near the interphalangeal joints. Each gives off a couple of dorsal branches which anastomose with the dorsal digital arteries, and supply the soft parts on the back of the second and third phalanges, including the matrix of the finger-nail. The proper volar digital artery for medial side of the little finger springs from the ulnar artery under cover of the Palmaris brevis. Applied Anatomy. — Wounds of the volar arches are of special interest, and are always difficult to deal with. When the superficial arch is involved it is generally possible (enlarging the wound when necessary) to secure the vessel and tie it on both sides of the bleeding point; or in cases where it is found impossible to encircle the vessel with a hgature, a pair of hemostatic forceps may be apphed and left on for twenty-four or forty-eight hours. FaiUng this, the wound may be plugged with gauze and an outside dressing carefully bandaged on. The plug should be allowed to remain untouched for three or four days. It is useless in these cases to ligature one of the arteries of the forearm alone, and indeed simultaneous ligature of both radial and uhiar arteries THE THORACIC AORTA 683 above the wrist is often unsuccessful, on account of the anastomosis carried on by the carpal arches. Therefore, upon the failure of jiressure to arrest hemorrhage, it is expedient to apply a ligature to the brachial artery. When an incision for deep-seated suppuration in the tendon sheath is required, the situation of the superficial arch must always be borne in mind, and the incisions placed either above or below it. The position of the common digital branches of the artery must also be remembered, and incisions must be made opposite the heads of the meta- carpal bones and not between them. THE ARTERIES OF THE TRUNK. THE DESCENDING AORTA. The descending aorta is (ii\'ided into two portions, the thoracic and abdominal, in correspondence Avith the t^vo great cavities of the trunk in which it is situated. The Thoracic Aorta (Aorta Thoracalis) (Fig. 606). The thoracic aorta is contained in the posterior mediastinal cavity. It begins at the lower border of the fourth thoracic vertebra where it is continuous with the aortic arch, and ends in front of the lower border of the twelfth at the aortic hiatus in the Diaphragma. At its commencement, it is situated on the left of the vertebral column; it approaches the median line as it descends; and, at its termina- tion, lies directly in front of the column. The vessel describes a curve which is concave forward, and as the branches given off from it are small, its diminution in size is inconsiderable. Relations. — It is in relation, anteriorly, from above downward, with the root of the left lung, the pericardium, the oesophagus, and the Diaphragma; 'posteriorly, with the vertebral column and the hemiazygos veins; on the right side, with the azygos vein and thoracic duct; on the lejt side, with the left pleura and limg. The oesophagus, with its accompanying plexus of nerves, lies on the right side of the aorta above; but at the lower part of the thorax it is placed in front of the aorta, and, close to the Diaphragma, is situated on its left side. Peculiarities. — The aorta is occasionally found to be obhterated at the junction of the arch with the thoracic aorta, just below the ductus arteriosus. Whether this is the result of disease, or of congenital malformation, is immaterial to oiu- present pm'pose; it affords an interesting opportunity of observing the resources of the collateral circulation. The course of the anastomos- ing vessels, by which the blood is brought from the upper to the lower part of the artery, will be found well described in an account of two cases in the Pathological Transactions, vols, viii and x. In the former, Sydney Jones thus sums up the detailed description of the anastomosing A^essels: The principal communications by which the circulation was carried on were: (1) The internal mammary, anastomosing with the intercostal arteries, with the inferior phrenic of the abdominal aorta by means of the musculophrenic and pericardiacophrenic, and largely with the inferior epigastric. (2) The costocervical trunk, anastomosing anteriorly by means of a large branch with the first aortic intercostal, and posteriorly with the posterior branch of the same artery. (3) The inferior thja-oid, by means of a branch about the size of an ordinary radial, forming a communication with the first aortic intercostal. (4) The transverse cervical, by means of very large communications with the posterior branches of the intercostals. (5) The branches (of the subclavian and axillary) going to the side of the chest were large, and anastomosed freel}^ with the lateral branches of the intercostals. In the second case Wood describes the anastomoses in a somewhat similar manner, adding the remark that "the blood which was brought into the aorta through the anastomosis of the intercostal arteries appeared to be expended principally in supplying the abdomen and pelvis; while the supply to the lower extremities had passed through the internal mammary and epigastrics." In a few cases an apparently double descending thoracic aorta has been found, the two vessels lying side bj' side, and eventually fusing to form a single tube in the lower part of the thorax or in the abdomen. One of them is the aorta, the other represents a dissecting aortic aneurism which has become canalized; opening above and below into the true aorta, and at first sight presenting the appearances of a proper bloodvessel. Applied Anatomy. — The effects likelj' to be produced by aneurism of the thoracic aorta, a disease of common occurrence, must now be considered. When the great depth of the vessel from the sm'face and the number of important structures which sm-round it are remembered, it may easily be conceived what a variety of obscure sj^mptoms are likely to arise from disease 684 AXGIOLOCjY of this part of the arterial system, and how they may be mistaken for tliose of other affections. Aneurism of the thoracic aorta most usually extends backward, along the left side of the vertebral column, producing absorption of the bodies of the vertebrae, with curvature of the column; while the irritation or pressure on the medulla spinalis will give rise to pain, either in the chest, back, or loins, with radiating pain in the left upper intercostal spaces, from pressure on the intercostal nerves; at the same time the tumor may project backward on either side of the vertebral column, beneath the integument, as a pulsating swelling, simulating abscess connected with diseased Highest intercostal artery Highest intercostal vein / Rami communicantes Lig. arterwsum bone; or it may displace the oesophagus and compress the lungs on one or the other side. If the tumor extend forward, it may press upon and displace the heart, giving rise to palpitation and other symptoms of disease of that organ; it may displace or compress the a?sophagus, caus- ing pain and difficulty of swallowing; and ultimately even open into it by ulceration, producing fatal hemorrhage. If the disease extend to the right side, it may press upon the thoracic duct; or it may burst into the pleural cavity, or into the trachea or lung; and lastly, it may open into the posterior mediastinal cavity. Pressure on one of the bronchi, usually the left, will cause cough, and in time set up bronchiectasis; pressure on the left pulmonary plexus has been said THE THORACIC AORTA 685 to give rise to asthmatic attacks. Of late years, the diagnosis of thoracic aneurism has been much facihtated by the cmj)loyment of the x-rays, by means of which the outhne of the sac may be demonstrated. Branches of the Thoracic Aorta.^ — Visceral Pericardial. ( Intcrrostal. Bronchial. Parietal. Subcostal. Oesophageal. ( Superior Phrenic. Mediastinal. The pericardial branches {rami pericardiaci) consist of a few small \'essels which are distributed to the posterior surface of the pericardium. The bronchial arteries (aa. bronchioles) vary in number, size, and origin. There is as a rule only one right bronchial artery, which arises from the first aortic inter- costal, or from the upper left bronchial artery. The left bronchial arteries are usually two in number, and arise from the thoracic aorta. The upper left bronchial arises opposite the fifth thoracic vertebra, the lower just below the level of the left bron- chus. Each vessel runs on the back part of its bronchus, dividing and subdividing along the bronchial tubes, supplying them, the areolar tissue of the lungs, the bronchial lymph glands, and the oesophagus. The (esophageal arteries (aa. oesophageae) four or five in number, arise from the front of the aorta, and pass obliquely downward to the oesophagus, forming a chain of anastomoses along that tube, anastomosing with the oesophageal branches of the inferior thyroid arteries above, and with ascending branches from the left inferior phrenic and left gastric arteries below. The mediastinal branches (rami mediastinales) are numerous small vessels which supply the lymph glands and loose areolar tissue in the posterior mediastinal cavity. Intercostal Arteries (aa. intercostal e s) . — There are usually nine pairs of aortic intercostal arteries. They arise from the back of the aorta, and a redistributed to the lower nine intercostal spaces, the first two spaces being supplied by the highest intercostal artery, a branch of the costocervical trunk of the subclavian. The right aortic intercostals are longer than the left, on account of the position of the aorta on the left side of the vertebral column; they pass across the bodies of the vertebrae behind the oesophagus, thoracic duct, and vena azygos, and are covered by the right lung and pleura. The left aortic intercostals run backward on the sides of the vertebrae and are covered by the left lung and pleura; the upper two vessels are crossed by the highest left intercostal vein, the lower vessels by the hemiazygos veins. The further course of the intercostal arteries is practically the same on both sides. Opposite the heads of the ribs the sympathetic trunk passes downward in front of them, and the splanchnic nerves also descend in front by the lower arteries. Each artery then divides into an anterior and a posterior ramus. The Anterior Ramus crosses the corresponding intercostal space obliquely toward the angle of the upper rib, and thence is continued forward in the costal groove. It is placed at first between the pleura and the posterior intercostal membrane, then it pierces this membrane, and lies between it and the Intercostalis externus as far as the angle of the rib; from this onward it runs between the Intercostales externus and internus, and anastomoses in front with the intercostal branch of the internal mammary or musculophrenic. Each artery is accompanied by a vein and a nerve, the former being above and the latter below the artery, except in the upper spaces, where the nerve is at first above the artery. The first aortic intercostal artery anastomoses with the intercostal branch of the costocervical trunk, and may form the chief supply of the second intercostal space. The lower two intercostal arteries 6S6 AXGIOLOGY are continued anteriorly from the intercostal spaces into the abdominal wall, and anastomose with the subcostal, superior epigastric, and lumbar arteries. Branches. — The anterior rami give off the following branches: Collateral Intercostal. Lateral Cutaneous. Muscular. ]\Iammary. The collateral intercostal branch comes off from the intercostal artery near the angle of the rib, and descends to the upper border of the rib below, along which it courses to anastomose with the intercostal branch of the internal mammary. Muscular branches are given to the Intercostales and Pectorales and to the Serratus anterior; they anastomose with the highest and lateral thoracic branches of the axillary artery. The lateral cutaneous branches accompany the lateral cutaneous branches of the thoracic nerves. Mammary branches are given off by the vessels in the third, fourth, and fifth spaces. They supply the mamma, and increase considerably in size during the period of lactation. The Posterior Ramus runs backward through a space which is bounded above and below by the necks of the ribs, medially by the body of a vertebra, and laterally by an anterior costotransverse ligament. It gives off a spinal branch which enters the vertebral canal through the intervertebral foramen and is distributed to the medulla spinalis and its membranes and the A^ertebrse. It then courses over the transverse process with the posterior division of the thoracic nerve, supplies branches to the muscles of the back and cutaneous branches which accompany the corresponding cutaneous branches of the posterior division of the nerve. Applied Anatomy. — The position of the anterior rami of the intercostal vessels should be borne in mind in performing the operation of paracentesis thoracis. The puncture should never be made nearer the middle line posteriorly than the angle of the rib, as the artery crosses the space medial to this point. In the lateral portion of the chest, where the puncture is usually made, the artery hes at the upper part of the intercostal space, and therefore the punctm-e should be made just above the upper border of the rib forming the lower boundary of the space. The subcostal arteries, so named because they lie below the last ribs, constitute the lowest pair of branches derived from the thoracic aorta, and are in series with the intercostal arteries. Each passes along the lower border of the twelfth rib behind the kidney and in front of the Quadratus lumborum muscle, and is accom- panied by the twelfth thoracic nerve. It then pierces the posterior aponeurosis of the Transversus abdominis, and, passing forward between this muscle and the Obliquus internus, anastomoses with the superior epigastric, lower intercostal, and lumbar arteries. Each subcostal artery gives off a posterior branch which has a similar distribution to the posterior ramus of an intercostal artery. The superior phrenic branches are small and arise from the lower part of the thoracic aorta; they are distributed to the posterior part of the upper surface of the Diaphragma, and anastomose with the musculophrenic and pericardiacophrenic arteries. A small aberrant artery is sometimes found arising from the right side of the thor- acic aorta near the origin of the right bronchial. It passes upward and to the right behind the trachea and the oesophagus, and may anastomose with the highest right intercostal artery. It represents the remains of the right dorsal aorta, and in a small proportion of cases is enlarged to form the first part of the right subclavian artery. The Abdominal Aorta (Aorta Abdominalis) (Fig. 607). The abdominal aorta begins at the aortic hiatus of the Diaphragma, in front of the lower border of the body of the last thoracic vertebra, and, descending in THE ABDOMIXAL AORTA 68- front of the vertebral column, ends on the body of the fourth lumbar vertebra, commonlv a little to the left of the middle line,^ by dividing; into the two common iliac arteries. It diminishes rapidly in size, in consequence of the many large branches which it gives off. As it lies upon the bodies of the vertebne, the curve which it describes is convex forward, the summit of the convexity correspondmg to the third lumbar vertebra. \ A P H R A Inferior phrenic arteries Internal sperjnatic vessels Fig 607 — The abdominal aurta ind its branches Relations.— The abdominal aorta is covered, anteriorly, by the lesser omentum and stomach, behind which are the branches of the coehac artery and the cceUac plexus; below these, by the Henal vein, the pancreas, the left renal vein, the inferior part of the duodenum, the mesentery, and aortic plexus. Posteriorly, it is separated from the lumbar vertebra? and mtervertebral fibrocartilages by the anterior longitudinal Ugament and left lumbar vems. On the right side it is in relation above with the azygos vein, cisterna chyh, thoracic duct, and the right mis ot the Diaphragma— the last separating it from the upper part of the inferior vena cava, and from the right coehac ganghon; the inferior vena cava is in contact with the aorta below. On the left side are the left crus of the Diaphragma, the left coehac ganghon, the ascending part of the duodenum, and some coils of the small intestine. Applied Anatomy.— The abdommal aorta may be the seat of an aneurism either at its upper part, close to and often involving the coehac artery, or at its lower part, near the bifurcation. 1 Lord Lister, having accuratelv examined 30 bodies in order to ascertain the exact point of termination of this vessel, found it "either absolutely, or almost absolutely, mesial m 1.5 while in 13 it de^nated more or le== to the left, and in 2 was slightly to the right. " System of Surgery, edited by T. Holmes, 2d ed., v, boJ. 688 ANGIOLOGY Occasionally aneurisms are met with on some of the branches of the aorta, the mesenteric or lienal, quite independent of the main trunk. When an aneurismal sac is connected with the posterior part of the abdominal aorta, it usually produces absorption of the bodies of the vertebra?. Pain is invariably present, and is usually of two kinds — a fixed and constant pain in the back, caused by the tumor pressing on or displacing the branches of the ca?liac plexus and splanchnic nerves; and a sharp lancinating pain, radiating along those branches of the lumbar nerves which are pressed on by the tumor; hence the pain in the loins, the testes, the hypogastrium, and in the lower hmb (generally of the left side). This form of aneurism usually bursts into or behind the peritoneal cavity. When an aneurismal sac is connected with the front of the aorta near the coeliac artery, it forms a pulsating tumor in the left hypochondriac or epigastric regions, usually attended with symptoms of disturbance of the digestive tube, as sickness, dyspepsia, or constipation, and accompanied bj^ pain, which is constant, but nearly always fixed, in the loins, epigastrium, or some part of the abdomen; the radiating pain being rare, as the lumbar nerves are seldom impli- cated. This form of aneurism may burst into the peritoneal cavity, behind the peritoneum, between the layers of the mesentery, or, more rarely, into the duodenum; it rarely extends back- ward so as to affect the vertebral column. Occlusion of the abdominal aorta by thrombosis or embohsm is rare, but produces very severe symptoms when it does occur. The patient complains of intense pain in the legs; pallor of the legs, followed by coldness, lividity, paresis, paralysis, and finally gangrene, are likely to succeed, death usually supervening within a fortnight. The abdominal aorta has been tied in several cases, and although none of the patients perma- nently recovered, still, as one case lived forty-eight days, the possibiUty of the reestablishment of the circulation may be considered to be proved. Collateral Circulation. — The collateral circulation would be carried on by the anastomoses between the internal mammary and the inferior epigastric; by the free communication between the superior and inferior mesenteries, if the Ugature were placed between these vessels; or by the anastomosis between the inferior mesenteric and the internal pudendal, when (as is more common) the point of Hgature is below the origin of the inferior mesenteric; and possibly by the anastomoses of the lumbar arteries with the branches of the hypogastric. Branches. — The branches of the abdominal aorta may be divided into three sets: visceral, parietal, and terminal. Visceral Branches. Parietal Branches. ■ Coeliac. Inferior Phrenics. Superior Mesenteric. ' Lumbars. Inferior Mesenteric. Middle Sacral. Middle Suprarenals. Renals. Internal Spermatics. Terminal .Branches. Ovarian (in the female). Common Iliacs. Of the visceral branches, the coeliac artery and the superior and inferior mes- enteric arteries are unpaired, while the suprarenals, renals, internal spermatics, and ovarian are paired. Of the parietal branches the inferior phrenics and lumbars are paired; the middle sacral is unpaired. The terminal branches are paired. The coeliac artery (a. coeliaca; coeliac axis) (Figs. 608, 609) is a short thick trunk, about 1.25 cm. in length, which arises from the front of the aorta, just below the aortic hiatus of the Diaphragma, and, passing nearly horizontally forward, divides into three large branches, the left gastric, the hepatic, and the splenic; it occasionally gives off one of the inferior phrenic arteries. Relations. — The coehac artery is covered by the lesser omentum. On the right side it is in relation with the right coehac ganglion and the caudate process of the hver; on the left side, with the left coehac ganghon'and the cardiac end of the stomach. Below, it is in relation to the upper border of the pancreas, and the henal vein. 1. The Left Gastric Artery (a. gastrica sinistra; gastric or coronary artery), the smallest of the three branches of the coeliac artery, passes upward and to the left, posterior to the omental bursa, to the cardiac orifice of the stomach. Here it dis- tributes branches to the oesophagus, which anastomose with the aortic oesophageal THE ABDOMINAL AORTA 689 arteries; others supply the cardiac part of the stomach, anastomosing with branches of the lienal artery. It then runs from left to right, along the lesser curvature of the stomach to the pylorus, between the layers of the lesser omentum ; it gives branches to both surfaces of the stomach and anastomoses with the right gastric artery. 2. The Hepatic Artery (a. hepatica) in the adult is intermediate in size between the left gastric and lienal; in the fetus, it is the largest of the three branches of the coeliac artery. It is first directed forward and to the right, to the upper margin of the superior part of the duodenum, forming the lower boundary of the epiploic foramen {foramen of JVinslow). It then crosses the portal vein anteriorly and ascends between the layers of the lesser omentum, and in front of the epiploic fora- men, to the porta hepatis, where it divides into two branches, right and left, which Cystic artery Fig. 60S. — The coeliac artery and its branches; the liver has been raised, and the lesser omentum and anterior layer of the greater omentum removed. supply the corresponding lobes of the liver, accompanying the ramifications of the portal vein and hepatic ducts. The hepatic artery, in its course along the right border of the lesser omentum, is in relation with the common bile-duct and portal vein, the duct lying to the right of the artery, and the vein behind. Its branches are: Right Gastric. Gastroduodenal l^^sK^^^t^o^P^Pl^i^- ' , { bupenor rancreaticoduodenal. Cystic. The right gastric artery {a. gastrica dextra; 'pyloric artery) arises from the hepatic, above the pylorus, descends to the pjdoric end of the stomach, and passes from 44 690 ANGIOLOGY right to left along its lesser curvature, supplying it with branches, and anastomosing with the left gastric artery. The gastroduodenal artery (a. gastroduodenalis) (Fig. 609) is a short but large branch, which descends, near the pylorus, between the superior part of the duo- denum and the neck of the pancreas, and divides at the lower border of the duodenum into two branches, the right gastroepiploic and the superior pancreaticoduodenal. Previous to its division it gives off two or three small branches to the pyloric end of the stomach and to the pancreas. Branches to greater omentum Fig. 609. — The coeliac artery and its branches; the stomach has been raised and the peritoneum removed. The right gastroepiploic artery (a. gastroepiploica dextra) runs from right to left along the greater curvature of the stomach, between the layers of the greater omentum, anastomosing with the left gastroepiploic branch of the lienal artery. Except at the pylorus, where it is in contact with the stomach, it lies about a finger's breadth from the greater curvature. This vessel gives off numerous branches, some of which ascend to supply both surfaces of the stomach, while others descend to supply the greater omentum and anastomose with branches of the middle colic. The superior pancreaticoduodenal artery (a. yancreaticoduodenalis superior) descends between the contiguous margins of the duodenum and pancreas. It supplies both these organs, and anastomoses with the inferior pancreaticoduodenal branch of the superior mesenteric artery, and with the pancreatic branches of the lienal artery. THE ABDOMINAL AORTA 691 The cystic artery {a. ci/stim) (Fig. ()()S), usually a branch of the right hepatic, passes downward and forward along the neck of the gall-bladder, and divides into two branches, one of which ramifies on the free surface, the other on the attached surface of the gall-bladder. 3. The Lienal or Splenic Artery (a. lienaUs), the largest branch of the coeliac artery, is remarkable for the tortuosity of its course. It passes horizontally to the left side, behind the stomach and the omental bursa of the peritoneum, and along the upper border of the pancreas, accompanied by the lienal vein, which lies below it; it crosses in front of the upper part of the left kidney, and, on arriving near the spleen, divides into branches, some of which enter the hilus of that organ between the two layers of the phrenicolienal ligament to be distributed to the tissues of the spleen; some are given to the pancreas, while others pass to the greater curva- ture of the stomach between the laj'ers of the gastrolienal ligament. Its branches are: Pancreatic. Short Gastric. Left Gastroepiploic. The pancreatic branches {rami pancreatici) are numerous small vessels derived from the lienal as it runs behind the upper border of the pancreas, supplying its body and tail. One of these, larger than the rest, is sometimes given oflF near the tail of the pancreas; it runs from left to right near the posterior surface of the gland, following the course of the pancreatic duct, and is called the arteria pancreatica magna. These vessels anastomose with the pancreatic branches of the pancreatico- duodenal and superior mesenteric arteries. The short gastric arteries {aa. gastricae breves; vasa hrevia) consist of from five to seven small branches, which arise from the end of the lienal artery, and from its terminal divisions. They pass from left to right, between the layers of the gastro- lienal ligament, and are distributed to the greater curvature of the stomach, anasto- mosing with branches of the left gastric and left gastroepiploic arteries. The left gastroepiploic artery (a. gastroepvploica sinistra) the largest branch of the lienal, runs from left to right about a finger's breadth or more from the greater curvature of the stomach, between the layers of the greater omentum, and anasto- moses with the right gastroepiploic. In its course it distributes several ascending branches to both surfaces of the stomach; others descend to supply the greater omentum and anastomose with branches of the middle colic. Applied Anatomy. — Embolism of branches of the henal artery is tolerably common in heart disease, the embolus coming from the left side of the heart. It is characterized by the occurrence of a sudden sharp pain or "stitch" in the splenic region, with subsequent local enlargement of the spleen from the formation of an infarct in its substance. The superior mesenteric artery (a. mesenterica superior) (Fig. 610) is a large vessel which supplies the wdiole length of the small intestine, except the superior part of the duodenum ; it also supplies the cecum and the ascending part of the colon and about one-half of the transverse part of the colon. It arises from the front of the aorta, about 1.25 cm. below the coeliac artery, and is crossed at its origin by the lienal vein and the neck of the pancreas. It passes downward and forward, anterior to the processus uncinatus of the head of the pancreas and inferior part of the duodenum, and descends between the layers of the mesentery to the right iliac fossa, where, considerably diminished in size, it anastomoses with one of its own branches, viz., the ileocolic. In its course it crosses in front of the inferior vena cava, the right ureter and Psoas major, and forms an arch, the convexity of which is directed forward and dow^nward to the left side, the concavity backward and upward to the right. It is accompanied by the superior mesenteric vein, which lies to its right side, and it is surrounded by the superior mesenteric plexus of nerves. 692 ANGIOLOGY Dissection. — In order to expose the superior mesenteric artery raise the great omentum and transverse colon, draw down the small intestines, and cut through the peritoneum where the transverse mesocolon and mesentery join; the artery will then be exposed just as it issues from over the processus uncinatus of the head of the pancreas. Fig. 610.— The superior mesenteric artery and its branches. Branches. — Its branches are: Inferior Pancreaticoduodenal. Ileocolic. Intestinal. Right Colic. Middle Colic. The Inferior Pancreaticoduodenal Artery (a. yancreaticoduodenalis inferior) is given off from the superior mesenteric or from its first intestinal branch, opposite the upper border of the inferior part of the duodenum. It courses to the right between the head of the pancreas and duodenum, and then ascends to anastomose with the superior pancreaticoduodenal artery. It distributes branches to the head of the pancreas and to the descending and inferior parts of the duodenum. The Intestinal Arteries {aa. intestinales; xasa intestini tenuis) arise from the convex side of the superior mesenteric artery. They are usually from twelve to fifteen in number, and are distributed to the jejunum and ileum. They run nearly parallel with one another between the layers of the mesentery, each vessel dividing into two branches, which unite with adjacent branches, forming a series of arches, the THE ABDOMINAL AORTA 693 convexities of which are directeil toward the intestine (Fig. Gil). From this first set of arches branches arise, which nnite with similar ])ranches from above and below and thus a second series of arches is formed; from the lower l)ranches of the artery, a third, a fourth, or even a fifth series of arches may be formed, diminishing in size the nearer they approach the intestine. In the short, upper part of the mesen- tery only one set of arches exists, but as the depth of the mesentery increases, second, third, fourth, or even fifth groups are developed. From the terminal arches numerous small straight vessels arise which encircle the intestine, upon which they are distributed, ramifying between its coats. From the intestinal arteries small branches are given off to the lymph glands and other structures between the layers of the mesentery. Fig. 611. — Loop of small intestine showing distribution of intestinal arteries. (From a preparation by Mr. Hamilton Drummond.) The vessels were injected while the gut was in situ; the gut was then removed, and an a;-ray photograph taken. The Ileocolic Artery (a. ileocolica) is the lowest branch arising from the concavity of the superior mesenteric artery. It passes downward and to the right behind the peritoneum toward the right iliac fossa, where it divides into a superior and an inferior branch; the inferior anastomoses with the end of the superior mesenteric artery, the superior with the right colic artery. The inferior branch of the ileocolic runs toward the upper border of the ileo- colic junction and supplies the following branches (Fig. 612) : (a) colic, which pass upward on the ascending colon; (b) anterior and posterior cecal, which are distributed to the front and back of the cecum; (c) an appendicular artery, which descends behind the termination of the ileum and enters the mesen- teriole of the vermiform process; it runs near the free margin of this mesenteriole and ends in branches which supply the vermiform process; and (d) ileal, which run 694 AXGIOLOGY upward and to the left on the lower part of the ileum, and anastomose with the termination of the superior mesenteric. The Right Colic Artery (a. colica dextra) arises from about the middle of the con- cavity of the superior mesenteric artery, or from a stem common to it and the ileo- colic. It passes to the right behind the peritoneum, and in front of the right internal spermatic or ovarian vessels, the right ureter and the Psoas major, toward the middle of the ascending colon; sometimes the vessel lies at a higher level, and crosses the descending part of the duodenum and the lower end of the right kidney. x\t the colon it divides into a descending branch, which anastomoses with the ileocolic, and an ascending branch, which anastomoses with the middle colic. These branches form arches, from the convexity of which vessels are distributed to the ascending colon. Termiiud fart of ileocolic CcBcal branches Ileal branches Appendicular artery '^•form process Fig. 612. — Arteries of cecum and vermiform process. The Middle Colic Artery (a. colica media) arises from the superior mesenteric just below the pancreas and, passing downward and forward between the layers of the transverse mesocolon, divides into two branches, right and left; the former anastomoses with the right colic; the latter with the left colic, a branch of the in- ferior mesenteric. The arches thus formed are placed about two fingers' breadth from the transverse colon, to which they distribute branches. The inferior mesenteric artery (a. mesenterica inferior) (Fig. 613) supplies the left half of the transverse part of the colon, the whole of the descending and iliac parts of the colon, the sigmoid colon, and the greater part of the rectum. It is smaller than the superior mesenteric, and arises from the aorta, about 3 or 4 cm. above its division into the common iliacs and close to the lower border of the inferior part of the duodenum. It passes downward posterior to the peritoneum, lying at first anterior to and then on the left side of the aorta. It crosses the left common iliac artery and is continued into the lesser pelvis under the name of the superior hemorrhoidal artery, which descends between the two layers of the sigmoid mesocolon and ends on the upper part of the rectum. THE ABDOMJXAL AORTA 695 Dissection. — In order to expose the inferior mesenteric artery draw the small intestines and mesentery over to the right side of the abdomen, raise the transverse colon toward the thorax, and divide the peritoneum covering the front of the aorta. Middle Hemorrhoidal Inferior Hemorrhoidal Fig. 613. — The inferior mesenteric artery and its branches. Branches. — Its branches are: Left Colic. Sigmoid. Superior Hemorrhoidal. The Left Colic Artery (a. coUca sinistra) runs to the left behind the peritoneum and in front of the Psoas major, and after a short, but variable, course divides into an ascending and a descending branch; the stem of the artery or its branches cross the left ureter and left internal spermatic vessels. The ascending branch crosses in front of the left kidney and ends, between the two layers of the transverse mesocolon, by anastomosing with the middle colic artery; the descending branch anastomoses with the highest sigmoid artery. From the arches formed by these anastomoses branches are distributed to the descending colon and the left part of the transverse colon. The Sigmoid Arteries (oo. sigmoideae) (Fig. 614), two or three in number, run obliciuely downward and to the left behind the peritoneum and in front of the Psoas major, ureter, and internal spermatic vessels. Their branches supply the lower part of the descending colon, the iliac colon, and the sigmoid or pelvic colon; anasto- mosing above with the left colic, and below with the superior hemorrhoidal artery. 696 ANGIOLOGY The Superior Hemorrhoidal Artery (a. haemorrhoidalis superior) (Fig. 614), the continuation of the inferior mesenteric, descends into the pelvis between the la\'ers of the mesentery of the sigmoid colon, crossing, in its course, the left common iliac vessels. It divides, opposite the third sacral vertebra, into two branches, which descend one on either side of the rectum, and about 10 or 12 cm. from the anus break up into several small branches. These pierce the muscular coat of the bowel and run downward, as straight vessels, placed at regular intervals from each other in the wall of the gut between its muscular and mucous coats, to the level of the Sphincter ani internus; here they form a series of loops around the lower end of the rectum, and communicate with the middle hemorrhoidal branches of the hypogastric, and with the inferior hemorrhoidal branches of the internal pudendal. J Q.'H'Uta. ) Fig. 614. — Sigmoid colon and rectum, showing distribution of branches of inferior mesenteric artery and their anastomoses. (From a preparation by Mr. Hamilton Drummond.) Prepared in same manner as Fig. 611. Applied Anatomy. — ^EmboHsm of the mesenteric arteries produces acute and severe symp- toms, of which the chief are abdominal pain and tenderness, nausea and vomiting, diarrhoea or constipation; blood is foimd in the stools of nearly half the patients. In many cases the symp- toms closely resemble those of intestinal obstruction. The middle suprarenal arteries (aa. swprarenales media; middle capsular arteries; suprarenal arteries) are two small vessels which arise, one from either side of the aorta, opposite the superior mesenteric artery. They pass lateralward and slightly upward, over the crura of the Diaphragma, to the suprarenal glands, where they anastomose with suprarenal branches of the inferior phrenic and renal arteries. In the fetus these arteries are of large size. The renal arteries {aa. renales) (Fig. 607), are two large trunks, which arise from the side of the aorta, immediately below the superior mesenteric artery. THE ABDOMINAL AORTA 097 Each is directed across the cms of the Diaphragma, so as to form nearly a right angle with the aorta. The right is longer than the left, on account of the position of the aorta; it passes behind the inferior vena cava, the right renal vein, the head of the pancreas, and the descending part of the duodenum. The left is somewhat higher than the right; it lies behind the left renal vein, the body of the pancreas and the lienal vein, and is crossed by the inferior mesenteric vein. Before reaching the hilus of the kidney, each artery divides into four or five branches; the greater number of these lie between the renal vein and ureter, the vein being in front, the ureter behind, but one or more branches are usually situated behind the ureter. Each vessel gives off some small inferior suprarenal branches to the suprarenal gland, the ureter, and the surrounding cellular tissue and muscles. One or two accessory renal arteries are frequently found, more especially on the left side they usually arise from the aorta, and may come off above or below the main artery, the former being the more common position. Instead of entering the kidney at the hilus, they usually pierce the upper or lower part of the gland. The internal spermatic arteries {aa. spermaticae internae; spermatic arteries) (Fig. 607) are distributed to the testes. They are two slender vessels of consid- erable length, and arise from the front of the aorta a little below the renal arteries. Each passes obliquely downward and lateralward behind the peritoneum, resting on the Psoas major, the right spermatic lying in front of the inferior vena cava and behind the middle colic and ileocolic arteries and the terminal part of the ileum, the left behind the left colic and sigmoid arteries and the iliac colon. Each crosses obliquely over the ureter and the lower part of the external iliac artery to reach the abdominal inguinal ring, through which it passes, and accompanies the other constituents of the spermatic cord along the inguinal canal to the scrotum, where it becomes tortuous, and divides into several branches. Two or three of these accompany the ductus deferens, and supply the epididymis, anasto- mosing with the artery of the ductus deferens; others pierce the back part of the tunica albuginea, and supply the substance of the testis. The internal spermatic artery supplies one or two small branches to the ureter, and in the inguinal canal gives one or two twigs to the Cremaster. The ovarian arteries {aa. ovaricae) are the corresponding arteries in the female to the internal spermatic in the male. They supply the ovaries, are shorter than the internal spermatics, and do not pass out of the abdominal cavity. The origin and course of the first part of each artery are the same as those of the internal spermatic, but on arriving at the upper opening of the lesser pelvis the ovarian artery passes inward, between the two layers of the ovariopelvic ligament and of the broad ligament of the uterus, to be distributed to the ovary. Small branches are given to the ureter and the uterine tube, and one passes on to the side of the uterus, and unites with the uterine arter3% Other offsets are continued on the round ligament of the uterus, through the inguinal canal, to the integument of the labium majus and groin. At an early period of fetal life, when the testes or ovaries lie by the side of the vertebral column, below the kidneys, the internal spermatic or ovarian arteries are short; but with the descent of these organs into the scrotum or lesser pelvis, the arteries are gradually lengthened. The inferior phrenic arteries {aa. phrenicae inferiores) (Fig, 607) are two small vessels, which supply the Diaphragma but present much variety in their origin. They may arise separately from the front of the aorta, immediately above the coeliac artery, or by a common trunk, which may spring either from the aorta or from the cceliac artery. Sometimes one is derived from the aorta, and the other from one of the renal arteries; they rarely arise as separate vessels from the aorta. They diverge from one another across the crura of the Diaphragma, and then run ob- liquely upward and lateralward upon its under surface. The left phrenic passes 698 ANGIOLOGY behind the oesophagus, and runs forward on the left side of the oesophageal hiatus. The right phrenic passes behind the inferior vena cava, and along the right side of the foramen which transmits that vein. Near the back part of the central tendon each vessel divides into a medial and a lateral branch. The medial branch curves forward, and anastomoses with its fellow of the opposite side, and with the musculophrenic and pericardiacophrenic arteries. The lateral branch passes toward the side of the thorax, and anastomoses with the lower intercostal arteries, and with the musculophrenic. The lateral branch of the right phrenic gives off a few vessels to the inferior vena cava; and the left one, some branches to the oesophagus. Each vessel gives off superior suprarenal branches to the suprarenal gland of its own side. The spleen and the liver also receive a few twigs from the left and right vessels respectively. The lumbar arteries iaa. liimhahs) are in series with the intercostals. They are usually four in number on either side, and arise from the back of the aorta, opposite the bodies of the upper four lumbar vertebrse. A fifth pair, small in size, is occasionally present: they arise from the middle sacral artery. They run lateral- ward and backward on the bodies of the lumbar vertebrae, behind the sympathetic trunk, to the intervals between the adjacent transverse processes, and are then continued into the abdominal wall. The arteries of the right side pass behind the inferior vena cava, and the upper two on each side run behind the corresponding crus of the Diaphragma. The arteries of both sides pass beneath the tendinous arches which give origin to the Psoas major, and are then continued behind this muscle and the lumbar plexus. They now cross the Quadratus lumborum, the upper three arteries running behind, the last usually in front of the muscle. At the lateral border of the Quadratus lumborum they pierce the posterior aponeurosis of the Transversus abdominis and are carried forward between this muscle and the Obliquus internus. They anastomose with the lower intercostal, the subcostal, the iliolumbar, the deep iliac circumflex, and the inferior epigastric arteries. Branches. — In the interval between the adjacent transverse processes each lumbar artery gives off a posterior ramus which is continued backward between the trans- verse processes and is distributed to the muscles and skin of the back; it furnishes a spinal branch which enters the vertebral canal and is distributed in a manner similar to the spinal branches of the posterior rami of the intercostal arteries (page 686). Muscular branches are supplied from each lumbar artery and from its posterior ramus to the neighboring muscles. The middle sacral artery {a. sacralis media) (Fig. 607) is a small vessel, which arises from the back of the aorta, a little above its bifurcation. It descends in the middle line in front of the fourth and fifth lumbar vertebrae, the sacrum and coccyx, and ends in the glomus coccygeum {coccygeal gland). From it, minute branches are said to pass to the posterior surface of the rectum. On the last lumbar vertebra it anastomoses with the lumbar branch of the iliolumbar artery; in front of the sacrum it anastomoses with the lateral sacral arteries, and sends offsets into the anterior sacral foramina. It is crossed by the left common iliac vein, and is accompanied by a pair of venae comitantes; these unite to form a single vessel, which opens into the left common iliac vein. THE COMMON ILIAC ARTERIES (AA. lUACAE COMMUNES) (Figs. 607, 615). The abdominal aorta divides, on the left side of the body of the fourth lumbar vertebra, into the two common iliac arteries. Each is about 5 cm. in length. They diverge from the termination of the aorta, pass downward and lateralward, and divide, opposite the intervertebral fibrocartilage between the last lumbar vertebra and the sacrum, into two branches, the external iliac and hypogastric arteries; THE COMMON ILIAC ARTERIES 699 the former su])i)lies tlie lower extremity; the hitter, the viscera and parietes of the pelvis. The right common iliac artery (Fig. (ilo) is somewhat loiif^^T than the left, and passes more ol)li(iuely across the body of the last lumbar vertebra. In fro7it of it are the peritoneuni, the small intestines, branches of the sympathetic nerves, and, at its point of division, the ureter. Behind, it is separated from the bodies of the fourth and fifth lumbar vertebne, and the intervening fibrocartilage, by the terminations of the two common iliac veins and the commencement of the inferior vena cava. Latr rally, it is in relation, above, with the inferior vena cava and the right common iliac vein; and, below, with the Psoas major. Medial to it, above, is the left common iliac vein. Middle saaal Sup hemoi rhoidcd Fig. 615. — The arteries of the pelvis. The left common iliac artery is in relation, in front, with the peritoneum, the small intestines, branches of the sympathetic nerves, and the superior hemorrhoidal artery; and is crossed at its point of bifurcation by the ureter. It rests on the bodies of the fourth and fifth lumbar vertebrae, and the intervening fibrocartilage. The left common iliac vein lies partly medial to, and partly behind the artery; laterally, the artery is in relation with the Psoas major. Branches. — The common iliac arteries give off small branches to the peritoneum. Psoas major, ureters, and the surrounding areolar tissue, and occasionally give origin to the iliolumbar, or accessory renal arteries. 700 AXGIOWGY Peculiarities. — The point of origin varies according to the bifurcation of the aorta. In three- fourths of a large number of cases, the aorta bifurcated either upon the fourth lumbar vertebra, or upon the fibrocartilage between it and the fifth; the bifurcation being, in one case out of nine, below, and in one out of eleven, above this point. In about SO per cent, of the cases the aorta bifurcated within 1.25 cm. above or below the level of the crest of the ilium; more frequently below than above. The point of division is subject to great variety. In two-thirds of a large number of cases it was between the last lumbar vertebra and the upper border of the sacrum; being above that point in one case out of eight, and below it in one case out of six. The left common iliac artery divides lower down more frequently than the right. The relative lengths, also, of the two common iliac arteries vary. The right common iliac was the longer in sixty-three cases; the left in fifty-two; while they were equal in fifty-three. The length of the arteries varied, in five-sevenths of the cases examined, from 3.5 to 7.5 cm.; in about half of the remaining cases the artery was longer, and in the other half, shorter; the minimum length being less than 1.25 cm., the maximum, 11 cm. In rare instances, the right common ihac has been found wanting, the external iliac and hypogastric arising directly from the aorta. Applied Anatomy. — The application of a ligature to the common iliac artery may be required on account of aneurism or hemorrhage, implicating the external iliac or hypogastric. The easiest and best method of tying the artery is by a transperitoneal route. The abdomen is opened, the intestines are drawn aside and the peritoneum covering the artery divided; the sheath is then opened and the needle passed from the medial to the lateral side. On the right side great care must be exercised in passing the needle, since both the common ihac veins lie behind the artery. After the vessel has been tied, the incision in the peritoneum over the artery should be sutured. Formerly there were different methods by which the common ihac artery was tied, without open- ing the peritoneal cavity, but these have now been discarded. Collateral Circulation. — The principal agents in carrying on the collateral circulation after the application of a hgature to the common iliac are: the anastomoses of the hemorrhoidal branches of the hypogastric with the superior hemorrhoidal from the inferior mesenteric; of the uterine, ovarian, and vesical arteries of the opposite sides; of the lateral sacral with the middle sacral artery; of the inferior epigastric with the internal mammary, inferior intercostal, and lumbar arteries; of the deep iliac circumflex with the lumbar arteries; of the iliolumbar with the last lumbar artery; of the obturator artery, by means of its pubic branch, with the vessel of the opposite side and with the inferior epigastric. The Hypogastric Artery (A. Hypogastrica ; Internal Iliac Artery) (Fig. 615). The hypogastric artery supplies the walls and viscera of the pelvis, the buttock, the generative organs^ and the medial side of the thigh. It is a short, thick vessel, smaller than the external iliac, and about 4 cm. in length. It arises at the bifur- cation of the common iliac, opposite the lumbosacral articulation, and, passing downward to the upper margin of the greater sciatic foramen, divides into two large trunks, an anterior and a posterior. Relations. — It is in relation in front with the ureter; behind, with the internal iliac vein, the lumbosacral trunk, and the Piriformis muscle; laterally, near its origin, with the external iliac vein, which lies between it and the Psoas major muscle; lower down, with the obturator nerve. In the fetus, the hypogastric artery is twice as large as the external iliac, and is the direct continuation of the common iliac. It ascends along the side of the bladder, and runs upward on the back of the anterior wall of the abdomen to the umbilicus, converging toward its fellow of the opposite side. Having passed through the umbilical opening, the two arteries, now termed umbilical, enter the umbilical cord, where they are coiled around the umbilical vein, and ultimately ramify in the placenta. At birth, when the placental circulation ceases, the pelvic portion only of the artery remains patent and constitutes the hypogastric and the first part of the superior vesical artery of the adult; the remainder of the vessel is converted into a solid fibrous cord, the lateral umbilical ligament (obliterated hypogastric artery) which extends from the pelvis to the umbilicus. Peculiarities as Regards Length. — In two-thirds of a large number of cases, the length of the hypogastric varied between 2.25 and 3.4 cm.; in the remaining third it was more frequently longer than shorter, the maximum length being about 7 cm. the minimum about 1 cm. THE HYPOGASTRIC ARTERY 701 Tho lengths of Llic coininon iliac and hypogastric arteries bear an inverse proportion to each other, the hypogastric artery being long when the common iliac is short, and vice versa. As Regards its Place of Division. — -The place of division of the hypogastric varies between tlie upper margin of the sacrum and the upper border of the greater sciatic foramen. Tlie right and left hyi)ogastric arteries in a series of cases often differed in length, but neither seemed constantly to exceed the other. Applied Anatomy. — -The application of a ligature to the hypogastric artery may be required in cases of aneurism or hemorrhage affecting one of its branches. The vessel may be best secured by an abdominal section in the median line, and reaching the vessel through the peritoneal cavity. It should be remembered that the vein lies behind, and, on the right side, a little lateral to the artery, and in close contact with it; the ureter, which lies in front, must also be avoided. The degree of facility in applying a Hgature to this vessel will mainly depend upon its length. It has been seen that, in the great majority of the cases examined, the artery was short, varying from 2 to 4 cm.; in these cases, the artery is deeply seated in the pelvis; when, on the contrary, the vessel is longer, it is found partly above that cavity. If the artery be very short, as occasionally happens, it would be preferable to apply a ligature to the common iliac. Collateral Circulation. — The circulation after ligature of the hypogastric artery is carried on by the anastomoses of the uterine and ovarian arteries; of the vesical arteries of the two sides; of the hemorrhoidal branches of the hypogastric with those from the inferior mesenteric; of the obturator artery, by means of its pubic branch, with the vessel of the opposite side, and with" the inferior epigastric and medial femoral circumflex; of the circumflex and perforating branches of the profunda femoris with the infei'ior gluteal; of the superior gluteal with the posterior branches of the lateral sacral arteries; of the iUolumbar with the last lumbar; of the lateral sacral with the middle sacral; and of the iliac circumflex with the iliolumbar and superior gluteal.^ Branches. — The branches of the hypogastric artery are: From the Anterior Trunk. From the Posterior Trunk. Superior Vesical. Iliolumbar. Middle Vesical. Lateral Sacral. Inferior Vesical. Superior Gluteal. Middle Hemorrhoidal. Obturator. Internal Pudendal. Inferior Gluteal. ■VT • 1 \ln the Female. Vagmal j The superior vesical artery (a. vesicalis superior) supplies numerous branches to the upper part of the bladder. From one of these a slender vessel, the artery to the ductus deferens, takes origin and accompanies the duct in its course to the testis, where it anastomoses with the internal spermatic artery. Other branches supply the ureter. The first part of the superior vesical artery represents the terminal section of the pervious portion of the fetal hypogastric artery. The middle vesical artery {a. vesicalis medialis), usually a branch of the superior, is distributed to the fundus of the bladder and the vesiculae seminales. The inferior vesical artery (a. vesicalis inferior) frequently arises in common with the middle hemorrhoidal, and is distributed to the fundus of the bladder, the prostate, and the vesiculae seminales. The branches to the prostate communicate with the corresponding vessels of the opposite side. The middle hemorrhoidal artery (a. haemorrhoidalis media) usually arises with the preceding vessel. It is distributed to the rectum, anastomosing with the inferior vesical and with the superior and inferior hemorrhoidal arteries. It gives offsets to the vesiculae seminales and prostate. The uterine artery (a. uterina) (Fig. 616) springs from the anterior division of the hypogastric and runs medialward on the Levator ani and toward the cervix uteri; about 2 cm. from the cervix it crosses above and in front of the ureter, to which it supplies a small branch. Reaching the side of the uterus it ascends in a tortuous manner between the two layers of the broad ligament to the junction 1 For a description of a case in which Owen made a dissection ten years after ligature of the hypogastric arterj-, see Med.-Chir. Trans., vol. xvi. 702 AXGIOLOGY of the uterine tube and uterus. It then runs laterahvard toward the hihis of the ovary, and ends by joining with the ovarian artery. It supphes l)ranches to the cervix uteri and others which descend on the vagina; the latter anastomose with branches of the ^•aginal arteries and form with them two median longitudinal vessels — the azygos arteries of the vagina — one of which runs down one in front of and the other behind the vagina. It supplies numerous branches to the body of the uterus, and from its terminal portion twigs are distributed to the uterine tube anfl the round ligament of the uterus. The vaginal artery (a. vaginalis) usually corresponds to the inferior vesical in the male; it descends upon the vagina, supplying its mucous membrane, and sends branches to the bulb of the vestibule, the fundus of the bladder, and the contiguous part of the rectum. It assists in forming the azygos arteries of the vagina, and is frequently represented by two or three branches. Branches to tube Brandies to fuiulus Fig. 616. — The arteries of the internal organs of generation of the female, seen from behind. (After Hyrtl.) The obturator artery (a. ohtundoria) passes forward and downward on the lateral wall of the pelvis, to the upper part of the obturator foramen, and, escaping from the pelvic cavity through the obturator canal, it divides into an anterior and a posterior branch. In the pelvic cavity this vessel is in relation, laterally, with the obturator fascia; medially, with the ureter, ductus deferens, and peritoneum; while a little below it is the obturator nerve. Branches. — Inside the pelvis the obturator artery gives off iliac branches to the iliac fossa, which suppl}' the bone and the Iliacus, and anastomose with the ilio- lumbar artery; a vesical branch, which runs backward to supply the bladder; and a pubic branch, which is given off from the ves.sel just before it leaves the pelvic cavity. The pubic branch ascends upon the back of the pubis, communicating vi-'iih the corresponding vessel of the opposite side, and with the inferior epigastric artery. Outside the pelvis, the obturator artery divides at the upper margin of the obtur- ator foramen, into an anterior and a posterior branch which encircle the foramen under cover of the Obturator externus. THE HYPOGASTRIC ARTERY 703 The anterior branch runs forward on tlie outer surface of the obturator mem- brane i\ud then curxes dowmvard along the anterior margin of the foramen. It distributes branches to the 01)turator externus, Pectineus, Adductores, and GraciHs, antl anastomoses with the posterior branch and with the medial femoral circum- flex artery. The posterior branch follows the posterior margin of the foramen and turns for- ward on the inferior ramus of the ischium, where it anastomoses with the anterior branch. It gives twigs to the muscles attached to the ischial tuberosity and anas- tomoses with the inferior gluteal. It also supplies an articular branch which enters the hip-joint through the acetabular notch, ramifies in the fat at the bottom of the acetabulum and sends a twdg along the ligamentum teres to the head of the femur. Peculiarities. — The obturator artery sometimes arises from the main stem or from the posterior trunk of the hypogastric, or it may spring from the superior gluteal artery; occasionally it arises from the external iliac. In about two out of every seven cases it springs fi'om the inferior epi- gastric and descends almost vertically to the upper part of the obtm-ator foramen. The artery in this course usually lies in contact with the external iUac vein, and on the lateral side of the femoral ring (Fig. 617^1) ; in such cases it would not be endangered in the operation for strangulated femoral hernia. Occasionally, however, it curves along the free margin of the lacunar hgament (Fig. 617 -B), and if in such circumstances a femoral hernia occurred, the vessel would almost completely encircle the neck of the hernial sac, and would be in gi'eat danger of being wounded if an operation were performed for strangulation. J? I Fig. 617. — Variations in origin and courses of obturator artery. The internal pudendal artery (a. pudenda interna; internal inidic artery) is the smaller of the two terminal branches of the anterior trunk of the hypogastric, and supplies the external organs of generation. Though the course of the artery is the same in the two sexes, the vessel is smaller in the female than in the male, and the distribution of its branches somew^hat different. The description of its arrange- ment in the male will first be given, and subsequently the differences which it presents in the female will be mentioned. The internal pudendal artery in the male passes downw^ard and outward to the lower border of the greater sciatic foramen, and emerges from the pelvis between the Piriformis and Coccygeus ; it then crosses the ischial spine, and enters the peri- neum through the lesser sciatic foramen. The artery now crosses the Obturator internus, along the lateral wall of the ischiorectal fossa, being situated about 4 cm. above the lower margin of the ischial tuberosity. It gradually approaches the margin of the inferior ramus of the ischium and passes forw^ard between the two layers of the fascia of the urogenital diaphragm; it then runs forw^ard along the medial margin of the inferior ramus of the pubis, and about 1.25 cm. behind the pubic arcuate ligament it pierces the inferior fascia of the urogenital diaphragm and divides into the dorsal and deep arteries of the penis. Relations. — Within the pelvis, it hes in front of the Piriformis muscle, the sacral plexus of nerves, and the inferior gluteal artery. As it crosses the ischial spine, it is covered by the Glutaeus maximus and overlapped by the sacrotuberous ligament. Here the pudendal nerve hes to the medial side and the nerve to the Obtm-ator internus to the lateral side of the vessel. In the peri- neum it lies on the lateral wall of the ischiorectal fossa, in a canal (Alcock's canal) formed by the ro4 ANGIOLOGY splitting of the obturator fascia. It is accompanied by a pair of venae comitantes and the pudendal nerve. Peculiarities. — The internal pudendal artery is sometimes smaller than usual, or fails to give off one or two of its usual branches; in such cases the deficienc}^ is supphed by branches derived from an additional vessel, the accessory pudendal, which generally arises from the internal pudendal artery before its exit from the greater sciatic foramen. It passes forw^ard along the lower part of the bladder and across the side of the prostate to the root of the penis, where it perforates the urogenital diaphragm, and gives off the branches usually derived from the internal pudendal artery. The deficiency most frequently met with is that in which the internal pudendal ends as the artery of the urethral bulb, the dorsal and deep arteries of the penis being derived from the accessory pudendal. The internal pudendal artery may also end as the perineal, the artery of the urethral bulb being derived, with the other two branches, from the accessory vessel. Occasionally the accessory pudendal artery is derived from one of the other branches of the hypogastric artery, most frequently the inferior vesical or the obturator. Branches. — The branches of the internal pudendal artery (Figs. 618, 619) are: Muscular. Artery of the Urethral Bulb. Inferior Hemorrhoidal. Urethral. Perineal. Deep Artery of the Penis. Dorsal Arterv of the Penis. Posterior scrotal arteries Posterior scrotal nerves Pudendal nerve Internal pudendal artery Fig. 618. — The superficial branches of the internal pudendal artecy. The Muscular Branches consist of two sets: one given off in the pelvis; the other, as the vessel crosses the ischial spine. The former consists of several small offsets which supply the Levator ani, the Obturator internus, the Piriformis, and the Coccygeus. The branches given off outside the pelvis are distributed to the adjacent parts of the Glutaeus maximus and external rotator muscles. They anastomose with branches of the inferior gluteal artery. The Inferior Hemorrhoidal Artery (a. haemorrJwidalis injerior) arises from the internal pudendal as it passes above the ischial tuberosity. Piercing the wall of Alcock's canal it divides into two or three branches which cross the ischiorectal fossa, and are distributed to the muscles and integument of the anal region, and THE HYPOGASTRIC ARTERY 705 send offshoots around the lower edge of tlie (dutaeus maximus to the skhi of the buttock. They anastomose with the corresponding vessels of the opposite side, with the suj)eri()r and middle hemorrhoidal, and with the perineal artery. The Perineal Artery {a. pcrinci; superficial ju'rliical artery) arises from the internal pudendal, in front of the preceding branches, and turns upward, crossing either over or under the Transversus perinaei superficialis, and runs forward, parallel to the pubic arch, in the interspace between the Bulbocavernous and Ischiocaver- nosus. both of which it supplies, and finally diNides into several posterior scrotal branches which are distributed to the skin and dartos tunic of the scrotum. As it crosses the Transversus perinaei superficialis it gives off the transverse perineal artery which runs transversely on the cutaneous surface of the muscle, and anasto- moses with the corresponding vessel of the opposite side and with the perineal and inferior hemorrhoidal arteries. It supplies the Transversus perinaei super- ficialis and the structures between the anus and the urethral bulb. Deep artcnj of penis Dorsal artery of penis Artery of urethral bulb Internal pudendal artery — ^ Bulbo-urethral gland Fig. 619. — The deeper branches of the internal pudendal artery. The Artery of the Urethral Bulb (o. bidbi urethrae) is a short vessel of large calibre which arises from the internal pudendal between the two layers of fascia of the uro- genital diaphragm; it passes medialward, pierces the inferior fascia of the urogenital diaphragm, and gives oft' branches which ramify in the bulb of the urethra and in the posterior part of the corpus cavernosum urethrae. It gives off a small branch to the bulbo-urethral gland. The Urethral Artery (a. urethralis) arises a short distance in front of the artery of the urethral bulb. It runs forward and medialward, pierces the inferior fascia of the urogenital diaphragm and enters the corpus cavernosum urethrae, in which it is continued forward to the glans penis. The Deep Artery of the Penis (a. profunda penis; artery to the corpus cavernosum), one of the terminal branches of the internal pudendal, arises from that vessel while it is situated between the two fascise of the urogenital diaphragm; it pierces the inferior fascia, and, entering the crus penis obliquely, runs forward in the centre of the corpus cavernosum penis, to which its branches are distributed. 45 706 ANGIOLOGY The Dorsal Artery of the Penis (a. dorsalis penis) ascends between the cms penis and the pubic symphysis, and, piercing the inferior fascia of the urogenital dia- phragm, passes between the two layers of the suspensory ligament of the penis, and runs forward on the dorsum of the penis to the glans, w'here it divides into two branches, which supply the glans and prepuce. On the penis, it lies between the dorsal nerve and deep dorsal vein, the former being on its lateral side. It supplies the integument and fibrous sheath of the corpus cavernosum penis, sending branches through the sheath to anastomose with the preceding vessel. The internal pudendal artery in the female is smaller than in the male. Its origin and course are similar, and there is considerable analogy in the distribution of its branches. The perineal artery supplies the labia pudendi; the SiTtery of the bulb supplies the bulbus vestibuli and the erectile tissue of the vagina; the deep artery of the clitoris supplies the corpus cavernosum clitoridis; and the dorsal artery of the clitoris supplies the dorsum of that organ, and ends in the glans and prepuce of the clitoris. The inferior gluteal artery (a. glutaea inferior; sciatic artery) (Fig. 620), the larger of the two terminal branches of the anterior trunk of the hypogastric, is distributed chiefly to the buttock and back of the thigh. It passes down on the sacral plexus of nerves and the Piriformis, behind the internal pudendal artery, to the lower part of the greater sciatic foramen, through which it escapes from the pelvis between the Piriformis and Coccygeus. It then descends in the interval betw^een the greater trochanter of the femur and tuberosity of the ischium, accom- panied by the sciatic and posterior femoral cutaneous nerves, and covered by the Glutaeus maximus, and is continued down the back of the thigh, supplying the skin, and anastomosing with branches of the perforating arteries. Inside the pelvis it distributes branches to the Piriformis, Coccygeus, and Levator ani; some branches w^hich supply the fat around the rectum, and occasionally take the place of the middle hemorrhoidal artery; and vesical branches to the fundus of the bladder, vesiculae seminales, and prostate. Outside the pekis it gives off the following branches : Muscular. Anastomotic. Coccygeal. Articular. Comitans Nervi Ischiadici. Cutaneous. The Muscular Branches supply the Glutaeus maximus, anastomosing with the superior gluteal artery in the substance of the muscle; the external rotators, anastomosing with the internal pudendal artery; and the muscles attached to the tuberosity of the ischium, anastomosing with the posterior branch of the obturator and the medial femoral circumflex arteries. The Coccygeal Branches run medialward, pierce the sacrotuberous ligament, and supply the Glutaeus maximus, the integument, and other structures on the back of the coccyx. The Arteria Comitans Nervi Ischiadici is a long, slender vessel, which accom- panies the sciatic nerve for a short distance ; it then penetrates it, and runs in its substance to the lower part of the thigh. The Anastomotic is directed downward across the external rotators, and assists in forming the so-called crucial anastomosis by joining with the first perforating and medial and lateral femoral circumflex arteries. The Articular Branch, generally derived from the anastomotic, is distributed to the capsule of the hip-joint. The Cutaneous Branches are distributed to the skin of the buttock and back of the thigh. The iliolumbar artery (a. iliolumbalis) a branch of the posterior trunk of the hypogastric, turns upward behind the obturator nerve and the external iliac vessels, THE HYPOGASTRIC ARTERY 707 to the mctlial border of the Psoas major, behind which it divides into a lumbar and an ihac branch. The Lumbar Branch (ramus lumhalis) supphes the Psoas major and Quadratus hniiboruni, anastomoses with the last lumbar artery, and sends a small spinal branch through the intervertebral foramen between the last lumbar vertebra and the sacrum, into the vertebral canal, to supply the Cauda equina. The Iliac Branch {ramus iliaciis) descends to supply the Iliacus; some offsets, running between the muscle and the bone, anastomose with the iliac branches of the ob- turator; one of these enters an oblique canal to supply the bone, w'hile others run along the crest of the ilium, distributing branches to the gluteal and abdominal muscles, and anastomosing in their course with the superior gluteal, iliac circumflex, and lateral femoral circumflex arteries. The lateral sacral arteries iaa. sacrales laterales) (Fig. 615) arise from the posterior division of the hypogastric; there are usually two, a superior and an inferior. The superior, of large size, passes medialward, and, after anastomos- ing with branches from the middle sacral, enters the first or second anterior sacral foramen, supplies branches to the contents of the sacral canal, and, escaping by the corresponding posterior sacral fora- men, is distributed to the skin and muscles on the dorsum of the sacrum, anastomosing with the superior gluteal. The inferior runs obliquely across the front of the Piriformis and the sacral nerves to the medial side of the anterior sacral foramina, de- scends on the front of the sacrum, and anastomoses over the coccyx wdth the middle sacral and opposite lateral sacral arterj'. In its course it gives off branches, which enter the anterior sacral foramina; these, after supplying the contents of the sacral canal, escapes by the posterior sacral foramina, and are distributed to the muscles and skin on the dorsal surface of the sacrum, anastomosing with the gluteal arteries. The superior gluteal artery (a. ghdaea superior; gluteal artery) (Fig. 620) is the largest branch of the hypogastric, and appears to be the continuation of the pos- terior division of that vessel. It is a short artery which runs backward between Termination cj medial femoral circumfiex First perforating Second perforating Third perforating Termination of profunda Superior muscular Lateral superior geniciclar — Medial superior genicular — Sural Fig. 620. — The arteries of the ghiteal and posterior femoral regions. 708 ANGIOLOGY the lumbosacral trunk and the first sacral nerve, and, passing out of the pelvis above the upper border of the Piriformis, immediately divides into a superficial and a deep branch. Within the pelvis it gives off a few branches to the Iliacus, Piriformis, and Obturator internus, and just previous to quitting that cavity, a nutrient artery which enters the ilium. The superficial branch enters the deep surface of the Glutaeus maximus, and divides into numerous branches, some of which supply the muscle and anastomose with the inferior gluteal, while others perforate its tendinous origin, and supply the integument covering the posterior surface of the sacrum, anastomosing with the posterior branches of the lateral sacral arteries. The deep branch lies under the Glutaeus medius and almost immediately sub- divides into two. Of these, the superior division, continuing the original course of the vessel, passes along the upper border of the Glutaeus minimus to the anterior superior spine of the ilium, anastomosing with the deep iliac circumflex artery and the ascending branch of the lateral femoral circumflex artery. The inferior division crosses the Glutaeus minimus obliquely to the greater trochanter, distributing branches to the Glutaei and anastomoses with the lateral femoral circumflex artery. Some branches pierce the Glutaeus minimus and supply the hip-joint. Applied Anatomy. — Any of these three vessels may require to be ligatured for a wound, or for aneurism which is generally traumatic. The superior gluteal artery is hgatured by turning the patient two-thirds over on to his face and making an incision from the posterior superior spine of the ilium to the upper and posterior angle of the greater trochanter. This must expose the Glutaeus maximus, and its fibres are to be separated through the whole thickness of the muscle and pulled apart with retractors. The contiguous margins of the Glutaeus medius and' Piriformis are now to be separated from each other, and the artery will be exposed emerging from the greater sciatic foramen. In ligature of the inferior gluteal artery, the incision should be made parallel with that for ligature of the superior gluteal but 4 cm. lower down. After the fibres of the Glutaeus maximus have been separated, the vessel is to be sought for at the lower border of the Piriformis; the sciatic nerve, which lies just above it, forms the chief guide to the artery. The External Iliac Artery (A. Iliaca Externa) (Fig. 615). The external iliac artery is larger than the hypogastric, and passes obliquely downward and lateralward along the medial border of the Psoas major, from the bifurcation of the common iliac to a point beneath the inguinal ligament, midway between the anterior superior spine of the ilium and the symphysis pubis, where it enters the thigh and becomes the femoral artery. Relations. — In front and medially, the artery is in relation with the peritoneum, subperitoneal areolar tissue, the termination of the ileum and frequently the vermiform process on the right side, and the sigmoid colon on the left, and a thin layer of fascia, derived from the iliac fascia, which surrounds the artery and vein. At its origin it is crossed by the ovarian vessels in the female, and occasionally by the ureter. The internal spermatic vessels lie for some distance upon it near its termination, and it is crossed in this situation by the external spermatic branch of the genitofemoral nerve and the deep iliac circumflex vein; the ductus deferens in the male, and the round ligament of the uterus in the female, curve down across its medial side. Behind, it is in relation with the medial border of the Psoas major, from which it is separated by the ihac fascia. At the upper part of its course, the external iliac vein lies partly behind it, but lower down lies entirely to its medial side. Laterally, it rests against the Psoas major, from which it is separated by the iliac fascia. Numerous lymphatic vessels and lymph glands he on the front and on the medial side of the vessel. Applied Anatomy. — The application of a ligature to the external ihac may be required in cases of aneurism of the femoral artery, iliofemoral aneurism, or for a wound of the artery. The vessel may be secured in any part of its com-se, excepting near its upper end, which is to be avoided on account of the proximity of the hypogastric, and near its lower end, which should also be avoided on account of the proximity of the inferior epigastric and deep iliac circumflex vessels. The operation may be performed by opening the abdomen and incising the peritoneum over the artery (transperitoneal) ; or by an incision in the ihac region, dividing all the structures down to the peritoneum, which is then reflected medialwai'd unopened from the iliac fossa until the artery is reached (retroperitoneal). THE EXTERNAL ILIAC ARTERY 709 The transperitoneal ligature requires an incision through the abdominal wall into the peritoneal cavity. The intestines are then pushed upward and held out of the way bj^ a broad abdominal retractor, and an incision matle through the peritoneum at the margin of the pelvis in the course of the artery; the vessel is secured in any part of its course which may seem desirable to the operator. The advantages of this operation appear to be, that if it is found necessary, the common iliac arterj- can be ligatured instead of the external iliac without extension or modification of the incision; and secondly, that the vessel can be ligatured without in any way interfering with the sac of an aneurism. The retroperitoneal ligature may be performed by an incision above and parallel to the lateral half of the inguinal ligament. The abdominal muscles and transversalis fascia having been cautiously divided, the peritoneum should be separated from the iliac fossa and raised toward the pelvis; and on introducing the finger to the bottom of the wound, the arterj- may be felt pulsating along the medial border of the Psoas major. The external iliac vein is generally found on the medial side of the arterj^, and must be cautiously separated from it, and the aneurism needle should be introduced on the medial side, between the artery and vein. Collateral Circulation. — ^The principal anastomoses in carrying on the collateral circulation, after the application of a ligature to the external ihac, are: the iholumbar with the iliac circum- flex; the superior gluteal with the lateral femoral circumflex; the obturator with the medial femoral circumflex; the inferior gluteal with the first perforating and circumflex branches of the profunda artery; and the internal pudendal with the external pudendal. When the obturator arises from the inferior epigastric, it is supplied with blood by branches, from either the hj-pogastric, the lateral sacral, or the internal pudendal. The inferior epigastric receives its supph- from the internal mammary and lower intercostal arteries, and from the hypogastric by the anastomoses of its branches with the obturator. ^ Branches. — Besides several small branches to the Psoas major and the neighbor- ing lymph glands, the external iliac gives off two branches of considerable size: Inferior Epigastric. Deep Iliac Circumflex. The inferior epigastric artery («. epigastrica inferior; deep epigastric artery) (Fig. 623) arises from the external iliac, immediately above the inguinal ligament. It curves forward in the subperitoneal tissue, and then ascends obliquely along the medial margin of the abdominal inguinal ring; continuing its course upward, it pierces the transversalis fascia, and, passing in front of the linea semicircularis, ascends between the Rectus abdominis and the posterior lamella of its sheath. It finally divides into numerous branches, which anastomose, above the umbilicus, with the superior epigastric branch of the internal mammary and with the lower intercostal arteries (Fig. 598). As the inferior epigastric artery passes obliquely upward from its origin it lies along the lower and medial margins of the abdominal inguinal ring, and behind the commencement of the spermatic cord. The ductus deferens, as it leaves the spermatic cord in the male, and the round ligament of the uterus in the female, winds around the lateral and posterior aspects of the artery. Branches. — The branches of the vessel are : the external spermatic artery (cremasteric artery), which accompanies the spermatic cord, and supplies the Cremaster and other coverings of the cord, anastomosing with the internal spermatic artery (in the female it is very small and accompanies the round ligament) ; a pubic branch which runs along the inguinal ligament, and then descends along the medial margin of the femoral ring to the back of the pubis, and there anastomoses with the pubic branch of the obturator artery; muscular branches, some of which are distributed to the abdominal muscles and peritoneum, anastomosing with the iliac circumflex and lumbar arteries; branches which perforate the tendon of the Obliquus externus, and supply the integument, anastomosing with branches of the super- ficial epigastric. Peculiarities. — The origin of the inferior epigastric maj' take place from anj" part of the external iliac between the inguinal ligament and a point 6 cm. above it; or it may arise below this ligament, from the femoral. It frequently' springs from the external ihac, by a common trunk with the obtm-ator. Sometimes it arises from the obtm-ator, the latter vessel being furnished bj' the 1 Sir Astley Cooper describes in Guy's Hospital Reports, vol. i, the dissection of a limb eighteen years after successful ligature of the external iliac artery. 710 ANGIOLOGY hypogastric, or it may be formed of two branches, one derived from the external ihac, the other from the hypogastric. Applied Anatomy. — The inferior epigastric artery has impoi'tant surgical relations, and is one of the principal means, through its anastomosis with the internal mammary, of establishing the collateral circulation after ligature of either the common or external iliac arteries. It lies close to the abdominal inguinal ring, and is therefore medial to an oblique inguinal hernia, but lateral to a direct inguinal hernia, as these emerge from the abdomen. It forms the lateral boundary of Hesselbach's triangle, and is in close relationship with the spermatic cord, which hes in front of it in the inguinal canal, separated only by the transvei'sahs fascia. The ductus deferens hooks around its lateral side. The deep iliac circumflex artery (a. circumflexa ilium profunda) arises from the lateral aspect of the external iliac nearly opposite the inferior epigastric artery. It ascends obliquely lateralward behind the inguinal ligament, contained in a fibrous sheath formed by the junction of the transversalis fascia and iliac fascia, to the anterior superior iliac spine, where it anastomoses with the ascending branch of the lateral femoral circumflex artery. It then pierces the transversalis fascia and passes along the inner lip of the crest of the ilium to about its middle, where it perforates the Transversus, and runs backward between that muscle and the Obliquus internus, to anastomose with the iliolumbar and superior gluteal arteries. Opposite the anterior superior spine of the ilium it gives off a large branch, which ascends between the Obliquus internus and Transversus muscles, supplying them, and anastomosing with the lumbar and inferior epigastric arteries. THE ARTERIES OF THE LOWER EXTREMITY. The artery which supplies the greater part of the lower extremity is the direct continuation of the external iliac. It runs as a single trunk from the inguinal ligament to the lower border of the Popliteus, where it divides into two branches, the anterior and posterior tibial. The upper part of the main trunk is named the femoral, the lower part the popliteal. THE FEMORAL ARTERY (A. FEMORALIS) (Figs. 624, 625). The femoral artery begins immediately behind the inguinal ligament, midway between the anterior superior spine of the ilium and the symphysis pubis, and passes down the front and medial side of the thigh. It ends at the junction of the middle with the lower third of the thigh, where it passes through an opening in the Adductor magnus to become the popliteal artery. The vessel, at the upper part of the thigh, lies in front of the hip-joint; in the lower part of its course it lies to the medial side of the body of the femur, and between these two parts, where it crosses the angle between the head and body, the vessel is some distance from the bone. The first 4 cm. of the vessel is enclosed, together with the femoral vein, in a fibrous sheath — the femoral sheath. In the upper third of the thigh the femoral artery is contained in the femoral triangle {Scarpa's triangle), and in the middle third of the thigh, in the adductor canal {Hunter's canal). The femoral sheath {crural sheath) (Figs. 621, 622) is formed by a prolongation downward, behind the inguinal ligament, of the fasciae which line the abdomen, the transversalis fascia being continued down in front of the femoral vessels and the iliac fascia behind them. The sheath assumes the form of a short funnel, the wide end of which is directed upward, while the lower, narrow end fuses with the fascial investment of the vessels, about 4 cm. below the inguinal ligament. It is strengthened in front by a band termed the deep crural arch (page 509) . The lateral wall of the sheath is vertical and is perforated by the lumboinguinal nerve; the medial wall is directed obliquely downward and lateralward, and is pierced by the THE FEMORAL ARTERY 711 Fig. 621. — Femoral sheath laid open to show its three compartments. Lai. fern, cutan. nerve / Femoral nerve Lumbo-inguinal ticrve Femoral artery Femoral sheath Femoral vein Femoral ring Lacunar ligament Fig. 622. — Structures passing behind the inguinal hgament. 712 AXGIOLOGY great saphenous vein and by some lymphatic vessels. The sheath is divided by two vertical partitions which stretch between its anterior and posterior walls. The lateral compartment contains the femoral artery, and the intermerliate the femoral vein, while the medial and smallest compartment is named the femoral canal, and contains some lymphatic vessels and a lymph gland imbedded in a small amount of areolar tissue. "The femoral canal is conical and measures about 1.25 cm. in length. Its base, directed upward and named the femoral ring, is oval in form, its long diameter being directed transversely and measuring about 1.25 cm. The femoral ring (Figs. 622, G23) is bounded in front by the inguinal ligament, hehmd by the Pectineus covered by the pectineal fascia, medially by the crescentic base of the lacunar ligament, and laterally by the fibrous septum on the medial side of the femoral vein. The spermatic cord in the male and the round ligament of the uterus in the female lie immediately above the anterior margin of the ring, while the inferior epigastric vessels are close to its upper and lateral angle. The femoral ring is closed by a somewhat condensed portion of the extraperitoneal fatty tissue, named the septum femorale (crural seidum), the abdominal surface Fig. 623. — The relations of the femoral and abdominal inguinal rings, seen from within the abdomen. Right side. of which supports a small lymph gland and is covered by the parietal layer of the peritoneum. The .septum femorale is pierced by numerous lymphatic vessels passing from the deep inguinal to the external iliac lymph glands, and the parietal peritoneum immediately above it presents a slight depression named the femoral fossa. The femoral triangle (trigonum femorale; Scarpa's triangle) (Fig. (324) corre- sponds to the depression seen immediately below the fold of the groin. Its apex is directed downward, and the sides are formed laterally by the medial margin of the Sartorius, medially by the medial margin of the Adductor longus, and above by the inguinal ligament. The floor of the space is formed from its lateral to its medial side by the Iliacus, Psoas major, Pectineus, in some cases a small part of the Adductor brevis, and the Adductor longus; and it is divided into two nearly equal parts by the femoral vessels, which extend from near the middle of its base to its apex: the artery giving off in this situation its superficial and profunda branches, the vein receiving the deep femoral and great saphenous tributaries. On the lateral side of the femoral artery is the femoral nerve dividing into its THE FEMORAL ARTERY ■13 branches. Besides the vessels and nerves, this space contains some fat and lymphatics. The adductor canal (caiKtlift adducforius; Hunter's canaJ) is an aponeurotic tunnel in the middle third of the thigh, extending; from the apex of the femoral triangle to the opening in the Adductor magnus. It is bounded, in front and later- ally, by the Vastus medialis; behind by the i\.dductores longus and magnus; and is covered in by a strong aponeurosis which extends from the Vastus medialis, across the femoral vessels to the Adductores longus and magnus; lying on the aponeurosis is the Sartorius muscle. The canal contains the femoral artery and vein, the saphenous nerve, and the nerve to the Vastus mediahs. Superficial iliac cu cumflex vessels Femoral nerve Superficial epiga^tiic vessels Superficial external pude^idal vessels Deep external pudendal vessels Great saphenous vein Fig. 624. — The left femoral triangle. Relations of the Femoral Artery. — In the femoral triangle (Fig. 624) the artery is superficial. In front of it are the skin and superficial fascia, the superficial subinguinal lymph glands, the superficial iliac circumflex vein, the superficial layer of the fascia lata and the anterior part of the femoral sheath. The lumboinguinal nerve courses for a short distance within the lateral compartment of the femoral sheath, and lies at first in front and then lateral to the artery. Near the apex of the femoral triangle the medial branch of the anterior femoral cutaneous nerve crosses the artery from its lateral to its medial side. Behind the artery are the posterior part of the femoral sheath, the pectineal fascia, the medial part of the tendon of the Psoas major, the Pectineus and the Adductor longus. The artery is separated from the capsule of the hip-joint by the tendon of the Psoas major, from the Pectineus by the femoral vein and profimda vessels, and from the Adductor longus by the femoral vein. The nerve to the Pectineus passes medialward behind the artery. On the lateral side of the artery, but separated from it by some fibres of the Psoas major, is the femoral nerve. The femora 714 ANGIOWGY vein is on the medial side of the upper part of the artery, but is behind the vessel in the lower part of the femoral triangle. In the adductor canal (Fig. 625) the femoral artery is more deeply situated, being covered by the integument, the superficial and deep fasciae, the Sartorius and the fibrous roof of the canal; the saphenous nerve crosses from its lateral to its medial side. Behind the artery are the Adduc- tores longus and magnus; in front and lateral to it is the Vastus medialis. The femoral vein lies posterior to the upper part, and lateral to the lower part of the artery Scrolmn - Saphenous nerve - ^ — Highest genicular Lateral sup. Lateral inf. genicular ~ Musculo-articular hr. of highest genicxdar Medial sup. genicular Medial inf. genicular Anterior tibial recurrent— jj;j-\-'^^i_ i . i . , , v/i j Fig. 625. — The femoral artery. Peculiarities. — Several cases are recorded in which the femoral artery divided into two trunks below the origin of the profunda, and became reunited near the opening in the Adductor magnus, so as to form a single pophteal artery. One occm-red in a patient who was operated upon for popliteal anemrism. A few cases have been recorded in which the femoral artery was absent, its place being suppUed by the inferior gluteal artery which accompanied the sciatic nerve to the THE FEMORAL ARTERY 715 popliteal fossa. The external iliac in these cases was small, and terminated in the profunda. The femoral vein is occasional^' placed along the medial side of the artery throughout the entire extent of the femoral trangle; or it may be split so that a large vein is placed on either side of the artery for a greater or lesser distance. Applied Anatomy. — Compression of the femoral artery, which is constantly requisite in ampu- tations and other operations on the lower Umb, is most effectually made immediatelj^ below the inguinal ligament. In this situation the artery is very superficial, and is merely separated from the superior ramus of the pubis by the Psoas major; here digital compression will effectually control the circulation through it. The vessel may also be controlled in the middle third of the thigh by a tourniquet, which presses the vessel against the medial side of the body of the female. The superficial position of the femoral artery in the femoral triangle renders it particularly liable to be injured in wounds, stabs, or gunshot injuries in the groin. On account of the close relationship between the artery and vein, the latter vessel is also liable to be wounded in these injuries. In such cases, the artery being compressed as it crosses the ramus of the pubis, the skin wound should be enlarged and the wound in the vessel sought for, and a ligature applied above and below the bleeding point. The application of a ligature to the femoral artery may be required in cases of wound or aneu- rism of the popHteal, femoral, or arteries of the leg; and the vessel may be exposed and tied in any part of its course. The most favorable situation for the application of a ligature to the femoral is at the apex of the femoral triangle. In order to reach the artery in this situation, an incision 7 cm. long should be made in the course of the vessel, the patient lying in the recumbent posi- tion, with the limb slightly flexed and abducted, and rotated outward. A large vein is frequently met with, passing in the course of the artery to join the great saphenous vein; this must be avoided, and the fascia lata having been cautiously divided, and the Sartorius displayed, that muscle must be drawn lateralward, in order to expose fully the sheath of the vessels. The finger having been introduced into the wound, and the pulsation of the artery felt, the sheath is opened on the lateral side of the vessel to a sufficient extent to allow of the introduction of the aneurism needle. In this part of the operation the saphenous nerve and the nerve to the Vastus medialis, which are in close relation with the sheath, should be avoided. The aneurism needle must be carefully introduced and kept close to the artery, to avoid the femoral vein, which lies behind the vessel in this part of its course, and is very closely bound up with it. To exjoose the artery in the adductor canal, an incision 7 cm. in length should be made through the integument, a finger's breadth medial to the line of the artery, the centre of the incision being in the middle of the thigh — i. e., midway between the groin and the knee. The fascia lata having been divided, and the lateral border of the Sartorius exposed, this muscle should be drawn medial- ward, when the strong fascia which is stretched across from the Adductors to the Vastus medialis will be observed, and must be freely divided; the sheath of the vessels is now seen, and must be opened, and the artery secured by passing the anem-ism needle between it and the vein, from the lateral to the medial side of the artery. In this situation the femoral vein lies lateral to, and the saphenous nerve in front of the artery. Collateral Circulation. — After Ugature of the femoral artery, the main channels for carrying on the circulation are the anastomoses between — (1) the superior and inferior gluteal branches of the hypogastric with the medial and lateral femoral circumflex and first perforating branches of the profunda femoris; (2) the obturator branch of the hypogastric with the medial femoral cu-cumflex of the profunda; (3) the internal pudendal of the hypogastric with the superficial and deep external pudendal of the femoral; (4) the deep iUac circumflex of the external ihac with the lateral femoral circumflex of the profunda and the superficial ihac circumflex of the femoral, and (5) the inferior gluteal of the hypogastric with the perforating branches of the profunda. Branches. — The branches of the femoral artery are; Superficial Epigastric. Deep External Pudendal. Superficial Iliac Circumflex. Muscular. Superficial External Pudendal. Profunda Femoris. Highest Genicular. The superficial epigastric artery (a. epigastrica superficialis) arises from the front of the femoral artery about 1 cm. below the inguinal ligament, and, passing through the femoral sheath and the fascia cribrosa, turns upward in front of the inguinal ligament, and ascends between the two layers of the superficial fascia of the abdominal wall nearly as far as the umbilicus. It distributes branches to the superficial subinguinal lymph glands, the superficial fascia, and the integument; it anastomoses with branches of the inferior epigastric, and with its fellow of the opposite side. 716 AXGIOLOGY The superficial iliac circumflex artery (a. circumflexa iliinu .s'upcrficialis), the smallest of the cutaneous branches, arises close to the preceding, and, piercing the fascia lata, runs laterahvard, parallel with the inguinal ligament, as far as the crest of the ilium; it di\-ides into branches which supply the integument of the groin, the superficial fascia, and the superficial subinguinal lymph glands, anas- tomosing with the deep iliac circumflex, the superior gluteal and lateral femoral circumflex arteries. The superficial external pudendal artery (a. pudenda externa superficialis; superficial external pudic artery) arises from the medial side of the femoral artery, close to the preceding vessels, and, after piercing the femoral sheath and fascia cribrosa, courses medialward, across the spermatic cord (or round ligament in the female), to be distributed to the integument on the lower part of the abdomen, the penis and scrotum in the male, and the labium majus in the female, anasto- mosing with branches of the internal pudendal. The deep external pudendal artery (a. pudenda externa profunda; deep external pudic artery), more deeply seated than the preceding, passes medialward across the Pectineus and the Adductor longus muscles; it is covered by the fascia lata, which it pierces at the medial side of the thigh, and is distributed, in the male, to the integument of the scrotum and perineum, in the female to the labium majus; its branches anastomose with the scrotal (or labial) branches of the perineal artery. Muscular branches {rami musculares) are supplied by the femoral artery to the Sartorius, Vastus medialis, and Adductores. The profunda femoris artery (a. profunda femoris; deep femoral artery) (Fig. (325) is a large vessel arising from the lateral and back part of the femoral artery, from 2 to 5 cm. below the inguinal ligament. At first it lies lateral to the femoral artery ; it then runs behind it and the femoral vein to the medial side of the femur, and, passing downward behind the Adductor longus, ends at the lower third of the thigh in a small branch, which pierces the Adductor magnus, and is distributed on the back of the thigh to the hamstring muscles. The terminal' part of the pro- funda is sometimes named the fourth perforating artery. Relations. — Behind it, from above downward, are the Iliacus, Pectineus, Adductor brevis, and Adductor magnus. In front it is separated from the femoral artery by the femoral and pro- funda veins above and by the Adductor longus below. Laterally, the origin of the Vastus medialis intervenes between it and the femur. Peculiarities. — This vessel sometimes arises from the medial side, and, more rarely, from the back of the femoral artery; but a more important pecuharity, from a surgical point of view, is that relating to the height at which the vessel arises. In three-fourths of a large number of cases it arose from 2.25 to 5 cm. below the inguinal ligament; in a few cases the distance was less than 2.2.5 cm.; more rarely, oppo.site the ligament; and in one case above the inguinal ligament, from the external ihac. Occasionally the distance between the origin of the vessel and the inguinal ligament exceeds 5 cm. Branches. — The profunda gives off the following branches: Lateral Femoral Circumflex. Perforating. Medial Femoral Circumflex. ]\Iuscular. The Lateral Femoral Circumflex Artery (a. circumflexa femoris lateralis; external circumflex artery) arises from the lateral side of the profunda, passes horizontally between the divisions of the femoral nerve, and behind the Sartorius and Rectus femoris, and divides into ascending, transverse, and descending branches. The ascending branch passes upward, beneath the Tensor fasciae latae, to the lateral aspect of the hip, and anastomoses with the terminal branches of the superior gluteal and deep iliac circumflex arteries. The descending branch runs downward, behind the Rectus femoris, upon the Vastus lateralis, to which it gives offsets; one long branch descends in the muscle as far as the knee, and anastomoses Avith the superior lateral genicular branch of THE FEMORAL ARTERY 717 the popliteal artery. It is accompanied by the branch of the femoral nerve to the Vastus lateralis. The transverse branch, the smallest, passes lateralward over the Vastus inter- medins, pierces the \'astus lateralis, and winds around the femur, just below the greater trochanter, anastomosing on the back of the thigh with the medial femoral circumflex, inferior gluteal, and first perforating arteries. The Medial Femoral Circumflex Artery (a. circiimflexa feinoris medialis; internal circumflex arteri/) arises from the medial and posterior aspect of the profunda, and winds around the medial side of the femur, passing first between the Pectineus and Psoas major, and then between the Obturator externus and the Adductor brevis. At the upper border of the Adductor brevis it gives off two branches: one is distributed to the Adductores, the Gracilis, and Obturator externus, and anastomoses with the obturator artery; the other descends beneath the Adductor brevis, to supply it and the iVdductor magnus; the contmuation of the vessel passes backward and divides into superficial, deep, and acetabular branches. The superficial branch appears between the Quadratus femoris and upper border of the Adductor magnus, and anastomoses with the inferior gluteal, lateral femoral circumflex, and first perforating arteries (crucial anastomosis). The deep branch runs obliquely upward upon the tendon of the Obturator externus and in front of the Quadratus femoris toward the trochanteric fossa, where it anastomoses with twigs from the gluteal arteries. The acetabular branch arises opposite the acetabular notch and enters the hip-joint beneath the transverse ligament in com- pany wdth an articular branch from the obturator artery; it supplies the fat in the bottom of the acetabulum, and is continued along the round ligament to the head of the femur. The Perforating Arteries (Fig. 620), usually three in number, are so named because they perforate the tendon of the Adductor magnus to reach the back of the thigh. They pass backward close to the linea aspera of the femur under cover of small tendinous arches in the muscle. The first is given oflF above the Adductor brevis, the second in front of that muscle, and the third immediately below it. The first perforating artery (a. perjorans prima) passes backward between the Pec- tineus and Adductor brevis (sometimes it perforates the latter) ; it then pierces the Adductor magnus close to the linea aspera. It gives branches to the Adductores brevis and magnus. Biceps femoris, and Glutaeus maximus, and anastomoses with the inferior gluteal, medial and lateral femoral circumfiex and second perforating arteries. The second perforating artery (a. perforans secunda), larger than the first, pierces the tendons of the Adductores brevis and magnus, and divides into ascending and descending branches, which supply the posterior femoral muscles, anasto- mosing with the first and third perforating. The second artery frequently arises in common with the first. The nutrient artery of the femur is usually given oft' from the second perforating artery; when two nutrient arteries exist, they usually spring from the first and third perforating vessels. The third perforating artery (a. perforans tertia) is given off below the Adductor brevis; it pierces the Adductor magnus, and divides into brandies wliich supply the posterior femoral muscles; anastomosing above witli the higher perforating arteries, and below with the terminal branches of the profunda and the muscular branches of the popliteal. The nutrient artery of the femur may arise from this branch. The termination of the profunda artery, already described, is sometimes termed the fourth perforating artery. Numerous muscular branches arise from the profunda; some of these end in the Adductores, others pierce the Adductor magnus, give branches to the hamstrings, and anastomose with the medial femoral circumflex artery and with the superior muscular branches of the popliteal. 718 ANGIOLOGY The highest genicular artery {a. genu suprema; cmasfomofica mar/na artery) (Fig. 625) arises from the femoral just before it passes through the opening in the tendon of the Adductor magnus, and immediately divides into a saphenous and a musculo-articular branch. The saphenous branch pierces the aponeurotic covering of the adductor canal, and accompanies the saphenous nerve to the medial side of the knee. It passes betAveen the Sartorius and Gracilis, and, piercing the fascia lata, is distributed to the integument of the upper and medial part of the leg, anastomosing with the medial inferior genicular artery. The musculoarticular branch descends in the substance of the Vastus medialis, and in front of the tendon of the Adductor magnus, to the medial side of the knee, where it anastomoses with the medial superior genicular artery and anterior recur- rent tibial artery. A branch from this vessel crosses above the patellar surface of the femur, forming an anastomotic arch with the lateral superior genicular artery, and supplying branches to the knee-joint. THE POPLITEAL FOSSA (Fig. 626). Dissection. — A vertical incision about eight inches in length should be made along the back part of the knee-joint, connected above and below by a transverse incision from the inner to the outer side of the hmb. The flaps of integument included between these incisions should be reflected in the direction shown in Fig. 570. Boundaries. — The popliteal fossa or space is a lozenge-shaped space, at the back of the knee-joint. Laterally it is bounded by the Biceps femoris above, and by the Plantaris and the lateral head of the Gastrocnemius below; medially it is limited by the Semitendinous and Semimembranosus above, and by the medial head of the Gastrocnemius below. The floor is formed by the popliteal surface of the femur, the oblique popliteal ligament of the knee-joint, the upper end of the tibia, and the fascia covering the Popliteus; the fossa is covered in by the fascia lata. Contents. — The popliteal fossa contains the popliteal vessels, the tibial and the common peroneal nerves, the termination of the small saphenous vein, the lower part of the posterior femoral cutaneous nerve, the articular branch from the obtur- ator nerve, a few small lymph glands, and a considerable quantity of fat. The tibial nerve descends through the middle of the fossa, lying under the deep fascia and crossing the vessels posteriorly from the lateral to the medial side. The com- mon peroneal nerve descends on the lateral side of the upper part of the fossa, close to the tendon of the Biceps femoris. On the floor of the fossa are the popliteal vessels, the vein being superficial to the artery and united to it by dense areolar tissue; the vein is a thick-walled vessel, and lies at first lateral to the artery, and then crosses it posteriorly to gain its medial side below; sometimes it is double, the artery lying between the two veins, which are usually connected by short trans- verse branches. The articular branch from the obturator nerve descends upon the artery to the knee-joint. The popliteal lymph glands, six or seven in number, are imbedded in the fat; one lies beneath the popliteal fascia near the termination of the external saphenous vein, another between the popliteal artery and the back of the knee-joint, while the others are placed at the sides of the popliteal vessel. Arising from the artery, and passing off from it at right angles, are its genicular branches. The Popliteal Artery (A. Poplitea) (Fig. 626). The popliteal artery is the continuation of the femoral, and courses through the popliteal fossa. It extends from the opening in the Adductor magnus, at the junc- tion of the middle and lower thirds of the thigh, downward and lateralward to the intercondyloid fossa of the femur, and then vertically downward to the lower border of the Popliteus, where it divides into anterior and posterior tibial arteries. THE POPLITEAL ARTERY 719 Relations. — In froni of the artery from above downward are the popHteal surface of the femur (which is separated from the vessel by some fat), the back of the knee-joint, and the fascia cover- ing the Poplitous. Behind, it is overlapped by the Semimembranosus above, and is covered by the Gastrocnemius and Plantaris below. In the middle part of its course the artery is separated from the integument and fascia? by a quantity of fat, and is crossed from the lateral to the medial side by the tibial nerve and the popliteal vein, the vein being between the nerve and the artery and closely ad- herent to the latter. On its lateral side, above, are the Biceps femoris, the tibial nerve, the popliteal vein, and the lateral condyle of the femur; below, the Plantaris and the lateral head of the Gastroc- nemius. On its medial side, above, are the Semi- membranosus and the medial condyle of the femur; below, the tibial nerve, the popUteal vein, and the medial head of the Gastrocnemius. The relations of the popliteal lymph glands to the arteiy are described above. Peculiarities in Point of Division. — Occasionally the popliteal artery divides into its terminal branches opposite the knee-joint. The anterior tibial under these circumstances usually passes in front of the Popliteus. Unusual Branches. — The artery sometimes divides into the anterior tibial and peroneal, the posterior tibial being wanting, or very small. Oc- casionally it divides into three branches, the ante- rior and posterior tibial, and peroneal. Applied Anatomy. — The popHteal artery is not infrequently the seat of injury. It may be torn by direct violence, as by the passage of a cart wheel over the knee, or by hyperextension of the knee. It may also be lacerated by fracture of the lower part of the body of the femur, or by antero-posterior dislocation of the knee-joint. It has been torn in breaking down adhesions in cases of fibrous anky- losis of the knee, and is in danger of being wounded, and in fact has been wounded, in performing Mac- ewen's operation of osteotomy of the lower end of the femur for genu valgum. The popliteal artery is more frequently the seat of aneurism than any other artery in the body, with the exception of the thoracic aorta. No doubt this is due in a great measure to the amoimt of movement to which it is subjected, and to the fact that it is supported by loose and lax tissue only, and not by muscles as is the case with most arteries. When the knee is acutely flexed the popHteal artery becomes bent on itself to such an extent as to entirely arrest the cir- culation through it. Ligature of the popliteal artery is reqiured in cases of wound of the vessel, but for aneitrism it is preferable to tie the femoral. The popliteal may be tied in the upper or lower part of its course; but in the middle of the fossa the operation is at- tended with considerable difficulty, from the great depth of the vessel, and from the extreme degree of tension of the lateral and medial boundaries of the fossa. In order to expose the upper part of the vessel, the patient should be placed in the supine posi- tion, with the knee flexed and the thigh abducted and rotated outward, so that it rests on its lateral surface; an incision 7 or 8 cm. in length, beginning at the junction of the middle and lower thirds of the thigh, is to be made paraUel Perf. branch of peroneal Fig. 626. — The popliteal, posterior tibial, and peroneal arteries. 720 A NG 10 LOGY to and immediately behind the tendon of the adductor magnus, and the skin, superficial and deep fasciiE divided. The tendon of the muscle is thus exposed, and is to be drawn forward, and the hamstring tendons backward. A quantity of fatty tissue will now be opened up, in which the artery will be felt pulsating. This is to be separated with the point of a director until the arterj^ is exposed. The vein and nerve will not be seen, as they lie to the lateral side of the artery. The sheath is to be opened and the aneurism needle passed from before backward, keeping its point close to the artery for fear of injuring the vein. The only structure to avoid in the superficial incision is the great saphenous vein. To expose the vessel in the lower part of its course, where the artery lies between the two heads of the Gastrocnemius, the patient should be placed in the prone position with the limb extended. An incision should then be made through the integument in the middle line, commenc- ing opposite the bend of the knee-joint, care being taken to avoid the small saphenous vein and the medial sural cutaneous nerve. After dividing the deep fascia, and separating some dense cellular tissue, the artery, vein, and nerve will be exposed, between the two heads of the Gastroc- nemius. Some muscular branches of the popliteal should be avoided if possible, or, if divided, tied immediately. The leg being now flexed, in order the more effectually to separate the two heads of the Gastrocnemius, the nerve should be drawn medialward and the vein lateralward, and the aneurism needle passed between the artery and vein from the lateral to the medial side. Branches. — The branches of the popliteal artery are: - , , f Superior Lateral Superior Genicular. Muscular ^^ g^^^j ^.^^^^ Genicular. Cutaneous. Medial Inferior Genicular, Medial Superior Genicular Lateral Inferior Genicular. The superior muscular branches, two or three in number, arise from the upper part of the artery, and are distributed to the lower parts of the Adductor magnus and hamstring muscles, anastomosing with the terminal part of the profunda femoris. The sural arteries (aa. swales; inferior viuscular arteries) are two large branches, which are distributed to the Gastrocnemius, Soleus, and Plantaris. They arise from the popliteal artery opposite the knee-joint. The cutaneous branches arise either from the popliteal artery or from some of its branches; they descend between the two heads of the Gastrocnemius, and, piercing the deep fascia, are distributed to the skin of the back of the leg. One branch usually accompanies the small saphenous vein. The superior genicular arteries {aa. genu superior es; superior articular arteries) (Figs. 625, 626), two in number, arise one on either side of the popliteal, and wind around the femur immediately above its condyles to the front of the knee-joint. The medial superior genicular runs in front of the Semimembranosus and Semitendinosus, above the medial head of the Gastrocnemius, and passes beneath the tendon of the Adductor magnus. It divides into two branches, one of which supplies the Vastus medialis, anastomosing with the highest genicular and medial inferior genicular arteries ; the other ramifies close to the surface of the femur, supplying it and the knee-joint, and anastomosing with the lateral superior genicular artery. The medial superior genicular artery is frequently of small size, a condition, which is associated with an increase in the size of the highest genicular. The lateral superior genicular passes above the lateral condyle of the femur, beneath the tendon of the Biceps femoris, and divides into a superficial and a deep branch; the superficial branch supplies the Vastus lateralis, and anastomoses with the descending branch of the lateral femoral circumflex and the lateral inferior genicular arteries; the deep branch supplies the lower part of the femur and knee-joint, and forms an anasto- motic arch across the front of the bone with the highest genicular and the medial inferior genicular arteries. The middle genicular artery (a. getiu media; azygos articular artery) is a small branch, arising opposite the back of the knee-joint. It pierces the oblique popliteal ligament, and supplies the ligaments and synovial membrane in the interior of the articulation. THE POPLITEAL ARTERY '21 The inferior genicular arteries (rtrt. gcim inferiores; inferior articular arteries) (Figs. 625, 62()), two in number, arise from the popliteal beneath the Gastrocnemius. The medial inferior genicular first descends along the upper margin of the Popliteus, to which it gives I)ranches; it then passes below the medial condyle of the tibia, beneath the tibial collateral ligament, at the anterior border of which it ascends to the front and medial side of the joint, to supply the upper end of the tibia and the articula- tion of the knee, anastomosing with the lateral inferior and medial superior genic- ular arteries. The lateral inferior genicular runs laterahvard above the head of the fibula to the front of the knee-joint, passing in its course beneath the lateral head of the Gastrocnemius, the fibular collateral ligament, and the tendon of the Biceps femoris. It ends by dividing into branches, which anastomose with the medial inferior and lateral superior genicular arteries, and with the anterior recurrent tibial artery. Descending hranch of lateral femoral circwmflex Lateral superic^r genicular Lateral inferior genicular Fibular -^-^ Anterior recurrent tibial Anterior tibial Highest genicular Musculo-articular branch of highest genicular Saphenoxis branch of highest genicular Medial superior genicular Medial inferior genicular Fig. 627. — Circumpatellar anastomosis. The Anastomosis Around the Knee-joint (Fig. 627). — Around and above the patella, and on the contiguous ends of the femur and tibia, is an intricate net-work of vessels forming a superficial and a deep plexus. The superficial plexus is situated between the fascia and skin around about the patella, and forms three well-defined arches : one, above the upper border of the patella, in the loose connective tissue over the Quadriceps femoris; the other two, below the level of the patella, are situated in the fat behind the ligamentum patellae. The deep plexus, which forms a close net-work of vessels, lies on the lower end of the femur and upper end of the tibia around their articular surfaces, and sends numerous offsets into the interior of the joint. The arteries which form this plexus are the two medial and the two lateral genicular branches of the popliteal, the highest genicular, the descending branch af the lateral femoral circumflex, and the anterior recurrent tibial. 46 722 ANGIOLOGY The Anterior Tibial Artery (A. Tibialis Anterior) (Fig. 62S). The anterior tibial artery commences at the bifurcation of the popHteal, at the lower border of the Popliteus, passes forward between the two heads of the Tibialis posterior, and through the aperture above the upper border of the interosseous membrane, to the deep part of the front of the leg : it here lies close to the medial side of the neck of the fibula. It then descends on the anterior surface of the inter- osseous membrane, gradually approaching the tibia; at the lower part of the leg it lies on this bone, and then on the front of the ankle-joint, where it is more superficial, and becomes the dorsalis pedis. Relations. — In the upper two-thirds of its extent, the anterior tibial artery rests upon the inter- osseous membrane; in the lower third, upon the front of the tibia, and the anterior hgament of the ankle-joint. In the upper third of its course, it lies between the TibiaHs anterior and Extensor digitorum longus; in the middle third between the Tibialis anterior and Extensor hallucis longus. At the ankle it is crossed from the lateral to the medial side by the tendon of the Extensor hallucis longus, and hes between it and the first tendon of the Extensor digitorum longus. It is covered in the upper two-thirds of its course, by the muscles which he on either side of it, and by the deep fascia; in the lower third, by the integument and fascia, and the transverse and cruciate crural ligaments. The anterior tibial artery is accompanied by a pair of venae comitantes which he one on either side of the artery; the deep peroneal nerve, coursing around the lateral side of the neck of the fibula, comes into relation with the lateral side of the artery shortly after it has reached the front of the leg; about the middle of the leg the nerve is in front of the artery; at the lower part it is generally again on the lateral side. Peculiarities in Size. — This vessel may be diminished in size, may be deficient to a greater or less extent, or may be entirely wanting, its place being supplied by perforating branches from the posterior tibial, or by the perforating branch of the peroneal artery. Course. — The artery occasionally deviates toward the fibular side of the leg, regaining its usual position at the front of the ankle. In rare instances the vessel has been found to approach the surface in the middle of the leg, being covered merely by the integument and fascia below that point. Applied Anatomy. — The anterior tibial artery is liable to be injin-ed in fractures of the lower third of the tibia, on account of its close proximity to the bone. The apphcation of a hgature to the vessel is rarely required, except in cases of wound or for traumatic aneurism. The opera- tion in the upper third of the leg is attended with great difficulty on accoimt of the depth of the vessel from the smface. An incision about 10 cm. in length is made in the line of the artery to about a hand's breadth below the level of the knee-joint. The skin and superficial structures having been divided and the deep fascia exposed, the wound must be carefully dried, its edges retracted, and the white Line separating the Tibiahs anterior from the Extensor digitorum longus sought for. When this has been clearly defined, the deep fascia is to be divided in this Une, and the Tibiahs anterior separated from adjacent muscles imtil the interosseous membrane is reached. The foot is to be flexed in order to relax the muscles, and upon drawing them apart the artery will be found lying on the interosseous membrane with the nerve lateral or superficial to it. The nerve should be drawn lateralward, the venae comitantes separated from the artery and the needle passed around it. To tie the vessel in the lower third of the leg above the ankle-joint, an incision about 7 cm. in length should be made through the integument between the tendons of the Tibiahs anterior and Extensor hallucis longus, the deep fascia being divided to the same extent. The tendon on either side should be retracted, when the vessel, accompanied by the venae comitantes, wiU be seen lying upon the tibia, with the nerve on the lateral side. Branches.^ — The branches of the anterior tibial artery are: Posterior Tibial Recurrent. Muscular. Fibular. Anterior Medial Malleolar. Anterior Tibial Recurrent. Anterior Lateral Malleolar. The posterior tibial recurrent artery {a. recurrens tibialis posterior) an inconstant branch, is given off from the anterior tibial before that vessel passes through the interosseous space. It ascends in front of the Popliteus, which it supplies, and anastomoses with the inferior genicular branches of the popliteal artery, giving an offset to the tibiofibular joint. THE ANTERIOR TIBIAL ARTERY 723 Lateral infeiior genicular Medial inferior genicular The fibular artery is sometimes derived from the anterior tibial, sometimes from the posterior tibial. It jxisses laterahvard, around the neck of the fibula, through the Soleus, which it suppHes, and ends in the substance of the Peroneus longus. The anterior tibial recurrent artery (a. recurrcns tibialis anterior) arises from the anterior tibial, as soon as that vessel has passed through the interosseous space; it ascends in the Tibialis anterior, ramifies on the front and sides of the knee-joint, and assists in the formation of the patellar plexus by anastomosing with the genicular branches of the popliteal, and with the highest genicular artery. The muscular branches (ravii muscu- lares) are numerous; they are distrib- uted to the muscles w-hich lie on either side of the vessel, some piercing the deep fascia to supply the integument, others passing through the interosseous membrane, and anastomosing with branches of the posterior tibial and peroneal arteries. The anterior medial malleolar artery (a. maUeolaris anterior mediaUs; inter- nal malleolar artery) arises about 5 cm. above the ankle-joint, and passes be- hind the tendons of the Extensor hallucis longus and Tibialis anterior, to the medial side of the ankle, upon which it ramifies, anastomosing with branches of the posterior tibial and medial plantar arteries and with the medial calcaneal from the posterior tibial. The anterior lateral malleolar artery (a. maUeolaris anterior lateralis; external malleolar artery) passes beneath the tendons of the Extensor digitorum longus and Peronaeus tertius and sup- plies the lateral side of the ankle, anastomosing wdth the perforating branch of the peroneal artery, and with ascending twigs from the lateral tarsal artery. The arteries around the ankle-joint anastomose freely with one another and form net-works below^ the corre- sponding malleoli. The medial malleolar net-work is formed by the anterior medial malleolar branch of the anterior tibial, the medial tarsal branches of the dorsalis pedis, the posterior medial malleolar and medial calcaneal branches of the posterior tibial and branches Yig. 628.— Anterior tibial and dcrsaUs pedis arteries. Perf. hr. of -peroneal Ant. lot. malleolar Ant. med. malleolar Deep plantar 724 AmiOLOGY from the medial plantar artery. The lateral malleolar net-work is formed by the anterior lateral malleolar branch of the anterior tibial, the lateral tarsal branch of the dorsalis pedis, the perforating and the lateral calcaneal branches of the peroneal, and twigs from the lateral plantar artery. The Arteria Dorsalis Pedis (Dorsalis Pedis Artery) (Fig. 628). The arteria dorsalis pedis, the continuation of the anterior tibial, passes forward from the ankle-joint along the tibial side of the dorsum of the foot to the proximal part of the first intermetatarsal space, where it divides into two branches, the first dorsal metatarsal and the deep plantar. Relations. — This vessel, in its course forward, rests upon the front of the articular capsule of the ankle-joint, the talus, navicular, and second cuneiform bones, and the ligaments connect- ing them, being covered by the integument, fascia and cruciate hgament, and crossed near its termination by the first tendon of the Extensor digitorum brevis. On its tibial side is the tendon of the Extensor hallucis longus; on its fibular side, the first tendon of the Extensor digitorum longus, and the termination of the deep peroneal nerve. It is accompanied by two veins. Peculiarities in Size. — The dorsal artery of the foot may be larger than usual, to compensate for a deficient plantar artery; or its terminal branches to the toes may be absent, the toes then being supphed by the medial plantar; or its place may be taken altogether by a large perforating branch of the peroneal artery. Position. — This artery frequently curves lateralward, lying lateral to the Une between the middle of the ankle and the back part of the first interosseous space. Applied Anatomy. — This artery may be tied, by making an incision 5 cm. in length, through the integument, on the fibular side of the tendon of the Extensor hallucis longus, in the interval between it and the medial border of the Extensor digitorum brevis. The incision should not extend farther forward than the proximal part of the first intermetatarsal space, as the artery divides m that situation. The deep fascia being divided to the same extent, the artery will be exposed, the deep peroneal nerve lying lateral to it. Branches. — The branches of the arteria dorsalis pedis are: Lateral Tarsal. iVrcuate. Medial Tarsal. First Dorsal Metatarsal. Deep Plantar. The lateral tarsal artery (a. tar sea lateralis; tarsal artery) arises from the dorsalis pedis, as that vessel crosses the navicular bone; it passes in an arched direction lateralward, lying upon the tarsal bones, and covered by the Extensor digitorum brevis; it supplies this muscle and the articulations of the tarsus, and anastomoses with branches of the arcuate, anterior lateral malleolar and lateral plantar arteries, and with the perforating branch of the peroneal artery. The medial tarsal arteries {aa. tarseae mediales) are two or three small branches which ramify on -the medial border of the foot and join the medial malleolar net-work. The arcuate artery (a. arcuata; metatarsal artery) arises a little anterior to the ' lateral tarsal artery; it passes lateralward, over the bases of the metatarsal bones, beneath the tendons of the Extensor digitorum brevis, its direction being influenced by its point of origin; and it anastomoses with the lateral tarsal and lateral plantar arteries. This vessel gives off the second, third, and fourth dorsal metatarsal arteries, which run forward upon the corresponding Interossei dorsales; in the clefts between the toes, each divides into two dorsal digital branches for the adjoining toes. At the proximal parts of the interosseous spaces these vessels receive the posterior perforating branches from the plantar arch, and at the distal parts of the spaces they are joined by the anterior perforating branches, from the plantar metatarsal arteries. The fourth dorsal metatarsal artery gives off a branch which supplies the lateral side of the fifth toe. The first dorsal metatarsal artery (o. dorsalis hallucis) runs forward on the first Interosseous dorsalis, and at the cleft between the first and second toes divides THE POSTERIOR TIBIAL ARTERY 725 into two branches, one of which passes beneath the tendon of the Extensor hallucis longns, and is distributed to the me(Hal border of the great toe; the other bifurcates to supply the adjoinino' sides of the great and second toes. The deep plantar artery {ramus plantaris profundus; communicating artery) descends into the sole of the foot, between the two heads of the first Interosseous dorsalis, and unites with the termination of the lateral plantar artery, to complete the plantar arch. It sends a branch along the medial side of the great toe, and is continued forward along the first interosseous space as the first plantar metatarsal artery, which bifurcates for the supply of the adjacent sides of the great and second toes. The Posterior Tibial Artery (A. Tibialis Posterior) (Fig. 626). The posterior tibial artery begins at the lower border of the Popliteus, opposite the interval between the tibia and fibula; it extends obliquely downward, and, as it descends, it approaches the tibial side of the leg, lying behind the tibia, and in the lower part of its course is situated midway between the medial malleolus and the medial process of the calcaneal tuberosity. Here it divides beneath the origin of the Adductor hallucis into the medial and lateral plantar arteries. Relations. — The posterior tibial artery lies successively upon the Tibialis posterior, the Flexor digitorum longus, the tibia, and the back of the ankle-joint. It is covered by the deep trans- verse fascia of the leg, which separates it above from the Gastrocnemius and Soleus ; at its termi- nation it is covered by the Abductor hallucis. In the lower third of the leg, where it is more superficial, it is covered only by the integument and fascia, and runs parallel with the medial border of the tendo calcaneus. It is accompanied by two veins, and by the tibial nerve, which lies at first to the medial side of the artery, but soon crosses it posteriorly, and is in the greater part of its com'se on its lateral side. Behind the medial malleolus, the tendons, bloodvessels, and nerve are arranged, under cover of the laciniate ligament, in the following order from the medial to the lateral side: (1) the tendons of the Tibialis posterior and Flexor_ digitorum longus, lying in the same groove, behind the malleolus, the former being the more medial. Next is the posterior tibial artery, with a vein on either side of it; and lateral to the vessels is the tibial nerve; about 1.25 cm. nearer the heel is the tendon of the Flexor hallucis longus. Peculiarities in Size. — -The posterior tibial is not infrequently smaller than usual, or absent, its place being supplied by a large peroneal artery, which either joins the small posterior tibial artery, or continues alone to the sole of the foot. Applied Anatomy. — The apphcation of a Ugature to the posterior tibial may be required in cases of wound of the sole of the foot, attended with great hemorrhage, when the vessel should be tied at the ankle. In cases of wound of the posterior tibial, it will be necessary to enlarge the opening so as to expose the vessel at the wounded point, excepting where the vessel is injured by a punctm-ed woimd from the front of the leg. In cases of aneurism from wound of the artery low down, the vessel should be tied in the middle of the leg. To tie the posterior tibial artery at the ankle, a semilunar incision, about 6 cm. in length, convex backward, should be made through the integument, midway between the heel and the medial malleolus, or a Uttle nearer the latter. The subcutaneous tissue having been divided, a strong and dense fascia, the laciniate (internal annular) Ugament, is exposed. This ligament is continuous above with the deep fascia of the leg, covers the vessels and nerves, and is intimately adherent to the sheaths of the tendons. This having been cautiously divided upon a director, the sheath of the vessels is exposed, and, being opened, the artery is seen with one of the venae comitantes on either side. The aneurism needle should be passed around the vessel from the heel toward the ankle, in order to avoid the tibial nerve, care at the same time being taken not to include the venae comitantes. The vessel may also be tied in the lower thu'd of the leg by making an incision about 8 cm. in length, parallel with the medial border of the tendo calcaneus. The great saphenous vein being carefully avoided, the two layers of fascia must be divided upon a director, when the artery is exposed along the lateral margin of the Flexor digitorum longus, with one of its venae comitantes on either side, and the nerve lying lateral to it. Ligature of the posterior tibial in the middle of the leg is a very difficult operation, on account of the great depth of the vessel from the surface. The patient being placed in the recumbent position, the injm-ed hmb should rest on its fibular side, the knee being partially bent, and the foot extended, so as to relax the muscles of the calf. An incision about 10 cm. in length should then be made through the integument, a finger's breadth behind the medial margin of the tibia, care being taken to avoid the great saphenous vein. The deep fascia having been divided, the 726 ANGIOLOGY margin of the Gastrocnemius is exposed, and must be drawn aside, and the tibial attachment of the Soleus divided. The artery may now be felt pulsating beneath the deep transverse fascia, about 2.5 cm. from the margin of the tibia. This fascia having been divided, and the limb placed in such a position as to relax the muscles of the calf as much as possible, the veins should be sepa- rated from the artery and the aneurism needle passed around the vessel from the lateral to the medial side, so as to avoid wounding the tibial nerve. Branches. — The branches of the posterior tibial artery are : Peroneal. Posterior Medial Malleolar. Nutrient. Communicating. Muscular. Medial Calcaneal. The peroneal artery (a. peronaea) is deeply seated on the back of the fibular side of the leg. It arises from the posterior tibial, about 2.5 cm. below the lower border of the Popliteus, passes obliquely toward the fibula, and then descends along the medial side of that bone, contained in a fibrous canal between the Tibialis posterior and the Flexor hallucis longus, or in the substance of the latter muscle. It then runs behind the tibiofibular syndesmosis and divides into lateral calcaneal branches which ramify on the lateral and posterior surfaces of the calcaneus. It is covered, in the upper part of its course, by the Soleus and deep transverse fascia of the leg; below, by the Flexor hallucis longus. Peculiarities in Origin. — The peroneal artery may arise 7 or 8 cm. below the Popliteus, or from the posterior tibial high up, or even from the popliteal. Its size is more frequently increased than diminished; and then it either reinforces the posterior tibial by its junction with it, or altogether takes the place of the posterior tibial in the lower part of the leg and foot, the latter vessel onlj^ existing as a short muscular branch. In those rare cases where the peroneal artery is smaller than usual, a branch from the posterior tibial supplies its place; and a branch from the anterior tibial compensates for the diminished anterio!" peroneal artery. In one case the peroneal artery was entirely wanting. Branches. — The branches of the peroneal are: Muscular. Perforating. Nutrient. Communicating. Lateral Calcaneal. Muscular Branches. — The peroneal artery, in its course, gives off branches to the Soleus, Tibialis posterior. Flexor hallucis longus, and Peronei. The Nutrient Artery (a. nutricia fibulae) supplies the fibula, and is directed downward. The Perforating Branch {ramus perforans; anterior peroneal artery) pierces the interosseous membrane, about 5 cm. above the lateral malleolus, to reach the front of the leg, where it anastomoses with the anterior lateral malleolar; it then passes down in front of the tibiofibular syndesmosis, gives branches to the tarsus, and anastomoses with the lateral tarsal. The perforating branch is sometimes enlarged, and takes the place of the dorsalis pedis artery. The Communicating Branch {ramus communicans) is given off from the peroneal about 2.5 cm. from its lower end, and joins the communicating branch of the posterior tibial. The Lateral Calcaneal {ramus calcaneus lateralis; external calcaneal) are the ter- minal branches of the peroneal artery; they pass to the lateral side of the heel, and communicate with the lateral malleolar and, on the back of the heel, with the medial calcaneal arteries. The nutrient artery (a. nutricia tibiae) of the tibia arises from the posterior tibial, near its origin, and after supplying a few muscular branches enters the nutrient canal of the bone, which it traverses obliquely from above downward. This is the largest nutrient artery of bone in the body. THE POSTERIOR TIBIAL ARTERY 727 The muscular branches of the posterior til)ial arc distributed to the Soleus and deep muscles along the back of the leg. The posterior medial malleolar artery (a. nudleolaris posterior inedUdis; internal malleolar artery) is a small branch which winds around the tibial malleolus and ends in the medial malleolar net-work. The communicating branch (ravivs communicans) runs transversely across the back of the tibia, about 5 cm. above its lower end, beneath the Flexor hallucis longus, and joins the communicating branch of the peroneal. The medial calcaneal {rami calcanei mediales; internal calcaneal) are several large arteries which arise from the posterior tibial just before its division; they pierce the laciniate ligament and are distributed to the fat and integument behind the tendo calcaneus and about the heel, and to the muscles on the tibial side of the sole, anastomosing with the peroneal and medial malleolar and, on the back of the heel, with the lateral calcaneal arteries. Deep plantar 1st plantar metatarsal \ Fig. 629. — The plantar arteries. Superficial view. Fig. 630. — The plantar arteries. Deep view. The medial plantar artery (a. plantaris medialis; internal plantar artery) (Figs. 629 and 630), much smaller than the lateral, passes forw^ard along the medial side of the foot. It is at first situated above the Abductor hallucis, and then between it and the Flexor digitorum brevis, both of which it supplies. At the base of the first metatarsal bone, wdiere it is much diminished in size, it passes along the medial border of the first toe, anastomosing with the first dorsal metatarsal artery. Small superficial digital branches accompany the digital branches of the medial plantar nerve and join the plantar metatarsal arteries of the first three spaces. The lateral plantar artery {a. plantaris lateralis; external plantar artery), much larger than the medial, passes obliquely lateralward and forward to the base of the fifth metatarsal bone. It then turns medialw^ard to the interval between the bases of the first and second metatarsal bones, w^here it unites with the deep plantar branch of the dorsalis pedis artery, thus completing the plantar arch. As this artery passes lateralward, it is first placed between the calcaneus and Abductor hallucis. 728 ANGIOLOGY and then between the Flexor digitorum brevis and Quadratus plantae; as it runs fonvard to the base of the little toe it lies more superficially between the Flexor digitorum brevis and Abductor digiti quinti, covered by the plantar aponeurosis and integument. The remaining portion of the vessel is deeply situated; it extends from the base of the fifth metatarsal bone to the proximal part of the first inter- osseous space, and forms the plantar arch; it is convex forward, lies below the bases of the second, third, and fourth metatarsal bones and the corresponding Interossei, and upon the oblique part of the Adductor hallucis. Applied Anatomy. — Wounds of the plantar arch are always serious, on account of the depth of the vessel and the important structures which must be interfered with in an attempt to liga- ture it. They must be treated on similar lines to those of wounds of the volar arches (see p. 682). Pressure locally, combined -^vith elevation of the limb, may in some cases be sufficient to arrest the bleeding, but this faiUng, an attempt should be made to find the bleeding point and ligature it. Should this prove unsuccessful, it may be necessary to Ugature the femoral below the origin* of the profunda femoris, as ligature of the anterior and posterior tibial arteries may not be sufiicient to control the hemorrhage, and it is safer and quicker to tie the femoral under the circumstances. Branches. — The plantar arch, besides distributing numerous branches to the muscles, integument, and fasciae in the sole, gives off the following branches: Perforating. Plantar Metatarsal. The Perforating Branches {rami jjerforantes) are three in number; they ascend through the proximal parts of the second, third, and fourth interosseous spaces, between the heads of the Interossei dorsales, and anastomose with the dorsal metatarsal arteries. The Plantar Metatarsal Arteries (aa. metatarseae plantares; digital branches) are four in number, and run forward between the metatarsal bones and in contact ^dth the Interossei. Each divides into a pair of plantar digital arteries which sup- ply the adjacent sides of the toes. Near their points of division each sends upward an anterior perforating branch to join the corresponding dorsal metatarsal artery. The first plantar metatarsal artery {arteria- 'princefjs hallucis) springs from the junc- tion between the lateral plantar and deep plantar arteries and sends a digital branch to the medial side of the first toe. The digital branch for the lateral side of the fifth toe arise from the lateral plantar artery near the base of the fifth metatarsal bone. THE VEINS. nnilE Veins convey the blood from the capillaries of the different parts of the -*- body to the heart. They consist of two distinct sets of vessels, the pulmonary and systemic. The Pulmonary Veins, unlike other veins, contain arterial blood, which they return from the lungs to the left atrium of the heart. The Systemic Veins return the venous blood from the body generally to the right atrium of the heart. The Portal Vein, an appendage to the systemic venous system, is confined to the abdominal cavity, and returns the venous blood from the spleen and the viscera of digestion to the liver. This vessel ramifies in the substance of the liver and there breaks up into a minute network of capillary-like vessels, from which the blood is conveyed by the hepatic veins to the inferior vena cava. The veins commence by minute plexuses w^hich receive the blood from the capil- laries. The branches arising from these plexuses unite together into trunks, and these, in their passage toward the heart, constantly increase in size as they receive tributaries, or join other veins. The veins are larger and altogether more numerous than the arteries; hence, the entire capacity of the venous system is much greater than that of the arterial; the capacity of the pulmonary veins, however, only slightly exceeds that of the pulmonary arteries. The veins are cylindrical like the arteries; their walls, however, are thin and they collapse when the vessels are empty, and the uniformity of their surfaces is interrupted at intervals by slight constrictions, which indicate the existence of valves in their interior. They com- municate very freely with one another, especially in certain regions of the body; and these communications exist between the larger trunks as well as between the smaller branches. Thus, between the venous sinuses of the cranium, and between the veins of the neck, where obstruction would be attended with imminent danger to the cerebral venous system, large and frequent anastomoses are found. The same free communication exists between the veins throughout the whole extent of the vertebral canal, and between the veins composing the various venous plexuses in the abdomen and pelvis, e. g., the spermatic, uterine, vesical, and pudendal. The systemic venous channels are subdivided into three sets, viz., superficial and deep veins, and venous sinuses. The Superficial Veins {cutaneous veins) are found between the layers of the superficial fascia immediately beneath the skin; they return the blood from these structures, and communicate with the deep veins by perforating the deep fascia. The Deep Veins accompany the arteries, and are usually enclosed in the same sheaths with those vessels. With the smaller arteries — as the radial, ulnar, brachial, tibial, peroneal — they exist generally in pairs, one lying on each side of the vessel, and are called venae comitantes. The larger arteries — such as the axillary, sub- clavian, popliteal, and femoral — have usually only one accompanying vein. In certain organs of the body, however, the deep veins do not accompany the arteries; for instance, the veins in the skull and vertebral canal, the hepatic veins in the liver, and the larger veins returning blood from the bones. Venous Sinuses are found only in the interior of the skull, and consist of canals formed by a separation of the two layers of the dura mater; their outer coat con- sists of fibrous tissue, their inner of an endothelial layer continuous with the lining membrane of the veins. 730 ANGIOLOGY THE PULMONARY VEINS (VENAE PULMONALES). The pulmonary veins return the arteriahzed blood from the kings to the left atrium of the heart. They are four in number, two from each lung, and are desti- tute of valves. The commence in a capillary net-work upon the walls of the air sacs, where they are continuous with the capillary ramifications of the pulmonary artery, and, joining together, form one vessel for each lobule. These vessels uniting successively, form a single trunk for each lobe, three for the right, and two for the left lung. The vein from the middle lobe of the right lung generally unites with that from the upper lobe, so that ultimately two trunks from each lung are formed; they perforate the fibrous layer of the pericardium and open separately into the upper and back part of the left atrium. Occasionally the three veins on the right side remain separate. Not infrequently the two left pulmonary veins end by a common opening. At the root of the hing, the superior pulmonary vein lies in front of and a little below the pulmonary artery; the inferior is situated at the lowest part of the hilus of the lung and on a plane posterior to the upper vein. Behind the pulmonary artery is the bronchus. Within the pericardium, their anterior surfaces are invested by the serous layer of this membrane. The right pulmonary veins pass behind the right atrium and superior vena cava; the left in front of the descending thoracic aorta. THE SYSTEMIC VEINS. The systemic veins may be arranged into three groups : (1) The veins of the heart. (2) The veins of the upper extremities, head, neck, and thorax, which end in the superior vena cava. (3) The veins of the lower extremities, abdomen, and pelvis, which end in the inferior vena cava. THE VEINS OF THE HEART (VV. Cordis) (Fig. 631). Coronary Sinus {sinus coronarius). — Most of the veins of the heart open into the coronary sinus. This is a wide venous channel about 2.25 cm. in length situated in the posterior part of the coronary sulcus, and covered by muscular fibres from the left atrium. It ends in the right atrium between the opening of the inferior vena cava and the atrioventricular aperture, its orifice being guarded by a semilunar valve, the valve of the coronary sinus {vahe of Thehesius). Tributaries. — Its tributaries are the great, small, and middle cardiac veins, the posterior vein of the left ventricle, and the oblique vein of the left atrium, all of which, except the last, are provided with valves at their orifices. 1. The Great Cardiac Vein (v. cordis magna; left coronary vein) begins at the apex of the heart and ascends along the anterior longitudinal sulcus to the base of the ventricles. It then curves to the left in the coronary sulcus, and reaching the back of the heart, opens into the left extremity of the coronary sinus. It receives tributaries from the left atrium and from both ventricles: one, the left marginal vein, is of considerable size, and ascends along the left margin of the heart. 2. The Small Cardiac Vein {v. cordis ixirm; right coronary vein) runs in the coronary sulcus between the right atrium and ventricle, and opens into the right extremity of the coronary sinus. It receives blood from the back of the right atrium and ventricle; the right marginal vein ascends along the right margin of the heart and joins it in the coronary sulcus, or opens directly into the right atrium. THE VEINS OF THE HEAD AND NECK 731 3. The Middle Cardiac Vein (r. cordis- iiicdUi) coinniciices at the apex of the heart, ascends in the posterior longitudinal sulcus, and ends in the coronary sinus near its right cxtrrniity. 4. The Posterior Vein of the Left Ventricle ( i\ po^'terior ventriculi sinistri) runs on the diaphragmatic surface of the left ventricle to the coronary sinus, hut may end in the great cardiac vein. 5. The Oblique Vein of the Left Atrium («. ohliqua atrii sinistri [Marshalli] ; oblique vein of Marshall) is a small vessel which descends obliquely on the back of the left atrium and ends in the coronary sinus near its left extremity; it is continuous above with the ligament of the left vena cava {lig. venae cav'ae sinistrae; vestigial fold of Marshall), and the two structures form the remnant of the left Cuverian duct. Azygos vein Left 'pulmonary veins Oblique vein of left atrium Great cardiac vein Left marginal vein Rigid pulmonary veins Small cardiac vein Posterior vein of left ventricle Middle cardiac vein, Fig. 631. — Base and diaphragmatic surface of heart. The following cardiac veins do not end in the coronary sinus: (1) the anterior cardiac veins, comprising three or four small vessels which collect blood from the front of the right ventricle and open into the right atrium ; the right marginal vein frequently opens into the right atrium, and is therefore sometimes regarded as belonging to this group; (2) the smallest cardiac veins {veins of Thehesius), con- sisting of a number of minute veins wdiich arise in the muscular wall of the heart; the majority open into the atria, but a few end in the ventricles. THE VEINS OF THE HEAD AND NECK. The veins of the head and neck may be subdivided into three groups: (1) The veins of the exterior of the head and face. (2) The veins of the neck. (3) The diploic veins, the veins of the brain, and the venous sinuses of the dura mater. 732 ANGIOLOGY The Veins of the Exterior of the Head and Face (Fig. G32). The veins of the exterior of the head and face are: Frontal. Supraorbital. Angular. Anterior Facial. Occipital. Superficial Temporal Internal Maxillary. Posterior Facial. Posterior Auricular. Frmfal Coiinininicating branch uith ophthalmic vein Angular Lingval PhatyngeaZ Superior thyroid Fig. 632. — Veins of the head and neck. The frontal vein (y. frontalis) hegins on the forehead in a venous plexus which communicates with the frontal branches of the superficial temporal vein. The veins converge to form a single trunk, which runs downward near the middle line of the forehead parallel with the vein of the opposite side. The two veins are joined, at the root of the nose, by a transverse branch, called the nasal arch, which receives some small veins from the dorsum of the nose. At the root of the nose the veins diverge, and, each at the medial angle of the orbit, joins the supraorbital vein, to THE VEINS OF THE EXTERIOR OF THE HEAD AND FACE 733 form the angular vein. Occasionally the frontal veins join to form a single trunk, Avhich bifurcates at the root of the nose into the two angular veins. The supraorbital vein {i\ siiprctorhitaJis) begins on the forehead where it com- municates with the frontal branch of the superficial temporal vein. It runs down- ward superficial to the Frontalis muscle, and joins the frontal vein at the medial angle of the orbit to form the angular vein. Prexious to its junction with the frontal vein, it sends through the supraorbital notch into the orbit a branch which com- municates with the ophthalmic vein; as this vessel passes through the notch, it receives the frontal diploic vein through a foramen at the bottom of the notch. The angular vein (v. angularis) formed by the junction of the frontal and supra- orbital veins, runs obliquely downward, on the side of the root of the nose, to the level of the lower margin of the orbit, where it becomes the anterior facial vein. It receives the veins of the ala nasi, and communicates with the superior ophthalmic vein through the nasofrontal vein, thus establishing an important anastomosis between the anterior facial vein and the cavernous sinus. The anterior facial vein {t. facialis anterior; facial rein) commences at the side of the root of the nose, and is a direct continuation of the angular vein. It lies behind the external maxillary (facial) artery and follows a less tortuous course. It runs obliquely dow'nward and backward, beneath the zygomaticus and zygo- matic head of the Quadratus labii superioris, descends along the anterior border and then on the superficial surface of the Masseter, crosses over the body of the mandible, and passes obliquely backward, beneath the Platysma and cervical fascia, superficial to the submaxillary gland, the Digastricus and Stylohyoideus. It unites with the posterior facial vein to form the common facial vein, which crosses the external carotid artery and enters the internal jugular xeva. at a vari- able point below the hyoid bone. From near its termination a communicating branch often runs down the anterior border of the Sternocleidomastoideus to join the lower part of the anterior jugular vein. Tributaries. — The anterior facial vein receives a branch of considerable size, the deep facial vein, from the pter3^goid venous plexus. It is also joined by the superior and inferior palpebral, the superior and inferior labial, the buccinator and the masseteric veins. Below the mandible it receives the submental, palatine, and submaxillary veins, and, generally, the vena comitans of the hypoglossal nerve. Applied Anatomy. — There are some points about the anterior facial vein which render it of great importance in surgery. It is not so flaccid as are most superficial veins, and, in consequence of this, remains more patent when divided. It has, moreover, no valves. It communicates freely with the intracranial circulation, not only at its commencement by the angular and supra- orbital veins which commimicate with the ophthalmic vein, a tributary of the cavernous sinus, but also by the deep facial vein, which communicates through the pterygoid plexus with the cavernous sinus by branches which pass through the foramen ovale and foramen lacerum (see p. 746). These facts have an important bearing upon the surgery of some diseases; any phlegmo- nous inflammation of the face following a poisoned wound is hable to set up thrombosis in the anterior facial vein, and detached portions of the clot may give rise to purulent foci in other parts of the body. On account of its communications with the cerebral sinuses, these thrombi are apt to extend upward into them, and so induce a fatal issue; this has been known to follow in cases of ordinary carbuncle of the face. The position of the vein should always be borne in mind when incisions are made for the rehef of suppm-ation about the mandible. The superficial temporal vein {v. temporalis siiperficialis) begins on the side and vertex of the skull in a plexus which communicates with the frontal and supra- orbital veins, with the corresponding vein of the opposite side, and with the pos- terior auricular and occipital veins. From this net-work frontal and parietal branches arise, and unite above the zygomatic arch to form the trunk of the vein, which is joined in this situation by the middle temporal vein, from the substance of the Tem- poralis. It then crosses the posterior root of the zygomatic arch, enters the sub- stance of the parotid gland, and unites with the internal maxillary vein to form the posterior facial vein. 734 ANGIOLOGY Tributaries.— The superficial temporal vein receives in its course some parotid veins, articular veins from the temporomandibular joint, anterior auricular veins from the auricula, and the transverse facial from the side of the face. The middle temporal vein receives the orbital vein, which is formed by some lateral palpebral branches, and passes backward between the layers of the temporal fascia to join the superficial temporal vein. The pterygoid plexus (plexus pterygoideus) is of considerable size, and is situated between the Temporalis and Pterygoideus externus, and partly between the two Pterygoidei. It receives tributaries corresponding with the branches of the internal maxillary artery. Thus it receives the sphenopalatine, the middle meningeal, the deep temporal, the pterygoid, masseteric, buccinator, alveolar, and some palatine veins, and a branch which communicates with the ophthalmic vein through the inferior orbital fissure. This plexus communicates freely with the anterior facial vein; it also communicates with the cavernous sinus, by branches through the foramen Vesalii, foramen ovale, and foramen lacerum. The internal maxillary vein {v. maxillaris interna) is a short trunk which accom- panies the first part of the internal maxillary artery. It is formed by a confluence of the veins of the pterygoid plexus, and passes backward between the spheno- mandibular ligament and the neck of the mandible, and unites with the temporal vein to form the posterior facial vein. The posterior facial vein («. facialis posterior; temporomaxillary vein), formed by the union of the superficial temporal and internal maxillary veins, descends in the substance of the parotid gland, superficial to the external carotid artery but beneath the facial nerve, between the ramus of the mandible and the Sternocleido- mastoideus muscle. It divides into two branches, an anterior, which passes forward and unites with the anterior facial vein to form the common facial vein and a pos- terior, which is joined by the posterior auricular vein and becomes the external jugular vein. The posterior auricular vein (y. auricularis posterior) begins upon the side of the head, in a plexus which communicates with the tributaries of the occipital, and superficial temporal veins. It descends behind the auricula, and joins the posterior division of the posterior facial vein to form the external jugular. It receive the stylomastoid vein, and some tributaries from the cranial surface of the auricula. The occipital vein iv. occipitalis) begins in a plexus at the back part of the vertex of the skull. From the plexus emerges a single vessel, which pierces the cranial attachment of the Trapezius and, dipping into the suboccipital triangle, joins the deep cervical and vertebral veins. Occasionally it follows the course of the occipital artery and ends in the internal jugular; in other instances, it joins the posterior auricular and through it opens into the external jugular. The parietal emissary vein connects it with the superior sagittal sinus; and as it passes across the mastoid portion of the temporal bone, it receives the mastoid emissary vein which connects it with the transverse sinus. The occipital diploic vein sometimes joins it. The Veins of the Neck (Fig. 633). The veins of the neck, which return the blood from the head and face, are : External Jugular. Anterior Jugular. Posterior External Jugular. Internal Jugular. Vertebral. The external jugular vein («. jugularis externa) receives the greater part of the blood from the exterior of the cranium and the deep parts of the face, being formed by the junction of the posterior division of the posterior facial with the posterior THE VEINS OF THE XECK 735 auricular vein. It commences in the substance of the parotid gland, on a level with the angle of the mandible, and runs perpendicularly down the neck, in the direction of a line drawn from the angle of the mandil)le to the middle of the clavicle at the posterior border of the Sternocleidomastoideus. In its course it crosses the Sternocleidomastoideus obliquely, and in the subclavian triangle perforates the deep fascia, and ends in the subclavian vein, lateral to or in front of the Scalenus anterior. It is separated from the Sternocleidomastoideus by the investing layer of the deep cer^'ical fascia, and is covered by the Platysma, the superficial fascia, and the integument; it crosses the cutaneous cervical nerve, and its upper half runs parallel with the great auricular nerve. The external jugular vein varies in Exl. carotid Subclavian vein Fig. 633. — The veins of the neck, viewed from in front. (After Spalteholz.) size, bearing an inverse proportion to the other veins of the neck, it is occasionally double. It is provided with two pairs of valves, the lower pair being placed at its entrance into the subclavian vein, the upper in most cases about 4 cm. above the clavicle. The portion of vein between the two sets of valves is often dilated, and is termed the sinus. These valves do not prevent the regurgitation of the blood, or the passage of injection from below upward. Tributaries. — ^This vein receives the occipital occasionally, the posterior external jugular, and, near its termination, the transverse cervical, transverse scapular, and anterior jugular veins; in the substance of the parotid, a large branch of commu- nication from the internal jugular joins it. 736 AXGIOLOGY Applied Anatomy. — Venesection used formerly to be performed on the external jugular vein, but is now probably never resorted to. The anatomical point to be remembered in performing this operation is to cut across the fibres of the Platysma in opening the vein, so that by their contraction they will expose the orifice in the vein and so allow the flow of blood. The posterior external jugular vein («. jngvlaris jxjsterior) begins in the occipital region and returns the blood from the skin and superficial muscles in the upper and back part of the neck, lying between the Splenius and Trapezius. It runs down the back part of the neck, and opens into the external jugular vein just below the middle of its course. The anterior jugular vein (v. jngvlaris anterior) begins near the hyoid bone by the confluence of several superficial veins from the submaxillary region. It descends between the median line and the anterior border of the Sternocleidomastoideus, and, at the lower part of the neck, passes beneath that muscle to open into the ter- mination of the external jugular, or, in some instances, into the subclavian vein (Figs. 632, 633). It varies considerably in size, bearing usually an inverse propor- tion to the external jugular; most frequently there are two anterior jugulars, a right and left; but sometimes only one. Its tributaries are some laryngeal veins, and occasionally a small thyroid vein. Just above the sternum the two anterior jugular veins communicate by a transverse trunk, the venous jugular arch, which receive tributaries from the inferior thyroid veins; each also communicates with the internal jugular. There are no valves in this vein. The internal jugular vein {v. jugularis interna) collects the blood from the brain, from the superficial parts of the face, and from the neck. It is directly continuous with the transverse sinus, and begins in the posterior compartment of the jugular foramen, at the base of the skull. At its origin it is somewhat dilated, and this dilatation is called the superior bulb. It runs down the side of the neck in a vertical direction, lying at first lateral to the internal carotid artery, and then lateral to the common carotid, and at the root of the neck unites with the subclavian vein to form the innominate vein; a little above its termination is a second dilatation, the inferior bulb. Above, it lies upon the Rectus capitis lateralis, behind the internal carotid artery and the nerves passing through the jugular foramen; lower down, the vein and artery lie upon the same plane, the glossopharyngeal and hypoglossal nerves passing forward between them; the vagus descends between and behind the vein and the artery in the same sheath, and the accessory riins obliquely backward, superficial or deep to the vein. At the root of the neck the right internal jugular vein is placed at a little distance from the common carotid arterj-, and crosses the first part of the subclavian artery, while the left internal jugular vein usually overlaps the common carotid artery. The left vein is generally smaller than the right, and each contains a pair of valves, which are placed about 2.5 cm. above the termination of the vessel. Tributaries. — This vein receives in its course the inferior petrosal sinus, the common facial, lingual, pharyngeal, superior and middle thyroid veins, and some- times the occipital. The thoracic duct on the left side and the right lymphatic duct on the right side open into the angle of union of the internal jugular and subclavian veins. The Inferior Petrosal Sinus (sinus petrosus inferior) leaves the skull through the anterior part of the jugular foramen, and joins the superior bulb of the internal jugular vein. The Lingual Veins (vv. linguales) begin on the dorsum, sides, and under surface of the tongue, and, passing backward along the course of the lingual artery, end in the internal jugular vein. The vena comitans of the hypoglassal nerve (ranine vein), a branch of considerable size, begins below the tip of the tongue, and may join the lingual; generally, however, it passes backw^ard on the Hyoglossus, and joins the common facial. THE VEINS OF THE NECK 737 The Pharyngeal Veins {in\ pliari/iigcac) begin in the pharyngeal plexus on the outer surface of the pharynx, and, after receiving some posterior meningeal veins and the vein of the pterygoid canal, end in the internal jugular. They occasionally open into the facial, lingual, or superior thyroid \'ein. The Superior Thyroid Vein (c. fin/reuidea siqjerioris) (Fig. ()34) begins in the sub- stance and on the surface of the thyroid gland, by tributaries corresponding with the branches of the superior thyroid artery, and ends in the upper part of the internal jugular vein. It receives the superior laryngeal and cricothyroid veins. The Middle Thyroid Vein (Fig. ()34) collects the blood from the lower part of the thyroid gland, and after being joined by some veins from the larynx and trachea, ends in the lower part of the internal jugular vein. The common facial and occipital veins have been described. External carotid artery Superior thyroid artery Vagus nerve ^j Superior thyroid vein — Middle thyroid vein Fig. 634. — The veins of the thyroid gland. Applied Anatomy. — The internal jugular vein requires ligature in cases of septic thrombosis of the transverse sinus, in order to prevent septic emboli being carried into the general circula- tion. This operation has been performed in many cases, with the most satisfactory results. The cases are generaUy those of chronic disease of the middle ear, with discharge of pus which perhaps has existed for many years. The patient is seized with acute septic inflammation, spread- ing to the mastoid cells, and setting up septic thrombosis of the transverse sinus and extending downward into the internal jugular vein. Such cases are always extremely grave, for there is danger of portions of the septic clot being detached and causing septic embohsm in the lungs, the portions of clot having passed through the right side of the heart. If the condition be sus- pected, the diseased bone should be removed at once from the mastoid process. The sinus is then investigated, and if it be found thrombosed, the surgeon should proceed to ligature the internal jugular vein, by an incision along the anterior border of the Sternocleidomastoideus, the centre of which is on a level with the greater cornu of the hyoid bone. The vein should be hgatured in two places and divided between. After the vessel has been seciu-ed and divided, the transverse sinus is to be thoroughly cleared out, and, by removing the ligature from the upper end of the divided vein, all septic clots removed by syringing from the sinus through the vein. If hemorrhage occur from the distal end of the sinus, it can be arrested by careful plugging with antiseptic gauze. 47 738 AXGIOLOGY The internal jugular vein is also surgically important, because it is surrounded by a large number of deep cervical lymph glands; and when these are enlarged in tuberculous or malignant disease, they are apt to become adherent to the vessel, rendering their removal difficult and often dangerous. The proper course to pm-sue in these cases is to ligatm-e the vessel above and below the glandular mass, and resect the included portion together with the glands. Cardiac pulsation is often demonstrable in the internal jugular vein at the root of the neck. There are no valves in the innominate veins or superior vena cava; in consequence, the systole of the right atrium causes a wave to pass up these vessels, and when the conditions are favorable this wave appears as a somewhat feeble flicker over the internal jugular vein at the root of the neck, quite distinct from, and just preceding, the more forcible impulse transmitted from the underlying common carotid artery and due to the ventricular systole. This atrial systolic venous impulse is much increased in conditions in which the right atrium is abnormally distended with blood or is hjTsertrophied, as is often the case in disease of the bicuspid valve. In Stokes-Adams disease (p. 614) it is this pulsation which gives evidence of the fact that the atria are beating faster — often two or three times faster — than the ventricles. The vertebral vein {a. Tertebralis) is formed in the suboccipital triangle, from numerous small tributaries which spring from the internal vertebral venous plexuses and issue from the vertebral canal above the posterior arch of the atlas. They unite with small veins from the deep muscles at the upper part of the back of the neck, and form a vessel which enters the foramen in the transverse process of the atlas, and descends, forming a dense plexus around the vertebral artery, in the canal formed by the foramina transversaria of the cervical vertebrae. This plexus ends in a single trunk, which emerges from the foramen transversarium of the sixth cervical vertebra, and opens at the root of the neck into the back part of the innominate vein near its origin, its mouth being guarded by a pair of valves. On the right side, it crosses the first part of the subclavian artery. Tributaries. — The vertebral vein communicates with the transverse sinus by a vein which passes through the condyloid canal, when that canal exists. It receives branches from the occipital vein and from the prevertebral muscles, from the internal and external vertebral venous plexuses, from the anterior vertebral and the deep cervical veins; close to its termination it is sometimes joined by the first intercostal vein. The Anterior Vertebral Vein commences in a plexus around the transverse pro- cesses of the upper cervical vertebrae, descends in company wdth the ascending cervical artery between the Scalenus anterior and Longus capitis muscles, and opens into the terminal part of the vertebral vein. The Deep Cervical Vein (v. cervicalis iirofunda; posterior vertebral or yosterior deep cervical vein) accompanies its artery between the Semispinales capitis and colli. It begins in the suboccipital region by communicating branches from the occipital vein and by small veins from the deep muscles at the back of the neck. It receives tributaries from the plexuses around the spinous processes of the cer- vical vertebrse, and terminates in the lower part of the vertebral vein. The Diploic Veins (Venae Diploicae) (Fig. 635). The diploic veins occupy channels in the diploe of the cranial bones. They are large and exhibit at irregular intervals pouch-like dilatations; their walls are thin, and formed of endothelium resting upon a layer of elastic tissue. So long as the cranial bones are separable from one another, these veins are confined to the particular bones; but when the sutures are obliterated, they unite with each other, and increase in size. They communicate with the meningeal veins and the sinuses of the dura mater, and with the veins of the pericranium. They consist of (1) the frontal, which opens into the supraorbital vein and the superior sagittal sinus; (2) the anterior temporal, which is confined chiefly to the frontal bone, and opens into the sphenoparietal sinus and into one of the deep temporal veins, through an aperture in the great wing of the sphenoid; (3) the THE VEIXS OF THE BRAiy 739 posterior temporal, which is situated in the parietal hone, and ends in the transverse sinus, through an aperture at the mastoid ang'le of the parietal bone or through the mastoid foramen; and (4) the occipital, the largest of the four, which is confined to the occipital hone, and opens either externally into the occipital vein, or inter- nally into the transverse sinus or into the confluence of the sinuses {torcular IlcrophUi). Fig. 635. — Veins of the diploe as displayed by the removal of the outer table of the skull. The Veins of the Brain. The veins of the brain possess no valves, and their walls, owing to the absence of muscular tissue, are extremely thin. They pierce the arachnoid membrane and the inner or meningeal layer of the dura mater, and open into the cranial venous sinuses. They may be divided into tw^o sets, cerebral and cerebellar. The cerebral veins {vv. cerebri) are divisible into external and internal groups according as they drain the outer surfaces or the inner parts of the hemispheres. The external veins are the superior, inferior, and middle cerebral. The Superior Cerebral Veins {vv. cerebri swperiores) , eight to twelve in number, drain the superior, lateral, and medial surfaces of the hemispheres, and are mainly lodged in the sulci between the gyri, but some run across the gyri. They open into the superior sagittal sinus; the anterior veins runs nearly at right angles to the sinus ; the posterior and larger veins are directed obliquely forward and open into the sinus in a direction more or less opposed to the current of the blood contained within it. The Middle Cerebral Vein {v. cerebri media; superficial Sylvian vein) begins on the lateral surface of the hemisphere, and, running along the lateral cerebral fissure, ends in the cavernous or the sphenoparietal sinus. It is connected (a) w-ith the superior sagittal sinus by the great anastomotic vein of Trolard, which opens into one of the superior cerebral veins; (b) wdth the transverse sinus by the posterior anasto- motic vein of Labbe, wdiich courses over the temporal lobe. The Inferior Cerebral Veins (vv. cerebri inferiores), of small size, drain the under surfaces of the hemispheres. Those on the orbital surface of the frontal lobe join the superior cerebral veins, and through these open into the superior sagittal sinus; those of the temporal lobe anastomose with the middle cerebral and basal veins, and join the cavernous, sphenoparietal, and superior petrosal sinuses. 740 ANGIOLOGY The basal vein is formed at the anterior perforated substance by the union of {a) a small anterior cerebral vein which accompanies the anterior cerebral artery, (6) the deep middle cerebral vein {deep Sylvian vein), which receives tributaries from the insula and neighboring gyri, and runs in the lower part of the lateral cerebral fissure, and (c) the inferior striate veins, which leave the corpus striatum through the anterior perforated substance. The basal vein passes backward around the cerebral peduncle, and ends in the internal cerebral vein (vein of Galen) ; it receives tributaries from the interpeduncular fossa, the inferior horn of the lateral ventricle, the hippocampal gyrus, and the mid-brain. The Internal Cerebral Veins {m. cerebri internae; veins of Galen; deep cerebral veins) drain the deep parts of the hemisphere and are two in number; each is formed near the interventricular foramen by the union of the terminal and choroid veins. They ran backward parallel with one another, between the layers of the tela chorioidea of the third ventricle, and beneath the splenium of the corpus callosum, where they unite to form a short trunk, the great cerebral vein; just before their union each receives the corresponding basal vein. The terminal vein (v. terminalis; vena corporis striati) commences in the groove between the corpus striatum and thalamus, receives numerous veins from both of these parts, and unites behind the crus fornicis with the choroid vein, to form one of the internal cerebral veins. The choroid vein runs along the whole length of the choroid plexus, and receives veins from the hippocampus, the fornix, and the corpus callosum. The Great Cerebral Vein (v. cerebri magna [Galeni]; great vein of Galen), formed by the union of the two internal cerebral veins, is a short median trunk which curves backward and upward around the splenium of the corpus callosum and ends in the anterior extremity of the straight sinus. The cerebellar veins are placed on the surface of the cerebellum, and are dis- posed in two sets, superior and inferior. The superior cerebellar veins (vv. cerebelli superiores) pass partly forward and medialward, across the superior vermis, to end in the straight sinus and the internal cerebral veins, partly lateralward to the trans- verse and superior petrosal sinuses. The inferior cerebellar veins {vv. cerebelli infe- riores) of large size, end in the transverse, superior petrosal, and occipital sinuses. The Sinuses of the Dura Mater (Sinus Durae Matris). Ophthalmic Veins and Emissary Veins. The sinuses of the dura mater are venous channels which drain the blood from the brain; they are devoid of valves, and are situated between the two layers of the dura mater and lined by endothelium continuous with that which lines the veins. They may be divided into two groups: (1) a postero-superior, at the upper and back part of the skull, and (2) an antero-inferior, at the base of the skull. The postero-superior group comprises the Superior Sagittal. Straight. Inferior Sagittal. Two Transverse. Occipital. The superior sagittal sinus {sinus sagittalis superior; superior longitudinal sinvs) (Figs. 636, 637) occupies the attached or convex margin of the falx cerebri. Com- mencing at the foramen cecum, through which it receives a vein from the nasal cavity, it runs from before backward, grooving the inner surface of the frontal, the adjacent margins of the two parietals, and the superior division of the cruciate eminence' of the occipital; near the internal occipital protuberance it deviates to one or other side (usually the right), and is continued as the corresponding trans- verse sinus. It is triangular in section, narrow in front, and gradually increases in THE SINUSES OF THE DURA MATER 741 size as it passes backward. Its inner surface presents the openings of the superior cerebral veins, which run, for the most part, obhquely forward, and open chiefly at the back part of tlie sinus, their orifices being concealed by fibrous folds ; numerous fibrous bands (chordae IVillLstl) extend transversely across the inferior angle of the sinus; and, lastly, small openings communicate with irregularly shaped venous spaces {venous lacunoe) in the dura mater near the sinus. There are usually three lacuntie on either side of the sinus: a small frontal, a large parietal, and an occipital, intermediate in size between the other two (Sargent^- Most of the cerebral veins from the outej surface of the hemisphere open into these lacunar, and numer- ous arachnoid granulations {Pacchionian bodies) project into them from below. The superior sagittal sinus receives the superior cerebral veins, veins from the diploe and dura mater, and, near the posterior extremity of the sagittal suture, veins from the pericranium, which pass through the parietal foramina. Dural vein Superior sagittal sinus |i;,. Venous lacuna Venous lacun Fig. 636. — Superior sagittal sinus laid open after removal of the skull cap. The chordae Willisii are clearly seen. The venous lacunae are also well shown; from two of them probes are passed into the superior sagittal sinus. (Poirier and Charpy.) Applied Anatomy. — The numerous communications which take place between this sinus and the veins of the nose, scalp, and diploe, cause it to be at times the seat of infective thrombosis from suppurative processes in these parts. The inferior sagittal sinus (sinus sagittalis inferior; inferior longitudinal sinus) (Fig. 637) is contained in the posterior half or two-thirds of the free margin of the falx cerebri. It is of a cylindrical form, increases in size as it passes backward, and ends in the straight sinus. It receives several veins from the falx cerebri, and occasionally a few from the medial surfaces of the hemispheres. The straight sinus (siiiiis rectus; tentorial sinus) (Figs. 637, 638) is situated at the line of junction of the falx cerebri with the tentorium cerebelli. It is triangular 1 Journal of Anatomy and Physiology, vol. xlv. 742 AXGIOLOGY in section, increases in size as it proceeds backward, and runs downward and back- ward from the end of the inferior sagittal sinus to the transverse sinus of the oppo- site side to that into which the superior sagittal sinus is prolonged. Its terminal part communicates by a cross branch with the confluence of the sinuses. Besides the inferior sagittal sinus, it receives the great cerebral vein (great vein of Galen) and the superior cerebellar veins. A few^ transverse bands cross its interior. Great cerebral vein Glossophai-yngeal nerve Vagus nerce Accessory nerve Acoustic nerve Facial nerve Abducent nerve Trigeminal nerve Fig. 637. — Dura mater and its processes exposed By removing part of the right half of the skull, and the brain. The transverse sinuses {sinus transversns; lateral sinuses) (Figs. 638, 639) are of large size and begin at the internal occipital protuberance; one, generally the right, being the direct continuation of the superior sagittal sinus, the other of the straight sinus. Each transverse sinus passes lateralward and forward, describing a slight curve with its convexity upward, to the base of the petrous portion of the temporal bone, and lies, in this part of its course, in the attached margin of the tentorium cerebelli; it then leaves the tentorium and curves downw^ard and medialward to reach the jugular foramen, where it ends in the internal jugular vein. In its course it rests upon the squama of the occipital, the mastoid angle of the parietal, the mastoid part of the temporal, and, just before its termination, the jugular process of the occipital; the portion which occupies the groove on the mastoid part of the temporal is sometimes termed the sigmoid sinus. The trans- verse sinuses are frequently of unequal size, that formed by the superior sagittal sinus being the larger; they increase in size as they proceed from behind forward. On transverse section the horizontal portion exhibits a prismatic, the curved THE SINUSES OF THE DURA MATER 743 portion a semicyliiidrical I'orm. They receive the blood from the superior petrosal sinuses at the base of the petrous portion of the temporal bone; they communicate with the veins of the pericranium by means of the mastoid and condyloid emissary veins; and they receive some of the inferior cerebral and inferior cerebellar veins, and some veins from the diploe. The petrosquamous sinus, when present, runs backward along the junction of the squama and petrous portion of the temporal, and opens into the transverse sinus. optic lien Biaphragma sellcti Free margin of tentorixtm Internal carotid artery Oculoinofor nerve Attached margin of tentorium Conjluence of the hunises Fig. 63S. — Tentorium cerebelli from above. The occipital sinus {sinus occipitalis) (Fig. 639) is the smallest of the cranial sinuses. It is situated in the attached margin of the falx cerebelli, and is generally single, but occasionally there are two. It commences around the margin of the for- amen magnum by several small venous channels, one of which joins the terminal part of the transverse sinus; it communicates with the posterior internal vertebral venous plexuses and ends in the confluence of the sinuses. The Confluence of the Sinuses {confluens siniium; torcidar Herophili) is the term applied to the dilated extremity of the superior sagittal sinus. It is of irregular form, and is lodged on one side (generally the right) of the internal occipital pro- tuberance. From it the transverse sinus of the same side is derived. It receives also the blood from the occipital sinus, and is connected across the middle hne with the commencement of the transverse sinus of the opposite side. The antero-inferior group of sinuses comprises the Two Cavernous. Two Superior Petrosal. Two Intercavernous. Tw^o Inferior Petrosal. Basilar Plexus. 744 ANGIOLOGY The cavernous sinuses (sim(s cavernosus) (Fig. 639) are so named because they present a reticidated structure, due to their being traversed by numerous inter- lacing fihiments. They are of irreguhir form, hirger behind than in front, and are placed one on either side of the body of the sphenoid bone, extending from the superior orbital fissure to the apex of the petrous portion of the temporal bone. Each opens behind into the petrosal sinuses. On the medial wall of each sinus is the internal carotid artery, accompanied by filaments of the carotid plexus; near the artery is the abducent ner^'e; on the lateral wall are the oculomotor and troch- lear nerves, and the ophthalmic and maxillary divisions of the trigeminal nerve Levator p^ilpebrce Rectus superior, Sup. oph- ihalmic vein Sphenoparietal s'nus End of straight sinus Vertebral artery Superior sagittal sinus Fig. 639. — The sinuses at the base of the skull. (Fig. 640). These structures are separated from the blood flowing along the sinus by the lining membrane of the sinus. The cavernous sinus receives the superior ophthalmic vein through the superior orbital fissure, some of the cerebral veins, and also the small sphenoparietal sinus, which courses along the under surface of the small wing of the sphenoid. It communicates with the transverse sinus by means of the superior petrosal sinus; with the internal jugular vein through the inferior petrosal sinus and a plexus of veins on the internal carotid artery; with the ptery- goid venous plexus through the foramen Vesalii, foramen ovale, and foramen lacerum, and with the angular vein through the ophthalmic vein. The two sinuses THE SINUSES OF THE DURA MATER 745 also communicate with each other hy means of the anterior and posterior inter- cavernous sinuses. Applied Anatomy. — An arteriovenous communication may be established between the cavernous sinus and the internal carotid artery, giving rise to a pulsating tumor in the orbit. Ilicse com- munications may be the result of injury, such as a bullet wound, a stab, or a blow, or fall suffi- ciently severe to cause a fracture of the base of the skull in this situation. The syini)toms are sudden noise and pain in the head, followed by exophthalmos, swelling and congestion of the lids and conjunctiva?, and dovelo])ment of Internal carotid artery Cavernous shms Oculoinotor nerve Trochlear nerve Ophthalmic nerve- Abducent nerve Maxillary nerve — ife W '''■^ a pulsating tumor at the margin of the orbit, with thrill and the characteristic bruit; accompanying these symptoms there may be impairment of sight, paralysis of the iris and orbital muscles, and pain of varying intensity. In some cases the opposite orbit becomes affected by the passage of the arterial blood into the opposite sinus by means of the intercavernous sinuses; or the arterial blood may find its way through the emissary veins (see p. 747) into the ptery- goid plexus, and thence into the veins of the face. Pulsating tumors of the . orbit may also be due to traumatic aneurism of one of the orbital arteries, and symptoms resembhng those of pulsating tumor may be produced by pressure on the ophthalmic vein, as it enters the sinus, by an aneurism of the internal carotid artery. Ligature of the internal or common carotid artery has been performed in these cases with considerable success. Of recent years more attention has been paid to thrombosis of the cavernous sinus than formerly, and it is now well established that caries in the upper parts of the nasal cavities and suppuration in certain of the accessory sinuses of the nose are frequently responsible for septic thrombosis of the cavernous sinuses, in exactly the same way as transverse sinus thrombosis is due to septic disease in the mastoid process. Many deaths from meningitis, hitherto unaccounted for, are in reality due to the spread of an infection from an ethmoidal or sphenoidal air cell to the cavernous sinus, and thence to the meninges. It is obvious, therefore, that no case of chronic nasal suppura- tion should be left untieated Fig. 640. — Oblique section through tlie cavernous sinus. Cavernous _^ sinus Inferior ophthalmic Fig. 641. — Veins of orbit. (Poirier and Charpy.) The ophthalmic veins (Fig. 641), two in number, superior and inferior, are devoid of valves. The Superior Ophthalmic Vein (v. ophthalmica suiJerior) begins at the inner angle of the orbit in a vein named the nasofrontal which communicates anteriorly with the angular vein; it pursues the same course as the ophthalmic artery, and receives 746 ANGIOLOGY tributaries corresponding to the branches of that vessel. Forming a short single trunk, it passes between the two heads of the Rectus lateralis and through the medial part of the superior orbital fissure, and ends in the cavernous sinus. The Inferior Ophthalmic Vein («. ophihalmica inferior) begins in a venous net-work at the forepart of the floor and medial wall of the orbit; it receives some veins from the Rectus inferior, Obliquus inferior, lacrimal sac and eyelids, runs backward in the lower part of the orbit and divides into two branches. One of these passes through the inferior orbital fissure and joins the pterygoid venous plexus, while the other enters the cranium through the superior orbital fissure and ends in the cavernous sinus, either by a separate opening, or more frequently in common with the superior ophthalmic vein. The intercavernous sinuses {sini intercavernosi) (Fig. 639) are two in number, an anterior and a posterior, and connect the two cavernous sinuses across the middle line. The anterior passes in front of the hypophysis cerebri, the posterior behind it, and they form with the cavernous sinuses a venous circle (circular sinus) around the hypophysis. The anterior one is usually the larger of the two, and one or other is occasionally absent. The superior petrosal sinus (sinus petrosus superior) (Fig. 639) small and narrow, connects the cavernous with the transverse sinus. It runs lateralward and back- ward, from the posterior end of the cavernous sinus, over the trigeminal nerve, and lies in the attached margin of the tentorium cerebelli and in the superior petrosal sulcus of the temporal bone; it joins the transverse sinus where the latter curves downward on the inner surface of the mastoid part of the temporal. It receives some cerebellar and inferior cerebral veins, and veins from the tympanic cavity. The inferior petrosal sinus (siiius petrosus inferior) (Fig. 639) is situated in the inferior petrosal sulcus formed by the junction of the petrous part of the temporal with the basilar part of the occipital. It begins in the postero-inferior part of the cavernous sinus, and, passing through the anterior part of the jugular foramen, ends in the superior bulb of the internal jugular vein. The inferior petrosal sinus receives the internal auditory veins and also veins from the medulla oblongata, pons, and under surface of the cerebellum. The exact relation of the parts to one another in the jugular foramen is as follows: the inferior petrosal sinus lies medially and anteriorly with the meningeal branch of the ascending pharyngeal artery, and is directed obliquely downward and back- ward; the transverse sinus is situated at the lateral and back part of the foramen with a meningeal branch of the occipital artery, and between the two sinuses are the glossopharyngeal, vagus, and accessory nerves. These three sets of structures are divided from each other by two processes of fibrous tissue. The junction of the inferior petrosal sinus with the internal jugular vein takes place on the lateral aspect of the nerves. The basilar plexus (plexus hasilaris; transverse or basilar sinus) (Fig. 640) con- sists of several interlacing venous channels between the layers of the dura mater over the basilar part of the occipital bone, and serves to connect the two inferior petrosal sinuses. It communicates with the anterior vertebral venous plexus. Emissary Veins (emissaria). — The emissary veins pass through apertures in the cranial wall and establish communication between the sinuses inside the skull and the veins external to it. Some are always present, others only occasionally so. The principal emissary veins are the following: (1) A mastoid emissary vein, usually present, runs through the mastoid foramen and unites the transverse sinus with the posterior auricular or with the occipital vein. (2) A parietal emissary vein passes through the parietal foramen and connects the superior sagittal sinus with the veins of the scalp. (3) A net-work of minute veins (rete canalis hypoglossi) traverses the hypoglossal canal and joins the transverse sinus with the vertebral THE SUPERFICIAL VEINS OF THE UPPER EXTREMITY 747 vein and deep veins of the neck. (4) An inconstant condyloid emissary vein passes through the condyloid canal and connects the transverse sinus with the deep veins of the neck. (5) A net-work of ^'eins (rete Joraminis qvalis) unites the cavernous sinus with the i)terygoid plexus through the foramen ovale. (6) Two or three small veins run through the foramen lacerum and connect the cavernous sinus with the pterygoid plexus. (7) The emissary vein of the foramen of Vesalius connects the same parts. (S) An internal carotid })lexus of veins traverses the carotid canal and unites the cavernous sinus with the internal jugular vein. (9) A vein is trans- mitted through the foramen caecum and connects the superior sagittal sinus with the veins of the nasal cavity. Applied Anatomy. — These emissary veins together with the other communications between the intra- and extracranial circulation are of great importance in surgery. Inflammatory processes commencing on the outside of the skull may travel inward through them, and lead to osteo- phlebitis of the diploe and inflammation of the membranes of the brain. To this in former days was to be attributed one of the principal dangers of wounds of the scalp. By means of these emissary veins blood may be abstracted from the intracranial circulation — e. g., leeches applied behind the ear drain blood almost directly from the transverse sinus", through the mastoid vein. Again, epistaxis in children will frequently relieve severe headache, the blood which flows from the nose being partly derived from the superior sagittal sinus by means of the vein passing through the foramen caecum. THE VEINS OF THE UPPER EXTREMITY AND THORAX. The veins of the upper extremity are divided into two sets, superficial and deep ; the two sets anastomose frequently with each other. The superficial veins are placed immediately beneath the integument between the two layers of superficial fascia. The deep veins accompany the arteries, and constitute the venae comi- tantes of those vessels. Both sets are provided with valves, which are more numerous in the deep than in the superficial veins. The Superficial Veins of the Upper Extremity. The superficial veins of the upper extremity are the digital, metacarpal, cephalic, basilic, median. Digital Veins. — The dorsal digital veins pass along the sides of the fingers and are joined to one another by oblique communicating branches. Those from the adjacent sides of the fingers unite to form three dorsal metacarpal veins (Fig. 642), which end in a dorsal venous net-work opposite the middle of the meta- carpus. The radial part of the net-work is joined hy the dorsal digital vein from the radial side of the index finger and by the dorsal digital veins of the thumb, and is prolonged upward as the cephalic vein. The ulnar part of the net-work receives the dorsal digital vein of the ulnar side of the little finger and is continued upward as the basilic vein. A communicating branch frequently connects the dorsal venous network with the cephalic vein about the middle of the forearm. The volar digital veins on each finger are connected to the dorsal digital veins by oblique intercapitular veins. They drain into a venous plexus which is situated over the thenar and hypothenar eminences and across the front of the wrist. The cephalic vein (Fig. 643) begins in the radial part of the dorsal venous net- work and winds upward around the radial border of the forearm, receiving tribu- taries from both surfaces. Below the front of the elbow it gives off the vena mediana cubiti {median basilic win), which receives a communicating branch from the deep veins of the forearm and passes across to join the basilic vein. The cephalic vein then ascends in front of the elbow in the groove between the Brachioradialis and the Biceps brachii. It crosses superficial to the musculocutaneous nerve and ascends in the groove along the lateral border of the Biceps brachii. In the upper third 748 ANGIOLOGY of the arm it passes between the Pectorahs major and Deltoideus, where it is accom- panied hx the deltoid branch of the thoracoacromial artery. It pierces the coraco- clavicular fascia and, crossing the axillary artery, ends in the axillary vein just below the clavicle. Sometimes it communicates with the external jugular vein by a branch which ascends in front of the clavicle. Dorsal venous neiworJ: Fig. 612. — The veins on the dorsum of the hand. (Bourgery.) The accessory cephalic vein (v. cephalica accessoria) arises either from a small tributory plexus on the back of the forearm or from the ulnar side of the dorsal venous net-work; it joins the cephalic below the elbow. In some cases the accessory cephalic springs from the cephalic above the wrist and joins it again higher up. A large oblique branch frequently connects the basilic and cephalic veins on the back of the forearm. The basilic vein (v. basilica) (Fig. 643) hegiiis in the ulnar part of the dorsal venous network. It runs up the posterior surface of the ulnar side of the forearm and inclines forward to the anterior surface below the elbow, where it is joined by the vena mediana cubiti. It ascends obliquely in the groove between the Biceps brachii and Pronator teres and crosses the brachial artery, from which it is separated THE SUPERFICIAL VEINS OF THE UPPER EXTREMITY 749 by the lacertus fihrosus; filaments of the medial antibrachial cutaneous nerve pass both in front of and l)ehind ward along the medial border of a little below the middle of the arm, and, ascending on the medial side of the brachial artery to the lower border of the Teres major, is con- tinued onward as the axillary vein. The median antibrachial vein {v. mediana antibrachii) drains the venous plexus on the volar surface of the hand. It ascends on the ulnar side of the front of the fore- arm and ends in the basilic vein or in the vena mediana cubiti; in a small proportion of cases it divides into two branches, one of which joins the basilic, the other the cephalic, below the elbow. Applied Anatomy. — Venesection is gen- erally performed at the bend of the elbow, and as a matter of practice the largest vein in this situation is com- monly selected. This is usually the vena mediana cubiti {median basilic), and there are anatomical advantages and disadvantages in selecting this vein. The advantages are, that in addition to its being the largest vessel, and therefore yielding a greater supply of blood, it is the least movable and can be easily steadied on the lacertus fibrosus (bicipital fascia), on which it rests. The disad- vantages are, that it is in close relation- ship with the brachial artery, separated only by the lacertus fibrosus; and for- merly, when venesection was frequently practised, arteriovenous aneurism was no uncommon result of this practice. Intravenous infusion of normal saline solution is very frequently required in modern surgery for all conditions of severe shock and after profuse hemor- rhages, the older method of transfusion of blood having quite sunk into oblivion. The patient's arm is surrounded by a tight bandage so as to impede the venous return, and a small incision is made over the largest vein visible in front of the elbow; a double ligature is now passed around the vein, and the lower one is tied; the vein is then opened and a cannula connected with a funnel by tubing and filled with hot saUne solution is inserted The bandage is next removed from the arm, and two, three, or more pints of fluid are allowed to flow into the vein; when a sufficient quantity has gone in, the upper ligature around the vein is tied and a stitch put in the skin wound. this portion of the vein. It then runs up- the Biceps brachii, perforates the deep fascia Cephalic vein Basilic vein Vena mediana cubiti Basilic vein Medial anti- brachial cutane- ous nerve Median anti- brachial vein Fig. 643. — The superficial veins of the upper extremity. 750 AXGIOLOGY The Deep Veins of the Upper Extremity. The deep veins follow the course of the arteries, forming their venae comitantes. They are generall}' arranged in pairs, and are situated one on either side of the corresponding artery, and connected at intervals by short transverse branches. Deep Veins of the Hand. — The superficial and deep volar arterial arches are each accompanied by a pair of venae comitantes which constitute respectively the superficial and deep volar venous arches, and receive the veins corresponding to the branches of the arterial arches; thus the common volar digital veins, formed by the union of the proper volar digital veins, open into the superficial, and the volar metacarpal veins into the deep volar venous arches. The dorsal metacarpal veins receive perforating branches from the volar metacarpal veins and end in the rarlial veins and in the superficial veins on the dorsum of the wrist. The deep veins of the forearm are the venae comitantes of the radial and ulnar veins and constitute respectively the upward continuations of the deep and super- ficial volar venous arches; they unite in front of the elbow to form the brachial veins. The radial veins are smaller than the ulnar and receive the dorsal meta- carpal veins. The ulnar veins receive tributaries from the deep volar venous arches and communicate wdth the superficial veins at the wrist; near the elbow they receive the volar and dorsal interosseous veins and send a large communicating branch (profunda vein) to the vena mediana cubiti. The brachial veins {vv. hrachiales) are placed one on either side of the brachial artery, receiving tributaries corresponding with the branches given off from that vessel; near the lower margin of the Subscapularis, they join the axillary vein; the medial one frequently joins the basilic vein. These deep veins have numerous anastomoses, not only with each other, but also with the superficial veins. The axillary vein (v. axillaris) begins at the lower border of the Teres major, as the continuation of the basilic vein, increases in size as it ascends, and ends at the outer border of the first rib as the subclavian vein. Near the lower border of the Subscapularis it receives the brachial veins and, close to its termination, the cephalic vein; its other tributaries correspond with the branches of the axillary artery. It lies on the medial side of the artery, w^hich it partly overlaps; between the two vessels are the medial cord of the brachial plexus, the median, the ulnar, and the medial anterior thoracic nerves. It is provided with a pair of valves oppo- site the lower border of the Subscapularis; valves are also found at the ends of the cephalic and subscapular A^eins. Applied Anatomy. — Since the axillary vein is superficial to and larger than the axillary artery, which it overlaps, it is more hable to be wounded than the artery in the operation of extirpation of the axillary glands, especially as these glands, when diseased, are apt to become adherent to it. When it is wounded, tTiere is always a danger of air being drawn into it, and death resulting. To avoid wounding the axillary vein in the extirpation of glands from the axilla, it is advisable to expose the vein as soon as possible; no sharp cutting instruments should be used after the axiUary cavity has been freely exposed; and care should be taken to use no undue force in isolating the glands (see p. 781). Should the vein be so imbedded in a maUgnant deposit that the latter cannot be removed without taking away a part of the vein, this must be done after the vessel has been ligatured above and below. The subclavian vein (v. subclavia), the continuation of the axillary, extends from the outer border of the first rib to the sternal end of the clavicle, where it unites wdth the internal jugular to form the innominate vein. It is in relation, in front, with the clavicle and Subclavius; hehind and above, with the subclavian artery, from which it is separated medially by the Scalenus anterior and the phrenic nerve. Beloic, it rests in a depression on the first rib and upon the pleura. It is usually provided with a pair of valves, which are situated about 2.5 cm. from its termination. THE VEINS OF THE THORAX 751 The subclavian vein occasionally rises in the neck to a level with the third part of the subclavian artery, and occasionally j^asses with this vessel behind the Scalenus anterior. Tributaries. — This vein receives the external ju^mlar vein, sometimes the anterior jugular vein, and occasionally a small branch, which ascends in front of the clavicle, from the cejihalic. At its angle of junction with the internal jugular, the left subcla^•ian \eu\ receives the thoracic duct, and the right subclavian \'ein the right lymphatic duct. The Veins of the Thorax (Fig. 644) The innominate veins i^vv. anonymae; bmchiucephalic veins) are tw^o large trunks, placed one on either side of the root of the neck, and formed by the union of the internal jugular and subclavian veins of the corresponding side; they are devoid of valves. The Right Innominate Vein (v. anonyma dextra) is a short vessel, about 2.5 cm. in length, which begins behind the sternal end of the clavicle, and, passing almost vertically downward, joins w-ith the left innominate vein just below the cartilage of the first rib, close to the right border of the sternum, to form the superior vena cava. It lies in front and to the right of the innominate artery; on its right side are the phrenic nerve and the pleura, w^hich are interposed between it and the apex of the lung. This vein, at its commencemnt, receives the right vertebral vein; and, lower down, the right internal mammary and right inferior thyroid veins, and some- times the vein from the first intercostal space. The Left Innominate Vein {v. anonyma sinistra), about 6 cm. in length, begins behind the sternal end of the clavicle and runs obliquely downw-ard and to the right behind the upper half of the manubrium sterni to the sternal end of the first right costal cartilage, where it unites with the right innominate vein to form the superior vena cava. It is separated from the manubrium sterni by the Sterno- hyoideus and Sternothyreoideus, the thymus or its remains, and some loose areolar tissue. Behind it are the three large arteries, innominate, left common carotid, and left subclavian, arising from the aortic arch, together wdth the vagus and phrenic nerves. The left innominate vein may occupy a higher level, crossing the jugular notch and lying directly in front of the trachea. Tributaries. — Its tributaries are the left vertebral, left internal mammary, left inferior thyroid, and the left highest intercostal veins, and occasionally some thymic and pericardiac veins. Peculiarities. — Sometimes the innominate veins open separately into the right atrium; in such cases the right vein takes the ordinary course of the superior vena cava; the left vein — left superior vena cava, as it is then termed — which may commimicate by a small branch with the right one, passes in front of the root of the left lung, and, turning to the back of the heart, ends in the right atrium. This occasional condition in the adult is due to the persistence of the early fetal condition, and is the normal state of things in birds and some mammaha. The internal mammary veins {vv. mammariae internae) are venae comitantes to the lower half of the internal mammary artery, and receive tributaries corre- sponding to the branches of the artery. They then unite to form a single trunk, which runs up on the medial side of the artery and ends in the corresponding innominate vein. The superior phrenic vein, i. e., the vein accompanying the peri- cardiacophrenic artery, usually opens into the internal mammary vein. The inferior thyroid veins (vv. thyreoideae inferiores) two, frequently three or four, in number, arise in the venous plexus on the thyroid gland, communicating with the middle and superior thyroid veins. They form a plexus in front of the trachea, behind the Sternothyreoidei. From this plexus, a left vein descends and joins the left innominate trunk, and a right vein passes obliquely downward and to the right across the innominate artery to open into the right innominate vein. 752 ANGIOLOGY just at its junction with the superior vena cava; sometimes the right and left veins open by a common trunk in the latter situation. These veins receive oesophageal, Anterior jugxdar Superior thyroid Middle thyroi External jugular Internal mammal 1/ Suprarenal Suprar Fig. 644. — The venae cavae and azygos veins, with their tributaries. tracheal, and inferior laryngeal veins, and are provided with valves at their terminations in the innominate veins. THE VEINS OF THE THORAX ■ 753 The highest intercostal vein (r. intcrcosiaUs suyrema; superior intercostal veins) (right and left) drain the blood from the upper three or four intercostal spaces. The right vein {v. intcrcostaJis suprema dextra) passes downward and opens into the vena azy^os; the left vein (r. intercostalis suprema sinistra) runs across the arch of the aorta and the origins of the left subclavian and left common carotid arteries antl opens into the left innominate xem. It usually receives the left bronchial vein, and sometimes the left superior phrenic vein, and communicates below witli the accessory hemiazygos vein. The superior vena cava (('. cava superior) drains the l)lood from the upper half of the body. It measures about 7 cm. in length, and is formed by the junction of the two innominate veins. It begins immediately below the cartilage of the right first rib close to the sternum, and, descending vertically behind the first and second intercostal spaces, ends in the upper part of the right atrium opposite the upper border of the third right costal cartilage : the lower half of the vessel is within the pericardium. In its course it describes a slight curve, the convexity of which is to the right side. Relations. — In front are the anterior margins of the right kmg and pleura with the pericardium intervening below; these separate it from the first and second intercostal spaces and from the second and third right costal cartilages; behind it are the root of the right lung and the right vagus nerve. On its right side are the phrenic nerve and right pleura; on its left side, the com- mencement of the innominate artery and the ascending aorta, the latter overlapping it. Just before it pierces the pericardium, it receives the azygos vein and several small veins from the pericardium and other contents of the mediastinal cavity. The portion contained within the pericardium is covered, in front and laterally, by the serous layer of the membrane. The superior vena cava has no valves. The azygos vein {v. azygos; vena azygos major) begins opposite the first or second lumbar vertebra, by a branch, the ascending lumbar vein (page 763) ; sometimes by a branch from the right renal vein, or from the inferior vena cava. It enters the thorax through the aortic hiatus in the Diaphragma, and passes along the right side of the vertebral column to the fourth thoracic vertebra, where it arches forward over the root of the right lung, and ends in the superior vena cava, just before that vessel pierces the pericardium. In the aortic hia*lus, it lies with the thoracic duct on the right side of the aorta; in the thorax it lies upon the intercostal arteries, on the right side of the aorta and thoracic duct, and is partly covered by pleura. Tributaries. — It receives the right subcostal and intercostal veins, the upper three or four of these latter opening by a common stem, the highest superior intercostal vein. It receives the hemiazygos veins, several oesophageal, mediastinal, and peri- cardial veins, and, near its termination, the right bronchial vein. A few imperfect valves are found in the azygos vein; but its tributaries are provided with complete valves. The intercostal veins on the left side, below the upper three intercostal spaces, usually form two trunks, named the hemiazygos and accessory hemiazygos veins. The Hemiazygos Veins {v. hemiazygos; vena azygos minor inferior) begins in the left ascending lumbar or renal vein, Tt enters the thorax, through the left crus of the Diaphragma, and, ascending on the left side of the vertebral column, as high as the ninth thoracic vertebra, passes across the column, behind the aorta, oeso- phagus, and thoracic duct, to end in the azygos vein. It receives the low^er four or five intercostal veins and the subcostal vein of the left side, and some oesophageal and mediastinal veins. The Accessory Hemiazygos Vein {v. hemiazygos accessoria; vena azygos minor supe- rior) descends on the left side of the vertebral column, and varies inversely in size with the highest left intercostal vein. It receives veins from the three or four intercostal spaces between the highest left intercostal vein and highest tributary of the hemiazygos; the left bronchial vein sometimes opens into it. It either crosses 48 754 ANGIOLOGY the body of the eighth thoracic vertebra to join the azygos vein or ends in the hemiazygos. When this vein is small, or altogether wanting, the left highest intercostal vein may extend as low as the fifth or sixth intercostal space. Applied Anatomy. — In obstruction of the superior vena cava, the azygos and hemiazygos veins are one of the principal means by which the venous circulation is carried on, connecting as thej^ do the superior and inferior venae cavae, and communicating with the common ihac veins by the ascending lumbar veins and with many of the tributaries of the inferior vena cava. Thrombosis of the superior vena cava is oftenest due to pressure exerted on the vessel by an aneurism or a tumor; it may also occur by propagation of clotting from a tributary peripheral vein. If occlusion of the vessel take place slowly, a collateral venous circulation may be estab- lished; the patient will have some oedema with dilatation and congestion of the veins about the head and neck, and may also suffer from attacks of dyspnoea and recurrent pleural effusion. In most cases, however, the blockage of the superior cava takes place rapidly, and is rapidly fatal . The Bronchial Veins (vv. bronchiales) return the blood from the larger bronchi, and from the structures at the roots of the lungs; that of the right side opens into the azygos vein, near its termination; that of the left side, into the highest left inter- costal or the accessory hemiazygos vein. A considerable quantity of the blood which is carried to the lungs through the bronchial arteries is returned to the left side of the heart through the pulmonary veins. Posterior external plexuses Fig. 645. — Transverse section of a thoracic vertebra, showing the vertebral venous plexuses. Fig. 6i6. — Median sagittal section of two thoracic verte- brae, showing the vertebral venous plexuses. The Veins of the Vertebral Column (Figs. 645, 646). The veins which drain the blood from the vertebral column, the neighboring muscles, and the meninges of the medulla spinalis form intricate plexuses extending along the entire length of the column; these plexuses may be divided into two groups, external and internal, according to their positions inside or outside the vertebral canal. The plexuses of the two groups anastomose freely with each other and end in the intervertebral veins. The external vertebral venous plexuses (plexus venosi vertehrales externi; extra- sinnal veins) best marked in the cervical region, consist of anterior and posterior plexuses which anastomose freely with each other. The anterior external plexuses lie in front of the bodies of the vertebrae, communicate with the basivertebral and intervertebral veins, and receive tributaries from the vertebral bodies. The pos- terior external plexuses are placed partly on the posterior surfaces of the vertebral THE VEINS OF THE LOWER EXTREMITY, ABDOMEN, AND PELVIS 755 arches and tlieir processes, and partly between the deep dorsal muscles. ' They are best developed in the cervical region, and there anastomose with the vertebral, occipital, and deep c(>r\ical \('iiis. The internal vertebral venous plexuses {plc.vu.s- venosl vertebrales inierni; intra- syinal veins) lie within the vertebral canal between the dura mater and the verte- brae, and receive tributaries from the bones and from the medulla spinalis. They form a closer net-work than the external plexuses, and, running mainly in a vertical direction, form four longitudinal veins, two in front and two behind; they therefore may be divided into anterior and posterior groups. The anterior internal plexuses consist of large veins which lie on the posterior surfaces of the vertebral bodies and intervertebral fibrocartilages on either side of the posterior longitudinal ligament; under cover of this ligament they are connected by transverse branches into which the basivertebral veins open. The posterior internal plexuses are placed, one on either side of the middle line in front of the vertebral arches and ligamenta flava, and anastomose by veins passing through those ligaments with the posterior exter- nal plexuses. The anterior and posterior plexuses communicate freely with one another by a series of venous rings {retia venosa vertebrarum) , one opposite each vertebra. Around the foramen magnum they form an intricate net-W'Ork which opens into the vertebral veins and is connected above with the occipital sinus, the basilar plexus, the condyloid emissary vein, and the rete canalis hypoglossi. The basivertebral veins (vv. basivertebrales) emerge from the foramina on the posterior surfaces of the vertebral bodies. They are contained in large, tortuous channels in the substance of the bones, similar in every respect to those found in the diploe of the cranial bones. They communicate through small openings on the front and sides of the bodies of the vertebrae with the anterior external vertebral plexuses, and converge behind to the principal canal, which is sometimes double toward its posterior part, and open by valved orifices into the transverse branches which unite the anterior internal vertebral plexuses. They become greatly enlarged in advanced age. The intervertebral veins (vv. intervertebrales) accompany the spinal nerves through the intervertebral foramina; they receive the veins from the medulla spinalis, drain the internal and external vertebral plexuses and end in the vertebral, intercostal, lumbar, and lateral sacral veins, their orifices being provided wdth valves. The veins of the medulla spinalis {vv. spinales; veins of the spinal cord) are situated in the pia mater and form a minute, tortuous, venous plexus. They emerge chiefly from the median fissures of the medulla spinalis and are largest in the lumbar region. In this plexus there are (1) two median longitudinal veins, one in front of the anterior fissure, and the other behind the posterior sulcus of the cord, and (2) four lateral longitudinal veins which run behind the nerve roots. They end in the intervertebral veins. Near the base of the skull they unite, and form two or three small trunks, which communicate with the vertebral veins, and then end in the inferior cerebellar veins, or in the inferior petrosal sinuses. THE VEINS OF THE LOWER EXTREMITY, ABDOMEN, AND PELVIS. The veins of the lower extremity are subdivided, like those of the upper, into two sets, superficial and deep ; the superficial veins are placed beneath the integument between the tw^o layers of superficial fascia; the deep veins accompany the arteries. Both sets of veins are provided with valves, which are more numerous in the deep than in the superficial set. Valves are also more numerous in the veins of the lower than in those of the upper limb. 756 AXGIOLOGY The Superficial Veins of the Lower Extremity. The superficial veins of the lower extremity are the great and small saphenous veins and their tributaries. On the dorsum of the foot the dorsal digital veins receive, in the clefts between the toes, the intercapitular veins from the plantar cutaneous venous arch and join to form short common digital veins which unite across the distal ends of the metatarsal bones in a dorsal venous arch. Proximal to this arch is an irregular venous net-work which receives tributariesf rom the i%l deep veins and is joined at the sides of the foot by a medial and a lateral marginal vein, formed mainly by the union of branches from the superficial parts of the sole of the foot. On the sole of the foot the superficial veins form a plantar cutaneous venous arch which extends across the roots of the toes and opens at the sides of the foot into the medial and lateral marginal veins. Proximal to this arch is a plantar cutaneous venous net-work which is especially dense in the fat beneath the heel; this net-work communicates with the cutaneous venous arch and with the deep veins, but is chiefly drained into the medial and lateral marginal veins. The great saphenous vein {v. saphena magna; internal or long sa'phenons win) (Fig. 647), the longest vein in the body, begins in the medial marginal vein of the dorsum of the foot and ends in the femoral vein about 3 cm. below the inguinal ligament. It ascends in front of the tibial malle- olus and along the medial side of the leg in rela- tion with the saphenous nerve. It runs upward behind the medial condyles of the tibia and femur and along the medial side of the thigh and, passing through the fossa ovalis, ends in the femoral vein. 8^ I 'fM^'\ Tributaries. — At the ankle it receives branches from the sole of the foot through the medial marginal vein; in the leg it anastomoses freely with the small saphenous vein, communicates with the anterior and posterior tibial veins and receives many cutaneous veins; in the thigh it communi- cates with the femoral vein and receives numerous tributaries; those from the medial and posterior parts of the thigh frequently unite to form a large accessory saphenous vein which joins the main vein at a variable level. Near the fossa ovalis (Fig. 648) it is joined by the superficial epi- gastric, superficial iliac circumflex, and superficial external pudendal veins. A vein, named the thoracoepigastric, runs along the lateral aspect of the trunk between the superficial epigastric vein below^ and the lateral thoracic vein above and establishes an important communication betw^een 647.-The^ greot^^sapheoous vein and ^j^^ femoral and axilkxy VciuS. J m Fig. THE SUPERFICIAL VEIXS OF THE LOWER EXTREMITY /ot The valves in the great saphenous vein \ary from ten to twenty in number; the.y are more numerous in the leg- than in the thigh. The small saphenous vein (/'. sajjlwim parra; external or short saphenous vein) (Fig. 649) hcyln.s- heliind the hiteral malk'ohis as a eontinuation of the lateral marginal vein; it first ascends along the lateral margin of the tendocalcaneus, and then crosses it to reach the middle of the back of the leg. Running directly upward, it perforates the deep fascia in the lower part of the popliteal fossa, and ends in the popliteal vein, between the heads of the Gastrocnemius. It communi- cates with the deep veins on the dorsum of the foot, and receives numerous large tributaries from the back of the leg. Before it pierces the deep fascia, it gives off a branch which runs upward and forward to join the great saphenous vein. The small saphenous \'ein possesses from nine to tweh'e valves, one of which is always found near its termination in the popliteal vein. In the lower third of the leg the small saphenous vein is in close relation with the sural nerve, in the upper two- thirds wath the medial sural cutaneous nerve. Fig. 648. — The great saphenous vein and its tributaries at the fossa ovalis. Applied Anatomy. — A varicose condition of the saphenous veins is more frequently met with than in the other veins of the body, except perhaps the spermatic and hemorrhoidal veins. The main cause of this is the high blood pressure, determined chiefly by the erect position, and the length of the column of blood, which has to be propelled in an uphill direction. In normal vessels there is only just sufficient force to perform this task; and in those cases where there is diminished resistance of the walls of the veins, these vessels are liable to dilate and a varicose condition is set up. This diminished resistance may be due to heredity, the vein walls being congenitally weak, or it may follow inflammatory conditions of the vessels. Increased blood pressure in the veins, caused by any obstacle to the return of the venous blood, such as the pressm-e of a tumor, '58 ANGIOLOGY or the gravid uterus, or tight gartering, may also produce varix. In the normal condition of the veins, the valves in their interior break up the column of blood into a number of smaller columns, and so to a considerable extent mitigate the ill effects of the erect position; but when the dilata- tion of the veins has reached a certain limit, the valves become incapable of supporting the over- lying column of blood, and the pressure is increased, tending to em- phasize also the varicose condition. Both the saphenous veins in the leg are accompanied by nerves, the great saphenous being joined by its companion nerve just below the level of the knee- joint. No doubt much of the pain of varicose veins in the leg is due to this fact. Operations for the rehef of varicose veins are frequently re- quired, portions of the veins being removed after having been ligatured above and below. It is important to note whether the main varicose area drains into the great or the small saphenous vein — the former condition being much the more common — and to control the venous retiun by removing a small portion of the main trunk just before it opens into the deep vein by passing through the deep fascia; thus in most cases a piece should be re- moved from the great saphenous just before it passes through the fossa ovalis {saphenous o-pening), and in addition the affected veins should be excised just above and just below the level of the knee-joint. In other cases the small saphenous will have to be dealt with immediately below the point where it pierces the fascial roof of the popliteal fossa. The Deep Veins of the Lower Extremity. The deep veins of the lower extremity accompany the arteries and their branches; they possess numerous valves. The plantar digital veins {m. digitales plantares) arise from plexuses on the plantar surfaces of the digits, and, after sending intercapitular veins to join the dorsal digital veins, unite to form four metatarsal veins; these run backward in the metatarsal spaces, communicate, by means of perforating veins, with the veins on the dorsum of the foot, and unite to form the deep plantar venous arch which lies alongside the plantar arterial arch. From the deep plantar venous arch the medial and lateral plantar veins run backward close to the corre- sponding arteries and, after communicating with the great and small saphenous veins, unite behind the medial malleolus to form the posterior tibial veins. The posterior tibial veins (vv. tibiales posteriores) accompany the posterior tibial artery, and are joined by the peroneal veins. The anterior tibial veins {vv. tibiales anteriores) are the upward continuation of the venae comitantes of the dorsalis pedis artery. They leave the front of -the leg by passing between the tibia and fibula, over the interosseous membrane, and unite with the posterior tibial, to form the popliteal vein. The Popliteal Vein (v. poplitea) is formed by the junction of the anterior and posterior tibial veins at the lower border of the Popliteus; it ascends through the popliteal fossa to the aperture in the Adductor magnus, where it becomes the femoral vein. In the lower part of its course it is placed medial to the artery; between the heads of the Gastrocnemius it is superficial to that vessel; but above the knee- joint, it is close to its lateral side. It receives tributaries corresponding to the branches of the popliteal artery, and it also receives the small saphenous vein. The valves in the popliteal vein are usually four in number. The femoral vein {v. femoralis) accompanies the femoral artery through the upper two-thirds of the thigh. In the lower part of its course it lies lateral to the Fig. 649. — The small saphenous vein. THE VEINS OF THE ABDOMEN AND PELVIS 759 artery; higher up, it is behind it; and at the inguinal hgament, it Hes on its medial side, and on the same plane. It receives numerous muscular tributaries, and about 4 cm. below the inguinal ligament is joined by the v. profunda femoris; near its termination it is joined by the great saphenous vein. The valves in the femoral vein are three in number. The Deep Femoral Vein {v. profunda femoris) receives tributaries corresponding to the perforating branches of the profunda artery, and through these establishes communications with the popliteal vein below and the inferior gluteal vein above. It also receives the medial and lateral femoral circumflex veins. Third hnnhar Deep circuinjiex Obturator — Prostatic plexus Deep dorsal vetii, of penis Scrotal Vesical plexus Internal pudendal Fig. 650. — The veins of the right half of the male pelvis. (Spalteholz.) The Veins of the Abdomen and Pelvis (Fig. 650). The external iliac vein (v. iliaca externa), the upw^ard continuation of the femoral vein, begins behind the inguinal ligament, and, passing upward along the brim of the lesser pelvis, ends opposite the sacroiliac articulation, by_ uniting with the hypogastric vein to form the common iliac vein. On the right side, it lies at first medial to the artery: but, as it passes upward, gradually inclines behind it. On 760 ' ANGIOLOGY the left side, it lies altogether on the medial side of the artery. It frequently contains one, sometimes two, valves. Tributaries, — The external iliac vein receives the inferior epigastric, deep iHac circumflex, and pubic veins. The Inferior Epigastric Vein {v. epigastrica inferior; deep epigastric vein) is formed by the union of the venae comitantes of the inferior epigastric artery, which com- municate above with the superior epigastric vein; it joins the external iliac about 1.25 cm. above the inguinal ligament. The Deep Iliac Circumflex Vein (v. circumfiexa ilium profunda) is formed by the union of the venae comitantes of the deep iliac circumflex artery, and joins the external iliac vein about 2 cm. above the inguinal ligament. The Pubic Vein communicates with the obturator vein in the obturator foramen, and ascends on the back of the pubis to the external iliac vein. The hypogastric vein {v. hypogastrica; internal iliac vein) begins near the upper part of the greater sciatic foramen, passes upward behind and slightly medial to the hypogastric artery and, at the brim of the pelvis, joins with the external iliac to form the common iliac vein. Tributaries, — With the exception of the fetal umbilical vein which passes upward and backward from the umbilicus to the liver, and the iliolumbar vein which usually joins the common iliac vein, the tributaries of the hypogastric vein correspond with the branches of the hypogastric artery. It receives (a) the gluteal, internal pudendal, and obturator veins, which have their origins outside the pelvis; (b) the lateral sacral veins, which lie in front of the sacrum; and (c) the middle hemorrhoidal, vesical, uterine, and vaginal veins, which originate in venous plexuses connected with the pelvic viscera. 1. The Superior Gluteal Veins (vv. glutaeae superiores; gluteal veins) are venae comitantes of the superior gluteal artery ; they receive tributaries from the buttock corresponding with the branches of the artery, and enter the pelvis through the greater sciatic foramen, above the Piriformis, and frequently unite before ending in the hypogastric vein. 2. The Inferior Gluteal Veins {vv. glutaeae infer lores; sciatic veins) , or venae comi- tantes of the inferior gluteal artery, begin on the upper part of the back of the thigh, where they anastomose with the medial femoral circumflex and first perfor- ating veins. They enter the pelvis through the lower part of the greater sciatic foramen and join to form a single stem wdiich opens into the lower part of the hypo- gastric vein. 3. The Internal Pudendal Veins {internal pudic veins) are the venae comitantes of the internal pudendal artery. They begin in the deep veins of the penis which issue from the corpus cavernosum penis, accompany the internal pudendal artery, and unite to form a single vessel, wdiich ends in the hypogastric vein. They receive the veins from the urethral bulb, and the perineal and inferior hemorrhoidal veins. The deep dorsal vein of the penis communicates with the internal pudendal veins, but ends mainly in the pudendal plexus, 4. The Obturator Vein {v. ohturatoria) begins in the upper portion of the adductor region of the thigh and enters the pelvis through the upper part of the obturator foramen. It runs backward and upward on the lateral wall of the pelvis below the obturator artery, and then passes between the ureter and the hypogastric artery, to end in the hypogastric vein. 5. The Lateral Sacral Veins (vv. sacrales laterales) accompany the lateral sacral arteries on the anterior surface of the sacrum and end in the hypogastric vein. 6. The Middle Hemorrhoidal Vein {v. haemorrhoidalis media) takes origin in the hemorrhoidal plexus and receives tributaries from the bladder, prostate, and seminal vesicle; it runs lateralward on the pelvic surface of the Levator ani to end in the hypogastric vein. THE VEINS OF THE ABDOMEN AND PELVIS 761 The hemorrhoidal plexus (plexus haemorrhoidaUs) surrounds the rectum, and communicates in front with the vesical plexus in the male, and the uterovaginal plexns in the female. It consists of two parts, an internal in the submucosa, and an external outside the muscular coat. The internal plexus presents a series of dilated pouches which are arranged in a circle around the tube, immediately above the anal orifice, and are connected by transverse branches. The lower part of the external plexus is drained by the inferior hemorrhoidal veins into the internal pudendal vein; the middle part by the middle hemorrhoidal vein which joins the hypogastric vein; and the upper part by the superior hemor- rhoidal XGXW which forms the commencement of the inferior mesenteric vein, a tributary of the portal vein. A free communication between the portal and sys- temic venous systems is established through the hemorrhoidal plexus. The pudendal plexus {plexus pudendalis; vesicoprostatic plexus) lies behind the arcuate pubic ligament and the lower part of the symphysis pubis, and in front of the bladder and prostate. Its chief tributary is the deep dorsal vein of the penis, but it also receives branches from the front of the bladder and prostate. It com- municates w'ith the vesical plexus and with the internal pudendal vein and drains into the vesical and hypogastric veins. The prostatic veins form a well-marked prostatic plexus which lies partly in the fascial sheath of the prostate and partly between the sheath and the prostatic capsule. It communicates with the pudendal and vesical plexuses. The vesical plexus (plexus ■vesicalis) envelops the lower part of the bladder and the base of the prostate and communicates wdth the pudendal and prostatic plexuses It is drained, by means of several vesical veins, into the hypogastric veins. Applied Anatomy. — The veins of the hemorrhoidal plexus are apt to become dilated and vari- cose, and form piles. This is due to several anatomical reasons: the vessels are contained in very loose, connective tissue, so that they get less support from surrounding structures than most other veins, and are less capable of resisting increased blood pressm'e; the condition is favored by gravitation, being influenced by the erect posture, either sitting or standing, and by the fact that the superior hemorrhoidal and portal veins have no valves; the veins pass through muscular tissue and are liable to be compressed by its contraction, especially during the act of defecation; they are affected by every form of portal obstruction. The prostatic plexus of veins is apt to become congested in many inflammatory conditions in the neighborhood, such as acute gonorrheal prostatitis. It is owing to the free communication which exists between this and the middle hemorrhoidal plexus that great relief can be given by free saline purgation. Hemorrhage may be very free from the prostatic plexus after operations on that gland, but can usually be checked by hot fluid irrigation. Septic thrombosis sometimes occurs after opera- tions, and infected emboli may find their way into the general circulation. The Dorsal Veins of the Penis (vv. dorsales penis) are tw'o in number, a superficial and a deep. The superficial vein drains the prepuce and skin of the penis, and, running backward in the subcutaneous tissue, inclines to the right or left, and opens into the corresponding superficial external pudendal vein, a tributary of the great saphenous vein. The deep vein lies beneath the deep fascia of the penis; it receives the blood from the glans penis and corpora cavernosa penis and courses backw^ard in the middle line between the dorsal arteries; near the root of the penis it passes between the two parts of the suspensory ligament and then through an aperture between the arcuate pubic ligament and the transverse ligament of the pelvis, and divides into two branches, which enter the pudendal plexus. The deep vein also communicates below^ the symphysis pubis with the internal pudendal vein. The uterine plexuses lie along the sides and superior angles of the uterus between the two layers of the broad ligament, and communicate with the ovarian and vaginal plexuses. They are drained by a pair of uterine veins on either side: these arise from the lower part of the plexuses, opposite the external orifice of the uterus, and open into the corresponding hypogastric vein. 762 AXGIOLOGY The vaginal plexuses are placed at the sides of the vagina; they communicate with the uterine, vesical, and hemorrhoidal plexuses, and are drained by the vaginal veins, one on either side, into the hypogastric veins. The common iliac veins (vv. iliacae communes) are formed by the union of the external iliac and hypogastric veins, in front of the sacroiliac articulation; passing obliquely upward toward the right side, they end upon the fifth lumbar vertebra, by uniting with each other at an acute angle to form the inferior vena cava. The right common iliac is shorter than the left, nearly vertical in its direction, and ascends behind and then lateral to its corresponding artery. The left common iliac, longer than the right and more oblique in its course, is at first situated on the medial side of the corresponding artery, and then behind the right common iliac. Each common iliac receives the iliolumbar, and sometimes the lateral sacral veins. The left receives, in addition, the middle sacral vein. No valves are found in these veins. The Middle Sacral Veins {w. sacrales mediales) accompany the corresponding artery along the front of the sacrum, and join to form a single vein, which ends in the left common iliac vein; sometimes in the angle of junction of the two iliac veins. Peculiarities. — The left common iliac vein, instead of joining with the right in its usual posi- tion, occasionally ascends on the left side of the aorta as high as the kidney, where, after receiving the left renal vein, it crosses over the aorta, and then joins with the right vein to form the vena cava. In these cases, the two common iliacs are connected by a small communicating branch at the spot where they are usually united. The inferior vena cava {v. cava inferior) (Fig. 644), returns to the heart the blood from the parts below the Diaphragma. It is formed by the junction of the two common iliac veins, on the right side- of the fifth lumbar vertebra. It ascends along the front of the vertebral column, on the right side of the aorta, and, having reached the liver, is continued in a groove on its posterior surface. It then perforates the Diaphragma between the median and right portions of its central tendon; it subsequently inclines forward and medialward for about 2.5 cm., and, piercing the fij^rous pericardium, passes behind the serous pericardium to open into the lower and back part of the right atrium. In front of its atrial orifice is a semilunar valve, termed the valve of the inferior vena cava: this is rudimentary in the adult but is of large size and exercises an important function in the fetus (see page 618). Relations. — The abdominal portion of the inferior vena cava is in relation in front, from below upward, with the right common iliac artery, the mesentery, the right internal spermatic artery, the inferior part of the duodenum, the pancreas, the common bile duct, the portal vein, and the posterior surface of the hver; the last partly overlaps and occasionally completely surroimds it; behind, with the vertebral column, the right Psoas major, the right crus of the Diaphragma, the right inferior phrenic, suprarenal, renal and lumbar arteries, right sympathetic trunk and right coeliac ganglion, and the medial part of the right suprarenal gland; on the right side, with the right kidney and ureter; on the left side, with the aorta, right crus of the Diaphragma, and the caudate lobe of the liver. The thoracic portion is only about 2.5 cm. in length, and is situated partly inside and partly outside the pericardial sac. The extrapericardial part is separated from the right pleura and lung by a fibrous band, named the right phrenicopericardiac ligament. This hgament, often feebly marked, is attached below to the margin of the vena-caval opening in the Diaphragma, and above to the pericardium in front of and behind the root of the right lung. The infrapericardiac part is very short, and is covered antero-laterally by the serous layer of the pericardium. Peculiarities. — In Position. — This vessel is sometimes placed on the left side of the aorta, as high as the left renal vein, and, after receiving this vein, crosses over to its usual position on the right side; or it may be placed altogether on the left side of the aorta, and in such a case the abdominal and thoracic viscera, together with the great vessels, are all transposed. Point of Termination. — Occasionally the inferior vena cava joins the azygos vein, which is then of large size. In such cases, the superior vena cava receives the whole of the blood from the body before transmitting it to the right atrium, except the blood from the hepatic veins, which passes directly into the right atrium. Applied Anatomy. — Thrombosis of the inferior vena cava is due to much the same causes as that of the superior (see p. 754). It usually causes oedema of the legs and back, without ascites; THE VEINS OF THE ABDOMEN AND PELVIS 763 if the renal veins are involved, blood and albumin will often ai)pear in the urine. An extensive collateral venous circulation is soon established by onlargemcnt either of the superficial or of the deep veins, or of both. In the first case the epigastric, the iliac circumflex, the lateral thoracic, the internal mammary, the intercostals, the external pudendal, and the lumbovertebral anasto- matic veins of Braune effect the communication with the superior cava; in the second, the deep anastomosis is made by the azygos and hemiazygos and the lumbar veins. ^ Tributaries. — The inferior vena cava receives the following veins: Lumbar. Renal. Inferior Phrenic. Right Spermatic or Ovarian. Suprarenal. . Hepatic, The Lumbar Veins (vv. lumbales) four in number on each side, collect the blood by dorsal tributaries from the muscles and integument of the loins, and by abdomi- nal tributaries from the walls of the abdomen, where they communicate with the epigastric veins. At the vertebral column, they receive veins from the vertebral plexuses, and then pass forward, around the sides of the bodies of the vertebrae, beneath the Psoas major, and end in the back part of the inferior cava. The left lumbar veins are longer than the right, and pass behind the aorta. The lumbar veins are connected together by a longitudinal vein which passes in front of the transverse processes of the lumbar vertebrae, and is called the ascending lumbar; it forms the most frequent origin of the corresponding azygos or hemiazygos vein, and serves to connect the common iliac, iliolumbar, and azygos or hemiazygos veins of its own side of the body. The Spermatic Veins (vv. spermaticae) emerge from the back of the testis, and receive tributaries from the epididymis; they unite and form a convoluted plexus, called the pampiniform plexus, which constitutes the greater mass of the spermatic cord; the vessels composing this plexus are very numerous, and ascend along the cord, in front of the ductus deferens. Below the subcutaneous inguinal ring they unite to form three or four veins, which pass along the inguinal canal, and, entering the abdomen through the abdominal inguinal ring, coalesce to form two veins, which ascend on the Psoas major, behind the peritoneum, lying one on either side of the internal spermatic artery. These unite to form a single vein, which opens on the right side into the inferior vena cava, at an acute angle; on the left side into the left renal vein, at a right angle. The spermatic veins are provided with valves.- The left spermatic vein passes behind the iliac colon, and is thus exposed to pressure from the contents of that part of the bowel. Applied Anatomy. — The spermatic veins are very frequently varicose, constituting the condi- tion known as varicocele. Though it is quite possible that the originating cause of this affection may be a congenital weakness of the walls of the veins of the pampiniform plexus, still it must be admitted that there are many anatomical reasons why these veins should become varicose, viz. : the imperfect support afforded to them by the loose tissue of the scrotum; their great length; their vertical course; their dependent position; their plexiform arrangement in the scrotum, with their termination in one small vein in the abdomen; their few and imperfect valves; and the fact that they may be subjected to pressure in their passage through the abdominal wall. Varicocele almost invariably occurs on the left side, and this has been accoimted for by the facts that the left spermatic vein joins the left renal at a right angle; that it is overlaid by the iliac colon, and that when this portion of the gut is full of fecal matter, in cases of constipation, its weight impedes the retiu-n of the venous blood; and that the left spermatic veins are somewhat longer than the right. The operation for the removal of a varicocele consists in making a small incision just over the subcutaneous inguinal ring and passing an aneurism needle around the mass of veins, taking care that the ductus deferens is not included. The veins are isolated from the ductus and hgatured above and below, as high and as low as possible, and the intermediate portion cut away; the divided ends are fixed together with a suture, and the skin woimd closed. 1 G. Blumer, in Osier and McCrae's Modern Medicine, Philadelphia, 1908, vol. iv. 2 Ri\'ington has pointed out that valves are usually found at the orifices of both the right and left spermatic veins. When no valves exist at the opening of the left spermatic vein into the left renal vein, valves are generally present in the left renal vein -ndthin 6 mm. from the orifice of the spermatic vein. — Journal of Anatomy and Physiologj-, vn, 163. 764 ANGIOLOGY The Ovarian Veins {m. ovaricae) correspond with the spermatic in the male; they form a plexus in the broad lio-ament near the oA'ar}- and uterine tube, and communi- cate with the uterine plexus. They end in the same way as the spermatic veins in the male. Valves are occasionally found in these veins. Like the uterine veins, they become much enlarged during pregnancy. The Renal Veins (vv. renales) are of large size, and placed in front of the renal arteries. The left is longer than- the right, and passes in front of the aorta, just below the origin of the superior mesenteric artery. It receives the left spermatic and left inferior phrenic veins, and, generally, the left suprarenal vein. It opens into the inferior vena cava at a slightly higher level than the right. The Suprarenal Veins {vv. supraremdes) are two in number: the right ends in the inferior vena cava; the left, in the left renal or left inferior phrenic vein. The Inferior Phrenic Veins {vv. yhrenicae iiiferiores) follow the course of the inferior phrenic arteries; the right ends in the inferior vena cava; the left is often repre- sented by two branches, one of which ends in the left renal or suprarenal vein, while the other passes in front of the oesophageal hiatus in the Diaphragma and opens into the inferior vena cava. The Hepatic "Veins {vv. hepaticae) commence in the substance of the liver, in the terminations of the portal vein and hepatic artery, and are arranged in two groups, upper and lower. The upper group usually consists of three large veins, which converge toward the posterior surface of the liver, and open into the inferior vena cava, while that vessel is situated in the groove on the back part of the liver. The veins of the lower group vary in number, and are of small size; they come from the right and caudate lobes. The hepatic veins run singly, and are in direct contact with the hepatic tissue. They are destitute of valves. THE PORTAL SYSTEM OF VEINS (Fig. 651). The portal system includes all the veins which drain the blood from the abdominal part of the digestive tube (with the exception of the lower part of the rectum) and from the spleen, pancreas, and gall-bladder. From these viscera the blood is conveyed to the liver by the portal vein. In the liver this vein ramifies like an artery and ends in capillary-like vessels termed sinusoids, from which the blood is conveyed to the inferior vena cava by the hepatic veins. From this it wdll be seen that the blood of the portal system passes through two sets of minute vessels, viz., (a) the capillaries of the digestive tube, spleen, pancreas, and gall-bladder; and (b) the sinusoids of the liver. In the adult the portal vein and its tributaries are destitute of valves; in the fetus and for a short time after birth valves can be demonstrated in the tributaries of the portal vein; as a rule thej'^ soon atrophy and disappear, but in some subjects they persist in a degenerate form. The portal vein {vena portae) is about 8 cm. in length, and is formed at the level of the second lumbar vertebra by the junction of the superior mesenteric and lienal veins, the union of these veins taking place in front of the inferior vena cava and behind the neck of the pancreas. It passes upward behind the superior part of the duodenum and then ascends in the right border of the lesser omentum to the right extremity of the porta hepatis, where it divides into a right and a left branch, which accompany the corresponding branches of the hepatic artery into the sub- stance of the liver. In the lesser omentum it is placed behind and between the common bile duct and the hepatic artery, the former lying to the right of the latter. It is surrounded by the hepatic plexus of nerves, and is accompanied by numerous lymphatic vessels and some lymph glands. The right branch of the portal vein enters the right lobe of the liver, but before doing so generally receives the cystic vein. The left branch, longer but of smaller calibre than the right, crosses the left THE PORTAL SYSTEM OF VEINS 705 sagittal fossa, gives branches to the caiuhite lobe, and then enters the left lobe of the liver. As it crosses the left sagittal fossa it is joined in front by a fibrous cord, the ligamentum teres (nhJUcvdied innhiltnil iriii), and is united to the inferior vena cava by a second fibrous cord, the ligamentum venosum (obliterated ductus venosus). Fig. 651. — The portal vein and its tributaries. Tributaries.— The tributaries of the portal vein are: Lienal. • Pyloric. Superior Mesenteric. Cystic. Coronary. Parumbilical. The Lienal Vein {v. lienalis; splenic vein) commences by five or six large branches which return the blood from the spleen. These unite to form a single vessel, which passes from left to right, grooving the upper and back part of the pancreas, below the lineal artery, and ends behind the neck of the pancreas by uniting at a right angle with the^uperior mesenteric to form the portal vein. The lienal vein is of large size, but is not tortuous like the artery. 766 ANGIOLOGY Tributaries. — The lineal vein receives the short gastric veins, the left gastro- epiploic vein, the pancreatic veins, and the inferior mesenteric veins. The short gastric veins (vv. gastricae breves) Joutot five in number, drain the fundus and left part of the greater curvature of the stomach, and pass between the two layers of the gastrolienal ligament to end in the lienal vein or in one of its large tributaries. The left gastroepiploic vein {v. gastroepiploica sinistra) receives branches from the antero-superior and postero-inf erior surfaces of the stomach and from the greater omentum; it runs from right to left along the greater curvature of the stomach and ends in the commencement of the lienal vein. The pancreatic veins {w. yancreaticae) consist of several small vessels which drain the body and tail of the pancreas, and open into the trunk of the lienal vein. The inferior mesenteric vein {v. mesenterica inferior) returns blood from the rectum and the sigmoid, and descending parts of the colon. It begins in the rectum as the superior hemorrhoidal vein, which has its origin in the hemorrhoidal plexus, and through this plexus communicates with the middle and inferior hemor- rhoidal veins. The superior Hemorrhoidal vein leaves the lesser pelvis and crosses the left common iliac vessels with the superior hemorrhoidal artery, and is con- tinued upward as the inferior mesenteric vein. This vein lies to the left of its artery, and ascends behind the peritoneum and in front of the left Psoas major; it then passes behind the body of the pancreas and opens into the lienal vein; sometimes it ends in the angle of union of the lienal and superior mesenteric veins. Tributaries. — The inferior mesenteric vein receives the sigmoid veins from the sigmoid colon and iliac colon, and the left colic vein from the descending colon and left colic flexure. The Superior Mesenteric Vein {v. mesenterica superior) returns the blood from the small intestine, from the cecum, and from the ascending and transverse portions of the colon. It begins in the right iliac fossa by the union of the veins which drain the terminal part of the ileum, the cecum, and vermiform process, and ascends between the two layers of the mesentery on the right side of the superior mes- enteric artery. In its upward course it passes in front of the right ureter, the inferior vena cava, the inferior part of the duodenum, and the lower portion of the head of the pancreas. Behind the neck of the pancreas it unites with the lienal vein to form the portal vein. Tributaries. — Besides the tributaries which correspond with the branches of the superior mesenteric artery, viz., the intestinal, ileocolic, right colic, and middle colic veins, the superior mesenteric vein is joined by the right gastroepiploic and pan- creaticoduodenal veins. The right gastroepiploic vein {v. gastroepiyloica dextra) receives branches from the greater omentum and from the lower parts of the antero-superior and postero- inf erior surfaces of the stomach; it runs from left to right along the greater curva- ture of the stomach between the two layers of the greater omentum. The pancreaticoduodenal veins {m. pancreaticoduodenales) accompany their corre- sponding arteries; the lower of the two frequently joins the right gastroepiploic vein. The Coronary Vein {v. coronaria ventriculi; gastric vein) derives tributaries from both surfaces of the stomach; it runs from right to left along the lesser curvature of the stomach, between the two layers of the lesser omentum, to the oesophageal opening of the stomach, where it receives some oesophageal veins. It then turns backward and passes from left to right behind the omental bursa and ends in the portal vein. The Pyloric Vein is of small size, and runs from left to right along the pyloric portion of the lesser curvature of the stomach, between the two layers of the lesser omentum, to end in the portal vein. THE PORTAL SYSTEM OF VEINS 767 The Cystic Vein (/'. ci/.sfica) drains the blood from the gall-bladder, and, accom- panying the cystic duct, usually ends in the right branch of the portal vein. Parumbilical Veins(rr. parumbilicales). — In the course of the ligamentum teres of the liver and of the middle umbilical ligament, small veins (parumbilical) are found which establish an anastomosis between the veins of the anterior abdominal wall and the portal, hypogastric, and iliac veins. The best marked of these small veins is one which commences at the umbilicus and runs backward and upward in, or on the surface of, the ligamentum teres between the layers of the falciform ligament to end in the left portal vein. Applied Anatomy. — Obstruction to the portal vein may produce ascites, and this may arise from many causes: as (1) the pressure of a tumor on the portal vein, such as cancer or hydatid cyst in the liver, enlarged lymph glands in the lesser omentum, or cancer of the head of the pancreas; (2) from cirrhosis of the liver, when the radicles of the portal vein are pressed upon by the contracting fibrous tissue in the portal canals; (3) from valvular disease of the heart, and back pressure on the hepatic veins, and so on the whole of the circulation through the liver. In this condition the prognosis as regards life and freedom from ascites may be much improved by the establishment of a good collateral venous circulation to relieve the portal obstruction in the liver. This is effected by communications between (a) the gastric veins and the oesophageal veins which often project as a varicose bunch into the stomach, emptying themselves into the hemiazygos vein; (b) the veins of the colon and duodenum and the left renal vein; (c) the accessory portal system of Sappey, branches of which pass in the round and falciform ligaments (particu- larly the latter) to unite with the epigastric and internal mammary veins, and through the dia- phragmatic veins with the azygos; a single large vein, shown to be a parumbilical vein, may pass from the hilus of the liver by the round ligament to the umbilicus, producing there a bunch of prominent varicose veins known as the caput medusae; (d) the veins of Retzius, which connect the intestinal veins with the inferior vena cava and its retroperitoneal branches; (e) the inferior mesenteric veins, and the hemorrhoidal veins that open into the hypogastrics; (/) very rarely the ductus venosus remains patent, affording a direct connection between the portal vein and the inferior vena cava. An operation for the relief of portal obstruction on these lines has been advocated by Ruther- ford Morison and by Talma. It consists in curetting the opposed surfaces of the hver and Dia- phragma and stitching them together, so as to secure vascular inflammatory adhesions between the two. The greater omentum may with advantage be interposed between them, so as to increase the amount of the adhesions, and the spleen has been similarly scraped and sutured to or into the abdominal wall. The operation should not be deferred imtil the patient is moribund. Thi'ombosis of the portal vein, or pylethrombosis, is a very serious event, and is oftenest due to pathological processes causing compression of the vessel or injury to its wall, such as tumors or inflammation about the pylorus, head of the pancreas, or vermiform process, or to gall-stones, or cirrhosis of the liver. If the thrombus is infected with bacteria, as is often the case when it is due to appendicitis, septic or suppurative pylephlebitis results; this condition is known also as portal pyemia. Fragments of the infected clot break off and are carried away to lodge in the smaller veins in the liver, with the development of multiple abscesses in its substance and a rapidly fatal result. When the thrombus is sterile, the chief signs produced are enlargement of the spleen, recurrent ascites, and the establishment of a collateral venous circulation, the case clinically resembling one of atrophic cirrhosis of the liver. The symptoms of thrombosis of the mesenteric veins are very much the same as those of embolism of the mesenteric arteries (see p. 696). THE LYMPHATIC SYSTEM. HTHE lymphatic system includes the lymphatic vessels and lymph glands. The lym- -^ phatic vessels of the small intestine receive the special designation of lacteals or chyliferous vessels ; they differ in no respect from the lymphatic vessels generally excepting that during the process of digestion they contain a milk-white fluid, the chyle. The lymphatic vessels are exceedingly delicate, and their coats are so transparent that the fluid they contain is readily seen through them. They are interrupted at intervals by constrictions, which give them a knotted or beaded appearance; these constrictions correspond to the situations of valves in their interior. Lym- phatic vessels have been found in nearly every texture and organ of the body which contains bloodvessels. Such non-vascular structures as cartilage, the nails, cuticle, and hair have none, but these with exceptions it is probable that eventually all parts will be found to be permeated by these vessels. Structure of Lymphatic Vessels. — The larger lymphatic vessels are each composed of three coats. The internal coat is thin, transparent, sUghtly elastic, and consists of a layer of elongated endothelial cells with wavy margins by which the contiguous cells are dovetailed into one another; the cells are supported on an elastic membrane. The middle coat is composed of smooth muscular and fine elastic fibres, disposed in a transverse direction. The external coat consists of connective tissue, intermixed with smooth muscular fibres longitudinally or obhquely disposed; it forms a protective covering to the other coats, and serves to connect the vessel with the neighboring structures. In the smaUer vessels there are no muscular or elastic fibres, and the waU consists only of a connective-tissue coat, hned by endothehum. The thoracic duct has a more complex structure than the other lymphatic vessels; it presents a distinct subendothehal layer of branched corpuscles, similar to that found ia the arteries; ia the middle coat there is, in addition to the muscular and elastic fibres, a layer of connective tissue with its fibres arranged longitudinally. The lymphatic vessels are supphed by nutrient vessels, which are distributed to their outer and middle coats; and here also have been traced many non-meduUated nerves in the form of a fine plexus of fibrils. The valves of the lymphatic vessels are formed of thin layers of fibrous tissue covered on both surfaces by endothelium which presents the same arrangement as on the valves of veins (p. 599). In form the valves are semilunar; they are attached by their convex edges to the wall of the vessel, the concave edges being free and directed along the course of the contained current. Usually two such valves, of equal size, are found opposite one another; but occasionally excep- tions occur, especiaUy at or near the anastomoses of lymphatic vessels. Thus, one valve may be of small size and the other increased in proportion. In the lymphatic vessels the valves are placed at much shorter intervals than in the veins. They are most numerous near the lymph glands, and are found more frequently in the lymphatic vessels of the neck and upper extremity than in those of the lower extremity. The waU of the lymphatic vessel immediately above the point of attachment of each segment of a valve is expanded into a pouch or sinus which gives to these vessels, when distended, the knotted or beaded appearance aheady referred to. Valves are wanting in the vessels composing the plexi- form net -work in which the lymphatic vessels usually originate on the surface of the body. The lymph glands ilymiolioglandulae) are small oval or bean-shaped bodies, situ- ated in the course of lymphatic and lacteal vessels so that the lymph and chyle pass through them on their way to the blood. Each generally presents on one side a slight depression — the hilus — through which the bloodvessels enter and leave the interior. The efferent lymphatic vessel also emerges from the gland at this spot, while the aff'erent vessels enter the organ at different parts of the periphery. On section (Fig. 652) a lymph gland displays two different structures: an external, STRCCTCRE OF LYMJ'JI GLANDS "09 of lighter color — the cortical; and an internal, darker — the medullary. The cortical structure does not form a complete investment, but is deficient at the hilum, where the medullary portion reaches the surface of the gland; so that the efl'erent vessel is derived directly from the medullary structures, while the afferent vessels empty themselves into the cortical substance. Lymphoid tissue in cortex Svbcaps^dar hjmph-path Lymjyh-path in medulla Fig. 652. — Section of small lymph gland of rabbit. X 100. Structure of Lymph Glands. — A lymph gland consists of (1) a fibrous envelope, or capsule, from wliicli a frame-work of processes (trabeculce) proceeds inward, imperfectly dividing the gland into open spaces freely communicating with each other; (2) a quantity of lymphoid tissue occupying these spaces without completely filUng them; (3) a free supply of bloodvessels, which Fig. 6-53. — Lymph gland tissue. Highly magnified, a, Trabeculae. 6. Small artery in substance of same, c. Lymph paths, d. Lymph corpuscles, e. Capillary plexus. are supported in the trabecule; and (4) the afferent and efferent vessels communicating through the Ij-mph paths in the substance of the gland. The nerves passmg into the hilus are few in number and are chiefly distributed to the bloodvessels supplying the gland. The capsule is composed of connective tissue with some plain muscle fibres, and from its internal surface are given off a number of membranous processes or trabeculse, consisting, in man, of connective tissue, with a smaU admixture of plain muscle fibres; but in many of the lower animals composed almost entirely of involuntary muscle. Thej- pass inward, radiating toward the centre 49 770 ANGIOLOGY of the gland, for a certain distance — that is to say, for about one-third or one-fourth of the space between the circumference and the centre of the gland. In some animals they are sufficiently well-marked to divide the peripheral or cortical portion of the gland into a number of compart- ments (so-called follicles), but in man this arrangement is not obvious. The larger trabeculse springing from the capsule break up into finer bands, and these interlace to form a mesh-work in the central or medullary portion of the gland. In these spaces formed by the interlacing trabeculse is contained the proper gland substance or lymphoid tissue. The gland pulp does not, however, completely fill the spaces, but leaves, between its outer margin and the enclosing trabecultp, a channel or space of uniform width throughout. This is termed the lymph path or l3rmph sinus (Fig. 652). Running across it are a number of finer trabecule of retiform con- nective tissue, the fibres of which are, for the most part, covered by ramifying cells. On account of the peculiar arrangement of the frame-work of the organ, the gland pulp in the cortical portion is disposed in the form of nodules, and in the medullary part in the form of rounded cords. It consists of ordinary lymphoid tissue (Fig. 653), being made up of a delicate net-work of retiform tissue, which is continuous with that in the lymph paths, but marked off from it by a closer reticulation; it is probable, moreover, that the reticular tissue of the gland pulp and the lymph paths is continuous with that of the trabeculse, and ultimately with that of the capsule of the gland. In its meshes, in the nodules and cords of lymphoid tissue, are closely packed lymph corpuscles. The gland pulp is traversed by a dense plexus of capillary bloodvessels. The nodules or follicles in the cortical portion of the gland frequently show, in their centres, areas where karyokinetic figures indicate a division of the lymph corpuscles. These areas are termed germ centres. The ceUs composing them have more abundant protoplasm than the peripheral cells. The afferent vessels, as stated above, enter at aU parts of the periphery of the gland, and after branching and forming a dense plexus in the substance of the capsule, open into the lymph sinuses of the cortical part. In doing this they lose aU their coats except their endothelial lining, which is continuous with a layer of similar cells Uning the lymph paths. In like manner the efferent vessel commences from the lymph sinuses of the medidlary portion. The stream of lymph carried to the gland by the afferent vessels thus passes through the plexus in the capsule to the lymph paths of the cortical portion, where it is exposed to the action of the gland pulp ; flowing through these it enters the paths or sinuses of the medullary portion, and finally emerges from the hilus by means of the efferent vessel. The stream of lymph in its passage through the lymph sinuses is much retarded by the presence of the reticulum, hence morphological elements, either normal or morbid, are easily arrested and deposited in the sinuses. Many lymph corpuscles pass with the efferent lymph stream to join the general blood stream. The arteries of the gland enter at the hilus, and either go at once to the gland pulp, to break up into a capillary plexus, or else run along the trabeculse, partly to supply them and partly running across the lymph paths, to assist in forming the capillary plexus of the gland pulp. This plexus traverses the lymphoid tissue, but does not enter into the lymph sinuses. From it the veins commence and emerge from the organ at the same place as that at which the arteries enter. The lymphatic vessels are arranged into a superficial and a deep set. On the surface of the body the superficial lymphatic vessels are placed immediately beneath the integument, accompanying the superficial veins; they join the deep lymphatic vessels in certain situations by perforating the deep fascia. In the interior of the body they lie in the submucous areolar tissue, throughout the whole length of the digestive, respiratory, and genito-urinary tracts; and in the subserous tissue of the thoracic and abdominal walls. Plexiform networks of minute lym- phatic vessels are found interspersed among the proper elements and bloodvessels of the several tissues; the vessels composing the net-work, as well as the meshes between them, are much larger than those of the capillary plexus. From these net-works small vessels emerge, which pass, either to a neighboring gland, or to join some larger lymphatic trunk. The deep lymphatic vessels, fewer in number, but larger than the superficial, accompany the deep bloodvessels. Their mode of origin is probably similar to that of the superficial vessels. The lymphatic vessels of any part or organ exceed the veins in number, but in size they are much smaller. Their anastomoses also, especially those of the large trunks, are more frequent, and are effected by vessels equal in diameter to those which they connect, the con- tinuous trunks retaining the same diameter. Applied Anatomy. — The lymphatic chaimels and lymph glands draining any infected area of the body are very liable to become infected, resulting in acute or chronic lymphangitis and lymphadenitis. In acute cases the paths of the superficial lymphatic vessels are often marked THE THORACIC DUCT 771 out on the skin by pain, redness, heat, and swelling, while the glands swell and may suppurate. Chronic inflammation leads to growth and fibrosis of the lymphatic vessels and the connective tissue around them; obstruction to the passage of the lymph results, as the fibrous tissue contracts and causes stenosis or obliteration of the lymphatic channels, and hard oedema of the involved skin and subcutaneous tissues follows {pachijdennia hjnphancjiectalica) . Chronic lymphangitis, together with the blocking of numerous lymiihatic vessels by the escaped ova of the minute parasitic worm Microfilaria nocturna, is the cause of elephantiasis, a condition common in the tropics and subtropics, and characterized by enormous enlargement and thickening of the integu- ments of some part of the body, most frequently of the leg. Tubercular and syi)hihtic enlarge- ments of the lymphatic vessels and glands are both very commonly met with. Primary tumors of the lymphatic vessels are lymphangioma and endothelioma; the so-called "congenital cystic hj'groma" of the neck, arm, trunk, or thigh, is a cystic lymphangioma. Primary tumors of the lymph glands may be innocent (lymphadenoma, myxoma, chondroma) or maUgnant (lympho- sarcoma") ; cancer is never met with as a primary affection, but is extremely common secondarily to cancer of some other part of the body. The appearance of secondary mahgnant deposits or of secondary infection in parts of the body that seem not to be directly associated by any lymphatic connection with the seat of the primary growth or infection has often been observed, and explained as due to "retrograde trans- port" of cancer cells or bacteria by a reversed flow of lymph. Weleminsky,^ however, believes that the explanation is to be found in the fact that when the infected glands have grown to a certain size they no longer permit the normal flow of lymph through them, and that under these circumstances very dehcate lymphatic connections, whose existence normally remains imsus- pected, develop to a surprising extent between groups of lymph glands that at first sight appear to be unconnected with one another. THE THORACIC DUCT. The thoracic duct {ductus thoracicus) (Fig. 654) conveys the greater part of the lymph and chyle into the blood. It is the common trunk of all the lymphatic vessels of the body, excepting those on the right side of the head, neck, and thorax, and right upper extremity, the right lung, right side of the heart, and the convex surface of the liver. In the adult it varies in length from 38 to 45 cm. and extends from the second lumbar vertebra to the root of the neck. It begins in the abdomen by a triangular dilatation, the cisterna chyli, which is situated on the front of the body of the second lumbar vertebra, to the right side of and behind the aorta, by the side of the right crus of the Diaphragma. It enters the thorax through the aortic hiatus of the Diaphragma, and ascends through the posterior mediastinal cavity between the aorta and azygos vein. Behind it in this region are the vertebral column, the right intercostal arteries, and the hemiazygos veins as they cross to open into the azygos vein; in front of it are the Diaphragma, oesophagus, and peri- cardium, the last being separated from it by a recess of the right pleural cavity. Opposite the fifth thoracic vertebra, it inclines toward the left side, enters the supe- rior mediastinal cavity, and ascends behind the aortic arch and the thoracic part of the left subclavian artery and between the left side of the oesophagus and the left pleura, to the upper orifice of the thorax. Passing into the neck it forms an arch which rises about 3 or 4 cm. above the clavicle and crosses anterior to the subclavian artery, the vertebral artery and vein, and the thyrocervical trunk or its branches. It also passes in front of the phrenic nerve and the medial border of the Scalenus anterior, but is separated from these two structures by the pre- vertebral fascia. In front of it are the left common carotid artery, vagus nerve, and internal jugular vein; it ends by opening into the angle of junction of the left subclavian vein with the left internal jugular vein. The thoracic duct, at its com- mencement, is about equal in diameter to a goose-quill, but it diminishes consid- erably in calibre in the middle of the thorax, and is again dilated just before its termination. It is generally flexuous, and constricted at intervals so as to present a varicose appearance. Not infrequently it divides in the middle of its course into two vessels of unequal size which soon reunite, or into several branches which form 1 Berliner klin. Woch., 1905, No. 24, p. 743. 772 ANGIOLOGY a plexiform interlacement. It occasionally divides at its upper part into two branches, right and left; the left ending in the usual manner, while the right opens into the right subclavian vein, in t^ connection wdth the right lymphatic duct. The thoracic duct has several valves; at its termination it is pro- vided with a pair, the free borders of which are turned toward the vein, so as to prevent the passage of venous blood into the duct. The cisterna chyli (receptacvlum chyli) (Fig. 655) receives the two lumbar lymphatic trunks, right and left, and the intestinal lymphatic trunk. The lumbar trunks are formed by the union of the efferent vessels from the lateral aortic lymph glands. They receive the lymph from the lower limbs, from the walls and viscera of the pelvis, from the kid- neys and suprarenal glands and the deep lymphatics of the greater part of the abdominal wall. The intes- tinal trunk receives the lymph from the stomach and intestine, from the pancreas and spleen, and from the lower and front part of the liver. Tributaries. — Opening into the commencement of the thoracic duct, on either side, is a descending trunk from the posterior intercostal lymph glands of the lower six or seven in- tercostal spaces. In the thorax the duct is joined, on either side, by a trunk which drains the upper lumbar lymph glands and pierces the crus of the Diaphragma. It also receives the efferents from the posterior mediastinal lymph glands and from the posterior intercostal lymph glands of the upper six left spaces. In the neck it is joined by the left jugular and left subclavian trunks, and sometimes by the left broncho- mediastinal trunk; the last-named, however, usually opens indepen- dently into the junction of the left subclavian and internal jugular veins. The right lymphatic duct (ductus lymyhaticus dexter) (Fig. 656), about 1.25 cm. in length, courses along the medial border of the Scalenus anterior at the root of the neck and ends in the right subclavian vein, at its angle of junction with the right internal jugular vein. Its orifice is guarded by two semilunar valves, which pre^'ent the passage of venous blood into the duct. Fig. 654. — The thoricic and right lymphatic ducts. THE THORACIC DUCT 773 Tributaries. — The right ]yin])liatic' diut receives the lymph from the right side of the liead and neek through tlie right jugular trunk; from the riglit upper extremity through the right subclavian trunk; from the right side of the thorax, right lung, right side of the heart, and part of the convex surface of the liver, through the right bronchomediastinal trunk. These three collecting trunks frequently open separately in the angle of union of the two veins. Fig. 655. — Modes of origin of thoracic duct. (Poirier and Charpy.) a. Thoracic duct. a'. Cisterna chyH. 6, c. Efferent trunks from lateral aortic glands, d. An efferent vessel which pierces the left crus of the diaphragm, e, f. Lateral aortic glands, h. Retroaortic glands, i. Intestinal trunk, j. Descending branch from intercostal lymphatics. Applied Anatomy. — Blockage of the thoracic duct by mature specimens of the minute parasitic worm Microfilaria nocturna gives rise to stasis of the chyle, and to its passage in various abnormal directions on its course past the obstruction. The neighboring abdominal, renal, and pelvic Ijanphatics become enlarged, varicose, and tortuous, and chyle may make its way into the urine (chyluria), the tunica vaginalis (chylocele), the abdominal cavity {chylous ascites), or the plem-al cavity (chylous pleural effusion), in consequence of rupture of some of these distended lymphatic vessels. Fig. 656. — Terminal collecting trunks of right side. (Poirier and Charpy.) a. Jugular trunk, b. trunk, c. Bronchomediastinal trunk, d. Right lymphatic trunk, e. Gland of internal mammary chain, of deep cervical chain. The thoracic duct may be secondarily infected in intestinal or pulmonary tuberculosis, and may contain either miliary tubercles, caseating tuberculous masses, or even tuberculous ulcers. It is often the seat of secondary carcinomatous deposits in cases of cancer of some abdominal viscus, becoming infiltrated throughout imtil it becomes a stiff moniliform rod as thick as a pencil, with multiple stenoses and dilatations of its kunen; in such cases the left supraclavicidar glands often become infected and enlarged, while the lungs remain entirely free from secondary growths. 774 ANGIOLOGY THE LYMPHATICS OF THE HEAD, FACE, AND NECK. The Lymph Glands of the Head (Fig. 657). The lymph glands of the head are arranged in the following groups: Occipital. Facial. Deep Facial. Lingual. Retropharyngeal. Posterior Auricular. Anterior Auricular. Parotid. Posterior auricular r^ glands \\ Occipital \\ glands ^^ Maxillary glaiids Parotid glands Buccinator glaiids Supramandihular glands Submaxillary glands Submental glands 'erior dec-p cervical glands Fig. 657.— Superficial lymph gland.s and lymphatic vessels of head and neck. The occipital glands (lymphoglandulae occipitales), one to three in number, are placed on the back of the head close to the margin of the Trapezius and resting on the insertion of the Semispinalis capitis. Their afferent vessels drain the occipi- tal region of the scalp, while their efferents pass to the superior deep cervical glands. The posterior auricular glands (lymphoglandulae auriculares; mastoid glands), usually two m number, are situated on the mastoid insertion of the Sternocleido- mastoideus, beneath the Auricularis posterior. Their afferent vessels drain the posterior part of the temporoparietal region, the upper part of the cranial surface THE LYMPH GLANDS OF THE HEAD 75 of the auricula or pinna, and the back of the external acoustic meatus; their eflerents pass to the superior deep cervical glands. The anterior auricular glands (lymphoghutdulae auricidares anteriores; suiwrficial parotid or prctniriciihtr glands), from one to three in number, lie immediately in front of the tragus. Their ali'erents drain the lateral surface of the auricula and the skin of the adjacent part of the temporal region; their efi'erents pass to the superior deep cervical glands. The parotid glands (lymphoglandidae parotidcae), form two groups in relation with the parotid salivary gland, viz., a group imbedded in the substance of the gland, and a group of subparotid glands lying on the lateral wall of the pharynx. Occa- sionally small glands are found in the subcutaneous tissue over the parotid gland. Their afferent vessels drain the root of the nose, the eyelids, the frontotemporal region, the external acoustic meatus and the tympanic cavity, possibly also the posterior parts of the palate and the floor of the nasal cavity. The efferents of these glands pass to the superior deep cervical glands. The afferents of the sub- parotid glands drain the nasal part of the pharynx and the posterior parts of the nasal cavities; their efferents pass to the superior deep cervical glands. ' Afferent vessel to deep cervical glands Glandular nodule Gland of deep cervical chain Efferent vessels of retro- pharyngeal glands Fig. 658. — Lymphatics of pharj^nx. (Poirier and Charpy.) The facial glands comprise three groups : (a) infraorbital or maxillary, scattered over the infraorbital region from the groove between the nose and cheek to the zygomatic arch; (b) buccinator, one or more placed on the Buccinator opposite the angle of the mouth; (c) supramandibular, on the outer surface of the mandible, in front of the JNIasseter and in contact with the external maxillary artery and anterior facial vein. Their efferent vessels drain the eyelids, the conjunctiva, and the skin and mucous membrane of the nose and cheek; their efferents pass to the submaxillary glands. The deep facial glands (lymphoglandulae faciales profunda; internal maxillary glands) are placed beneath the ramus of the mandible, on the outer surface of the Pterygoideus externus, in relation to the internal maxillary artery. Their afferent vessels drain the temporal and infratemporal fossae and the nasal part of the pharynx their efferents pass to the superior deep cervical glands. The lingual glands {lymplioglandulae linguales) are two or three small nodules lying on the Hyoglossus and under the Genioglossus. They form merely glandular substations in the course of the lymphatic vessels of the tongue. 776 ANGIOLOGY The retropharyngeal glands (Fig. 658), from one to three in number, lie in the buccopharyngeal fascia, behind the upper part of the pharynx and in front of the arch of the atlas, being separated, however, from the latter by the Longus capitis. Their aft'erents drain the nasal cavities, the nasal part of the pharynx, and the auditory tubes; their efferents pass to the superior deep cervical glands. The lymphatic vessels of the scalp are divisible into (a) those of the frontal region, which terminate in the anterior auricular and parotid glands; (b) those of the temporoparietal region, which end in the parotid and posterior auricular glands; and (c) those of the occipital region, which terminate partly in the occipital glands and partly in a trunk w^hich runs down along the posterior border of the Sternocleidomastoideus to end in the inferior deep cervical glands. The lymphatic vessels of the auricula and external acoustic meatus are also divisible into three groups: (a) an anterior, from the lateral surface of the auricula and anterior wall of the meatus to the anterior auricular glands; (b) a posterior, from the margin of the auricula, the upper part of its cranial surface, the internal surface and posterior wall of the meatus to the posterior auricular and superior deep cervical glands; (c) an inferior, from the floor of the meatus and from the lobule of the auric- ula to the superficial and superior deep cervical glands. Parotid glaiids Superficial cervi- cal glands Facial glands Submaxillary glands Deep cervical glands Fig. 659. — The lymphatics of the face. (After Kiittner.) The lymphatic vessels of the face (Fig. 659) are more numerous than those of the scalp. Those from the eyelids and conjunctiva terminate partly in the submaxillary but mainly in the parotid glands. The vessels from the posterior part of the cheek also pass to the parotid glands, w^hile those from the anterior portion of the cheek, the side of the nose, the upper lip, and the lateral portions of the lower lip end in the submaxillary glands. The deeper vessels from the temporal and infratemporal fosste pass to the deep facial and superior deep cervical glands. The deeper vessels of the cheek and lips end, like the superficial, in the submaxillary glands. Both superficial and deep vessels of the central part of the lower lip run to the submental glands. The lymphatic vessels of the nasal cavities can be injected from the subdural and subarachnoid cavities. Those from the anterior parts of the nasal cavities THE LYMPH GLANDS OF THE HEAD communicate with the \es.scls of the integument of the nose and end in the sub- maxillary glands; those from the posterior two-thirds of the nasal cavities and from the accessory air sinuses pass partly to the retropharyngeal and partly to the sui)erior deej) cervical glands. Lymphatic Vessels of the Mouth. — The vessels of the gums pass to the submaxillary glands; those of the hard plate are continuous in front with those of the upper gum, but pass backward to pierce the Constrictor pharyngis superior and end in the superior deep cervical and subparotid glands; those of the soft palate pass backward anil lateralward and end partly in the retropharyngeal and subparotid, and partly in the superior deep cervical glands. The vessels of the anterior part of the floor of the mouth pass either directly to the inferior glands of the superior deep cervical group, or indirectly through the submental glands; from the rest of the floor of the mouth the vessels pass to the submaxillary and superior deep cervical glands. Vessels from root of tongue Vessels from margin of tongue Principal gland of tongue \ V essels from -' apex Submental gland } Trunks from margin of tongue — Interrupting nodule Supra - omoli yo id gland Fig. 660. — Lymphatics of the tongue. (Poirier.) The lymphatic vessels of the palatine tonsil, usually three to five in number, pierce the buccopharyngeal fascia and constrictor pharyngis superior and pass between the Stylohyoideus and internal jugular vein to the uppermost of the superior deep cervical glands. They end in a gland which lies at the side of the posterior belly of the Digastricus, on the internal jugular vein; occasionally one or two additional vessels run to small glands on the lateral .side of the vein under cover of the Sternocleidomastoideus. 778 ANGIOLOGY The lymphatic vessels of the tongue (Fig. 660) are drained chiefly into the deep cervical glands lying between the posterior belly of the Digastricus and the superior belly of the Omohyoideus; one gland situated at the bifurcation of the common carotid artery is so intimately associated with these vessels that it is known as the principal gland of the tongue. The lymphatic vessels of the tongue may be divided into four groups: (1) apical, from the tip of the tongue to the suprahyoid glands and principal gland of the tongue; (2) lateral, from the margin of the tongue — some of these pierce the Mylohyoideus to end in the submaxillary glands, others pass down on the Hyoglossus to the superior deep cervical glands; (3) basal, from the region of the papillae A'allatae to the superior deep cervical glands; and (4) ■ median, a few of which perforate the Mylohyoideus to reach the submaxillary glands, -while the majority turn around the posterior border of the muscle to enter the superior deep cervical glands. The Lymph Glands of the Neck. The lymph glands of the neck include the following groups: Submaxillary. Superficial Cervical. Submental. Anterior Cer\dcal. Deep Cervical. The submaxillary glands (lymphoglandulae submaxillares) (Fig. 659), three to six in number, are placed beneath the body of the mandible in the submaxillary triangle, and rest on the superficial surface of the submaxillary salivary gland. One gland, the middle gland of Stahr, which lies on the external maxillary artery as it turns over the mandible, is the most constant of the series; small lymph glands are sometimes found on the deep surface of the submaxillary salivary glands. The afferents of the submaxillary glands drain the medial palpebral commissure, the cheek, the side of the nose, the upper lip, the lateral part of the lower lip, the gums, and the anterior part of the margin of the tongue; efferent vessels from the facial and submental glands also enter the submaxillary glands. Their efferent vessels pass to the superior deep cervical glands. The submental or suprahyoid glands are situated between the anterior bellies of the Digastrici. Their af!'erents drain the central portions of the lower lip and floor of the mouth and the apex of the tongue; their efferents pass partly to the submaxillary glands and partly to a gland of the deep cervical group situated on the internal jugular vein at the level of the cricoid cartilage. The superficial cervical glands (lymphoglandulae cervicales superficiahs) lie in close relationship with the external jugular vein as it emerges from the parotid gland, and, therefore, superficial to the Sternocleidomastoideus. Their afferents drain the lower parts of the auricula and parotid region, while their efferents pass around the anterior margin of the Sternocleidomastoideus to join the superior deep cervical glands. The anterior cervical glands form an irregular and inconstant group on the front of the larynx and trachea. They may be divided into (a) a superficial set, placed on the anterior jugular vein; (b) a deeper set, which is further subdivided into prelarATigeal, on the middle cricothyroid ligament, and pretracheal, on the front of the trachea. This deeper set drains the lower part of the larynx, the thyroid gland, and the upper part of the trachea; its efferents pass to the lowest of the superior deep cervical glands. The deep cervical glands (lymphoglandidae cervicales profundae) (Figs. 657, 660) are numerous and of large size : they form a chain along the carotid sheath, lying by the side of the pharynx, oesophagus, and trachea, and extending from the base of the skull to the root of the neck. They are usually described in two groups: THE LYMPH GLANDS OF THE UPPER EXTREMITY 779 d) the superior deep cervical glands lying under the Sternocleidomastoideus in close rehition with the accessory nerve and the internal iugular vein, some of the glands lying in front of and others behind the vessel; (2) the inferior deep cervical glands extentling i)eyond the posterior margin of the Sternocleidomastoideus into the supraclavicular triangle, where they are closely related to the brachial plexus and subclavian vein. A few minute paratracheal glands are situated along- side the recurrent nerves on the lateral aspects of the trachea and oesophagus. The superior deep cervical glands drain the occipital portion of the scalp, the auricula, the back of the neck, a considerable part of the tongue, the larynx, thyroid gland, trachea, nasal part of the pharynx, nasal cavities, palate, and oesophagus. They receive also the efferent vessels from all the other glands of the head and neck, except those from the inferior deep cervical glands. The inferior deep cervical glands drain the back of the scalp and neck, the superficial pectoral region, part of the arm (see page 782), and, occasionally, part of the superior surface of the liver. In addition, the}' receive vessels from the superior deep cervical glands. The efferents of the superior deep cervical glands pass partly to the inferior deep cervical glands and partly to a trunk which unites with the efferent vessel of the inferior deep cervical glands and forms the jugular trunk. On the right side, this trunk ends in the junction of the internal jugular and subclavian veins; on the left side it joins the thoracic duct. The lymphatic vessels of the skin and muscles of the neck pass to the deep cervical glands. From the upper part of the pharynx the lymphatic vessels pass to the retro- pharyngeal, from the lower part to the deep cervical glands. From the larynx two sets of vessels arise, an upper and a lower. The vessels of the upper set pierce the hyothyroid membrane and join the superior deep cer\acal glands. Of the lower set, some pierce the conus elasticus and join the pretracheal and pre- laryngeal glands; others run between the cricoid and first tracheal ring and enter the inferior deep cervical glands. The h-mphatic vessels of the thyroid gland con- sist of two sets, an upper, which accompanies the superior th^Toid artery and enters the superior deep cervical glands, and a lower, which runs partly to the pretracheal glands and partly to the small paratracheal glands which accompany the recurrent nerves. These latter glands receive also the lymphatic vessels from the cervical portion of the trachea. Applied Anatomy. — The cerWcal glands are very frequently the seat of tuberculous disease. This condition is most usually set up by some lesion in those parts from which they receive their lymph. It is very desirable therefore for the sm-geon, ia deahng with these cases, to possess a knowledge of the relation of the respective groups of glands to the peripher3% while in order to eradicate them by operation a long and difficult dissection maj- be required. THE LYMPHATICS OF THE UPPER EXTREMITY. The Lymph Glands of the Upper Extremity (Fig. 661). The lymph glands of the upper extremity are divided into two sets, superficial and deep. The superficial lymph glands are few and of small size. One or two supra- trochlear glands are placed above the medial epicondyle of the humerus, medial to the basilic vein. Their afferents drain the middle, ring, and little fingers, the medial portion of the hand, and the superficial area over the ulnar side of the fore- arm; these vessels are, however, in free communication with the other lymphatic vessels of the forearm. Their efferents accompany the basilic vein and join the deeper vessels. One or two deltoideopectoral glands are found beside the cephalic vein, between the Pectoralis major and Deltoideus, immediately below the clavicle. They are situated in the course of the external collecting trunks of the arm. 780 ANGIOLOGY The deep lymph glands are chiefly grouped in the axilla, although a few may be found in the forearm, in the course of the radial, ulnar, and interosseous vessels, and in the arm along the medial side of the brachial artery. Deltoideo- pectoral glayids Axillary glands Fig. 661. — The superficial lymph glands and lymphatic vessels of the upper extremity. The Axillary Glands {lymphoglandulae axillares) (Fig. 662) are of large size, vary from twent}^ to thirty in number, and may be arranged in the following groups: 1. A lateral' group of from four to six glands lies in relation to the medial and posterior aspects of the axillary vein; the afferents of these glands drain the whole arm with the exception of that portion whose vessels accompany the cephalic vein. The efferent vessels pass partly to the central and subclavicular groups of axillary glands and partly to the inferior deep cervical glands. 2. An anterior or pectoral group consists of four or five glands along the lower border of the Pectoralis minor, in relation with the lateral thoracic artery. Their afferents drain the skin and muscles of the anterior and lateral thoracic walls, and the central and lateral parts of the mamma; their efferents pass partly to the central and partly to the subclavicular groups of axillary glands. THE LYMPHATIC VESSELS OF THE UPPER EXTREMITY 781 3. A posterior or subscapular group of six or seven glands is placed along the lower margin of the posterior wall of the axilla in the course of the subscapular artery. The atferents of this group drain the skin and muscles of the lower part of the back of the neck and of the posterior thoracic wall; their efferents pass to the central group of axillary glands. 4. A central or intermediate group of three or four large glands is imbedded in the adipose tissue near the base of the axilla. Its aft'erents are the efl'erent vessels of all the preceding groups of axillary glands; its eft'erents pass to the subclavicular group. Lateral group Deltoideopcctoral glands ,— ^l a I lunar y hjmphaiic ending in svbclavicular glands Pectoral group Matnmary collecting trunks Subareolar plexus Cidaneous collecting trunk from the thorccic icall Cutaneous collecting flunks Collecting trunks passing to internal mammary glands Fig. 662. — Lymphatics of the mamma, and the axillary glands (semidiagrammatic) . (Poirier and Charpj-.) 5. A medial or subclavicular group of six to twelve glands is situated partly posterior to the upper portion of the Pectoralis minor and partly above the upper border of this muscle. Its only direct territorial aff erents are those which accompany the cephalic vein and one which drains the upper peripheral part of the mamma, but it receives the efferents of all the other axillary glands. The efferent vessels of the subclavicular group unite to form the subclavian trunk, which opens either directly into the junction of the internal jugular and subclavian veins or into the jugular lymphatic trunk; on the left side it may end in the thoracic duct. A few efferents from the subclavicular glands usually pass to the inferior deep cervical glands. Applied Anatomy. — In malignant disease or infectious processes implicating the upper part of the back and shoulder, the front of the chest and mamma, the upper part of the front and side of the abdomen, or the hand, forearm, and arm, enlargement of the axillary glands is very often found. The Lymphatic Vessels of the Upper Extremity. The lymphatic vessels of the upper extremity are divided into two sets, super- ficial and deep. The superficial lymphatic vessels commence (Fig. 663) in the lymphatic plexus which everj-where pervades the skin; the meshes of the plexus are much finer in the 782 ANGIOLOGY palm and on the flexor aspect of the digits than elsewhere. The digital plexuses are drained by a pair of vessels which run on the sides of each digit, and incline backward to reach the dorsum of the hand. From the dense plexus of the palm, vessels pass in different direc- tions, viz., upward toward the wrist, downward to join the digital vessels, medialward to join the vessels on the ulnar border of the hand, and lateral- ward to those on the thumb. Sev- eral vessels from the central part of the plexus unite to form a trunk, which passes around the metacarpal bone of the index finger to join the vessels on the back of that digit and on the back of the thumb. Running upward in front of and behind the wrist, the lymphatic vessels are col- lected into radial, median, and ulnar groups, which accompany' respectively the cephalic, median, and basilic veins in the forearm. A few of the ulnar lymphatics end in the supratrochlear glands, but the majority pass directly to the lateral group of axillary glands. Some of the radial vessels are collected into a trunk which ascends wdth the cephalic vein to the deltoideopectoral glands; the efferents from this group pass either to the subclavicular axillary glands or to the inferior cervical glands. The deep lymphatic vessels accompany the deep bloodvessels. In the fore- arm, they consist of four sets, corresponding with the radial, ulnar, volar, and dorsal interosseous arteries; they communicate at intervals with the superficial lymphatics, and some of them end in the glands which are occasionally found beside the arteries. In their course upward, a few end in the glands which lie upon the brachial artery; but most of them pass to the lateral group of axillary glands. FlG. 663. — Lymphatic vessels of the dorsal surface of the hand. (Sappey.) THE LYMPHATICS OF THE LOWER EXTREMITY. The Lymph Glands of the Lower Extremity. The lymph glands of the lower extremity consist of the anterior tibial gland and the popliteal and inguinal glands. The anterior tibial gland (lymphoglandula tibialis anterior) is small and incon- stant. It lies on the interosseous membrane in relation to the upper part of the anterior tibial vessels, and constitutes a substation in the course of the anterior tibial lymphatic trunks. The popliteal glands (lymphoglandulae popliteae) (Fig. 664), small in size and some six or seven in number, are imbedded in the fat contained in the popliteal fossa. One lies immediately beneath the popliteal fascia, near the terminal part of the small saphenous vein, and drains the region from which this vein derives THE LYMPH GLANDS OF THE LOWER EXTREMITY 783 its tributaries. Another is placed between the popliteal artery and the posterior surface of the knee-joint; it receives the lymphatic vessels from the knee-joint together with those which accompany the genicular arteries. The others lie at the sides of the popliteal vessels, and receive as efl'erents the trunks which accom- pany the anterior and posterior tibial vessels. The efferents of the popliteal glands pass almost entirely alongside the femoral vessels to the deep inguinal glands, but a few may accompany the great saphenous vein, and end in the glands of the superficial subinguinal group. The inguinal glands {hjmphoglandulae mguinales) (Fig. 665), from twelve to twenty in number, are situated at the upper part of the femoral triangle. They may be divided into two groups by a horizontal line at the level of the termination of the great saphenous vein; those lying above this line are termed the superficial inguinal glands, and those below it the subinguinal glands, the latter group consisting of a superficial and a deep set. ^ — Tibial nerve — Popliteal vein Popliteal artery Common peronceal nerve Gland at side of popliteal vessels Gland on back of knee joint Gland at termination of small saph. vein Fig. 664. — Lymph glands of popliteal fossa. (Poirier and Charpy.) The Superficial Inguinal Glands form a chain immediately below the inguinal ligament. They receive as afferents lymphatic vessels from the integument of the penis, scrotum, perineum, buttock, and abdominal wall below the level of the umbilicus. The Superficial Subinguinal Glands (lymphoglandulae suhinguinales superficiales) are placed on either side of the upper part of the great saphenous vein; their efferents consist chiefly of the superficial lymphatic vessels of the lower extremity; but they also receive some of the vessels which drain the integument of the penis, scrotum, perineum, and buttock. The Deep Subinguinal Glands (lyviphoglandulae suhinguinales profundae) vary from one to three in number, and are placed under the fascia lata, on the medial side of the femoral vein. When three are present, the lowest is situated just below the junction of the great saphenous and femoral veins, the middle in the femoral canal, and the highest in the lateral part of the femoral ring. The middle one is the most inconstant of the three, but the highest, the gland of Cloquet or Rosenmiiller, 784 ANGIOLOGY .Ouperficial ingmnal ■ glands Sicperficial suhinguinal- glands \-i=^ is also frequently absent. They receive as afferents the deep lymphatic trunks which accompany the femoral vessels, the h'mphatics from the glans penis vel clitoridis, and also some of the efferents from the superficial subinguinal glands. Applied Anatomy. — Inflammation and sup- puration of the popliteal glands are most com- monly due to a sore on the lateral side of the heel. The inguinal and subinguinal glands fre- quently become enlarged in diseases implicat- ing the parts from which their lymphatic vessels originate. Thus in mahgnant or syphi- litic affections of the prepuce and penis, or labia majora, in cancer of the scrotum, in abscess in the perineum, or in similar diseases affecting the integument and superficial struc- tures in those parts, or the subumbilical part of the abdominal wall, or the gluteal region, the upper group of glands is almost invariably en- larged, the lower groups being implicated in diseases affecting the lower limb. '<) ^ Fig. 665- -The superficial lymph glands and lymphatic vessels of the lower extremity. The Lymphatic Vessels of the Lower Extremity. The lymphatic vessels of the lower extremity consist of two sets, superficial and deep, and in their distribution corre- spond closely with the veins. The superficial lymphatic vessels lie in the superficial fascia, and are divi- sible into two groups: a medial, which follows the course of the great saphenous vein, and a lateral, which accompanies the small saphenous vein. The vessels of the medial group (Fig. 665) are larger and more numerous than those of the lateral group, and commence on the tibial side and dorsum of the foot ; they ascend both in front of and behind the medial malleolus, run up the leg with the great saphenous vein, pass with it behind the medial condyle of the femur, and accompany it to the groin, where they end in the subinguinal group of super- ficial glands. The vessels of the lateral group arise from the fibular side of the foot; some ascend in front of the leg, and, just below the knee, cross the tibia to join the lymphatics on the medial side of the thigh; others pass behind the lateral malleolus, and, accompanying the small saphenous vein, enter the popliteal glands. THE LYMPH GLANDS OF THE ABDOMEN AND PELVIS 785 The deep lymphatic vessels arc few in number, and accompany the deep blood- vessels. In the leg, they consist of three sets, the anterior tibial, posterior tibial, and peroneal, which accompany the corresponding bloodvessels, two or three with each artery; they enter the popliteal lymi)h glands. The deep lymphatic vessels of the gluteal and ischial regions follow the course of the corresponding bloodvessels. Those accompanying the superior gluteal vessels end in a gland which lies on the intrapelvic portion of the superior gluteal artery near the upper border of the greater sciatic foramen. Those following the inferior gluteal vessels traverse one or two small glands which lie below the Piriformis muscle, and end in the hypogastric glands. Rigid lateral aoitic Lift latual ao)tic C'Gmmoii lUac Gland m front of iucnd promonto) y Coimnon iliac ■ External iliac Common iliac External iliac p— External iliac Obturator atiti Obturator gland Fig. 666. — The parietal lymph glands of the pelvis. (Cun^o and Marcille.) THE LYMPHATICS OF THE ABDOMEN AND PELVIS. The Lymph Glands of the Abdomen and Pelvis. The lymph glands of the abdomen and pelvis may be divided, from their situa- tions, into {a) parietal, lying behind the peritoneum and in close association with the larger bloodvessels; and (h) visceral, which are found in relation to the visceral arteries. 50 786 ANGIOLOGY The parietal glands (Figs. 666, 667) include the following groups: Iliac Circumflex. Hypogastric. Sacral. [Lateral Aortic. Lumbar - Preaortic. iRetroaortic. External IHac. Common Iliac. Epigastric. The External Iliac Glands, from eight to ten in number, lie along the external iUac vessels. They are arranged in three groups, one on the lateral, another on the medial, and a third on the anterior aspect of the vessels; the third group is, however, sometimes absent. Their principal afferents are derived from the inguinal and subinguinal glands, the deep lymphatics of the abdominal wall below the umbili- cus and of the adductor region of the thigh, and the lymphatics from the glans penis vel clitoridis, the membranous urethra, the prostate, the fundus of the bladder, the cervix uteri, and upper part of the vagina. Hypogastric Qland in front of sacral promontory / Lateral sacral External iliac glands Internal lymphatic>> of bladder Lyynphatic from glans penis Lymphatics ofhladdei Hypogastric Satellite trunk of internal puden- i dal vessels. Trunk of middle hcemorrhoidal vessels. Pioitatic collecting trunk Uiethial collecting ttunks Glandular nodule mfiont of symphysis Piostatic collectinq trunk Fig. 667. — Uiopelvic glands (lateral view) . (Cun6o and Marcille.) The Common Iliac Glands, four to six in number, are grouped behind and on the sides of the common iliac artery, one or two being placed below the bifurcation of the aorta, in front of the fifth lumbar vertebra. They drain chiefly the hypo- gastric and external iliac glands, and their efferents pass to the lateral aortic glands. The Epigastric Glands {lymphoglandulae eingastricae) , three or four in number, are placed alongside the lower portion of the inferior epigastric vessels. The Iliac Circumflex Glands, two to four in number, are situated along the course of the deep iliac circumflex vessels; they are sometimes absent. The Hypogastric Glands (lymphoglandulae hypogastricae; internal iliac gland) (Fig. 667) surround the hypogastric vessels, and receive the lymphatics corre- sponding to the distribution of the branches of the hypogastric artery, i. e., they receive lymphatics from all the pelvic viscera, from the deeper parts of the perineum, THE LYMPHATIC VESSELS OF THE ABDOMEN AND PELVIS 787 including- the nu'nihranoiis and ca^•crn()ll.s portions of the urethra, and from the l)uttock and back of the thigh. An obturator gland is sometimes seen in the upper part of the obturator foramen. The Sacral Glands are phiced in the concavity of the sacrum, in relation to the middle and lateral sacral arteries; they receive lymphatics from the rectum and posterior wall of the pelvis. The etferents of the hypogastric group end in the common iliac glands. The Lumbar Glands (lymphoglandulae lumbales) are very numerous, and consist of right and left lateral aortic, preaortic, and retroaortic groups. The right lateral aortic glands are situated partly in front of the inferior vena cava, near the termination of the renal vein, and partly behind it on the origin of the Psoas major, and on the right crus of the Diaphragma. The left lateral aortic glands form a chain on the left side of the abdominal aorta in front of the origin of the Psoas major and left crus of the Diaphragma. The glands on either side receive (a) the efferents of the common iliac glands, (b) the lymphatics from the testis in the male and from the ovary, uterine tube, and body of the uterus in the female; (c) the lymphatics from the kidney and suprarenal gland; and {d) the lymphatics draining the lateral abdominal muscles and accompanjdng the lumbar veins. Most of the efferent vessels of the lateral aortic glands converge to form the right and left lumbar trunks which join the cisterna chyli, but some enter the pre- and retroaortic glands, and others pierce the crura of the Diaphragma to join the lower end of the thoracic duct. The preaortic glands lie in front of the aorta, and may be divided into coeliac, superior mesenteric, and inferior mesenteric groups, arranged around the origins of the corresponding arteries. They receive a few vessels from the lateral aortic glands, but their principal afferents are derived from the viscera supplied by the three arteries with which they are associated. Some of their efferents pass to the retroaortic glands, but the majority unite to form the intestinal trunk, which enters the cisterna chyli. The retroaortic glands are placed below the cisterna chyli, on the bodies of the third and fourth lumbar vertebrse. They receive lymphatic trunks from the lateral and preaortic glands, while their efferents end in the cisterna chyli. The Lymphatic Vessels of the Abdomen and Pelvis. The lymphatic vessels of the walls of the abdomen and pelvis may be divided into two sets, superficial and deep. The superficial vessels follow^ the course of the superficial bloodvessels and converge to the superficial inguinal glands; those derived from the integument of the front of the abdomen below the umbilicus follow^ the course of the superficial epigastric vessels, and those from the sides of the lumbar part of the abdominal wall pass along the crest of the ilium, wdth the superficial iliac circumflex vessels. The superficial lymphatic vessels of the gluteal region turn horizontally around the buttock, and join the superficial inguinal and subinguinal glands. The deep vessels run alongside the principal bloodvessels. Those of the parietes of the pelvis, which accompany the superior and inferior gluteal, and obturator vessels, follow the course of the hypogastric artery, and ultimately join the lateral aortic glands. Lymphatic Vessels of the Perineum and External Genitals. — The lymphatic vessels of the perineum, of the integument of the penis, and of the scrotum (or vulva), follow the course of the external pudendal vessels, and end in the superficial ingui- nal and subinguinal glands. Those of the glans penis vel clitoridis terminate partly in the deep subinguinal glands and partly in the external iliac glands. The visceral glands are associated with the branches of the coeliac, superior 788 ANGIOLOGY and inferior mesenteric arteries. Those related to the branches of the coeliac artery form three sets, gastric, hepatic, and pancreaticoHenal. The Gastric Glands fFigs. (j(>*^, OOO) consist of two sets, superior and inferior. The Superior Gastric Glands {lymphoglandulae gastricae siiperiores) acc(jmpany the left gastric artery and are divisible into three groups, viz.: (a) upper, on the stem of the artery; (b) lower, accompanying the descending branches of the artery along the cardiac half of the lesser curA-atiire of the stomach, })et\veen the two layers of the lesser omentum; and (c) paracardial outlying members of the gastric glands, disposed in a manner comparable to a chain of beads around the neck of the stomach (Jamieson and Dobson^). They receive their afferents from the stomach; their efferents pass to the coeliac group of preaortic glands. Paracardial glands Superior gastric gland- Eepaiic glands Svbpyioric glands 1 Pa/icreaticolienal glands Inferior gastric glands Fig. 668. — Lymphatics of stomach, etc. (.Jamieson and Dobson.) The Inferior Gastric Glands (lymphoglandulae gastricae inferiores; right gastro- epipjloic gland), four to seven in number, lie between the two layers of the greater omentum along the pyloric half of the greater curvature of the stomach, and may be regarded as an outlying group of the hepatic glands. The Hepatic Glands (lymphoglandidae hepaticae) (Fig. 668), consist of the follow- ing groups: ici) hepatic, on the stem of the hepatic artery, and extending upward along the common bile duct, between the two layers of the lesser omentum, as far as the porta hepatis; the cystic gland, a member of this group, is placed near the neck of the gall-bladder; ih) subpyloric, four or five in number, in close relation to the bifurcation of the gastroduodenal artery, in the angle between the superior and descending parts of the duodenum; an outlying member of this group is some- times found above the duodenum on the right gastric (pyloric) artery. The glands of the hepatic chain receive afferents from the stomach, duodenum, liver, gall- bladder, and pancreas; their efferents join the coeliac group of preaortic glands. The PancreaticoHenal Glands (lymphoglandidae pancreaticolienales; splenic glands) (Fig. 669) accompany the lienal (splenic) artery, and are situated in rela- tion to the posterior surface and upper border of the pancreas; one or two members 1 Lancet. April 20 and 27, 1907. THE LYMPHATIC VESSELS OF THE ABDOMEX AXD PELVIS 7 89 of this o-roup are found in the gastrolienal ligament (Jamieson and Dobson, op. cit.). Their ali'erents are derived from the stomaeh, spleen, and pancreas, their efferents join the ccvliac groui) of preaortic glands. _ The superior mesenteric glands may be divided into three pruicipal groups: mesenteric, ileocolic, and mesocolic. The Mesenteric Glands (h/wplio(ihimIuJae mesentericae) lie between the layers ot the mesentery. Tlic\ \ary from one hundred to one hundred and fifty in number, and mav be grouped into three sets, viz. : one lying close to the wall of the small intestine, among the terminal twigs of the superior mesenteric artery; a second, in relation to the loops and primary branches of the vessels; and a third along the trunk of the artery. Svbpylonc glands Fig. 669. — Lymphatics of stomach, etc. The stomach has been turned upward. (Jamieson and Dobson.) Applied Anatomy. — Enlargement of the mesenteric Ij-mphatic glands is seen in most diseased conditions of the intestinal tract, and is well-marked in enteric fever, tuberculous ulceration or malignant growths of the bowel. The enlarged glands can often be palpated through the wall of the abdomen. The Ileocolic glands (Figs. 670, 671), from ten to twenty in number, form a chain around the ileocolic artery, but show a tendency to subdivision into two groups, one near the duodenum and another on the lower part of the trunk of the artery. Where the vessel divides into its terminal branches the chain is broken up into sev- eral groups, viz.: (a) ileal, in relation to the ileal branch of the artery; (6) anterior ileocolic, usually of three glands, in the ileocolic fold, near the wall of the cecum; (c) posterior ileocolic, mostly placed in the angle between the ileum and the colon, but partly lying behind the cecum at its junction with the ascending colon; {d) ■90 ANGIOLOGY a single gland, between the layers of the mesenteriole of the vermiform process; (e) right colic, along the medial side of the ascending colon. Duodenum Upper group of ileocolic glands Lower group of ileocolic glands Cecum Vermiform process Fig. 670. — The lymphatics of cecum and vermiform process from the front. (Jamieson and Dobson.) Upper group of ileocolic glands Lower group of ileocolic glands Vermiform process Cecum Fig. 671. — The lymphatics of cecum and vermiform process from behind. (Jamieson and Dobson.) THE LYMPHATIC VESSELS OF ABDOMINAL AND PELVIC VISCERA 791 The Mesocolic Glands (It/niphoglandulae mesocolicae) are numerous, and lie between the layers of the transverse niesocok)n, in chxse relation to the transverse colon; they are best developed in the neighborhood of the right and left colic flexures. One or two small glands are occasionally seen along the trunk of the right colic artery and others are found in relation to the trunk and branches of the middle colic artery. The superior mesenteric glands receive afferents from the jejunum, ileum, cecum, vermiform process, and the ascending and transverse parts of the colon; their efferents pass to the preaortic glands. Inferior mesenteric glands Fig. 672. — Lymphatics of colon. (Jamieson and Dobson ) The inferior mesenteric glands (Fig. 672) consist of: (a) small glands on the branches of the left colic and sigmoid arteries; (6) a group in the sigmoid mesocolon, around the superior hemorrhoidal artery; and (c) a pararectal group in contact with the muscular coat of the» rectum. They drain the descending iliac and sigmoid parts of the colon and the upper part of the rectum; their efferents pass to the preaortic glands. The Lymphatic Vessels of the Abdominal and Pelvic Viscera. The lymphatic vessels of the abdominal and pelvic viscera consist of (1) those of the subdiaphragmatic portion of the digestive tube and its associated glands, the liver and pancreas; (2) those of the spleen and suprarenal glands; (3) those of the urinary organs; (4) those of the reproductive organs. ^ 1. The lymphatic vessels of the subdiaphragmatic portion of the digestive tube are situated partly in the mucous membrane and partly in the seromuscular coats, but as the former system drains into the latter, the two may be considered as one. 792 ANGIOLOGY The Lymphatic Vessels of the Stomach (Figs. 6GS, 669) are continuous at the cardiac orifice with those of the oesophagus, and at the pylorus with those of the duodenum. They mainly follow the bloodvessels, and may be arranged in four sets. Those of the first set accompany the branches of the left gastric artery, receiving tributaries from a large area on either surface of the stomach, and ter- minate in the superior gastric glands. Those of the second set drain the fundus and body of the stomach on the left of a line drawn vertically from the oesophagus; they accompany, more or less closely, the short gastric and left gastroepiploic arteries, and end in the pancreaticolienal glands. The vessels of the third set drain the right portion of the greater curvature as far as the pyloric portion, and end in the inferior gastric glands, the efferents of which pass to the subpyloric group. Those of the fourth set drain the pyloric portion and pass to the hepatic and subpyloric glands, and to the superior gastric glands. The Lymphatic Vessels of the Duodenum consist of an anterior and a posterior set, which open into a series of small pancreaticoduodenal glands on the anterior and posterior aspects of the groove between the head of the pancreas and the duo- denum. The efferents of these glands run in two directions, upward to the hepatic glands and downward to the preaortic glands around the origin of the superior mesenteric artery. The Lymphatic Vessels of the Jejunum and Ileum are termed lacteals, from the milk-white fluid they contain during intestinal digestion. They run between the layers of the mesentery and enter the mesenteric glands, the efferents of which end in the preaortic glands. The Lymphatic Vessels of the Vermiform Process and Cecum (Figs. 670, 671) are numerous, since in the wall of this process there is a large amount of adenoid tissue. From the body and tail of the vermiform process eight to fifteen vessels ascend between the layers of the mesenteriole, one or two being interrupted in the gland which lies between the layers of this peritoneal fold. They unite to form three or four vessels, which end partly in the lower and partly in the upper glands of the ileocolic chain. The vessels from the root of the vermiform process and from the cecum consist of an anterior and a posterior group. The anterior vessels pass in front of the cecum, and end in the anterior ileocolic glands and in the upper and lower glands of the ileocolic chain; the posterior vessels ascend over the back of the cecum and terminate in the posterior ileocolic glands and in the lower glands of the ileocolic chain. Lymphatic Vessels of the Colon (Fig. 672). — The lymphatic vessels of the ascend- ing and transverse parts of the colon finally end in the mesenteric glands, after traversing the right colic and mesocolic glands. Those of the descending and iliac sigmoid parts of the colon are interrupted by the small glands on the branches of the left colic and sigmoid arteries, and ultimately end in the preaortic glands around the origin of the inferior mesenteric artery. Lymphatic Vessels of the Anus, Anal Canal, and Rectum. — The lymphatics from the anus pass forward and end with those of the integument of the perineum and scrotum in the superficial inguinal glands; those from the anal canal accompany •the middle and inferior hemorrhoidal arteries, and end in the hypogastric glands; while the vessels from the rectum traverse the pararectal glands and pass to those in the sigmoid mesocolon; the eft'erents of the latter terminate in the preaortic glands around the origin of the inferior mesenteric artery. The Lymphatic Vessels of the Liver are divisible into two sets, superficial and deep. The former arise in the subperitoneal areolar tissue over the entire surface of the organ, and may be grouped into (a) those on the convex surface, (b) those on the inferior surface. (a) On the convex surface: The vessels from the back part of this surface reach THE LYMPHATIC VESSELS OF ABDOMINAL AND PELVIC VISCERA 793 their terminal glands by three different routes; the vessels of the middle set, five or six in number, pass through the vena-caval foramen in the Diaphragma and end in one or two glands which are situated around the terminal part of the inferior vena ca^'a; a few vessels from the left side pass backward toward the oesophageal hiatus, and terminate in the paracardial group of superior gastric glands; the vessels from the right side, one or two in number, run on the abdominal surface of the Diaphragma, and, after crossing its right crus, end in the preaortic glands which surround the origin of the coeliac artery. From the portions of the right and left lobes adjacent to the falciform ligament, the lymphatic vessels converge to form two trunks, one of which accompanies the inferior vena cava through the Dia- phragma, and ends in the glands around the terminal part of this vessel; the other runs downward and forward, and, turning around the anterior sharp margin of the liver, accompanies the upper part of the ligamentum teres, and ends in the upper hepatic glands. From the anterior surface a few additional vessels turn around the anterior sharp margin to reach the upper hepatic glands. (6) On the inferior surface: The vessels from this surface mostly converge to the porta hepatis, and accompany the deep lymphatics, emerging from the porta to the hepatic glands; one or two from the posterior parts of the right and caudate lobes accompany the inferior vena cava through the Diaphragma, and end in the glands around the terminal part of this vein. The deep lymphatics converge to ascending and descending trunks. The ascend- ing trunks accompany the hepatic veins and pass through the Diaphragma to end in the glands around the terminal part of the inferior vena cava. The descending trunks emerge from the porta hepatis, and end in the hepatic glands. The Lymphatic Vessels of the Gall-bladder pass to the hepatic glands in the porta hepatis; those of the common bile duct to the hepatic glands alongside the duct and to the upper pancreaticoduodenal glands. The Lymphatic Vessels of the Pancreas follow the course of its bloodvessels. Most of them enter the pancreaticolienal glands, but some end in the pancreatico- duodenal glands, and others in the preaortic glands near the origin of the superior mesenteric artery. 2. The lymphatic vessels of the spleen and suprarenal glands. The Lymphatic Vessels of the Spleen, both superficial and deep, pass to the pan- creaticolienal glands. The Lymphatic Vessels of the Suprarenal Glands usually accompany the suprarenal veins, and end in the lateral aortic glands; occasionally some of them pierce the crura of the Diaphragma and end in the glands of the posterior mediastinal cavity. 3. The lymphatic vessels of the urinary organs. The Lymphatic Vessels of the Kidney form three plexuses: one in the substance of the kidney, a second beneath its fibrous capsule, and a third in the perinephric fat; the second and third communicate freely with each other. The vessels from the plexus in the kidney substance converge to form four or five trunks which issue at the hiius. Here they are joined by vessels from the plexus under the capsule, and, following the course of the renal vein, end in the lateral aortic glands. The perinephric plexus is drained directly into the upper lateral aortic glands. The Lymphatic Vessels of the Ureter run in different directions. Those from its upper portion end partly in the efferent vessels of the kidney and partly in the lateral aortic glands; those from the portion immediately above the brim of the lesser pelvis are drained into the common iliac glands; while the vessels from the intrapelvic portion of the tube either join the efferents from the bladder, or end in the hypogastric glands. The Lymphatic Vessels of the Bladder (Fig. 673) originate in two plexuses, an intra- and an extramuscular, it being generally admitted that the mucous mem- 794 ANGIOLOGY brane is devoid of lymphatic.^ The efferent vessels are arranged in two groups, one from the anterior and another from the posterior surface of the bladder. The vessels from the anterior surface pass to the external iliac glands, but in their course minute glands are situated. These minute glands are arranged in two groups, an anterior vesical, in front of the bladder, and a lateral vesical, in relation to the lateral umbilical ligament. The vessels from the posterior surface pass to the hypo- gastric, external, and common iliac glands; those draining the upper part of this surface traverse the lateral vesical glands. The Lymphatic Vessels of the Prostate (Fig. 674) terminate chiefly in the hypo- gastric and sacral glands, but one trunk from the posterior surface ends in the exter- nal iliac glands, and another from the anterior surface joins the vessels which drain the membranous part of the urethra. Common iliac artery External iliac \\L\\lii glands Lyrn'phntics C irom, bladder \ Gland in front of sacral promontory Hypogastric glands Ureter I J il Lymph'xiics from bladder Fig. 673. — Lymphatics of the bladder. (Cun6o and Marcille.) Lymphatic Vessels of the Urethra. — The lymphatics of the cavernous portion of the urethra accompany those of the glans penis, and terminate with them in the deep subinguinal and external iliac glands. Those of the membranous and prostatic portions, and those of the whole urethra in the female, pass to the hypogastric glands. (4) The lymphatic vessels of the reproductive organs. The Lymphatic Vessels of the Testes consist of two sets, superficial and deep, the former commencing on the surface of the tunica vaginalis, the latter in the epididymis and body of the testis. They form from four to eight collecting trunks which ascend with the spermatic veins in the spermatic cord and along the front of the Psoas major to the level where the spermatic vessels cross the ureter and end in the lateral and preaortic groups of lumbar glands.^ The Lymphatic Vessels of the Ductus Deferens pass to the external iliac glands; those of the vesiculae seminales partly to the hypogastric and partly to the external glands. 1 Some authorities maintain that a plexus of lymphatic vessels does exist in the mucous membrane of the bladder (consult M6decine op6ratoire des Voies urinaires, par J. Albarran, Paris, 1909). - "The Lymphatics of the Testicle," by Jamieson and Dobson, Lancet, February 19, 1900. THE LYMPHATIC VE.'SSELS OF ABDOMIXAL AND PELVIC VISCERA 795 The Lymphatic Vessels of the Ovary are similar to those of the testis, and ascend with the ovarian artery to the lateral and preaortic glands. The Lymphatic Vessels of the Uterine Tube pass partly with those of the ovary and partly w ith those of the uterus. Fig. 674. — Lymphatics of the prostate. (Cuneo and Marcille.) a, b. Externa.1 iliac glands, c. Vessel draining into external iliac glands, d. Retroprostatic lymph nodes, e. Vessels draining into gland on sacral promontory. /. Gland in front of sacral p^omontorJ^ g. Lateral sacral glands, h. Middle hemorrhoidal gland, i. Middle hemor- rhoidal lymphatic vessels. The Lymphatic Vessels of the Uterus (Fig. 675) consist of two sets, superficial and deep, the former being placed beneath the peritoneum, the latter in the sub- stance of the organ. The lymphatics of the cervix uteri run in three directions: transversely to the external iliac glands, postero-laterally to the hypogastric glands, and posteriorly to the common iliac glands. The majority of the vessels of the body and fundus of the uterus pass lateralward in the broad ligaments, and are continued up wdth the ovarian vessels to the lateral and preaortic glands; a few^, however, run to the external iliac glands, and one or tw^o to the superficial inguinal glands. In the unimpregnated uterus the lymphatic vessels are very small, but during gestation they are greatly enlarged. The Lymphatic Vessels of the Vagina are carried in three directions: those of the upper part of the vagina to the external iliac glands, those of the middle part to the hypogastric glands, and those of the low^er part to the common iliac glands. 796 ANGIOLOGY On the course of the vessels from the middle and lower i)arts small glands are situated. Some lymphatic vessels from the lower part of the vagina join those of the vulva and pass to the superficial inguinal glands. The lymphatics of the vagina anastomose with those of the cervix uteri, vulva, and rectum, but not with those of the bladder. Fig 675. — Lymphatics of the uterus. (Cuneo and Marnille.) a. Efierents to lateral aortic glands. 6, c, d. Efferents to external iliac glands, e. Net-work on lateral asoect of cervix uteri. /. Glands in front of sacral promontory. _ g. Efferents to galnds in front of sacral promontorj-. h. HjTJOgastric glands, i. Lateral sacral glands, j. Vessels drain- ing into bj-pogastric glands, k. Vessels passing to lateral sacral glands. THE LYMPHATICS OF THE THORAX. The lymph glands of the thorax may be divided into parietal and visceral — the former being situated in the thoracic wall, the latter in relation to the viscera. The parietal lymph glands include the sternal, intercostal, and diaphragmatic glands. 1. The Sternal Glands (lymphoglanchdae sternales; internal mammary glands) are placed at the anterior ends of the intercostal spaces, by the side of the internal mammary artery. They derive afferents from the mamma, from the deeper struc- tures of the anterior abdominal wall above the level of the umbilicus, from the upper surface of the liver through a small group of glands which lie behind the xiphoid process, and from the deeper parts of the anterior portion of the thoracic wall. Their efferents usually unite to form a single trunk on either side; this may open directly into the junction of the internal jugular and subclavian veins, or THE LYMPHATICS OF THE THORAX 797 that of the right side may join the right subcUivian trunk, and that of the left the thoracie duct. 2. The Intercostal Glands {liimyhocjlandidae inter cosialcs) occupy the posterior parts of the intercostal spaces, in relation to the intercostal vessels. They receive the deep lymphatics from the postero- lateral aspect of the chest; some of these vessels are interrupted by small lateral intercostal glands. The efferents of the glands in the lower four or five spaces unite to form a trunk, which descends and opens either into the cisterna chyli or into the commencement of the thoracic duct. The efferents of the glands in the upper spaces of the left side end in the thoracic duct; those of the corresponding right spaces, in the right lymphatic duct. 3. The Diaphragmatic Glands lie on the thoracic aspect of the Diaphragma, and consist of three sets, anterior, middle, and posterior. The anterior set comprises (a) two or three small glands behind the base of the xiphoid process, which receive afferents from the convex surface of the liver, and (6) one or two glands on either side near the junction of the seventh rib with its cartilage, which receive lymphatic vessels from the front part of the Diaphragma. The efferent vessels of the anterior set pass to the sternal glands. The middle set consists of two or three glands on either side close to where the phrenic nerves enter the Diaphragma. On the right side some of the glands of this group lie within the fibrous sac of the pericardium, on the front of the termination of the inferior vena cava. The afferents of this set are derived from the middle part of the Diaphragma, those on the right side also receiving afferents from the convex surface of the liver. Their efferents pass to the posterior mediastinal glands. The posterior set consists of a few glands situated on the back of the crura of the Diaphragma, and connected on the one hand with the lumbar glands and on the other with the posterior mediastinal glands. The superficial lymphatic vessels of the thoracic wall ramify beneath the skin and converge to the axillary glands. Those over the Trapezius and Latissimus dorsi run forward and unite to form about ten or twelve trunks which end in the subscapular group. Those over the pectoral region, including the vessels from the skin covering the peripheral part of the mamma, run backward, and those over the Serratus anterior upward, to the pectoral group. Others near the lateral margin of the sternum pass inward between the rib cartilages and end in the sternal glands, while the vessels of opposite sides anastomose across the front of the sternum. A few vessels from the upper part of the pectoral region ascend over the clavicle to the supraclavicular group of cervical glands. The Lymphatic Vessels of the Mamma originate in a plexus in the interlobular spaces and on the walls of the galactophorous ducts. Those from the central part of the gland pass to an intricate plexus situated beneath the areola, a plexus which receives also the lymphatics from the skin over the central part of the gland and those from the areola and nipple. Its efferents are collected into two trunks which pass to the pectoral group of axillary glands. The vessels which drain the medial part of the mamma pierce the thoracic wall and end in the sternal glands, while a vessel has occasionally been seen to emerge from the upper part of the mamma and, piercing the Pectoralis major, terminate in the subclavicular glands (Fig. 662). The deep lymphatic vessels of the thoracic wall consist of: 1. The lymphatics of the muscles which lie on the ribs: most of these end in the axillary glands, but some from the Pectoralis major pass to the sternal glands. 2. The intercostal vessels which drain the Intercostales and parietal pleura. Those draining the Intercostales externi run backward and, after receiving the vessels which accompany the posterior branches of the intercostal arteries, end in the intercostal glands. Those of the Intercostales interni and parietal pleura consist of a single trunk in each space. These trunks run forward in the subpleural tissue and the upper six open separately into the sternal glands or into the vessels which 798 ANGIOLOGY unite them; those of the lower spaces unite to forni a single trunk which terminates in the lowest of the sternal glands. 3. The lymphatic vessels of the Diaphragma, which form two plexuses, one on its thoracic and another on its abdominal surface. These plexuses anastomose freely with each other, and are best marked on the parts covered respectively by the pleurae and peritoneum. That on the thoracic surface communicates with the lymphatics of the costal and mediastinal parts of the pleura, and its efferents consist of three groups : (a) anterior, passing to the gland which lie near the junction of the seventh rib with its cartilage; (b) middle, to the glands on the oesophagus and to those around the termination of the inferior vena cava; and (c) posterior, to the glands which surround the aorta at the point where this vessel leaves the thoracic cavity. The plexus on the abdominal surface is composed of fine vessels, and anasto- moses with the lymphatics of the liver and, at the periphery of the Diaphragma, with those of the subperitoneal tissue. The efferents from the right half of this plexus terminate partly in a group of glands on the trunk of the corresponding inferior phrenic artery, while others end in the right lateral aortic glands. Those from the left half of the plexus pass to the pre- and lateral aortic glands and to the glands on the terminal portion of the oesophagus. The visceral lymph glands consist of three groups, viz.: anterior mediastinal, posterior mediastinal, and tracheobronchial. The Anterior Mediastinal Glands {lymylioglandulae mediastinales anteriores) are placed in the anterior part of the superior mediastinal cavity, in front of the aortic arch and in relation to the innominate veins and the large arterial trunks which arise from the aortic arch. They receive afferents from the thymus and pericar- dium, and from the sternal glands; their efferents unite with those of the tracheo- bronchial glands, to form the right and left bronchomediastinal trunks. The Posterior Mediastinal Glands {lymyhoglandulae mediastinales posteriores) lie behind the pericardium in relation to the oesophagus and descending thoracic aorta. Their afferents are derived from the oesophagus,' the posterior part of the pericardium, the Diaphragma, and the convex surface of the liver. Their efferents mostly end in the thoracic duct, but some join the tracheobronchial glands. The Tracheobronchial Glands (Fig. 676) form four main groups: (a) tracheal, on either side of the trachea; (b) bronchial, in the angles between the lower part of the trachea and bronchi and in the angle between the two bronchi ; (c) broncho- pulmonary, in the hilus of each lung; and (d) pulmonary, in the lung substance, on the larger branches of the bronchi. The afferents of the tracheobronchial glands drain the lungs and bronchi, the thoracic part of the trachea and the heart; some of the efferents of the posterior mediastinal glands also end in this group. Their efferent vessels ascend upon the trachea and unite with efferents of the internal mammary and anterior mediastinal glands to form the right and left broncho- mediastinal trunks. The right bronchomediastinal trunk may join the right lymphatic duct, and the left the thoracic duct, but more frequently they open independently of these ducts into the junction of the internal jugular and subclavian veins of their own side. Applied Anatomy. — In all town dwellers there are continually being swept into these glands from the bronchi and alveoli large quantities of the dust and black carbonaceous pigment that are so freely inhaled in cities. At first the glands are moderately enlarged, firm, inky black, and gritty on section; later they enlarge still further, often becoming fibrous from the irritation set up by the minute foreign bodies with which they are crammed, and may break down into a soft slimy mass or may calcify. In tuberculosis of the lungs these glands are practically always infected; they enlarge, being filled with tuberculous deposits that may soften, or become fibrous, or calcify. Not infrequently an enlarged tuberculous gland perforates into a bronchus, discharg- ing its contents into the tube. When this happens there is great danger of acute pulmonary tuberculosis, the infecting gland substance being rapidly spread throughout the bronchial system by the coughing its presence in the air passages excites. THE LYMPHATICS OF THE THORAX 799 The lymphatic vessels of the thoracic viscera comprise those of the heart and pericardium, lungs and pleura, thymus, and oesophagus. The Lymphatic Vessels of the Heart consist of two plexuses: (a) deep, immediately under the endocardium; and (6) superficial, subjacent to the visceral pericardium. The deep plexus opens into the superficial, the efferents of which form right and left collecting trunks. The left trunks, two or three in number, ascend in the anterior longitudinal sulcus, receiving, in their course, vessels from both ventricles. On reaching the coronary sulcus they are joined b\' a large trunk from the diaphragmatic surface of the heart, and then unite to form a single vessel which ascends between the pulmonary artery and the left atrium and ends in one of the tracheobronchial R. recurrent nerve Paratracheal glands Innominate artery L. iracheobronchial glands L. ironcJiopulmo- nary glands R. tracheobronchial glands %£^^^CJ — 'ZP"^' b'^onchoptdmon- r^/^^/ ary glands Fig. 676. — The tracheobronchial lymph glands. (From a figure designed by M. Hall6.) glands. The right trunk receives its afferents from the right atrium and from the right border and diaphragmatic surface of the right ventricle. It ascends in the posterior longitudinal sulcus and then runs forward in the coronary sulcus, and passes up behind the pulmonary artery, to end in one of the tracheobronchial glands. The Lymphatic Vessels of the Lungs originate in two plexuses, a superficial and a deep. The superficial plexus is placed beneath the pulmonary pleura. The deep accompanies the branches of the pulmonary vessels and the ramifications of the bronchi. In the case of the larger bronchi the deep plexus consists of two net-works — one, submucous, beneath the mucous membrane, and another, peribronchial, outside the walls of the bronchi. In the smaller bronchi there is but a single plexus, which extends as far as the bronchioles, but fails to reach the alveoli, in the walls 800 ANGIOLOGY of which there are no traces of lymphatic vessels. The superficial efferents turn around the borders of the lungs and the margins of their fissures, and converge to end in some glands situated at the hilus; the deep efferents are conducted to the hilus along the pulmonary vessels and bronchi, and end in the tracheobronchial glands. Little or no anastomosis occurs between the superficial and deep lymph- atics of the lungs, except in the region of the hilus. The Lymphatic Vessels of the Pleura consist of two sets — one in the visceral and another in the parietal part of the membrane. Those of the visceral pleura drain into the superficial eft'erents of the lung, while the lymphatics of the parietal pleura have three modes of ending, viz.: (a) those of the costal portion join the lymphatics of the Intercostales interni and so reach the sternal glands; (b) those of the diaphragmatic part are drained by the efferents of the Diaphragma; while (c) those of the mediastinal portion terminate in the posterior mediastinal glands. The Lymphatic Vessels of the Thymus end in the anterior mediastinal, tracheo- bronchial, and sternal glands. The Lymphatic Vessels of the (Esophagus form a plexus around that tube, and the collecting vessels from the plexus drain into the posterior mediastinal glands. NEUROLOGY. T^HE Nervous System is the most complicated and highly organized of the various systems which make up the human body. It may be divided into two parts, central and peripheral. The central nervous system consists of (a) an upper expanded portion, the enceph- alon or brain, contained within the cranium, and (b) a lower, elongated, nearly cylindrical portion, the medulla spinalis or spinal cord, lodged in the vertebral canal; the two portions are continuous with one another at the level of the upper border of the atlas vertebra. The peripheral nervous system consists of a series of nerves by which the central nervous system is connected with the various tissues of the body. For descriptive purposes these nerves may be arranged in two groups, cerebrospinal and sympathetic, the arrangement, however, being an arbitrary one, since the two groups are inti- mateh^ connected and closely intermingled. The cerebrospinal nerves are forty- three in number on either side — twelve cerebral, attached to the brain, and thirty- one spinal, to the medulla spinalis. They are associated with the functions of the special and general senses and with the voluntary movements of the body. The sympathetic nerves transmit the impulses which regulate the movements of the viscera, determine the calibre of the bloodvessels, and control the phenomena of secretion. In relation with them are two rows of central ganglia, situated one on either side of the middle line in front of the vertebral column; these ganglia are intimately connected with the medulla spinalis and the spinal nerves, and are also joined to each other by vertical strands of nerve fibres so. as to constitute a pair of knotted cords, the sympathetic trunks, which reach from the base of the skull to the coccyx. The sympathetic nerves issuing from the ganglia form three great prevertebral plexuses which supply the thoracic, abdominal, and pelvic viscera; in relation to the walls of these viscera intricate nerve plexuses and numerous peripheral ganglia are found. The nervous system is built up of nervous and non-nervous tissues — the former consisting of nerve cells and nerve fibres; the latter, of neuroglia and bloodvessels, together with certain enveloping membranes. The minute structure of the nervous elements, and of the neuroglia, has been described in the chapter on Histology (pp. 69 to 76) ; and an outline of the devel- opment of the nervous system furnished in that on Embryology (pp. 117 to 133). The structure of the individual parts of the brain is given under their specific descriptions. Structure of the Peripheral Nerves and GangUa. — The cerebrospinal nerves consist of numerous nerve fibres collected together and enclosed in membranous sheaths (Fig. 677). A small bundle of fibres, enclosed in a tubular sheath, is called a funiculus ; if the nerve is of small size, it may consist only of a single funiculus; but if large, the funiculi are collected together into larger bundles or fasciculi, which are boimd together in a common membranous investment. In structure, the common membranous investment, or sheath of the whole nerve (epineurium) , as well as the septa given off from it to separate the fasciculi, consist of connective tissue, composed of white and yellow elastic fibres, the latter existing in great abundance. The tubular sheath of the funiculi (perineurium) is a fine, smooth, transparent membrane, which may be easily separated, in the form of a tube, from the fibres it encloses; in structure it is made up of connective tissue, which has a distinctly lamellar arrangement. The nerve fibres are held together and supported within 51 802 NEUROLOGY the funiculus by delicate connective tissue, called the endoneurium. It is continuous with septa which pass inward from the innermost layer of the perineurium, and shows a ground substance in which are imbedded fine bundles of fibrous connective tissue running for the most part longitudinally. It serves to support capillary vessels, arranged so as to form a net-work with elongated meshes. The cerebrospinal nerves consist almost exclusively of medullated nerve fibres, only a very small proportion of non-meduUated being present. The bloodvessels supplying a nerve end in a minute capillary plexus, the vessels composing which pierce the perineurium, and run, for the most part, parallel with the fibres; they are con- nected together by short, transverse vessels, forming narrow, oblong meshes, similar to the capillary system of muscle. Fine non-meduUated nerve fibres, vasomotor fibres, accompany these capillary vessels, and break up into elementary fibrils, which form a network around the vessels. Horsley has demonstrated certain medullated fibres running in the epineurium and terminating in small spheroidal tactile corpuscles or end bulbs of Krause. These nerve fibres, which Marshall beheves to be sensory, and which he has termed nervi nervorum, are considered by him^to have an important bearing upon certain neuralgic pains. Cpincurium 4'^<'»S»»JS". / set / - / y r Fig. 677. — Transverse section of human tibial nen^e. The nerve fibres, so far as is at present knowm, do not coalesce, but pursue an uninterrupted course from the centre to the periphery. In separating a nerve, however, into its component funicuh, it may be seen that these do not pursue a perfectly insulated course, but occasionally join at a very acute angle with other funiculi proceeding in the same dii'ection; from this, branches are given off, to join again in Like manner with other funiculi. It must be distinctly understood, however, that in these communications the individual nerve fibres do not coalesce, but merely pass into the sheath of the adjacent nerve, become intermixed with its nerve fibres, and again pass on to intermingle with the nerve fibres in some adjoining funiculus. Nerves, in their com-se, subdivide into branches, and these frequently communicate with branches of a neighboring nerve. The communications which thus take place form what is called a plexus. Sometimes a plexus is formed by the primary branches of the trunks of the nerves — as the cervical, brachial, lumbar, and sacral plexuses — and occasionally by the terminal funiculi, as in the plexuses formed at the periphery of the body In the formation of a plexus, the compo- nent nerves divide, then join, and again subdivide in such a complex manner that the indiA'idual funiculi become interlaced most intricately; so that each branch leaving a plexus may contain filaments from all the primary nervous trunks which form the plexus. In the formation also *of smaller plexuses at the periphery of the body there is a free interchange of the funiculi and primitive fibres. In each case, however, the individual fibres remain separate and distinct. It is probable that through this interchange of fibres, every branch passing off from a plexus has a more extensive connection with the spinal cord than if it had proceeded to its distribution without forming connections with other nerves. Consequently the parts supphed by these nerves have more extended relations -nath the nervous centres; by this means, also, groups of muscles may be associated for combined action. PERIPHERAL TERMIXATIOXS OF NERVES 803 The sympathetic nerves are constructed in the same manner as the cerebrospinal nerves, but consist mainly of nou-medullated fibres, collected in funiculi and enclosed in sheaths of connective tissue. There is, however, in these nerves a certain admixture of meduUated fibres. The number of the latter varies in different nerves, and may be estimated by the color of the nerve. Those branches of the sympathetic which present a well-marked gray color are composed chiefly of non-meduUated nerve fibres, intermixed with a few medullated fibres; while those of a white color contain manj' of the latter fibres, and few of the former. The cerebrospinal and sympathetic nerve fibres convey various impressions. The sensory nerves, called also centripetal or afferent nerves, transmit to the nervous centres impressions maile upon the peripheral extremities of the nerves, and in this wa}^ the mind, tlirough the medium of the brain, becomes conscious of external objects. The centrifugal or efferent nerves transmit impressions from the nervous centres to the parts to which the nerves are distributed, these impressions either exciting muscular contraction, or influencing the processes of nutrition, growth, and secretion. Origins and Terminations of Nerves. — By the expression "the terminations of nerve fibres" is signifietl their connections with the nerve centres and with the parts thej^ suppty. The former are sometimes called theu- origins or central terminations ; the latter their peripheral terminations. Origins of Nerves. — ^The origin in some cases is single — that is to say, the whole nerve emerges from the nervous centre by a single root; in other instances the nerve arises by two or more roots which come off from different parts of the nerve centre, sometimes widely apart from each other, and it often happens, when a nerve arises in this way by two roots, that the functions of these two roots are different; as, for example, in the spinal nerves, each of which arises by two roots, the anterior of which is motor, and the posterior sensory. The point where the nerve root or roots emerge from the surface of the nervous centre is named the superficial or apparent origin, but the fibres of the nerve can be traced for a certain distance into the substance of the nervous centre to some portion of the gi'ay matter, which constitutes the deep or real origin of the nerve. The centrifugal or efferent nerve fibres originate in the nerve cells of the gray substance, the axis-cj^linder processes of these cells being prolonged to form the fibres. In the case of the centrip- etal or afferent nerves the fibres grow" inward either from nerve cells in the organs of special sense, e. g., the retina, or from nerve cells in the gangha. Having entered the nerve centre they branch and send their ultimate twigs among the cells, without, however, uniting with them. Peripheral Terminations of Nerves. — Nerve fibres terminate peripherally in various ways, and these may be conveniently studied in the sensory and motor nerves respectively. The terminations of the sensory nerves are dealt with in the section on Sense Organs. Motor nerves can be traced into either unstriped or striped muscular fibres. In the unstriped or involuntary 77iuscles the nerves are derived from the sympathetic, and are composed mainly of non-medullated fibres. Near their terminations they di\dde into nimierous branches, which commimicate and form intimate plexuses. At the junctions of the branches small triangular nuclear bodies (ganghon cells) are situated. From these plexuses minute branches are given off which divide and break up into the ultimate fibrillae of w^hich the nerves are composed. These fibrillse coui-se between the involuntary muscle cells, and, according to EHscher, terminate on the surfaces of the ceUs, opposite the nuclei, in minute swellings. In the striped or voluntary muscle, the nerves supplying the muscular fibres are derived from the cerebrospinal nerves, and are composed mainly of medullated fibres. The nerve, after enter- ing the sheath of the muscle, breaks up into fibres or bundles of fibres, w^hich form plexuses, and gi-aduallj^ divide untU, as a rule, a single nerve fibre enters a single muscular fibre. Some- times, however, if the muscular fibre be long, more than one nerve fibre enters it. Within the muscular fibre the nerve terminates in a special expansion, called by Klihne, who first accurately described it, a motor end plate (Fig. 678) . The nerve fibre, on approaching the muscular fibre, suddenly loses its medullary sheath, the neiu-olemma becomes continuous with the sarcolemma of the muscle, and only the axis-cylinder enters the muscular fibre. There it at once spreads out, ramifying like the roots of a tree, immediately beneath the sarcolemma, and becomes imbedded in a layer of gi-anular matter, containing a number of clear, oblong nuclei, the w^hole constituting an end-plate from which the contractile wave of the muscular fibre is said to start. Ganglia are small aggregations of nerve cells. They are found on the posterior roots of the spinal nerves ; on the sensory roots of the trigeminal, facial, glossopharyngeal, and vagus nerves, and on the acoustic nerves. They are also found in connection with the sympathetic nerves. On section they are seen to consist of a reddish-graj^ substance, traversed by numerous white nerve fibres; they vary considerably in form and size; the largest are found in the cavitj^ of the abdomen; the smallest, not visible to the naked eye, exist in considerable numbers upon the nerves distributed to the different viscera. Each ganghon is invested bj^ a smooth and firm, closely adhering, membranous envelope, consisting of dense areolar tissue; this sheath is con- tinuous with the perinemium of the nerves, and sends numerous processes into the interior to support the bloodvessels supplying the substance of the ganghon. In structure aU gangha are essentially similar, consisting of the same structirral elements — viz., nerve cells and nerve fibres. Each nerve cell has a nucleated sheath which is continuous 804 NEUROLOGY with the neurolemma of the nerve fibre with which the cell is connected. The nerve cells in the gangUa of the spinal nerves (Fig. 679) are pjTiform in shape, and have each a single process. A short distance from the cell and while stiU within the ganglion this process divides in a T-shaped manner, one limb of the cross-bar turning into the medulla spinalis, the other limb passing out- ward to the periphery. In the sympathetic gangha (Fig. 680) the nerve cells are multipolar and each has one axis-cyUnder process and several dendrons; the axon emerges from the ganglion Fig. 678. — Muscular fibres of Lacerta viridis with the terminations of nerves, a. Seen in profile. P P. The nerve end-plates. S S. The base of the plate, consisting of a granular mass with nuclei. 6. The same as seen in looking at a perfectly fresh fibre, the nervous ends being probably stiU excitable. (The forms of the variously divided plate can hardly be represented in a woodcut by sufficiently delicate and pale contours to reproduce correctly what is seen in nature.) c. The same as seen two hours after death frorii poisoning by curare. as a non-medullated nerve fibre. Similar cells are found in the ganglia connected with the tri- geminal nerve, and these gangha are therefore regarded as the cerebral portions of the "autonomic" system. The autonomic nervous system includes those portions of the nervous mechanism in which a meduUated nerve fibre from the central system passes to a ganghon, sympathetic or peripheral, from which fibres, usually non-medullated, are distributed to such structures, e. g., bloodvessels, as are not under voluntary control. The spinal and sympathetic gangha differ somewhat in the size and disposition of the cells and in the number of nerve fibres entering and Fig. 679. — Transverse section of spinal ganglion of rabbit. A. Ganglion. X 30. a. Large clear nerve cell. 6. Small deeply staining nerve cell. c. Nuclei of capsule. X 250. The lines in the centre point to the corresponding cells in the ganglion. leaving them. In the spinal gangha (Fig. 679) the nerve cells are much larger and for the most part collected in groups near the periphery, while the fibres, which are mostly meduUated, traverse the central portion of the ganghon; whereas in the sympathetic ganglia (Fig. 680) the cells are smaller and distributed in irregular groups throughout the whole ganglion; the fibres also are irregulary scattered; some of the entering ones are meduUated, while many of those leaving the ganghon are non-meduUated. THE MEDULLA SPLXALIS OR SPINAL CORD 805 Neuron Theory. — The nerve cell and its processes collectively constitute what is termed a neuron, and AA'aldeycr formulated the theory that the nervous system is built up of numerous neurons, "anatomically and genetically independent of one another." According to this theory {neuron theory) the processes of one neuron only come into contact, and are never in direct continuity, with thoseof other neurons; while impulses are transmitted from one nerve cell to another through these points of contact. This theory is based on the following facts, viz.: (1) embryonic nerve cells or neuroblasts are entirely distinct from one another; (2) when nervous tissues are stained by the Golgi method no continuity is seen even between neighboring neurons; and (3) when degenerative changes occur in nervous tissue, either as the result of disease or experiment, they never spread from one nem-on to another, but are limited to the individual nem-ons, or gi'oups of neurons, primarily affected. It must, however, be Nerve-cells of ganglion i: K'^:h^^-? Fig. 680. — Transverse section of sympathetic ganglion of cat. A. Ganglion. X 50. a. A nerve cell. X 250. Fig. 681. — Sagittal section of vertebral canal to show the lower end of the meduUa spinalis and the filum terminale. (Testut.) Li, Lv. First and fifth lumbar vertebrse. Sii. Second sacral vertebra. 1. I3ura mater. 2. Lower part of tube of dura mater. 3. Lower extremity of medulla spinalis. 4. Intradural, and 5, Extra- dural portions of filum terminale. 6. Attach- ment of filum terminale to first segment of coccyx. added that within the past few years the validity of the neuron theory has been called in question bj^ certain eminent histologists, who maintain that by the emplojrment of more deU- cate histological methods, minute fibrils can be followed from one nerve cell into another. THE MEDULLA SPINALIS OR SPINAL CORD. Dissection. — To dissect the medulla spinaUs and its membranes it will be necessary to lay open the whole length of the vertebral canal. For this purpose the muscles must be separated from the vertebral grooves, so as to expose the spinous processes and laminae of the vertebrae; and the latter must be sawn through on each side, close to the roots of the transverse processes, from the third or fom-th cervical vertebra above to the sacrum below. The vertebral arches ha^'ing been displaced by means of a chisel and the separate fragment^ removed, the dura will be exposed, covered by a plexus of veins and a quantity of loose areolar tissue, often infiltrated with serous fluid. The arches of the upper vertebrae are best divided by means of a strong pair of cutting bone forceps or by a rachitome. The medulla spinalis or spinal cord forms the elongated, nearly cylindrical, part of the central nervous system which occupies the upper two-thirds of the vertebral canal. Its average length in the male is about 45 cm., in the female from -42 to 43 cm., while its weight amounts to about 30 gms. It extends from the level of the upper border of the atlas to that of the lower border of the first, or upper border 806 NEUROLOGY of the second, lumbar vertebra. Above, it is continuous with the brain; below, it ends in a conical extremity, the conus medullaris, from the apex of which a delicate filament, the filum terminale, descends as far as the first segment of the coccyx (Fig. 681). The position of the medulla spinalis varies wdth the movements of the vertebral column, its lower extremity being drawn slightly upward when the column is flexed. It also varies at different periods of life; up to the third month of fetal life the medulla spinalis is as long as the vertebral canal, but from this stage onward the vertebral column elongates more rapidly than the medulla spinalis, so that by the end of the fifth month the medulla spinahs terminates at the base of the sacrum, and at birth about the third lumbar vertebra. The medulla spinalis does not fill the part of the vertebral canal in which it lies; it is ensheathed by three protective membranes, separated from each other by two concentric spaces. The three membranes are named from without inward, the dura mater, the arachnoid, and the pia mater. The dura mater is a strong, fibrous membrane which forms a wide, tubular sheath; this sheath extends below the ter- mination of the medulla spinalis and ends in a pointed cul-de-sac at the level of the lower border of the second sacral vertebra. The dura mater is separated from the wall of the vertebral canal by the epidural cavity, which contains a quantity of loose areolar tissue and a plexus of veins; between the dura mater and the subjacent arachnoid is a capillary interval, the subdural cavity, which contains a small quan- tity of fluid, probably of the nature of lymph. The arachnoid is a thin, transparent sheath, separated from the pia mater by a comparatively wide interval, the sub- arachnoid cavity, w^hich is filled with cerebrospinal fluid. The pia mater closely invests the medulla spinalis and sends delicate septa into its substance; a narrow band, the ligamentum denticulatum, extends along each of its lateral surfaces and is attached by a series of pointed processes to the inner surface of the dura mater. Thirty-one pairs of spinal nerves spring from the medulla spinahs, each nerve having an anterior or ventral, and a posterior or dorsal root, the latter being dis- tinguished by the presence of an oval swelling, the spinal ganglion, which contains numerous nerve cells. Each root consists of several bundles of nerve fibres, and at its attachment extends for some distance along the side of the medulla spinalis. The pairs of spinal nerves are grouped as follows: cervical 8, thoracic 12, lumbar 5, sacral 5, coccygeal 1, and, for convenience of description, the medulla spinalis is divided into cervical, thoracic, lumbar and sacral regions, corresponding with the attachments of the different groups of nerves. Although no trace of transverse segmentation is visible on the surface of the medulla spinalis, it is convenient to regard it as being built up of a series of super- imposed spinal segments or neuromeres, each of which has a length equivalent to the extent of attachment of a pair of spinal nerves. Since the extent of attach- ment of the successive pairs of nerves varies in different parts, it follows that the spinal segments are of varying lengths; thus, in the cervical region they average about 13 mm., in the mid-thoracic region about 26 mm., while in the lumbar and sacral regions they diminish rapidly from about 15 mm. at the level of the first pair of lumbar nerves to about 4 mm. opposite the attachments of the lower sacral nerves. As a consequence of the relative inequality in the rates of growth of the medulla spinalis and vertebral column, the nerve roots, which in the early embryo passed transversely outward to reach their respective intervertebral foramina, become more and more oblique in direction from above downward, so that the lumbar and sacral nerves descend almost vertically to reach their points of exit. From the appearance these nerves present at their attachment to the medulla spinalis and from their great length they are collectively termed the cauda equina (Fig. 682). THE MEDULLA SPINALIS OR SPINAL CORD 807 The filum terminale is a delicate filament, about 20 cm. in length, prolonged downAvard from the apex of the conns medullaris. It consists of two parts, an upper and a l()\\er. The upper ])art, or filum terminale internum, measures about 15 cm. in length and reaches as far as the lower border of the second sacral verte- bra. It is contained within the tubular sheath of dura mater, and is surrounded by the nerves forming the cauda equina, from which it can be readily recognized by its bluish-white color. The lower part, or filum terminale externum, is closely invested by, and is adherent to, the dura mater; it extends downward from the apex of the tubular sheath Decussation nf the 'pyramids Anterior median fissure Dura mater Conus medullaris Posterior nerveroots Filum terminale Postero- ■ intermediate sulcus Cervical enlargement Posterior median sulcus Postero- lateral sulcus — Filum Lumbar enlargement ■ Comis Fig. 682. — Cauda equina and filum terminale seen from behind. The dura mater has been opened and spread out, and the arachnoid has been removed. Ventral aspect Dorsal aspect Fig. 6S3. — Diagrams of the medulla spinalis. 808 NEUROLOGY and is attached to the back of the first segment of the coccyx. The filum ter- minale consists mainly of fibrous tissue, continuous above with that of the pia mater. Adhering to its outer surface, however, are a few strands of nerve fibres which probably represent rudimentary second and third coccygeal nerves; further, the central canal of the medulla spinalis extends downward into it for 5 or 6 cm. Enlargements. — The medulla spinalis is not quite cylindrical, being slightly flattened from before backward; it also presents two swellings or enlargements, an upper or cervical, and a lower or lumbar (Fig. 683). The cervical enlargement is the more pronounced, and corresponds with the attach- ments of the large nerves which supply the upper limbs. It extends from about the third cervical to the second thoracic vertebra, its maximum circumference (about 38 mm.) being on a level with the attachment of the sixth pair of cervical nerves. The lumbar enlargement gives attachment to the nerves which supply the lower limbs. It commences about the level of the ninth thoracic vertebra, and reaches its maximum circumference, of about 33 mm., opposite the last thoracic vertebra, below which it tapers rapidly into the conus medullaris. Fissures and Sulci (Fig. 684). — An anterior median fissure and a posterior median sulcus incompletely divide the medulla spinalis into two symmetrical parts, which are joined across the middle line by a commissural band of nervous matter. The Anterior Median Fissure {fissura viediana anterior) has an average depth of about 3 mm., but this is increased in the lower part of the medulla spinalis. It contains a double fold of pia mater, and its floor is formed by a transverse band of white substance, the anterior white commissure, which is perforated by blood- vessels on their way to or from the central part of the medulla spinalis. The Posterior Median Sulcus (sulcus medianus posterior) is very shallow; from it a septum of neuroglia reaches rather more than half-way into the substance of the medulla spinalis; this septum varies in depth from 4 to 6 mm., but diminishes considerably in the lower part of the medulla spinalis. On either side of the posterior median sulcus, and at a short distance from it, the posterior nerve roots are attached along a vertical furrow named the postero- lateral sulcus. The portion of the medulla spinalis which lies between this and the posterior median sulcus is named the posterior funiculus. In the cervical and upper thoracic regions this funiculus presents a longitudinal furrow, the postero-inter- mediate sulcus; this marks the position of a septum which extends into the posterior funiculus and subdivides it into two fasciculi — a medial, named the fasciculus gracilis (tract of Goll); and a lateral, the fasciculus cuneatus (tract of Burdach) (Fig. 690). The portion of the medulla spinalis which lies in front of the postero- lateral sulcus is termed the antero-lateral region. The anterior nerve roots, unlike the posterior, are not attached in linear series, and their position of exit is not marked by a sulcus. They arise by separate bundles wdiich spring from the anterior column of gray substance and, passing forw^ard through the white substance, emerge over an area of some slight wndth. The most lateral of these bundles is generally taken as a dividing line which. separates the antero-lateral region into two parts, viz., an anterior funiculus, between the anterior median fissure and the most lateral of the anterior nerve roots; and a lateral funiculus, between the exit of these roots and the postero-lateral sulcus. In the upper part of the cervical region a series of nerve roots passes outward through the lateral funiculus of the medulla spinalis; these unite to form the spinal portion of the accessory nerve, which runs upward and enters the cranial cavity through the foramen magnum. The Internal Structure of the Medulla Spinalis. — On examining a transverse section of the medulla spinalis (Fig. 684) it is seen to consist of gray and white nervous substance, the former being enclosed within the latter. THE MEDULLA SPINALIS OR SPINAL CORD 809 Gray Substance {suhstaidla (/risea centralis). — The gray substance consists of two symmetrical portions, one in each half of the medulla spinalis: these are joined across the middle line by a transverse commissure of gray substance, through which runs a minute canal, the central canal, just \'isible to the naked eye. In a transverse section each half of the gray substance is shaped like a comma or crescent, the concavity of which is directed laterally; and these, together with the intervening gray commissure, present the appearance of the letter H. An imaginary coronal plane through the central canal serves to divide each crescent into an anterior or ventral, and a posterior or dorsal column. The Anterior Column {columna anterior; anterior' cornu), directed forward, is broad and of a rounded or quadrangular shape. Its posterior part is termed the base, and its anterior part the head, but these are not differentiated from each other by any well-defined constriction. It is separated from the surface of the medulla spinalis by a layer of white substance which is traversed by the bundles of the anterior nerve roots. In the thoracic region, the postero-lateral part of the anterior column projects lateralward as a triangular field, which is named the lateral column (columna lateralis; lateral cornu). Posterior median sulcus Posterior median septum Postero-lateral sulcus Posterior column Formatio reticularis Lateral column Anterior column Anterior nerve roots Anterior median fissure Fig. 684. — Transverse section of the medulla spinalis in the mid-thoracic region. The Posterior Column {columna yosterior; posterior cornu) is long and slender, and is directed backward and lateralward : it reaches almost as far as the postero- lateral sulcus, from which it is separated by a thin layer of white substance, the tract of Lissauer. It consists of a base, directly continuous with the base of the anterior horn, and a neck or slightly constricted portion, which is succeeded by an oval or fusiform area, termed the head, of which the apex approaches the postero- lateral sulcus. The apex is capped by a V-shaped or crescentic mass of trans- lucent, gelatinous neuroglia, termed the substantia gelatinosa of Rolando, which contains both neuroglia cells, and small nerve cells. Between the anterior and posterior columns the gray substance extends as a series of processes into the lateral funiculus, to form a net-work called the formatio reticularis. The quantity of gray substance, as well as the form which it presents on trans- verse section, varies markedly at different levels. In the thoracic region it is small, not only in amount but relatively to the surrounding w^hite substance. In the 810 NEUROLOGY CI C2, as. cervical and lumbar enlargements it is greatly increased : in the latter, and especially in the conns mediillaris, its proportion to the white substance is greatest (Fig. 685). In the cervical region its posterior column is comparatively narrow, while its anterior is broad and expanded; in the thoracic region, both columns are attenuated, and the lateral column is evident; in the lumbar enlargement, both are expanded; while in the conus medullaris the gray substance assumes the form of two oval masses, one in each half of the cord, connected together by a broad gray commissure. The Central Canal (canalis ceniraJis) runs through- out the entire length of the medulla spinalis. The portion of gray substance in front of the canal is named the anterior gray commissure ; that behind it, the posterior gray commissure. The former is thin, and is in contact anteriorly with the anterior white commissure: it contains a couple of longitudinal veins, one on either side of the middle line. The posterior gray commissure reaches from the central canal to the posterior median septum, and is thin- nest in the thoracic region, and thickest in the conus medullaris. The central canal is continued upward through the lower part of the medulla oblongata, and opens into the fourth ventricle of the brain; below, it reaches for a short distance into the filum termi- nale. In the lower part of the conus medullaris it exhibits a fusiform dilatation, the terminal ventricle; this has a vertical measurement of from 8 to 10 mm., is triangular on cross-section with its base directed forward, and tends to undergo obliteration after the age of forty years. Throughout the cervical and thoracic regions the central canal is situated in the anterior third of the medulla spinalis; in the lumbar enlargement it is near the middle, and in the conus medullaris it approaches the posterior surface. It is filled with cerebrospinal fluid, and lined by ciliated, columnar epithelium, outside of which is an encircling band of gelatinous substance, the substantia gelatinosa centralis. This gelatinous substance consists mainly of neuroglia, but contains a few nerve cells and fibres; it is traversed by processes from the deep ends of the columnar ciliated cells which line the central canal 'Fig. 686). Structure of the Gray Substance. — The gray sub- stance consists of numerous nerve cells and nerve fibres held together by neuroglia. Throughout the greater part of the gray substance the neuroglia presents the appearance of a sponge-like net-work, but around the central canal and on the apices of the posterior columns it consists of the gelatinous substance already referred to. The nerve cells are multipolar, and vary greatly in size and shape. They consist of (1) motor cells of large size, which are C.8. Th2. ThS, Th12 L.3. S.2. Coa Fio. 685. — Trans\'erse sections of the medulla spinalis at different levels. THE MEDULLA SPINALIS OR SPIXAL CORD 811 situated in the anterior horn, and are especially numerous in the cervical and lumbar enlargements; the axons of most of these cells pass out to form the anterior nerve roots, but before leaving the white substance they frequently give off collaterals, which reenter and ramify in the gray substance.^ (2) Cells of small OF medium size, whose axons pass into the white matter, where some pursue an ascending, and others a descending course, but most of them divide in a T-shape manner into descending and ascending processes. They give off collaterals which enter and ramify in the gray substance, and the terminations of the axons behave in a similar manner. The lengths of these axons vary greatly : some are short and pass only between adjoining spinal segments, while others are longer and connect more distant segments. These cells and their processes constitute a series of association or interseg- mental neurons (Fig. 687), which link together the different parts of the medulla spinalis. The axons of most of these cells are confined to that side of the medulla spinalis in which the nerve cells are situ- ated, but some cross to the oppo- site side through the anterior com- missure, and are termed crossed commissural fibres. Some of these latter end directly in the gray sub- stance, while others enter the wdiite Neuroglial cells Ejiendymal cells Fig. 686. — Section of central canal of medulla spinalis, showing ependymal and neuroglial cells, (v. Lenhossek.) ; ^^^-'^ Collateral — Ascending \-- Descending "Arborisation Fig. 687. — Cells of medulla spinalis. (Poirier.) Diagram showing in longitudinal section the intersegmental neurons of the medulla spinalis. The gray and white parts corre- spond respectively to the gray and white substance of the medulla spinalis. substance, and ascend or descend in it for varying distances, before finally termi- nating in the gray substance. (3) Cells of the type II of Golgi, limited to the posterior column, are found in the substantia gelatinosa of Rolando; their axons are short and entirely confined to the gray substance, in w^hich they break up into numerous fine filaments. Most of the nerve cells are arranged in longitu- dinal column, and appear as groups on transverse section (Figs. 688, 689). Nerve Cells in the Anterior Column. — The nerve cells in the anterior column are arranged in columns of varying length. The longest occupies the medial part of 1 Lenhossek and Cajal found that in the chick embrj'o the axons of a few of these nerve cells passed backward through the posterior column, and emerged as the motor fibres of the posterior nerve roots. These fibres are said to control the peristaltic movements of the intestine. Their presence, in man, has not j'et been determined. 812 NEUROLOGY the anterior column, and is named the antero-medial column: it is absent only in the fifth lumbar, the first sacral and the upper part of the second sacral segments (Bruce). ^ Behind it is a dorso-medial column of small cells, which extends from the second thoracic to the first lumbar segment, and is also present in the first, sixth, and seventh cervical segments. -11 Fig. 688. — Mode of distribution of the nerve cells in the gray substance. (Schematic.) (Testut.) 1, 2. Medial and lateral groups of nerve cells in anterior column. 3. Nerve cells in lateral column. 4,4. Dorsal nucleus. 5. Group of nerve cells in substantia gelatinosa of Rolando. 6. Nerve cell of anterior column, the axon of which is passing into the posterior nerve root. 7. Cells of substantia gelatinosa centralis. 8, S'. Solitary cells. 9. Cells of Golgi. 10. Cells of origin of the superficial antero-lateral fasciculus. 11. Anterior root. 12. Posterior root. 13. Spinal ganglion. In the cervical and lumbar enlargements, where the anterior column is expanded in a lateral direction, the following additional columns are present, viz. : (a) antero- lateral, in the fourth, fifth, and sixth cervical and the second thoracic segments, and in the lower four lumbar and upper two sacral segments; (6) postero-lateral, in the lower five cervical, lower four lumbar, and upper three sacral segments; (c) post-postero-lateral, in the last cervical, first thoracic, and upper three sacral segments; and {d) a central, in the lower four lumbar and upper two sacral segments. Throughout the base of the anterior column are scattered solitary cells, the axons of some of which form crossed commissural fibres, while others constitute the motor fibres of the posterior nerve roots. (See footnote, page 811.) Nerve Cells in the Lateral Column. — These form a column which is best marked where the lateral gray column is differentiated, viz., in the thoracic region;- but it can be traced throughout the entire length of the medulla spinalis in the form of groups of small cells wdiich are situated in the anterior part of the formatio reticularis. The cells of this column are fusiform or star-shaped, and of a medium size : the axons of some of them pass into the anterior nerve roots, by w' hich they are carried to the sympathetic nerves; while the axons of others pass into the anterior and lateral funiculi, where they become longitudinal. 1 Topographical Atlas of the Spinal Cord, 1901. 2 According to Bruce and Pirie (B. M. J., November 17, 1906) this column extends from the middle of the eighth cervical segment to the lower part of the second lumbar or the upper part of the third lumbar segment. THE MEDULLA SLLXALLS OR SPINAL CORD 813 Lateral column' Postero- lateral column Dorso-medial column Antero-medial column Nerve Cells in the Posterior Column. — 1. The dorsal nucleus (nucleus- don-ali.'i; col- umn of Clarke) occupies the medial j)art of the base of the posterior cohiinu, and appears on the transverse section as a well-defined oval area. It begins below at the level of the second or third lumbar nerve, and reaches its maximum size opposite the twelfth thoracic nerve. Above the level of the ninth thoracic nerve its size diminishes, and the column ends opposite the last cer- vical or first thoracic nerve. It is represented, however, in the other regions by scattered cells, which become aggregated to form a cer- vical nucleus opposite the third cervical nerve, and a sacral nucleus in the middle and lower part of the sacral region. Its cells are of medium size, and of an oval or pyriform shape; their axons pass into the peripheral part of the lateral funiculus of the same side, and there ascend, under the name of the cerebellospinal {direct cerebellar) fasciculus. 2. The nerve cells in the substantia gelatinosa of Rolando are arranged in three zones: a posterior or marginal, of large angular or fusi- form cells; an intermediate, of small fusiform cells; and an anterior, of star-shaped cells. The axons of these cells pass into the lateral and posterior funiculi, and there assume a vertical course. In the anterior zone some Golgi cells are found whose short axons ramify in the gray substance. 3. Solitary cells of varying form and size are scat- tered throughout the posterior column. Some of these are grouped to form the posterior basal column in the base of the posterior column, lateral to the dorsal nucleus; the posterior basal column is wellr marked in the gorilla (Waldeyer), but is ill-defined in man. The axons of its cells pass partly to the pos- terior and lateral funiculi of the same side, and partly through the anterior white commissure to the lateral funiculus of the opposite side. Before leaving the gray substance,' a considerable number run longitu- dinally for a varying distance in the head of the posterior column, form- ing what is termed the longitudinal fasciculus of the posterior column. Antero-medial column Antero-laieral, columyi Postero-lateral colmnn Central t column Fig. 689. — Transverse sections of the medulla spinalis at different levels to show the arrangement of the principal cell columns. • 814 NEUROLOGY A few star-shaped or fusiform nerve cells of varying size are found in the sub- stantia gelatinosa centraHs. Their axons pass into the hxteral funicuhis of the same, or of the opposite side. The nerve fibres in the gray substance form a dense interlacement of minute fibrils among the nerve cells. This interlacement is formed partly of axons which pass from the cells in the gray substance to enter the white funiculi or nerve roots; partly of the axons of Golgi's cells which ramify only in the gray substance; and partly of collaterals from the nerve fibres in the white funiculi which, as already stated, enter the gray substance and ramify within it. Posterior median iulcus Cornucmnmissural fasciculus Fasciculus gracilis Com in a fasciculus Fasciculus cuneatus Lissaucr's fasciculus Lateral cerebro- spinal fasciculus Cerebellospinal fasciculus Rubrospinal fasciculus Lateral proper fasciculus Superficial anterolateral fasciculus Olivospinal fasciculus A nterior propter fasciculus Anterior cerebrospinal fasciculus A nterior median fissure Fig. 690. — Diagram of the principal fasciculi in the medulla spinalis. White Substance {substantia alba). — The white substance of the medulla spinalis consists of medullated nerve fibres imbedded in a sponge-like net-work of neuroglia, and is arranged in three funiculi: anterior, lateral, and posterior. The anterior funiculus lies between the anterior median fissure and the most lateral of the ante- rior nerve roots: the lateral funiculus between these nerve roots and the postero- lateral sulcus; and the posterior funiculus between the postero-lateral and the pos- terior median sulci (Fig. 690). The fibres vary greatly in thickness, the smallest being found in the fasciculus gracilis, the tract of Lissauer, and inner part of the lateral funiculus ; while the largest are situated in the anterior funiculus, and in the peripheral part of the lateral funiculus. Some of the nerve fibres assume a more or less transverse direction, as for example those which cross from side to side in the anterior white commissure, but the majority pursue a longitudinal course and are divisible into (1) those connecting the medulla spinalis with the brain and conveying impulses to or from the latter, and (2) those which are confined to the medulla spinalis and link together its different segments, i. e., intersegmental or association fibres. Nerve Fasciculi. — The longitudinal fibres are grouped into more or less definite bundles or fasciculi. These are not recognizable from each other in the normal A nterior nerve roots THE MEDULLA SPINALLH OR SPINAL CORD 815 state, and their existence has been determined by the following methods: (1) A. Waller discovered that if a bundle of nerve fibres be cut, the portions of the fibres which are separated from their cells rapidly degenerate and become atrophied, Avhile the cells and the parts of the fibres connected with them undergo little alter- ation.^ This is known as Wallerian degeneration. Similarly, if a group of nerve cells be destroyed, the fibres arising from them undergo degeneration. Thus, if the motor cells of the cerebral cortex be destroyed, or if the fibres arising from these cells be severed, a descending degeneration from the seat of injury ta,kes place in the fibres. In the same manner, if a spinal ganglion be destroyed, or the fibres which ])ass from it into the medulla spinalis be cut, an ascending degenera- tion will extend along these fibres. (2) By tracing the development of the nervous system, it has been observed that at first the nerve fibres are merely naked axis- cjdinders, and that they do not all acquire their medullary sheaths at the same time; hence the fibres can be grouped into difl'erent bundles according to the dates at which the}^ receive their medullary sheaths. (3) Various methods of staining nervous tissue are of great value in tracing the course and mode of termination of the axis-cylinder processes. Fasciculi in the Anterior Funiculus. — The principal fasciculus is the anterior cerebro- spinal (fasciculus cerehrospinalis anterior; direct 'pyramidal tract), which is usually small, but varies inversely in size with the lateral cerebrospinal fasciculus. It lies close to the anterior median fissure, and is present only in the upper part of the medulla spinalis; gradually diminishing in size as it descends, it ends about the middle of the thoracic region. It consists of descending fibres which arise from cells in the motor area of the cerebral hemisphere of the same side, and which, as they run downward in the medulla spinalis, cross in succession through the anterior white commissure to the opposite side, where they end by arborizing around the motor cells in the anterior column. In addition to the anterior cerebrospinal fasciculus there are strands of fibres in the anterior funiculus connecting certain ganglia in the brain with the gray sub- stance of the medulla spinalis. The most important of these is the vestibulospinal, situated chiefly in the marginal part of the funiculus and mainly derived from the cells of Deiters' nucleus, i. e., the chief terminal nucleus of the vestibular division of the acoustic nerve. Of the other descending fibres some pass downward from the corpora quadrigemina (tectospinal) and others are continuous with the medial longitudinal fasciculus. The remaining fibres of the anterior funiculus constitute what is termed the anterior proper fasciculus {fasciculus anterior proprius; anterior basis bundle). It consists of (a) longitudinal intersegmental fibres which arise from cells in the gray substance, more especially from those of the medial group of the anterior column, and, after a longer or shorter course, reenter the gray substance; (6) fibres which cross in the anterior white commissure from the gray substance of the opposite side; (c) fibres arising from cells of the cerebellum and extending down the medulla spinalis to end around the cells of the anterior column — these fibres constitute an irregular tract, cerebellospinal tract of Lowenthal, disposed in the peripheral portions of the anterior and lateral proper fasciculi; and {d) fibres of the anterior nerve roots, which run obliquely forward to reach the surface of the medulla spinalis. Fasciculi in the Lateral Funiculus. — 1. Descending Fasciculi. — (a) The lateral cerebrospinal fasciculus (fasciculus cerebrospinalis lateralis; crossed pyramidal tract) extends throughout the entire length of the medulla spinalis, and on trans- verse section appears as an oval area in front of the posterior column and medial 1 Somewhat later a change, termed chromalolysis, takes place in the nerve cells, and consists of a breaking down and an ultimate disappearance of the Nissl bodies. Further, the body of the cell is swollen, the nucleus displaced toward the periphery, and the part of the axon still attached to the altered cell is diminished in size and somewhat atrophied. Under favorable conditions the cell is capable of reassuming its normal appearance, and its axon may grow again. 816 NEUROLOGY to the cerebellospinal. Its fibres arise from cells in the motor area of the cerebral hemisphere of the opposite side. They pass downward in company with those of the anterior cerebrospinal fasciculus through the same side of the brain as that from which they originate, but they cross to the opposite side in the medulla oblon- gata and descend in the lateral funiculus of the medulla spinalis; they end by arborizing around the motor cells in the anterior column.^ The anterior and lateral cerebrospinal fasciculi constitute the motor fasciculi of the medulla spinalis and have their origins in the motor cells of the cerebral cortex. They descend through the internal capsule of the cerebrum, traverse the cerebral peduncles and pons and enter the pyramid of the medulla oblongata. In the lower part of the latter about two-thirds of them cross the middle line and run downward in the lateral funiculus as the lateral cerebrospinal fasciculus, while the remaining fibres do not cross the middle line, but are continued into the same side of the medulla spinalis, where they form the anterior cerebrospinal fasciculus. The fibres of the latter, however, cross the middle line in the anterior white com- missure, and thus all the motor fibres from one side of the brain ultimately reach the opposite side of the medulla spinalis. The proportion of fibres which cross in the medulla oblongata is not a constant one, and thus the anterior and lateral cerebrospinal fasciculi ^-ary inversely in size. Sometimes the former is absent, and in such cases it may be presumed that the decussation of the motor fibres in the medulla oblongata has been complete. The fibres of these two fasciculi do not acquire their medullary sheaths until after birth. In some animals the motor fibres are situated in the posterior funiculus. (6) The rubrospinal fasciculus (Monakow) {prepyr amidol tract), lies on the ventral aspect of the lateral cerebrospinal fasciculus and on transverse section appears as a somewhat triangular area. Its fibres descend from the mid-brain, where they have their origin in the red nucleus of the tegmentum of the opposite side. (c) The tectospinal fasciculus originates in the superior colliculus (upper quad- rigeminal body) of the opposite side, and its fibres are partly intermingled with those of the rubrospinal fasciculus, and are partly contained in the anterior funiculus. {d) The olivospinal fasciculus (Helweg) arises in the vicinity of the inferior olivary nucleus in the medulla oblongata, and is seen only in the cervical region of the medulla spinalis, where it forms a small triangular area at the periphery, close to the most lateral of the anterior nerve roots. Its exact origin and its mode of ending have not yet been definitely made out. 2. Ascending Fasciculi. — (a) The cerebellospinal fasciculus {fasciculus cerehello- spinalis; direct cerebellar tract of Flechsig) is situated at the periphery of the pos- terior part of the lateral funiculus, and on transverse section appears as a flattened band reaching as far forward as a line drawn transversely through the central canal. Medially, it is in contact with the lateral cerebrospinal fasciculus, behind, with the fasciculus of Lissauer. It begins about the level of the second or third lumbar nerve and, increasing in size as it ascends, passes to the cerebellum through tlie restiform body. Its fibres are generally regarded as being formed b}' the axons of the cells of the dorsal nucleus (Clarke's column); the}' receive their medullary sheaths about the sixth or seventh month of fetal life. (b) The superficial antero-lateral fasciculus (fasciculus anterolateralis superficialis; tract of Gowers) skirts the periphery of the lateral funiculus in front of the cerebello- spinal fasciculus. In transverse section it is shaped somewhat like a comma, the expanded end of which lies in front of the lateral cerebrospinal fasciculus while the tail reaches forward into the anterior funiculus. Its fibres come from the oppo- 1 It is probable (Sohafer, Proc. Physiolog. Soc, 1899) that the fibres of the anterior and lateral cerebrospinal fasciculi are not related in this direct manner -nith the cells of the anterior column, but terminate by arborizing around the cells at the base of the posterior column and the cells of Clarke's column, which in turn link them to the motor cells in the anterior column, usually of several segments of the cord. In consequence of these interposed neurons the fibres of the cerebrospinal fasciculi correspond not to individual muscles, but to associated groups of "muscles. THE MEDULLA SPINALIS OR SPINAL CORD 817 site side of the medulla spiiuilis and cross in the anterior white commissure; they are derived from the cells of the dorsal nucleus and from other cells of the posterior column. The superficial antero-lateral fasciculus begins about the level of the third pair of lumbar nerves, and, increasing in size as it ascends, can l)e followed into the me(hiUa oblongata and pons. It consists of three fasciculi: (1) the ventral spino- cerebellar, the largest of the three, passes to the cerebellum by way of the brachia conjunctiva; (2) the spinothalamic ends in the thalamus, and is sometimes termed the secondary sensory fasciculus; and (3) the spinotectal passes to the corpora quadrigemina. (c) The fasciculus of Lissauer is a small strand situated in relation to the tip of the posterior column close to the entrance of the posterior nerve roots. It consists of fine fibres which do not receive their medullary sheaths until toward the close of fetal life. It is usually regarded as being formed by some of the fibres of the posterior nerve roots, which ascend for a short distance in the tract and then enter the posterior column, but since its fibres are myelinated later than those of the posterior nerve roots, and do not undergo degeneration in locomotor ataxia, they are probably intersegmental in character. (d) The lateral proper fasciculus (fasciculus lateralis i^roprius; lateral basis bundle) constitutes the remainder of the lateral column, and is continuous in front with the anterior proper fasciculus. It consists chiefly of intersegmental fibres which arise from cells in the gray substance, and, after a longer or shorter course, reenter the gray substance and ramify in it. Some of its fibres are, however, continued upward into the brain under the name of the medial longitudinal fasciculus. Fasciculi in the Posterior Funiculus. — This funiculus comprises two main fasciculi, viz., the fasciculus gracilis, and the fasciculus cuneatus. These are separated from each other in the cervical and upper thoracic regions by the postero-intermediate septum, and consist mainly of ascending fibres derived from the posterior nerve roots. The fasciculus gracilis (tract of Goll) is wedge-shaped on transverse section, and lies next the posterior median septum, its base being at the surface of the medulla spinalis, and its apex directed toward the posterior gray commissure. It increases in size from below^ upward, and consists of long thin fibres which are derived from the posterior nerve roots, and ascend as far as the medulla oblongata, w^here they end in the nucleus gracilis. The fasciculus cuneatus {tract of Burdach) is triangular on transverse section, and lies between the fasciculus gracilis and the posterior column, its base corre- sponding wdth the surface of the medulla spinalis. Its fibres, larger than those of the fasciculus gracilis, are mostly derived from the same source, viz., the posterior nerve roots. Some ascend for only a short distance in the tract, and, entering the gray matter, come into close relationship with the cells of the dorsal nucleus; while others can be traced as far as the medulla oblongata, where they end in the gracile and cuneate nuclei. Occupying the ventral part of the posterior funiculus is a strand of fibres termed the cornu-commissural fasciculus. It is somewhat triangular on transverse section, and occupies the angle between the posterior gray commissure and the posterior column. It is best marked in the lumbar region, but can be traced into the thoracic and cervical regions. Its fibres, derived from the cells of the posterior column, divide into ascending and descending branches which reenter and ramify in the gray substance. It has been found to preserve its integrity in certain cases of locomotor ataxia. Descending Fibres in the Posterior Funiculus (Fig. 692) . — The posterior funiculus contains some descending fibres which occupy different parts at different levels. In the cervical and upper thoracic regions, they appear as a comma-shaped fasciculus in the lateral part of the fasciculus cuneatus, the blunt end of the comma being 52 818 NEUROLOGY directed toward the posterior gray commissure; in the lower thoracic region they form a dorsal peripheral band on the posterior surface of the funiculus; in the lumbar region, they are situated by the side of the posterior median septum, and appear on section as a semi-elliptical bundle, which, together with the corresponding bundle of the opposite side, forms the oval area of Flechsig; while in the conus medullaris they assume the form of a triangular strand in the postero-medial part First thoracic 7ierve Descending comma fasciculus \\ Sacral A'l ' nerves I N Posterior column \ Posterior column Oval area of FlecJisig. Posterior / / / ■ ;:fy column Fig. 691. — Formation of the fasciculus gracilis. (Poirier.) IMedulla spinalis viewed from behind. To the left, the fasciculus gracilis is shaded. To the right, the drawing shows that the fasciculus gracihs is formed by the long fibres of the posterior roots, and that in this tract the sacral nerves lie next the median plane, the lumbar to their lateral side, and the thoracic stiU more laterally. ^i, Posterior column Fig. 692. — Descending fibres in the posterior funiculi, shown at different levels. (After Testut.) A. In the conus medullaris. _ B. In the lumbar region. C. In the lower thoracic region. D. In the upper thoracic region. of the fasciculus gracilis. These descending fibres are mainly intersegmental in character and derived from cells in the posterior column, but some consist of the descending branches of the posterior nerve roots. The comma-shaped fasciculus was supposed to belong to the second category, but against this view is the fact that it does not undergo descending degeneration when the posterior nerve roots are destroyed. Roots of the Spinal Nerves. — As already stated, each spinal nerve possesses two roots, an anterior and a posterior, which are attached to the surface of the THE MEDULLA SPINALIS OR SPINAL CORD 819 medulla si)inalis oppDsite the corresponding- eoliunn of gray substance (Fig. 093); their fibres become medullated about the fifth month of fetal life. The Anterior Nerve Root (radix anterior) consists of efferent fibres, which are the axons of the ner\e cells in the ventral part of the anterior column. A short distance from their origins, these axons are invested by medullary sheaths and, passing forward, emerge in two or three irregular rows ov^er an area which measures about 3 mm. in width. The Posterior Root (radix posterior) comprises some six or eight fasciculi, attached in linear series along the postero-lateral sulcus. It consists of afferent fibres which arise from the nerve cells in a spinal ganglion. Each ganglion cell gives oft' a single fibre which divides in a T-shaped manner into two processes, medial and lateral. The medial processes of the ganglion cells grow into the medulla spinalis as the posterior roots of the spinal nerves, while the lateral are directed toward the periphery. Fig. 693. — A spinal nerve with its an- terior and posterior roots. (Testut.) 1 A portion of the medulla spinali, viewed from the left side. 2. Anterior median fis- sure. 3. Anterior column. 4. Posterior column. 5. Lateral columns. 6. Formatio reticularis. 7. Anterior root. S. Posterior root, with 8', its ganglion. 9. Spinal nerve; 9', its posterior division. Fig. 694. — Posterior roots entering medulla spinalis and dividing into ascending and descending branches. (Van Gehuchten.) o. Stem fibre. 6, 6. Ascending and descending limbs of bifurcation, c. Collateral arising from stem fibre. The posterior nerve root enters the medulla spinalis in three chief bundles, medial, intermediate, and lateral. The medial strand passes directly into the fas- ciculus cuneatus : it consists of coarse fibres, which acquire their medullary sheaths about the fifth month of intrauterine life ; the intermediate strand consists of coarse fibres, which enter the gelatinous substance of Rolando; the lateral is composed of fine fibres, which assume a longitudinal direction in the tract of Lissauer, and do not acquire their medullary sheaths until after birth. Having entered the medulla spinalis, all the fibres of the posterior nerve roots divide into ascending and descending branches, and these in their turn give off collaterals which enter the gray substance (Fig. 694). The descending fibres are short, and soon enter the gray substance. The ascending fibres are grouped into long, short, and intermediate: the long fibres ascend in the fasciculus cuneatus and fasciculus gracilis as far as the medulla oblongata, where they end by arbori- zing around the cells of the cuneate and gracile nuclei; the short fibres run upward for a distance of only 5 or 6 mm. and enter the gray substance; while the inter- 820 NEUROLOGY mediate fibres, after a somewhat longer course, have a similar destination. All fibres entering the gray substance end b}' arborizing around its nerve cells, those of intermediate length being especially associated with the cells of the dorsal nucleus. The fibres of the posterior nerve roots pursue an oblique course upward, being situated at first in the lateral part of the fasciculus cuneatus: higher up, they occupy the middle of this fasciculus, having been displaced by the accession of other entering fibres; while still higher, they ascend in the fasciculus gracilis. The upper cervical fibres do not reach this fasciculus, but are entirely confined to the fascic- ulus cuneatus. The localization of these fibres is very precise: the sacral nerves lie in the medial part of the fasciculus gracilis and near its periphery, the lumbar nerves lateral to them, the thoracic nerves still more laterally; while the cervical nerves are confined to the fasciculus cuneatus (Fig. 691). The development of the medulla spinalis is described in the section on Embry- ology (pages 117 to 120). Applied Anatomy. — Several cases have been recorded^ in which a local doubling of the medulla spinalis has taken place. The condition is probably due to some interference with the develop- ment of the neural tube in the embryo; in a few it was associated with spina bifida, while in one recent case^ the two parts were separated by a dermoid tumor. Other congenital abnormalities of the medulla spinalis occur in connection with spina bifida (see p. 214), and also in syringo- myelia. In this latter chronic condition an abnormal prohferation of the neurogUa takes place, generally near the central canal and in the cervical enlargement, and later this mass becomes absorbed, leaving an irregular cavity in its place. This gives rise to a number of interesting signs and symptoms, such as analgesia (or insensitiveness to pain), inability to distinguish between cold and heat, progressive atrophy in the muscles of the hands and arms, trophic changes in the bones and joints, and painless whitlows. Severe injuries to the medulla spinahs may occur in fra.ctures or fracture-dislocations of the vertebral column anywhere above the second lumbar vertebra. If the meduUa spinalis is completely crushed or torn across, total paralysis and anes- thesia of all parts of the body drawing their nerve supply from below the injured spot will follow, with loss of control over the actions of the bladder and rectum. The higher up such a lesion occurs, the worse the prognosis. Thus, when the medulla spinaUs is crushed by fracture of the atlas or axis, the vital centres in the meduUa oblongata are injured, and death occurs at once. If the origin of the phrenic nerve — mainly the fourth cervical — just escape in a case where the neck is broken, respiration will have to be carried on by the Diaphragma alone, and death is likely to ensue before long from pulmonary complications. When the back is broken in the lower thoracic region, hfe is not immediately threatened; but unless the patient is carefully nursed, death may foUow at any time from the development of bed-sores in the anesthetic area, or from septic infection spreading up the ureters into the kidneys and secondary to the cystitis that is so prone to occur in patients who have no control over the bladder. Inflammation of the medulla spinalis, or spinal myelitis, sometimes foUows influenza or one of the acute specific fevers. A transverse patch of such myeUtis extending completely across the medulla spinahs produces more or less complete interruption of the passage of nervous impulses through it. Hence it will occasion more or less complete paralysis and anesthesia of the parts of the body obtaining their nerve supply from below it, and, in addition, a zone of cutaneous hyperesthesia at its level, in consequence of the irritation of the sensory fibres entering the inflamed region of the meduUa spinalis. The disease mainly attacking children, and known as infantile spinal paralysis, or acute anterior poliomyelitis, is a bacterial infection of the pia mater that spreads into the medulla spinalis along the bloodvessels, and destroys groups of the motor neurons aggregated in the anterior column. Destruction of the cells causes rapid and permanent paralysis of the muscles innervated, and groups of muscles in one or more of the hmbs are commonly picked out for attack. The affected limbs are thus partially paralyzed, and their subsequent growth and nutri- tion both suffer. Further, the muscles that normally antagonize the affected groups of muscles, finding their actions unopposed, tend to assume a state of spastic contraction. In consequence, much dwarfing and deformity follow later, and may demand for their reUef such operations as tenotomy, the transplantation of tendons, or even amputation. Inflammation of the gangha on one or more of any of the posterior nerve roots is the cause of shingles^ or herpes zoster, in which there is a painful eruption of groups of cutaneous vesicles corresponding to the distribution of the nerves derived from the affected ganglia. It is com- ' For an analysis of these cases consult paper by Bruce, Stuart !McDonald, and Pirie, Review of Neurology and Psychiatry, January, 1906. 2 Harriehausen, D. Ztschrft. f. Nervenheilk., Band xxxvi, Heft 3 and 4, S. 268. ^ From Lat. cingulum, a belt. THE RHOMBENCEPHALON OR HIND-BRAIN 821 monest along the course of the intercostal nerves; the eruption is often preceded and followed, as well as accompanied, by girdle pains, and in old people these may be prolonged and serious in character. Herpes is the analogue on the sensory side to anterior poUomyelitis on the motor side of the nervous system. THE ENCEPHALON OR BRAIN. Dissection. — To examine the brain with its membranes, the skull-cap must be removed. In order to effect this, saw through the external table, the section commencing, in front, about 2 cm. (* inch) above the margin of the orbits, and extending, behind, to a little above the level of the occipital protuberance. Then break the internal table with the chisel and hammer, to avoid injuring the investing membranes or brain; loosen and forcibly detach the skull-cap, and the dm-a will be exposed. The adhesion between the bone and the dura often is very intimate, par- ticularly along the sutures. General Considerations and Divisions.— The encephalon, or brain, is contained within the cranium, and constitutes the upper, greatly expanded part of the central nervous system. In its early em- bryonic condition it consists of three hollow vesicles, termed the rhomb- encephalon or hind-brain, the mesen- cephalon or mid-brain, and the prosencephalon or fore-brain; and the parts derived from each of these can be recognized in the adult (Fig. 695). Thus in the pro- cess of development the wall of the rhombencephalon undergoes modi- fication to form the medulla ob- longata, the pons, and cerebellum, while its cavity is expanded to form the fourth ventricle. The mesencephalon forms only a small part of the adult brain; its cavity becomes the cerebral aqueduct (aqueduct of Sylvius), which serves as a tubular communication be- tween the third and fourth ventricles; while its walls are thickened to form the corpora quadrigemina and cerebral peduncles. The prosencephalon undergoes great modification: its anterior part or telencephalon expands laterally in the form of tw^o hollow vesicles, the cavities of which become the lateral ventricles, while the surrounding walls form the cerebral hemispheres and their commissures; the cavity of the posterior part or diencephalon forms the greater part of the third ventricle, and from its walls are developed most of the structures wdiich bound that cavity. Further details regarding these important changes are given in the section on Embryology (pages 120 to 132). Cerebral peduncle Brcpchium conjunctivum Brachium pontis Bestiform body Medulla oblongata Fig. 695. — Scheme showing the connections of the several parts of the brain. (After Schwalbe.) THE RHOMBENCEPHALON OR HIND-BRAIN. The rhombencephalon or hind-brain occupies the posterior fossa of the cranial cavity and lies below a fold of dura mater, the tentorium cerebelli. It consists of {a) the myelencephalon, comprising the medulla oblongata and the lower part of the fourth ventricle; {h) the metencephalon, consisting of the pons, cerebellum, and the intermediate part of the fourth ventricle; and (c) the isthmus rhomben- cephali, a constricted portion immediately adjoining the mesencephalon and includ- 822 NEUROLOGY ing the brachia, conjunctiva of the cerebellum, the anterior medullary velum, and the upper part of the fourth ventricle. The Medulla Oblongata (spinal bulb). — The medulla oblongata is the lowest and smallest division of the brain; its structure, however, is extremeh' complex, since it gives attachment to many of the cerebral nerves, and forms the connecting link between the medulla spinalis below and the cerebrum and cerebellum above. It extends from the lower margin of the pons to a plane passing transversely below the pyramidal decussation and above the first pair of cervical nerves; this plane corresponds with the upper border of the atlas behind, and the middle of the odontoid process of the epistropheus or axis in front; at this level the medulla oblongata is continuous with the medulla spinalis. Its anterior surface is separated from the basilar part of the occipital bone and the upper part of the odontoid process by the membranes of the brain and the occipitoaxial ligaments. Its pos- terior surface is received into the fossa between the hemispheres of the cerebellum, and the upper portion of it forms the lower part of the floor of the fourth ventricle. The vertebral arteries pass upward and forward in relation to its lateral surfaces; they then curve forward on to its anterior surface and unite at the lower border of the pons to form the basilar artery. The medulla oblongata is pyramidal in shape, its broad extremity being directed upward toward the pons, while its narrow, lower end is continuous with the medulla spinalis. It measures about 3 cm. in length, about 2 cm. in breadth at its widest part, and about 1.25 cm. in thickness. The central canal of the medulla spinalis is prolonged into its lower half, and then opens into the cavity of the fourth ven- tricle; the medulla oblongata may therefore be divided into a lower closed part containing the central canal, and an upper open part corresponding with the lower portion of the fourth ventricle. Its anterior and posterior surfaces are marked by median fissures. The Anterior Median Fissure (fissura mediana anterior; ventral or xeniromedian fissure) contains a fold of pia mater, and extends along the entire length of the medulla oblongata: it ends at the lower border of the pons in a small triangular expansion, termed the foramen caecum. Its lower part is interrupted by bundles of fibres which cross obliquely from one side to the other, and constitute the pyra- midal decussation. Some fibres, termed the anterior external arcuate fibres, emerge from the fissure above this decussation and curve lateralward and upward over the surface of the medulla oblongata. The Posterior Median Fissure (fissura mediana posterior; dorsal or dorsomedian fissure) is a narrow groove; and exists only in the closed part of the medulla oblon- gata; it becomes gradually shallower from below upward, and finally ends about the middle of the medulla oblongata, where the central canal expands into the cavity of the fourth ventricle. These two fissures divide the closed part of the medulla oblongata into sym- metrical halves, each presenting elongated eminences which, on surface view, are continuous with the funiculi of the medulla spinalis. In the open part the halves are separated by the anterior median fissure, and by a median raphe which extends from the bottom of the fissure to the floor of the fourth ventricle. Further, certain of the cerebral nerves pass through the substance of the medulla oblongata, and are attached to its surface in series with the roots of the spinal nerves; thus, the fibres of the hjqjoglossal nerve represent the upward continuation of the anterior nerve roots, and emerge in linear series from a furrow termed the antero-lateral sulcus. Similarly, the accessory, vagus, and glossopharyngeal nerves correspond with the posterior nerve roots, and are attached to the bottom of a sulcus named the postero-lateral sulcus. Advantage is taken of this arrangement to sub- divide each half of the medulla oblongata into three districts, anterior, middle, and posterior. Although these three districts appear to be directly continuous THE RHOMBENCEPHALON OR HIND-BRAIN 823 with the corresponding funiculi of the medulla spinalis, they do not necessarily contain the same fibres, since some of the fasciculi of the medulla spinalis end in the medulla oblongata, while others alter their course in passing through it. The anterior district {Fig. 09(3) is named the pyramid (pyramis meduUae ohlongatae) and lies between the anterior median fissure and the antero-lateral sulcus. Its upper end is slightly constricted, and between it and the pons "' the fibres of the abducent nerve emerge; a little below the pons it becomes enlarged and prominent, and finally tapers into the anterior funiculus of the medulla spinalis, with which, at first sight, it ap- pears to be directly continuous. The two pyramids contain the motor fibres which pass from the brain to the medulla spinalis. When these pyramidal fibres are traced downward it is found that some two-thirds or more of them Bracliium pout is cerebelli Fig. 696. — Medulla oblongata and pons. Anterior surface. Fig. 697. — Decussation of pyramids. Scheme showing pas- sage of various fasciculi from medulla spinalis to medulla ob- longata. (Testut.) a. Pons. b. Medulla oblongata, c. Decussation of the pj-ramids. d. Section of cer^-ical part of medulla spinalis. 1. Anterior cerebrospinal fasciculus (in red). 2. Lateral cerebrospinal fasciculus (in red). 3. Sensory- tract (fasciculi gracilis et cuneatus) (in blue). 3'. Gracile and cuneate nuclei. 4. Antero-lateral proper fasciculus (in dotted line). 5. Pyramid. 6.^ Lemniscus. 7. Medial longi- tudinal fasciculus. 8. Superficial antero-lateral fasciculus (in blue). 9. Cerebellospinal fasciculus (in j'ellow). leave the pyramids in successive bundles, and decussate in the anterior median fissure, forming what is termed the pyramidal decussation. Having crossed the middle line, they pass down in the posterior part of the lateral funiculus as the lateral cerebrospinal fasciculus. The remaining fibres — i. e., those which occupy' the lateral part of the pyramid — do not cross the middle line, but are carried downw^ard as the anterior cerebrospinal fasciculus (Fig. 697) into the anterior funiculus of the same side. The greater part of the anterior proper fasciculus of the medulla spinalis is con- tinued upward through the medulla oblongata under the name of the medial longitudinal fasciculus. The lateral district (Fig. 698) is limited in front by the antero-lateral sulcus and the roots of the hj-poglossal nerve, and behind by the postero-lateral sulcus and the roots of the accessory, vagus, and glossopharyngeal nerves. Its upper part consists of a prominent oval mass which is named the olive, while its lower part 824 NEUROLOGY is of the same width as the lateral funiculus of the medulla spinalis, and appears on the surface to be a direct continuation of it. As a matter of fact, only a portion of the lateral funiculus is continued upward into this district, for the lateral cerebro- spinal fasciculus passes into the pyramid of the opposite side, and the cerebello- spinal fasciculus is carried into the restiform body in the posterior district. The remainder of the lateral funiculus, which consists chiefly of the lateral proper fasciculus and the superficial antero-lateral fasciculus can be traced into the lateral district. Most of these fibres dip beneath the olive and disappear from the surface; but a small strand remains superficial, and ascends between the olive and the postero-lateral sulcus. In a depression at the upper end of this strand is the acoustic nerve. Superior hraclihmi Lateral geniculate body Inferior brachium \ I ^ledial geniculate body 1/ / / Optic tract Pulvinar Pineatbody Superior collicidi Inferior collicidi Frenulum veli Trochlear nerve Lateral lemniscus Brachium conjunctivum Brachium pontis Hhomboid fossa Clava — Glossopharyngeal and vagus nerve. Optic commissure Oculomotor nerve Trigeminal nerve Acoustic nerve Facial nerce Abducent nerve Hypoglossal nerve Accessory verve ^ Fig. 698. — Hind- and mid-brains; postero-lateral view. The olive {olim; olivary body) is situated lateral to the pyramid, from which it is separated by the antero-lateral sulcus, and the fibres of the hypoglossal nerve. Behind, it is separated from the postero-lateral sulcus by the small superficial strand of the lateral funiculus already referred to. It measures about 1.25 cm. in length, and between its upper end and the pons there is a slight depression to which the roots of the facial nerve are attached. The external arcuate fibres wind across the lower part of the pyramid and olive and enter the restiform body. The posterior district (Fig. 699) lies behind the postero-lateral sulcus and the roots of the accessory, vagus, and the glossopharyngeal nerves, and, like the lateral district, is divisible into a lower and an upper portion. The lower part is limited behind by the posterior median fissure, and consists of the fasciculus gracilis and the fasciculus cuneatus. The fasciculus gracilis is placed parallel to and along the side of the posterior median fissure, and separated from the fasciculus cuneatus by the postero-intermediate sulcus and septum. The gracile and cuneate fasciculi are at first vertical in direction; but at the lower part of the rhomboid fossa they diverge from the middle line in a V-shaped manner, and each presents an elongated swelling. That on the fasciculus gracilis is named the clava, and is produced by a subjacent nucelus of gray matter, the nucleus THE RHOMBENCEPHALOS OR UIXD-BRAIX 825 gracilis; that on the fascicukis cuneatus is termed the cuneate tubercle, and is Uke- wise caused by a gray nucleus, named the nucleus cuneatus. The fibres of these fasciculi terminate by arborizing around the cells in their respective nuclei. A third elevation, produced by the substantia gelatinosa of Rolando, is present in the lower part of the posterior district of the medulla o})longata. It lies on the lateral aspect of the fasciculus cuneatus, and is sei)aratcd from the surface of the medulla oblongata by a band of nerve fibres which form the spinal tract (spinal root) of the trigeminal nerve. Narrow below, this elevation gradually expands above, and ends, about 1.25 cm. below the pons, in a tubercle, the tubercle of Rolando (iuhcr cinercum). — Cerebral peduncle Trochlear nerve Trigeminal nerve Facial nerve Acoustic nerve achiiun conj^(,nctivum Brachium pontis Hcati/orm body Glossopharyngeal nerve Vagus nerve Accessory nerve (cerebral part) Hypoglossal nerve Accessory nerve (spinal part) fertebral artery Clava Fasciculus ciineatus Fasciculus gracilis Dura mater (laid open) Fig. 699. — Upper part of medulla spinalis and hind- and mid-brains; posterior aspect, exposed in situ. The upper part of the posterior district of the medulla oblongata is occupied by the restiform body, a thick rope-like strand situated between the lower part of the fourth ventricle and the roots of the glossopharyngeal and A^agus nerves. The restiform bodies connect the medulla spinalis and medulla oblongata with the cerebellum, and are sometimes named the inferior peduncles of the cerebellum. As they pass upward, they diverge from each other, and assist in forming the lower part of the lateral boundaries of the fourth ventricle; higher up, they are directed backward, each passing to the corresponding cerebellar hemisphere. Near their entrance into the cerebellum they are crossed by several strands of fibres, which run to the median sulcus of the rhomboid fossa, and are named the striae medullares. 826 NEUROLOGY The restiform body appears to be the upward continuation of the fasciculus gracilis and fasciculus cuneatus; this, however, is not so, as the fibres of these fasciculi end in the gracile and cuneate nuclei. The constitution of the restiform body will be subsequently discussed. Internal Structure of the Medulla Oblongata. — Although the external form of the medulla oblongata bears a certain resemblance to that of the upper part of the medulla spinalis, its internal structure differs widely from that of the latter, and this for the following principal reasons: (1) certain fasciculi which extend from the medulla spinalis to the brain, and vice versa, undergo a rearrangement in their passage through the medulla oblongata; (2) others which exist in the medulla spin- alis end in the medulla oblongata; (3) new fasciculi originate in the gray substance of the medulla oblongata and pass to different parts of the brain; (4) the gray sub- stance, which in the medulla spinalis forms a continuous H-shaped column, becomes greatly modified and subdivided in the medulla oblongata, where also new masses of gray substance are added ; (o) on account of the opening out of the central canal Fig. 700. — Section of the medulla oblongata through the lower part of the decussation of the pjTamids. (Tes- tut.) 1. Anterior median fissure. 2. Posterior median sulcus. 3. Anterior column (in red), with 3', anterior root. 4. Posterior column (in blue), with 4', posterior roots. .5. Lateral cerebrospinal fasciculus. 6. Posterior funiculus. The red arrow, a, a', indicates the course the lateral cerebrospinal fasciculus takes at the level of the decussation of the pyramids; the blue arrow, 6, h', indi- cates the course which the sensorj^ fibres take. Fig. 701. — Section of the medulla oblongata at the level of the decussation of the pyramids. (Testut.) 1 Anterior median fissure. 2. Posterior median sulcus. 3. Motor roots. 4. Sensory roots. .5. Base of the anterior column, from which the head (.5') has been detached by the lateral cerebrospinal fasciculus. 6. Decussation of the lateral cerebrospinal fasciculus. 7. Posterior columns (in blue;. 8. Gracile nucleus. of the medulla spinalis, certain parts of the gray substance, which in the medulla spinalis were more or less centrally situated, are displayed in the rhomboid fossa; (6) the medulla oblongata is intimately associated with many of the cerebral nerves, some arising from, and others ending in, nuclei within its substance. The internal structure of the medulla oblongata is best studied in series of transverse (Figs. 704, 705) and of longitudinal sections. A short description of the course taken by the principal fasciculi, and of the arrangement of the gray substance, will now be given. The Cerebrospinal Fasciculi. — The downward course of these fasciculi from the pyramids of the medulla oblongata and their partial decussation have already been described (page 816). In crossing to reach the lateral funiculus of the oppo- site side, the fibres of the lateral cerebrospinal fasciculi extend backward through the anterior columns, and separates the head of each of these columns from its base (Figs. 700, 701). The base retains its position in relation to the ventral aspect of the central canal, and, when the latter opens into the fourth ventricle, appears in the rhomboid fossa close to the middle line, where it forms the nuclei of the hypoglossal and abducent nerves; while above the level of the ventricle it exi.sts as the nuclei of the trochlear and oculomotor nerves in relation to the floor of the cerebral aqueduct. The head of the column is pushed lateralward and forms the nucleus ambiguus, which gives origin from below upward to the cerebral part THE RHOMBENCEPHALON OR HIND-BRAIN 827 of the accessory and the motor fibres of the va^us and glossopharyngeal, and still, higher to the motor fibres of the facial and trigeminal nerves. The fasciculus gracilis and fasciculus cuneatus constitute the posterior sensory fasciculi of the medulla spinalis; they are prolonged upward into the lower part of the medulla oblongata, where they end respectively in the nucleus gracilis and nucleus cuneatus. These two nuclei are continuous with the central gray substance of the medulla spinalis, and may be regarded as dorsal projections of this, each being covered superficially by the fibres of the corresponding fasciculus. On transverse section (Fig. 704) the nucleus gracilis appears as a single, more or less quadrangular mass, while the nucleus cuneatus consists of two parts: a larger, somewhat triangular, medial nucleus, composed of small or medium-sized cells, and a smaller lateral nucleus containing large cells. The fibres of the, fasciculus gracilis and fasciculus cuneatus end by arborizing 7 6 2 Fig. 702. — Superior terminations of the posterior fas- ciculi of the medulla spinaUs. (Testut.) 1. Posterior median sulcus. 2. Fasciculus gracilis. 3. Fasciculus cuneatus. 4. Gracile nucleus. 5. Cuneate nucleus. 6, 6', 6". Sensory fibres forming the lemniscus. 7. Sen- sory decussation. 8. Cerebellar fibres uncrossed (in black). 9. Cerebellar fibres crossed (in black). Fig. 703. — Transverse section passing through the sensory decussation. (Schematic.) (Testut.) 1. Ante- rior median fissure. 2. Posterior median sulcus. 3, 3. Head and base of anterior column (in red) . 4. Hypo- glossal nerve. 5. Bases of posterior columns. 6. Gracile nucleus. 7. Cuneate nucleus. 8, 8. Lemniscus. 9. Sensory decussation. 10. Cerebrospinal fasciculus. around the cells of these nuclei (Fig. 702). From the cells of the nuclei new fibres arise ; some of these are continued as the posterior external arcuate fibres into the restiform body, and through it to the cerebellum, but most of them pass forward through the neck of the posterior column, thus cutting off its head from its base (Fig. 703) . Curving forward, they decussate in the middle line with the correspond- ing fibres of the opposite side, and run upward immediately behind the cerebro- spinal fibres, as a flattened band, named the lemniscus or fillet. The decussation of these sensory fibres is situated above that of the motor fibres, and is named the decussation of the lemniscus or sensory decussation. The lemniscus is joined by the spinothalamic fasciculus (page 817), the fibres of w^hich are derived from the cells of the gray substance of the opposite side of the medulla spinalis. The base of the posterior column at first lies on the dorsal aspect of the central canal, but when the latter opens into the fourth ventricle, it appears in the lateral part of the rhomboid fossa. It forms the terminal nuclei of the sensory fibres of the vagus and glossopharyngeal nerves, and is associated with the vestibular part of the acoustic nerve and the sensory root of the facial nerve. Still higher, it forms a mass of pigmented cells — the locus coeruleus — in which some of the sensory fibres 828 NEUROLOGY of the trigeminal nerve appear to end. The head of the posterior column forms a long nucleus, in which the fibres of the spinal tract of the trigeminal nerve largely end. glossal Nticleus of medial eminence nucleus Hypo- ^'T? ^''^''^" nuclei Raphe ~ Formatio reticularis grisea — Formatio reticularis alba ^" Accessory olivary nuclei _^_-, Nucleus gracilis Nucleus cuneatus Restiform hody Spinal tract of Yi trigeminal nerve Vagus nerve Arcuate fibres Infaior olivary nucleus Hypoglossal nerve Anterior median fissure Fig. 704. — Section of the medulla oblongata at about the middle of the olive. (Schwalbe.) Nucleus of vagus Ligula I Medial longitudinal fasciculus Nucleus intercalatus Eypoglossal 'nucleus Fourth ventricle Fasciculus solitarius Descending root of vestibular nerve Restiform body Nucleus lateralis Spinal tract of tri- geminal nerve Vagus nerve Nucleus amhiguus Dorsal accessory olivary nucleus Inferior olivary nucleus Hypoglossal ne7-ve Cerebrospinal fasciculus / \ Medial accessory olivary nucleus Lemniscus Nucleus arcuatus Fig. 705. — Transverse section of medulla oblongata below the middle of the olive. The cerebellospinal fasciculus {fasciculus cerebellospiJialis; direct cerebellar tract) leaves the lateral district of the medulla oblongata; most of its fibres are carried backward into the restiform body of the same side, and through it are conveyed THE RHOMBENCEPHALOX OR HIND-BRAIN 829 to tlie cerebelliiin ; but some run ui)\varcl with the fil)res of the lemniscus, and, reaching the inferior colHcuhis, undergo decussation, and are carried to the cerebehum through tlie brachium conjunctivum. The proper fasciculi (baffi^- bundles) of the anterior and lateral funiculi largely consist of intersegmental fibres, which link together the difl'erent segments of the medulla spinalis; they assist in the production of the formatio reticularis of the medulla oblon- gata, and many of them are ac- cumulated into a fasciculus which runs up close to the median raphe between the lemniscus and the rhomboid fossa; this strand is named the medial longitudinal fasciculus, and will be again re- ferred to. Gray Substance of the Medulla Oblongata (Figs. 704, 705).— In addition to the gracile and cun- eate nuclei, there are several other nuclei to be considered. Some of these are traceable from the gray substance of the medulla spinalis, while others are unrepre- sented in it. 1. The hypoglossal nucleus is derived from the base of the anterior column; in the lower closed part of the medulla ob- longata it is situated on the ven- trolateral aspect of the central canal; but in the upper part it approaches the rhomboid fossa, where it lies close to the middle line, under an eminence named the trigonum hypoglossi (Fig. 719). The nucleus measures about 2 cm. in length, and consists of large multipolar nerve cells, whose axons constitute the roots of the hypoglossal nerve. These nerve roots pass forward between the anterior and lateral districts of the medulla oblongata, and emerge from the antero-lateral sulcus. 2. The motor nucleus (Figs. 706, 707), common to the glossopharyngeal, vagus, and cerebral part of the accessory nerves, is named the nucleus ambiguus. It rep- resents the head of the anterior column, lies deeply in the formatio reticularis grisea, and extends throughout nearly the whole length of the medulla oblongata. 3. The sensory nucleus (Figs. 706, 708), or terminal nucleus of the sensory fibres of the glossopharyngeal and vagus, represents the base of the posterior column. It measures about 2 cm. in length, and in the lower, closed part of the medulla oblongata is situated behind the hypoglossal nucleus; whereas in the upper, open part it lies lateral to that nucleus, and corresponds to an eminence, named the ala cinerea {trigonum vagi), in the rhomboid fossa. Nucleus (IX i Fig. 706. — The cerebral nerve nuclei schematically represented; dorsal -vaew. Motor nuclei in red; sensory in blue. (The olfactory and optic centres are not represented.) 830 NEUROLOGY 4. The nuclei of the acoustic nerve are described on page 830. 5. The olivary nuclei (Fig. 704) are three in number on either side of the middle line, viz., the inferior ohvary nucleus, and the medial and dorsal accessory olivary nuclei; they consist of small, round, yellowish cells and numerous fine nerve fibres. (a) The inferior olivary nucleus is the largest, and is situated within the olive. It consists of a gray folded lamina arranged in the form of an incomplete capsule, opening medially by an aperture called the hilus ; emerging from the hilus are numer- ous fibres which collectively constitute the peduncle of the olive, ih) The medial accessory olivary nucleus lies between the inferior olivary nucleus and the pyramid, and forms a curved lamina, the concavity of which is directed laterally. The fibres of the hypoglossal nerve, as they traverse the medulla, pass between the medial accessory and the inferior olivary nuclei, (c) The dorsal accessory olivary nucleus is the smallest, and appears on transverse section as a curved lamina behind the inferior olivarv nucleus. Cervical nerves Fig. 707. — Nuclei of origin of cerebral motor nerves schematically represented; lateral view. The inferior olivary nucleus is connected (1) with that of the opposite side by fibres which cross through the raphe ; (2) with the anterior column of the same side of the medulla spinalis by the spinoblivary fasciculus; (3) with the thalamus of the cerebrum by the cerebroolivary fasciculus which passes through the pons and tegmentum; (4) with the opposite cerebellar hemisphere b}^ the cerebello- oiivary fasciculus, the fibres of w^hich cross the raphe and turn backward to enter the deep part of the restiform body. Removal of one cerebellar hemisphere is followed by atrophy of the opposite olivary nucleus. 6. The nucleus arcuatus is described below with the anterior external arcuate fibres. Restiform Bodies (corpus restiformes) . — ^The position of the restiform bodies has already been described (page 825). Each comprises: (1) the cerebellospinal THE RHOMBENCEPHALON OR HIND-BRAIN 831 fasciculus, ^vhicll ascends from the lateral funiculus of the medulla spinalis; (2) descending cerebellar fibres, many of which are disseminated throughout the per- ipheral part of the anterior and lateral funiculi of the medulla spinalis, while others are conducted to the motor nuclei of the cerebral nerves; and (3) the arcuate fibres, which are arranged in three sets, viz., internal, and anterior and posterior external. The internal arcuate fibres form the deeper and larger part of the restiform body. They decussate in the middle line of the medulla oblongata, and having reached the ()i)posite side, terminate partly in the gracile and cuneate nuclei, while many of them enter the hilus of the inferior olivar}^ nucleus, and constitute the cerebelloolivary tract already described (Fig. 7G9). Fig. 708. — Primary terminal nuclei of the afferent (sensory) cerebral nerves schematically represented; lateral view. The olfactory and optic centres are not represented. The anterior external arcuate fibres vary as to their prominence in diflFerent cases : in some they form an almost continuous layer covering the pyramid and olive, w^hile in others they are barely visible on the surface. They arise from the cells of the gracile and cuneate nuclei, and passing forward through the formatio reticu- laris, decussate in the middle line. Most of them reach the surface by way of the anterior median fissure, and arch backward over the pyramid. Reinforced by others which emerge between the pyramid and olive, they pass backward over the olive and lateral district of the medulla oblongata, and enter the restiform body. They thus connect the cerebellum with the gracile and cuneate nuclei of the opposite side. As the fibres arch across the pyramid, they enclose a small nucleus which lies in front of and medial to the pyramid. This is named the nucleus arcuatus, and is serially continuous above with the nuclei pontis in the pons; it contains small fusiform cells, around which some of the arcuate fibres end, and from which others arise. i.'^o NEUROLOGY The posterior external arcuate fibres also take origin in the gracile and cuneate nuclei; they pass to the restiform body of the same side. Fig. 709. — Diagram showing the course of the arcuate fibres. (Testut.) 1. Medulla oblongata anterior surface. 2. Anterior median fissure. 3. Fourth ventricle. 4. Inferior olivary nucleus, with the accessory olivary nuclei. 5. Gracile nucleus. 6. Cuneate nucleus. 7. Trigeminal. 8. Restiform bodies, seen from in front. 9. Posterior external arcuate fibres. 10. Anterior external arcuate fibres. 11. Internal arcuate fibres. 12. Peduncle of inferior olivary nucleus. 13. Nucleus arcuatus. 14. Vagus. 15. Hypoglossal. Fig. 710. — The formatio reticularis of the medulla oblongata, shown by a transverse section passing through the middle of the olive. (Testut.) 1. Anterior median fissure. 2. Fourth ventricle. 3. Formatio reticularis, with 3', its internal part (reticularis alba), and 3", its external part (reticularis grisea). 4. Raph6. 5. Pyramid. 6. Lemniscus. 7. Inferior oUvary nucleus with the two accessory ohvary nuclei. 8. Hypoglossal nerve, with S', its nucleus of origm. 9. Vagus nerve, with 9', its nucleus of termination. 10. Lateral dorsal acoustic nucleus. 11. Nucleus ambiguus (nucleus of origin of motor fibres of glossopharyngeal, vagus, and cerebral portion of spinal accessory). 12. Gracile nucleus. 13. Cuneate nucleus. 14. Head of posterior column, with 14', the lower sensory root' of trigeminal nerve. 15. Fasciculus soUtarius. 16. Anterior external arcuate fibres, with 16', the nucleus arcuatus. 17. Nucleus laterahs 18. Nucleus of fasciculus teres. 19. Ligula. Formatio Reticularis (Fig. 710). — This term is applied to the coarse reticulum which occupies the anterior and lateral districts of the medulla oblongata. It TIIK lillOMHESCEI'IIALOX OR HIXD-HRMX 833 is situated behiiul the jnraniid and olJN'e, extending- laterally as far as the restifurm bodies, and dorsally to within a short distance of the rhomboid fossa. The reticulum is caused by the intersection of bundles of fibres running at right angles to each other, some being longitudinal, others more or less transverse in direction. The formatio reticularis presents a ditt'erent appearance in the anterior district from what it does in the lateral; in the former, there is an almost entire absence of nerve cells, and hence this part is known as the reticularis alba; whereas in the lateral district nerve cells are numerous, and as a consequence it presents a gray appear- ance, and is termed the reticularis grisea. In the substance of the formatio reticularis are two small nuclei of gray matter: one, the inferior central nucleus {luicleus of Roller), near the dorsal aspect of the hilus of the inferior olivary nucleus; the other, the nucleus lateralis, between the olive and the spinal tract of the trigeminal nerve. In the reticularis alba the longitudinal fibres form two well-defined fasciculi, viz.: (1) the lemniscus, which lies close to the raphe, immediately behind the fibres of the pyramid ; and (2) the medial longitudinal fasciculus, which is continued upward from the anterior and lateral proper fasciculi of the medulla spinalis, and, in the upper part of the medulla oblongata, lies between the lemniscus and the gray substance of the rhomboid fossa. The longitudinal fibres in the reticularis grisea are derived from the lateral funiculus of the medulla spinalis after the lateral cerebrospinal fasciculus has passed over to the opposite side, and the cerebello- spinal fasciculus has entered the restiform body. They form indeterminate fibres, with the exception of a bundle named the fasciculus solitarius, which is made up of descending fibres of the vagus and glossopharyngeal nerves. The trans- verse fibres of the formatio reticularis are the arcuate fibres already described (page 831). Applied Anatomy. — In bulbar paralysis, i. e., paralysis of the medulla oblongata, which is realty a special form of a progressive degeneration affecting the whole efferent or motor tract, the disease begins with impairment of the movements of the lips, tongue, pharynx, and larynx, due to degeneration of the motor cells in the nuclei of the medulla oblongata. Speech and swallow- ing become difficult, and the saliva dribbles from the open mouth. Other groups of muscles soon become involved, and death often occm-s from "aspiration pneumonia/' set up by food that has accidentally passed down the trachea. The Pons (j^ons Varoli). — The pons or forepart of the rhombencephalon is situated in front of the cerebellum. From its superior surface the cerebral peduncles emerge, one on either side of the middle line. Curving around each peduncle, close to the upper surface of the pons, a thin white band, the taenia pontis, is frequently seen ; it enters the cerebellum between the brachium pontis and brachium conjunc- tivum. Behind and below, the pons is continuous with the medulla oblongata, but is separated from it in front by a furrow in which the abducent, facial, and acoustic nerves appear. Its ventral or anterior surface (pars hasilaris pontis) is very prominent, markedly convex from side to side, less so from above downward. It consists of transverse fibres arched like a bridge across the middle line, and gathered on either side into a compact mass which forms the brachium pontis. It rests upon the clivus of the sphenoidal bone, and is limited above and below by well-defined borders. In the middle line is the sulcus basilaris for the lodgement of the basilar artery; this sulcus is bounded on either side by an eminence caused by the descent of the cerebrospinal fibres through the substance of the pons. Outside these eminences, near the upper border of the pons, the trigeminal nerves make their exit, each consisting of a smaller, medial, motor root, and a larger, lateral, sensory root; vertical lines drawn immediately beyond the trigeminal nerves, may be taken as the boundaries betw^een the ventral surface of the pons and the brachia pontis. 53 834 NEUROLOGY Its dorsal or posterior surface ipar-s dorsalis pontis), triangular in shape, is liidden by the cerebellum, and is bounded laterally by the brachia conjunctiva ; it forms the upper part of the rhomboid fossa, with which it will be described. Structure (Fig. 711). — ^Transverse sections of the pons show it to be composed of two parts which differ in appearance and structure: thus, the basilar or ventral portion consists for the most part of fibres arranged in transverse and longitudinal bundles, together with a small amount of gray substance; while the dorsal tegmental portion is a continuation of the reticular formation of the medulla oblongata, and most of its constituents are continued into the tegmenta of the cerebral peduncles. Fig. 711. — Coronal section of the pons, at its upper part. (Testut.) 1. Fourth ventricle; its ependyma in yellow. 2. Anterior mediillary velum, with 2', its white stratum, and 2", its gray stratum. 3. MesencephaUc root of trigeminal. 4. Nerve cells associated with this root. 5. Medial longitudinal fasciculus. 6. Formatio reticularis. 7. Lateral sulcus. 8. Section of brachium conjunotivum. 9. Medial lemniscus. 9'. Lateral lemniscus. 10, 10. Transverse fibres of pons. 11, 11. Cerebrospinal fasciculi. 12. Raph6. V. Trigeminal. The basilar part of the pons consists of — {a) superficial and deep transverse fibres, (h) longitudinal fasciculi, and (c) some small nuclei of gray substance, termed the nuclei pontis. The superficial transverse fibres [fihrae pontis superficiales) constitute a rather thick layer on the ventral surface of the pons, and are collected into a large rounded bundle on either side of the middle line. This bundle, with the addition of some transverse fibres from the deeper part of the pons, forms the greater part of the brachium pontis. The deep transverse fibres {fihrae pontis profundae) partly intersect and partly lie on the dorsal aspect of the cerebrospinal fibres. They course to the lateral border of the pons, and form part of the brachium pontis; the further connections of this brachium will be discussed with the anatomy of the cerebellum. The longitudinal fasciculi (fasciculi longitudinales) are derived from the cerebral peduncles, and enter the upper surface of the pons. They stream downward on either side of the middle line in larger or smaller bundles, separated from each other by the deep transverse fibres; these longitudinal bundles cause a forward projection of the superficial transverse fibres, and thus give rise to the eminences on the anterior surface. Some of these fibres end in the nuclei pontis, and others, THE RHOMBENCEPHALON OR IIIND-BRAIN 835 after decussating, in the motor nuclei of the trigeminal, abducent, facial, and hypo- glossal nerves ; but most of them are carried through the pons, and at its lower surface are collected into the pyramids of the medulla. The fibres which end in the motor nuclei of the cerebral nerves are derived from the cells of the cerebral cortex, and bear the siune relation to the motor cells of the cerebral nerves that the cerebro- spinal fibres bear to the motor cells in the anterior column of the medulla spinalis. The nuclei pontis are serially continuous with the arcuate nuclei in the medulla, and consist of small groups of multipolar nerve cells which are scattered between the bundles of transverse fibres. The dorsal or tegmental part of the pons is chiefly composed of an upward con- tinuation of the reticular formation and gray substance of the medulla oblongata. It consists of transverse and longitudinal fibres and also contains important gray nuclei, and is subdivided by a median raphe, which, however, does not extend into the basilar part, being obliterated by the transverse fibres. The transverse fibres in the lower part of the pons are collected into a distinct strand, named the trapezoid body. This consists of fibres which arise from the cells of the ventral or accessory acoustic nucleus, and will be referred to in connection with the cochlear division of the acoustic nerve. In the substance of the trapezoid body is a collec- tion of nerve cells, which constitutes the trapezoid nucleus. The longitudinal fibres, which are continuous with those of the medulla oblongata, are mostly collected into two fasciculi on either side. One of these lies between the trapezoid body and the reticular, formation, and forms the upward prolongation of the lemniscus; the second is situated near the floor of the fourth ventricle, and is the medial longitudinal fasciculus. Other longitudinal fibres, more diffusely distributed, arise from the cells of the gray substance of the pons. The rest of the dorsal part of the pons is a continuation upward of the formatio reticularis of the medulla oblongata, and, like it, presents the appearance of a net- work, in the meshes of which are numerous nerve cells. Besides these scattered nerve cells, there are some larger masses of gray substance, viz., the superior olivary nucleus and the nuclei of the trigeminal, abducent, facial, and acoustic nerves (Fig. 706). 1. The superior olivary nucleus {nucleus olivaris sujjerior) is a small mass of gray substance situated on the dorsal surface of the lateral part of the trapezoid body. Rudimentary in man, but well developed in certain animals, it exhibits the same structure as the inferior olivary nucleus, and is situated immediately above it. Some of the fibres of the trapezoid body end by arborizing around the cells of this nucleus, while others arise from these cells. 2. The nuclei of the trigeminal nerve (nuclei n. trigemini) in the pons are two in number: a motor and a sensory. The motor nucleus is situated in the upper part of the pons, close to its posterior surface and along the line of the lateral margin of the fourth ventricle. The axis-cylinder processes of its cells form a portion of the motor root of the trigeminal nerve : the remaining fibres of the motor root of this nerve con- sist of a fasciculus which arises from the gray substance of the floor of the cerebral aqueduct, and hence is named the mesencephalic root. The sensory nucleus is lateral to the motor one, and beneath the brachium conjunctivum. Some of the sensory fibres of the trigeminal nerve end in this nucleus; but the greater number descend, under the name of the spinal tract of the trigeminal nerve, to end in the substantia gelatinosa of Rolando. The roots, motor and sensory, of the trigeminal nerve pass through the substance of the pons and emerge near the upper margin of its anterior surface. 3. The nucleus of the abducent nerve {nucleus n. ahducentis) is a circular mass of gray substance situated close to the fioor of the fourth ventricle, above the striae medullares and subjacent to the medial eminence: it lies a little lateral to the ascending part of the facial nerve. The fibres of the abducent nerve pass forward 836 NEUROLOGY through the entire thickness of the pons on the medial side of the superior ohvary nucleus, and between the lateral fasciculi of the cerebrospinal fibres, and emerge in the furrow between the lower border of the pons and the pyramid of the medulla oblongata. 4. The nucleus of the facial nerve (nucleus n. fascial i.s-) is situated deeply in the reticular formation of the pons, on the dorsal aspect of the superior oli^-ary nucleus, and the roots of the nerve derived from it pursue a remarkably tortuous course in the substance of the pons. At first they pass backward and medial ward until they reach the rhomboid fossa, close to the median sulcus, where they are collected into a round bundle; this passes upward and forward, producing an elevation, the colliculus facialis, in the rhomboid fossa, and then takes a sharp bend, and arches lateralward through the substance of the pons to emerge at its lower border in the interval between the olive and the restiform body of the medulla oblongata. 5. The nuclei of the acoustic nerve {nuclei n. acustici) consists of a cochlear and a vestibular division. The fibres of the cochlear division end in two nuclei: (a) the lateral cochlear nucleus, corresponding to the tuberculum acusticum on the dorso- lateral surface of the restiform body; and (6) the ventral or accessory cochlear nucleus, placed between the two divisions of the nerve, on the ventral aspect of the restiform body. The nuclei in which the vestibular division ends are (a) the dorsal or chief vestibular nucleus, corresponding to the low^er part of the area acustica in the rhomboid fossa; the caudal end of this nucleus is sometimes termed the descending or spinal vestibular nucleus; (6) the nucleus of Deiters, con- sisting of large cells and situated in the lateral angle of the rhomboid fossa; the dorso-lateral part of this nucleus is sometimes termed the nucleus of Bechterew. Applied Anatomy. — Injury to the pons, such as may occur on the occlusion or rupture of one of its bloodvessels, often gives rise to a special train of symptoms that is almost diagnostic. Pon- tine lesions are characterized mainly by "alternate paralyses;" that is to say, by paralysis of one of the motor cerebral nerves on one side, and of the limbs on the other side of the body. Thus a hemorrhage into the lower part of the pons might cause paralysis of the face, Imuer segment paralysis, on the same side, from destruction of the facial nucleus or nerve root, and paralysis of the arm and leg on the opposite side from injury to the adjacent cerebrospinal tract. In the same way, paralysis of the Rectus lateralis of one eye and of the Rectus mediahs of the other, conjugate paralysis, of the muscles turning the two eyes in one direction, and often paralysis of one side of the face as well, together with palsy of the hmbs on the opposite side of the body, may be found when the lesion occurs about the nucleus of the abducent nerve. Hearing is often unaffected in pontine lesions, possibly because the central acoustic tract occupies a ventral and lateral position in the pons. The Cerebellum. — The cerebellum constitutes the largest part of the hind- brain. It lies behind the pons and medulla oblongata; between its central portion and these structures is the cavity of the fourth ventricle. It rests on the inferior occipital fossse, while above it is the tentorium cerebelli, a fold of dura mater which separates it from the tentorial surface of the cerebrum. It is somewhat oval in form, but constricted medially and flattened from abo^-e downward, its greatest diameter being from side to side. Its surface is not convoluted like that of the cerebrum, but is traversed by numerous curved furrows or sulci, which vary in depth at different parts, and separate the laminae of which it is composed. Its average weight in the male is about 150 gms. In the adult the proportion between the cerebellum and cerebrum is about 1 to 8, in the infant about 1 to 20. Lobes of the Cerebellum. — The cerebellum consists of three parts, a median and two lateral, which are continuous with each other, and are substantially the same in structure. The median portion is constricted, and is called the vermis, from its annulated appearance which it owes to the transverse ridges and furrows upon it; the lateral expanded portions are named the hemispheres. On the upper surface of the cerebellum the vermis is elevated above the level of the hemispheres, but on the under surface it is sunk almost out of sight in the bottom of a deep depres- THE RHOMBENCEPHALON OR HIND-BRAIN 837 sion between tliein; this depression is ealled the vallecula cerebelli, and lodges the posterior part of the medulla oblongata. The part of the vermis on the upper surface of the cerebellum is named the superior vermis; that on the lower surface, the inferior vermis. The hemispheres are separated below and behind by a deep notch, the posterior cerebellar notch, and in front by a broader shallower notch, the anterior cerebellar notch. The anterior notch lies close to the pons and upper part of the medulla, and its superior edge encircles the inferior colliculi and the brachia conjunctiva cerebelli. The posterior notch contains the upper part of the falx cerebelli, a fold of dura mater. The cerebellum is characterized by its laminated or foliated appearance; it is marked by deep, somewhat curved fissures, which extend for a considerable dis- tance into its substance, and divide it into a series of layers or leaves. The largest and deepest fissure is named the horizontal sulcus. It commences in front of the pons, and passes horizontally around the free margin of the hemisphere to the middle line behind, and divides the cerebellum into an upper and a lower portion. Several secondary but deep fissures separate the cerebellum into lobes, and these are further subdivided by shallower sulci, which separate the individual folia or lamina? from each other. Sections across the laminae show that the folia, though differing in appearance from the convolutions of the cerebrum, are analogous to them, inasmuch as they consist of central white substance covered by gray substance. Ala lobuli centralis Prceclival fissure Lohulus centralis \ ^°:*Z'!i"'^ ..^^ I Postclival fissure Horizontal sulcus Fig. 712. — Upper surface of the cerebellum. (Schafer.) The cerebellum is connected to the cerebrum, pons, and medulla oblongata; to the cerebrum by the brachia conjunctiva, to the pons by the brachia pontis, and to the medulla oblongata by the restiform bodies. The upper surface of the cerebellum (Fig. 712) is elevated in the middle and sloped toward the circumference^ the hemispheres being connected together by the supe- rior vermis, which assumes the form of a raised median ridge, most prominent in front, but not sharply defined from the hemispheres. The superior vermis is subdivided from before backward into the lingula, the lobulus centralis, the mon- ticulus and the folium vermis, and each of these, with the exception of the lingula, is continuous with the corresponding parts of the hemispheres — the lobulus centralis with the alae, the monticulus with the quadrangular lobules, and the folium vermis with the superior semilunar lobules. The lingula (lingula cerebelli) is a small tongue-shaped process, consisting of four or five folia; it lies in front of the lobulus centralis, and is concealed by it. Anteriorly, it rests on the dorsal surface of the anterior medullary velum, and its w^hite substance is continuous w-ith that of the velum. 838 NEUROLOGY The Lobulus Centralis and Alae. — The lobulus centralis is a small square lobule, situated in the anterior cerebellar notch. It overlaps the lingula, from which it is separated b}^ the precentral fissure; laterally, it extends along the upper and anterior part of each hemisphere, where it forms a wing-like prolongation, the ala lobuli centralis. The Monticulus and Quadrangular Lobules. — The monticulus is the largest part of the superior vermis. Anteriorly, it overlaps the lobulus centralis, from which it is separated by the postcentral fissure; laterally, it is continuous with the quad- rangular lobule in the hemispheres. It is divided by the preclival fissure into an anterior, raised part, the culmen or summit, and a posterior sloped part, the clivus; the quadrangular lobule is similarly divided. The culmen and the anterior parts of the quadrangular lobules form the lobus culminis; the clivus and the posterior parts, the lobus clivi. The Folium Vermis and Superior Semilunar Lobule. — The folium vermis {folium cacuminis; cacuminal lobe) is a short, narrow, concealed band at the posterior extremity of the vermis, consisting apparently of a single folium, but in reality marked on its upper and under surfaces by secondary fissures. Laterally, it expands in either hemisphere into a considerable lobule, the superior semilunar lobule {lobulus semilunaris superior; postero-superior lobules), which occupies the posterior third of the upper surface of the hemisphere, and is bounded below by the horizontal sulcus. The superior semilunar lobules and the folium vermis form the lobus semilunaris. Ala lohuli centralis Flocculus Postnodular fissure Ant. medullary velwm Lobulus centralis Horizontal sulcus Tuber vermis Fig. 713. — Under surface of the cerebellum. (Schafer.) The under surface of the cerebellum (Fig. 713) presents, in the middle line, the inferior vermis, buried in the vallecula, and separated from the hemisphere on either side by a deep groove, the sulcus valleculas. Here, as on the upper surface, there are deep fissures, dividing it into separate segments or lobules ; but the arrangement is more complicated, and the relation of the segments of the vermis to those of the hemispheres is less clearly marked. The inferior vermis is subdivided from before backward, into (1) the nodule, (2) the uvula, (3) the pyramid, and (4) the tuber vermis; the corresponding parts on the hemispheres are (1) the flocculus, (2) the tonsilla cerebelli, (3) the biventral lobule, and (4) the inferior semilunar lobule. The three main fissures are (1) the postnodular fissure, which runs transversely across the vermis, between the nodule and the uvula. In the hemispheres this fissure passes in front of the tonsil, crosses between the flocculus in front and the biventral lobule behind, and joins the anterior end of the horizontal sulcus. (2) The pre- THE RHOMBENCEPHALON OR HIND-BRAIN 839 pyramidal fissure crosses the vermis between the uvuhi in front and the pyramid behind, then curves forward between the tonsil and the biventral lobe, to join the postnodular fissure. (3) The postpyramidal fissure passes across the vermis between the ])yrami(l and the tuber \ermis, and, in the hemispheres, courses behind the tonsil and biventral lobules, and then along the lateral border of the biventral lobule to the postnodular sulcus; in the hemisphere it forms the anterior boundary of the inferior semilunar lobule. The Nodule and Flocculus. — The nodule {nodulus vermis; nochiJar lohe) , or anterior end of the inferior vermis, abuts against the roof of the fourth ventricle, and can only be distinctlj^ seen after the cerebellum has been separated from the medulla oblongata and pons. On either side of the nodule is a thin layer of white sub- stance, named the posterior medullary velum. It is semilunar in form, its convex border being continuous with the white substance of the cerebellum; it extends on either side as far as the flocculus. The flocculus is a prominent, irregular lobule, situated in front of the biventral lobule, between it and the brachium pontis cerebelli. It is subdivided into a few small laminae, and is connected to the inferior medullary velum by its central white core. The flocculi, together with the posterior medullary velum and nodule, constitute the lobus noduli. The Uvula and Tonsilla. — The uvula {uvula vermis; uvular lobe) forms a consid- erable portion of the inferior vermis; it is separated on either side from the tonsil by the sulcus valleculse, at the bottom of which it is connected to the tonsil by a ridge of gray matter, indented on its surface by shallow furrows, and hence called the furrowed band. The tonsilla (tonsilla cerebelli; amygdaline nucleus) is a rounded mass, situated in the hemispheres. Each lies in a deep fossa, termed the bird's nest {nidus avis), between the uvula and the biventral lobule. The uvula and ton- sillse form the lobus uvulae. The Pyramid and Biventral lobules constitute the lobus pyramidis. The pyramid is a conical projection, forming the largest prominence of the inferior vermis. It is separated from the hemispheres by the sulcus valleculae, across which it is connected to the biventral lobule by an indistinct gray band, analogous to the furrowed band already described. The biventral lobule is triangular in shape; its apex points backward, and is joined by the gray band to the pyramid. The lateral border is separated from the inferior semilunar lobule by the postpyramidal fissure. The base is directed forward, and is on a line with the anterior border of the tonsil, and is separated from the flocculus by the postnodular fissure. The Tuber Vermis (tuber valvulae) and the Inferior Semilunar Lobule (lobulus semi- lunaris inferior; postero-superior lobule) collectively form the lobus tuberus (tuberae lobe). The tuber vermis, the most posterior division of the inferior vermis, is of small size, and laterally spreads out into the large inferior semilunar lobules, which comprise at least two-thirds of the inferior surface of the hemisphere. Internal Structure of the Cerebellum. — The cerebellum consists of white and gray substance. White Substance. — If a sagittal section (Fig. 714) be made through either hem- isphere, the interior will be found to consist of a central stem of white substance, in the middle of which is a gray mass, the dentate nucleus. From the surface of this central white stem a series of plates are prolonged; these are covered with gray substance and form the laminae. In consequence of the main branches from the central stem dividing and subdividing, a characteristic appearance, named the arbor vitae, is presented. If the sagittal section be made through the middle of the vermis, it will be found that the central stem divides into a vertical and a hor- izontal branch. The vertical branch passes upward to the culmen monticuli, where it subdivides freely, one of its ramifications passing forward and upward to the central lobule. The horizontal branch passes backward to the folium vermis, greath' diminished in size in consequence of having given oft' large secondary 840 NEUROLOGY branches; one, from its upper surface, ascends to the chvus monticuh; the others descend, and enter the lobes in the inferior vermis, viz., the tuber vermis, the pyramid, the uvula, and the nodule. Ala lohidi CdtUalis L/ingula \V Brachiuin coniunctivum Horizontal sulcus TONSll- Nodule Fourth ventricle Fig. 714. — Sagittal section of the cerebellum, near the junction of the vermis with the hemisphere. (Schafer ) Brachium conjunctivwin I Bestiform body Biathnim pontes Trigeminal nerve Acoustic nerve Pyramid Olive Eestiform body Fig. 715. — Dissection showing the projection fibres of the cerebellum. (After E. B. Jamieson.) The white substance of the cerebellum includes two sets of nerve fibres: (1) projection fibres, (2) fibrae propriae. Projection Fibres. — The cerebellum is connected to the other parts of the brain by three large bundles of projection fibres, viz., to the cerebrum by the brachia conjunctiva, to the pons by the brachia pontis, and to the medulla oblongata by the rcstiform bodies (Fig. 715). THE RHOMBENCEPHALON OH HIND-BRAIN 841 The brachia conjunctiva (superior cerebellar peduncles), two in number, emerge from the upper and medial part of the white substance of the hemispheres and are placed under cover of the upper part of the cerebellum. They are joined to each other across the middle line by the anterior medullary velum, and can be followed upward as far as the inferior colliculi, under which they disappear. Below, they form the upper lateral boundaries of the fourth ventricle, but as they ascend they converge on the dorsal aspect of the ventricle and thus assist in roofing it in. The fibres of the brachium conjunctivum are mainly derived from the cells of the dentate nucleus of the cerebellum and emerge from the hilus of this nucleus; a few arise from the cells of the smaller gray nuclei in the cerebellar white sub- stance, and others from the cells of the cerebellar cortex. They are continued upward beneath the corpora quadrigemina, and the fibres of the two brachia under- go a complete decussation ventral to the Sylvian aqueduct. Having crossed the middle line they divide into ascending and descending groups of fibres, the former ending in the red nucleus, the thalamus, and the nucleus of the oculomotor nerve, while the descending fibres can be traced as far as the dorsal part of the pons; Cajal believes them to be continued into the anterior funiculus of the medulla spinalis. As already stated (page 816), the majority of the fibres of the superficial antero- lateral fasciculi of the medulla spinalis pass to the cerebellum, which they reach b}^ way of the brachia conjunctiva. The brachia pontis {middle cerebellar peduncles) (Fig. 715) are composed entirely of centripetal fibres, which arise from the cells of the nuclei pontis of the opposite side and end in the cerebellar cortex; the fibres are arranged in three fasciculi, superior, inferior, and deep. The superior fasciculus, the most superficial, is derived from the upper transverse fibres of the pons; it is directed backward and lateralward superficial to the other two fasciculi, and is distributed mainly to the lobules on the inferior surface of the cerebellar hemisphere and to the parts of the superior surface adjoining the posterior and lateral margins. The inferior fasciculus is formed by the lowest transverse fibres of the pons ; it passes under cover of the superior fasciculus and is continued downward and backward more or less parallel with it, to be distributed to the folia on the under surface close to the vermis. The deep fasciculus comprises most of the deep transverse fibres of the pons. It is at first covered by the superior and inferior fasciculi, but crosses obliquely and appears on the medial side of the superior, from which it receives a bundle; its fibres spread out and pass to the upper anterior cerebellar folia. The fibres of this fasciculus cover those of the restiform body.^ The restiform bodies {corpus restiformes ; inferior cerebellar peduncles) pass at first upward and lateralward, forming part of the lateral walls of the fourth ventricle, and then bend abruptly backward to enter the cerebellum between the brachia conjunctiva and brachia pontis. Each contains the following fasciculi: (1) the cerebellospinal fasciculus of the medulla spinalis, which ends mainly in the superior vermis; (2) fibres from the gracile and cuneate nuclei of the same and of the opposite sides; (3) fibres from the opposite olivary nuclei; (4) crossed and uncrossed fibres from the reticular formation of the medulla oblongata; (5) vestibular fibres, derived partly from the vestibular division of the acoustic nerve and partly from the nuclei in which this division ends — these fibres occupy the medial segment of the restiform body and divide into ascending and descending groups of fibres; the ascending fibres partly end in the roof nucleus of the opposite side of the cerebellum; (6) cerebellobulbar fibres which come from the opposite roof nucleus and probably from the dentate nucleus, and are said to end in the nucleus of Deiters and in the formatio reticularis of the medulla oblongata. ^ See article by E. B. Jamieson, Journal of Anatomy and Physiology, vol. xliv. 842 NEUROLOGY The anterior medullary velum {velum medullar e anterius; valve of Vieussens; superior medullary velum) is a thin, transparent lamina of white substance, which stretches between the brachial conjunctiva; on the dorsal surface of its lower half the folia and lingula are prolonged. It forms, together with the brachia conjunctiva, the roof of the upper part of the fourth ventricle; it is narrow above, where it passes beneath the inferior colliculi, and broader below, where it is continuous with the white substance of the superior vermis. A slightl}^ elevated ridge, the fraenulum veli, descends upon its upper part from betw^een the inferior colliculi, and on either side of this the trochlear nerve emerges. The posterior medullary velum {velum medullare yosterius; inferior medullary velum) is a thin layer of white substance, prolonged from the white centre of the cerebellum, above and on either side of the nodule; it forms a part of the roof of the fourth ventricle. Somewhat semilunar in shape, its convex edge is continuous with the white substance of the cerebellum, while its thin concave margin is apparently free; in reality, however, it is continuous with the epithehum of the ventricle, which is prolonged downward from the posterior medullary velum to the ligulse. The two medullary vela are in contact with each other along their line of emer- gence from the white substance of the cerebellum; and this line of contact forms the summit of the roof of the fourth ventricle, which, in a vertical section through the cavity, appears as a pointed angle. The Fibrae Propriae of the cerebellum are of two kinds: (1) commissural fibres, which cross the middle line at the anterior and posterior parts of the vermis and connect the opposite halves of the cerebellum; (2) arcuate or association fibres, which connect adjacent laminae wdth each other. Gray Substance. — The gray substance of the cerebellum is found in two situations : (1) on the surface, forming the cortex; (2) as independent masses in the anterior. (1) The gray substance of the cortex presents a characteristic foliated appearance, due to the series of laminae which are given off from the central white substance; these in their turn give off secondary laminae, which are covered by gray substance. Externally, the cortex is covered by pia mater; internally is the medullary centre, consisting mainly of nerve fibres. Microscopic Appearance of the Cortex (Fig. 716). — The cortex consists of two layers, viz., an external gray molecular layer, and an internal rust-colored nuclear layer; between these is an incomplete stratum of cells which are characteristic of the cerebellum, viz., the cells of Purkinje. The external gray or molecular layer consists of fibres and cells. The nerve fibres are delicate fibrillse, and are derived from the following sources: (a) the dendrites and axon collaterals of Purkinje's cells; (6) fibres from cells in the nuclear layer; (c) fibres from the central white substance of the cerebellum; {d) fibres derived from cells in the molecular layer itself. In addition to these are other fibres, which have a vertical direction, and are the processes of large neuroglia cells, situated in the nuclear layer. They pass outward to the periphery of the gray matter, where they expand into little conical enlargements which form a sort of limiting membrane beneath the pia mater, analogous to the membrana limitans interna in the retina, formed by the sustentacular fibres of Miiller. The cells of the molecular layer are small, and are arranged in two strata, an outer and an inner. They all possess branched axons; those of the inner layer are termed basket cells ; they run for some distance parallel with the surface of the folium — giving off collaterals which pass in a vertical direction toward the bodies of Purkinje's cells, around which they become enlarged, and form basket-like net-works. The cells of Purkinje form a single stratum of large, flask-shaped cells at the junction of the molecular and nuclear layers, their bases resting against the latter; in fishes and reptiles they are arranged in several layers. The cells are flattened THE RHOMBENCEPHALON OR HIND-BRAIN 843 in a direction transverse to the long axis of the foHum, and thus appear broad in sections carried across the fohum, and fusiform in sections parallel to the long axis of the folium. From the neck of the flask one or more dendrites arise and pass into the molecular layer, where they subdivide and form an extremely rich arbores- cence, the various subdivisions of the dendrites being covered by lateral spine- like processes. This arborescence is not circular, but, like the cell, is flattened at right angles to the long axis of the folium; in other words, it does not resemble a round bush, but has been aptly compared by Obersteiner to the branches of a fruit tree trained against a trellis or a wall. Hence, in sections carried across the folium the arborescence is broad and expanded; whereas in those which are parallel to the long axis of the folium, the arborescence, like the cell itself, is seen in profile, and is limited to a narrow area. Cell of Purkinje Axons of granule cells cut trans- versely Small cell of molecular layer Basket cell. \ Molecular layer '^ i Golgi cell VNv^lear layer Neuroglia cell i I Axon of cell of Purhinje • Tendril fibre Moss fibre Fig. 716. — Transverse section of a cerebellar folium. (Diagrammatic, after Cajal and KoUiker.) From the bottom of the flask-shaped cell the axon arises; this passes through the nuclear layer, and, becoming medullated, is continued as a nerve fibre in the subjacent white substance. As this axon traverses the granular layer it gives off fine collaterals, some of which run back into the molecular layer. The internal rust-colored or nuclear layer (Fig. 716) is characterized by containing numerous small nerve cells of a reddish-brown color, together with many nerve 844 NEUROLOGY fibrils. Most of the cells are nearly spherical and provided with short dendrites which spread out in a spider-like manner in the nuclear layer. Their axons pass outward into the molecular layer, and, bifurcating at right angles, run for some distance parallel with the surface. In the outer part of the nuclear la^-er are some larger cells, of the type II of Golgi. Their axons undergo frequent division as soon as the}^ leave the nerve cells, and pass into the nuclear la\^er; while their dendrites ramify chiefly in the molecular layer. Finally, in the gray substance of the cerebellar cortex there are fibres which come from the white centre and penetrate the cortex. The cell-origin of these fibres is unknown, though it is believed that it is probably in the gray substance of the medulla spinalis. Some of these fibres end in the nuclear layer by dividing into numerous branches, on which are to be seen peculiar moss-like appendages; hence they have been termed b}' Ramon y Cajal the moss fibres; they form an arborescence around the cells of the nuclear layer. Other fibres, the clinging or tendril fibres, derived from the medullary centre can be traced into the molecular layer, where their branches cling around the dendrites of Purkinje's cells. (2) The independent centres of gray substance in the cerebellum are four in number on either side: one is of large size, and is known as the nucleus dentatus; the other three, much smaller, are situated near the middle of the cerebellum, and are known as the nucleus emboliformis, nucleus globosus, and nucleus fastigii. Nucleus dentaius Braduum conjundivum Corpora quadrigemina hiferior olivary nucleus Fig. 717. — Sagittal section through right cerebellar hemi-sphere. The right olive has also been cut sagitally. The nucleus dentatus (Fig. 717) is situated a little to the medial side of the centre of the stem of the white substance of the hemisphere. It consists of an irregularly folded lamina, of a grayish-yellow color, containing white fibres, and presenting on its antero-medial aspect an opening, the hilus, from which most of the fibres of the brachium conjunctiva emerge (page 841). The nucleus emboliformis lies immediately to the medial side of the nucleus dentatus, and partly covering its hilus. The nucleus globosus is an elongated mass, directed antero-posteriorly, and placed medial to preceding. The nucleus fastigii is somewhat larger than the other two, and is situated close to the middle line at the anterior end of the superior vermis, and immediately over the roof of the fourth ventricle, from which it is separated by a thin layer of white substance. Applied Anatomy. — The general functions of the cerebellum in the human economy appear to be the coordination of movements and equilibration. The exact functions of its different parts are still quite uncertain, owing to the contradictory nature of the evidence furnished by THE RHOMBENCEPHALON OR HIND-BRAIN 845 (1) abhitioii ex])ci'imcnts upon animals, and (2) clinical observations in man of the effects pro- duced by abscesses or tumors affecting tlifferent portions of the organ. According to W. Aldren Turner, "The following localizing sj'^nijitoms would therefore indicate the presence of a tumor implicating the right cerebellar hemisphere and middle peduncle; deafness in the right ear, un- associated with middle-ear complications; an imsteadj'^ and imcertain gait, with a tendency to fall more particular!}' to the right side; coarse nystagmoid oscillations on looking to the right; movements resembling those of disseminated sclerosis on volitional effort of the right arm; an awkward uncertain action of the right leg; a slight increase of the right knee-jei-k; and, perhaps, slight blunting of sensibility over the right cornea and side of the face." The Fourth Ventricle {ventricuhis quarius). — The fourth ventricle, or cavity of the rhombencephalon, i.s situated in front of the cereheUum and behind the pons and upper half of the medulla oblongata. Developmentally considered, the fourth ventricle consists of three parts: a superior belonging to the isthmus rhombencephali, an intermediate, to the metencephalon, and an inferior, to the myelencephalon. It is lined by ciliated epitheliiuii, and is continuous bek)W with the central canal of the medulla oblongata;^ above, it communicates, by means of a passage termed the cerebral aqueduct, with the cavity of the third ^•entricle. It presents four angles, and possesses a roof or dorsal wall, a floor or^ ventral wall, and lateral boundaries. Angles. — The superior angle is on a level wath the upper border of the pons, and is continuous with the lower end of the cerebral aqueduct. The inferior angle is on a level with the lower end of the olive, and opens into the central canal of the medulla oblongata. Each lateral angle corresponds with the point of meeting of the brachia and restiform body. A little below the lateral angles, on a level with the striae medullares, the ventricular cavity is prolonged outward in the form of two narroM" lateral recesses, one on either side; these are situated between the restiform bodies and the flocculi, and reach as far as the attachments of the glosso- pharyngeal and vagus nerves. Lateral Boundaries. — The lower part of each lateral boundary is constituted by the clava, the fasciculus cuneatus, and the restiform body; the upper part by the brachium pontis and the brachium conjunctivum. Roof or Dorsal Wall (Fig. 718). — The upper portion of the roof is formed by the brachia conjunctiva and the anterior medullary velum; the lower portion, by the posterior medullary velum, the epithelial lining of the ventricle covered by the tela chorioidea inferior, the taeniae of the fourth ventricle, and the obex. The brachia conjunctiva (page 841), on emerging from the central w-hite sub- stance of the cerebellum, pass upward and forward, forming at first the lateral boundaries of the upper part of the cavity; on approaching the inferior colliculi, they converge, and their medial portions overlap the cavity and form part of its roof. The anterior medullary velum (page 842) fills in the angular interval between the brachia conjunctiva, and is continuous behind with the central white sub- stance of the cerebellum; it is covered on its dorsal surface by the lingula of the superior vermis. The posterior medullary velum (page 842) is continued downward and forward from the central white substance of the cerebellum in front of the nodule and tonsils, and ends inferiorly in a thin, concave, somewhat ragged margin. Below this margin the roof is devoid of nervous matter except in the immediate vicinity of the lower lateral boundaries of the ventricle, where two narrow white bands, the taeniae of the fourth ventricle (ligulae), appear; these bands meet over the inferior angle of the ventricle in a thin triangular lamina, the obex. The non-nervous part of the roof is formed by the epithelial lining of the ventricle, which is prolonged downward as a thin membrane, from the deep surface of the posterior medullary 1 J. T. Wilson (Journal of Anatomy and Physiology, vol. xl) has pointed out that the central canal of the medulla oblongata, immediately below its entrance into the fourth ventricle, retains the cleft-like form presented by the fetal medulla spinalis, and that it is marked by dorso- and ventro-lateral sulci. 846 NEUROLOGY velum to the corresponding surface of the obex and taeniae, and thence on to the floor of the ventricular cavity; it is covered and strengthened by a portion of the pia mater, which is named the tela chorioidea of the fourth ventricle. The taeniae of the fourth ventricle {taenia ventriculi qnartl; ligula) are two narrow bands of white matter, one on either side, which complete the lower part of the roof of the cavity. Each consists of a vertical and a horizontal part. The vertical part is continuous below the obex with the clava, to which it is adherent by its lateral border. The horizontal portion extends transversely across the restiform body, below the striae medullares, and roofs in the lower and posterior part of the lateral recess; it is attached by its lower margin to the restiform body, and partly encloses the choroid plexus, which, however, projects beyond it like a cluster of grapes; and hence this part of the taenia has been termed the cornucopia (Bochdalek). The obex is a thin, triangular, gray lamina, which roofs in the lower angle of the ventricle and is attached by its lateral margins to the clavae.^ The tela chorioidea of the fourth ventricle is the name applied to the triangular fold of pia mater w^hich is carried upward between the cerebellum and the medulla oblongata. It consists of two Corpora quadrigemina Cerebral pedu7icle A nterior medullary velum Ependymal lining of ventricle Posterior medullary velum Chorioid plexus Cisterna cerKbollmnedidlaris of subarachnoid cavity Central canal ^ , /^ ., . , , • <• Cisterna pontis oj subarachnoid cavity Fig. 718. — Scheme of roof of fourth ventricle. The arrow is in the foramen of Majendie. layers, which are continuous with each other in front, and are more or less adherent throughout. The posterior layer covers the antero-inferior surface of the cere- bellum, while the anterior is applied to the structures wdiich form the lower part of the roof of the ventricle, and is continuous inferiorly with the pia mater on the restiform bodies and closed part of the medulla. Choroid Plexuses. — These consist of two highly vascular inflexions of the tela chorioidea, which invaginate the lower part of the roof of the ventricle and are everywhere covered by the epithelial lining of the cavity. Each consists of a ver- tical and a horizontal portion : the former lies close to the middle line, and the latter passes into the lateral recess and projects beyond its apex. The vertical parts of the plexuses are distinct from each other, but the horizontal portions are joined in the middle line; and hence the entire structure presents the form of the letter T, the vertical limb of which, however, is double. 1 J. T. Wilson, op. cit., recognizes two forms of obex: (o) the true obex, constituted by a medullary thickening of the roof plate, and (6) a false or membranous obex, where the medullary thickening fails to take place, and where the roof plate is represented only by the ependymal layer clothing the ventral surface of a pial reduplication which forms the main substance of the membranous fold in question. THE RHOMBENCEPHALON OR HIND-BRAIN 847 Openings in the Roof. — In the roof of the fourth ventricle there are three openings, a medial and two lateral: the medial aperture (foramen Majendii), is situated imme- diately above the inferior angle of the ventricle; the lateral apertures are found at the extremities of the lateral recesses. By means of these three openings the ventricle communicates with the subarachnoid cavity, and the cerebrospinal fluid can circulate from the one to the other. Rhomboid Fossa (fossa rhomboidea; "floor'" of the fourth ventricle) (Fig. 719). — The anterior part of the fourth ventricle is named, from its shape, the rhomboid fossa, and its anterior wall, formed b}' the back of the pons and medulla oblongata, constitutes the floor of the fourth ventricle. It is covered by a thin layer of gray substance continuous with that of the medulla spinalis; superficial to this is a thin lamina of neuroglia which constitutes the ependyma of the ventricle and supports a layer of ciliated epithelium. The fossa consists of three parts, superior, inter- Tcenia pont Frenulum veil Trochlear nerve Ant. medullary velum Bi a chiu m conjunct ivum Nucleus deniatus Superior fovea Collicidus facialis Striae medulla/ Si, ^\^ Area acustica^ Trigonum hypoglossi / Ala, cineieii Tcenia of fourth ventrid Fig. 719. 'Funiculus separans Aiea postrema Obex Clava -Rhomboid fossa. mediate, and inferior. The superior part is triangular in shape and limited laterally by the brachia conjunctiva cerebelli; its apex, directed upward, is continuous with the cerebral aqueduct; its base it represented by an imaginary line at the level of the upper ends of the superior fovese. The intermediate part extends from this level to that of the horizontal portions of the taeniae of the ventricle ; it is narrow above where it is limited laterally by the brachia pontis, but widens below and is pro- longed into the lateral recesses of the ventricle. The inferior part is triangular, and its downwardly directed apex, named the calamus scriptorius, is continuous with the central canal of the closed part of the medulla oblongata. The rhomboid fossa is divided into symmetrical halves by a median sulcus which reaches from the upper to the lower angles of the fossa and is deeper below than above. On either side of this sulcus is an elevation, the medial eminence, bounded laterally by a sulcus, the sulcus limitans. In the superior part of the fossa the medial eminence has a width equal to that of the corresponding half of the 848 NEUROLOGY fossa, but opposite the superior fovea it forms an elongated swelling, the colliculus facialis, which overlies the nucleus of the abducent nerve, and is, in part at least, produced by the ascending portion of the root of the facial nerve. In the inferior part of the fossa the medial eminence assumes the form of a triangular area, the trigonum hypoglossi. When examined under water with a lens this trigone is seen to consist of a medial and a lateral area separated by a series of oblique furrows; the medial area corresponds with the upper part of the nucleus of the hypoglossal nerve, the lateral with a small nucleus, the nucleus intercalatus. The sulcus limitans forms the lateral boundary of the medial eminence. In the superior part of the rhomboid fossa it corresponds with the lateral limit of the fossa and presents a bluish-gray area, the locus coeruleus, which owes its color to an underlying patch of deeply pigmented nerve cells, termed the substantia ferruginea. At the level of the colliculus facialis the sulcus limitans widens into a flattened depression, the superior fovea, and in the inferior part of the fossa appears as a distinct dimple, the inferior fovea. Lateral to the fovese is a rounded elevation named the area acustica, which extends into the lateral recess and there forms a feebly marked swelling, the tuberculum acusticum. Winding around the restiform body and crossing the area acustica and the medial eminence are a number of white strands, the striae medullares, which form a portion of the cochlear division of the acoustic nerve and disappear into the median sulcus. Below the inferior fovea, and betw^een the trigonum hypoglossi and the lower part of the area acustica is a triangular dark field, the ala cinerea, w^hich corresponds to the sensory nucleus of the vagus and glossopharyngeal nerves. The lower end of the ala cinerea is crossed by a narrow translucent ridge, the funiculus separans, and between this funiculus and the clava, is a small tongue-shaped area, the area postrema. On section it is seen that the funiculus separans is formed by a strip of thickened ependyma, and the area postrema by loose, highly vascular, neuroglial tissue con- taining nerve cells of moderate size. THE MESENCEPHALON OR MID-BRAIN. The mesencephalon or mid-brain (Fig. 725) is the short, constricted portion which connects the pons and cerebellum with the thalamencephalon and cerebral hemi- spheres. It is directed upward and forward, and consists of (1) a ventro-lateral portion, composed of a pair of cylindrical bodies, named the cerebral peduncles; (2) a dorsal portion, consisting of four rounded eminences, named the corpora quadrigemina; and (3) an intervening passage or tunnel, the cerebral aqueduct, which represents the original cavity of the mid-brain and connects the third with the fourth ventricle (Fig. 720). The cerebral peduncles (pechmculvs cerebri; cms cerebri) are two cylindrical masses situated at the base of the brain, and largely hidden by the temporal lobes of the cerebrum, which must be drawn aside or removed in order to expose them. They emerge from the upper surface of the pons, one on either side of the middle line, and, diverging as they pass upward and forward, disappear into the substance of the cerebral hemispheres. The depressed area between the crura is termed the interpeduncular fossa, and consists of a layer of grayish substance, the posterior perforated substance, which is pierced by small apertures for the transmission of bloodvessels; its lower part lies on the ventral aspect of the medial portions of the tegmenta, and contains a nucleus named the interpeduncular ganglion (page 850) ; its upper part assists in forming the floor of the third ventricle. The ventral sur- face of each peduncle is crossed from the medial to the lateral side by the superior cerebellar and posterior cerebral arteries; its lateral surface is in relation to the gyrus hippocampi of the cerebral hemisphere and is crossed from behind forward THE MESENCEPHALON OR MID-BRAIN 849 by the trochlear nerve. Close to the point of disappearance of the peduncle into the cerebral hemipshere, the optic tract winds forward around its ventro-lateral surface. The medial surface of the " peduncle forms the lateral boundary of the interpeduncular fossa, and is marked by a longitudinal furrow, the oculomotor sulcus, from which the roots of the oculomotor nerve emerge. On the lateral surface of each peduncle there is a second longitudinal furrow, termed the lateral sulcus ; the fibres of the lateral lemniscus come to the sur- face in this sulcus, and pass backward and upward, to disappear under the inferior colliculus. Structure of the Cerebral Peduncles (Figs. 721, 722). — On transverse sec- tion, each peduncle is seen to consist of a dorsal and a ventral part, separ- ated by a deeply pigmented lamina of gray substance, termed the substantia nigra. The dorsal part is named the tegmentum; the ventral, the base or cnista; the two bases are separated from each other, but the tegmenta are joined in the median plane by a for- d.. 6..J Fig. 720. — Coronal section through mid-brain. (Sche- matic.) (Testut.) 1. Corpora quadrigemina. 2. Cere- bral aqueduct. 3. Central gray stratum. 4. Interpedun- cular space. 5. Sulcus lateralis. 6. Substantia nigra. 7. Red nucleus of tegmentum. 8. Oculomotor nerve, with 8', 1 1 . PI lypi '^^ nucleus of origin, a. Lemniscus (in blue) with a' the ward prolongation or the raphe or the medial lemniscus and a" the lateral lemniscus. 6. T , -11 ,1 , , n Medial longitudinal fasciculus, c. Raph6. d. Temporo- pons. Laterally, the tegmenta are tree; pontine fibres, e. Portlonof medial lemniscus, which runs dorsally, they blend with the corpora ll,£" ^'-''°'"" -^?l'^-«--^d insula. /. Cerebrospinal quadrigemina. g. Frontopontine fibres. Inferior coUiculi Cerebral aqueduct Nucleus of oczdomotor nerve ■ Laterallemniscus Medial longitudinal fasciculus Medial lemniscus Fig. 721. Eaphe -Transverse section of mid-brain at level of inferior colHculi. The base (basis peduncidi; cnista or pes) is semilunar on transverse section, and consists almost entirely of longitudinal bundles of efferent fibres, which arise from the cells of the cerebral cortex and are grouped into three principal sets, viz., cerebrospinal, frontopontine, and temporopontine (Fig. 720). The cerebrospinal 54 850 NEUROLOGY fibres, (leri\e(l from the cells of the motor area of the cerebral cortex, occupy the middle three-fifths of the base; they are continued partly to the nuclei of the motor cerebral nerves, but mainly into the pyramids of the medulla oblongata. The frontopontine fibres are situated in the medial fifth of the base; they arise from the cells of the frontal lobe and end in the nuclei of the pons. The temporopontine fibres are lateral to the cerebrospinal fibres; they originate in the tempcjral lobe and end in the nuclei pontis.^ Su2)enor colliciili I aijuc'iho-t ucleus of oculomotor nerve Medial longitudinal fasciculus Fig. 722. — Transverse .section of mid-brain at level of superior colliculi. The substantia nigra ( inter calatum) is a layer of gray substance containing numerous deeply pigmented, multipolar nerve cells. It is semilunar on transverse section, its concavitj- being directed toward the tegmentum; from its convexity, prolongations extend between the fibres of the base of the peduncle. Thicker medially than laterally, it reaches from the oculomotor sulcus to the lateral sulcus, and extends from the upper surface of the pons to the subthalamic region; its medial part is traversed by the fibres of the oculomotor nerve as these stream for- ward to reach the oculomotor sulcus. The connections of the cells of the substantia nigra have not been definitely established. The tegmentum is continuous below with the reticular formation of the pons, and, like it, consists of longitudinal and transverse fibres, together with a consider- able amount of gray substance. The principal gray masses of the tegmentum are the red nucleus and the interpeduncular ganglion; of its fibres the chief longi- tudinal tracts are the brachiurn conjunctivum, the medial longitudinal fasciculus, and the lemniscus. Gray Substance. — ^The red nucleus is situated in the anterior part of the teg- mentum, and is continued upward into the posterior part of the subthalamic region. In sections at the level of the superior colliculus it appears as a circular mass which is traversed by the fibres of the oculomotor nerve. Most of the fibres of the brachium conjunctivum end in it (page 847). The axons of its larger cells cross the middle line and are continued downward into the lateral funiculus of the medulla spinalis as the rubrospinal tract (page 816); those of its smaller cells end mainly in the thalamus. ■ The interpeduncular ganglion is a median collection of nerve cells situated in the ventral part of the tegmentum. The fibres of the fasciculus retroflexus of 1 A band of fibres, the Iraclus peduncularis transversus, is sometimes seen emerging from in front of the superior collic- ulus; it passes around the ventral aspect of the peduncle about midway between the pon.s and the optic tract, and dips into the oculomotor sulcus. This band is a constant structure in many mammals, but is only present in about 30 per cent, of human brains. Since it undergoes atrophj' after enucleation of the eyeballs, it may be considered as forming a path for visual sensations. THE MESENCEPHALOX OH MID-BRAIX 851 Meyncrt, which have their origin in the cells of the ganglion habenuhe (page 859), end in it. Besides the two nuclei mentioned, there are small collections of cells which form the dorsal and ventral nuclei and the central nucleus or nucleus of the raphe. White Substance. — (1) The origin and course of the brachium conjunctivum have already been described (page 841). (2) The medial (posterior) longitudinal fasciculus (Fig. 723) is continuous below with the proper fasciculi of the anterior and lateral funiculi of the medulla spinalis, and has been traced by Edinger as far as a nucleus, the nucleus of the medial longi- tudinal fasciculus, situated in the hypothalamus, immediately in front of the cerebral aqueduct. In the medulla oblongata and pons it runs close to the middle line, near the floor of the fourth ventricle; in the mesencephalon it is situated on the Xudeus of medial longitudinal jaxcicidus Superior cullicidug Xuclcia of oculoinotor nerve Xiicleus of trigeminal nerve Xiicleiis of abducent nerve Xucleiis of facial nerve Xudeus of glossopharyn geal and vagus nerves Xudeus of hypoglossal nerve Xi>clei(s of accessor)/ nerve Fig. 723. — Scheme of the medial longitudinal fasciculus; motor fibres in red, sensory in blue. ventral aspect of the cerebral aqueduct, below the nuclei of the oculomotor and trochlear nerves. Its connections are imperfectly known, but it consists largely of ascending and descending intersegmental or association fibres, which connect the nuclei of the rhombencephalon and mesencephalon to each other. Many of the descending fibres arise in the superior coUiculus, and, after decussating in the middle line, end in the motor nuclei of the pons and medulla oblongata. The ascending fibres arise from the cells of the gray substance of the upper part of the medulla spinalis, and from the nuclei in the medulla oblongata and pons, and pass 852 NEUROLOGY without undergoing decussation to the higher nuclei. Fibres are also carried through the medial longitudinal fasciculus from the nucleus of the abducent nerve into the oculomotor nerve of the opposite side, and through this nerve to the. Rectus medialis oculi. Again, fibres are said to be prolonged through this fasciculus from the nucleus of the oculomotor nerve into the facial nerve, and are distributed to the Orbicularis oculi, the Corrugator, and the Frontalis.^ Corpora quadn'gemina Superior olivary nucleus Cochlear nucleus Sensory cerebral nuclei Nucleus gracilis Nucleus cuneatus Fig. 724. — Scheme showing the course of the fibres of the lemniscus; medial lemniscus in blue, lateral in red. (3) The lemniscus or fillet (Fig. 724). — The fibres of the lemniscus take origin in the gracile and cuneate nuclei of the medulla oblongata, and cross to the oppo- site side in the sensory decussation (page 827). They then pass upward through the medulla oblongata, in which they are situated behind the cerebrospinal fibres and between the olives. Here they are joined by the fibres of the superficial antero- lateral fasciculus, these having already undergone decussation in the medulla spinalis. As the lemniscus ascends, it receives additional fibres from the terminal nuclei of the sensory cerebral nerves of the opposite side. In the pons, it assumes a flattened, ribbon-like appearance, and is placed dorsal to the trapezium. In 1 A. Bruce and J. H. Harvey Pirrie, "On the Origin of the Facial Nerve," Review of Neurology and Psychiatry, December, 1908, No. 12, vol. vi, produce weighty evidence against the view that the facial nerve derives fibres from the nucleus of the oculomotor nerve. THE MESENCEPHALON OR MID-BRAIN 853 6 2 :.. ,„.o- the mesencephalon, its lateral part is folded backward and forms nearly a right angle with its medial portion; and hence it is customary to speak of the lemniscus as consisting of lateral and medial parts. The lateral lemniscus (Icm)ii6-cus lateralis) comes to the surface of the mes- encephalon along its lateral sulcus, and disappears under the inferior colliculus. It consists of fibres from the terminal nuclei of the cochlear division of the acoustic nerve, together with others from the superior olivary and trapezoid nuclei. Most of these fibres are crossed, but some are uncrossed. Many of them pass to the inferior colliculus of the same or opposite side, but others are prolonged to the thalamus, and thence through the occipital part of the internal capsule to the middle and superior temporal gyri. The medial lemniscus (lemniscus medialis) begins in the gracile and cuneate nuclei of the opposite side, and is joined by the superficial antero-lateral fasciculus of the medulla spinalis and by fibres from the terminal nuclei of the sensory cerebral nerves of the opposite side, excepting the cochlear division of the acoustic. In the cerebral pe- duncle, a few of its fibres pass upward in the lateral part of the base of the peduncle, on the dorsal aspect of the temporopontine fibres, and reach the lentiform nucleus and the insula. The greater part of the medial lemniscus, on the other hand, is prolonged through the teg- mentum, and most of its fibres end in the thalamus ; probably some are continued directly through the occipital part of the internal capsule to the cerebral cortex. From the cells of the thalamus a relay of fibres is prolonged to the cerebral cortex. In the tegmentum there are, besides these three tracts, the tectospinal fasciculus from the superior colliculus and the rubrospinal fascic- ulus from the red nucleus; these cross the middle line and are continued downward into the medulla spinalis. The corpora quadrigemina (Fig. 729) are four rounded eminences which form the dorsal part of the mesencephalon. They are situated above and in front of the anterior medullary velum and brachia conjunctiva, and below and behind the third ventricle and posterior commissure. They are covered by the splenium of the corpus callosum, and are partly overlapped on either side by the medial angle, or pulvlnar, of the posterior end of the thalamus; on the lateral aspect, under cover of the pulvinar, is an oval eminence, named the medial geniculate body. The corpora quadrigemina are arranged in pairs (superior and inferior colliculi), and are separated from one another by a crucial sulcus. The longitudinal part of this sulcus expands superiorly to form a slight depression which supports the pineal body, a cone-like structure which projects backward from the thalam- encephalon and partly obscures the superior colliculi. From the inferior end of the longitudinal sulcus, a white band, termed the frinulum veli, is prolonged down- ward to the anterior medullary velum; on either side of this band the trochlear nerve emerges, and passes forward on the lateral aspect of the cerebral peduncle to reach the base of the brain. The superior colliculi are larger and darker in color than the inferior, and are oval in shape. The inferior colliculi are hemispherical, and somewhat more prominent than the superior. The superior colliculi are associated with the sense of sight, the inferior with that of hearing. From the lateral aspect of each colliculus a w^hite band, termed the brachium, Fig. 725. — Transverse section passing through the sensory decussation. Schematic. (Testut.) 1. Anterior median fissure. 2. Posterior median sulcus. 3, 3'. Head and base of anterior column (in red). 4. Hypoglossal nerve. 5. Bases of posterior column. 6. Gracile nucleus. 7. Cune- ate nucleus. 8, 8. Lemniscus. 9. Sensory decussation. 10. Cerebrospinal fasciculus. 854 NEUROLOGY is prolonged upward and forward. The superior brachium extends laterahvard from the superior colhculus, and, passing between the pulvinar and medial genicu- late body, is partly continued into an eminence called the lateral geniculate body, and partly into the optic tract. The inferior brachium passes forward and upward from the inferior colliculus and disappears under cover of the medial geniculate body. In close relationship with the corpora quadrigemina are the brachia conjunctiva, which emerge from the upper and medial parts of the cerebellar hemispheres. They run upward and forward, and, passing under the inferior colliculi, enter the tegmenta as already described (page 841). Structure of the Corpora Quadrigemina. — The inferior colliculus (coUiculvs inferior; inferior quadrigeminal body; postgeinina) consists of a compact nucleus of gray substance containing large and small multipolar nerve cells, and more or less completely surrounded by white fibres derived from the lateral lemniscus. Most of these fibres end in the gray nucleus of the same side, but some cross the middle line and end in that of the opposite side. From the cells of the gray nucleus, fibres are prolonged through the inferior brachium into, the tegmentum of the cerebral peduncle, and are carried to the thalamus and the cortex of the temporal lobe; other fibres cross the middle fine and end in the opposite colliculus. The superior colliculus {colliculus superior; sujjerior quadrigeminal body; pregemina) is covered by a thin stratum (stratum zonale) of white fibres, the majority of which are derived from the optic tract. Beneath this is the stratum cinereum, a cap-like layer of gray substance, thicker in the centre than at the circumference, and consisting of numerous small multipolar nerve cells, imbedded in a fine netw^ork of nerve fibres. Still deeper is the stratum opticum, containing large multipolar nerve cells, separated by numerous fine nerve fibres. Finally, there is the stratum lemnisci, consisting of fibres derived partly from the lemniscus and partly from the cells of the stratum opticum; interspersed among these fibres are many large multipolar nerve cells. The two last-named strata are sometimes termed the gray-white layers, from the fact that they consist of both gray and white substance. Of the afterent fibres which reach the superior colliculus, some are derived from the lemniscus, but the majority have their origins in the retina and are conveyed to it through the superior brachium; all of them end by arborizing around the cells of the gray substance. Of the efferent fibres, some cross the middle line to the opposite colliculus; many ascend through the superior brachium, and finally reach the cortex of the occipital lobe of the cerebrum; while others, after undergoing decussation (fountain decussation of Meynert) form the tectospinal fasciculus which descends through the formatio reticularis of the mesen- cephalon, pons, and medulla oblongata into the medulla spinalis, where it is found partly in the anterior funiculus and partly intermingled w^ith the fibres of the rubrospinal tract. The corpora quadrigemina are larger in the lower animals than in man. In fishes, reptiles, and birds they are hollow, and only two in number (corpora bigemina); they represent the superior colliculi of mammals, and are frequently termed the optic lobes, because of their intimate connection with the optic tracts. The cerebral aqueduct {aqueductus cerebri; aqueduct of Sylvius) is a narrow- canal, about 15 mm. long, situated between the corpora quadrigemina and teg- menta, and connecting the third with the fourth ventricle. Its shape, as seen in transverse section, varies at different levels, being T-shaped, triangular above, and oval in the middle; the central part is slightly dilated, and was named by Retzius the ventricle of the mid-brain. It is lined by ciliated columnar epithelium, and is surrounded by a layer of gray substance named the central gray stratum: this is continuous below with the gray substance in the rhomboid fossa, and above with that of the thhd ventricle. Dorsally, it is partly separated from the gray THE PROSENCEPMALOX OR FORE-BRAIN 855 substance of the ([iiadrigeminal bodies by the fibres of the lemniscus; ventral to it are the medial longitudinal fasciculus, and the formatio reticularis of the teg- mentum. Scattered throughout the central gray stratum are immerous nerve cells of various sizes, interlaced, by a net-work of fine fibres. Besides these scattered cells it contains three groups which constitute the nuclei of the oculomotor and trochlear ner\es, and the nucleus of the mesencephalic root of the trigeminal nerve. The nucleus of the trigeminal nerve extends along the entire length of the aqueduct, and occupies the lateral part of the gray stratum, while the nuclei of the oculo- motor and trochlear nerves are situated in its ventral part. The nucleus of the oculomotor nerve is about 10 cm. long, and lies under the superior colliculus, beyond which, lu)we^■er, it extends for a short distance into the gray substance of the third ventricle. The nucleus of the trochlear nerve is small and nearly circular, and is on a level with a plane carried transversely through the upper part of the inferior colliculus. THE PROSENCEPHALON OR FORE-BRAIN. The prosencephalon or fore-brain consists of: (1) the diencephalon, corresponding in a large measure to the third ventricle and the structures which bound it; and (2) the telencephalon, comprising the largest part of the brain, viz., the cerebral hemispheres; these hemispheres are intimately connected with each other across the middle line, and each contains a large ca^dty, named the lateral ventricle. The lateral ventricles communicate through the interventricular foramen with the third ventricle, but are separated from each other by a medial septum, the septum pellucidum; this contains a slit- like cavity, which does not communicate with the ventricles. The Diencephalon. — The diencephalon is connected above and in front with the cerebral hemispheres; behind with the mesencephalon. Its upper surface is concealed by the corpus callosum, and is covered by a fold of pia mater, named the tela chorioidea of the third ventricle; inferiorlv it reaches to the base of the brain. The diencephalon comprises: (1) the thalamencephalon ; (2) the pars mamillaria hypothalami; and (3) the posterior part of the third ventricle. For descriptive purposes, however, it is more convenient to consider the whole of the third ventricle and its boundaries together; this necessitates the inclusion, under this heading, of the pars optica h^t'pothalami and the corresponding part of the third ventricle — structures which properly belong to the telencephalon. The Thalamencephalon. — The thalamencephalon comprises: (1) the thalamus; (2) the metathalamus or corpora geniculata; and (3) the epithalamus, consisting of the trigonum habenulae, the pineal body, and the posterior commissure. The Thalami {optic thalamus) (Figs. 726, 727) are two large ovoid masses, situated one on either side of the third ventricle and reaching for some distance behind that cavity. Each measures about 4 cm. in length, and presents two extremities, an anterior and a posterior, and four surfaces, superior, inferior, medial, and lateral. The anterior extremity is narrow; it lies close to the middle line and forms the posterior boundary of the interventricular foramen. The posterior extremity is expanded, directed backward and lateralward, and overlaps the superior colliculus. Medially it presents an angular prominence, the pulvinar, which is continued laterally into an oval swelling, the lateral geniculate body, while beneath the pulvinar, but separated from it by the superior brachium, is a second oval swelling, the medial geniculate body. The superior surface is free, slightly convex, and covered by a layer of white substance, termed the stratum zonale. It is separated laterally from the caudate nucleus by a white band, the stria terminalis, and by the terminal vein. It is divided into a medial and a lateral portion by an oblique shallow furrow which runs from 856 NEUROLOGY behind forward and medialward and corresponds with the lateral margin of the fornix; the lateral part forms a portion of the floor of the lateral ventricle, and is .covered by the epithelial lining of this cavity; the medial part is covered by the tela chorioidea of the third ventricle, and is destitute of an epithelial covering. In front, the superior is separated from the medial surface by a salient margin, the taenia thalami, along which the epithelial lining of the third ventricle is reflected on to the under surface of the tela chorioidea. Behind, it is limited medially by a groove, the sulcus habenulae, which intervenes between it and a small triangular area, termed the trigonum habenulae. The inferior surface rests upon and is continuous with the upward prolongation of the tegmentum (subthalamic tegmental region), in front of which it is related to the substantia innominata of Meynsrt. Fig. 726. — Dissection showing the ventricles of the brain. The medial surface constitutes the upper part of the lateral wall of the third ventricle, and is connected to the corresponding surface of the opposite thalamus by a flattened gray band, the massa intermedia {jniddle or gray commissure) . This mass averages about 1 cm. in its antero-posterior diameter: it sometimes consists of two parts and occasionally is absent. It contains nerve cells and nerve fibres; a few of the latter may cross the middle line, but most of them pass toward the middle line and then curve lateralward on the same side. The lateral surface is in contact with a thick band of white substance which forms the occipital part of the internal capsule and separates the thalamus from the lentiform nucleus of the corpus striatum. Structure. — The thalamus consists chiefly of gray substance, but its upper sur- face is covered by a layer of white substance, named the stratum zonale, and its lateral surface by a similar layer termed the lateral medullary lamina. Its gray THE PROSENCEPHALON OR FORE-BRAIN 857 substance is incompletely sul)(li\i(le(l into three parts — anterior, medial, and lateral — by a white layer, the medial medullary lamina. The anterior part comprises the anterior tubercle, the medial part lies next the lateral wall of the third ventricle while the lateral and largest part is interposed between the medullary laminae and includes the pulvinar. The lateral part is traversed by numerous fibres which radiate from the thalamus into the internal capsule, and i^ass through the latter to the cerebral cortex. These three parts are built up of numerous nuclei, the connections of many of which are imperfectly known. Thalamus Lateral ventricle Caudate nucleus Internal capsule Lcntiforni nucleus Claustrum Insula Corpus callosutn Choroid plexu.t of lateral ventricle ' Fornix Choroid plexus of third ventricle Third ventricle Red nucleus Substantia nigra Post. perf. substance Base of peduncle Nucleus of Luys Toenia hippocampi Inferior cornu of lateral ventricle Hippocampus Gyrus dentatus Caudate nucleus Fig. 727. — Coronal section of brain immediately in front of pons. Comiections.— The thalamus may be regarded as a large ganglionic mass in which the ascending tracts of the tegmentum and a considerable proportion of the fibres of the optic tract end, and from the cells of which numerous fibres (thalamocortical) take origin, and radiate to almost every part of the cerebral cortex. The lemniscus, together with the other longitudinal strands of the tegmentum, enters its ventral part: the thalamomamillary fasciculus {bundle of Vicq d'Azyr), from the corpus mamillare, enters in its anterior tubercle, while many of the fibres of the optic tract terminate in its posterior end. The thalamus also receives numerous fibres (corticothalamic) from the cells of the cerebral cortex. The fibres that arise from the cells of the thalamus form four principal groups or stalks: (a) those of the ante- rior stalk pass through the frontal part of the internal capsule to the frontal lobe; (6) the fibres of the posterior stalk {optic radiations) arise in the pulvinar and are 858 NEUROLOGY conveyed through the occipital part of the internal capsule to the occipital lobe; (c) the fibres of the inferior stalk leave the under and medial surfaces of the thalamus, and pass beneath the lentiform nucleus to the temporal lobe and insula; {d) those of the parietal stalk pass from the lateral nucleus of the thalamus to the parietal lobe. Fibres also extend from the thalamus into the corpus striatum — those destined for the caudate nucleus leave the lateral surface, and those for the lenti- form nucleus, the inferior surface of the thalamus. Thalamus Caudate nucleun Internal capxule Globus pallidiis Putame.n Claustrum ■>^l J»!-ula Corpus callosuin Lateral ventricle Choroid plexus Fornix Third ventricle Medial inedullary lamina I ntermediate mass Third ventricle Ojitic tract Amygdaloid nucleus Fig. 728. — Coronal section of brain through intermediate mass of third ventricle. The Metathalamus (Fig. 729) comprises the geniculate bodies, which are two in number — a medial and a lateral — on each side. The medial geniculate body {corpus geniculatum mediale; internal geniculate body; yostgeniculatum) lies under cover of the pulvinar of the thalamus and on the lateral aspect of the corpora quadrigemina. Oval in shape, with its long axis directed forward and lateralward, it is lighter in color and smaller in size than the lateral. The inferior brachium from the inferior colliculus disappears under cover of it while from its lateral extremity a strand of fibres passes to join the optic tract. Entering it are many acoustic fibres from the lateral lemniscus. The medial geniculate bodies are connected with one another by the commissure of Gudden, which passes through the posterior part of the optic chiasma. The lateral geniculate body (corpus geniculatum laterale; external geniculate body; pregenicidatum) is an oval elevation on the lateral part of the posterior end of the 77//-; PROSENCEPHALON OP FORE-BRAIN 859 thalanuis, aiul is connected with the sni)cri()r collicnlus by the superior brachium. It is of a dark color, and presents a himinated arrangement consisting of alternate layers of gray and white substance. It receives numerous fibres from the optic tract, while other fibres of tliis tract pass over or through it into tlie pulvinar. Its cells are large and ])ignuMite{l; their axons i)ass to tiie visual area in the occipital part of the cerebral cortex. The superior colliculus, the ])ul\inar, and the lateral geniculate body receive many fibres from the optic tracts, and are therefore Intimately connected with sight, constituting what are termed the lower visual centres. Extirpation of the eyes in a newly born animal entails an arrest of the development of these centres, but has no effect on the medial geniculate bodies or on the inferior colliculi. More- over, the latter are well-developed in the mole, an animal in which the superior colliculi are rudimentary. Superior brachiuia Lateral geniculate hmly Inferior brachium Pulvinar Pineal body Medial geniculate body I Opt 10 t/ait Superior colliculi Inferior colliculi Frenulum veil Trochlear nerve Lateral lemniscus Brachiuyn conjunctivum Brachium pontis Rhomboid fossa Glossopharyngeal and vagus nerves Optic cuinntissure Oculom,otor nei-ve Trigeminal nerve Arowitic nerve I<'acial nei i^e Abducent nerve Hypoglossal nerve Accessory nerve Fig. 729. — Hind- and mid-brains; postero-lateral view. The Epithalamus comprises the trigonum habenulae, the pineal body, and the posterior commissure. The trigonum habenulae is a small depressed triangular area situated in front of the superior colliculus and on the lateral aspect of the posterior part of the taenia thalami. It contains a group of nerve cells termed the ganglion habenulae. Fibres enter it from the stalk of the pineal body, and others, forming what is termed the habenular commissure, pass across the middle line to the corresponding ganglion of the opposite side. Most of its fibres are, how^ever, directed downward and form a bundle, the fasciculus retroflexus of Meynert, which passes medial to the red nucleus, and, after decussating wdth the corresponding fasciculus of the opposite side, ends in the interpeduncular ganglion. The pineal body {corpus ijineale; ejn'physis) is a small, conical, reddish-gray body which lies in the depression betw^een the superior colliculi. It is placed beneath the splenium of the corpus callosum, but is separated from this by the tela chorioidea of the third ventricle, the lowTr layer of which envelops it. It measures about 8 cm. in length, and its base, directed forward, is attached by a stalk or peduncle 860 NEUROLOGY of white substance. The stalk of the pineal body divides anteriorly into two laminse, a dorsal and a ventral, separated from one another by the pineal recess of the third ventricle. The ventral lamina is continuous with the posterior com- missure; the dorsal lamina is continuous with the habenular commissure and divides into two strands the medullary striee, which run forward, one on either side, along the junction of the medial and upper surfaces of the thalamus to blend in front with the columns of the fornix. Structure. — The pineal body is destitute of nervous substance, and consists of follicles Lined by epithelium and enveloped by connective tissue. These follicles contain a variable quantity of gritty material, composed of phosphate and carbonate of calcium, phosphate of magnesium and ammonia, and a little animal matter. The pineal body is generally believed to be the homologue of the pineal eye of lizards. In these animals it is attached by an elongated stalk and projects through an aperture in the roof of the cranium. Its extremity hes immediately under the epidermis, and, on microscopic exami- nation, presents in a rudimentary fashion structures similar to those found in the eyeball. Recent observations tend to the conclusion that the pineal body arises as a paired structure, probably serially homologous with the paired eyes. The posterior commissure is a rounded band of white fibres crossing the middle line on the dorsal aspect of the upper end of the cerebral aqueduct. Its fibres acquire their medullary sheaths early, but their connections have not been definitely determined. Most of them have their origin in a nucleus, the nucleus of the poste- rior commissure {nucleus of Darkschewitsch) , which lies in the central gray substance of the upper end of the cerebral aqueduct, in front of the nucleus of the oculomotor nerve. Some are probably derived from the posterior part of the thalamus and from the superior colliculus, while others are believed to be continued downward into the medial longitudinal fasciculus. The Hypothalamus (Fig. 730) includes the subthalamic tegmental region and the structures forming the greater part of the floor of the third ventricle, viz., the corpora mamillaria, tuber cinereum, infundibulum, hypophysis, and optic chiasma. The subthalamic tegmental region consists of the upward continuation of the tegmentum; it lies on the ventro-lateral aspect of the thalamus and separates it from the fibres of the internal capsule. The red nucleus and the substantia nigra are prolonged into its lower part; in front it is continuous with the substantia innominate of Meynert, medially with the gray substance of the floor of the third ventricle. It consists from above downward of three strata: (1) stratum dorsale, directly applied to the under surface of the thalamus and consisting of fine longitudinal fibres; (2) zona incerta, a continuation forward of the formatio reticularis of the tegmentum; and (3) the corpus subthalamicum (nucleus of Luys), a brownish mass presenting a lenticular .shape on transverse section, and situated on the dorsal aspect of the fibres of the base of the cerebral peduncle; it is encapsuled by a lamina of nerve fibres and contains numerous medium-sized nerve cells, the connections of which are as yet not fully determined. The corpora mamillaria {corjnis alhicantia) are two round white masses, each about the size of a small pea, placed side by side below the gray substance of the floor of the third ventricle in front of the posterior perforated substance. They consist of white substance externally and of gray substance internally, the cells of the latter forming two nuclei, a medial of smaller and a lateral of larger cells. The white substance is mainly formed by the fibres of the columns of the fornix, which descend to the base of the brain and end partly in the corpora mamillaria. From the cells of the gray substance of each mamillary body two fasciculi arise: one, the thalamomamillary fasciculus {bundle of Vicq d'Azyr), passes upward into the anterior nucleus of the thalamus; the other is directed downward into the tegmen- tum. Afferent fibres are believed to reach the corpus mamillare from the medial lemniscus and from the tegmentum. THE PROSENCEPHALON OR FORE-BRAIN 861 The tuber cinereum is a hollow cmineiice of ^rji>' substance situated between the corpora niainillaria behind, and the oi)tic chiasma in front. Laterally it is Corpora fixiadrigem ina Tela chorioidea of third ventricle. Posterior commissure Intermediate mass Interventricular foramen , / Pineal body \ -^ / 'iplemnm N ^4 P'ft mater Genu / / ^ Rostnun / / ^ Anteno) commissure ^ / Lamina teiminalis Optxe recas Optic chiasma Injundibul Coipits onamilla) Oculomotor • Cerebral aqueduct Chorioid plexus Fourth ventricle Fig. 730. — Median sagittal section of brain. The relations of the pia mater are indicated by the red color. continuous with the anterior per-' forated substances and anteriorly with a thin lamina, the lamina terminalis. From the under surface of the tuber cinereum a hollow conical process, the infundibulum, projects downward and forward and is attached to the posterior lobe of the hypophysis. In the lateral part of the tuber eine- reum is a nucleus of nerve ceils, the basal optic nucleus of Meynert, while close to the ca\ity of the third ventricle are three additional nuclei. Between the tuber cineremn and the corpora mamiUaria a small elevation, with a corresponding depression in the third ventricle, is some- times seen. Retzius has named it the eminentia saccularis, and regards it as a representative of the saccus vasculosus found in this situation in some of the lower vertebrates. The hypophysis (pituitary body) (Fig. 731) is a reddish-gray, somewhat oval mass, measuring about 1.25 cm. in its transverse, and about 8 cm. in its antero- FiG. 731. — The hypophysis cerebri, in position. Shown in sagittal section. (Testut.) 1, 1'. Anterior and posterior lobes of hj-pophysis. 2. Infundibulum. 3. Optic chiasma. 4. Lamina terminalis. 5. Optic recess. 6. Anterior commissure. 7, 7'. Circular sinus. 8. Anterior cerebral artery. 9. Basilar artery. 10. Posterior cerebral artery. 11. Corpus mamillare. 12. Cerebral peduncle. 13. Pons. 862 NEUROLOGY posterior diameter. It is attached to the end of the iiifundibiikiin, and is sitnated in the fossa hypophyseos of the sphenoidal bone, where it is retained by a circular fold of dura mater, the diaphragma sella; this fold almost completely roofs in the fossa, leaving only a small central aperture through which the infundibulum passes. The hypophysis consists of an anterior and a posterior lobe, which differ from one another in their mode of development and in their structure (Fig. 732). The anterior lobe is the larger, and is somewhat kidney-shaped, the concavity being directed backward and embracing the posterior lobe. It is developed from a diver- ticulum of the ectoderm of the primitive buccal cavity or stomodeum (see page 166) and consists of a pars anterior and a pars intermedia, separated from each other by a narrow cleft, the remnant of the pouch or diverticulum. The pars anterior is extremely vascular and consists of epithelial cells of varying size and shape, arranged in cord-like trabeculse or alveoli and separated by large, thin- walled bloodvessels. The pars intermedia is a thin lamina closely applied to the body and neck of the posterior lobe and extending on to the neighboring parts of the brain ; it contains few bloodvessels and consists of finely granular cells between which are small masses of colloid material. The posterior lobe is developed as a downgrowth from the floor of the embryonic brain, and during early fetal life con- tains a cavity continuous with that of the third ventricle. In some animals, e. g., OpUc cliiasma I Zrd ventricle Extension of pars intermedia into brain substance Process of pars intermedia , "v ^''S^^^S^^^et^J '' ^-rt- -i^\ Anterior lobe ^ '"^^^^^^^^^^^^^ Posterior lobe Intraglandular cleft Pars intermedia Fig. 732. — Median sagittal section through the hypophysis of an adult monkey. Semidiagrammatic. (Herring.) cat, this cavity persists throughout life. Although of nervous origin the posterior lobe contains no nerve cells or fibres. It consists of neuroglia cells and fibres and is invaded by columns which grow into it from the pars intermedia; imbedded in it are large quantities of a colloid substance histologically similar to that found in the thyroid gland. In certain of the lower vertebrates, e. g., fishes, nervous structures are present, and the lobe is of large size. Applied Anatomy. — Prof. Schafer has isolated from the pars intermedia a substance, no doubt an internal secretion, that causes constriction of the bloodvessels, rise of arterial blood pressure, and increased secretion of urine, when injected subcutaneously. Enlargement of the hypo- physis and of the cavity of the sella turcica are found in the rare disease acromegaly, which is characterized by gradual enlargement of the face, hands, and feet, with headache and often a pecuhar type of bhndness. This blindness is due to the pressure of the enlarging hypophysis on the optic chiasma (Fig. 731). The pressure causes atrophy, for the most part of the nerve fibres coming from the nasal sides of the retinse; with the result that the patient loses his two temporal fields of vision while retaining his nasal fields (bitemporal hemianopsy). Optic Chiasma {chiasma oyticum; optic commissure). — The optic chiasma is a flattened, somewhat quadrilateral band of fibres, situated at the junction of the floor and anterior wall of the third ventricle. Most of its fibres have their origins THE PROSENCEPHALON OR FORE-BRAIN sm in the retina, and reacli the chiasnia tlirough tlie ()i)tic- nerves, which are continuous with its antero-hiteral angles. In the chiasma, they undergo a partial decussation (Fig. 733) ; the fibres from the nasal half of the retina decussate and enter the optic tract of the opposite side, while the fibres from the temporal half of the retina do not undergo decussation, but pass back into the (^ptic tract of the same side. Occup^-ing the posterior part of the commissure, however, is a strand of fibres, the commisure of Gudden, which is not derived from the optic nerves; it forms a connecting link between the medial geniculate bodies. 7 Optic nerve 7 Crossed fibres Uncrossed fibres Optic chiasnia Commissure of Gudden Pidvinar Lateral genicidate body Superior colliculus Medial genicidate body Nucleus of oculomotor nerve Nucleus of trochlear nerve Nucleus of abducent nerve Cortex of occipital lobes Fig. 733.— Scheme showing central connections of the optic nerves and optic tracts. Optic Tracts.— The optic tracts are continued backward and lateralward from the postero-lateral angles of the optic chiasma. Each passes between the anterior perforated substance and the tuber cinereum, and, winding around the ventro- lateral aspect of the cerebral peduncle, divides into a medial and a lateral root. The former comprises the fibres of Gudden's commissure. The lateral root consists mainly of afferent fibres which arise in the retina and undergo partial decussation in the optic chiasma, as described; but it also contains a few fine efferent fibres which have their origins in the brain and their terminations m the retina, \\hen traced backward, the afferent fibres of the lateral root are found to end m the lateral geniculate bodv and pulvinar of the thalamus, and in the superior colliculus; and 864 NEUROLOGY these three structures constitute the lower visual centres. Fibres arise from the nerve cells in these centres and pass through the occipital part of the internal capsule, under the name of the optic radiations, to the cortex of the occipital lobe of the cerebrum, where the higher or cortical visual centre is situated. Some of the fibres of the optic radiations take an opposite course, arising from the cells of the occipital cortex and passing to the lower visual centres. Some fibres are detached from the optic tract, and pass through the cerebral peduncle to the nucleus of the oculomotor nerve. These may be regarded as the afferent branches for the Sphincter pupillae and Ciliaris muscles. Other fibres have been described as reaching the cerebellum through the brachia conjunctiva; while others, again, are lost in the pons. The Third Ventricle {ventriculus tertius) (Figs. 726, 730). — The third ventricle is a median cleft between the two thalami. Behind, it communicates with the fourth ventricle through the cerebral aqueduct, and in front with the lateral ventricles through the interventricular foramen. Somewhat triangular in shape, with the apex directed backward, it has a roof, a floor, an anterior and a posterior boundary and a pair of lateral walls. Lateral ventricle Tela chorioidea Internal cerebral veins Epithelial lining of ventricle Epithelial lining of ventricle Termiiud vein Choroid plexus of lateral ventricle Choroid plexuses of third ventricle Third ventricle Fig. 734. — Coronal section of lateral and third ventricles. (Diagrammatic.) The roof (Fig. 7.34) is formed by a layer of epithelium, which stretches between the upper edges of the lateral walls of the cavity and is continuous with the epithe- lial lining of the ventricle. It is covered by and adherent to a fold of pia mater, named the tela chorioidea of the third ventricle, from the under surface of which a pair of vascular fringed processes, the choroid plexuses of the third ventricle, project downward, one on either side of the middle line, and invaginate the epithelial roof into the ventricular cavity. The floor slopes downward and forward and is formed mainly b}^ the structures w'hich constitute the hypothalamus: from before backward these are: the optic chiasma, the tuber cinereum and infundibulum, and the corpora mamillaria. Behind the last, the floor is formed by the interpeduncular fossa and the tegmenta of the cerebral peduncles. The ventricle is prolonged downward as a funnel- shaped recess, the recessus infundibuli, into the infundibulum, and to the apex of the latter the hj-pophysis is attached. The anterior boundary is constituted below by the lamina terminalis, a thin layer of gray substance stretching from the upper surface of the optic chiasma to the rostrum of the corpus callosum; above by the columns of the fornix and the anterior commissure. At the junction of the floor and anterior wall, immediately above the optic chiasma, the ventricle presents a small angular recess or diverticulum, THE PROSENCEPHALON OR FORE-BRAIN 865 the optic recess. Between the cukimns of the fornix, and above the anterior commissure, is a second recess termed the vulva. At the junction of the roof and anterior wall of the ventricle, and situated between the thalami behind and the columns of the fornix in front, is the interventricular foramen (foramen of Monro) through which the third communicates with the lateral ventricles. The posterior boundary is constituted by the pineal body, the posterior commissure and the cerebral aqueduct. A small recess, the recessus pinealis, projects into the stalk of the pineal body, while in front of and above the pineal body is a second recess, the recessus suprapinealis, consisting of a diverticulum of the epithelium which forms the ventricular roof. Each lateral wall consists of an upper portion formed by the medial surface of the anterior two-thirds of the thalamus, and a lower consisting of an upward continuation of the gray substance of the ventricular floor. These two parts correspond to the alar and basal laminse respectively of the lateral w'all of the fore-brain vesicle and are separated from each other by a furrow, the sulcus of Monro, wdiich extends from the interventricular foramen to the cerebral aqueduct (pages 125 and 126). The lateral w^all is limited above by the taenia thalami. The columns of the fornix curve downward in front of the interventricular foramen, and then run in the lateral walls of the ventricle, where, at first, they form distinct prominences, but subsequently are lost to sight. The lateral w^alls are joined to each other across the cavity of the ventricle by a band of gray matter, the massa intermedia (page 856). Interpeduncular Fossa (Fig. 735). — This is a somewhat lozenge-shaped area of the base of the brain, limited in front by the optic chiasma, behind by the antero- superior surface of the pons, antero-laterally by the converging optic tracts, and postero-laterally by the diverging cerebral peduncles. The structures con- tained in it have already been described; from behind forward, they are the pos- terior perforated substance, corpora mamillaria, tuber cinereum, infundibulum, and hypophysis. The Telencephalon. — The telencephalon includes: (1) the cerebral hemispheres with their cavities, the lateral ventricles; and (2) the pars optica hypothalami and the anterior portion of the third ventricle (already described under the dienceph- alon). As stated in the chapter on Embryology (page 128), each cerebral hemi- sphere may be divided into three fundamental parts, viz., the rhinencephalon, the corpus striatum, and the neopallium. The rhinencephalon, associated with the sense of smell, is the oldest part of the telencephalon, and forms almost the whole of the hemisphere in some of the lower animals, e. g., fishes, amphibians, and reptiles. In man it is rudimentary, whereas the neopallium undergoes great development and forms the chief part of the hemisphere. The Cerebral Hemispheres. — The cerebral hemispheres constitute the largest part of the encephalon, and, when viewed together from above, assume the form of an ovoid mass broader behind than in front, the greatest transverse diameter corresponding with a line connecting the tw^o parietal eminences. The hemispheres are separated medially by a deep cleft, named the longitudinal cerebral fissure, and each possesses a central cavity, the lateral ventricle. The Longitudinal Cerebral Fissure (fissiira cerebri longitudinalis; great longitudinal fissure) contains a sickle-shaped process of dura mater, the falx cerebri. It front and behind, the fissure extends from the upper to the under surfaces of the hemi- spheres and completely separates them, but its middle portion only separates them for about one-half of their vertical extent; for at this part they are connected across the middle line by a great central white commissure, the corpus callosum. In a median sagittal section (Fig. 730) the cut corpus callosum presents the appearance of a broad, arched band. Its thick posterior end, termed the splehium, overlaps the mid-brain, but is separated from it by the tela chorioidea of the third 866 NEUROLOGY ventricle and the pineal body. Its anterior curved end, termed the genu, gradually tapers into a thinner portion, the rostrum, which is continued downward and back- ward in front of the anterior commissure to join the lamina terminalis. Arching backward from immediately behind the anterior commissure to the under surface of the splenium is a second white band named the fornix: between this and the corpus callosum are the laminae and cavity of the septum pellucidum. Frontal lobe Temporal lobe Occipital lobe Fig. 735. — Base of brain. Surfaces of the Cerebral Hemispheres. — Each hemisphere presents three surfaces: lateral, medial, and inferior. The lateral surface is convex in adaptation to the concavity of the corresponding half of the vault of the cranium. The medial surface is flat and vertical, and is separated from that of the opposite hemipshere by the great longitudinal fissure and the falx cerebri. The inferior surface is of an irregular form, and may be divided into three areas: anterior, middle, and posterior. The anterior area, formed by the orbital surface of the frontal lobe, is concave, and rests on the roof of the orbit and nose; the middle area is convex, and consists of the under surface of the tem- poral lobe: it is adapted to the corresponding half of the middle cranial fossa. The posterior area is concave, directed medialward as well as downward, and is named the tentorial surface, since it rests upon the tentorium cerebelli, which intervenes between it and the upper surface of the cerebellum. These three surfaces are separated from each other by the following borders: THE PROSENCEPHALON OR FORE-BRAIN 867 (a) supero-medial, hetwocn the lateral and medial surfaces; (b) infero-lateral, between the lateral and inferior surfaces; the anterior part of this border separating the lateral from the orbital surface, is known as the superciliary border; (c) medial occipital, separatin"' the medial and tentorial surfaces; and (d) medial orbital, separating the orbital from the medial surface. The anterior end of the hemisphere is named the frontal pole; the posterior, the occipital pole; and the anterior end of the temporal lobe, the temporal pole. About 5 cm. in front of the occipital pole on the infero-lateral border is an indentation or notch, named the preoccipital notch. The surfaces of the hemispheres are moulded into a number of irregular eminences, named gyri or convolutions, and separated by furrows termed fissures and sulci. The furrows are of two kinds, complete and incomplete. The former appear early in fetal life, are few in number, and are produced by infoldings of the entire thickness of the brain wall, and give rise to corresponding elevations in the interior of the ventricle. They comprise the hippocampal fis- sure, and parts of the calcarine and collateral fissures. The incomplete furroW'S are very numerous, and only indent the subjacent wdiite substance, without producing any corresponding elevations in the ventricular cavity. The gyri and their intervening fissures and the sulci are fairly constant in their arrange- ment ; at the same time they vary within certain limits, not only in different individuals, but on the two hemispheres of the same brain. The convoluted condition of the surface permits of a great increase of the gray matter without the sacrifice of much additional space. The num- ber and extent of the gyri, as well as the depth of the intervening furrows, appear to bear a direct relation to the intellectual powers of the individual. Certain of the fissures and sulci are utilized for the purpose of dividing the hemi- sphere into lobes, and are therefore termed interlobular; included under this category are the lateral cerebral, parietooccipital, calcarine, and collateral fissures, the central and cingulate sulci, and the sulcus circularis. The Lateral Cerebral Fissure {fissura cerebri lateralis [Sykii] ; fissure of Sylvius) (Fig. 737) is a well-marked cleft on the inferior and lateral surfaces of the hemisphere, and consists of a short stem w^hich divides into three rami. The stem is situated on the base of the brain, and commences in a depression at the lateral angle of the anterior perforated substance. From this point it extends between the anterior part of the temporal lobe and the orbital surface of the frontal lobe, and reaches the lateral surface of the hemisphere. Here it divides into three rami: an anterior horizontal, an anterior ascending, and a posterior. The anterior horizontal ramus passes forward for about 2.5 cm. into the inferior frontal gyrus, while the anterior ascending ramus extends upward into the same convolution for about an equal distance. The posterior ramus is the longest; it runs backward and slightly upward for about 7 cm., and ends by an upward inflexion in the parietal lobe. Fig. 736. — Lateral surface of left cerebral hemisphere, viewed from above. 868 NEUROLOGY The Central Sulcus {sulcus centralis [Rolaiidi] ; fissure of li^daudo; central fissure) (Figs. 736, 737) is situated about the middle of the lateral surface of the hemisphere, and begins in or near the longitudinal cerebral fissure, a little behind its mid-point. It runs sinuously downward and forward, and ends a little above the posterior Fig. 737. — Lateral surface of left cerebral hemisphere, viewed from the side. ramus of the lateral fissure, and about 2.5 cm. behind the anterior ascending ramus of the same fissure. It described two chief curves: a superior genu with its con- cavity directed forward, and an inferior genu with its concavity directed backward. The central sulcus forms an angle opening forward of about 70° with the median plane. Fig. 738. — Medial surface of left cerebral hemisphere. The Parietooccipital Fissure (fissura parietooccipitalis). — Only a small part of this fissure is seen on the lateral surface of the hemisphere, its chief part being on the medial surface. THE PROSENCEPHALOX OR FORE-BRAIN 869 The lateral part of tlie parietooccipital fissure (Fig. 737) is situated aliout 5 cm. in front of the occipital pole of the hemisphere, and measures about 1.25 cm. in length. The medial part of the parietooccipital fissure (Fig. 738) runs downward and for- ward as a deep cleft on the medial surface of the hemisphere, and joins the calcarine fissure below and behind the posterior end of the corpus callosum. In most cases it contains a submerged gyrus. The Calcarine Fissure (fissiira ccdcarina) (Fig. 738) is on the medial surface of the hemisphere. It begins near the occipital pole in two converging rami, and runs forward to a point a little below the splenium of the corpus callosum, where it is joined at an acute angle by the medial part of the parietooccipital fissure. The anterior part of this fissure gives rise to the prominence of the calcar avis in the posterior cornu of the lateral ventricle. The Cingulate Sulcus {sulcus cinguli; caUosomarginal fissure) (Fig. 738) is on the medial surface of the hemisphere; it begins below the anterior end of the corpus callosum and runs upward and forward nearly parallel to the rostrum of this body and, curving in front of the genu, is continued backward above the corpus callosum, and finally ascends to the supero-medial border of the hemisphere a short distance behind the upper end of the central sulcus. It separates the superior frontal from the cingulate gyrus. The Collateral Fissure {fissura collaieralis) (Fig. 738) is on the tentorial surface of the hemisphere and extends from near the occipital pole to within a short dis- tance of the temporal pole. Behind, it lies below and lateral to the calcarine fissure, from which it is separated by the lingual gyrus; in front, it is situated between the hippocampal gyrus and the anterior part of the fusiform gjTus. The Sulcus Circularis {circuminsular fissure) (Fig. 741) is on the lower and lateral surfaces of the hemisphere: it surrounds the insula and separates it from the frontal, parietal, and temporal lobes. Lobes of the Hemispheres.^ — By means of these fissures and sulci, assisted by certain arbitrary lines, each hemisphere is divided into the following lobes: the frontal, the parietal, the temporal, the occipital, the limbic, and the insula. Frontal Lobe ilobus frontalis) . — On the lateral surface of the hemisphere this lobe extends from the frontal pole to the central sulcus, the latter separating it from the parietal lobe. Below, it is limited by the posterior ramus of the lateral fissure, which intervenes between it and the central lobe. On the medial sur- face, it is separated from the cingulate gyrus by the cingulate sulcus; and on the inferior smface, it is bounded behind by the stem of the lateral fissure. The lateral surface of the frontal lobe (Fig. 737) is traversed by three sulci which divide it into four gyri: the sulci are named the precentral, and the superior and inferior frontal; the gyri are the anterior central, and the superior, middle, and inferior frontal. The precentral sulcus runs parallel to the central sulcus, and is usually divided into an upper and a lower part; between it and the central sulcus is the anterior central gyms. From the precentral sulcus, the superior and inferior frontal sulci run forward and downward, and divide the remainder of the lateral surface of the lobe into three parallel gyri, named, respectively the superior, middle, and inferior frontal gyri. The anterior central gyrus {gyrus centralis anterior; ascending frontal convolution; precentral gyre) is bounded in front by the precentral sulcus, behind by the central sulcus; it extends from the supero-medial border of the hemisphere to the posterior ramus of the lateral fissure. The superior frontal gyrus {gyrus frontalis superior; superfrontal gyre) is situated above the superior frontal sulcus and is continued on to the medial surface of the hemisphere. The portion on the lateral surface of the hemisphere is usually more or less completely subdivided into an upper and a lower part by an antero- 870 NEUROLOGY posterior sulcus, the paramedial sulcus, which, ho\ve\Tr, is frequently interrupted by bridging gyri. The middle frontal gyrus (gyrus frontalis medius; inedifrontal gyre), between the superior and inferior frontal sulci, is continuous with the anterior orbital gyrus on the inferior surface of the hemisphere; it is frequently subdivided into two by a horizontal sulcus, the medial frontal sulcus of Eberstaller, which ends anteriorly in a wide bifurcation. The inferior frontal gyrus {gyrus frontalis inferior; subfrontal gyre) lies below the inferior frontal sulcus, and extends forward from the lower part of the precentral sulcus; it is continuous with the lateral and posterior orbital gyri on the under surface of the lobe. It is subdivided by the anterior horizontal and ascending rami of the lateral fissure into three parts, viz., (1) the orbital part, below^ the anterior horizontal ramus of the fissure; (2) the triangular part (cap of Broca), between the ascending and horizontal rami; and (3) the basilar part, behind the anterior ascending ramus. The left inferior frontal gyrus is, as a rule, more highly developed than the right, and is named the gyrus of Broca, from the fact that Broca described it as the centre for articulate speech. The inferior or orbital surface of the frontal lobe is concave, and rests on the orbital plate of the frontal bone (Fig. 739). It is divided into four orbital gyri by a well- marked H-shaped orbital sulcus. These are named, from their position, the medial, anterior, lateral, and posterior orbital gyri. The medial orbital gyrus presents a well-marked antero- posterior sulcus, the olfactory sulcus, for the olfactory tract; the portion medial to this is named the straight gyrus, and is continuous with the superior frontal gyrus on the medial surface. The medial surface of the frontal lobe is occu- pied by the medial part of the superior frontal gyrus (marginal gyrus) (Fig. 738). It lies be- tween the cingulate sulcus and the supero-medial margin of the hemisphere. The posterior part of this gyrus is sometimes marked off by a ver- tical sulcus, and is distinguished as the paracen- tral lobule, because it is continuous with the anterior and posterior central gyri. Parietal Lobe (lohus parietalis). — The parietal lobe is separated from the frontal lobe by the central sulcus, but its boundaries below and behind are not so definite. Posteriorly, it is limited by the parietooccipital fissure, and by a line carried across the hemisphere from the end of this fissure toward the preoccipital notch. Below, it is separated from the temporal lobe by the posterior ramus of the lateral fissure, and by a line carried backward from it to meet the line passing downward to the preoccipital notch. The lateral surface of the parietal lobe (Fig. 737) is cleft by a well-marked furrow, the intraparietal sulcus of Turner, which consists of an oblique and a horizontal portion. The oblique part is named the postcentral sulcus, and commences beloAV, about midway between the lower end of the central sulcus and the upturned end of the lateral fissure. It runs upward and backward, parallel to the central sulcus, and is sometimes divided into an upper and a lower ramus. It forms the hinder limit of the posterior central gyrus. From about the middle of the postcentral sulcus, or from the upper end of its inferior ramus, the horizontal portion of the intraparietal sulcus is carried backward and slightly upward on the parietal lobe, and is prolonged, under the name of the Fig. 739. — Orbital surface of left frontal lobe. THE PROSENCEPHALON OR FORE-BRAIN 871 occipital ramus, on to the occipital Iol)r, where it divides into two parts, which form nearly a right angle with the main stem and constitute the transverse occipital sulcus. The part of the parietal lobe above the horizontal portion of the iiitraparietal sulcus is named the superior parietal lobule ; the part l)elow, the inferior parietal lobule. The posterior central gyrus {gyrus centralis posterior; ascending imrietal conrolution; 'postcentral gyre) extends from the longitudinal fissure above to the posterior ramus of the lateral fissure below. It lies parallel with the anterior central gyrus, with which it is connected below, and also, sometimes, above, the central sulcus. The superior parietal lobule {lobulus parietalis superior) is bounded in front by the upper part of the postcentral sulcus, but is usually connected with the pos- terior central gyrus above the end of the sulcus; behind it is the lateral part of the parietooccipital fissure, around the end of which it is joined to the occipital lobe by a curved gyrus, the arcus parietobccipitalis ; below, it is separated from the inferior parietal lobule by the horizontal portion of the intraparietal sulcus. The inferior parietal lobule {lobulus parietalis inferior; suhparietal district or lobule) lies below^ the horizontal portion of the intraparietal sulcus, and behind the lower part of the postcentral sulcus. It is divided from before backward into two gyri. One, the supramarginal, arches over the upturned end of the lateral fissure; it is continuous in front with the postcentral gyrus, and behind with the superior tem- poral gyrus. The second, the angular, arches over the posterior end of the superior temporal sulcus, behind which it is continuous with the middle temporal gyrus. The medial surface of the parietal lobe (Fig. 738) is bounded behind by the medial part of the parietooccipital fissure; in front, by the posterior end of the cin- gulate sulcus; and below, it is separated from the cingulate gyrus by the subparietal sulcus. It is of small size, and consists of a square-shaped convolution, which is termed the precuneus or quadrate lobe. Occipital Lobe {lobus occipitalis). — The occipital lobe is small and pyramidal in shape; it presents three surfaces: lateral, medial, and tentorial. The lateral surface is limited in front by the lateral part of the parietooccipital fissure, and by a line carried from the end of this fissure to the preoccipital notch; it is traversed by the transverse occipital and the lateral occipital sulci. The transverse occipital sulcus is continuous with the posterior end of the occipital ramus of the intraparietal sulcus, and runs across the upper part of the lobe, a short distance behind the parietooccipital fissure. The lateral occipital sulcus extends from behind forward, and divides the lateral surface of the occipital lobe into a superior and an inferior gyrus, which are continuous in front with the parietal and temporal lobes. ^ The medial surface of the occipital lobe is bounded in front by the medial part of the parietooccipital fissure, and is traversed by the calcarine fissure, which subdivides it into the cuneus and the lingual gyrus. The cuneus is a wedge-shaped area between the calcarine fissure and the medial part of the parietooccipital fissure. The lingual gyrus lies between the calcarine fissure and the posterior part of the collateral fissure; behind, it reaches the occipital pole; in front, it is con- tinued on to the tentorial surface of the temporal lobe, and joins the hippocampal gyrus. The tentorial surface of the occipital lobe is limited in front by an imaginary transverse line through the preoccipital notch, and consists of the posterior part of the fusiform gyrus (occipitotemporal convolution) and the lower part of the lingual gyrus, which are separated from each other by the posterior segment of the collateral fissure. Temporal Lobe {lobus temporalis). — The temporal lobe presents superior, lateral, and inferior surfaces. 1 Elliot Smith has named the lateral occipital sulcus the sulcus lunatus; he regards it as the representative, in the human brain, of the " Affenspalte " of the brain of the ape. 872 NEUROLOGY The superior surface forms the lower Hmit of the lateral fissure and overlaps the insula. On opening out the lateral fissure, three or four gyri will be seen spring- ing from the depth of the hinder end of the fissure, and running obliquely forward and outward on the posterior part of the upper surface of the superior temporal gyrus; these are named the transverse temporal gyri (Heschl) (Fig. 740). The lateral surface (Fig. 737) is bounded above by the posterior ramus of the lateral fissure, and by the imaginary line continued backward from it; below, it is limited by the infero-lateral border of the hemisphere. It is divided into superior, middle, and inferior gyi'i by the superior and middle temporal sulci. The superior temporal sulcus runs from before backward across the temporal lobe, some little distance below, but parallel with, the posterior ramus of the lateral fissure; and hence it is often termed the parallel sulcus. The middle temporal sulcus takes the same direction as the superior, but is situated at a lower level, and is usually subdivided into two or more parts. The superior temporal gyrus lies between Clauslrum Insula Transverse tem2')oral gyri Optic tract Lentijorm nucleus Internal capsule Thalamus Fimbria »7 -J — Tail of caudate nucleus — ^^j — Inferior cornu of lateral ventricle Fig. 740. — Section of brain showing upper surface of temporal lobe. the posterior ramus of the lateral fissure and the superior temporal sulcus, and is continuous behind with the supramarginal and angular gyri. The middle temporal gyrus is placed between the superior and middle temporal sulci, and is joined pos- teriorly with the angular gyrus. The inferior temporal gyrus is placed below the middle temporal sulcus, and is connected behind with the inferior occipital gj^rus; it also extends around the infero-lateral border on to the inferior surface of the temporal lobe, where it is limited by the inferior sulcus. The inferior surface is concave, and is continuous posteriorly with the tentorial surface of the occipital lobe. It is traversed by the inferior temporal sulcus, which extends from near the occipital pole behind, to within a short distance of the tem- poral pole in front, but is frequently subdivided b}'^ bridging gyri. Lateral to this fissure is the narrow tentorial part of the inferior temporal gyrus, and medial to it the fusiform gyrus, which extends from the occipital to the temporal pole; this gyrus is limited medially by the collateral fissure, which separates it from the lingual gyrus behind and from the hippocampal gyrus in front. Till': I'h'OSENCEPHALOA Oh' FORK BRAIN 873 The Insula {isUutd of Rcll; veidrnl lohc) {Vii;. 741) lies deeply in the lateral or Sylvian fissure, and can only be seen when the lips of that fissure are widely sep- arated, since it is overlapped and hidden l)y the gyri which bound the fissure. These gyri are termed the opercula of the insula; they are separated from each other by the three rami of the lateral fissure, and arc named the orl)ital, frontal, fronto- parietal, and temj)oral opercula. The orbital operculum lies l)el()vv the anterior horizontal ramus of the fissure, the frontal between this and the anterior ascending ramus, the parietal between the anterior ascending ramus and the upturned end of the i)osterior ramus, and the temporal below the posterior ramus. The frontal operculum is of small size in those cases where the anterior horizontal and ascending rami of the lateral fissure arise from a common stem. The insula is surrounded by a deep circular sulcus which separates it from the frontal, parietal, and temporal lobes. When the opercula have been removed, the insula is seen as a triangular eminence, the apex of which is directed tow^ard the anterior perforated substance. It is divided into a larger anterior and a smaller posterior part by a deep sulcus, which runs backward and upward from the apex of the insula. The anterior part is subdivided by shallow sulci into three or four short gyri, while the posterior part is formed by one long gyrus, which is often bifurcated at its upper end. The cortical gray substance of the insula is continuous Avith that of the different opercula, w^hile its deep surface corresponds with the lentiform nucleus of the corpus striatum. Fig. 741. — The insula of the left side, exposed by removing the opercula. Limbic Lobe (Fig. 738). — The term limbic lobe was introduced by Broca, and under it he included the cingulate and hippocampal gyri, which together arch around the corpus callosum and the hippocampal fissure. These he separated on the morphological ground that they are well-developed in animals possessing a keen sense of smell (osmatic animals), such as the dog and fox. They were thus regarded as a part of the rhinencephalon, but it is now recognized that the}^ belong to the neopallium; the cingulate gyrus is therefore sometimes described as a part of the frontal lobe, and the hippocampal as a part of the temporal lobe. The cingulate gyrus {gyrus cinguli; caUosal convolution) is an arch-shaped convo- lution, lying in close relation to the superficial surface of the corpus callosum, from which it is separated by a slit-like fissure, the cailosal fissure. It commences below^ the rostrum of the corpus callosum, curves around in front of the genu, extends along the upper surface of the body, and finally turns downward behind the splenium, where it is connected by a narrow^ isthmus wdth the hippocampal 874 NEUROLOGY gyrus. It is separated from the medial part of the superior frontal gyrus by the cingulate sulcus, and from the precuneus by the subparietal sulcus. The hippocampal gyrus {gyrus hippocampi) is bounded above by the hippocampal fissure, and below by the anterior part of the collateral fissure. Behind, it is con- tinuous superiorly, through the isthmus, with the cingulate gyrus and inferiorly with the lingual gyrus. Running in the substance of the cingulate and hippocampal gyri, and connecting them together, is a tract of arched fibres, named the cingulum (page 890). The anterior extremity of the hippocampal gyrus is recurved in the form of a hook (uncus), which is separated from the apex of the temporal lobe by a slight fissure, the incisura temporalis. Although superficially continuous with the hippocampal gyrus, the uncus forms morphologically a part of the rhinencephalon. The Hippocampal Fissure {fissura hippocampi; dentate fissure) begins immediately behind the splenium of the corpus callosum, and runs forward between the hippo- campal and dentate gyri to end in the uncus. It is a complete fissure (page 867), and gives rise to the prominence of the hippocampus in the inferior cornu of the lateral ventricle. Gyrus supracallosus 4- Fascia dentata hippocampi Uncus Anterior perforated substance / Band of Giacomini Fig. 742. — Scheme of rhinencephalon. Rhinencephalon (Fig. 742). — The rhinencephalon comprises the olfactory lobe, the uncus, the subcallosal and supracallosal gyri, the fascia dentata hippocampi, the septum pellucidum, the fornix, and the hippocampus. 1. The Olfactory Lobe (lohtis olfactorius) is situated under the inferior or orbital surface of the frontal lobe. In many vertebrates it constitutes a well-marked portion of the hemisphere and contains an extension of the lateral ventricle; but in man and some other mammals it is rudimentary. It consists of the olfactory bulb and tract, the olfactory trigone, the parolfactory area of Broca, and the anterior perforated substance. (a) The olfactory bulb (bulbus olfactorius) is an oval, reddish-gray mass which rests on the cribriform plate of the ethmoid and forms the anterior expanded extremity of the olfactory tract. Its under surface receives the olfactory nerves, which pass upward through the cribriform plate from the olfactory region of the nasal cavity. Its minute structure is described on page 893. (b) The olfactory tract (tractus olfactorius) is a narroM' white band, triangular on coronal section, the apex being directed upward. It lies in the olfactory sulcus on the inferior surface of the frontal lobe, and divides posteriorly into two striae, a medial and a lateral. The lateral stria is directed across the lateral part of the THE PROSENCEPHALON OR FORE-BRAIN 875 anterior perforated substance and then bends abruptly medialward toward the uncus of the hippocampal gyrus. The medial stria turns medialward behind the parolfactory area and ends in the subcallosal gyrus; in some cases a small intermediate stria is seen running backward to the anterior perforated substance. (c) The olfactory trigone {tn'gomnn ol f actor imn) is a small triangular area in front of the anterior perforated substance. Its apex, directed forward, occupies the posterior part of the olfactory sulcus, and is brought into view by throwing back the olfactory tract. (d) The parolfactory area of Broca (area par olf actor ia) is a small triangular field on the medial surface of the hemisphere in front of the subcallosal gyrus, from which it is separated by the posterior parolfactory sulcus; it is. continuous below with the olfactory trigone, and above and in front with the cingulate gyrus; it is limited anteriorly by the anterior parolfactory sulcus. (e) The anterior perforated substance {substantia perforata anterior) is an irregularly quadrilateral area in front of the optic tract and behind the olfactory trigone, from which it is separated by the fissure prima ; medially and in front it is continuous with the subcallosal gyrus; laterally it is bounded by the' lateral stria of the olfactory tract and is continued into the uncus. Its gray substance is confluent above with that of the corpus striatum, and is perforated anteriorly by numerous small bloodvessels. 2. The Uncus has already been described (page 874) as the recurved, hook-like portion of the hippocampal gyrus. 3. The Subcallosal, Supracallosal, and Dentate Gyri form a rudimentary arch- shaped lamina of gray substance extending over the corpus callosum and above the hippocampal gyrus from the anterior perforated substance to the uncus. (a) The subcallosal gyrus (gyrus suhcallosus; peduncle of the corpus callosum) is a narrow lamina on the medial surface of the hemisphere in front of the lamina terminalis, behind the parolfactory area, and below the rostrum of the corpus callosum. It is continuous around the genu of the corpus callosum with the supra- callosal gyrus. (b) The supracallosal gyrus (indusiuin griseum; gyrus epicallosus) consists of a thin layer of gray substance in contact with the upper surface of the corpus callosum and continuous laterally with the gray substance of the cingulate gyrus. It contains two longitudinally directed strands of fibres termed respectively the medial and lateral longitudinal striae. The supracallosal gyrus is prolonged around the splenium of the corpus callosum as a delicate lamina, the fasciola cinerea, which is continuous below with the fascia dentata hippocampi. (c) The fascia dentata hippocampi (gyrus dentatus) is a narrow band extending downward and forward above the hippocampal gyrus but separated from it by the hippocampal fissure; its free margin is notched and overlapped by the fimbria — the fimbriodentate fissure intervening. Anteriorly it is continued into the notch of the uncus, where it forms a sharp bend and is then prolonged as a delicate band, the band of Giacomini, over the incus, on the lateral surface of which it is lost. The remaining parts of the rhinencephalon, viz., the septum pellucidum, fornix, and hippocampus, will be described in connection with the lateral ventricle. Interior of the Cerebral Hemispheres. — If the upper part of either hemisphere be removed, at a level about 1.25 cm. above the corpus callosum, the central white sub- stance will be exposed as an oval-shaped area, the centrum ovale minus, surrounded by a narrow convoluted margin of gray substance, and studded with numerous minute red dots (puncta vasculosa), produced by the escape of blood from divided bloodvessels. If the remaining portions of the hemispheres be slightly drawn apart a broad band of white substance, the corpus callosum, will be observed, connecting them at the bottom of the longitudinal fissure; the margins of the hemispheres which overlap the corpus callosum are called the labia cerebri. Each labrium is 876 NEUROLOGY part of the cingulate gyrus already described; and the sHt-hke interval between it and the upper surface of the corpus callosum is termed the callosal fissure (Fig. 738) . If the hemispheres be sliced off to a level with the upper surface of the corpus callosum, the white substance of that structure will be seen connecting the two hemispheres. The large expanse of medullary matter now exposed, surrounded by the convoluted margin of gray substance, is called the centrum ovale majus. The Corpus Callosum (Fig. 743) is the great transverse commissure which unites the cerebral hemispheres and roofs in the lateral ventricles. A good conception of its position and size is obtained by examining a median sagittal section of the brain (Fig. 730), when it is seen to form an arched structure about 10 cm. long. Its anterior end is about 4 cm. from the frontal pole, and its posterior end about 6 cm. from the occipital pole of the hemisphere. Fig. 743. — Corpus callosum from above. The anterior end is named the genu, and is bent downward and backward in front of the septum pellucidum; diminishing rapidly in thickness, it is prolonged backward under the name of the rostrum, which is connected below with the lamina terminalis. The anterior cerebral arteries are in contact with the under surface of the rostrum; they then arch over the front of the genu, and are carried backward above the body of the corpus callosum. The posterior end is termed the splenium and constitutes the thickest part of the corpus callosum. It overlaps the tela chorioidea of the third ventricle and the mesencephalon, and ends in a thick, convex, free border. A sagittal section of THE PROSENCEPHALON OR FORE-BRAIN 877 the spleniiim shows that the posterior end of the corpus callosum is acutely bent forward, the upper and lower parts being appHed to each other. The superior surface is convex from before backward, and is about 2.5 cm. wide. Its medial i)art forms the bottom of the k)ngitudinal fissure, and is in contact posteriori}^ with the lower border of the falx cerebri. Laterally it is overlapped by the cingulate gyrus, but is separated from it by the slit-like callosal fissure. It is traversed by numerous transverse ridges and furrows, and is covered by a thin layer of gray matter, the supracallosal gyrus, which exhibits on either side of the middle line the medial and lateral longitudinal striae, already described (page 875) . The inferior surface is concave, and forms on either side of the middle line the roof of the lateral ventricle. Medially, this surface is attached in front to the septum pellucidum; behind this it is fused with the upper surface of the body of the fornix, while the splenium is in contact with the tela chorioidea. On either side, the fibres of the corpus callosum radiate in the white substance and pass to the various parts of the cerebral cortex; those curving forward from the genu into the frontal lobe constitute the forceps anterior, and those curving backward into the occipital lobe, the forceps posterior. Between'these two parts is the main body of the fibres which constitute the tapetum and extend laterally on either side into the temporal lobe, and cover in the central part of the lateral ventricle. Cerebral aqueduct Fourth ventricle Fig. 744. — Scheme showing relations of the ventricles to the surface of the brain. The Lateral Ventricles {tentriculus lateralis) (Fig. 744). — The two lateral ventricles are irregular cavities situated in the lower and medial parts of the cerebral hemi- spheres, one on either side of the middle line. They are separated from each other by a median vertical partition, the septum pellucidum, but communicate with the third ventricle and indirectly with each other through the interventricular foramen. They are lined by a thin, diaphanous membrane, the ependyma, covered by ciliated epithelium, and contain cerebrospinal fluid, which, even in health, may be secreted in considerable amount. Each lateral ventricle consists of a central part or body, and three prolongations from it, termed cornua (Figs. 745, 746) . The central part {jjars centralis ventriculi lateralis; cello) (Fig. 747) of the lateral ventricle extends from the interventricular foramen to the splenium of the corpus NEUROLOGY callosum. It is an irregularly curved cavity, triangular on transverse section, with a roof, a floor, and a medial wall. The roof is formed by the under surface of the corpus callosum; the floor by the following parts, enumerated in their order of position, from before backward: the caudate nucleus of the corpus striatum, the Third ventricle Suprapineal recess Fig. 745. — Drawing of a cast of the ventricular cavities, viewed from above. (Retzius.) stria terminalis and the terminal vein, the lateral portion of the upper surface of the thalamus, the choroid plexus, and the lateral part of the fornix; the medial wall is the posterior part of the septum pellucidum, which separates it from the opposite ventricle. Interventricular foramen commissure Suprapineal recess Cerebral aqueduct Optic recess Infundihuium Lateral recess Fig. 746. — Drawing of a cast of the ventricular cavities, -viewed from the side. (Retzius. J The anterior cornu (cornu anterius; anterior horn; 'precornu) (Fig. 746) passes forward and lateralward, with a slight inclination downward, from the interventric- ular foramen into the frontal lobe, curving around the anterior end of the caudate nucleus. Its floor is formed by the upper surface of the reflected portion of the THE PROSENCEPHALOX OP FORE-BRAIX 879 corpus callosum, the rostrum. It is bounded medially by the anterior portion of the septum pellucidum, and laterally by the head of the caudate nucleus. Its apex reaches the posterior surface of the genu of the corpus callosum. The posterior cornu {cornu posterins; yostcornu) (Figs. 747, 748) passes into the occipital lobe, its direction being backward and lateralward, and then medialward. Its roof is formed by the fibres of the corpus callosum passing to the temporal and occipital lobes. On its medial wall is a longitudinal eminence, the calcar avis {Mppocampiis minor) , which is an involution of the ventricular wall produced by the calcarine fissure. Above this the forceps posterior of the corpus callosum, sweeping around to enter the occipital lobe,. causes another projection, termed the bulb of the posterior cornu. The calcar avis and bulb of the posterior cornu are extremely variable in their degree of development; in some cases they are ill- defined, in others prominent. Fig. 747. — Central part and anterior and posterior cornua of lateral ventricles exposed from above. The inferior cornu (cornu inferior; descending horn; middle horn; medicornu) (Fig. 749), the largest of the three, traverses the temporal lobe of the brain, forming in its course a curve around the posterior end of the thalamus. It passes at first backward, lateralward, and downward, and then curves forward to within 2.5 cm. of the apex of the temporal lobe, its direction being fairly well indicated on the surface of the brain by that of the superior temporal sulcus. Its roof is formed chiefly by the inferior surface of the tapetum of the corpus callosum, but the tail of the caudate nucleus and the stria terminalis also extend forward in the roof of the inferior cornu to its extremity, where they end in a mass of gray substance, 880 NEUROLOGY the nucleus amygdalae. Its floor presents the following parts: the hippocampus, the fimbria hippocampi, the collateral eminence, and the choroirl plexus. When the Bulb of posterior cormi Posterior cornu—r Calcar avis—^ Collateral eminence Calcarine fissure Collateral fissure - Fig. 748. — Coronal section through posterior cornu of lateral ventricle. choroid plexus is removed, a cleft-like opening is left along the medial wall of the inferior cornu; this cleft constitutes the lower part of the choroidal fissure. Clioroid plexus Riilb of posterior cornu Calcar avis Latetal cerebral fissuie Collateral eminei \ Fimbria hippoannpi Hippocampus Fig. 749. — Posterior and inferior cornua of left lateral ventricle exposed from the side. The hippocampus (hippocampus major) (Figs. 749, 750) is a curved eminence, about 5 cm. long, which extends throughout the entire length of the floor of the THE PROSENCEPHALON OR FORE-BRAIN 881 inferior cornu. Its lower end is enlarged, and presents two or tiiree rounded eleva- tions or digitations which give it a paw-like appearance, and hence it is named the pes hippocampi. If a transverse section be made through the hippocampus, it will be seen that this eminence is produced by the folding of the wall of the hemisphere to form the hippocampal fissure. The main mass of the hippocampus consists of gray substance, but on its ventricular surface is a thin white layer, the alveus, which is continuous with the fimbria hippocampi. The collateral eminence {eminentia collaieralis) (Fig. 750) is an elongated swelling lying lateral to and parallel with the hippocampus. It corresponds with the middle part of the collateral fissure, and its size depends on the depth and direction of this fissure. It is continuous behind with a flattened triangular area, the trigonum collaterale, situated between the posterior and inferior cornua. The fimbria hippocampi is a continuation of the crus of the fornix, and will be discussed with that body; a description of the choroid plexus will be found on page 887. The corpus striatum has received its name from the striped appearance which a section of its ante- rior part presents, in consequence of diverging white fibres being mixed with the gray substance which forms its chief mass. A part of the corpus striatum is imbedded in the white substance of the hemi- sphere, and is therefore external to the ventricle; it is termed the extraventricular portion, or the lenti- form nucleus ; the remainder, however, projects into the ventricle, and is named the intraventricular por- tion, or the caudate nucleus (Fig. 747). The caudate nucleus (nucleus caudatus: candaium) (Fig. 751) is a pear-shaped, highly arched gray mass; its broad extremity, or head, is directed forward into the anterior cornu of the lateral ven- tricle, and is continuous with the anterior perforated substance and with the anterior end of the lentiform nucleus; its narrow end, or tail, is directed backward on the lateral side of the thalamus, from which it is separated by the stria terminalis and the terminal vein. It is then continued down- ward into the roof of the inferior cornu, and ends in the nucleus amygdalae, at the apex of the temporal lobe. It is covered by the lining of the ventricle, and crossed by some veins of considerable size. It is separated from the lentiform nucleus, in the greater part of its extent, by a thick lamina of white substance, called the internal capsule, but the two portions of the corpus striatum are united in front (Figs. 752, 753). The lentiform nucleus {nucleus lentiformis; lenticular nucleus; lenticula) is lateral to the caudate nucleus and thalamus, and is seen only in sections of the hemisphere. When divided horizontally, it exhibits, to some extent, the appearance of a biconvex lens (Fig. 751), while a coronal section of its central part presents a somewhat triangular outline. It is shorter than the caudate nucleus and does not extend as far forward. It is bounded laterally by a lamina of white substance called the external capsule, and lateral to this is a thin layer of gray substance termed the claustrum. Its anterior end is continuous with the lower part of the head of the caudate nucleus and with the anterior perforated substance. In a coronal section through the middle of the lentiform nucleus, two medullary laminae are seen dividing it into three parts. The lateral and largest part is of a 56 750. — Inferior and posterior cornua, -s-iewed from above. 52 NEUROLOGY reddish color, and is known as the putamen, while the medial and intermediate are of a yellowish tint, and together constitute the globus pallidus; all three are marked bv fine radiating white fibres, which are most distinct in the putamen (Fig. 753): The gray substance of the corpus striatum is traversed by nerve fibres, some of which originate in it. The cells are multipolar, both large and small; those of the lentiform nucleus contain yellow pigment. The caudate and lentiform nuclei are not only directly continuous with each other anteriorly, but are connected to each other by numerous fibres. The corpus striatum is also connected: (1) to the Gemi, of corpus callosum Anterior cornu of lateral ventricle Caudate nucleus •lituni' pellucidiim. Internal capsule (Jrontal part) Column of fornix —!^ Genu of internal capsule __ Putamen . Globus pallidus Wv'// Internal capsule {occipital part ) Postenor cornu of lateral ventricl External capsule, Claustrum Insula Tail of caudate nude Hippocampus — -y Inferior cornu of lateral ventricle Optic radiation Fig. 751. — Horizontal section of right cerebral hemisphere. cerebral cortex, by what are termed the corticostriate fibres; (2) to the thalamus, by fibres which pass through the internal capsule, and by a strand named the ansa lentif ormis ; (3) to the cerebral peduncle, by fibres which leave the lower aspect of the caudate and lentiform nuclei. The claustrum (Figs. 751, 753) is a thin layer of gray substance, situated on the lateral surface of the external capsule. Its transverse section is triangular, with the apex directed upward. Its medial surface, contiguous to the external capsule, is smooth, but its lateral surface presents ridges and furrows corresponding with the gyri and sulci of the insula, with which it is in close relationship. The claustrum is. regarded as a detached portion of the gray substance of the insula, from w^hich THE PROSEXCEPHALOX OR FORE-BRAIX 883 it is separated by a layer of white fibres, the capsula extrema {band of Baillarger). Its cells are small and spindle-shaped, and contain yellow pigment; they are similar to those of the deepest layer of the cortex. The nucleus amygdalae {avu/gdala) is an ovoid gray mass, situated at the lower end of the roof of the inferior cornii. It is merely a localized thickening of the gray cortex, continuous with that of the uncus; in front it is continuous with the putamen, behind with the stria terminalis and the tail of the caudate nucleus. Superior frontal gyrus Middle frontal Corpus callosum Anterior eormi SeptiLm pellucidum Caudate nucleus Internal capsule Lentiform nucleus Sulcus clfactonus Insula I Temporal lobt Inferior frontal gyru8 Fig. 752. — Coronal section through anterior cornua of lateral ventricles. The internal capsule (capsula interna) (Fig. 754) is a flattened band of white fibres, between the lentiform nucleus on the lateral side and the caudate nucleus and thalamus on the medial side. In horizontal section (Figs. 751) it is seen to be somewhat abruptly curved, with its convexity inward; the prominence of the curve is called the genu, and projects between the caudate nucleus and the thalamus. The portion in front of the genu is termed the frontal part, and separates the len- tiform from the caudate nucleus; the portion behind the genu is the occipital part, and separates the lentiform nucleus from the thalamus. The frontal part of the internal capsule contains: (1) fibres running from the thalamus to the frontal lobe; (2) fibres connecting the lentiform and caudate nuclei; (3) fibres connecting the cortex with the corpus striatum; and (4) fibres passing from the frontal lobe through the medial fifth of the base of the cerebral peduncle to the nuclei pontis. The fibres in the region of the genu are named the geniculate fibres ; they originate in the motor part of the cerebral cortex, and, after passing downward through the base of the cerebral peduncle with the cerebro- 884 NEUROLOGY spinal fibres, undergo decussation and end in the motor nuclei of the cerebral nerves of the opposite side. The anterior two-thirds of the occipital part of the internal capsule contains the cerebrospinal fibres, which arise in the motor area of the cerebral cortex and, passing downward through the middle three-fifths of the base of the cerebral peduncle, are continued into the pyramids of the medulla oblongata. The posterior third of the occipital part contains: (1) sensory fibres, largely derived from the thalamus, though some may be continued upward from the medial lemniscus; (2) the fibres of optic radiation, from the lower visual centres to the cortex of the occipital lobe; (3) acoustic fibres, from the lateral lemniscus to the temporal lobe ; and (4) fibres which pass from the occipital and temporal lobes to the nuclei pontis. Corpus callosum^ Anterior corniju^ Cavity of septum pellucidum Columns of fornix Anterior commissure Third ventricle Optic chiasma ^Caudate nucleus Internal capsule Putamen Globus pallidus ' — Claustrum In.sida Fig. 753. — Coronal section of brain through anterior comniissure. The fibres of the internal capsule radiate widely as they pass to and from the various parts of the cerebral cortex, forming the corona radiata (Fig. 754) and intermingling with the fibres of the corpus callosum. The external capsule (capsula externa) (Fig. 751) is a lamina of white substance, situated lateral to the lentiform nucleus, between it and the claustrum, and con- tinuous with the internal capsule below and behind the lentiform nucleus. It probably contains fibres derived from the thalamus, the anterior commissure, and the subthalamic region. The substantia innominata of Meynert is a stratum consisting partly of gray and partly of white substance, which lies below the anterior part of the thalamus and lentiform nucleus. It consists of three layers, superior, middle, and inferior. The superior layer is named the ansa lentiformis, and its fibres, derived from the medullary lamina of the lentiform nucleus, pass medially to end in the thalamus THE PROSENCEPHALON OR FORE-BRAIN 885 and subthalamic region, while others are said to end in the tegmentum and red nucleus. The middle layer consists of nerve cells and nerve fibres; fibres enter it from the parietal lobe through the external capsule, while others are said to con- nect it with the medial longitudinal fasciculus. The inferior layer forms the main part of the inferior stalk of the thalamus, and connects this body with the temporal lobe and the insula. The stria terminalis (taenia semicircular is) is a narrow band of white substance situated in the depression between the caudate nucleus and the thalamus. Ante- riorly, its fibres are partly continued into the column of the fornix ; some, however, pass over the anterior commissure to the gray substance between the caudate nucleus and septum pellucidum, while others are said to enter the caudate nucleus. Posteriorly, it is continued into the roof of the inferior cornu of the lateral ventricle, at the extremity of which it enters the nucleus amygdalse. Superficial to it is a R. oculomotor nerve L. oculomotor nerve Brachium conjunciivum Pijramid Olive Fig. 754. — Dissection sho-nang the course of the cerebrospinal fibres. (E. B. Jamieson.) Restifotm body large vein, the terminal vein (wem of the corpus striatum), which receives numerous tributaries from the corpus striatum and thalamus; it runs forward to the inter- ventricular foramen and there joins with the vein of the choroid plexus to form the corresponding internal cerebral vein. On the surface of the terminal vein is a narrow white band, named the lamina affixa. The Fornix (Figs. 730, 755) is a longitudinal, arch-shaped lamella of w^hite substance, situated below the corpus callosum, and continuous with it behind, but separated from it in front by the septum pellucidum. It may be described as consisting of two symmetrical bands, one for either hemisphere. The two portions are not united to each other in front and behind, but their central parts are joined together in the middle line. The anterior parts are called the columns of the fornix; the intermediate united portions, the body; and the posterior parts, the crura. 886 NEUROLOGY The body (corpus fornicis) of the fornix is triangular, narrow in front, and broad behind. The medial part of its upper surface is connected to the septum pellucidum in front and to the corpus callosum behind. The lateral portion of this surface forms part of the floor of the lateral ventricle, and is covered by the ventricular epithelium. Its lateral edge overlaps the choroid plexus, and is continuous with the epithelial covering of this structure. The under surface rests upon the tela chorioidea of the third ventricle, which separates it from the epithelial roof of that cavity, and from the medial portions of the upper surfaces of the thalami. Below, the lateral portions of the body of the fornix are joined by a thin triangular lamina, named the psalterium (lyra). This lamina contains some transverse fibres which connect the two hippocampi across the middle line and constitute the hippocampal commissure. Between the psalterium and the corpus callosum a horizontal cleft, the so-called ventricle of the fornix {ventricle of Verga), is sometimes found. Cavity of septum 2}ellucidum ic chiasma ic nerve T^iber cinerexim Optic trad Corpora mamUlaria Corpus callosum (under mirface) Fimbria hippocampi Fig. 755. — The fornix and corpus callosum from below. (From a specimen in the Department of Human Anatomy of the University of Oxford.) The columns (columna fornicis; anterior pillars; fornicolumns) of the fornix arch downward in front of the interventricular foramen and behind the anterior commis- sure, and each descends through the gray substance in the lateral wall of the third ventricle to the base of the brain, where it ends in the corpus mamillare. From the cells of the corpus mamillare the thalamomamillary fasciculus (bundle of Vicq d'Azyr) takes origin and is prolonged into the anterior nucleus of the thalamus. The column of the fornix and the thalamomamillary fasciculus together form a loop resembling the figure 8, but the continuity of the loop is broken in the corpus THE PROSENCEPHALON OR FORE-BRAIN 887 mamillare. The column of the fornix is joined by the stria medullaris of the pineal body and by the superficial fibres of the stria terminalis, and is said to receive also fibres from the septum pellncidum. Zuekerkandl describes an olfactory fascic- ulus which becomes detached from the main portion of the column of the fornix, and passes downward in front of the anterior commissure to the base of the brain, where it divides into two bundles, one joining the medial stria of the olfactory tract; the other joins the subcallosal gyrus, and through it reaches the hippocampal gyrus. The crura {crus fornicis; posterior pillars) of the fornix are prolonged backward from the body. They are flattened bands,, and at their commencement are inti- matel}'' connected with the under surface of the corpus callosum. Diverging from one another, each curves around the posterior end of the thalamus, and passes downward and forward into the inferior cornu of the lateral ventricle (Fig. 757). Here it lies along the concavity of the hippocampus, on the surface of which some of its fibres are spread out to form the alveus, while the remainder are continued as a narrow white band, the fimbria hippocampi, which is prolonged into the uncus of the hippocampal gyrus. The inner edge of the fitnbria overlaps the fascia dentata hippocampi {dentate gyrus) (page 875), from which it is separated by the fimbriodentate fissure ; from its lateral margin, which is thin and ragged, the ventric- ular epithelium is reflected over the choroid plexus as the latter projects into the chorioidal fissure. Interventricular Foramen {foramen of Monro). — Between the columns of the fornix and the anterior ends of the thalami, an oval aperture is present on either side: this is the interventricular foramen, and through it the lateral ventricles communi- cate Avith the third ventricle. Behind the epithelial lining of the foramen the choroid plexuses of the lateral ventricles are joined across the middle line. The Anterior Commissure {precommissure) is a bundle of white fibres, connecting the two cerebral hemispheres across the middle line, and placed in front of the columns of the fornix. On sagittal section it is oval in shape, its long diameter being vertical and measuring about 5 mm. Its fibres can be traced lateralward and backward on either side beneath the corpus striatum into the substance of the temporal lobe. It serves in this way to connect the two temporal lobes, but it also contains decussating fibres from the olfactory tracts. The Septum Pellucidum {septum lucidum) (Fig. 730) is a thin, verticallj' placed partition consisting of two laminae, separated in the greater part of their extent by a narrow chink or interval, the cavity of the septum pellucidum. It is attached, above, to the under surface of the corpus callosum; below, to the anterior part of the fornix behind, and the reflected portion of the corpus callosum in front. It is triangular in form, broad in front and narrow behind; its inferior angle corre- sponds with the upper part of the anterior commissure. The lateral surface of each lamina is directed toward the body and anterior cornu of the lateral ventricle, and is covered by the ependyma of that cavity. The cavity of the septum pellucidum {cavum septi pellucidi; pseudocele; fifth ventricle) is generally regarded as part of the longitudinal cerebral fissure, which has become shut off by the union of the hemispheres in the formation of the corpus callosum above and the fornix below. Each half of the septum therefore forms part of the medial wall of the hemisphere, and consists of a medial layer of gray substance, derived from that of the cortex, and a lateral layer of white substance continuous with that of the cerebral hemispheres. This cavity is not developed from the cavity of the cerebral vesicles, and never communicates with the ventricles of the brain. The Choroid Plexus of the Lateral Ventricle {plexus chorioideiis ventricidus later- alis; paraplexus) (Fig. 757) is a highly vascular, fringe-like process of pia mater, which projects into the ventricular cavity. The plexus, however, is everj^where NEUROLOGY covered by a layer 'of epithelium continuous with the epithelial lining of the ventricle. It extends from the interventricular foramen, where it is joined with the plexus of the opposite ventricle, to the end of the inferior cornu. The part in relation to the body of the ventricle forms the vascular fringed margin of a triangular process of pia mater, named the tela chorioidea of the third ventricle, and projects from under cover of the lateral edge of the fornix. It lies upon the upper surface of the thalamus, from which the epithelium is reflected over the plexus on to the edge of the fornix (Fig. 734). The portion in relation to the inferior cornu lies in the concavity of the hippocampus and overlaps the fimbria hippocampi: from the lateral edge of the fimbria the epithelium is reflected over the plexus on to the roof of the cornu (Fig. 756). It consists of minute and highly vascular villous processes, each with an afferent and an efferent vessel. The arteries of the plexus are: (a) the anterior choroidal, a branch of the internal carotid, which enters the plexus at the end of the inferior cornu; and (6) the posterior choroidal, one or two small branches of the posterior cerebral, which pass forward under the splenium. The veins of the choroid plexus unite to form a tortuous vein, which courses from behind forward to the interventricular foramen and there joins with the terminal vein to form the corresponding internal cerebral vein. Tail of caudate nucleus Choroid plexu-s Epithelial lifting of ventricle Pia mater Fimbria Fimbriodentate fissure Alveus Fascia den lata hippocampi Dentate fissure' Fig. 756. — Coronal section of inferior horn of lateral ventricle. (Diagrammatic.) When the choroid plexus is pulled away, the continuity between its epithelial covering and the epithelial lining of the ventricle is severed, and a cleft-like space is produced. This is named the choroidal fissure; like the plexus, it extends from the interventricular foramen to the end of the inferior cornu. The upper part of the fissure, i. e., the part nearest the interventricular foramen is situated between the lateral edge of the fornix and the upper surface of the thalamus; farther back at the beginning of the inferior cornu it is between the commencement of the fim- bria hippocampi and the posterior end of the thalamus, while in the inferior cornu it lies between the fimbria in the floor and the stria terminalis in the roof of the cornu. The tela chorioidea of the third ventricle (iela chorioidea rentriculi tertii; velum interpositum) (Fig. 757) is a double fold of pia mater, triangular in shape, which lies beneath the fornix. The lateral portions of its lower surface rest upon the thalami, while its medial portion is in contact with the epithelial roof of the third ventricle. Its apex is situated at the interventricular foramen; its base corresponds with the splenium of the corpus callosum, and occupies the interval between that structure above and the corpora quadrigemina and pineal body below. This THE PROSENCEPHALOX OR FORE-BRAIX 889 interval^ together with the h)\ver portions of the ehoroiiUil fissures, is sometimes spoken of as the transverse fissure of the brain. At its base the two laj-ers of the vekim separate from each other, and are continuous with the pia mater investing the brain in this region. Its lateral margins are modified to form the highly vas- cular choroid plexuses of the lateral ventricles. It is supplied by the anterior and posterior choroidal arteries already described. The veins of the tela chorioidea are named the internal cerebral veins {venae Galeni) ; they are two in number, and run backward between its layers, each being formed at the interventricular foramen by the union of the terminal vein with the choroidal \em. The internal cerebral veins unite posteriorly in a single trunk, the great cerebral vein {vena magna Galeni), which passes backward beneath the splenium and ends in the straight sinus. Fig. -Tela chorioidea of the third ventricle, and the choroid plexus of the left lateral ventricle, exposed from above. Structure of the Cerebral Hemispheres. — The cerebral hemispheres are composed of gray and white substance: the former covers their surface, and is termed the cortex; the latter occupies the interior of the hemispheres. The white substance consists of medullated fibres, varying in size, and arranged in bundles separated by neuroglia. They may be divided, according to their course and connections, into three distinct systems. (1) Projection fibres connect the hemisphere with the lower parts of the brain and with the medulla spinalis. (2) Transverse or commissural fibres unite the two hemispheres. (3) Association fibres connect different structures in the same hemisphere; these are, in many 890 NEUROLOGY instances, collateral branches of the i)rojection fibres, but others are the axons of independent cells. 1. The projection fibres consist of eft'erent and afferent fibres uniting the cortex with the lower parts of the brain and with the medulla spinalis. The principal efferent strands are: (1) the motor tract, occupying the genu and anterior two-thirds of the occipital part of the internal capsule, and consisting of (a) the geniculate fibres, which decussate and end in the motor nuclei of the cerebral nerves of the opposite side; and (6) the cerebrospinal fibres, which are prolonged through the pyramid of the medulla oblongata into the medulla spinalis: (2) the corticopontine fibres, ending in the nuclei pontis. The chief afferent fibres are: (1) those of the lemniscus which are not interrupted in the thalamus; (2) those of the brachia conjunctiva cerebelli which are not interrupted in the red nucleus and thalamus; (3) numerous fibres arising within the thalamus, and passing through its stalks to the difterent parts of the cortex (page 857); (4) optic and acoustic fibres, the former passing to the occipital, the latter to the temporal lobe. 2. The transverse or commissural fibres connect the two hemispheres. They include: (a) the transverse fibres of the corpus callosum, (b) the anterior commissure, (c) the posterior commissure, and (d) the lyra or hippocampal commissure; they have alreadv been described. Fig. 758. — Diagram showing principal systems of association fibres in the cerebrum. 3. The association fibres (Fig. 758) unite different parts of the same hemi- sphere, and are of two kinds: (1) those connecting adjacent gyri, short association fibres ; (2) those passing between more distant parts, long association fibres. The short association fibres lie immediately beneath the gra}" substance of the cortex of the hemispheres, and connect together adjacent gyri. The lojig association fibres include the following: (a) the uncinate fasciculus; (6) the cingulum; (c) the superior longitudinal fasciculus; (d) the inferior longi- tudinal fasciculus; (e) the perpendicular fasciculus; (/) the occipitofrontal fasciculus; and (g) the fornix. (a) The uncinate fascicidvs passes across the bottom of the lateral fissure, and unites the gyri of the frontal lobe with the anterior end of the temporal lobe. (b) The cingulum is a band of white matter contained within the cingulate gyrus. Beginning in front at the anterior perforated substance, it passes forward and upward parallel with the rostrum, winds around the genu, runs backward above the corpus callosum, turns around the splenium, and ends in the hippocampal gyrus. THE PROSENCEPHALOX OR FORE-BRAIN 891 (c) The fiupcriur luiigitiidinal fasciculus passes backward from the frontal lobe above the lentiform nucleus and insula; some of its fibres end in the occipital lobe, and others curve d()\Ainvar(l and forward into the temporal lobe. (d) The inferior longiiudinal fasciculus connects the temporal and occipital lobes, running along- the lateral walls of the inferior and posterior cornua of the lateral ventricle. {e) The 'peryendiculur fasciculvs runs vertically through the front part of the occipital lobe, and connects the inferior parietal lobule with the fusiform gyrus. (/) The occipiUfrovtal fasciculus passes backward from the frontal lobe, along the lateral border of the caudate nucleus, and on the mesial aspect of the corona radiata; its fibres radiate in a fan-like manner and pass into the occipital and tem- poral lobes lateral to the posterior and inferior cornua. Dejerine regards the fibres of the tapetum as being derived from this fasciculus, and not from the corpus callosum. (g) The fornix connects the hippocampal gyrus with the corpus mamillare and, by means of the thalamomamillary fasciculus, with the thalamus (see page SS()). Through the fibres of the hippocampal commissure it probably also unites the opposite hippocampal gyri. The gray substance of the hemisphere is divided into: (1) that of the cerebral cortex, and (2) that of the caudate nucleus, the lentiform nucleus, the claustrum, and the nucleus amygdala?. Structure of the Cerebral Cortex (Fig. 759). — The cerebral cortex differs in thickness and structure in different parts of the hemisphere. It is thinner in the occipital region than in the anterior and posterior central gyi'i, and it is also much thinner at the bottom of the sulci than on the top of the gyri. Again, the minute structure of the anterior central differs from that of the posterior central gyrus, and areas possessing a speciahzed type of cortex can be mapped out in the occipital lobe. On examining a section of the cortex with a lens, it is seen to consist of alternating white and gray layers thus disposed from the sm-face inwai'd: (1) a thin layer of white substance; (2) a layer of gray substance; (3) a second white layer (outer band of Baillarger or hand of Gennari); (4) a second gray layer; (5) a third white layer {inner hand of Baillarger) ; (6) a third gray layer, which rests on the meduUary substance of the gyrus. The cortex is made up of nerve cells of varying size and shape, and of nerve fibres which are either meduUated or naked axis-cylinders, imbedded in a matrix of neuroglia. Nerve Cells. — According to Cajal, the nerve cells are arranged in four layers, named from the sm-face inward as follows: (1) the molecular layer, (2) the layer of small pyramidal cells, (3) the layer of large pyramidal ceUs, (4) the layer of polymorphous cells. The Molecular Layer. — In this layer the cells are polygonal, triangular, or fusiform in shape. Each polygonal cell gives off some four or five dendrites, while its axon may arise directly from the cell or from one of its dendrites. Each triangular cell gives off two or three dendrites, from one of which the axon arises. The fusiform cells are placed with their long axes parallel to the surface and are mostly bipolar, each pole being prolonged into a dendrite, which runs horizontally for some distance and furnishes ascending branches. Their axons, two or three in number, arise from the dendrites, and, like them, take a horizontal course, giving off numerous ascending collaterals. The distribution of the axons and dendrites of all three sets of cells is hmited to the molecular layer. The Layer of Small and the Layer of Large Pyramidal Cells. — The cells in these two layers may be studied together, since, with the exception of the difference in size and the more super- ficial position of the smaller cells, they resemble each other. The average length of the small cells is from 10 to 15m; that of the large cells from 20 to 30m. The body of each cell is pyramidal in shape, its base being directed to the deeper parts and its apex toward the sm-face. It contains granular pigment, and stains deeply with ordinary reagents. The nucleus is of large size, and round or oval in shape. The base of the cell gives off the axis cyhnder, and this runs into the central white substance, giving off collaterals in its course, and is distributed as a projection, commissural, or association fibre. The apical and basal parts of the cell give off dendrites; the apical dendrite is directed toward the surface, and ends in the molecular layer by dividing into niunerous branches, all of which may be seen, when prepared by the silver or methylene-blue method, to be studded with projecting bristle-hke processes. The largest pyramidal cells are found in the upper part of the anterior central gyrus and in the paracentral lobule; they are often arranged in groups or nests of from three to five, and are named the gia7it cells of Betz. 892 NEUROLOGY In the former situation they may exceed 50m in length and 40m in breadth, while in the para- central lobule they may attain a length of 65m. Layer of Polymor-phous Cells. — The cells in this layer, as their name imphes, are very irregular in contour; they may be fusiform, oval, triangular, or star-shaped. Their dendrites are directed outward, but do not reach so far as the molecular layer; their axons pass into the subjacent white matter. Molecular ■ layer Layer of small 'pyramidal cells Layer of large pyramidal cells Layer of polymorphou s cells Plexzis of Exner Q^^^ ~ Band of Beckterew Outer band of Bail- larger, or band of Gennari Vertical fibres Internal band of Baillarger 2 Deep tangential fibres \ " White medullary ^ ~^ substance jTjQ 759. —Cerebral cortex. (Poirier.) To the left, the groups of cells; to the right, the systems of fibres. Quite to the left of the figure a sensory nerve fibre is shown. There are two other kinds of cells in the cerebral cortex. They are: (a) the cells of Golgi, the axons of which divide immediately after their origins into a large number of branches, which are directed toward the surface of the cortex; (6) the cells of MartinoUi, which are chiefly foiind in the polymorphous layer; theh- dendrites are short, and may have an ascending or descendmg course, while their axons pass out into the molecular layer and form an extensive horizontal arborization. , „ , u j i Nerve Fibres.— These fill up a large part of the intervals between the cells, and may be medul- lated or non-meduliated— the latter comprising the axons of the smallest pjTamidal cells and the cells of Golgi. In their direction the fibres may be either tangential or radial. The tangential fibres run parallel to the surface of the hemisphere, intersecting the radial fibres at a right angle. THE PROSENCEPHALON OR FORE-BRAIN 893 They constitute sevcnil stnilii, t)f wliich the following tire the more inijjortant: (1) a stratum of white fibres covering the Kuperfioial aspect of the molecular layer (plexus of Exner) ; (2) the band of Bechterew, in the outer part of the layer of small i)yramidal cells; (3) the band of Gennari or external band of Baillarger, running through the layer of large pyramidal cells; (4) the internal band of Baillarger, between the layer of large pyramidal cells and the polymorphous layer; (5) the deep tangential fibres, in the lower part of the polymorphous layer. The tangential fibres consist of (o) the collaterals of the pyramidal and polymorphous cells and of the cells of Martinotti; (b) the branching axons of Golgi's cells; (c) the collaterals and terminal arborizations of the projection, commissural, or association fibres. The radial fibres. — Some of these, viz., the axons of the pyramidal and polymorphous cells, descend into the central white matter, while others, the terminations of the projection, commissural, or association fibres, ascend to end in the cortex. The axons of the cells of Martinotti are also ascending fibres. Special Types of Cerebral Cortex. — It has been already pointed out that the minute structure of the cortex differs in different regions of the hemisphere; and A. W. CampbelP has endeavored to pi'ove, as the result of an exhaustive examination of a series of human and anthropoid brains, "that there exists a direct correlation between physiological function and histological structure." The principal regions where the "typical" structure is departed from will now be referred to. 1. In the calcarine fissure and the gyri bounding it, the internal band of Baillarger is absent, while the band of Gennari is of considerable thickness, and forms a characteristic featm-e of this region of the cortex. If a section be examined microscopically, an additional layer of ceUs is seen to be interpolated between the molecular layer and the lay^r of small pyramidal cells. This extra layer consists of two or three strata of fusiform cells, the long axes of which are at right angles to the surface; each cell gives off two dendrites, external and internal, from the latter of wliich the axon arises and passes into the white central substance. In the layer of small pyi'amidal ceUs, fusiform cells, identical with the above, are seen, as well as ovoid or star-like cells with ascending axons {cells of Martinotti) . This is the visual area of the cortex, and it has been shown by J. S. Bolton^ that in old-standing cases of optic atrophy the thickness of Gennari's band is reduced by nearly 50 per cent. A. W. Campbell says: "Histologically, two distinct types of cortex can be made out in the occipital lobe. The first of these coats the walls and boimding convolutions of the calcarine fissure, and is distinguished by the well-known line of Gennari or Vicq d'Azyr; the second area forms an investing zone a centimetre or more broad around the first, and is characterized by a remarkable wealth of fibres, as well as by curious pyriform cells of large size richly stocked with chromophihc elements — cells which seem to have escaped the observation of Ramon y Cajal, Bolton, and others who have worked at this region. As to the functions of these two regions there is abundant evidence, anatomical, embryological, and pathological, to show that the first or calcarine area is that to which visual sensations primarily pass, and we are gradually obtain- ing proof to the effect that the second investing area is constituted for the interpretation and further elaboration of these sensations. These areas therefore deserve the names visuo-sensory and visuo-psychic." 2. The anterior central gyrus is characterized by the presence of the giant cells of Betz and by "a wealth of nerve fibres immeasurably superior to that of any other part" (Campbell), and in these respects differs from the posterior central gyrus. These two gyri, together with the paracentral lobide, were long regarded as constituting the "motor areas" of the hemisphere; but Sherrington and Grunbaum have shown^ that in the chimpanzee the motor area never extends on to the free face of the posterior central gyrus, but occupies the entire length of the anterior central gyrus, and in most cases the greater part or the whole of its width. It extends into the depth of the central sulcus, occupying the anterior wall, and in some places the floor, and in some extending even into the deeper part of the posterior wall of the sulcus. 3. In the hippocampus the molecular layer is very thick and contains a large number of Golgi cells. It has been divided into three strata: (a) s. convolutum or s. granulosum, containing many tangential fibres; (6) s. lacunosum, presenting niunerous vascular spaces; (c) s. radiatum, exhibiting a rich plexus of fibrils. The two layers of pyramidal cells are condensed into one, and the cells are mostly of large size. The axons of the cells in the polymorphous layer may rim in an ascending, a descending, or a horizontal direction. Between the polymorphous layer and the ventricular ependyma is the white substance of the alveus. 4. In the fascia dentata hippocampi or dentate gyrus the molecular layer contains some pyrami- dal cells, while the layer of pyramidal cells is almost entirely represented by small ovoid cells. 5. The Olfactory Bidb. — In many of the lower animals this contains a cavity which communi- cates through the olfactory tract with the lateral ventricle. In man the original cavity is fiUed up by neurogUa and its wall becomes thickened, but much more so on its ventral than on its dorsal aspect. Its dorsal part contains a small amount of gray and white substance, but it is scanty and ill-defined. A section through the ventral part (Fig. 760) shows it to consist of the following layers from without inward: 1 Histological Studies on the Localization of Cerebral Function, Cambridge University Press 2 Philosophical Transactions of Royal Society, Series B, cxciii, 165. ' Transactions of the Pathological Society of London, vol. liii. 894 NEUROLOGY 1. A layer of olfactoiy nerve fibres, which are fhe non-medullated axons prolonged from the olfactory cells of the nasal cavity, and reach the bulb by passing through the cribriform plate of the ethmoid bone. At first they cover the bulb, and then penetrate it to end by forming synapses with the dendrites of the mitral cells, presently to be described. 2. Glomerular Layer.— This contains numerous spheroidal reticulated enlargements, termed glomeruli, produced by the branching and arborization of the processes of the olfactory nerve fibres with the descending dendrites of the mitral cells. 3. Molecular Layer. — This is formed of a matrix of neuroglia, imbedded in which are the mitral cells. These cells are pyramidal in shape, and the basal part of each gives off a thick dendrite which descends into the glomerular layer, where it arborizes as indicated above, and others which interlace with similar dendrites of neighboring mitral cells. The axons pass through the next layer into the white matter of the bulb, and after becoming bent on themselves at a right angle, are continued into the olfactory tract. 4. Nerve Fibre Layer.— This hes next the central core of neuroglia, and its fibres consist of the axons or afferent processes of the mitral cells passing to the brain; some efferent fibres are, however, also present, and end in the molecular layer, but nothing is known as to their exact origin. White suhstnnce dorsnl part) .Neuroglia TI hUe substance {ventral part) Medullary layer - Mitral cells 2Iolecular '' layer Glomerular layer Layer of olfactoJ y nerve fibres Fig. 760. — Coronal section of olfactory bulb. (Schwalbe.) Weight of the Encephalon. — The average weight of the brain, in the adult male, is about 1380 gms.; that of the female, about 1250 gms. In the male, the maximum weight out of 278 cases was 1840 gms. and the minimum weight 964 gms. The maximum weight of the adult female brain, out of 191 cases, was 1585 gms. and the minimum weight 879 gms. The brain increases rapidly during the first four years of life, and reaches its maximum weight by about the twentieth year. As age advances, the brain decreases slowly in weight; in old age the decrease takes place more rapidly, to the extent of about 28 gms. The human brain is heavier than that of any of the lower animals, except the elephant and whale. The brain of the former weighs from 3.5 to 4.5 kilogm., and that of a whale, in a speci- men 22.8 metres long, weighed rather more than 225 kilogm. Cerebral Localization. — Physiological and pathological research have now gone far to prove that a considerable part of the surface of the brain may be mapped out into a series of more or less definite areas, each of which is intimately connected with some well-defined function. The chief areas are indicated in Figs. 761 and 762. Motor Areas. — The motor area occupies the anterior central and frontal gyri and the para- central lobule. The centres for the lower limb are located on the uppermost part of the anterior central gyrus and its continuation on to the paracentral lobule; those for the trunk are on the upper portion, and those for the upper hmb on the middle portion of the anterior central gyrus. The facial centres are situated on the lower part of the anterior central gyrus, those for the tongue, larynx, muscles of mastication, and pharynx on the frontal operculum, while those for the head and neck occupy the posterior end of the middle frontal gyrus. Sensory Areas. — Tactile and temperature senses are located on the posterior central gyrus, while the sense of form and sohdity is on the superior parietal lobule and precuneus. With regard to the special senses, the area for the sense of taste is probably related to the imcus and THE PROSENCEPJIAWX OR FORE-BUAIN 895 hippocampal gyrus. The auditory area occujiies the middle third of the superior temporal gyrus and the adjacent gyri in the lateral fissure; the visual area, the calcarine fissure and cuncus; the olfactory area, the rhineneephalon. As special centres of much importance may be noted: the emissive centre for speech on the left inferior frontal and anterior central gyri (Broca) ; the auditory receptive centre on the transverse and sujierior tenijioral gyri, and the visual receptive centre on the lingual gyrus and cuneus. Fig. 761. — Areas of localization on lateral surface of hemisphere. Motor area in red. Area of general sensations in blue. Auditory area in green. Visual area in yellow. The psj-chic portions are in lighter tints. Applied Anatomy. — The internal capsule is of great interest to the clinician because it is so often the seat of hemorrhage (from the lenticulo-striate and lenticulo-optic arteries, Charcot's "arteries of cerebral hemorrhage"), oi' of thrombosis, in patients whose vessels are weakened by old age Fig. 762. — Areas of localization on medial surface of hemisphere. Motor area in red. Area of general sensations in blue. 'S'isual area in yellow. Olfactory area in purple. The psychic portions are in lighter tints. or disease. A stroke or apoplexy is the result; blood is effused from the ruptm-ed vessel and tears up the surroimding brain tissue, and also interferes with the neighboring fibres by the compres- sion set up by its mass. If the hemorrhage is sudden and at all large, rapid and complete loss of consciousness follows, with paralj'sis of the opposite side of the body and loss of control over 896 NE I HO LOGY the sphincters. If it is the occipital part of the internal capsule tliat is involved, tlie paralysis will be more marked in the leg than in the arm, and will be associated with hemianesthesia, and also with homonymous hemianopsia or blindness of the corresponding halves of the two retinae, the patient being unable to see objects on the opposite side of the body. If the hemorrhage is very extensive blood often makes its way into the ventricles, and death may follow in a few hours or days without recovery of consciousness, and with hyperpyrexia. If the hemorrhage is small, consciousness is soon regained, and a fair degree of recovery from the paralysis follows, particu- larly in the leg. If the hemorrhage takes place very slowly, the hemiplegia sets in gradually {ingravescent apoplexy), with headache and gradual clouding of the faculties. It is the upper motor neuron (see below) that is injured in cerebral hemorrhage; hence the muscles on the affected side of the body become spastic, with increased reflexes, while such muscular atrophy as follows is mainly due to disuse. THE MOTOR AND SENSORY TRACTS. The anatomy of the various parts of the central nervous system having been described, a short account will now be given of the motor and sensory nerve tracts connecting the brain and the medulla spinalis. The methods employed in elucidat- ing this complex subject have already been referred to (page 815). The Motor Tract (Fig. 763). — The constituent fibres of this tract are the axis- cylinder processes of cells situated in the motor area of the cortex. The fibres are at first somewhat widely diffused, but as they descend through the corona radiata they gradually approach each other, and pass between the lentiform nucleus and thalamus, in the genu and anterior two-thirds of the occipital part of the inter- nal capsule ; those in the genu are named the geniculate fibres, while the remainder constitute the cerebrospinal fibres; proceeding downward they enter the middle three-fifths of the base of the cerebral peduncle. The geniculate fibres cross the middle line, and end by arborizing around the cells of the motor nuclei of the cere- bral nerves. The cerebrospinal fibres are continued downward into the pyramids of the medulla oblongata, and the transit of the fibres from the medulla oblongata is effected by two paths. The fibres nearest to the anterior median fissure cross the middle line, forming the decussation of the pyramids, and descend in the opposite side of the medulla spinalis, as the lateral cerebrospinal fasciculus {crossed pyramidal tract) . Throughout the length of the medulla spinalis fibres from this column pass into the gray substance, to terminate by ramifying around the motor cells of the anterior column. The more laterally placed portion of the tract does not decussate in the medulla oblongata, but descends as the anterior cerebrospinal fasciculus {direct pyramidal tract) ; these fibres, however, end in the anterior gray column of the opposite side of the medulla spinalis by passing across in the anterior white commissure. There is considerable variation in the extent to which decus- sation takes place in the medulla oblongata; about two-thirds or three-fourths of the fibres usu-ally decussate in the medulla oblongata and the remainder in the medulla spinalis. The axons of the motor cells in the anterior column pass out as the fibres of the anterior roots of the spinal nerves, along which the impulses are conducted to the muscles of the trunk and limbs. From this it will be seen that all the fibres of the motor tract pass to the nuclei of the motor nerves on the opposite side of the brain or medulla spinaHs, a fact which explains why a lesion involving the motor area of one side causes paralysis of the muscles of the opposite side of the body. Further, it will be seen that there is a break in the continuity of the motor chain; in the case of the cerebral nerves this break occurs in the nuclei of these nerves; and in the case of the spinal nerves, in the anterior gray column of the medulla spinalis. For clinical purposes it is convenient to emphasize this break and divide the motor tract into two portions : (1) a series of upper motor neurons which comprises the motor cells in the cortex THE MOTOR AND SENSORY TRACTS 897 and their descending fibres down to the nuclei of the motor nerves; (2) a series of lower motor neurons a\ hich inchides the cells of the nuclei of the motor cerebral nerves or the cells of the anterior columns of the medulla spinalis and their axis- cylinder processes to the periphery.^ Jeniculate fibres Motor area of cortex Internal capsule Decussation of pyramids Anterior cerebrospinal fasciculus Lateral cerebrospinal fasciculus Anterior nerve roots Fig. 763. — The motor tract. (Modified from Poirier.) The Sensory Tract (Fig. 764) .—Sensory impulses are conveyed to the medulla spinalis through the posterior roots of the spinal nerves. On entering the medulla spinalis these root fibres divide into descending and ascending branches; the former soon enter the gray substance : some of the latter end in the gray substance after a longer or shorter course, while others are continued directly into the posterior 1 As already mentioned (footnote, p. 816), a neuron in the posterior column of the medulla spinalis is probably inter- posed between each upper and lower motor neuron. 57 898 NEUROLOGY funiculi, where they form the fascicukis gracihs and fasciculus cuneatus. From the cells of the posterior column, fibres arise which cross the middle line and ascend in the superficial antero-lateral fasciculus. The fibres of the fasciculus gracilis and fasciculus cuneatus end by arborizing around the cells of the gracile and cuneate nuclei in the medulla oblongata, and from these cells the fibres of the medial Medial lemniscus Sensory decussation Fasciculus cuneatus Fasciculus gracilis Nucleus cuneaius Nucleus gracilis — ■ Posterior nerve roots Fig. 764. — The sensory tract. (Modified from Poirier.) lemniscus take origin and cross to the opposite side in the sensory decussation. The medial lemniscus is then joined by the fibres of the superficial antero-lateral fasciculus, which have already crossed in the medulla spinalis, and in its further course receives fibres from the cerebral sensory nuclei of the opposite side, with the exception of the cochlear division of the acoustic nerve. Ascending through the cerebral peduncle, the lemniscus gives off some fibres to the lentiform nucleus THE MOTOR AND SEXSORY TRACTS 899 and insula, but the greater part of it is carried into the thalamus, where most of its fibres end — only a small proportion being continued directly into the cerebral cortex. From the gray substance of the thalamus the fibres of the third link in the chain arise and pass to the cerebral cortex. The fibres from the terminal nuclei of the cochlear nerve pass upward in the lateral lemniscus, and are carried through the occipital part of the internal capsule to the temporal lobe. Further, the super- ficial antero-lateral fasciculus gives off fibres which reach the cerebellum through the brachia conjunctiva. It will be evident, therefore, that in most cases there are three cell-stations interposed in the course of the sensory impulses. For clinical purposes, therefore, three neurons are described: (1) the lowest sensory neurons comprise the cells of the posterior root ganglia and their peripheral and central processes; (2) the intermediate sensory neurons are the cells of the nuclei cuneati and gracilis and their processes, while (3) the highest sensory neurons are the cells of the thalami and the fibres passing from these to the cerebral cortex. Applied Anatomy. — The chief sjTnptoms of diseases of the brain and medulla spinaUs depend upon the particular systems of neurons picked out for attack, a^d some of them may be briefly summarized as foUows: Motor paralysis of the spastic type, with rigidity of the muscles and increased reflexes, follows destruction of the upper motor neurons; flaccid paralysis, with loss of the reflexes and rapid muscular atrophy, foUows destruction of the lower motor neurons. Sensory paralysis foUows injury to any part of the sensory path; in tabes it is due to injury of the lowest sensory neurons, in hemiplegia to destruction of the highest sensory axon as it traverses the occipital part of the internal capsule. Dissociation of sensations, or the loss of some forms of sensation while others remain imimpaired, is seen in a number of conditions such as tabes or syringomyelia; it shows that the paths through which various forms of sensation travel to the brain are different. Abnormalities of reflex actions are of very great help in the diagnosis of nervous complaints. The numerous superficial or skin reflexes, e. g., the scapular, irritation of the skin over the scapula produces contraction of the scapular muscles; the abdominal, stroking the abdomen causes its retraction; the cremasteric, stroking the inner side of the thigh causes retrac- tion of the testis on that side; the plantar, tickling the sole of the foot brings on plantar flexion of the toes, if present, show that the reflex arcs on whose integrity their existence depends are intact; but they are often absent in health, and so cannot be trusted to indicate disease. The deep reflexes or tendon reactions, such as the knee-jerk or the tendo-calcaneus jerk, are increased in chronic degeneration of, or gradually increasing pressure on, the cerebrospinal fibres (upper motor neuron), in nervous or hysterical patients, and when the irritabihty of the cells of the anterior column (lower motor neuron) is increased, as happens in tetanus or in poisoning by strychnine. They are lost when the lower motor or lower sensory neurons are diseased, and in a few other conditions; absence of the knee-jerk is very rare in health, and suggests disease in some part of its reflex arc, in the third and fourth Imnbar segments of the cord, or else, more rarely, grave intracranial or spinal disease cutting off the lower from the higher nervous centres. The organic reflexes of the pupil, bladder, and rectum are of the greatest practical importance. The commonest defect in the reflexes of the pupil is reflex iridoplegia, or failm'e to contract on exposm-e to hght, without failure to contract on convergence or accommodation (Argyll-Robert- son pupil). The pupil is also contracted (miosis), and may or may not dilate when the skui of the neck is pinched (the cihospinal reflex) . Micturition is a spinal reflex much under the control of the brain; if the centre for mictm'ition in the second sacral segment is destroyed the sphincter and the walls of the bladder are paralyzed, the bladder becomes distended with m-ine, and incon- tinence from overflow results. If this centre escapes injury but is cut off more or less completely from impulses descending to it from above, there will be more or less interference with micturition. This varies in degi'ee from the "precipitate mictm-ition" of tabetic patients, who must perforce hurry to pass water the moment the impulse seizes them, to the state of "reflex incontinence," when the bladder automatically empties itseK from time to time, almost without the patient's knowledge. Defecation is a very similar spinal reflex, and is hable to very similar disorders of function. The upper motor neuron (p. 896) is affected in hemiplegia, the lower motor neuron (p. 897) in infantile spinal paralysis; both these systems of nem'ons are diseased together in the somewhat rare disorders known as amyotrophic lateral sclerosis and progressive muscidar atrophy. The chief symptom here is wasting and weakness in certain groups of muscles; the palsy wiU be flaccid, with loss of the reflexes, or spastic, with increased reflexes, according as the degeneration mainly involves the lower or the upper motor neuron. The sphincters are affected only in the later stages of these diseases. Pathological changes in the lowest sensory neuron are the cause of tabes dorsalis or locomotor ataxy, which occurs almost entirely in adults who have had syphihs. In the early or preataxic 900 NEUROLOGY stage the patient may exhibit tlic Argyll-Rol)(>rt.son pupil (page SOU), and loss of the knee-jerks, and complain of sharp, stabbing pains ("lightning pains") in the limbs, difficult or precipitate micturition, and sometimes of severe and painful attacks of indigestion (gastric crises). In the second or ataxic stage, coming on perhaps years later, he will complain, in addition, of inter- ference with his powers of getting about and turning, although his muscular strength is well preserved. He is unable to stand steady with his eyes shut or in the dark, his gait becomes exaggerated and stamping in character, he has to use a stout stick to walk with, and he may suffer from painful crises in various parts of the body. Control over the sphincters is further weakened, and on examination there will be found marked incoordination of the limbs, zones of anesthesia about the trunk or down the limbs, and marked analgesia (or insensitiveness to pain) when pressure is applied to the bones, tendons, trachea, tongue, eyeballs, mammae, and testes.^ The ataxy progresses until the third or bedridden stage is reached; control over the sphincters is still further lost, and the patient is likely to die of intercurrent disease or of general paralysis of the insane. No nervous disease is recognized as dependent upon degeneration of either the intermediate or highest sensory neuron. MENINGES OF THE BRAIN AND MEDULLA SPINALIS. The brain and medulla spinalis are enclosed within three membranes. These are named from without inward : the dura mater, the arachnoid, and the pia mater. The Dura Mater. The dura mater is a thick and dense inelastic membrane. The portion which encloses the brain differs in several essential particulars from that which surrounds the medulla spinalis, and therefore it is necessary to describe them separately; but at the same time it must be distinctly understood that the two form one com- plete membrane, and are continuous with each other at the foramen magnum. The cerebral dura mater {dura mater encephali; dura of the brain) lines the interior of the skull, and serves the two-fold purpose of an internal periosteum to the bones, and a membrane for the protection of the brain. It is composed of two layers, an inner or meningeal and an outer or endosteal, closely connected together, except in certain situations, where, as already described (page 729), they separate to form sinuses for the passage of venous blood. Its outer surface is rough and fibrillated, and adheres closely to the inner surfaces of the bones, the adhesions being most marked opposite the sutures and at the base of the skull its inner surface is smooth and lined by a layer of endothelium. It sends inward four processes which divide the cavity of the skull into a series of freely communica- ting compartments, for the lodgement and protection of the different parts of the brain; and it is prolonged to the outer surface of the skull, through the various foramina which exist at the base, and thus becomes continuous with the peri- cranium; its fibrous layer forms sheaths for the nerves which pass through these apertures. Around the margin of the foramen magnum it is closely adherent to the bone, and is continuous with the spinal dura mater. Processes. — The processes of the cerebral dura mater, which projects into the cavity of the skull, are formed by reduplications of the inner or meningeal layer of the membrane, and are four in number: the falx cerebri, the tentorium cerebelli, the falx cerebelli, and the diaphragma sellse. The falx cerebri (Fig. 765), so named from its sickle-like form, is a strong, arched process which descends vertically in the longitudinal fissure between the cerebral hemispheres. It is narrow in front, where it is attached to the crista galli of the ethmoid; and broad behind, where it is connected with the upper surface of the tentorium cerebelli. Its upper margin is convex, and attached to the inner surface of the skull in the middle line, as far back as the internal occipital protuberance; it contains the superior sagittal sinus. Its lower margin is free and concave, and contains the inferior sagittal sinus. 1 J. Grasset, Le Tabes, Maladie de la Sensibilite profonde, Montpellier, 1909. THK DURA MATKR 901 The tentorium cerebelli (Fig. 766) is an arched lamina, elevated in the middle, and inciinini:; downward toward the circumference. It covers the superior surface of the cerebellum, and supports the occij)ital lobes of the brain. Its anterior border is free and conca^'e, and bounds a large oval opening, the incisura tentorii, for the transmission of the cerebral peduncles. It is attached, behind, by its convex border, to the transverse ridges upon the inner surface of the occipital bone, and there encloses the transverse sinuses; in front, to the superior angle of the petrous part of the temporal bone on either side, enclosing the superior petrosal sinuses. At the apex of the petrous part of the temporal bone the free and attached borders meet, and, crossing one another, are continued forward to be fixed to the anterior and posterior clinoid processes respectively. To the middle line of its upper surface the posterior border of the falx cerebri is attached, the straight sinus being placed at their line of junction. Great cerebral vein GlonsopharyiLijeal nerve Vagus nerve Accessory nerve Acoustic nerve Facial nerve Abducent nerve Trigeminal nerve Fig. 765. — Dura mater and its processes exposed by removing part of the right half of the skull and the brain. The falx cerebelli is a small triangular process of dura mater, received into the posterior cerebellar notch. Its base is attached, above, to the under and back part of the tentorium; its posterior margin, to the lower division of the vertical crest on the inner surface of the occipital bone. As it descends, it sometimes divides into two smaller folds, which are lost on the sides of the foramen magnum. The diaphragma sellae is a small circular horizontal fold, which roofs in the sella turcica and afmost completely covers the hypophysis; a small central opening transmits the infundibulum. 902 NEUROLOGY Structure. — The cranial dura mater consists of white fibrous tissue and clastic fibres arranged in flattened lamina; which are imperfectly separated by lacunar spaces and bloodvessels into two layers, endosteal and meningeal. The endosteal layer is the internal periosteum for the cranial bones, and contains the bloodvessels for their supply. At the margin of the foramen magnum it is continuous with the periosteum lining the vertebral canal. The meningeal or supporting layer is lined on its inner surface by a layer of nucleated endothehum, similar to that found on serous membranes. Optic nei-ve Internal carotid artery Oculomotor nerve Attached margin of tentorium Free margin of tentouum niaphragma sellce \ E7id of superior sagittal sinus Fig. 766. — Tentorium cerebelli seen from above. The arteries of the dura mater are very numerous. Those in the anterior fossa are the anterior meningeal branches of the anterior and posterior ethmoidal and internal carotid, and a branch from the middle meningeal. Those in the middle fossa are the middle and accessory meningeal of the internal maxillary; a branch from the ascending pharyngeal, which enters the skull through the foramen lacerum; branches from the internal carotid, and a recurrent branch from the lacrimal. Those in the posterior fossa are meningeal branches from the occipital, one entering the skull through the jugular foramen, and another through the mastoid foramen; the posterior meningeal from the vertebral; occasional meningeal branches from the ascending pharyngeal, entering the skull through the jugular foramen and hypoglossal canal; and a branch from the middle meningeal. The veins returning the blood from the cranial dura mater anastomose with the diploic veins and end in the various sinuses. Many of the meningeal veins do not open directly into the sinuses, but indirectly through a series of ampullae, termed venous lacunae. These are found on either side of the superior sagittal sinus, especially near its middle portion, and are often invaginated by arachnoid granulations; they also exist near the transverse and straight sinuses. They communicate with the underlying cerebral veins, and also with the diploic and emissary veins. The nerves of the cerebral dm-a mater are filaments from the semilunar ganglion, from the ophthalmic, maxillary, mandibular, vagus, and hypoglossal nerves, and from the sympathetic. The spinal dura mater (dura mater spinalis; spinal dura) (Fig. 767) forms a loose sheath around the medulla spinalis, and represents^ onl}' the inner or meningeal layer of the cerebral dura mater; the outer or endosteal layer ceases at the foramen magnum, its place being taken by the periosteum lining the vertebral canal. The THE ARACHNOID 903 spinal dura mater is separated from the arachnoid by a potential cavity, the sub- dural cavity; the two membranes are, in fact, in contact with each other, except where they are separated by a minute quantity of fluid, which serves to moisten the apposed surfaces. It is separated from the wall of the vertebral canal by a space, the epidural space, which contains a quan- tity of loose areolar tissue and a plexus of veins; the situation of these veins between the dura mater and the periosteum of the vertebrae corresponds therefore to that of the cranial sinuses between the meningeal and endosteal layers of the cerebral dura mater. The spinal dura mater is attached to the circumference of the foramen magnum, and to the second and third cervical vertebrae; it is also connected to the pos- terior longitudinal ligament, especially near the low^er end of the vertebral canal, by fibrous slips. The subdural cavity ends at the lower border of the second sacral vertebra ; below this le-s^el the dura mater closely invests the filum terminale and descends to the back of the coccyx, where it blends with the periosteum. The sheath of dura mater is much larger than is necessary for the accommodation of its contents, and its size is greater in the cervical and lumbar regions than in the thoracic. On each side may be seen the double openings which transmit the two roots of the corre- sponding spinal nerve, the dura mater being continued in the form of tubular prolongations on them as they pass through the interverte- bral foramina. These prolongations are short in the upper part of the vertebral column, but gradually become longer below, forming a number of tubes of fibrous membrane, which enclose the lower spinal nerves and are contained in the verte- bral canal. Structure. — The spinal dvira mater resembles in structure the meningeal or supporting layer of the cranial dm-a mater, consisting of white fibrous and elastic tissue arranged in bands or lamellae which, for the most part, are parallel with one another and have a longitudinal arrange- ment. Its internal surface is smooth and covered by a layer of endothehum. It is sparingly supplied with bloodvessels, and a few nerves have been traced into it. Fig. 767. — The medulla spinalis and its membranes. The Arachnoid. The arachnoid is a delicate membrane enveloping the brain and medulla spinalis and lying between the pia mater internally and the dura mater externally; it is separated from the pia mater by the subarachnoid cavity, which is filled with cerebrospinal fluid. The cerebral part (arachnoidea encepJiali) of the arachnoid invests the brain loosely, and does not dip into the sulci between the gyri, nor into the fissures, with the exception of the longitudinal. On the upper surface of the brain the arachnoid is thin and transparent; at the base it is thicker, and slightly opaque toward the central part, w^here it extends across between the two temporal lobes in front of the pons, so as to leave a considerable interval between it and the brain. The spinal part (arachnoidea spinalis) of the arachnoid is a thin, delicate, tubular membrane loosely investing the medulla spinalis. Above, it is continuous with the cerebral arachnoid; beloiv, it widens out and invests the cauda equina and the nerves proceeding from it. It is separated from the dura mater by the subdural space, but here and there this space is traversed by isolated connective-tissue trabeculse, w^hich are most numerous on the posterior surface of the medulla spinalis. 904 NEUROLOGY The arachnoid surrounds the cerebral and spinal nerves, and encloses them in loose sheaths as far as their points of exit from the skull and vertebral canal; Structure. — The arachnoid consists of bundles of white fibrous and elastic tissue intimately- blended together. Its outer surface is covered with a layer of endothelium. Vessels of consider- able size, but few in number, and, according to Bochdalek, a rich plexus of nerves derived from the motor root of the trigeminal, the facial, and the accessory nerves, are found in the arachnoid The subarachnoid cavity {cavum suharachnoideale; subarachnoid space) is the interval between the arachnoid and pia mater. It is occupied by a spongy tissue consisting of trabeculse of delicate connective tissue, and intercommunicating channels in which the subarachnoid fluid is contained. This cavity is small on the surface of the hemispheres of the brain; on the summit of each gyrus the pia mater and the arachnoid are in close contact ; but in the sulci between the gyri, triangular spaces are left, in which the subarachnoid trabecular tissue is found, for the pia mater dips into the sulci, whereas the arachnoid bridges across them from gyrus to gyrus. At certain parts of the base of the brain, the arachnoid is separated from the pia mater by wide intervals, which communicate freely with each other and are named subarachnoid cisternse; in these the subarachnoid tissue is less abundant. Otitic chiasma Oisterna interpeduncu laris Fourth ventricle Cisterna poniia Cisterna cerebellomcchdlaris Fig. 768. — Diagram showing the positions of the three principal subarachnoid cisternse. Subarachnoid Cisternse (cistemae subarachnoidales) (Fig. 768). — The cisterna cerebellomedullaris (cisterna magna) is triangular on" sagittal section, and results from the arachnoid bridging over the interval between the medulla oblongata and the under surfaces of the hemispheres of the cerebellum; it is continuous with the subarachnoid cavity of the medulla spinalis at the level of the foramen magnum. The cisterna pontis is a considerable space on the ventral aspect of the pons. It contains the basilar artery, and is continuous behind with the subarach- noid cavity of the medulla spinalis, and with the cisterna cerebellomedullaris; and in front of the pons with the cisterna interpeduncularis. The cisterna interpeduncu- laris (cisterna basalis) is a wide cavity where the arachnoid extends across between the two temporal lobes. It encloses the cerebral peduncles and the structures contained in the interpeduncular fossa, and contains the arterial circle of Willis. In front, the cisterna interpeduncularis extends forward across the optic chiasma, forming the cisterna chiasmatis, and on to the upper surface of the corpus callosum, for the arachnoid stretches across from one cerebral hemisphere to the other immedi- ately beneath the free border of the falx cerebri, and thus leaves a space in which THE ARACHNOID 905 the anterior cerebral arteries are contained. The cisterna fossae cerebri lateralis is formed in front of either temporal lobe by the arachnoid bridging across the lateral fissure. This cavity contains the middle cerebral artery. The cisterna venae magnae cerebri occupies the interval between the splenium of the corpus callosum and the superior surface of the cerebellum; it extends between the layers of the tela chorioidea of the third ventricle and contains the great cerebral vein. The subarachnoid cavity communicates with the general ventricular cavity of the brain by three openings; one, the foramen of Majendie, is in the middle line at the inferior part of the roof of the fourth ventricle; the other two are at the extremities of the lateral recesses of that ventricle, behind the upper roots of the glossopharyngeal nerves. It is stated by Meckel that the lateral ventricles also communicate with the subarachnoid cavity at the apices of their inferior cornua. There is no direct communication between the subdural and subarachnoid cavities. Emissary tiein Venous lacuna \ \ Cerebral vei Diploic vein \ Sup. sagittal sinus Arachnoid granulation Meningeal vein Subdural cavity Subarachnoid cavity Dura mater Arachnoid Cerebral cortex Pia mater Fig. 769. — Diagrammatic representation of a section across the top of the skull, showing the membranes of the brain, etc. (Modified from Testut.) The spinal part of the subarachnoid cavity is a very wide interval, and is the largest at the lower part of the vertebral canal, where the arachnoid encloses the nerves which form the cauda equina. Above, it is continuous with the cranial subarachnoid cavity; below, it ends at the level of the lower border of the second sacral vertebra. It is partially divided by a longitudinal septum, the subarachnoid septum, which connects the arachnoid with the pia mater opposite the posterior median sulcus of the medulla spinalis, and forms a partition, incomplete and cribri- form above, but more perfect in the thoracic region. The spinal subarachnoid cavity is further subdivided by the ligamentum denticulatum, which wall be described with the pia mater. The cerebrospinal fluid is a clear limpid fluid, having a saltish taste, and a sUghtly alkaline reaction. According to Lassaigne, it consists of 98.5 parts of water, the remaining 1.5 per cent, being solid matters, animal and saUne. It varies in quantity, being most abundant in old persons, and is quickly secreted. The arachnoid granulations {granulationes arachnoideales; glandulae Pacchioni; arachnoid villi; Pacchionian bodies) (Fig. 769) are small, fleshy-looking eleva- 906 NEUROLOGY tions, usually collected into clusters of variable size, which are present upon the outer surface of the dura mater, in the vicinity of the superior sagittal sinus, and in some other situations. Upon laying open the sagittal sinus and the venous lacunse on either side of it granulations will be found protruding into its interior. They are not seen in infancy, and very rarely until the third year. They are usually found after the seventh year; and from this period they increase in number and size as age advances. They are not glandular in structure, but are enlarged normal villi of the arachnoid. As they grow they push the thinned dura mater before them, and cause absorption of the bone from pressure, and so produce the pits or depressions on the inner wall of the calvarium. Structure. — An arachnoidal granulation consists of the following parts: (1) In the interior is a core of subarachnoid tissue, continuous with the mesh-work of the general subarachnoid tissue through a narrow pedicle, by which the granulation is attached to the arachnoid. (2) Around this tissue is a layer of arachnoid membrane, limiting and enclosing the subaraclxnoid tissue. (3) Outside this is the thinned wall of the lacuna, which is separated from the arachnoid by a space which corresponds to and is continuous with the subdural cavity. (4) And finally, if the granulation projects into the sagittal sinus, it will be covered by the greatly thinned upper waUs of the sinus. It will be seen, therefore, that fluid injected into the subarachnoid cavity will find its way into these granulations, and it has been found experimentally that it passes by osmosis from the granulations into the venous sinuses into which they project. The Pia Mater. The pia mater is a vascular membrane, consisting of a minute plexus of blood- vessels, held together by an extremely fine areolar tissue. The cerebral pia mater {yia mater enceyhali; pia of the brain) invests the entire surface of the brain, dips between the cerebral gyri and cerebellar laminae, and is invaginated to form the tela chorioidea of the third ventricle, and the choroid plexuses of the lateral and third ventricles (pages 887 and 888) ; as it passes over the roof of the fourth ventricle, it forms the tela chorioidea and the choroid plexuses of this ventricle. Upon the surfaces of the hemispheres, where it covers the gray substance, it gives oflf from its deep surface a multitude of sheaths, around the minute vessels, that extend perpendicularly for some distance into the cerebral substance. On the cerebellum the membrane is more delicate; the vessels from its deep surface are shorter, and its relations to the cortex are not so intimate. Subdural cavity Pia mater Arachnoid Dura mater Subdural cavity Fig. 770. — Diagrammatic transverse section of the medulla spinalis and its membranes. The spinal pia mater (pia mater spinalis; pia of the cord) (Figs. 767, 770) is thicker, firmer, and less vascular than the cerebral pia mater : this is due to the fact that it consists of two layers, the outer or additional one being composed of bundles of connective-tissue fibres, arranged for the most part longitudinally. Between the layers are cleft-like spaces which communicate with the subarachnoid cavity, and a number of bloodvessels which are enclosed in perivascular Ij^mphatic sheaths. THE CEREBRAL NERVES 907 The spinal pia mater covers the entire surface of the me(killa spinaHs, and is very intimately adherent to it; in front it sends a process backward into the anterior fissure. A longitudinal fibrous band, called the linea splendens, extends along the middle line of the anterior surface; and a somewhat similar band, the ligamentum denticulatum, is situated on either side. Below the conus medullaris, the pia mater is continued as a long, slender filament (filum terminale), which descends through the centre of the mass of nerves forming the cauda equina. It blends with the dura mater at the level of the lower border of the second sacral vertebra, and extends downward as far as the base of the coccyx, where it fuses with the periosteum. It assists in maintaining the medulla spinalis in its position during the movements of the trunk, and is, from this circumstance, called the central ligament of the medulla spinalis. The pia mater forms sheaths for the cerebral and spinal nerves; these sheaths are closely connected with the nerves, and blend with their common membranous investments. The ligamentum denticulatum {defitate ligament) (Fig. 767) is a narrow fibrous band situated on either side of the medulla spinalis throughout its entire length, and separating the anterior from the posterior nerve roots. Its medial border is continuous with the pia mater at the side of the medulla spinalis. Its lateral border presents a series of triangular tooth-like processes, the points of w^hich are fixed at intervals to the dura mater. These processes are twenty-one in number, on either side, the first being attached to the dura mater, opposite the margin of the foramen magnum, between the vertebral artery and the hypoglossal nerve; and the last near the lower end of the medulla spinalis. Applied Anatomy. — -Evidence of great value in the diagnosis of meningitis may sometimes be obtained by puncturing the spinal membranes and withdrawing some of the cerebrospinal fluid; moreover, the operation of lumbar puncture is in many cases curative, under the suppo- sition that the draining of some of the cerebrospinal fluid reUeves the patient by diminishing the intracranial pressure. The operation is performed by inserting a trocar, of the smallest size, between the laminae of the third and fourth, or of the fourth and fifth lumbar vertebrae, through the ligamentum flavum. The medulla spinaUs, even of a child at birth, does not reach below the third lumbar vertebra, and therefore the canal may be punctured between the third and fourth lumbar vertebrae without any risk of injuring this structure. The point of puncture is indicated by laying the patient on the side and dropping a perpendicular line from the highest point of the iliac crest ; this will cross the upper border of the spinous process of the f om-th lumbar vertebra, and wiU indicate the level at which the trocar should be inserted a little to one side of the middle line. The punctiire may require to be repeated more than once, and the greatest precaution must be taken not to allow septic infection of the meninges. If there be any appre- ciable increase of pressure, the fluid will flow through the trocar with the greatest freedom. In addition to the constitutional signs and symptoms of fever, acute spinal meningitis exhibits certain characteristic features. Pain and tenderness to pressure along the vertebral column are common, and so are pains in the hmbs or around the trunk from irritation of the posterior nerve roots by the inflammatory products. Irritation of the anterior nerve roots is shown by the increased tone of the muscles, which may go on to the point where they pass into a state of spasm with much increased reflexes; this is often seen in the retraction of the head and neck. Later in the disease the reflexes are often lost, when, also, the urine and feces may be passed involuntarily. THE CEREBRAL NERVES (NERVI CEREBRALES; CRANIAL NERVES). There are twelve pairs of cerebral nerves; they are attached to the brain and are transmitted through foramina in the base of the cranium. The different pairs are named from before backward as follows : 1st. Olfactory. 7th. Facial. 2d. Optic. 8th. Acoustic. 3rd. Oculomotor. 9th. Glossopharyngeal. 4th. Trochlear. 10th. Vagus. 5th. Trigeminal. 11th. Accessory. 6th. Abducent. 12th. Hypoglossal. 908 NEUROLOGY The area of attachment of a cerebral nerve to the surface of the brain is termed its superficial or apparent origin. The fibres of the nerve can be traced into the sub- stance of the brain to a special nucleus of gray substance. The motor or efferent cerebral nerves arise within the brain from groups of nerve cells which constitute their nuclei of origin. The sensory or afferent cerebral nerves arise from groups of nerve cells outside the brain; these nerve cells may be grouped to form ganglia on the trunks of the nerves or may be situated in peripheral sensory organs such as the nose and eye. The central processes of these cells run into the brain, and there end by arborizing around nerve cells, which are grouped to form nuclei of termination. The nuclei of origin of the motor nerves and the nuclei of termination of the sensory nerves are brought into relationship with the cerebral cortex, the former through the geniculate fibres of the internal capsule, the latter through the lemniscus. The geniculate fibres arise from the cells of the motor area of the cortex, and, after crossing the middle line, end by arborizing around the cells of the nuclei of origin of the motor cerebral nerves. On the other hand, fibres arise from the cells of the nuclei of termination of the sensory nerves, and after crossing to the opposite side, join the lemniscus, and thus connect these nuclei, directly or indirectly, with the cerebral cortex. THE OLFACTORY NERVES (NN. OLFACT^RII; FIRST NERVE) (Fig. 771). The olfactory nerves or nerves of smell are distributed to the mucous membrane of the olfactory region of the nasal cavity : this region comprises the superior nasal concha, and the corresponding part of the nasal septum. The nerves originate from the central or deep processes of the olfactory cells of the nasal mucous mem- brane. They form a plexiform net-work in the mucous membrane, and are then collected into about twenty branches, which pierce the cribriform plate of the eth- moid bone in two groups, a lateral and a medial group, and end in the glomeruli Fibres of olfactory tract Mitral cells 1 — . Glomeruli Olfactory cell Olfactory epithelium mil-. Olfactory \AxUJ enaiih Fig. 771.^Nerves of septum of nose. Right side. Fig. 772. — Plan of olfactory neurons of the olfactor}^ bulb (Fig. 772). Each branch receives tubular sheaths from the dura mater and pia mater, the former being lost in the periosteum of the nose, the latter in the neurolemma of the nerve. The olfactory nerves are non-medullated, and consist of axis-cylinders surrounded by nucleated sheaths, in which, however, there are fewer nuclei than are found in the sheaths of ordinary non-medullated nerve fibres. The olfactory centre in the cortex is generally associated with the rhinencephalon (page 874). THE OPTIC NERVE 909 Applied Anatomy. — In severe injuries to the head involving the anterior fossa of the base of the skull, tlie olfactory bulb may become separated from the olfactory nerves, or the nerves may be torn, thus producing loss of smell {anostiiia), and with this there is a considerable loss in the sense of taste, since much of the perfection of the sense of taste is due to the substances being also odorous, and simultaneously exciting the sense of smell. Anosmia often occurs after influenza or other acute infection of the nose. Parosmia, or a per- version of the sense of smell, may occur in lesions of the cortical olfactory centres, or in insanity. THE OPTIC NERVE (N. OPTICUS; SECOND NERVE) (Fig. 773). Fig. 773. — The left optic nerve and the optic tracts. The optic nerve, or nerve of sight, is distributed exclusively to the bulb of the eye. The nerves of opposite sides are connected together at the optic chiasma, and from the back of the chiasma the nerve fibres may be traced to the brain, in the optic tracts. The optic tract, at its connection with the brain, is divided into two bands, lateral and medial. The lateral band is larger; it is con- nected with the lateral geniculate body, the pulvinar of the thalamus and the superior collic- ulus. The medial band ends in the medial genic- ulate body; its fibres are merely commissural, forming Gudden's commissure. From these attachments the tract winds obliquely across the under surface of the cerebral peduncle in the form of a flattened band, and is attached to the peduncle by its anterior margin. It then assumes a cylindrical form, and, as it passes for- ward, is connected with the tuber cinereum and lamina terminalis. It finally joins with the tract of the opposite side to form the optic chiasma. The optic chiasma {chiasma oyticum), somewhat quadrilateral in form, rests upon the tuberculum sellae and on the anterior part of the diaphragma sellae. It is in relation, above, with the lamina terminalis; behind , with the tuber cinereum; on either side, with the anterior perforated substance. Within the chiasma, the optic nerves undergo a partial decussation. The fibres forming the medial part of each tract and posterior part of the chiasma have no connection with the optic nerves. They simply cross in the chiasma, and connect the medial geniculate bodies of the two sides; they form the commissure of Gudden. The remaining and principal part of the chiasma consists of two sets of fibres, crossed and uncrossed. The crossed fibres which are the more numerous, occupy the central part of the chiasma, and pass from the optic nerve of one side to the optic tract of the other, decussating in the chiasma with similar fibres of the opposite optic nerve. The uncrossed fibres occupy the lateral part of the chiasma, and pass from the nerve of one side into the tract of the same side.^ The great majority of the fibres of the optic nerve (Fig. 774) consist of the afferent fibres of nerve cells in the retina; a few, however, are efferent fibres, and grow out from cells in the brain. They become medullated about the tenth week after birth. The afterent fibres end in arborizations around the cells in the lateral geniculate body, pulvinar, and superior colliculus, which constitute the lower visual centres. From the cells of these centres fibres are prolonged to the cortical visual centre, situated in the cuneus and in the neighborhood of the calcarine fissure. 1 A specimen of congenital absence of the optic chiasma is to be found in the Museum of the Westminister Hospital. See also Henle, Nervenlehre, p. 393, ed. 2. 910 NEUROLOGY Some fibres are detached from the optic tract, and pass through the cerebral peduncle to the nucleus of the oculomotor nerve. These fibres are small, and may be regarded as afferent branches for the Sphincter pupil lae and Ciliaris muscles. Other fibres pass to the cerebellum through the brachia conjunctiva, while others end in the nuclei in the pons. The optic nerves arise from the forepart of the chiasma, and, diverging from one another, each becomes rounded in form and firm in texture, and is enclosed in a sheath derived from the pia mater and arachnoid. The nerve passes beneath the anterior cerebral artery, and enters the optic foramen, receiving as it does so Optic nerve Crossed fibres Uncrossed fibres Optic chiasma Optic tract Commissure of Gudden Pidvinar Lateral geniculate body , Superior colliculus Medial genicidate body Nucleus of Qculomotor nerve Nucleus of trochlear nerve Niicleus of abducent nerve Fig. 774.- Cortex of occipital lobes -Scheme showing central connections of the optic nerves and optic tracts. a sheath from the dura mater. When the nerve reaches the orbit this sheath divides into two layers, one of which becomes continuous with the periosteum of the orbit ; the other forms the proper sheath of the nerve, and surrounds it as far as the bulb of the eye. The nerve runs forward and lateralward through the cavity of the orbit, pierces the sclera and choroid at the back part of the bulb of the eye, about 3 to 4 mm. to the nasal side of its centre, and expands to form the stratum opticum of the retina. A little behind the bulb of the eye the arteria centralis retinae perforates the optic nerve, and runs along its interior in a tubular canal of fibrous tissue. It supplies the retina, and is accompanied by corresponding veins. The retina is described with the anatomy of the eyeball. THE OCULOMOTOR NERVE 911 Applied Anatomy. — The optic nerve is peculiarly liable to become the seat of neuritis or undergo atrophy iu affection of the central nervous system, and as a rule the pathological relationship between the two affections is exceedingly difficult to trace. There are, however, certain points in connection with the anatomy of this nerve which tend to throw light upon the frequent asso- ciation of these affections with intracranial disease. (1) From its mode of development, and from its structure, the optic nerve must be regarded as a prolongation of the brain substance, rather than as an ordinary cerebrospinal nerve. (2) As it passes from the brain it receives sheaths from the three cerebral membranes, a perineural sheath from the ])ia mater, an intermediate sheath from the arachnoid, and an outer sheath from the dura mater, which is also connected with the periosteum as it passes through the optic foramen. These sheaths are separated from each other bj^ cavities which communicate with the subdural and subarachnoid cavities respec- tively. The innermost or perinem-al sheath sends a process around the arteria centralis retinae into the interior of the nerve, and enters intimately into its structm-e. Thus inflammatory affections of the meninges or of the brain may readily extend along these spaces, or along the interstitial connective tissue in the nerve. The com-se of the fibres in the optic chiasma has an important pathological bearing, and has been the subject of much controversy. Microscopic examination, experiments, and pathology aU seem to point to the fact that there is a partial decussation of the fibres, each optic tract supply- ing the corresponding haK of each eye, so that the right tract suppUes the right half of each eye, and the left tract the left half of each eye. At the same time Charcot believes, and his \i%w has met with general acceptation, that the fibres which do not decussate at the optic chiasma undergo decussation in the corpora quadrigemina, so that the lesion of the cerebral centre of one side causes complete blindness of the opposite eye, because both sets of decussating fibres are destroyed; whereas if one tract, say the right, be destroyed by disease, there will be blindness of the right half of both retinae. An antero-posterior section through the chiasma would divide the decussating fibres, and would therefore produce blindness of the medial half of each eye; while a section at the margin of the side of the optic chiasma would produce blindness of the lateral half of the retina of the same side. An earlj^ symptom of tumor growth in the hypophysis is pressure on the chiasma. The optic nerve may also be affected in injuries or diseases involving the orbit; in fractures of the anterior fossa of the base of the skuU; in tumors of the orbit itself, or those invading this cavity from neighboring parts. THE OCULOMOTOR NERVE (N. OCULOMOTORIUS ; THIRD NERVE) (Figs. 776, 777, 778). The oculomotor nerve supplies all the ocular muscles, except the Obliquus superior and Rectus lateralis; it also supplies through its connections with the ciliary ganglion, the Sphincter pupillae and the Ciliaris muscles. The fibres of the oculomotor nerve arise from a nucleus which lies in the gray substance of the floor of the cerebral aqueduct and extends in front of the aqueduct for a short distance into the floor of the third ventricle. From this nucleus the fibres pass forward through the tegmentum, the red nucleus, and the medial part of the substantia nigra, forming a series of curves with a lateral convexity, and emerge from the oculomotor sulcus on the medial side of the cerebral peduncle. The nucleus of the oculomotor nerve does not consist of a continuous column of cells, but is broken up into a number of smaller nuclei, which are arranged in two groups, anterior and posterior. Those of the posterior group are six in number, five of which are symmetrical on the two. sides of the middle line, while the sixth is centrally placed and is common to the nerves of both sides. The anterior group consists of two nuclei, an antero-medial and an antero-lateral (Fig. 775). The nucleus of the third nerve is said to give fibres to the facial nerve, which probably supply the Orbicularis oculi, Corrugator, and Frontalis muscles.^ It is also connected with the nuclei of the trochlear and abducent nerves, with the cerebellum, the superior colliculus, and the cortex of the occipital lobe of the cerebrum. The nucleus of the oculomotor nerve, considered from a physiological standpoint, can be subdivided into several smaller groups of cells, each group controlling a 1 See footnote, p. S52. 912 NEUROLOGY 6.- 5- 4'_ .r _ /' ^' .>^ 1-; X particular muscle. The nerves to the different muscles appear to take their origin from behind forward, as follows: Obliquus inferior, Rectus inferior, Rectus superior. Levator palpebrae superioris, and Rectus medialis; while from the anterior end of the nucleus the fibres for the Ciliaris and the Sphincter pupillse take their origin. On emerging from the brain, the nerve is invested with a sheath of pia mater, and enclosed in a prolongation from the arachnoid. It passes between the superior cerebellar and posterior cerebral arteries, and then pierces the dura mater in front of and lateral to the posterior clinoid process, passing between the free and attached borders of the tentorium cerebelli. It runs along the lateral wall of the cavernous sinus, above the other orbital nerves, receiving in its course one or two filaments from the cavernous plexus of the sympathetic, and a communicating branch from the ophthalmic division of the trigemi- nal. It then divides into two branches, which enter the orbit through the superior orbital fissure, betw-een the two heads of the Rectus lateralis. Here the nerve is placed below the trochlear nerve and the frontal and lacrimal branches of the ophthalmic nerve, while the nasociliary nerve is placed between its two rami. The superior ramus, the smaller, passes medialward over the optic nerve, and sup- plies the Rectus superior and Levator palpe- brae superioris. The inferior ramus, the larger, divides into three branches. One passes be- neath the optic nerve to the Rectus medialis; another, to the Rectus inferior; the third and longest runs forward between the Recti inferior and lateralis to the Obliquus inferior. From the last a short thick branch is given off to the lower part of the e -f-: l— - ..r mw ^ 9 [) Fig. 775. — Figure showing the different groups of cells, which constitute, according to Perlia, the nucleus of origin of the oculomotor nerve. (Testut.) 1. Posterior dorsal nucleus. 1'. Pos- terior ventral nucleus. 2. Anterior dorsal nucleus. 2'. Anterior ventral nucleus. 3. Central nucleus. 4. Nucleus of Edinger and Westphal. 5. Antero- internal nucleus. 6. Antero-external nucleus. 8. Crossed fibres. 9. Trochlear nerve, with 9', its nucleus of origin, and 9", its decussation. 10. Third ventricle. M, M. Median line. LEVATOR PALPEBR/E RECTUS SUPERIOR Short ciliary RECTUS MEDIALIS RECTUS INFERIOR OBLIQUUS INFERIOR Fig. 776 — Plan of oculomotor nerve. ciliary ganglion, and forms its short root. All these branches enter the muscles on their ocular surfaces, with the exception of the nerve to the Obliquus inferior which enters the muscle at its posterior border. THE TROCHLEAR NERVE 913 Applied Anatomy. — -Paralysis of the oculomotor nerve may be the result of many causes, such as cerebral disease; or conditions causing pressure on the cavernous sinus; or periostitis of the bones entering into the formation of the superior orbital fissure. It results, when complete, in (1) ptosis, or drooping of the upper eyelid, in consequence of the Levator palpebrae superioris being paralyzed; (2) external strabismus, on account of the unopposed action of the Rectus lateralis and Obliquus superior, which are not supplied by the oculomotor nerve and are there- fore not paralyzed; (3) dilatation of the pupil, because the Sphincter pupillae is paralyzed; (4) loss of power of acconnnodation and of contraction on exposm-e to light, as the Sphincter pupillae and the Ciliaris are paralyzed; (5) shght prominence of the eyeball, owing to most of its muscles being relaxed; and (6) the patient will complain of the resulting diplopia, or double vision, the false image being higher than the true, and the separation of the two images increasing with medial movements. Occasionally paralysis may affect only a part of the nerve — that is to say, there may be, for example, a dilated and fixed pupil, with ptosis, but no other signs. Irritation of the nerve causes spasm of one or other of the muscles supplied by it; thus, there may be internal strabismus from spasm of the Rectus medialis; accommodation for near objects only, from spasm of the Ciharis; or miosis (contraction of the pupil) from irritation of the Sphincter pupillae. The oculomotor nerve is particularly liable to become involved in a syphilitic periarteritis as it leaves the base of the brain, when passing between the posterior cerebral and superior cere- bellar arteries; associated with locomotor ataxia various partial or complete paralyses of the nerve are often seen. THE TROCHLEAR NERVE (N. TROCHLEARIS; FOURTH NERVE) (Fig. 777). The trochlear nerve, the smallest of the cerebral nerves, supplies the Obhquus superior oculi. It arises from a nucleus situated in the floor of the cerebral aqueduct, opposite the upper part of the inferior coUiculus. From its origin it runs downward through the tegmentum, and then turns backward into the upper part of the anterior medul- lary velum. Here it decussates with its fellow of the opposite side and emerges from the surface of the velum at the side of the frenulum veli, immediately behind the inferior colliculus. The nerve is directed across the brach- ium conjunctiva cerebelli, and then winds forward around the cerebral peduncle, immediately above the pons, pierces the dura mater in the free border of the ten- torium cerebelli, just behind, and lateral to, the posterior clinoid process, and passes forward in the lateral wall of the cavernous sinus, between the oculomotor nerve and the ophthalmic division of the trigeminal. It crosses the oculomotor nerve, and enters the orbit through the superior orbital fissure. It now becomes the highest of all the nerves, and lies medial to the frontal nerve. In the orbit it passes medialward, above the origin of the Levator palpebrae superioris, and finally enters the orbital surface of the Obliquus superior. In the lateral wall of the cavernous sinus the trochlear nerve forms communica- tions with the ophthalmic division of the trigeminal and with the cavernous plexus 58 Motor root Sensory root' Recurrent filament to dura mater Fig. 777. — Nerves of the orbit. Seen from above. 914 NEUROLOGY of the sympathetic. In the superior orbital fissure it occasionally gives off a branch to the lacrimal nerve. It gives off a recurrent branch which passes back- ward between the layers of the tentorium cerebelli and divides into two or three filaments which may be traced as far as the wall of the transverse sinus. Applied Anatomy. — When the trochlear nerve is paralyzed there is loss of function in the Obhquus superior, so that the patient is unable to turn his eye downward and outward. Should the patient attempt to do this, the eye of the affected side is rotated inward, producing diplopia or double vision. Single vision exists in the whole of the field so long as the eyes look above the horizontal plane, but diplopia occurs on looking downward. To counteract this the patient holds his head forward, and also inchnes it to the sound side. THE TRIGEMINAL NERVE (N. TRIGEMINUS; FIFTH OR TRIFACIAL NERVE). The trigeminal nerve is the largest cerebral nerve and is the great sensory nerve of the head and face, and the motor nerve of the muscles of mastication. It emerges from the side of the pons, near its upper border, by a small motor and a large sensory root — the former being situated in front of and medial to the latter. Motor Root. — The fibres of the motor root arise from two nuclei, a superior and an inferior. The superior nucleus consists of a strand of cells occupying the whole length of the lateral portion of the gray substance of the cerebral aqueduct. The inferior or chief nucleus is situated in the upper part of the pons, close to its dorsal surface, and along the line of the lateral margin of the rhomboid fossa. The fibres from the superior nucleus constitute the mesencephalic root : they descend through the mesencephalon, and, entering the pons, join with the fibres from the lower nucleus, and the motor root, thus formed, passes forward through the pons to its point of emergence. Sensory Root. — The fibres of the sensory root arise from the cells of the semilunar ganglion which lies in a cavity of the dura mater near the apex of the petrous part of the temporal bone. They pass backward below the superior petrosal sinus and tentorium cerebelli, and, entering the pons, divide into upper and lower roots. The upper root ends partly in a nucleus which is situated in the pons lateral to the lower motor nucleus, and partly in the locus caeruleus; the lower root descends through the pons and medulla oblongata, and ends in the upper part of the sub- stantia gelatinosa of Rolando. This lower root is sometimes named the spinal root of the nerve. Medullation of the fibres of the sensory root begins about the fifth month of fetal life, but the whole of its fibres are not medullated until the third month after birth. The semilunar ganglion (ganglion semilunare [Gasseri]; Gasserian ganglion) occu- pies a cavity (cavum Meckelii) in the dura mater covering the trigeminal impression near the apex of the petrous part of the temporal bone. It is somewhat crescentic in shape, with its convexity directed forward : medially, it is in relation with the inter- nal carotid artery and the posterior part of the cavernous sinus. The motor root runs in front of and medial to the sensory root, and passes beneath the ganglion; it leaves the skull through the foramen ovale, and, immediately below this foramen, joins the mandibular nerve. The greater superficial petrosal nerve lies also underneath the ganglion. The ganglion receives, on its medial side, filaments from the carotid plexus of the sympathetic. It give oft' minute branches to the tentorium cerebelli, and to the dura mater in the middle fossa of the cranium. From its convex border, which is directed forward and lateralward, three large nerves proceed, viz., the ophthalmic, maxillary, and mandibular. The ophthalmic and maxillary consist exclusively of sensory fibres; the mandibular is joined outside the cranium by the motor root. 77/A' TRIGEMINAL NERVE 915 Associated with the three (Ii\isioiis of the tri<;'eniiiuil nerve are four small ganglia. The ciliary ganglion is connected with the o])htlialmic nerve; the sphenopalatine ganglion with the maxillary nerve; and the otic and submaxillary ganglia with the mandibular nerve. All four receive sensory filaments from the trigeminal, and motor and sym])athetic filaments from various sources; these filaments are called the roots of the ganglia. The ophthalmic nerve (?;. ophthalmicAis) (Figs. 777, 778), or first division of the trigeminal, is a sensory nerve. It supplies branches to the cornea, ciliary body, and iris; to the lacrimal gland and conjunctiva; to the part of the mucous membrane of the nasal cavity; and to the skin of the eyelids, eyebrow, forehead, and nose. It is the smallest of the three divisions of the trigeminal, and arises from the upper part of the semilunar ganglion as a short, flattened band, about 2.5 cm. long, which passes forward along the lateral wall of the cavernous sinus, below the oculomotor and trochlear nerves; just before entering the orbit, through the supe- rior orbital fissure, it divides into three branches, lacrimal, frontal, and nasociliary. Internal carotid artery Upper division of and carotid plexus oculomotor nerve Fig. 778. — Nerves of the orbit, and the ciliary ganghon. Side view. The ophthalmic nerve is joined by filaments from the cavernous plexus of the sympathetic, and communicates with the oculomotor, trochlear, and abducent nerves; it gives off a recurrent filament which passes between the layers of the tentorium. The Lacrimal Nerve {n. lacrimalis) is the smallest of the three branches of the ophthalmic. It sometimes receives a filament from the trochlear nerve, but this is possibly derived from the branch which goes from the ophthalmic to the troch- lear nerve. It passes forward in a separate tube of dura mater, and enters the orbit through the narrowest part of the superior orbital fissure. In the orbit it runs along the upper border of the Rectus lateralis, with the lacrimal artery, and com- municates with the zygomatic branch of the maxillary nerve. It enters the lacrimal gland and gives oflF several filaments, which supply the gland and the conjunctiva. Finally it pierces the orbital septum, and ends in the skin of the upper eyelid, joining with filaments of the facial nerve. The lacrimal nerve is occasionally absent, and its place is then taken by the zygomaticotemporal branch of the max- illary. Sometimes the latter branch is absent, and a continuation of the lacrimal is substituted for it. 916 NEUROLOGY The Frontal Nerve {n. frontalis) is the largest branch of the ophthalmic, and may be regarded, both from its size and direction, as the continuation of the nerve. It enters the orbit through the superior orbital fissure, and runs forward between the Levator palpebrae superioris and the periosteum. Midway between the apex and base of the orbit it divides into two branches, supratrochlear and supraorbital. The supratrochlear nerve {n. supratrochharis) , the smaller of the two, passes above the pullej^ of the Obliquus superior, and gives off a descending filament, to join the infratrochlear branch of the nasociliarj^ nerve. It then escapes from the orbit between the pulley of the Obliquus superior and the supraorbital foramen, curves up on to the forehead close to the bone, ascends beneath the Corrugator and Frontalis, and dividing into branches which pierce these muscles, it supplies the skin of the lower part of the forehead close to the middle line and sends filaments to the conjunctiva and skin of the upper eyelid. The supraorbital nerve (n. supraorhitalis) passes through the supraorbital foramen, and gives off, in this situation, palpebral filaments to the upper eyelid. It then ascends upon the forehead, and ends in two branches, a medial and a lateral, which supply the integument of the scalp, reaching nearly as far back as the lamb- doidal suture; they are at first situated beneath the Frontalis, the medial branch perforating the muscle, the lateral branch the galea aponeurotica. Both branches supply small twigs to the pericranium. The Nasociliary Nerve {n. nasociliaris; nasal nerve) is intermediate in size between the frontal and lacrimal, and is more deeply placed. It enters the orbit between the two heads of the Rectus lateralis, and betw^een the superior and inferior rami of the oculomotor nerve. It passes across the optic nerve and runs obliquely beneath the Rectus superior and Obliquus superior, to the medial wall of the orbital cavity. Here it passes through the anterior ethmoidal foramen, and, entering the cavity of the cranium, traverses a shallow groove on the lateral margin of the front part of the cribriform plate of the ethmoid bone, and runs down, through a slit at the side of the crista galli, into the nasal cavity. It supplies internal nasal branches to the mucous membrane of the front part of the septum and lateral w^all of the nasal cavity. Finally, it emerges, as the external nasal branch, between the lower border of the nasal bone and the lateral nasal cartilage, and, passing down beneath the Nasalis muscle, supplies the skin of the ala and apex of the nose. The nasociliary nerve gives off the following branches, viz. : the long root of the ciliary ganglion, the long ciliary, and the ethmoidal nerves. The long root of the ciliary ganglion {radix longa ganglii ciliaris) usually arises from the nasociliary between the two heads of the Rectus lateralis. It passes forward on the lateral side of the optic nerve, and enters the postero-superior angle of the ciliary ganglion; it is sometimes joined by a filament from the cavernous plexus of the sympathetic, or from the superior ramus of the trochlear nerve. The long ciliary nerves (nn. ciliares longi), two or three in number, are given off from the nasociliary, as it crosses the optic nerve. They accompany the short ciliary nerves from the ciliary ganglion, pierce the posterior part of the sclera, and running forward between it and the choroid, are distributed to the Ciliaris muscle, iris, and cornea. The infratrochlear nerve (n. infratrocJilearis) is given off from the nasociliary just before it enters the anterior ethmoidal foramen. It runs forward along the upper border of the Rectus medialis, and is joined, near the pulley of the Obliquus superior, by a filament from the supratrochlear nerve. It then passes to the medial angle of the eye, and supplies the skin of the eyelids and side of the nose, the conjunctiva, lacrimal sac, and caruncula lacrimalis. The ethmoidal branches {nn. ethmoidales) supply the ethmoidal cells; the posterior branch leaves the orbital cavity through the posterior ethmoidal foramen and gives some filaments to the sphenoidal sinus. THE TRIGEMINAL NERVE 917 The Ciliary Ganglion (gdiu/lion cillare; ojihtluthtilc or lenticular gamjlion) (Figs. 776, 77S). — The ciliary ganglion is a small, quadrangular, flattened ganglion, of a reddish-gray color, and about the size of a pin's head; it is situated at the back part of the orbit, in some loose fat between the optic nerve and the Rectus lateralis muscle, lying generall}' on the lateral side of the ophthalmic artery. Its roots are three in number, and enter its posterior border. One, the long or sensory root, is derived from the nasociliary nerve, and joins its postero-superior angle. The second, the short or motor root, is a thick nerve (occasionally divided into two parts) derived from the branch of the oculomotor nerve to the Obliquus inferior, and connected with the postero-inferior angle of the ganglion. The third, the sympathetic root, is a slender filament from the cavernous plexus of the sym- pathetic; it is frequently blended with the long root. According to Tiedemann, the ciliary ganglion receives a twig of communication from the sphenopalatine ganglion. Its branches are the short ciliary nerves. These are delicate jfilaments, from six to ten in number, which arise from the forepart of the ganglion in two bundles connected with its superior and inferior angles; the Tower bundle is the larger. They run forward with the ciliary arteries in a wavy course, one set above and the other below the optic nerve, and are accompanied by the long ciliary nerves from the nasociliary. They pierce the sclera at the back part of the bulb of the eye, pass forward in delicate grooves on the inner surface of the sclera, and are distributed to the Ciliaris muscle, iris, and cornea. Tiedemann has described a small branch as penetrating the optic nerve with the arteria centralis retinae. The maxillary nerve {n. maxillaris; superior maxillary nerve) (Fig. 779), or second division of the trigeminal, is a sensory nerve. It is intermediate, both in position and size, between the ophthalmic and mandibular. It begins at the middle of the semilunar ganglion as a flattened plexiform band, and, passing horizontally forward, it leaves the skull through the foramen rotundum, where it becomes more cylindrical in form, and firmer in texture. It then crosses the pterygopalatine fossa, inclines lateralward on the back of the maxilla, and enters the orbit through the inferior orbital fissure; it traverses the infraorbital groove and canal in the floor of the orbit, and appears upon the face at the infraorbital foramen. '^ At its termination, the nerve lies beneath the Quadratus labii superioris, and divides into a leash of branches which spread out upon the side of the nose, the lower eyelid, and the upper lip, joining with filaments of the facial nerve. Branches. — Its branches may be divided into four groups, according as they are given off in the cranium, in the pterygopalatine fossa, in the infraorbital canal, or on the face. In the Cranium Middle meningeal. [ Zygomatic. In the Pterygopalatine Fossa . < Sphenopalatine. { Posterior superior alveolar. T ^1 T J 1 •. 1 /-( 1 ( Anterior superior alveolar. In the Intraorbital Canal . . i tv/t-jji • ^ i I Middle superior alveolar. f Inferior palpebral. On the Face <^ External nasal. [ Superior labial. The Middle Meningeal Nerve (w. menijigeus medius; meningeal or dural branch) is given off from the maxillary nerve directly after its origin from the semilunar ganglion; it accompanies the middle meningeal artery and supplies the dura mater. The Zygomatic Nerve {n. zygomaticus; temporomalar nerve; orbital nerve) arises in the pterygopalatine fossa, enters the orbit by the inferior orbital fissure, * After it enters the infraorbital canal, the nerve is frequently called the infraorbital. 918 NEUROLOGY and divides at the back of that cavity into two branches, zygomaticotemporal and zygomaticofacial. The zygomaticotemporal branch (raiNVs zygoviaticotemyorcdw; temyoral branch) runs along the lateral wall of the orbit in a groove in the zygomatic bone, receives a branch of comm.unication from the lacrimal, and, passing through a foramen in the zygomatic bone, enters the temporal fossa. It ascends between the bone, and substance of the Temporalis muscle, pierces the temporal fascia about 2.5 cm. above the zygomatic arch, and is distributed to the skin of the side of the fore- head, and communicates with the facial nerve and with. the auriculotemporal branch of the mandibular nerve. As it pierces the temporal fascia, it gives off a slender twig, which runs between the two laj^ers of the fascia to the lateral angle of the orbit. Sensory root Motor root A uriculotemporcd nerve Fig. 779. — Distribution of the maxillary and mandibular nerves, and the submaxillary ganghon. The zygomaticofacial branch (ramus zycjomaiicofacialis; malar branch) passes along the infero-lateral angle of the orbit, emerges upon the face through a foramen in the zygomatic bone, and, perforating the Orbicularis oculi, supplies the skin on the prominence of the cheek. It joins with the facial nerve and wdth the inferior palpebral branches of the maxillary. The Sphenopalatine Branches {nn. sphenopalatini) , two in number, descend to the sphenopalatine ganglion. The Posterior Superior Alveolar Branches {rami alveolares superiores posteriores; -posterior sup)erior dental branches) arise from the trunk of the nerve just before it enters the infraorbital groove; they are generally two in number, but sometimes arise by a single trunk. They descend on the tuberosity of the maxilla and give off THE TRIGEMINAL NERVE 919 several twigs to the gums and neighboring parts of the mucous membrane of the cheek. They then enter the posterior alveolar canals on the infratemporal surface of the maxilla, and, passing from behind forward in the substance of the bone, communicate with the middle superior alveolar nerve, and give ofi' branches to the lining membrane of the maxillary sinus and three twigs to each molar tooth; these twigs enter the foramina at the apices of the roots of the teeth. The Middle Superior Alveolar Branch (ramus aheolaris superior medius; middle superior dental branch), is given off from the nerve in the posterior part of the infra- orbital canal, and runs downward and forward in a canal in the lateral wall of the maxillary sinus to supply the two premolar teeth. It forms a superior dental plexus with the anterior and posterior superior alveolar branches. The Anterior Superior Alveolar Branch (ramus aheolaris superior anteriores; ante- rior superior dental branch), of considerable size, is given off from the nerve just before its exit from the infraorbital foramen; it descends in a canal in the anterior wall of the maxillary sinus, and divides into branches which supply the incisor and canine teeth. It communicates with the middle superior alveolar branch, and gives off a nasal branch, which passes through a minute canal in the lateral wall of the inferior meatus, and supplies the mucous membrane of the anterior part of the inferior meatus and the floor of the nasal cavity, communicating with the nasal branches from the sphenopalatine ganglion. The Inferior Palpebral Branches (rami palpebrales; inferiores palpebral branches) ascend behind the Orbicularis oculi. They supply the skin and conjunctiva of the lower eyelid, joining at the lateral angle of the orbit with the facial and zygomatico- facial nerves. The External Nasal Branches (rami nasales externi) supply the skin of the side of the nose and of the septum mobile nasi, and join with the terminal twigs of the nasociliary nerve. The Superior Labial Branches (rami labiales superior es; labial branches) , ihelargest and most numerous, descend behind the Quadratus labii superioris, and are dis- tributed to the skin of the upper lip, the mucous membrane of the mouth, and labial glands. They are joined, immediately beneath the orbit, by filaments from the facial nerve, forming with them the infraorbital plexus. Sphenopalatine Ganglion (ganglion sphenopalatinum; ganglion of Meckel) (Fig. 780). — ^The sphenopalatine ganglion, the largest of the ganglia associated with the branches of the trigeminal nerve, is deeply placed in the pterygopalatine fossa, close to the sphenopalatine foramen. It is triangular or heart-shaped, of a reddish- gray color, and is situated just below the maxillary nerve as it crosses the fossa. It receives a sensory, a motor, and a sympathetic root. Its sensory root is derived from two sphenopalatine branches of the maxillary nerve; their fibres, for the most part, pass directly into the palatine nerves; a few, however, enter the ganglion, constituting its sensory root. Its motor root is probably derived from the facial nerve through the greater superficial petrosal nerve and its sympathetic root from the carotid plexus through the deep petrosal nerve. These two nerves join to form the nerve of the pterygoid canal, before their entrance into the ganglion. The greater superficial petrosal nerve (n. petrosus superficialis major; large super- ficial petrosal nerve) is given oft' from the genicular ganglion of the facial nerve; it passes through the hiatus of the facial canal, enters the cranial cavity, and runs forward beneath the dura mater in a groove on the anterior surface of the petrous portion of the temporal bone. It then enters the cartilaginous substance which fills the foramen lacerum, and joining with the deep petrosal branch forms the nerve of the pterygoid canal. The deep petrosal nerve (n. petrosus profundus; large deep petrosal nerve) is given off from the carotid plexus, and runs through the carotid canal lateral to the internal 920 NEUROLOGY carotid artery. It then enters the cartilaginous substance which fills the foramen lacerum, and joins with the greater superficial petrosal nerve to form the nerve of the pterygoid canal. The nerve of the pterygoid canal (?i. ccmalis pterygoidei [Vidii]; Vidian nerve), formed by the junction of the two preceding nerves in the cartilaginous substance which fills the foramen lacerum, passes forward, through the pterygoid canal, with the corresponding artery, and is joined by a small ascending sphenoidal branch from the otic ganglion. Finally, it enters the pterygopalatine fossa, and joins the posterior angle of the pterygopalatine ganglion. Termination of \ -ff, nasopalatine nerve Fig. 780. — The sphenopalatine ganglion and its branches. Branches of Distribution. — These are divisible into four groups, viz., orbital, palatine, posterior, superior nasal, and pharyngeal. The orbital branches (rcuni orbitales; ascending branches) are two or three delicate filaments, wdiich enter the orbit by the inferior orbital fissure, and supply the peri- osteum. According to Luschka, some filaments pass through foramina in the fronto- ethmoidal suture to supply the mucous membrane of the posterior ethmoidal and sphenoidal sinuses. The palatine nerves {nn. jjalatini; descending branches) are distributed to the roof of the mouth, soft palate, tonsil, and lining membrane of the nasal cavity. Most of their fibres are derived from the sphenopalatine branches of the maxillary nerve. They are three in number: anterior, middle, and posterior. The anterior palatine nerve {n. palatinus anterior) descends through the pterygo- palatine canal, emerges upon the hard palate through the greater palatine foramen, and passes forward in a groove in the hard palate, nearly as far as the incisor teeth. It supplies the gums, the mucous membrane and glands of the hard palate, and communicates in front with the terminal filaments of the nasopalatine nerve. While in the pterygopalatine canal, it gives off posterior inferior nasal branches, which enter the nasal cavitj^ through openings in the palatine bone, and ramify THE TRIGEMINAL NERVE 921 over the inferior nasal concha and niichlle and inferior meatuses; at its exit from the canal, a palatine branch is distributed to both surfaces of the soft palate. The middle palatine nerve {n. palatinus medium) emerges thrf)ugh one of the minor palatine canals and distributes branches to the uvula, tonsil, and soft palate. It is occasionally wanting. The posterior palatine nerve (/i. palatinus posterior) descends through the pterygo- palatine canal, and emerges by a separate opening behind the greater palatine foramen; it supplies the soft palate, tonsil, and uvula. The middle and posterior palatine join with the tonsillar branches of the glossopharyngeal to form a plexus (circulus tonsillaris) around the tonsil. The posterior superior nasal branches (rami nasales posteriores superiores) are dis- tributed to the septum and lateral wall of the nasal fossa. They enter the posterior part of the nasal cavity by the sphenopalatine foramen and supply the mucous membrane covering the superior and middle nasal conchse, the lining of the poste- rior ethmoidal cells, and the posterior part of the septum. One branch, longer and larger than the others, is named the nasopalatine nerve. It enters the nasal cavity through the sphenopalatine foramen, passes across the roof of the nasal cavity below the orifice of the sphenoidal sinus to reach the septum, and then runs obliquely downward and forward between the periosteum and mucous membrane of the low^er part of the septum. It descends to the roof of the mouth through the incisive canal and communicates with the corresponding nerve of the opposite side and with the anterior palatine nerve. It furnishes a few filaments to the mucous membrane of the nasal septum. The pharyngeal nerve {pterygopalatine 7ierve) is a small branch arising from the posterior part of the ganglion. It passes through the pharyngeal canal with the pharyngeal branch of the internal maxillary artery, and is distributed to the mucous membrane of the nasal part of the pharynx, behind the auditory tube. The mandibular nerve {n. mandibularis; inferior maxillary nerve) (Figs. 779, 781) supplies the teeth and gums of the mandible, the skin of the temporal region, the auricula, the lower lip, the lower part of the face, and the muscles of mastica- tion; it also supplies the mucous membrane of the anterior two-thirds of the tongue. It is the largest of the three divisions of the fifth, and is made up of two roots : a large, sensory root proceeding from the inferior angle of the semilunar ganglion, and a small motor root (the motor part of the trigeminal), which passes beneath the ganglion, and unites with the sensory root, just after its exit through the foramen ovale. Immediately beneath the base of the skull, the nerve gives off from its medial side a recurrent branch (nervus spinosus) and the nerve to the Pterygoideus internus, and then divides into two trunks, an anterior and a posterior. The Nervus Spinous (recurrent or meningeal branch) enters the skull through the foramen spinosum with the middle meningeal artery. It divides into two branches, anterior and posterior, which accompany the main divisions of the artery and supply the dura mater; the posterior branch also supplies the mucous lining of the mastoid cells; the anterior communicates with the meningeal branch of the maxillary nerve. The Internal Pterygoid Nerve (n. pterygoideus internus) . — The nerve to the Ptery- goideus internus is a slender branch, which enters the deep surface of the muscle; it gives off one or two filaments to the otic ganglion. The anterior and smaller division of the mandibular nerve receives nearly the whole of the fibres of the motor root of the nerve, and supplies the muscles of mastication and the skin and mucous membrane of the cheek. Its branches are the masseteric, deep temporal, buccinator, and external pterygoid. The Masseteric Nerve (/i. massetericus) passes lateralward, above the Pterygoideus externus, in front of the temporomandibular articulation, and behind the tendon of the Temporalis; it crosses the mandibular notch with the masseteric artery. 922 NEUROLOGY to the deep surface of the Masseter, in which it ramifies nearly as far as its anterior border. It gives a filament to the temporomandibular joint. The Deep Temporal Nerves {nn. temporales frofundi) are two in number, anterior and posterior. They pass above the upper border of the Pterygoideus externus and enter the deep surface of the Temporalis. The posterior branch, of small size, is placed at the back of the temporal fossa, and sometimes arises in common with the masseteric nerve. The anterior branch is frequently given off from the buccina- tor nerve, and then turns upward over the upper head of the Pterygoideus externus. Frequently a third or intermediate branch is present. A uriculotemporal Deep temporal Masseteric Splienomandibvlar ligament Inferior alveolar Mylohyoid Lingual Ramus of man- dible (cut) Fig. 781. — The Pterj'goideus externus and the branches of the mandibular nerve in relation to it. The Buccinator Nerve (??. buccinatorus; long buccal nerve) passes forward between the two heads of the Pterygoideus externus, and downward beneath or through the lower part of the Temporalis ; it emerges from under the anterior border of the Masseter, ramifies on the surface of the Buccinator, and unites wdth the buccal branches of the facial nerve. It supplies a branch to the Pterygoideus externus during its passage through that muscle, and may give off the anterior deep temporal nerve. The buccinator nerve supplies the skin over the Buccinator, and the mucous membrane lining its inner surface. External Pterygoid Nerve {n. yterygoideus externus). — ^The nerve to the Ptery- goideus externus frequently arises in conjunction wdth the buccinator nerve, but it may be given off separately from the anterior division of the mandibular nerve. It enters the deep surface of the muscle. The posterior and larger division of the mandibular nerve is for the most part sensory, but receives a few filaments from the motor root. It divides into auriculo- temporal, lingual, and inferior alveolar nerves. THE TRIGEMINAL NERVE 923 The Auriculotemporal Nerve (ii. auriculotemjjoralis) generally arises by two roots, between which the middle meningeal artery ascends. It runs backward beneath the Pterygoideiis externus to the medial side of the neck of the mandible. It then turns upward with the superficial temporal artery, between the auricula and con- dyle of the mandible, under cover of the parotid gland; escaping from beneath the gland, it ascends over the zygomatic arch, and divides into superficial temporal branches. The branches of communication of the auriculotemporal nerve are with the facial nerve and with the otic ganglion. The branches to the facial, usually two in number, pass forward from behind the neck of the mandible and join the facial nerve at the posterior border of the Masseter. The filaments to the otic ganglion are derived from the roots of the auriculotemporal nerve close to their origin. Its branches of distribution are: Anterior auricular. Articular. Branches to the external acoustic meatus. Parotid. Superficial temporal. The anterior auricular branches {nn. auriculares anteriores) are usually two in number; they supply the front of the upper part of the auricula, being distributed principally to the skin covering the front of the helix and tragus. The branches to the external acoustic meatus {n. meatus auditorii externi), two in number, enter the meatus between its bony and cartilaginous portions and supply the skin lining it; the upper one sends a filament to the tympanic membrane. The articular branches consist of one or two twigs which enter the posterior part of the temporomandibular joint. The parotid branches {rami iiarotidei) supply the parotid gland. The superficial temporal branches {rami temporales swperficiales) accompany the superficial temporal artery to the vertex of the skull; they supply the skin of the temporal region and communicate with the facial and zygomaticotemporal nerves. The Lingual Nerve {n. lingualis) supplies the mucous membrane of the anterior two-thirds of the tongue. It lies at first beneath the Pterygoideus externus, medial to and in front of the inferior alveolar nerve, and is occasionally joined to this nerve, by a branch which may cross the internal maxillary artery. The chorda tympani also joins it at an acute angle in this situation. The nerve then passes between the Pterygoideus internus and the ramus of the mandible, and crosses obliquely to the side of the tongue over the Constrictor pharyngis superior and Styloglossus, and then between the Hj^oglossus and deep part of the submaxillary gland ; it finally runs across the duct of the submaxillary gland, and along the tongue to its tip, lying immediately beneath the mucous membrane. Its branches of communication are with the facial (through the chorda tympani), the inferior alveolar and hypoglossal nerves, and the submaxillary ganglion. The branches to the submaxillary ganglion are two or three in number; those connected with the hypoglossal nerve form a plexus at the anterior margin of the Hyoglossus. Its branches of distribution supply the sublingual gland, the mucous membrane of the mouth, the gums, and the mucous membrane of the anterior two-thirds of the tongue; the terminal filaments communicate, at the tip of the tongue, with the hypoglossal nerve. The Inferior Alveolar Nerve {n. aheolaris inferior; inferior dental nerve) is the largest branch of the mandibular nerve. It descends with the inferior alveolar artery, at first beneath the Pterygoideus externus, and then between the sphenomandibular ligament and the ramus of the mandible to the mandibular foramen. It then passes forward in the mandibular canal, beneath the teeth, as far as the mental foramen, where it divides into two terminal branches, incisive and mental. 924 NEUROLOGY The braiielR's of the inferior alveohir nerve are the mylohyoid, dental, incisive, and mental. The mylohyoid nerve (/z. mi/lohyoideus) is derived from the inferior alveolar just before it enters the mandibular foramen. It descends in a groove on the deep surface of the ramus of the mandible, and reaching the under surface of the Mylohyoideus supplies this muscle and the anterior belly of the Digastricus. The dental branches supply the molar and premolar teeth. They correspond in number to the roots of those teeth; each nerve entering the orifice at the point of the root, and supplying the pulp of the tooth; above the alveolar nerve they form an inferior dental plexus. The incisive branch is continued onward within the bone, and supplies the canine and incisor teeth. The mental nerve {n. mentalis) emerges at the mental foramen, and divides beneath the Triangularis muscle into three branches; one descends to the skin of the chin, and two ascend to the skin and mucous membrane of the lower lip; these branches communicate freely with the facial nerve. Two small ganglia, the otic and the submaxillary, are connected with the man- dibular nerve. Fig. .782. — The otic ganglion and its branches. Otic Ganglion {ganglion oticum) (Fig. 782). — The otic ganglion is a small, oval- shaped, flattened ganglion of a reddish-gray color, situated immediately below the foramen ovale; it lies on the medial surface of the mandibular nerve, and surrounds the origin of the nerve to the Pterygoideus internus. It is in relation, laterally, with the trunk of the mandibular nerve at the point where the motor and sensory roots join; medially, with the cartilaginous part of the auditory tube, and the origin of the Tensor veli palatini; ^posteriorly , with the middle meningeal artery. Branches of Communication. — It is connected by two or three short filaments with the nerve to the Pterygoideus internus, from which it may obtain a motor, and possibly a sensory root. It communicates with the glossopharyngeal and facial nerves, through the lesser, superficial petrosal nerve continued from the tympanic plexus, and through this nerve it probably receives a sensory root from the glosso- pharyngeal and a motor root from the facial; its sympathetic root consists of a filament from the plexus surrounding the middle meningeal artery. The ganglion THE TRIGEMINAL NERVE 925 also communicates with the auriculotemporal nerve by a branch which is prob- ably derived from the glossopharyngeal, and wJiich passes to the ganglion, and then through it and auriculotemporal nerve to the i)arotid gland. A slender filament (sphenoidal) ascends from it to the nerve of the Pterygoid canal, and a small branch connects it with the chorda tympani. Its branches of distribution are: a filament to the Tensor tympani, and one to the Tensor veli palatini. The former passes backward, lateral to the auditory tube; the latter arises from the ganglion, near the origin of the nerve to the Ptery- goideus internus, and is directed forward. The fibres of these nerves are, however, mainly derived from the nerve to the Pterygoideus internus. Submaxillary Ganglion (ganglion submaxillare) (Fig. 779). — The submaxillary ganglion is of small size and is fusiform in shape. It is situated above the deep portion of the submaxillary gland, on the hyoglossus, near the posterior border of the Mylohyoideus, and is connected by filaments with the lower border of the lingual nerve. It is suspended from the lingual nerve by two filaments which join the anterior and posterior parts of the ganglion. Through the posterior of these it receives a branch from the chorda tympani nerve which runs in the sheath of the lingual; it communicates with the sympathetic by filaments from the sympathetic plexus around the external maxillary artery. Its branches of distribution are five or six in number; they arise from the lower part of the ganglion, and supply the mucous membrane of the mouth and the duct of the submaxillary gland, some being lost in the submaxillary gland. The branch of communication from the lingual to the forepart of the ganglion is by some regarded as a branch of distribution, through which filaments pass from the gan- glion to the lingual nerve, and by it are conveyed to the sublingual gland and the tongue. Applied Anatomy. — Paralysis of the trigeminal nerve causes anesthesia of the corresponding anterior half of the scalp, and of the face, excepting over a small area near the angle of the man- dible supplied by the cervical nerves, and of the cornea and conjunctiva, and of the mucous membrane of the nose, mouth, and tongue. Taste is lost (ageusia) on the affected side. Paralysis and atrophy follow in the Temporalis, Masseter, and Pterygoidei, possibly also in the Tensor tympani; when the mouth is opened the mandible is thrust over toward the paralyzed side. Inter- ference with the secretion of the tears, the nasal mucus, and the sahva, causes dryness of the corresponding mucous membranes. The sense of smell is gradually lost on the affected side from the trophic changes that follow in the nasal mucous membrane. Inflammation of the eye- ball, under these circumstances known as neuroparalytic ophthalmia, is not rare, and is due to the dryness and insensitiveness of the conjimctiva; it is not a "trophic" phenomenon, but depends on the occurrence and neglect of traumatic inflammation in the anesthetic eye. Trigeminal Nerve Reflexes. — Pains referred to various branches of the trigeminal nerve are of very frequent occurrence, and should always lead to a careful examination in order to discover a local cause. As a general rule the diffusion of pain over the various branches of the nerve is at first confined to one only of the main divisions, and the search for the causative lesion should always commence with a thorough examination of all those parts which are supplied by that division; although in severe cases pain may radiate over the branches of the other main divisions. The commonest example of this condition is the neuralgia which is so often associated with dental caries — here, although the tooth itself may not appear to be painful, the most distressing referred pains may be experienced, and these are at once reUeved by treatment directed to the affected tooth. Many other examples of trigeminal reflexes could be quoted, but it will be sufficient to mention the more common ones. Dealing with the ophthalmic nerve, severe supraorbital pain is com- monly associated with acute glaucoma or with disease of the frontal or ethmoidal air cells. Malig- nant growths or empyema of the maxillary antrum, or unhealthy conditions about the inferior conchae or the septum of the nose, are often found giving rise to "second division" neuralgia, and should be always looked for in the absence of dental disease in the maxilla. It is on the mandibular nerve, however, that some of the most striking reflexes are seen. It is quite common to meet with patients who complain of pain in the ear, in whom there is no sign of aural disease, and the cause is usually to be found in a carious tooth in the mandible. More- over, with an ulcer or cancer of the tongue, often the first pain to be experienced is one which radiates to the ear and temporal fossa, over the distribution of the auriculotemporal nerve. 926 NEUROLOGY The trigeminal nerve is often the seat of severe neuralgia for which no local cause can be dis- covered; each of the three divisions has been divided, or a portion of the nerve excised, for this affection, usually, however, with only temporary relief. The supraorbital nerve may be exposed by making an incision 4 cm. in length along the supraorbital margin, below the eyebrow which is to be drawn upward, the centre of the incision corresponding to the supraorbital notch. The skin and Orbicularis oculi having been divided, the nerve can be easily found emerging from the notch, and lying in some loose cellular tissue. It should be drawn up by a blunt hook and 1.25 cm. of it resected, or the nerve can be injected with absolute alcohol. The infraorbital nerve has been divided at its exit by an incision on the cheek; or the floor of the orbit has been exposed, the infraorbital canal opened up, and the anterior part of the nerve resected; or the whole nerve, together with sphenopalatine ganglion as far back as the foramen rotundum may be removed, but even then a return of the neuralgia in some other branches of the trigeminal nerve is the rule rather than the exception. The operation is performed as follows: the maxilla is first exposed by a T-shaped incision, one hmb passing along the lower margin of the orbit, the other from the centre of this vertically down the cheek to the angle of the mouth. The nerve is to be found, divided, and a piece of silk tied to it as a guide. A smaU trephine (half- inch) is applied to the bone, below, but including the infraorbital foramen, and the maxiUary sinus opened. The trephine is then applied to the posterior wall of the sinus, and the pterygo- palatine fossa exposed. The infraorbital canal is opened up from below, and the nerve drawn down into the trephine hole, and held on the stretch by means of the piece of silk; it is severed with fine curved scissors as near the foramen rotundum as possible, any branches coming off from the ganglion being also divided. Fig. 783. — Diagram showing cutaneous areas of face and scalp. The inferior alveolar nerve can be reached by a transverse incision over the ramus of the man- dible placed so as to avoid injury to the facial nerve; the Masseter having been divided, a small trephine is apphed to the ramus immediately beneath the mandibular notch, and, when the bone has been removed, the nerve is found lying on the Pterygoideus internus just as it enters the mandibular foramen, and it can here be resected. The lingual nerve is occasionally divided with the view of reheving the pain in cancerous disease of the tongue. This may be done in that part of its course where it hes below and behind the last molar tooth. If a line be drawn from the middle of the crown of the last molar tooth to the angle of the mandible it will cross the nerve, which hes about 1.25 cm. behind the tooth, parallel to the bulging alveolar ridge on the inner side of the body of the bone. The tongue should be pulled forward and over to the opposite side, when the nerve can be seen standing out as a firm cord under the mucous membrane by the side of the tongue, and after division of the mucous membrane can be easily seized with a hook and a portion excised. This is a simple enough operation on the cadaver, but when the disease is extensive and has extended to the floor of the mouth, as is generally the case when the division is required, the operation is not practicable. THE ABDUCENT NERVE 927 In severe cases of neuralgia of the trigeminal nerve, the semilunar ganglion has been removed in whole or in part with a considerable measure of success. Rose was the first to perform this operation; and he reached the ganglion by trcjihining the base of the skull in the position of the foramen ovale, after dividing the zygomatic arch, in front and behind, and turning it and the Massetcr downward, and cutting through the coronoid process of the mandible, and turning it and the Temporalis upward. A more efficient method appears to be that known as the Krause- Hartley method. The bone forming the temporal fossa having been removed to a sufficient extent, the dura mater beneath the temporal lobe of the brain is gradually raised from the middle fossa, until the foramen spinosum, with the middle meningeal artery passing through it, is exposed. This vessel is to be ligatured in two places, and divided between the ligatures; and then by further raising the diu-a mater, the foramina ovale and rotundum will be exposed, with the mandibular and maxillary nerves passing through them. These nerves are to be clearly defined and divided. The dura mater is then to be raised from the ganglion, when the ophthalmic nerve will be exposed and must be divided, and the gangfion, by means of a little careful dissection, raised from its bed and removed. In some cases where the neuralgia has been limited to the maxillary nerve an intracranial resection of that nerve alone has been performed with gi-eat success. In other cases where the disease has not affected the ophthalmic division, resection of the lateral half of the ganglion only, with the maxillary and mandibular nerves, has been performed, thus leaving the sensory nerve supply to the cornea intact. The motor root is usually resected with the man- dibular nerve, leading to complete paralysis of the muscles of mastication on that side. THE ABDUCENT NERVE (N. ABDUCENS; SIXTH NERVE) (Fig. 778). The abducent nerve supplies the Rectus lateraHs oculi. Its fibres arise from a small nucleus situated in the upper part of the rhomboid fossa, close to the middle line and beneath the colliculus facialis. They pass down- ward and forward through the pons, and emerge in the furrow between the lower border of the pons and the upper end of the pyramid of the medulla oblongata. From the nucleus of the sixth nerve, fibres pass through the medial longitudinal fascic- ulus to the oculomotor nerve of the opposite side, along which they are carried to the Rectus medialis. The Rectus lateralis of one eye and the Rectus medialis of the other may therefore be said to receive their nerves from the same nucleus (Fig. 784). The nerve pierces the dura mater on the dorsum sellae of the sphenoid, runs through a notch in the bone below the posterior clinoid process, and passes forward through the cavernous sinus, on the lateral side of the internal carotid artery. It enters the orbit through the superior orbital fissure, above the ophthalmic vein, from which it is sepa- rated by a lamina of dura mater. It then passes between the two heads of the Rectus lateralis, and enters the ocular surface of that muscle. The abducent nerve is joined by sev- eral filaments from the carotid and cavernous plexuses, and by one from the ophthalmic nerve. The oculomotor, trochlear, ophthalmic, and abducent nerves bear certain relations to each other in the cavernous sinus,- at the superior orbital fissure, and in the cavity of the orbit, as follows: Fig. 784.- Figure showing the mode of inner- vation of the Recti medialis and laterahs of the eye (after Duval and Laborde). (Testut.) a. Left eyeball, b. Right eyeball. 1. Rectus late- ralis. 2. Rectus medialis. 3. Rhomboid fossa. 4. Nucleus of abducent nerve. 5. Nucleus of oculomotor nerve. 6. Abducent nerve. 7. Nerve to Rectus medialis arising from the nucleus of the oculomotor of the same side. 7'. Nerve to Rectus medialis arising from the nucleus of the abducent of the opposite side. 8. Decussation of the fibres of the abducent nerve to the Rectus medialis. 928 NEUROLOGY In the cavernous sinus (Fig. 785), the oculomotor, trochlear, and ophthalmic nerves are placed in the lateral wall of the sinus, in the order given, from above downward. The abducent nerve lies at the lateral side of the internal carotid artery. As these nerves pass forward to the superior orbital fissure, the oculo- motor and ophthalmic divide into Internal carotui artery branches, and the abduccut nerve Cavernous sinus ' ^ i . . i • approaches the others; so that their relative positions are considerably- changed. In the superior orbital fissure (Fig. 786), the trochlear nerve and the frontal and lacrimal divisions of the ophthalmic lie in this order from the medial to the lateral side upon the same plane; they enter the cavity of the orbit above the muscles. The remaining nerves enter the orbit be- tween the two heads of the Rectus lateralis. The superior division of the oculomotor is the highest of these; beneath this lies the nasociliary branch of the ophthalmic; then the inferior division of the oculomotor; and the abducent lowest of all. Oculomotor iv Trochlear nerve O'phtlialiidc nerve Abducent nerve Maxillary nerve Fia. 785. -Oblique section through the right cavernous sinus. Frontal nerve Sup. ruTnus of oculomotor nerve Suj}. orbital fissure Lacrimal nerve \ Levator palpebrce I Nasociliary nerve I Trochlear nerve Trochlea Abducent neri'i Inf. ramus of oculomotor Inf. orbital Optic foramen nerve fissure Fig. 786. — Dissection showing origins of right ocular muscles, and nerves entering by the superior orbital fissure. In the orbit, the trochlear, frontal, and lacrimal nerves lie immediately beneath the periosteum, the trochlear nerve resting on the Obliquus superior, the frontal on the Levator palpebrae superioris, and the lacrimal on the Rectus lateralis. The superior division of the oculomotor nerve lies unmediately beneath the Rectus superior, while the nasociliary nerve crosses the optic nerve to reach the medial wall of the orbit. Beneath these is the optic nerve, surrounded in front by the ciliary nerves, and having the ciliary ganglion on its lateral side, between it and the Rectus lateralis. Below the optic nerve are the inferior division of the oculomotor, and the abducent, the latter lying on the medial surface of the Rectus lateralis. THE FACIAL NERVE 929 Applied Anatomy. — The abducent nerve is frequently involved in fractures of the base of the skull. The result of paralysis of this nerve is medial or convergent squint. Diplopia is also present. When injured so that its function is destroyed there is, in addition to the paralysis of the Rectus lateralis oculi, often a certain amount of contraction of the pupil, because some of the sympathetic fibres to the Dilatator pupillae muscle are conveyed through this nerve. THE FACIAL NERVE (N. FACIALIS; SEVENTH NERVE) (Figs. 787, 789). The facial nerve consists of a motor and a sensory part, the latter being frequently described under the name of the nemis intermedins {yars intermedii of Wrisberg) (Fig. 787). The two parts emerge at the lower border of the pons in the recess between the olive and the restiform body, the motor part being the more medial; immediately to the lateral side of the sensory part is the acoustic nerve. To Acoustic Com. with auric, branch of vagus Genicular oanglion Greaterjuperficial Petrpsgi er _supei yic/^^^ 'Deep petrosal Nerve of "pteryg. canal Otic ganglion Lingual, To posterior belli/ of DIGASTRICUS TO STYLOHYOiDEUS Mccndibular I Cervical Fig. 787. — Plan of the facial nerve. The course of the sensory fibres is represented by the blue Unes. The motor part supplies the muscles of the face, scalp, and auricular, the Buc- cinator and Platysma, the Stapedius, the Stylohyoideus, and posterior belly of the Digastricus; it also contains some fibres which constitute the vasodilator nerves of the submaxillary and sublingual glands, and are conve^^ed to these glands through the chorda tympani nerve. The sensory part contains the fibres of taste for the anterior two-thirds of the tongue. The motor root arises from a nucleus which lies deeply in the reticular formation of the lower part of the pons. This nucleus is situated above the nucleus ambiguus, behind the superior olivary nucleus, and medial to the spinal tract of the trige- minal nerve. From this origin the fibres pursue a curved course in the substance 59 930 NEUROLOGY of the pons. The}' first pass backward and medialward toward the rhomboid fossa, and, reaching the posterior end of the nucleus of the abducent nerve, run upward close to the middle line beneath the colliculus fascialis. At the anterior end of the nucleus of the abducent nerve they make a second bend, and run down- ward and forward through the pons to their point of emergence between the olive and the restiform body. Some fibres from the nucleus of the oculomotor nerve are said to descend in the medial longitudinal fasciculus and join the motor root of the facial nerve before it leaves the pons. These fibres are believed to supply the Orbicularis oculi, Cor- rugator, and Frontalis, since these muscles have been observed to escape paralysis in lesions of the motor nucleus of the facial nerve. ^ The sensory root arises from the genicular ganglion, which is situated on the genic- ulum of the facial nerve in the facial canal, behind the hiatus of the canal. The cells of this ganglion are unipolar, and the single process divides in a T-shaped manner into central and peripheral branches. The central branches leave the trunk of the facial nerve in the internal acoustic meatus, and form the sensory root; the peripheral branches are continued into the chorda tympani and greater super- ficial petrosal nerves. Entering the brain at the lower border of the pons between the motor root and the acoustic nerve, the fibres of the sensory root pass into the substance of the medulla oblongata and end in the upper part of the terminal nucleus of the glossopharyngeal nerve and in the fasciculus solitarius. From their superficial attachments to the brain, the two roots of the facial nerve pass lateralward and forward with the acoustic nerve to the internal acoustic meatus. In the meatus the motor root lies in a groove on the upper and anterior surface of the acoustic nerve, the sensory root being placed between them. At the bottom of the meatus, the facial nerve enters the facial canal, which it traverses to its termination at the stylomastoid foramen. It is at first directed lateralward between the cochlea and vestibule toward the medial wall of the tympanic cavity; it then bends suddenly backw^ard and arches downward behind the tympanic cavity to the stylomastoid foramen. The point w^here it changes its direction is named the geniculum ; it presents a reddish ganglif orm swelling, the genicular ganglion {ganglion geniculi; geniculate ganglion; nucleus of the sensory root External superficial petrosal Branch to join lesser superficial petrosal Greater superficial petrosal Genicular ganglimi Facial Acoustic Fig. 788. — The course and connections of the facial nerve in the temporal bone. oj the nerve) (Fig. 788). On emerging from the stylomastoid foramen, the facial nerve runs forw^ard in the substance of the parotid gland, crosses the external carotid artery, and divides behind the ramus of the mandible into branches, from which numerous offsets are distributed over the side of the head, face, and upper part of the neck, supplying the superficial muscles in these regions. The branches and their offsets unite to form the parotid plexus. Branches of Communication. — The branches of communication of the facial nerve may be arranged as follows: 1 See footnote, p. 852. THE FACIAL NERVE 931 In the internal acoustic meatus . At the genicular ganglion In the facial canal . At its exit from the stylo- mastoid foramen . Behind the ear On the face In the neck With the acoustic nerve. With the sphenopalatine ganglion by the greater superficial petrosal nerve. With the otic ganglion by a branch which joins the lesser superficial petrosal nerve. With the sympathetic on the middle meningeal artery. With the auricular branch of the vagus. With the glossopharyngeal. With the vagus. I With the great auricular, [with the auriculotemporal. With the lesser occipital. With the trigeminal. With the cutaneous cervical. In the internal acoustic meatus some minute filaments pass from the facial to the acoustic nerve. The greater superficial petrosal nerve {large superficial petrosal nerve) arises from the genicular ganglion, and consists chiefly of sensory branches which are dis- tributed to the mucous membrane of the soft palate; but it probably contains a few motor fibres which form the motor root of the sphenopalatine ganglion. It passes forward through the hiatus of the facial canal, and runs in a sulcus on the anterior surface of the petrous portion of the temporal bone beneath the semilunar ganglion, to the foramen lacerum. It receives a twig from the tympanic plexus, and in the foramen is joined by the deep petrosal, from the sympathetic plexus on the internal carotid artery, to form the nerve of the pterygoid canal which passes forward through the pterygoid canal and ends in the sphenopalatine ganglion. The genicular ganglion is connected with the otic ganglion by a branch which joins the lesser superficial petrosal nerve, and also with the sympathetic filaments accompanying the middle meningeal artery. According to Arnold, a twig passes back from the ganglion to the acoustic nerve. Just before the facial nerve emerges from the stylomastoid foramen, it generally receives a twig from the auricular branch of the vagus. After its exit from the stylomastoid foramen, the facial nerve sends a twig to the glossopharyngeal, and communicates with the auricular branch of the vagus, with the great auricular nerve of the cervical plexus, with the auriculotemporal nerve in the parotid gland, and with the lesser occipital behind the ear; on the face with the terminal branches of the trigeminal, and in the neck with the cutaneous cervical nerve. Branches of Distribution. — The branches of distribution (Fig. 787) of the facial nerve may be thus arranged: With the facial canal At its exit from the stylo- mastoid foramen On the face f Nerve to the Stapedius muscle. \ Chorda tympani. ( Posterior auricular. ■I Digastric, t Stylohyoid. Temporal. Zygomatic. Buccal. Mandibular. Cervical. 932 NEUROLOGY The Nerve to the Stapedius in. stapedius: tympanic branch) arises opposite the pyramidal eminence (page 1052); it passes through a small canal in this eminence to reach the muscle. The Chorda Tympani Nerve is gi\'en off from the facial as it passes downward behind the tympanic cavity, about 6 mm. from the stylomastoid foramen. It runs upward and forward in a canal, and enters the tympanic cavity, through an aperture (iter chordae posterius) on its posterior wall, close to the medial surface of the posterior border of the tympanic membrane and on a level M-ith the upper Termination of supratrochlear of infratrochlear of nasociliary Fig. 789. — The nerves of the scalp, face, and side of neck. end of the manubrium of the malleus. It traverses the tympanic cavity, between the fibrous and mucous layers of the tympanic membrane, crosses the manubrium of the malleus, and emerges from the cavity through a foramen situated at the inner end of the petrotympanic fissure, and named the iter chordae anterius {canal of Huguier). It then descends between the Pterygoid eus externus and internus on the medial surface of the spina angularis of the sphenoid, which it sometimes grooves, and joins, at an acute angle, the posterior border of the lingual nerve. It receives a few efferent fibres from the motor root; these enter the submaxillary ganglion, and through it are distributed to the submaxillary and sublingual glands; THE FACIAL NERVE 933 the majority of its fibres are efferent, and are eontinued onward through the mus- cular substance of the tongue to the mucous membrane covering its anterior two-thirds; tliey constitute the ner\'e of taste for tliis portion of the tongue. Before uniting witli tlie Ungual nerve the chorda tympani is joined by a small branch from the otic ganglion. The Posterior Auricular Nerve (??. aiiricularis ■posterior) arises close to the stylo- mastoid foramen, and runs upward in front of the mastoid process; here it is joined by a filament from the auricular branch of the vagus, and communicates with the posterior branch of the great auricular, and with the lesser occipital. As it ascends between the external acoustic meatus and mastoid process it divides into auricular and occipital branches. The auricular branch supplies the Auricularis posterior and the intrinsic muscles on the cranial surface of the auricula. The occipital branch, the larger, passes backward along the superior nuchal line of the occipital bone, and supplies the Occipitalis. The Digastric Branch {ramus digasfricus) arises close to the stylomastoid foramen, and divides into several filaments, which supply the posterior belly of the Digas- tricus; one of these filaments joins the glossopharyngeall nerve. The Stylohyoid Branch (ramus stylohyoideus) frequently arises in conjunction with the digastric branch ; it is long and slender, and enters the Stylohyoideus about its middle. The Temporal Branches {rami temporales) cross the zygomatic arch to the temporal region, supplying the Auriculares anterior and superior, and joining with the zygo- maticotemporal branch of the maxillary, and with the auriculotemporal branch of the mandibular. The more anterior branches supply the Frontalis, the Orbicu- laris oculi, and the Corrugator, and join the supraorbital and lacrimal branches of the ophthalmic. The Zygomatic Branches {rami zygomatici; malar branches) run across the zygo- matic bone to the lateral angle of the orbit, where they supply the Orbicularis oculi, and join with filaments from the lacrimal nerve and the zygomaticofacial branch of the maxillary nerve. The Buccal Branches {rami buccales; infraorbital branches), of larger size than the rest, pass horizontally forw^ard to be distributed below the orbit and around the mouth. The superficial branches run beneath the skin and above the superficial muscles of the face, which they supply: some are distributed to the Procerus, joining at the medial angle of the orbit with the infratrochlear and nasociliary branches of the ophthalmic. The deep branches pass beneath the Zygomaticus and the Quadratus labii superioris, supplying them and forming an infraorbital plexus w^ith the infraorbital branch of the maxillary nerve. These branches also supply the small muscles of the nose. The lower deep branches supply the Buccinator and Orbicularis oris, and join with filaments of the buccinator branch of the mandibular nerve. The Mandibular Branch {ramus marginalis mandibulae) passes forward beneath the Platysma and Triangularis, supplying the muscles of the lower lip and chin, and communicating with the mental branch of the inferior alveolar nerve. The Cervical Branch {ramus colli) runs forward beneath the Platysma, and forms a series of arches across the side of the neck over the suprahyoid region. One branch descends to join the cervical cutaneous nerve from the cervical plexus; others supply the Platysma. Applied Anatomy. — Facial palsy is commonly miilateral, and may be either: (1) peripheral, from lesion of the facial nerve; (2) nuclear, from destruction of the facial nucleus; or (3) central, cerebral, or supranuclear, from injury in the brain to the fibres passing from the cortex through the internal capsule to the facial nucleus, or from injury to the face area of the motor cortex itself. In supranuclear facial paralysis, which is usually part of a hemiplegia, it is the lower part of the face that is chiefly affected, while the forehead can be freely wrinkled on the palsied side, the eye can be closed fairly well, and the eyeball is not rolled up under the upper Ud; emotional 934 NEUROLOGY movements of the face are much better executed than voluntary; and the electrical reactions of the muscles on the affected side are not altered. If the paralysis is due to lesion of the facial nucleus, the Orbicularis oris escapes, as the nuclear origin of the nerve to this muscle seems to be connected with that of the tongue nerves; otherwise the symptoms arc identical with those of the common peripheral facial palsy, of which several types may be distinguished according to the point in its course at which the facial nerve is injured. If the lesion occurs (a) in the pons, facial paralysis is produced as in (d) below; taste and hearing are not affected, but the abducent nerve also will be paralyzed because the fibres of the facial nerve loop aiound its nucleus in the pons. When the nerve is paralyzed (6) in the petrous bone, in addition to the paralysis of the muscles of expression, there is loss of taste in the anterior part of the tongue, and the patient is unable to recognize the difference between bitters and sweets, acids and salines, from involvement of the chorda tympani. The mouth is dry, because the salivary glands are not secreting; and the sense of hearing is affected from paralysis of the Stapedius. When the cause of the paralysis is (c) fracture of the base of the skull, the acoustic and petrosal nerves are usually involved. But by far the commonest cause of facial palsy is (d) exposure of the nerve to cold or injury at or after its exit from the stylomastoid foramen {Bell's paralysis). In these cases the face looks asymmetrical even when at rest, and more so in the old than in the yoxmg. The affected side of the face and forehead remains motionless when voluntary or emotional movement is attempted. The lines on the forehead are smoothed out, the eye can be shut only by hand, tears fail to enter the lacrimal puncta because they are no longer in contact with the conjimctiva, the conjimctival reflex is absent, and efforts to close the eye merely cause the eyeball to roll upward until the cornea hes under the upper hd. The tip of the nose is drawn over toward the soxind side; the nasolabial fold is partially obliterated on the affected side, and the ala nasi does not move properly on respiration. The Ups remain in contact on the paralyzed side,, and cannot be put together for whistUng; when a smile is attempted the angle of the mouth is drawn up on the unaffected side; on the affected side the Ups remain nearly closed, and the mouth assumes a characteristic triangular form. During mastication food accumulates in the cheek, from paralysis of the Bucci- nator, and dribbles or is pushed out from between the paralyzed lips. On protrusion the tongue seems to be thrust over toward the palsied side, but verification of its position by reference to the incisor teeth will show that this is not really so. The Platysma and the muscles of the auricula are paralyzed; in severe cases the articulation of labials is impaired The electrical reactions of the affected muscles are altered (reaction of degeneration), and the degree to which this alteration has taken place after a week or ten days gives a valuable guide to the prognosis. Most cases of Bell's palsy recover completely. The facial nerve is at fault in cases of so-called histrionic spasm, which consists in an almost constant and uncontrollable twitching of some or all of the muscles of the face. This twitching is sometimes so severe as to cause great discomfort and annoyance to the patient, and to interfere with sleep, and for its relief the facial nerve has been stretched. The operation is performed by making an incision behind the ear, from the root of the mastoid process to the angle of the man- dible. The parotid is turned forward and the dissection carried along the anterior border of the Stemocleidomastoideus and mastoid process, imtil the upper border of the posterior belly of the Digastricus is found. The nerve is parallel to this on about the level of the middle of the mastoid process. When found, the nerve must be stretched by passing a blimt hook beneath it and pulling it forward and outward. Too great force must not be used, for fear of permanent injury to the nerve. THE ACOUSTIC NERVE (N. ACUSTICUS; EIGHTH OR AUDITORY NERVE). The acoustic nerve, or nerve of hearing, is distributed exclusively to the internal ear. It consists of two sets of fibres, which, although differing in their central connections, are both concerned in the transmission of afferent impulses from the internal ear to the medulla oblongata and pons, and from there, by means of fibres which arise from collections of gray substance in these structures, to the cerebrum and cerebellum. One set of fibres forms the vestibular root of the nerve, and arises from the cells in the vestibular ganglion situated in the internal acoustic meatus; the other set constitutes the cochlear root, and takes origin from the cells in the ganglion spirale, which occupies the spiral canal of the cochlea. Both of these gangha consist of bipolar nerve cells; from each of the cells a central fibre passes to the brain, a peripheral fibre to the internal ear. At its connection with the brain the eighth nerve occupies the groove between the pons and medulla, lying behind the facial nerve and in front of the restiform body. THE ACOUSTIC NERVE 935 Vestibular Root (radix vestibularis; vestibular nerve) (Fig. 790). — The fibres of this root enter the iiieckilla oblongata on the medial side of those of the cochlear root, and pass between the restifonn body and the spinal tract of the trigeminal. They then divide into ascentling and descending fibres. The latter end by arbor- izing around the cells of the medial nucleus, which is situated in the area acustica of the rhomboid fossa. The ascending fibres either end in the same manner or in the lateral nucleus, which is situated lateral to the area acustica and farther from the ventricular floor; the lateral nucleus consists of two parts, a medial, the nucleus of Deiters, and a lateral, the nucleus of Bechterew. Some of the axons of the cells of the lateral nucleus, and possibly also of the medial nucleus, are continued upward through the restiform body to the roof nuclei of the opposite side of the cerebellum, to which also other fibres of the vestibular root are prolonged with- out interruption in the nuclei of the medulla oblongata. A second set of fibres from the medial and lateral nuclei end partly in the tegmentum, while the remainder ascend in the medial longitudinal fasciculus to arborize around the cells of the nuclei of the oculo- motor nerve. Cochlear Root (radix cochlearis; cochlear nerve) (Fig. 791). — The cochlear root is placed lateral to the vestibular root. Its fibres end in two nuclei: one, the accessory nucleus, lies immediately in front of the restiform body; the other, the tuberculum acusticum, some- what lateral to it. The striae medullares (striae acusticae) are the axons of the cells of the tuberculum gicusticum. They pass over the restiform bpdy, and across the rhomboid fossa to the median sulcus. Here they dip into the substance of the pons, to end around the cells of the superior olivary nuclei of both sides. There are, however, other fibres, and these are both direct and crossed, which pass into the lateral lemniscus. The cells of the accessory nucleus give origin to fibres which run transversely in the pons and constitute the trapezium. Of the trapezoid fibres some end around the cells of the superior olivary nucleus or of the trapezoid nucleus of the same or opposite side, while others, crossed or uncrossed, pass directly into the lateral lemniscus. If the further connections of the cochlear nerve of one side, say the left, be con- sidered, it is found that they lie lateral to the main sensory tract, the lemniscus, and are therefore termed the lateral lemniscus. The fibres comprising the left lateral lemniscus arise in the superior olivary and trapezoid nuclei of the same or opposite side, while others are the uninterrupted fibres already alluded to, and these are either crossed or uncrossed, the former being the axons of the cells of the right accessory nucleus or of the cells of the right tuberculum acusticum, while the latter are derived from the cells of the left nuclei. In the upper part of the lateral lemniscus there is a collection of nerve cells, the nucleus of the lateral lemniscus, around the cells of which some of the fibres arborize and from the cells of which axons originate to continue upward the tract of the lateral lemniscus. The ultimate Fig. 790. — Terminal nuclei of the vestibular root of the acous- tic nerve, with their upper connections. (Schematic.) (Testut.) 1. Posterior or cochlear root, with its two nuclei. 2. Accessory- nucleus. 3. Tuberculum acusticum. 4. Anterior or vestibular root. 5. Internal nucleus. 6 . Nucleus of Deiters. 7. Nucleus of Bechterew. 8. Inferior or descending root of acoustic. 9. As- cending cerebellar fibres. 10. Fibres going to raph6. 11. Fibres taking an oblique course. 12. Lemniscus. 13. Inferior sensory- root of trigeminal. 14. Cerebrospinal fasciculus. 15. Raph6. 16. Fourth ventricle. 17. Restiform body. 18. Origin of striae medullares. 936 NEUROLOGY ending of the left lateral lemniscus is parth' in tlie opposite medial geniculate body, and partly in the inferior colliculi. From the cells of these bodies new fibres arise and ascend in the occipital part of the internal capsule to reach the posterior three-fifths of the left superior temporal gyrus and the transverse temporal gyri. The acoustic nerve contains a few efferent fibres which arise in the quadrigeminal bodies, the nucleus of the lateral lemniscus, the superior olivary and trapezoid nuclei. 6 14 Fig. 791. — Terminal nuclei of the cochlear root of the acoustic nerve, with their upper connections. (Schematic.) (Testut.) The vestibular root with its terminal nuclei and their efferent fibres have been suppressed. On the other hand, in order not to obscure the trapezoid body, the efferent fibres of the terminal nuclei on the right side have been resected in a considerable portion of their extent. The trapezoid body, therefore, shows only one-half of its fibres, viz., those which come from the left. 1. Vestibular root of the acoustic, divided at its entrance into the meduUa oblongata. 2. Cochlear root. 3. Accessory nucleus of acoustic nerve. 4. Tuberculum acusticum. 5. Efferent fibres of accessory nucleus. 6. Efferent fibres of tuberculum acusticum, forming the striae medullares, with 6', their direct bundle going to the superior olivary nucleus of the same side; 6", their decussating bundles going to the superior olivary nucleus of the opposite side. 7. Superior oilvary nucleus. 8. Trapezoid body. 9. Trapezoid nucleus. 10. Central acoustic tract (lateral lemniscus). 11. Raph6. 12. Cerebrospinal fasciculus. 13. Fourth ventricle. 14. Restiform body. The acoustic nerve is soft in texture, and destitute of neurilemma. After leaving the medulla oblongata it passes forward across the posterior border of the brachium pontis, in company with the facial nerve, from which it is partially separated by the internal auditory artery. It then enters the internal acoustic meatus wdth the facial nerve. At the bottom of the meatus it receives one or two filaments from the facial nerve, and then divides into its two branches, cochlear and vestibular, the distribution of which will be described with the anatomy of the internal ear. Applied Anatomy. — The acoustic nerve is frequently injured, together with the facial nerve, in fracture of the middle fossa of the base of the skull implicating the internal acoustic meatus. The nerve may be either torn across, producing permanent deafness, or it may be bruised or pressed upon by extravasated blood or inflammatory exudation, when the deafness will in all probability be temporary. The nerve may also be injured by violent blows on the head without any fracture of the bones of the skull taking place, and deafness may arise from loud explosions from dynamite, etc., probably from some lesion of this nerve, which is more liable to be injured than the other cerebral nerves on account of its structure. "Nerve deafness" as contrasted with deafness due to changes in the middle ear or meatus, is suggested if (1) a sounding tuning fork placed on the middle line of the head is heard better (Weber's test) by the unaffected ear; or if (2) the sounding tuning fork is heard longer when held before the affected ear ( = air conduc- tion) than when it is stood on the corresponding mastoid ( = bone conduction, Rinn^'s test); or if (3) the sounding tuning fork applied to the vertex or mastoid is heard less well when the air in the meatus is compressed by the use of a Siegle's speculum (Gelle's test) ; or if (4) the tuning fork placed on the mastoid is heard for a shorter time than its sound is perceptible to a normal individual ( = evidence that bone conduction is diminished, Schwabach's test). It must be THE GLOSSOPHARYNGEAL NERVE 937 remembered tliat all these tests are liable to anomalies and exceptions, and are not applicable to old people. If, however, concordant results are yielded by the tests of Weber, Rinn6, and Gelle, Bezold's "triad of symptoms," nerve deafness rather than deafness due to disease of the conducting structures is rendered highly probable. Tinnitus aurium, or the hearing of sounds in the ear that have no objective cause outside the body, is said to be present in as many as 60 per cent, of cases of ear disease of all sorts, and is commonest in disease of the labyrinth or of the nerve. It is very variable in intensity; the worst forms are purely subjective and due to irritation of the nerve itself. The sounds heard are of the most varied nature — buzzing, hissing, whistling, rushing, bell ringing, and so forth — and may occupy the patient's attention so completely that he is no longer able to attend- to his business; he may even commit suicide in order to escape from them. In the insane, tinnitus is associated with delusions and hallucinations of hearing; cases of insanity have even been recorded in which cure was effected by the removal of cerumen impacted in the meatus and giving rise to persistent tinnitus. THE GLOSSOPHARYNGEAL NERVE (N. GLOSSOPHARYNGEUS; NINTH NERVE) (Figs. 792, 793, 794). Awricular The glossopharyngeal nerve contains both motor and sensory fibres, and is dis- tributed, as its name implies, to the tongue and pharynx. It is the nerve of ordinary sensation to the mucous membrane of the pharynx, fauces, and palatine tonsil, and the nerve of taste to the posterior part of the tongue. It is attached by three or four filaments to the upper part of the medulla oblon- gata, in the groove between the olive and the restiform body. The sensory fibres arise from the cells of the supe- rior and petrous ganglia, which are situated on the trunk of the nerve, and Mall be presently described. When traced into the me- dulla, some of the sensory fibres end by arborizing around the cells of the upper part of a nucleus which lies beneath the ala cinera in the lower part of the rhomboid fossa. Many of the fibres, however, con- tribute to form a strand, named the fasciculus soli- tarius, which descends in the medulla oblongata. Associated with this strand are numerous nerve cells, and around these the fibres of the fasciculus end. The motor fibres spring from the cells of the nucleus ambiguus, which lies some distance from the surface of the rhomboid fossa in the lateral part of the medulla and is continuous below with the anterior gray column of the medulla spinalis. From this nucleus the fibres are first directed backward, and then they bend for- ward and lateralward to join the fibres of the sensory root. The nucleus ambiguus gives origin to the motor branches of the glossopharyngeal and vagus nerves, and to the cerebral part of the accessory nerve. Pharyngeal Laryngeal Fig. 792. — Plan of upper portions of glossopharyngeal, vagus, and accessory nerves. 938 NEUROLOGY From the medulla oblongata, the glossopharyngeal nerve passes lateralward across the flocculus, and leaves the skull through the central part of the jugular foramen, in a separate sheath of the dura mater, lateral to and in front of the vagus and accessory nerves (Fig. 793). In its passage through the jugular foramen, it grooves the lower border of the petrous part of the temporal bone; and, at its exit from the skull, passes forward between the internal jugular vein and internal carotid artery; it descends in front of the latter vessel, and beneath the styloid process and the muscles connected with it, to the lower border of the Stylo- pharyngeus. It then curves forward, forming an arch on the side of the neck and lying upon the Stylopharyngeus and Constrictor pharyngis medius. Thence it passes under cover of the Hyoglossus, and is finally distributed to the palatine tonsil, the mucous membrane of the fauces and base of the tongue, and the mucous glands of the mouth. Trochlear verve Trigeminal nerve Facial nerve Acoustic nerve Cereb) al peduncle Bracliiiim conjunctivitm Brachi2i,m pontis Restiform body Glossopharyngeal, nerve Vagus nerve A ccessory nerve cerebral part Hypoglossal nerve Accessory nerve \ {spinal part) Medulkt spinalis Dura inater (laid open) Fasciculus cuneatus Fasciculus gracilis Fig. 793. — Upper part of medulla spinalis and hind- and mid-brains; posterior aspect, exposed in situ. In passing through the jugular foramen, the nerve presents two ganglia, the superior and the petrous (Fig. 792). The superior ganglion {ganglion superius; jugular ganglion) is situated in the upper part of the groove in which the nerve is lodged during its passage through the jugular foramen. It is very small, and is usually regarded as a detached portion of the petrous ganglion. THE GLOSSOPHARYNGEAL NERVE 939 The petrous ganglion (ganglion petrosum; inferior ganglion) is larger than the superior ami is situated in a depression in the lower border of the petrous portion of the temporal bone. ophai yngcal Va \f Glo Branches of Communication. — The glossopharyngeal nerve com- munieates with the vagus, sym- pathetic, and facial. The branches to the vagus are two filaments which arise from the petrous ganglion, one pass- ing to the auricular branch, and the other to the jugular gang- lion, of the vagus. The petrous ganglion is connected by a fila- ment with the superior cervical ganglion of the sympathetic. The branch of communication with the facial perforates the posterior belly of theDigastricus. It arises from the trunk of the glossopharyngeal below the pet- rous ganglion, and joins thefacial just after tKe exit of that nerve from the stylomastoid foramen. Branches of Distribution. — The branches of distribution of the glossopharyngeal are: the tym- panic, carotid, pharyngeal, mus- cular, tonsillar, and lingual. The Tympanic Nerve {71. tym- yanicus; nerve of Jacohson) arises from the petrous ganglion, and ascends to the tympanic cavity through a small canal on the under surface of the petrous portion of the temporal bone on the ridge which separates the carotid canal from the jugular fossa. In the tympanic cavity it divides into branches which form the tympanic plexus and are contained in grooves upon the surface of the promontory. This plexus gives oflF: (1) the lesser superficial petrosal nerve; (2) a branch to join the greater superficial petrosal nerve; and (3) branches to the tympanic cavity, all of which will be described in connection with the anatomy of the middle ear. The Carotid Branches {n. caroticofympanicus superior and 7i. caroticotympanicus inferior) descend along thje trunk of the internal carotid artery as far as its origin, communicating with the pharyngeal branch of the vagus, and with branches of the sympathetic. Fig. 794.- -Course and distribution of the glossopharyngeal, vagus, and accessory nerves. 940 NEUROLOGY The Pharyngeal Branches ()-ami phuryiigei) are three or four hlaraents which unite, opposite the Constrictor pharyngis medius, with the pharyngeal branches of the vagus and sympathetic, to form the pharyngeal plexus; ])ranches from this plexus perforate the muscular coat of the pharynx and supply its muscles and mucous membrane. The Muscular Branch {ramus stylopharyngeus) is distributed to the Stylo- pharyngeus. The Tonsillar Branches (rami tonsillares) supply the palatine tonsil, forming around it a plexus from which filaments are distributed to the soft palate and fauces, where they communicate with the palatine nerves. , The Lingual Branches {rami linguales) are two in number; one supplies the papillae vallatae and the mucous membrane covering the base of the tongue; the other supplies the mucous membrane and follicular glands of the posterior part of the tongue, and communicates with the lingual nerve. THE VAGUS NERVE (N. VAGUS; TENTH NERVE; PNEUMOGASTRIC NERVE) (Figs. 792, 793, 794). The vagus nerve is composed of both motor and sensory fibres, and has a more extensive course and distribution than any of the other cerebral nerves, since it passes through the neck and thorax to the abdomen. The vagus is attached by eight or ten filaments to the medulla oblongata in the groove between the olive and the restiform body, below the glossopharyngeal. The sensory fibres arise from the cells of the jugular ganglion and ganglion nodosum of the nerve, and, when traced into the medulla oblongata mostly end by arborizing around the cells of the inferior part of a nucleus which lie beneath the ala cinerea in the lower part of the rhomboid fossa. Some of the sensory fibres of the glosso- pharyngeal nerve have been seen to end in the upper part of this nucleus. A few of the sensory fibres of the vagus descend in the fasciculus solitarius and end around its cells. The motor fibres arise from the cells of the nucleus ambiguus, already referred to in connection with the motor root of the glossopharyngeal nerve (page 937). The filaments of the nerve unite, and form a flat cord, which passes beneath the flocculus to the jugular foramen, through which it leaves the cranium. In emerging through this opening, the vagus is accompanied by and contained in the same sheath of dura mater with the accessory nerve, a septum separating them from the glossopharyngeal which lies in front (Fig. 793). In this situation the vagus presents a well-marked ganglionic enlargement, which is called the jugular ganglion {ganglion of the root) ; to it the accessory nerve is connected by one or two filaments. After its exit from the jugular foramen the vagus is joined by the cere- bral portion of the accessory nerve, and enlarges into a second gangliform swelling, called the ganglion nodosum {ganglion of the trunk) ; through this the fibres of the cerebral portion of the accessory pass without interruption, being principally distributed to the pharyngeal and superior laryngeal branches of the vagus, but some of its fibres descend in the trunk of the vagus, to be distributed with the recurrent nerve and probably also with the cardiac nerves. The vagus nerve passes vertically down the neck within the carotid sheath, lying between the internal jugular vein and internal carotid artery as far as the upper border of the thyroid cartilage, and then between the same vein and the common carotid artery to the root of the neck. The further course of the nerve differs on the two sides of the body. On the right side, the nerve passes across the subclavian artery between it and the right innominate vein, and descends by the side of the trachea to the back of THE VAGUS NERVE 941 the root of tlic lung, where it spreads out in the posterior pulmonary plexus. From the k)wer part of this plexus two cords descend on tlie (cs()j)liafjus, and divide to form, with branches from the opposite nerve, the oesophageal plexus. Below, these branches are collected into a single cord, which runs along the back of the oesophagus enters the abdomen, and is distributed to the postero-inferior surface of the stomach, joining the left side of the coeliac plexus, and sending filaments to the lienal plexus. On the left side, the vagus enters the thorax between the left carotid and sub- clavian arteries, behind the left innominate vein. It crosses the left side of the arch of the aorta, and descends behind the root of the left lung, forming there the posterior pulmonary plexus. From this it, runs along the anterior surface of the oesophagus, where it unites with the nerve of the right side in the oesophageal plexus, and is continued to the stomach, distributing branches over its antero- superior surface; some of these extend over the fundus, and others along the lesser curvature. Filaments from these branches enter the lesser omentum, and join the hepatic plexus. The jugular ganglion {ganglion jugulare; ganglion of the root) is of a grayish color, spherical in form, about 4 mm. in diameter. ■ Branches of Communication. — ^This ganglion is connected by several delicate filaments to the cerebral portion of the accessory nerve; it also communicates by a twig with the petrous ganglion of the glossopharyngeal, with the facial nerve by means of its auricular branch, and with the sympathetic by means of an ascend- ing filament from the superior cervical ganglion. The ganglion nodosum (ganglion of the trunk; inferior ganglion) is cylindrical in form, of a reddish color, and 2.5 cm. in length. Passing through it is the cerebral portion of the accessory nerve, which blends with the vagus below the ganglion. Branches of Communication. — This ganglion is connected with the hypoglossal, the superior cervical ganglion of the sympathetic, and the loop between the first and second cervical nerves. Branches of Distribution. — The branches of distribution of the vagus are: In the Jugular Fossa i a • i ^ [Auricular. ^Pharyngeal. In the Neck i Superior laryngeak I Uecurrent. [ Superior cardiac. , f Inferior cardiac. In the Thorax Anterior bronchial. Posterior bronchial. , Oesophageal. f Gastric. In the Abdomen I Coeliac. [ Hepatic. The Meningeal Branch {ramus meningeus; dural branch) is a recurrent filament given off from the jugular ganglion; it is distributed to the dura mater in the posterior fossa of the base of the skull. The Auricular Branch {ramus auricularis; nerve of Arnold) arises from the jugular ganglion, and is joined soon after its origin by a filament from the petrous ganglion of the glossopharyngeal; it passes behind the internal jugular vein, and enters the mastoid canaliculus on the lateral wall of the jugular fossa. Traversing the sub- stance of the temporal bone, it crosses the facial canal about 4 mm. above the stylo- mastoid foramen, and here it gives off an- ascending branch which joins the facial nerve. The nerve reaches the surface by passing through the tympanomastoid fissure between the mastoid process and the tympanic part of the temporal bone,. 942 NEUROLOGY and divides into two branches: one joins the posterior auricular nerve, the other is distributed to the skin of the back of the auricuhi and to the posterior part of the external acoustic meatus. The Pharyngeal Branch {ramus pharyngeus), the principal motor nerve of the pharynx, arises from the upper part of the ganglion nodosum, and consists prin- cipally of filaments from the cerebral portion of the accessory nerve. It passes across the internal carotid artery to the upper border of the Constrictor pharyngis medius, where it divides into numerous filaments, which join with branches from the glossopharyngeal, sympathetic, and external laryngeal to form the pharyngeal plexus. From the plexus, branches are distributed to the muscles and mucous membrane of the pharynx and the muscles of the soft palate, except the Tensor veli palatini. A minute filament descends and joins the hypoglossal nerve as it winds around the occipital artery. The Superior Laryngeal Nerve {n. laryngeus superior) larger than the preceding, arises from the middle of the ganglion nodosum and in its course receives a branch from the superior cervical ganglion of the sympathetic. It descends, by the side of the pharynx, behind the internal carotid artery, and divides into two branches, external and internal. The external branch {ramus externus), the smaller, descends on the larynx, beneath the Sternothyreoideus, to supply the Cricothyreoideus. It gives branches to the pharyngeal plexus and the Constrictor pharyngis inferior, and communicates with the superior cardiac nerve, behind the common carotid artery. The internal branch {ramus internus) descends to the hyothyroid membrane, pierces it in company wdth the superior laryngeal artery, and is distributed to the mucous membrane of the larynx. Of these branches some are distributed to the epiglottis, the base of the tongue, and the epiglottic glands; others pass backward, in the ary epiglottic fold, to supply the mucous membrane surrounding the entrance of the larynx, and that lining the cavity of the larynx as low down as the vocal folds. A filament descends beneath the mucous membrane on the inner surface of the thyroid cartilage and joins the recurrent nerve. The Recurrent Nerve {n. recurrens; inferior or recurrent laryngeal nerve) arises, on the right side, in front of the subclavian artery; winds from before back- ward around that vessel, and ascends obliquely to the side of the trachea behind the common carotid artery, and either in front of or behind the inferior thyroid artery. On the left side, it arises on the left of the arch of the aorta, and winds below the aorta at the point where the ligamentum arteriosum is attached, and then ascends to the side of the trachea. The nerve on either side ascends in the groove between the trachea and oesophagus, passes under the lower border of the Con- strictor pharyngis inferior, and enters the larynx behind the articulation of the inferior cornu of the thyroid cartilage with the cricoid; it is distributed to all the muscles of the larynx, excepting the Cricothyreoideus. It communicates with the internal branch of the superior laryngeal nerve, and gives off a few filaments to the mucous membrane of the lower part of the larynx. As the recurrent nerve hooks around the subclavian artery or aorta, it gives off several cardiac filaments to the deep part of the cardiac plexus. As it ascends in the neck it gives off branches, more numerous on the left than on the right side, to the mucous membrane and muscular coat of the oesophagus; branches to the mucous membrane and muscular fibres of the trachea; and some pharyngeal filaments to the Constrictor pharyngis inferior. The Superior Cardiac Branches {rami cardiaci superior es; cervical cardiac branches), two or three in number, arise from the vagus, at the upper and lower parts of the neck. The upper branches are small, and communicate with the cardiac branches of the sympathetic. They can be traced to the deep part of the cardiac plexus. THE VAGUS NERVE 943 The lower branch arises at the root of the neck, just above the first rib. That from the right vagus passes in front or by the side of the innominate artery, and proceeds to the deep part of tlie canUac plexus; that from the left runs down across the left side of the arch of the aorta, and joins the superficial part of the cardiac plexus. The Inferior Cardiac Branches {rami cardiaci inferiores; thoracic cardiac branches), on the right side, arise from the trunk of the vagus as it lies by the side of the trachea, and from its recurrent nerve; on the left side from the recurrent nerve only; passing inward, they end in the deep part of the cardiac plexus. The Anterior Bronchial Branches (rami bronchiales anteriores; anterior or ventral pulmonary branches), two or three in" number, and of small size, are distributed on the anterior surface of the root of the lung. They join with filaments from the sympathetic, and form the anterior pulmonary plexus. The Posterior Bronchial Branches {rami bronchiales posteriores; posterior or dorsal pulmonary branches), more numerous and larger than the anterior, are distributed on the posterior surface of the root of the lung; they are joined by filaments from the third and fourth (sometimes also from the first and second) thoracic ganglia of the sympathetic trunk, and form the posterior pulmonary plexus. Branches from this plexus accompany the ramifications of the bronchi through the substance of the lung. The (Esophageal Branches {rami oesophagei) are given off both above and below the bronchial branches; the lower are numerous and larger than the upper. They form, together with the branches from the opposite nerve, the oesophageal plexus. From this plexus filaments are distributed to the back of the pericardium. The Gastric Branches {rami gastrici) are distributed to the stomach. The right vagus forms tlie posterior gastric plexus on the postero-inferior surface of the stomach and the left the anterior gastric plexus on the antero-superior surface. The Coeliac Branches {rami coeliaci) are mainly derived from the right vagus: they join the coeliac plexus and through it supply branches to the pancreas, spleen, kidneys, suprarenal bodies, and intestine. The Hepatic Branches {rami hepatici) arise from the left vagus : they join the hepatic plexus and through it are conveyed to the liver. Applied Anatomy. — The trunk of the vagus is rarely injured, but the functions of the nerve may be interfered with by damage to its nucleus of origin in the medulla; by thickening or growth from the meninges or bones, or anem-ism of the basilar artery, before its exit from the skull; injuries such as gimshot or pimctured wounds in the neck, or injiu'ies during such operations as Ugatiu-e of the carotid artery, removal of tuberculous glands or other deep-seated tumors. The vagus may also be compressed by aneurisms of the carotid artery, and its deep origin becomes affected in bulbar paralysis. The symptoms produced by paralysis of the nerve are palpitation, with increased frequency of the pulse, constant vomiting, slowing of the respiration, and a sensa- tion of suffocation. "Reflexes" on the branches of the vagus are not at aU imcommonly met with. The "ear cough" is perhaps one of the commonest, where a plug of wax in the acoustic meatus may by irritating the filaments of the auricular (Arnold's) nerve be responsible for a persistent cough. Syringing the external acoustic meatus frequently produces cough, and, in children, vomiting is not uncommon as the result of such a procedure; moreover, in people with weak hearts, syringing the ear has been responsible for a sudden fatal syncope, by reflex irritation of the cardiac branches. Another very common example is the persistent cough which is frequently due to enlarged bronchial glands in children, the irritation of which is referred to the superior laryngeal filaments. The anatomy of the laryngeal nerves is of importance in considering some of the morbid condi- tions of the larynx. When the peripheral terminations of the superior laryngeal nerve are irri- tated by some foreign body passing over them, reflex spasm of the glottis is the result. When its trunk is pressed upon by, for instance, a goitre or an aneiirism of the upper part of the carotid, there is a peculiar dry, brassy cough. When the nerve is paralyzed, there is anesthesia of the mucous membrane of the larjmx, so that foreign bodies can readily enter the cavity, and, as the nerve also supplies the Cricothyreoideus muscle, the vocal folds cannot be made tense, and the voice is deep and hoarse. Paralysis may be the result of bulbar paralysis; may be a sequel to diphtheria, when both nerves are usually involved; or it may, though less commonly, be caused 944 NEUROLOGY by the pressure of tumors or aneurisms, when the paralysis is generally unilateral. Irritation of the recurrent nerves produces spasm of the muscles of the larynx. When both recurrent nerves are paralyzed, the vocal folds are motionless, in the so-called " cadaveric position"— that is to say, in the position in which they are found in ordinary tranquil respiration; neither closed as in phonation, nor open as in deep inspiratory efforts. When one recurrent nerve is paralyzed, the vocal fold of the same side is motionless, while the opposite one crosses the middle line to accommodate itself to the affected one; hence phonation is possible, but the voice is altered and weak in timbre. The nerves may be paralyzed in bulbar paralysis or after diphtheria, when the paralysis usually affects both sides; or they may be affected by the pressure of aneurisms of the aorta, innominate, or subclavian arteries; by mediastinal tumors; by gummata; or by cancer of the upper part of the oesophagus, when the paralysis is often unilateral. Paralysis of the adductor muscles of the larynx on both sides is quite common, and is usually functional in nature. The voice is reduced to a whisper, but the power of coughing is preserved. Fig. 795. — Hypoglossal nerve, cervical plexus, and their branches. THE ACCESSORY NERVE (N. ACCESSORIUS; ELEVENTH NERVE; SPINAL ACCESSORY NERVE) (Figs. 793, 794, 795). The accessory nerve consists of two parts : a cerebral and a spinal. The cerebral part {ramus internus; accessory portion) is the smaller of the two. Its fibres arise from the cells of the nucleus ambiguus and emerge as four or five delicate rootlets from the side of the medulla oblongata, below the roots of the vagus. It runs lateralward to the jugular foramen, where it interchanges fibres with the spinal portion or becomes united to it for a short distance; here it is also connected by one or two filaments with the jugular ganglion of the vagus. It THE HYPOGLOSSAL NERVE 945 then passes through the juguhir foramen, separates from the spinal portion and is continued over the surface of the ganglion nodosum of the vagus, to the surface of which it is atlherent, and is distributed principally to the pharyngeal and superior laryngeal branches of the vagus. Through the pharyngeal branch it probably sup- plies the Musculus uvulae and Levator veli palatini. Some few filaments from it are continued into the trunk of the vagus below the ganglion, to be distributed with the recurrent nerve and probably also with the cardiac nerves. The spinal part (ramus e.vfernus; spinal portion) is firm in texture, and its fibres arise from the motor cells in the lateral part of the anterior column of the gray sub- stance of the medulla spinalis as low as the fifth cervical nerve. Passing through the lateral funiculus of the medulla spinalis, they emerge on its surface and unite to form a single trunk, which ascends between the ligamentum denticulatum and the posterior roots of the spinal nerves, enters the skull through the foramen magnum, and is then directed to the jugular foramen, through which it passes, lying in the same sheath of dura mater as the vagus, but separated from it by a fold of the arachnoid. In the jugular foramen, it recei^'es one or two filaments from the cere- bral part of the nerve, or else joins it for a short dista^nce and then separates from it again. iVs its exit from the jugular foramen, it runs backward in front of the internal jugular vein in 66.6 per cent, of cases, and behind in it 33.3 per cent. (Tandler). The nerve then descends obliquely behind the Digastricus and Stylo- hyoideus to the upper part of the Sternocleidomastoideus; it pierces this muscle, and courses obliquely across the posterior triangle of the neck, to end in the deep surface of the Trapezius. As it traverses the Sternocleidomastoideus it gives several filaments to the muscle, and joins with branches from the second cervical nerve. In the posterior triangle it unites with the second and third cervical nerves, while beneath the Trapezius it forms a plexus with the third and fourth cervical nerves, and from this plexus fibres are distributed to the muscle. Applied Anatomy. — The functions of the accessory nerve may be interfered with either by central changes; or at its exit from the skull, by fractures running across the jugular foramen; or in the neck, by inflamed lymph glands, etc. The acute wiy-neck in children is most commonly due to inflamed or suppurating glands, and rapidly subsides with appropriate treatment. Central irritation causes clonic spasm of the Sternocleidomastoideus and Trapezius muscles, or, as it is termed, spasmodic torticollis. In cases of this affection in which all previous paUiative treat- ment has failed, and the spasms are so severe as to undermine the patient's health, division or excision of a portion of the accessory nerve has been resorted to. This must be done from the anterior border of the Sternocleidomastoideus. The operation consists in making an incision, 8 cm. in length, from the apex of the mastoid process along the anterior border of the muscle, which is defined and pulled backward, so as to stretch the nerve, which is then to be sought for beneath the Digastricus, about 5 cm. below the apex of the mastoid process. Unfortunately, the operation does not yield a satisfactory or permanent cm-e, as the spasms tend to recm- after an interval, either in the same muscles or in other groups of neck muscles. In cases where extensive dissections are undertaken for enlarged glands in the neck, it is essential that this nerve should be at once sought for and isolated from the mass of inflamed glands so as to maintain its continuity. THE HYPOGLOSSAL NERVE (N. HYPOGLOSSUS; TWELFTH NERVE) (Figs. 795, 796). The hypoglossal nerve is the motor nerve of the tongue. Its fibres arise from the cells of the hypoglossal nucleus, which is an upward prolongation of the base of the anterior column of gray substance of the medulla spinalis. This nucleus is about 2 cm. in length, and its upper part corresponds with the trigonum hypoglossi, or lower portion of the medial eminence of the rhom- boid fossa (page 848). The lower part of the nucleus extends downward into the closed part of the medulla oblongata, and there lies in relation to the ventro-lateral aspect of the central canal. The fibres run forward through the medulla oblongata, and emerge in the antero-lateral sulcus between the pyramid and the olive. 60 946 NEUROLOGY The rootlets of this nerve are collected into two bundles, which perforate the dura mater separately, opposite the hypoglossal canal in the occipital bone, and unite together after their passage through it; in some cases the canal is di\ided into two by a small bony spicule. The nerve descends almost vertically to a point corresponding with the angle of the mandible. It is at first deeply seated beneath the internal carotid artery and internal jugular vein, and intimately connected with the vagus nerve; it then passes forward between the vein and artery, and lower down in the neck becomes superficial below the Digastricus. The nerve then loops To Dura uiatc To Lingual nerve TO GENIOHYOIDEUS TO SUPERIOR BELLY OF OMOHYOIDEUS TO STERNOHYOIDEUS TO STERNOTHYREOIDEUS TO INFERIOR BELLY OF OMOHYOIDEUS Fig. 796. — Plan of hypoglossal nerve. around the occipital artery, and crosses the external carotid and lingual arteries below the tendon of the Digastricus. It passes beneath the tendon of the Digas- tricus, the Stylohyoideus, and the Mylohyoideus, lying between the last-named muscle and the Hyoglossus, and communicates at the anterior border of the Hyo- glossus with the lingual nerve; it is then continued forward in the fibres of the Genioglossus as far as the tip of the tongue, distributing branches to its muscular substance. Branches of Communication.^ — Its branches of communication are, with the Vagus. Sympathetic. First and second cervical nerves. Lingual. The communications with the vagus take place close to the skull, numerous ^laments passing between the hypoglossal and the ganglion nodosum of the vagus THE SPINAL NERVES 947 through the mass of connective tissue whicli unites tlie two nerves. As the nerve winds around the occipital artery it gives off a filament to the pharyngeal plexus. The communication with the sympathetic takes place opposite the atlas by branches derived from the superior cervical ganglion, and in the same situation the nerve is joined by a filament derived from the loop connecting the first and second cervical nerves. The communications with the lingual take place near the anterior border of the Hyoglossus by numerous filaments which ascend upon the muscle. Branches of Distribution. — The branches of distribution of the hypoglossal nerve are: ^Meningeal. Thyrohyoid. Descending. . Muscular. Of these branches, the meningeal, descending, thyrohyoid, and the muscular twig to the Geniohyoideus, are probably derived mainly from the branch which passes from the loop between the first and second cervical to join the hypoglossal (Fig. 796). Meningeal Branches {dural branches). — As the hypoglossal nerve passes through the hypoglossal canal it gives off, according to Luschka, several filaments to the dura mater in the posterior fossa of the skull. The Descending Ramus {ramus descendens; descendens hypoglossi), long and slender, quits the hypoglossal where it turns around the occipital artery and descends in front of or in the sheath of the carotid vessels; it gives a branch to the superior belly of the Omohyoideus, and then joins the communicantes cervicales from the second and third cervical nerves; just below the middle of the neck, to form a loop, the ansa hypoglossi. From the convexity of this loop branches pass to supply the Sternohyoideus, the Sternothyreoideus, and the inferior belly of the Omo- hyoideus. According to Arnold, another filament descends in front of the vessels into the thorax, and joins the cardiac and phrenic nerves. The Thyrohyoid Branch {ramus thyreohyoideus) arises from the hypoglossal near the posterior border of the hyoglossus; it runs obliquely across the greater cornu of the hyoid bone, and supplies the Thyreohyoideus muscle. The Muscular Branches are distributed to the Styloglossus, Hyoglossus, Genio- hyoideus, and Genioglossus. At the under surface of the tongue numerous slender branches pass upward into the substance of the organ to supply its intrinsic muscles. Applied Anatomy. — The hypoglossal nerve is an important guide in the operation of ligature of the lingual artery (see p. 632). It runs forward on the Hyoglossus just above the greater cornu of the hyoid bone, and forms the upper boundary of the triangular space in which the artery is to be sought for by cutting through the fibres of the Hyoglossus. In cases where the nerve is involved by gumma or new growth of the base of the skull, or where it has been injured on one side of the neck, or in some cases of bulbar paralysis, unilateral paralysis, together with hemiatrophy of the tongue, results; the tongue, when protruded, being directed to the paralyzed side owing to the unopposed action of the Genioglossus of the opposite side. On retraction, the wasted and paralyzed side of the tongue rises up higher than the other. The larynx may deviate toward the soimd side on swallowing, from the unilateral paralysis of the depressors of the hyoid bone. If the paralysis is bilateral, the tongue lies motionless in the mouth, while articulation and mastication are much interfered with. THE SPINAL NERVES (NERVI SPINALES). The spinal nerves spring from the medulla spinalis, and are transmitted through the intervertebral foramina. They number thirty-one pairs, which are grouped as follows: Cervical, 8; Thoracic, 12; Lumbar, 5; Sacral, 5; Coccygeal, 1. The first cervical nerve emerges from the vertebral canal between the occipital bone and the atlas, and is therefore called the suboccipital nerve; the eighth issues between the seventh cervical and first thoracic vertebrae. 948 NEUROLOGY Nerve Roots. — Each nerve is attached to the mecUiHa spinalis by two roots, an anterior or ventral, and a posterior or dorsal, the hitter being characterized by the presence of a ganghon, the spinal ganglion. The Anterior Root {radix anterior; ventral ruut) emerges from the anterior surface of the medulla spinalis as a number of rootlets or filaments (fila radicularia) , which coalesce to form two bundles near the intervertebral foramen. The Posterior Root [radix yosterior; dorsal root) is larger than the anterior owing to the greater size and number of its rootlets; these are attacherl along the postero- lateral furrow of the medulla spinalis and unite to form two bundles which join the spinal ganglion. The posterior root of the first cervical nerve is exceptional in that it is smaller than the anterior; it is occasionally wanting. Ventral aspect Dorsal aspect Fig. 797. — Distribution of cutaneous norvL-.s. The Spinal Ganglia (ganglion spinale) are collections of nerve cells on the posterior roots of the spinal nerves. Each ganglion is oval in shape, reddish in color, and its size bears a proportion to that of the nerve root on which it is situated; it is bifid medially where it is joined by the two bundles of the posterior nerve root. THE SPINAL NERVES 949 The ganglia are usually placed in the inter\'ertebral foramina, immediately outside the points where the nerve roots perforate the dura mater, but there are exceptions to this rule; thus the ganglia of the first and second cervical nerves lie on the verte- bral arches of the atlas and axis respectively, those of the sacral nerves are inside the vertebral canal, while that on the posterior root of the coccygeal nerve is placed within the sheath of dura mater. Structure (Fig. 679). — The ganglia consist chiefly of unipolar nerve cells, and from these the fibres of the posterior root take origin — the single process of each cell dividing after a short course into a central fibre which enters the medulla spinalis and a peripheral fibre which runs into the spinal nerve. Two other forms of cells are, however, present, viz.: (a) the cells of Dogiel, whose axons ramifj^ close to the cell (type II, of Golgi), and are distributed entirely within the ganglion; and (b) multipolar cells similar to those found in the sympathetic ganglia. The ganglia of the first cervical nerve may be absent, while small aberrant ganglia consisting of groups of nerve cells are sometiines found on the posterior roots between the spinal ganglia and the medulla spinalis. Each nerve root receives a covering from the pia mater, and is loosely invested by the arachnoid, the latter being prolonged as far as, the points where the roots pierce the dura mater. The two roots pierce the dura mater separately, each receiv- ing a sheath from this membrane; where the roots join to form the spinal nerve this sheath is continuous with the epineurium of the nerve. Size and Direction. — Tlie roots of the upper four cervical nerves are small, those of the lower four are large. The posterior roots of the cervical nerves bear a pro- portion to the anterior of three to one, which is greater than in the other regions; their individual filaments are also larger than those of the anterior roots. The posterior root of the first cervical is an exception to this rule, being smaller than the anterior root; in eight per cent, of cases it is wanting. The roots of the first and second cervical nerves are short, and run nearly horizontally to their points of exit from the vertebral canal. From the second to the eighth cervical they are directed obliquely downward, the obliquity and length of the roots successively increasing; the distance, however, between the level of attachment of any of these roots to the medulla spinalis and the points of exit of the corresponding nerves never exceeds the depth of one vertebra. The roots of the thoracic nerves, with the exception of the first, are of small size, and the posterior only slightly exceed the anterior in thickness. They increase successively in length, from above downward, and in the lower part of the thoracic region descend in contact with the medulla spinalis for a distance equal to the height of at least two vertebrae before they emerge from the vertebral canal. The roots of the lower lumbar and upper sacral nerves are the largest, and their individual filaments the most numerous of all the spinal nerves, while the roots of the coccygeal nerve are the smallest. The roots of the lumbar, sacral, and coccygeal nerves rim vertically downward to their respective exits, and as the medulla spinalis ends near the lower border of the first lumbar vertebra it follows that the length of the successive roots must rapidly increase. As already mentioned (page 806), the term cauda equina is applied to this collection of nerve roots. From the description given it Avill be seen that the largest nerve roots, and consequently the largest spinal nerves, are attached to the cervical and lumbar swellings of the medulla spinalis; these nerves are distributed to the upper and lower limbs. Connections with Sympathetic. — Immediately beyond the spinal ganglion, the anterior and posterior nerve roots unite to form the spinal nerve which emerges through the intervertebral foramen. Each spinal nerve receives a branch (gray ramus communicans) from the adjacent ganglion of the sympathetic trunk, while the thoracic, and the first and second lumbar nerves each contribute a branch 950 NEUROLOGY (white ramus communicans) to the adjoining sympathetic ganglion. The second, third, and fourth sacral nerves also supply white rami; these, however, are not connected with the ganglia of the sympathetic trunk, but run directly into the pelvic plexuses of the sympathetic. Structure. — Each typical spinal nerve contains fibres belonging to two systems, viz., the somatic, and the sympathetic or splanchnic, as well as fibres connecting these systems with each other (Fig. 798). 1. The somatic fibres are efferent and afferent. The efferent fibres originate in the cells of the anterior column of the medulla spinalis, and run outward through the anterior nerve roots to the spinal nerve. They convey impulses to the voluntary muscles, and are continuous from their origin to their peripheral distribution. The afferent fibres convey impressions inward from the skin, etc., and originate in the unipolar nerve cells of the spinal ganglia. The single processes of these cells divide into peripheral and central fibres, and the latter enter the medulla spinalis through the posterior nerve roots. Sympathetif ganglion Spinal nerve Fig. 7£ !. — Scheme showing structure of a typical spinal nerve. 1. Somatic efferent. Splanchnic efferent. 6, 7. Splanchnic afferent. 2. Somatic afferent. 3,4,5. 2. The sympathetic fibres are also efferent and afferent. The efferent fibres originate in the lateral column of the medulla spinalis, and are conveyed through the anterior nerve root and the white ramus communicans to the corresponding ganghon of the sympathetic trunk; here they may end by forming synapses around its cells, or may run through the ganglion to end in another of the ganglia of the sympathetic trunk, or in a more distally placed ganglion in one of the sympa- thetic plexuses. In all cases they end by forming synapses around other nerve cells. From the cells of the gangUa of the sympathetic trunk other fibres take origin; some of these run through the gray rami communicantes to join the spinal nerves, along which they are carried to the blood- vessels of the trunk and limbs, while others pass to the viscera, either directly or after interrup- tion in one of the distal ganglia. The afferent fibres are derived partly from the unipolar cells and partly from the multipolar cells of the spinal gangha. Their peripheral processes are carried through the white rami communicantes, and after passing through one or more sympathetic ganglia (but always without interruption in them) finally end in the tissues of the viscera. The central processes of the unipolar cells enter the medulla spinahs through the posterior nerve root and form synapses around either somatic or sympathetic efferent neurons, thus completing reflex arcs. The dendrites of the multipolar nerve cells form synapses arormd the cells of type II (cells of Dogiel) in the spinal ganglia, and by this path the original impulse is transferred from the sympathetic to the somatic system, through which it is conveyed to the sensorium. THE CERVICAL NERVES 951 Divisions. — After emerains from the intervertebral foramen, each spinal nerve gives olf a small meningeal branch which reenters the vertebral canal through the intervertebral foramen and supplies the ^'erteb^a5 and their ligaments, and the blood^-essels of the medulla spinalis and its membranes. The spinal nerve then splits into a posterior or dorsal, and an anterior or ventral division, each recei\'ing fibres from both ner^'e roots. POSTERIOR DIVISIONS OF THE SPINAL NERVES (RAMI POSTERIORES). The posterior divisions are as a rule smaller than the anterior. They are directed backward, and, with the exceptions of those of the first cervical, the fourth and fifth sacral, and the coccygeal, divide into medial and lateral branches for the supply of the muscles and skin (Figs. 799, 800) of the posterior part of the trunk. The Cervical Nerves (Nn. Cervicales). The posterior division of the first cervical or suboccipital nerve is larger than the anterior division, and emerges above the posterior arch of the atlas and beneath the vertebral artery. It enters the suboccipital triangle and supplies the muscles which bound this triangle, viz., the Rectus capitis posterior major, and the Obliqui superior and inferior; it gives branches also to the Rectus capitis posterior minor and the Semispinalis capitis. A filament from the branch to the Obliquus inferior joins the posterior division of the second cervical nerve. The nerve occasionally gives off a cutaneous branch which accompanies the occipital artery to the scalp, and communicates with the greater and lesser occipital nerves. The posterior division of the second cervical nerve is much larger than the anterior division, and is the greatest of all the cervical posterior divisions. It emerges between the posterior arch of the atlas and the lamina of the axis, below the Obliquus inferior. It supplies a twig to this muscle, receives a communicating filament from the posterior division of the first cervical, and then divides into a large medial and a small lateral branch. The medial branch {ramus medialis; internal branch), called from its size and distribution the greater occipital nerve (n. occipitalis major; great occipital nerve), ascends obliquely between the Obliquus inferior and the Semispinalis capitis, and pierces the latter muscle and the Trapezius near their attachments to the occipital bone (Fig. 799). It is then joined by a filament from the medial branch of the posterior division of the third cervical, and, ascending on the back of the head with the occipital artery, divides into branches which communicate with the lesser occipital nerve and supply the skin of the scalp as far forward as the vertex of the skull. It gives off muscular branches to the Semispinalis capitis, and occasionally a twig to the back of the auricula. The lateral branch (ramus lateralis; external branch) supplies filaments to the Splenius, Longus capitis, and Semispinalis capitis, and is often joined by the corresponding branch of the third cervical. The posterior division of the third cervical is intermediate in size between those of the second and fourth. Its medial branch runs between the Semispinalis capitis and cervicis, and, piercing the Splenius and Trapezius, ends in the skin. While under the Trapezius it gives off a branch called the third occipital nerve, which pierces the Trapezius and ends in the skin of the lower part of the back of the head (Fig. 799). It lies medial to the greater occipital and communicates with it. The lateral branch often joins that of the second cervical. • The posterior division of the suboccipital, and the medial branches of the posterior division of the second and third cervical nerves are sometimes joined by commvmicating loops to form the -posterior cervical -plexus (Cruveiihier) . The posterior divisions of the lower five cervical nerves divide into medial and lateral branches. The medial branches of the fourth and fifth run between the 952 NEUROLOGY Semispinales cervicis and capitis, and, lia\ing reached the spinous processes, pierce the Splenius and Trapezius to end in the skin (Fig. 799). Sometimes the branch of the fifth fails to reach the skin. Those of the lower three ner\'es are small, and end hi the Semispinales cervicis and capitis, Multifidus, and Inter- spinales. The lateral branches of the lower five nerves supply the Iliocostalis cervicis, Longissimus cervicis, and Longissimus capitis. Fig. 799. — Diagram of the distribution of the cutaneous branches of the posterior divisions of the spinal nerves. Fig. 800. — Areas of distribution of the cutaneous branches of the posterior divisions of the spinal nerves. (H. ]M. Johnston.) The areas of the medial branches are in black, those of the lateral in red. The Thoracic Nerves (Nn. Thoracalesj. The medial branches {ramus medialis; internal branch) of the posterior divisions of the upper six thoracic nerves run between the Semispinalis dorsi and ^lultifidus, which they supply; they then pierce the Rhomboidei and Trapezius, and reach the skin by the sides of the spinous processes (Fig. 799). The medial branches THE SACRAL XERVES 953 of the lower six are (listril)ute(l chiefly to the Muhifi(his and Longissimus dorsi; occasionally they give off filaments to the skin near the middle line. The lateral branches {ra)iim lateralis; external branch) increase in size from above downward. They run through or beneath the Longissimus dorsi to the interval between it and the Iliocostales, and supply these muscles; the lower five or six also give off cutaneous branches which pierce the Serratus posterior inferior and Latissimus dorsi in a line with the angles of the ribs (Fig. 799). The lateral branches of a variable number of the upper thoracic nerves also give filaments to the skin. The lateral branch of the twelfth thoracic, after sending a filament medialward along the iliac crest, passes downward to the skin of the buttock. The medial cutaneous branches of the posterior divisions of the thoracic nerves descend for some distance close to the spinous processes before reaching the skin, while the lateral branches travel downward for a considerable distance — it ma}' be as much as the breadth of four ribs — before thej' become superficial; the branch from the twelfth thoracic, for instance, reaches the skin only a little way above the iliac crest. ^ The Lumbar Nerves (Nn. Lumbales). The medial branches of the posterior divisions of the lurnbar nerves run close to the articular processes of the vertebrse and end in the Multifidus. The lateral branches supply the Sacrospinalis. The upper three give off cutaneous nerves which pierce the aponeurosis of the Latissimus dorsi at the lateral border of the Sacrospinalis and descend across the posterior part of the iliac crest to the skin of the buttock (Fig. 799), some of their twigs running as far as the level of the greater trochanter. ■^ Anterio-r branches ^ of lower sacral nerves J Fig. SOI. — The posterior divisions of the sacral nerves. The Sacral Nerves (Nn. Sacrales). The posterior divisions of the sacral nerves (rami posteriores) (Fig. SQl) are small, and diminish in size from above downward; they emerge, except the last, 1 See article bj- H. M. Johnston, Journal of Anatomj- and Phj-siology, vol. xliii. 954 NEUROLOGY through the posterior sacral foramina. The upper three are covered at their points of exit by the Miiltifidiis, and divide into medial and lateral branches. The medial branches are small, and end in the Multifidus. The lateral branches join with one another and with the lateral branches of the posterior divisions of the last lumbar and fourth sacral to form loops on the dorsal surface of the sacrum. From these loops branches run to the dorsal surface of the sacrotuberous ligament and form a second series of loops under the Glutaeus naaxi- mus. From this second series cutaneous branches, two or three in number, pierce the Glutaeus maximus along a line drawn from the posterior superior iliac spine to the tip of the coccyx; they supply the skin over the posterior part of the buttock. The posterior divisions of the lower two sacral nerves are small and lie below the Multifidus. They do not divide into medial and lateral branches, but unite with each other and with the posterior division of the coccygeal nerve to form loops on the back of the sacrum; filaments from these loops supply the skin over the coccyx. The Coccygeal Nerve (N. Coccygeus). The posterior division of the coccygeal nerve {ramus posterior) does not divide into a medial and a lateral branch, but receives, as already stated, a communicating branch from the last sacral; it is distributed to the skin over the back of the coccyx. ANTERIOR DIVISIONS OF THE SPINAL NERVES (RAMI ANTERIORES). The anterior divisions of the spinal nerves supply the antero-lateral parts of the trunk, and the limbs; they are for the most part larger than the posterior divisions. In the thoracic region they run independently of one another, but in the cervical, lumbar, and sacral regions they unite near their origins to form plexuses. The Cervical Nerves (Nn. Cervicales). The anterior divisions of the cervical nerves {rami anteriores) , with the exception of the first, pass outward between the Intertransversarii anterior and posterior, lying on the grooved upper surfaces of the transverse processes of the vertebrae. The anterior division of the first or suboccipital nerve issues from the vertebral canal above the posterior arch of the atlas and runs forward around the lateral aspect of its superior articular process, medial to the vertebral artery. In most cases it descends medial to and in front of the Rectus capitis lateralis, but occasionally it pierces the muscle. The anterior divisions of the upper four cervical nerves unite to form the cervical plexus, and each receives a gray ramus communicans from the superior cervical ganglion of the sympathetic trunk. Those of the lower four cervical, together with the greater part of the first thoracic, form the brachial plexus. They each receive a gray ramus communicans, those for the fifth and sixth being derived from the middle, and those for the seventh and eighth from the lowest, cervical ganglion of the sympathetic trunk. The Cervical Plexus {plexus cervicalis) (Fig. 802). — The cervical plexus is formed by the anterior divisions of the upper four cervical nerves; each nerve, except the first, divides into an upper and a lower branch, and the branches unite to form three loops. The plexus is situated opposite the upper four cervical vertebrae, in front of the Levator scapulae and Scalenus medius, and covered by the Sterno- cleidomastoideus. Its branches are divided into two groups, superficial and deep, and are here given in tabular form; the figures following the names indicate the nerves from which the different branches take origin: THE CERVICAL NERVES 955 Superficial Internal Deep External Smaller occipital Great auricular . Cutaneous cervical Suprachn-icular fCommunicatino; ''Muscular With hypoglossal " vagus . " sympathetic Rectus capitis lateralis Rectus capitis anterior Longus capitis Communicantes cervi- cales .Phrenic Communicating with accessory fSternocleidomastoideus Muscular Trapezius 1 Levator' scapulae [Scalenus medius 2,C. 2, 3, C. 2, 3, C. 3, 4, C. 1, 2, C. 1, 2, C. 1,2,3,4,C. 1,C. 1, 2, C. 1, 2, 3, C. 2, 3, C. 3, 4, 5, C. 2, 3, 4, C. 2, C. 3, 4, C. 3, 4, C. 3, 4, C. Smaller occipital To Vagus Great auricular To Sternocleido- mastoideus To Lev. scapulae Cutaneous cervical To Rectus lateralis To Rect. cap. ant. and Long. cap. To Longus capitis and Longus colli To Scalenus mediu. Phrenic To Longus capitis and Longus colli To Geniohyoideus To Thyreohyoideus Descendens hypoglossi Communicantes cervicales — To Longus colli Ansa hypoglossi Supraclavicular Fig. 802. — Plan of cervical plexus. 956 NEUROLOGY Superficial Branches of the Cervical Plexus (Fig. 803). — The Smaller Occipital Nerve {n. occipifalis mi nor; small occipital nerve) arises from the second cer\-ical ner\'e, sometimes also from the third; it curves around and ascends along the posterior border of the Sternocleidomastoideus, Near the cranium it perforates the deep fascia, and is continued upward along the side of the head behind the auricula, supplying the skin and communicating with the greater occipital, the great auricular, and the posterior auricular branch of the facial. The smaller occipital varies in size, and is sometimes duplicated. Fig. 803. — The nerves of the scalp, face, and side of neck. It gives off an auricular branch, which supplies the skin of the upper and back part of the auricula, communicating with the mastoid branch of the great auricular. This branch is occasionally derived from the greater occipital nerve. The Great Auricular Nerve {n. auricidaris magnus) is the largest of the ascending branches. It arises from the second and third cervical nerves, winds around the posterior border of the Sternocleidomastoideus, and, after perforating the deep fascia, ascends upon that muscle beneath the Platysma to the parotid gland, where it divides into an anterior and a posterior branch. The anterior branch (ramus anterior; facial branch) is distributed to the skin of the face over the parotid gland, and communicates in the substance of the gland with the facial nerve. THE CERVICAL NERVES 957 The posterior branch (m/z/z/.v inhstcrior; mantuld branch) supplies tlie skin o\er the mastoid process and on the back of the auricula, except at its upper part; a fiLament pierces the auricuhi to reach its hiteral surface, wliere it is distributed to the h)bule and knver ])art of the concha. Tlic posterior l)ranch communicates witli the smaller occipital, the auricular branch of the vagus, and the posterior auricular branch of the facial. The Cutaneous Cervical (//. ciifaiietts colli; .superficial or iransverse cervical nerve) arisc'i from the second and third cervical nerves, turns around the posterior border of the Sternocleidomastoideus about its middle, and, passing obliquely forward beneath the external jugular vein to the anterior border of the muscle, it perforates the deep cervical fascia, and divides beneath the Platysma into ascending and descending branches, which are distributed to the antero-lateral parts of the neck. The ascending branches {rami superiores) pass upward to the submaxillary region, and form a plexus with the cervical branch of the facial nerve beneath the Platysma; others pierce that muscle, and are distributed to the skin of the upper and front part of the neck. The descending branches {rami inferiores) pierce the Platysma, and are distributed to the skin of the side and front of the neck, as low as the sternum. The Supraclavicular Nerves {nn. supraclaviculares ; descending branches) arise from the third and fourth cervical nerves; they emerge beneath the posterior border of the Sternocleidomastoideus, and descend in the posterior triangle of the neck beneath the Platysma and deep cervical fascia. Near the clavicle they perforate the fascia and Platysma to become cutaneous, and are arranged, according to their position, into three groups — anterior, middle and posterior. The anterior supraclavicular nerves {nn. supraclaviculares anteriores; suprasternal nerves) cross obliquely over the external jugular vein and the clavicular and sternal heads of the Sternocleidomastoideus, and supply the skin as far as the middle line. They furnish one or two filaments to the sternoclavicular joint. The middle supraclavicular nerves {nn. supraclaviculares viedii; supraclavicular nerves) cross the clavicle, and supply the skin over the Pectoralis major and Del- toideus, communicating with the cutaneous branches of the upper intercostal nerves. The posterior supraclavicular nerves {7in. supraclaviculares posteriores; supra-acromial nerves) pass obliquely across the outer surface of the Trapezius and the acromion, and supply the skin of the upper and posterior parts of the shoulder. Deep Branches of the Cervicle Plexus. Internal Series. — The Communicating Branches consist of several filaments, which pass from the loop between the first and second cervical nerves to the vagus, hypoglossal, and sympathetic. The branch to the hypoglossal ultimately leaves that nerve as a series of branches, viz., the descending ramus, the nerve to the Thyreohyoideus and the nerve, to the Genio- hyoideus (see page 947). A communicating branch also passes from the fourth to the fifth cervical, while each of the first four cervical nerves receives a gray ramus communicans from the superior cervical ganglion of the sympathetic. Muscular Branches supply the Longus capitis, Rectus capitis anterior, and Rectus capitis lateralis. The Communicantes Cervicales {communicantes hypoglossi) (Fig. 802) consist usually of two filaments, one derived from the second, and the other from the third ce^^'ical. These filaments join to form the descendens cervicalis, which passes downward on the lateral side of the internal jugular vein, crosses in front of the vein a little below the middle of the neck, and forms a loop (ansa hypoglossi) with the descending ramus of the hypoglossal in front of the sheath of the carotid vessels (see page 947). Occasionally, the loop is formed within the sheath. The Phrenic Nerve {n. phrenicus; internal respiratory nerve of Bell) contains motor and sensory fibres in the proportion of about two to one. It arises chiefly from the 958 NEUROLOGY fourth cervical nerve, but receives a branch from the third and another from the fifth; the fibres from the fifth occasionally come through the nerve to the Sub- clavius. It descends to the root of the neck, running obliquely across the front of the Scalenus anterior, and beneath the Sternocleidornastoideus, the inferior belly of the Omohyoideus, and the transverse cervical and transverse scapular vessels. It next passes in front of the first part of the subclavian artery, between it and the subclavian vein, and, as it enters the thorax, crosses the internal mam- mary artery near its origin. Within the thorax, it descends nearly vertically in front of the root of the lung, and then between the pericardium and the medias- tinal pleura, to the Diaphragma, where it divides into branches, which pierce that muscle, and are distributed to its under surface. In the thorax it is accom- panied by the pericardiacophrenic branch of the internal mammary artery. The two phrenic nerves differ in their length, and also in their relations at the upper part of the thorax. The right nerve is situated more deeply, and is shorter and more vertical in direction than the left; it lies lateral to the right innominate vein and superior vena cava. The left nerve is rather longer than the right, from the inclination of the heart to the left side, and from the Diaphragma being lower on this than on the right side. At the root of the neck it is crossed by the thoracic duct; in the superior mediastinal cavity it lies between the left common carotid and left subclavian arteries, and crosses superficial to the vagus on the left side of the arch of the aorta. Each nerve supplies filaments to the pericardium and pleura, and at the root of the neck is joined by a filament from the sympathetic, and, occasionally, by one from the ansa hypoglossi. Branches have been described as passing to the peritoneum. From the right nerve, one or two filaments pass to join in a small phrenic ganglion with phrenic branches of the coeliac plexus; and branches from this ganglion are distributed to the falciform and coronary ligaments of the liver, the suprarenal gland, inferior vena cava, and right atrium. From the left nerve, filaments pass to join the phrenic branches of the coeliac plexus, but without any ganglionic enlarge- ment; and a twig is distributed to the left suprarenal gland. Deep Branches of the Cervical Plexus. External SERiES.^Communicating Branches. — The external series of deep branches of the cervical plexus communi- cates with the accessory nerve, in the substance of the Sternocleidomastoideus, in the posterior triangle, and beneath the Trapezius. Muscular Branches are distributed to the Sternocleidomastoideus, Trapezius, Levator scapulae, and Scalenus medius. The branch for the Sternocleidomastoideus is derived from the second cervical ; the Trapezius and Levator scapulae receive branches from the third and fourth. The Scalenus medius receives twigs either from the third or fourth, or occasionally from both. Applied Anatomy, — Pains referred to the terminal branches of the cervical plexus are not uncommon in caries of the cervical vertebrse, where pain may be felt radiating over the occipital bone, if the disease is situated high up in the vertebral column. The Brachial Plexus {ylexus brachialis) (Fig. 804).— The brachial plexus is formed by the union of the anterior divisions of the lower four cervical nerves and the greater part of the anterior division of the first thoracic nerve; the fourth cer- vical usually gives a branch to the fifth cervical, and the first thoracic frequently receives one from the second thoracic. The plexus extends from the lower part of the side of the neck to the axilla. The nerves which form it are nearly equal in size, but their mode of communication is subject to some variation. The following THE CERVICAL NERVES 959 is, however, the most constant arrangement. The fifth and sixth cervical unite s6on after their exit from the intervertebral foramina to form a trunk. The eighth cervical and first thoracic also unite to form one trunk, while the seventh cervical runs out alone. Three trunks— upper, middle, and lower— are thus formed, and, as they pass beneath the clavicle, each splits into an anterior and a posterior divi- sion.^ The anterior divisions of the upper and middle trunks unite to form a cord, which is situated on the lateral side of the second part of the axillary artery, and is called the lateral cord or fasciculus of the plexus. The anterior division of the lower trunk passes down on the medial side of the axillary artery, and forms the medial cord or fasciculus of the brachial plexus. The posterior divisions of all three trunks unite to form the posterior cord or fasciculus of the plexus, which is situated behind the second portion of the axillary artery. FronYIC. To Rhomboidel- Tojoin the jjhremc Suprascajndar To Subclavius Lateral anteri thoracic To Lo'iigus colli and Scaleni — To LonnuB colli and Scaleni To Longus colli and Scaleni Long thoracic To Longiis colli and Scaleni Median Ulnar J 2ledial brachial Media I a ntibrach ia I cutaneous cutaneous Fig. 804. — Plan of brachial plexus. Relations.— In. the neck, the brachial plexus lies in the posterior triangle, being covered by the skin, Platysma, and deep fascia; it is crossed by the supraclavicular nerves, the inferior belly of the Omohyoideus, the external jugular vein, and the transverse cervical artery. It emerges between the Scaleni anterior and medius; its upper part lies above the third part of the sub- clavian artery, while the trunk formed by the union of the eighth cervical and first thoracic is placed behind the artery; the plexus next passes behind the clavicle, the Subclavius, and the trans- verse scapular vessels, and lies upon the first digitation of the Serratus anterior, and the Sub- scapularis. In the axilla it is placed lateral to the first portion of the axillary artery; it surrounds the second part of the artery, one cord lying medial to it, one lateral to it, and one behmd it; at the lower part of the axilla it gives off its terminal branches to the upper limb. 1 The posterior division of the lower trunk is very much smaUer than the others, and is frequently derived entirely from the eighth cervical nerve. . 5C. . 5, 6 C. . . 5, 6 C. . 5, 6, 7 C. . 5, 6, 7, 8 C 960 NEUROLOGY Branches of Communication.- — Close to their exit from the intervertebral foramina the fifth and sixth cervical nerves each receive a gray ramus communicans from the middle cervical ganglion of the sympathetic trunk, and the seventh and eighth cervical similar twigs from the inferior ganglion. The first thoracic nerve receives a gray ramus from, and contributes a white ramus to, the first thoracic ganglion. On the Scalenus anterior the phrenic nerve is joined by a branch from the fifth cervical. Branches of Distribution. — The branches of distribution of the brachial plexus may be arranged into two groups, viz., those given oft" above and those below the clavicle. Supraclavicular Branches. Dorsal scapular . Suprascapular Nerve to Subclavius Long thoracic To Longus colli and Scaleni The Dorsal Scapular Nerve {n. dorsaUs scajmlae; nerve to the Rhomboidei; posterior scajyular nerve) arises from the fifth cervical, pierces the Scalenus medius, passes beneath the Levator scapulae, to which it occasionally gives a twig, and ends in the Rhomboidei. The Suprascapular (n. sitprascapidaris) (Fig. 810) arises from the trunk formed by the union of the fifth and sixth cervical nerves. It runs lateralward beneath the Trapezius and the Omohyoideus, and enters the supraspinatous fossa through the suprascapular notch, below, the superior transverse scapular ligament; it then passes beneath the Supraspinatus, and curves around the lateral border of the spine of the scapula to the infraspinatous fossa. In the supraspinatous fossa it gives off two branches to the Supraspinatus muscle, and an articular filament to the shoulder-joint; and in the infraspinatous fossa it gives off two branches to the Infraspinatous muscle, besides some filaments to the shoulder-joint and scapula. The Nerve to the Subclavius (n. subclavius) is a small filament, which arises from the point of junction of the fifth and sixth cervical nerves; it descends to the muscle in front of the third part of the subclavian artery and the lower trunk of the plexus, and is usually connected by a filament with the phrenic nerve. The Long Thoracic Nerve (n. thoracalis longus; external respiratory nerve of Bell; posterior thoracic nerve) (Fig. 809) supplies the Serratus anterior. It usually arises by three roots from the fifth, sixth, and seventh cervical nerves; but the root from the seventh nerve may be absent. The roots from the fifth and sixth nerves pierce the Scalenus medius, while that from the seventh passes in front of the muscle. The nerve descends behind the brachial plexus and the axillary vessels, resting on the outer surface of the Serratus anterior. It extends along the side of the thorax to the lower border of that muscle, supplying filaments to each of its digitations. The branches for the Longus colli and Scaleni arise from the lower four cervical nerves at their exit from the intervertebral foramina. Infraclavicular Branches. The infraclavicular branches are derived from the three cords of the brachial plexus, but the fasciculi of the nerves may be traced through the plexus to the spinal nerves from which thev originate. They are as follows: THE CERVICAL NERVES 961 Lateral cord IMedial cord Posterior cord AiusculocutaiieoLis Lateral anterior thoracic Lateral head of median . Medial anterior thoracic Medial antihrachial cutaneous Medial brachial cutaneous Ulnar Medial head of median Upper subscapular . Lower subscapular . Thoracodorsal . Axillary Radial 5, 6, 7 C. 5, 6, 7 C. (), 7 C. 8 C, 1 T. 5, 6C. 5, 6C. 5, 6, 7 C. 5, 6C. 6, 7, S C, 1 T. The Anterior Thoracic Nerves {nn. thoracales anteriores) (Fig. 809) supply the Pectorales major and minor. The lateral anterior thoracic {fasciculus lateralis) the; larger of the two, arises from the lateral cord of the brachial plexus, and through it from the fifth, sixth, and seventh cervical nerves. It passes across the axillary artery and vein, pierces the coracoclavicular fascia, and is distributed to the deep surface of the Pectoralis major. It sends a filament to join the medial anterior thoracic and form with it a loop in front of the first part of the axillary artery. The medial anterior thoracic {fasciculus medialis) arises from the medial cord of the plexus and through it from the eighth cervical and first thoracic. It passes behind the first part of the axillary artery, curves forward between the axillary artery and vein, and unites in front of the artery with a filament from the lateral nerve. It then enters the deep surface of the Pectoralis minor, where it divides into a number of branches, which supply the muscle. Two or three branches pierce the muscle and end in the Pectoralis major. The Subscapular Nerves {nn. subscajndares) , two in number, spring from the posterior cord of the plexus and through it from the fifth and sixth cervical nerves. The upper subscapular {short suhscajmlar) , the smaller enters the upper part of the Subscapularis, and is frequently represented by two branches. The lower subscapular supplies the lower part of the Subscapularis, and ends in the Teres major; the latter muscle is sometimes supplied by a separate branch. The Thoracodorsal Nerve (w. thoracodorsalis; middle or long suhscapular nerve), a branch of the posterior cord of the plexus, derives its fibres from the fifth, sixth, and seventh cervical nerves; it follows the course of the subscapular artery, along the posterior wall of the axilla to the Latissimus dorsi, in which it ma}^ be traced as far as the lower border of the muscle. The Axillary Nerve {ii. axillaris; circumflex nerve) (Fig. 810) arises from the pos- terior cord of the brachial plexus, and its fibres are derived from the fifth and sixth cervical nerves. It lies at first behind the axillary artery, and in front of the Subscapularis, and passes downward to the lower border of that muscle. It.then winds backward, in company with the posterior humeral circumflex artery, through a quadrilateral space bounded above by the Subscapularis, below by the Teres major, medially by the long head of the Triceps brachii, and laterally by the surgical neck of the humerus, and divides into an anterior and a posterior branch. The anterior branch {upper branch) winds around the surgical neck of the humerus, beneath the Deltoideus, with the posterior humeral circumflex vessels, as far as the anterior border of that muscle, supplying it, and giving off a few small cutaneous branches, which pierce the muscle and ramify in the skin covering its low^er part. The posterior branch {lower branch) supplies the Teres minor and the posterior part of the Deltoideus; upon the branch to the Teres minor an oval enlargement 61 962 NEUROLOGY (pseudoganglion) usually exists. The posterior branch then pierces the deep fascia and is continued as the lateral brachial cutaneous nerve, which sweeps around the posterior border of the Deltoideus and supplies the skin over the lower two-thirds of the posterior part of this muscle, as well as that covering the long head of the Triceps brachii (Figs 805, 807). Fig. 805. — Cutaneous nerves of right upper extremity. Anterior view. Fig, 806. — Diagram of segmental distribution of the cutaneous nerves of the right upper extremity. Anterior view. The trunk of the axillary nerve gives off an articular filament which enters the shoulder-joint below the Subscapularis. The Musculocutaneous Nerve (n. musculocutaneus) (Fig. 809) arises from the lateral cord of the brachial plexus, opposite the lower border of the Pectoralis minor, its fibres being derived from the fifth, sixth, and seventh cervical nerves. THE CERVICAL NERVES 963 It pierces the Coracobrachialis muscle and passes obliquely between the Biceps brachii and the Brachialis, to the lateral side of the arm; a little above the elbow- it pierces the deep fascia lateral to the tendon of the liiccps brachii and is continued into the forearm as the lateral antibrachial cutaneous nerve. In its course through the arm it supplies the Coracobrachialis, Biceps brachii,. and the greater part of the Fig. 807. — Cutaneous nerves of right upper extremity. Posterior view. Fig. 808. — Diagram of segmental distribution ofi'the cuta- neous nerves of the right upper extremity. Posterior view Brachialis. The branch to the Coracobrachialis is given off from the nerve close to its origin, and in some instances as a separate filament from the lateral cord of the plexus; it is derived from the seventh cervical nerve. The branches to the Biceps brachii and Brachialis are given off after the musculocutaneous has pierced the Coracobrachialis; that supplying the Brachialis gives a filament to the elbow- 964 NEUROLOGY joint. The nerve also sends a small branch to the bone, which enters the nntrient foramen with the accom})anying artery. The lateral antibrachial cutaneous nerve {ii. cuiaiieus anfibrachii cutaneou.s lateralis; branch of inusculocidaneous nerve) passes behind the cephalic vein, and divides, opposite the elbow-joint, into a volar and a dorsal branch (Figs. 805, 807). The volar branch {ramus volaris; anterior branch) descends along the radial border of the forearm to the wrist, and supplies the skin over the lateral half of its volar surface. At the wrist-joint it is placed in front of the radial artery, and some filaments, piercing the deep fascia, accompany that vessel to the dorsal surface of the carpus. The nerve then passes downward to the ball of the thumb, where it ends in cutaneous filaments. It communicates with the superficial branch of the radial ner\'e, and with the palmar cutaneous branch of the median nerve. The dorsal branch (ramus dorsalis; posterior branch) descends, along the dorsal surface of the radial side of the forearm to the wrist. It supplies the skin of the lower two-thirds of the dorso-lateral surface of the forearm, communicating with the superficial branch of the radial nerve and the dorsal antibrachial cutaneous branch of the radial. The musculocutaneous nerve presents frequent irregularities. It may adhere for some distance to the median and then pass outward, beneath the Biceps brachii, instead of through the Coracobrachialis. Some of the fibres of the median may run for some distance in the musculo-cutaneous and then leave it to join their proper trunk; less frequently the reverse is the case, and the median sends a branch to join the musculocutaneous. The nerve may pass under the Coracobrachialis or through the Biceps brachii. Occasionally it gives a filament to the Pronator teres, and it supplies the dorsal surface of the thumb when the superficial branch of the radial nerve is absent. The Medial Antibrachial Cutaneous Nerve (/i. cutaneus antibrachii medialis; iniernal cutaneous nerve) (Fig. 809) arises from the medial cord of the brachial plexus. It derives its fibres from the eighth cervical and first thoracic nerves, and at its com- mencement is placed medial to the axillary artery. It gives off, near the axilla, a filament, which pierces the fascia and supplies the integument covering the Biceps brachii, nearly as far as the elbow. The nerve then runs down the ulnar side of the arm medial to the brachial artery, pierces the deep fascia with the basilic vein, about the middle of the arm, and divides into a volar and an ulnar branch. The volar branch (ramus volaris; anterior branch), the larger, passes usually in front of, but occasionally behind, the vena mediana cubiti '{inedian basilic vein). It then descends on the front of the ulnar side of the forearm, distributing filaments to the skin as far as the wrist, and communicating with the palmar cutaneous branch of the ulnar nerve (Fig. 805). The ulnar branch (ramus unlaris; posterior branch) passes obliquely downward on the medial side of the basilic vein, in front of the medial epicondyle of the humerus, to the back of the forearm, and descends on its ulnar side as far as the wrist, dis- tributing filaments to the skin. It communicates with the medial brachial cutaneous, the dorsal antibrachial cutaneous branch of the radial, and the dorsal branch of the ulnar (Fig. 807). The Medial Brachial Cutaneous Nerve (ii. cutaneus brachii medialis; lesser internal cutaneous nerve; nerve of Wrisberg) is distributed to the skin on the ulnar side of the arm (Figs. 805, 807). It is the smallest branch of the brachial plexus, and arising from the medial cord receives its fibres from the eighth cervical and first thoracic nerves. It passes through the axilla, at first lying behind, and then medial to the axillary vein, and communicates with the intercostobrachial nerve. It descends along the medial side of the brachial artery to the middle of the arm, where it pierces the deep fascia, and is distributed to the skin of the back of the lower third of the arm, extending as far as the elbow, where some filaments are lost in the skin in TIIK CERVICAL NERVES 965 front of the medial epicoiulyle, and others o\'er the olecranon. It communicates with the ulnar branch of the medial antibrachial cutaneous nerve. In some cases the medial brachial cutaneous and interciostobrachial are connected by two or three filaments, which form a plexus in the axilla. In other cases the intercostobrachial is of large size, and takes the place of the medial bra(!hial cutaneous, receiving merely a filament of communication from the brachial plexus, which represents the latter nerve; in a few cases, this filament is wanting. The Median Nerve (/?. mcdianus) (Fig. 809) extends along the mifldle of the arm and forearm to the hand. It arises by two roots, one from the lateral and one from the medial cord of the brachial plexus; these embrace the lower part of the axillary artery, uniting either in front of or lateral to that vessel. Its fibres are derived from the sixth, seventh, and eighth cervical and first thoracic nerves. As it descends through the arm, it lies at first lateral to the brachial artery; about the level of the insertion of the Coracobrachialis it crosses the artery, usually in front of, but occasion- ally behind it, and lies on its medial side at the bend of the elbow, where it is situated behind the lacertus fibrosus {bicipital fascia) , and is separated from the elbow-joint by the Brachialis. In the forearm it passes between the two heads of the Pronator teres and crosses the ulnar artery, but is separated from this vessel by the deep head of the Pronator teres. It descends beneath the Flexor digitorum sublimis, lying on the Flexor digitorum profundus, to within 5 cm. of the transverse carpal ligament; here it becomes more superficial, and is situated between the tendons of the Flexor digitorum sublimis and Flexor carpi radialis. In this situation it lies behind, and rather to the radial side of, the tendon of the Palmaris longus, and is covered by the skin and fascia. It then passes behind the transverse carpal liga- ment into the palm of the hand. In its course through the forearm it is accompanied by the median artery, a branch of the volar interroseous artery. Branches. — With the exception of the nerve to the Pronator teres, which some- times arises above the elbow-joint, the median nerve gives off no branches in the arm. As it passes in front of the elbow, it supplies one or two twigs to the joint. In the forearm its branches are : muscular, volar interosseous, and palmar. The muscular branches (rami musculares) are derived from the nerve near the elbow and supply all the superficial muscles on the front of the forearm, except the Flexor carpi ulnaris. The volar interosseous nerve {n. interosseus [antibrachii] volaris; anterior inter- osseous nerve) supplies the deep muscles on the front of the forearm, except the ulnar half of the Flexor digitorum profundus. It accompanies the volar interosseous artery along the front of the interosseous membrane, in the interval between the Flexor pollicis longus and Flexor digitorum profundus, supplying the whole of the former and the radial half of the latter, and ending below in the Pronator quadratus and wrist-joint. The palmar branch (ramus cutaneus palmaris n. mediani) of the median nerve arises at the lower part of the forearm. It pierces the volar carpal ligament, and divides into a lateral and a medial branch; the lateral branch supplies the skin over the ball of the thumb, and communicates with the volar branch of the lateral antibrachial cutaneous nerve; the medial branch supplies the skin of the palm and communi- cates with the palmar cutaneous branch of the ulnar. In the palm of the hand the median nerve is covered by the skin and the palmar aponeurosis, and rests on the tendons of the Flexor muscles. Immediately after emerging from under the transverse carpal ligament the nerve becomes enlarged and flattened and splits into a smaller, lateral, and a larger, medial portion. The lateral portion supplies a short, stout branch to certain of the muscles of the ball of the thumb, viz., the x^bductor brevis, the Opponens, and the superficial head of the Flexor brevis, and then divides into three proper volar digital nerves ; two of these supply the sides of the thumb, while the third gives a twig to the first Lumbricalis 966 NEUROLOGY and is distributed to the radial side of the index finger. The medial portion of the nerve divides into two common volar digital nerves. The first of these gives a twig Lalaal unto 101 thoracic Jlediul anterior thoracic 2Iusculocutaneous J — I — Median Radial Deep br. of radial Superjic. br. of radial Volar interosseous Fig. 809, — Nervea of the left upper extremity. ^ THE CERVICAL NERVES 967 to the second Lumbricalis and runs toward the cleft between the index and middle fingers, where it divides into two proper digital nerves for the adjoining sides of these digits; the second runs toward the cleft between the middle and ring fingers, and splits into two proper digital nerves for the adjoining sides of these digits; it communicates with a branch from the ulnar nerve and sometimes sends a twig to the third Lumbricalis. Each proper digital nerve, opposite the base of the first phalanx, gives off a dorsal branch which joins the dorsal digital nerve from the superficial branch of the radial nerve, and supplies the integument on the dorsal aspect of the last phalanx. At the end of the digit, the proper digital nerve divides into two branches, one of which supplies the pulp of the finger, the other ramifies around and beneath the nail. The proper digital nerves, as they run along the fingers, are placed superficial to the corresponding arteries. The Ulnar Nerve {n. ulnaris) (Fig. 809) is placed along the medial side of the limb, and is distributed to the muscles and skin of the forearm and hand. It arises from the medial cord of the brachial plexus, and derives its fibres from the eighth cervical and first thoracic nerves. It is smaller than the median, and lies at first behind it, but diverges from it in its course down the arm. At its origin it lies medial to the axillary artery, and bears the same relation to the brachial artery as far as the middle of the arm. Here it pierces the medial intermuscular septum, runs obliquely across the medial head of the Triceps brachii, and descends to the groove between the medial epicondyle and the olecranon, accompanied by the superior ulnar collateral artery. At the elbow, it rests upon the back of the medial epicondyle, and enters the forearm between the two heads of the Flexor carpi ulnaris. In the forearm, it descends along the ulnar side, lying upon the Flexor digitorum profundus; its upper half is covered by the Flexor carpi ulnaris, its lower half lies on the lateral side of the muscle, covered by the integument and fascia. In the upper third of the forearm, it is separated from the ulnar artery by a consider- able interval, but in the rest of its extent lies close to the medial side of the artery. About 5 cm. above the wrist it ends by dividing into a dorsal and a volar branch. The branches of the ulnar nerve are: articular to the elbow-joint, muscular, palmar cutaneous, dorsal, and volar. The articular branches to the elbow-joint are several small filaments which arise from the nerve as it lies in the groove between the medial epicondyle and olecranon. The muscular branches {rami musculares) two in number, arise near the elbow: one supplies the Flexor carpi ulnaris; the other, the ulnar half of the Flexor digitorum profundus. The palmar cutaneous branch {ramus cutaneus palmaris) arises about the middle of the forearm, and descends on the ulnar artery, giving off some filaments to the vessel. It perforates the volar carpal ligament and ends in the skin of the palm, communicating with the palmar branch of the median nerve. The dorsal branch {ramus dorsalis manus) arises about 5 cm. above the wrist; it passes backward beneath the Flexor carpi ulnaris, perforates the deep fascia, and, running along the ulnar side of the back of the wrist and hand, divides into two dorsal digital branches; one supplies the ulnar side of the little finger; the other, the adjacent sides of the little and ring fingers. It also sends a twig to join that given by the superficial branch of the radial nerve for the adjoining sides of the middle and ring fingers, and assists in supplying them. A branch is distributed to the metacarpal region of the hand, communicating with a twig of the superficial branch of the radial nerve (Fig. 807) . On the little finger the dorsal digital branches extend only as far as the base of the terminal phalanx, and on the ring finger as far as the base of the second phalanx; the more distal parts of these digits are supplied by dorsal branches derived from the proper volar digital branches of the ulnar nerve. 968 NEUROLOGY Axillary ~Radial The volar branch (ramus voJaris maniis) crosses the transverse carpal Hgament on the hiteral side of the pisiform bone, medial to and a little behind the ulnar artery. It ends by dividing into Suprascapular "^^ a Superficial and a deej) branch. The superficial branch {ramus superficialisin. ulnaris]) supplies the Palmaris brevis, and the skin on the ulnar side of the hand, and divides into a proper volar digital branch for the ulnar side of the little finger, and a common volar digital branch which gives a communicating twig to the median nerve and divides into two proper digital nerves for the adjoining sides of the little and ring fingers (Fig. 805). The proper digital branches are distributed to the fingers in the same manner as those of the median. The deep branch [ramus iwo- fundus) accompanied by the deep branch of the ulnar artery, passes between the Abductor digiti quinti and Flexor digiti quinti brevis; it then perforates the Opponens digiti quinti and follows the course of the deejp volar arch beneath the Flexor tendons. At its origin it sup- plies the three short muscles of the little finger. As it crosses the deep part of the hand, it sup- plies all the Interossei and the third and fourth Lumbricalis; it ends by supplying the Adduc- tores pollicis and the medial head of the Flexor pollicis brevis. It also sends articular filaments to the wrist-joint. It has been pointed out that the ulnar part of the Flexor digitorum profundus is supplied by the ulnar nerve; the third and fourth Lumbricales, which are connected with the tendons of this part of the muscle, are supplied by the same nerve. In like manner the lateral part of the Flexor digitorum profundus and the first and second Lumbri- cales are supplied by the median nerve; the third Lumbricalis frequently receives an additional twig from the median nerve. The Radial Nerve {n. radialis; musculospiral nerve) (Fig. 810), the largest branch of the brachial plexus, is the continuation of the posterior cord of the plexus. Its fibres are derived from the fifth, sixth, seventh, and eighth cervical and first thoracic Deep branch of radial Fig. 810. — The suprascapular, axillary, and radial nerves. THE CERVICAL NERVES 969 nerves. It descriuls bt'liind the first part of the axillary artery and the npper part i)f the hraehial artery, and in front of the tendons of the Latissimus dorsi and Teres major. It then winds around from the medial to the hiteral side of the humerus in a groove with the a. profunda brachii, between the medial and lateral heads of the Triceps brachii. It pierces the lateral internuiscular sejjtum, and passes between the Brachialis and Brachioradialis to the front of the lateral epicond\le, where it divides into a superficial and a deep branch. The branches of the musculospiral nerve are: ]\luscular. Superficial. Cutaneous. Deep. The muscular branches (/•(///;/ iiiNscuIarc.-t) supply the Triceps brachii, Anconaeus, Brachioradialis, Extensor carpi radialis longus, and Brachialis, and are grouped as medial, posterior, and lateral. The medial muscular branches supply the medial and long heads of the Triceps brachii. That to the medial head is a long, slender filament, which lies close to the ulnar nerve as far as the lower third of the arm, and is therefore frequently spoken of as the uhiar collateral nerve. The posterior muscular branch, of large size, arises from the nerve in the groove between the Triceps brachii and the humerus. It divides into filaments, which supply the medial and lateral heads of the Triceps brachii and the Anconaeus muscles. The branch for the latter muscle is a long, slender filament, which descends in the substance of the medial head of the Triceps brachii. The lateral muscular branches supply the Brachioradialis, Extensor carpi radialis longus, and the lateral part of the Brachialis. The cutaneous branches are two in number, the posterior brachial cutaneous and the dorsal antibrachial cutaneous. The posterior brachial cutaneous nerve (». cutaneus brachii posterior; internal cutaneous branch of musculospiral) arises in the axilla, with the medial muscular branch. It is of small size, and passes through the axilla to the medial side of the area supplying the skin on its dorsal surface nearly as far as the olecranon. In its course it crosses behind, and communicates with, the intercostobrachial. The dorsal antibrachial cutaneous nerve {n. cutaneus antibrachii dorsalis; external cutaneous branch of musculospiral) perforates the lateral head of the Triceps brachii at its attachment to the humerus. The upper and smaller branch of the nerve passes to the front of the elbow, lying close to the cephalic vein, and supplies the skin of the lower half of the arm (Fig. 805) . The lower branch pierces the deep fascia below the insertion of the Deltoideus, and descends along the lateral side of the arm and elbow, and then along the back of the forearm to the wrist, supplying the skin in its course, and joining, near its termination, with the dorsal branch of the lateral antibrachial cutaneous nerve (Fig. 807). The Superficial Branch of the Radial Nerve (ramus superficialis radial nerve) passes along the front of the radial side of the forearm to the commencement of its lower third. It lies at first slightly lateral to the radial artery, concealed beneath the Brachioradialis. In the middle third of the forearm, it lies behind the same muscle, close to the lateral side of the artery. It quits the artery about 7 cm. above the wrist, passes beneath the tendon of the Brachioradialis, and, piercing the deep fascia, divides into two branches (Fig. 807). The lateral branch, the smaller, supplies the skin of the radial side and ball of the thumb, joining with the volar branch of the lateral antibrachial cutaneous nerve. The medial branch communicates, above the wrist, with the dorsal branch of the lateral antibrachial cutaneous, and, on the back of the hand, with the dorsal branch of the ulnar nerve. It then di^•ides into four digital nerves, which are 970 NEUROLOGY distributed as follows: the first supplies the ulnar side of the thumb; the second, the radial side of the index finger; the third, the adjoinino- sides of the index and middle fingers; the fourth communicates with a filament from the dorsal branch of the ulnar nerve, and supplies the adjacent sides of the middle and ring fingers.^ The Deep Branch of the Radial Nerve {n. interosseus dorsalis; dorsal or posterior interosseous nerve) winds to the back of the forearm around the lateral side of the radius between the two planes of fibres of the Supinator, and is prolonged down- ward between the superficial and deep layers of muscles, to the middle of the forearm. Considerably diminished in size, it descends, as the dorsal interosseous nerve, on the interosseous membrane, in front of the Extensor pollicis longus, to the back of the carpus, where it presents a gangliform enlargement from which filaments are distributed to the ligaments and articulations of the carpus. It supplies all the muscles on the radial side and dorsal surface of the forearm, excepting the Anconaeus, Brachioradialis, and Extenosr carpi radialis longus. Applied Anatomy. — The brachial plexus may be injured by faUs from a height on to the side of the head and shoulder, whereby the nerves of the plexus are violently stretched; the fifth cervical nerve sustains the greatest amount of injury, and the subsequent paralysis may be con- fined to the muscles supplied by this nerve, viz., the Deltoideus, Biceps brachii, Brachialis, and Brachioradialis, with sometimes the Supra- and Infraspinatus and the Supinator. The position of the limb, under such conditions, is characteristic; the arm hangs by the side and is rotated inward; the forearm is extended and pronated. The arm cannot be raised from the side; all power of flexion of the elbow is lost, as is also supination of the forearm. This is known as ErVs -paralysis, and a very similar condition is occasionally met with in newborn children, either from injury to the fifth nerve from the pressure of forceps used in affecting delivery, or from traction of the head in breech presentations. A second variety of partial palsy of the brachial plexus is known as Klumpke's paralysis. In this it is the eighth cervical and first thoracic nerves that are injiu-ed, either before or after they have joined to form the lower trunk. Atrophy follows in the intrinsic muscles of the hand, and in the Flexors of the fingers and wrist; the thenar and hypothenar eminences waste and flatten; the fingers cannot be spread out or approximated, on account of the paralysis of the Interossei, and become clawed. The injury to the nerves may follow direct violence or a gunshot wound. The brachial plexus may also be injured by violent traction on the arm, or by efforts at reduc- ing a dislocation of the shoxilder-joint; and the amoimt of paralysis will depend upon the amount of injury to the constituent nerves. When the entire plexus is involved, the whole of the upper extremity will be paralyzed and anesthetic. In these cases the injury appears to be rather a tearing away of the roots of the nerves from the medulla spinahs, than a rupture of the nerves themselves. The brachial plexus in the axilla is often damaged from the pressure of a crutch, producing the condition known as crutch paralysis. In these cases the radial seems most fre- quently to be the nerve implicated; the ulnar nerve suffers next in frequency. The median and radial nerves often suffer from "sleep palsies," paralysis from pressure coming on while the patient is profoundly asleep under the influence of alcohol or some narcotic. Paralysis of the long thoracic nerve throws the Serratus anterior out of action, and may occur in porters in whom the nerve is exposed to injury as it crosses the posterior triangle of the neck. The inferior angle of the scapula is drawn toward the middle line, by the unopposed action of the Rhomboidei and Levator scapulae, and tends to project backward when the arm is held hori- zontally forward. The arm cannot be raised above the horizontal unless the inferior angle of the scapula is pushed lateralward for the patient. The axillary {circumflex) nerve, on account of its course around the surgical neck of the humerus, is liable to be torn in fractures of this part of the bone, and in dislocations of the shoulder-joint; paralysis of the Deltoideus, and anesthesia of the skin over the lower part of that muscle, result. According to Erb, inflammation of the shoulder-joint is liable to be followed by a nem-itis of this nerve from extension of the inflammation to it. Paralysis of the Deltoideus renders abduction of the arm to the horizontal level impossible. The associated paralysis of the Teres minor is not easily demonstrated. Hilton gave the axillary nerve as an illustration of a law which he laid down, that "the same trunks of nerves whose branches supply the groups of muscles moving a joint, furnish also a 1 According to Hutchison, the digital nerve to the thumb reaches only as high as the root of the nail; the one to the forefinger as high as the middle of the second phalanx; and the one to the middle and ring fingers not higher than the first phalangeal joint. — London Hosp. Gaz., iii, 319. THE CERVICAL NERVES 971 distribution of iicives to the skin oxev the insertions of the same muscles, and tlie interior of the joint receives its nerves from the same source." In this way he explains the fact that an inflamed joint becomes rigid. The median nerve is liable to injury in wounds of the forearm. In such (tases there is loss of flexion of the second phalanges of all the fingers, and of the terminal phalanges of the index and middle fingers. Flexion of the terminal plialanges of tlie ring and little fingers is effected by that portion of the Flexor digitorum profundus which is supplied by the idnar nerve. There is power to flex the proximal phalanges through the Interossei. The thumb cannot be flexed or opposed, and is maintained in a position of extension and adduction. There is loss in the power of pronat- ing the forearm; the Brachioradialis has the power of bringing the forearm into a position of mid- pronation, but beyond this no further pronation can be effected. The wrist can be flexed, if the hand is first adductcd by the action of the Flexor carpi ulnaris. There is loss or impairment of sensation on the volar surfaces of the thumb, index, middle, and radial half of ring fingers, and on the dorsal surfaces of the same fingers over the last two phalanges; except in the thumb, where the loss of sensation would be limited to the back of the last phalanx. In old cases the unopposed action of the Interossei produces backward dislocation of the interphalangeal joints. The thumb is extended and adducted to the index finger, cannot be flexed or abducted, and cannot be apposed to any one of the fingers; in consequence an "ape'-hke" hand is produced. More commonly, however, the nerve is injured just above the annular ligament when the power of flexion of the fingers and pronation of the forearm remain intact unless the Flexor tendons are also divided. This injury seriously interferes with the use of the hand, as, bfesides the wasting of the muscles of the thenar eminence, great trouble is experienced from the trophic changes which result about the skin and nails of the fingers which are anesthetic. In order to expose the median nerve, for the purpose of uniting the divided ends, supposing the injury to be just above the wrist, and incision should be made along the radial side of the tendon of the pahnaris longus, which serves as a guide to the nerve. The ulnar nerve is also liable to be injured in wounds of the forearm, such injury leading to impaired power of ulnar flexion, and upon an attempt being made to flex the wrist, the hand is drawn to the radial side from paralysis of the Flexor carpi ulnaris; there is inability to spread out the fingers from paralysis of the Interossei, and for the same reason the fingers, especially . the ring and little fingers, cannot be flexed at the metacarpophalangeal joints or extended at the interphalangeal joints, and the hand assumes a claw shape from the action of the opposing muscles; there is loss of power of flexion in the little and ring fingers; and there is inability to adduct the thumb. The muscles of the hypothenar eminence become wasted. Sensation is lost, or impaired, in the skin supplied by the nerve. In order to expose the nerve in the lower part of the forearm, an incision should be made along the radial border of the tendon of the Flexor carpi ulnaris, and the nerve will be found lying on the ulnar side of the ulnar artery. This nerve may be also affected in cases of dislocation of the shoulder or fracture of the svu-gical neck of the humerus. Wasting of the muscles which it suppUes is not imcommonly seen where a "cervical rib" is present, the lower end of the plexus passing between this and the first thoracic rib. The radial (musculospiral) nerve is also frequently injured. In consequence of its close rela- tionship to the humerus, it is often torn or injured in fractures of this bone, or subsequently involved in the callus that may be thrown out around a fracture, and thus pressed upon and its functions interfered with. It is also liable to be contused against the bone by kicks or blows,, or to be divided in wounds of the arm. When paralyzed, the hand is flexed at the wrist and lies flaccid. This is known as wrist drop. The fingers are also flexed, and on an attempt being made to extend them, the last two phalanges only will be extended, through the action of the Interossei; the first phalanges remaining flexed. There is no power of extending the wrist. Supination is completely lost when the forearm is extended on the arm, but is possible to a certain extent if the forearm be flexed so as to allow of the action of the Biceps brachii. The power of extension of the forearm is lost on account of paralysis of the Triceps brachii, if the injury to the nerve has taken place near its origin. In cases due to pressure, sensation is hardly affected; severe injury to the nerve occasions anesthesia over the area supplied by the superficial branch of the radial nerve, and, if the lesion be high up, on the lateral side of the upper arm and the back of the forearm (posterior brachial and dorsal antibrachial cutaneous branches) as well. The nerve is best exposed by making an incision along the medial border of the Brachioradialis, just above the level of the elbow-joint. The skin and superficial structures are to be divided and the deep fascia exposed. The white Une in the fascia indicating the border of the muscle is to be defined, and the deep fascia divided in this line. On raising the Brachioradiahs, the nerve will be found lying between it and the Brachialis. The muscles supphed by the deep branch of the radial nerve are also particularly liable to be affected in chronic lead poisoning; here the affection is probably in the cells of the anterior column of the medulla spinalis. Incisions down to the neck of the radius posteriorly or on the lateral side should never be made, as the deep branch of the radial nerve would be severed. 972 NEUROLOGY The Thoracic Nerves (Nn. Thoracales). The anterior divisions of the thoracic nerves {raiui aiiteriores; ventral divisionfi) are twelve in iiumber on either side. Eleven of them are situated l)etween the ribs, and are therefore termed intercostal; the twelfth lies below the last rib. Each nerve is connected with the adjoining ganglion of the sympathetic trunk by a gray and a white ramus communicans. The intercostal nerves are distributed chiefly to the parietes of the thorax and abdomen, and differ from the anterior division's of the other spinal nerves, in that each pursues an independent course, i. e., there is no plexus formation. The first two nerves supply fibres to the upper limb in addition to their thoracic branches; the next four are limited in their distribution to the parietes of the thorax; the lower five supply the parietes of" the thorax and abdomen. The twelfth thoracic is distributed to the abdominal wall and the skin of the buttock. The First Thoracic Nerve. — The anterior division of the first thoracic nerve divides into two branches : one, the larger, leaves the thorax in front of the neck of the first rib, and enters the brachial plexus; the other and smaller branch, the first intercostal nerve, runs along the first intercostal space, and ends on the front of the chest as the first anterior cutaneous branch of the thorax. Occasionally this anterior cuta- neous branch is wanting. The first intercostal nerve as a rule gives oft' no lateral cutaneous branch; but sometimes it sends a small branch to communicate with the intercostobrachial. From the second thoracic nerve it frequently receives a connecting twig, which ascends over the neck of the second rib. Posterior divisio Lateral cutaneous Anterior cutaneous Fig. 811. — Diagram of the course and branches of a typical intercostal nerve. The Upper Thoracic Nerves {nn. iniercostales) . — The anterior, divisions of the second, third, fourth, fifth, and sixth thoracic nerves, and the small branch from the first thoracic, are confined to the parietes of the thorax, and are named thoracic intercostal nerves. They pass forward (Fig. 811) in the intercostal spaces below the intercostal vessels. At the back of the chest they lie between the pleura and the posterior intercostal membranes, but soon pierce the latter and run between the two planes of Intercostal muscles as far as the middle of the rib. They then enter the substance of the Intercostales interni, and, running amidst their fibres as far as THE THORACIC NERVES 973 the costal cartilages, they gain the inner surfaces of the muscles and lie l^etween them and the pleura. Near the sternum, they cross in front of the internal mammary artery and Transversus thoracis muscle, pierce the Intercostales interni, the anterior intercostal membranes, and Pectoralis major, and supply the integument of the front of the thorax and over the mamma, forming the anterior cutaneous branches of the thorax; the branch from the second nerve unites with the anterior supra- clavicular nerves of the cervical plexus. Branches. — Numerous slender muscular filaments supply the Intercostales, the Subcostales, the Levatores costarum, the Serratus posterior superior, and the Trans- versus thoracis. x\t the front of the thorax some of these branches cross the costal cartilages from one intercostal space to another. Lateral cutaneous branches {rami cutanei laterales) are derived from the intercostal nerves, about midway between the vertebrae and sternum; they pierce the Inter- costales externi and Serratus anterior, and divide into anterior and posterior branches. The anterior branches run forward to the side and the forepart of the chest, supplying the skin and the niamma; those of the fifth and sixth nerves supply the upper digitations of the Obliquus externus abdominis. The posterior branches run backward, and supply the skin over the scapula and Latissimus dorsi. The lateral cutaneous branch of the second intercostal nerve does not divide, like the others, into an anterior and a posterior branch; it is named the intercosto- brachial nerve (Fig. 809). It pierces the Intercostalis externus and the Serratus anterior, crosses the axilla to the medial side of the arm, and joins with- a filament from the medial brachial cutaneous nerve. It then pierces the fascia, and supplies the skin of the upper half of the medial and posterior part of the arm, communicat- ing with the posterior brachial cutaneous branch of the radial nerve. The size of the intercostobrachial nerve is in inverse proportion to that of the medial brachial cutaneous nerve. A second intercostobrachial nerve is frequently given off from the lateral cutaneous branch of the third intercostal; it supplies filaments to the axilla and medial side of the arm. The Lower Thoracic Nerves. — Th-e anterior divisions of the seventh, eighth^ ninth, tenth, and eleventh thoracic nerves are continued anteriorly from the intercostal spaces into the abdominal wall; hence they are named thoracicoabdominal inter- costal nerves. They have the same arrangement as the upper ones as far as the anterior ends of the intercostal spaces, where they pass behind the costal cartilages, and between the Obliquus internus and Transversus abdominis, to the sheath of the Rectus abdominis, which they perforate. They supply the Rectus abdominis and end as the anterior cutaneous branches of the abdomen; they supply the skin of the front of the abdomen. The lower intercostal nerves supply the Intercostales and abdominal muscles; the last three send branches to the Serratus posterior inferior. About the middle of their course they give off lateral cutaneous branches. These pierce the Intercostales externi and the Obliquus externus abdominis, in the same line as the lateral cutaneous branches of the upper thoracic nerves, and divide into anterior and posterior branches, which are distributed to the skin of the abdo- men and back; the anterior branches supply the digitations of the Obliquus externus abdominis, and extend downward and forward nearly as far as the margin of the Rectus abdominis; the posterior branches pass backward to supply the skin over the Latissimus dorsi. The anterior division of the twelfth thoracic nerve is larger than the others; it runs along the lower border of the twelfth rib, often gives a communicating branch to the first lumbar nerve, and passes under the lateral lumbocostal arch. It then runs in front of the Quadratus lumborum, perforates the Transversus, and passes forward between it and the Obliquus internus to be distributed in the same manner as the lower intercostal nerves. It communicates with the iliohypogastric nerve of the lumbar plexus, and gives a branch to the Pyramidalis. The lateral cutaneous 974 NEUROLOGY branch of the last thoracic nerve is large, and does not divide into an anterior and a posterior branch. It perforates the Obliqui internus and externus, descends over the iliac crest in front of the lateral cutaneous branch of the iliohypogastric (Fig. 819), and is distributed to the skin of the front part of the gluteal region, some of its filaments extending as low as the greater trochanter. Applied Anatomy. — The lower seven thoracic nerves and the iliohypogastric from the first lumbar nerve supply the skin of the abdominal wall. They run downward and forward fairly equidistant from each other. The sixth and seventh supply the skin over the "pit of the stomach;" the eighth corresponds to about the position of the middle tendinous inscription of the Rectus abdominis; the tenth to the umbihcus; and the ihohypogastric supphes the skin over the pubis and subcutaneous inguinal ring. In many diseases affecting the nerve trunks at or near their origins, the pain is referred to their peripheral terminations. Thus, in Pott's disease of the verte- brae, children often suffer from pain in the abdomen. When the irritation is confined to a single pair of nerves, the sensation complained of is often a feeling of constriction, as if a cord were tied around the abdomen, and in these cases the situation of the sense of constriction may serve to locahze the disease in the vertebral column. In other cases where the bone disease is more ex- tensive, and two or more nerves are involved, a more general, diffused pain in the abdomen is felt. Again, it must be borne in mind that the nerves which supply the skin of the abdomen supply also the planes of muscle which constitute the greater pai't of the abdominal wall. Hence, any irritation applied to the peripheral ends of the cutaneous branches in the skin of the abdomen is immediately followed by reflex contraction of the abdominal muscles. The supply of both muscles and skin from the same source is of importance in protecting the abdominal viscera from injury. A blow on the abdomen, even of a severe character, will do no injury to the viscera if the muscles are in a condition of firm contraction; whereas in cases where the muscles have been taken unawares, and the blow has been struck while they were in a state of rest, an injury insufficient to produce any lesion of the abdominal wall has been attended with rupture of some of the abdominal contents. The importance, therefore, of immediate reflex contraction upon the receipt of an injury cannot be overestimated, and the intimate association of the cutaneous and muscular fibres in the same nerve produces a much more rapid response on the part of the muscles to any peripheral stimulation of the cutaneous filaments than would be the case if the two sets of fibres were derived from independent sources. The nerves supplying the abdominal muscles and skin, derived from the lower intercostal nerves, are intimately connected with the sympathetic supplying the abdominal viscera through the lower thoracic ganglia from which the splanchnic nerves are derived. In consequence qf this, in laceration of the abdominal viscera and in acute peritonitis, the muscles of the belly wall become firmly contracted, and thus as far as possible preserve the abdominal contents in a condition of rest. I- The Lumbosacral Plexus (Plexus Lumbosacralis). The anterior divisions of the lumbar, sacral, and coccygeal nerves form the lumbosacral plexus, the first lumbar nerve being frequently joined by a branch from the twelfth thoracic. For descriptive purposes this plexus is usually divided into three parts — the lumbar, sacral, and pudendal plexuses. The Lumbar Nerves (Nn. Lumbales). The anterior divisions of the lumbar nerves {rami anteriores) increase in size from above downward. They are joined, near their origins, by gray rami com- municantes from the lumbar ganglia of the sympathetic trunk. These rami consist of long, slender branches which accompany the lumbar arteries around the sides of the vertebral bodies, beneath the Psoas major. Their arrangement is somewhat irregular: one ganglion may give rami to two lumbar nerves, or one lumbar nerve may receive rami from two ganglia. The first and second, and sometimes the third and fourth lumbar nerves are each connected with the lumbar part of the sympathetic trunk by a tvhite ramus communicans. The nerves pass obliquely outward behind the Psoas major, or between its fasciculi, distributing filaments to it and the Quadratus lumborum. The first three and the greater part of the fourth are connected together in this situation by anastomotic loops, and form the lumbar plexus. The smaller part of the fourth THE LUMBAR NERVES 975 joins with the fifth to form the lumbosacral trunk, which assists in the formation of the sacral plexus. The fourth nerve is named the nervus furcalis, from the fact that it is subdivided between the two plexuses."^ The Lumbar Plexus {plexus lunihalis) (Figs. 812, 813). — The lumbar plexus is formed by the loops of communication between the anterior divisions of the first three and the greater part of the fourth lumbar nerves; the first lumbar often receives a branch from the last thoracic nerve. It is situated in the posterior part of the Psoas major, in front of the transverse processes of the lumbar vertebrae. — From 12th thoracic —1st lumbar Ilioinguinal Iliohypogastric Lat. fe^noral cutaneous To Psoas and Iliacus '2nd lumbar 3rd lumbar 4:th lumbar oth lumbar Femoral Accessory obturator Obturator Luvibosacral trunk Fig. 812. — Plan of lumbar plexus. The mode in which the plexus is arranged varies in different subjects. It differs from the brachial plexus in not forming an intricate interlacement, but the several nerves of distribution arise from one or more of the spinal nerves, in the following manner: the first lumbar nerve, frequently supplemented by a twig from the last thoracic, splits into an upper and lower branch; the upper and larger branch divides into the iliohypogastric and ilioinguinal nerves; the lower and smaller branch unites with a branch of the second lumbar to form the genitofemoral nerve. The remainder of the second nerve, and the third and fourth nerves, divide into ventral and dorsal divisions. The ventral division of the second unites with the ventral divisions of the third and fourth nerves to form the obturator nerve. The dorsal divisions of the second and third nerves divide into two branches, a smaller branch from each uniting to form the lateral femoral cutaneous nerve, and a larger branch ] In most cases the fourth lumbar is the nermis furcalis; but this arrangement is frequently departed from. The third is occasionallj'^ the lowest nerve which enters the lumbar plexus, giving at the same time some fibres to the sacral plexus, and thus forming the nervus furcalis; or both the third and fourth may be f ureal nerves. When this occurs, the plexus is termed high or ■prefixed. More frequently the fifth nerve is divided between the lumbar and sacral plexuses, and constitutes the nervus furcalis; and when this takes place, the plexus is distinguished as a low or postfixed plexus. These variations necessarily produce corresponding modifications in the sacral plexus. 976 NEUROLOGY from each joining with the dorsal di\'ision of the fourth ner\'e to form the femoral nerve. The accessory obturator, when it exists, is formed by the union of two small branches given off from the third and fourth nerves. Fig. 813. — The lumbar ple.xus and its branches. The branches of the lumbar plexus may therefore be arranged as follows: Iliohypogastric Ilioinguinal . Genitofemoral Lateral femoral cutaneous Femoral. Obturator Accessorv obturator 1 L. 1 L. 1,2L. Dorsal divisions. 2, 3 L. 2, 3, 4 L. Ventral divisions. . 2, 3, 4 L. 3, 4 L. The Iliohypogastric Nerve (??. iliohyixjgastricus) arises from the first lumbar nerve. It emerges from the upper part of the lateral border of the Psoas major, and crosses obliquely in front of the Quadratus lumborum to the iliac crest. It then perforates the posterior part of the Transversus abdominis, near the crest of the ilium, and THE LUMBAR NERVES 977 divides between that muscle and the ObHqims interniis abdominis into a lateral and an anterior cutaneous branch. The lateral cutaneous branch (ramus cutaneus laieraUs; iliac braitch) pierces the Obhqui interniis and externus immediately above the iliac crest, and is distributed to the skin of the gluteal region, behind the lateral cutaneous branch of the last thoracic nerve (Fig. S19) ; the size of this branch bears an inverse proportion to that of the lateral cutaneous branch of the last thoracic nerve. The anterior cutaneous branch {ramus cutaneus anterior; hypogastric branch) (Fig. 814) continues onward between the Obliquus internus and Trans versus. It then pierces the Obliquus internus, becomes cutaneous by perforating the aponeu- rosis of the Obliquus externus about 2.5 cm. above the subcutaneous inguinal ring, and is distributed to the skin of the hypogastric region. The iliohypogastric nerve communicates with the last thoracic and ilioinguinal nerves. The Ilioinguinal Nerve (ji. ilioinguinalis) , smaller than the preceding, arises with it from the first lumbar nerve. It emerges from the lateral border of the Psoas major just below the iliohypogastric, and, passing obliquely across the Quadratus lumborum and Iliacus, perforates the Transversus abdominis, near the anterior part of the iliac crest, and communicates with the iliohypogastric nerve between the Transversus and the Obliquus internus. The nerve then pierces the Obliquus internus, distributing filaments to it, and, accompanying the spermatic cord through the subcutaneous inguinal ring, is distributed to the skin of the upper and medial part of the thigh, to the skin over the root of the penis and upper part of the scrotum in the male, and to the skin covering the mons pubis and labium majus in the female. The size of this nerve is in inverse proportion to that of the iliohypogastric. Occa- sionall}^ it is very small, and ends by joining the iliohypogastric; in such cases, a branch from the iliohypogastric takes the place of the ilioinguinal, or the latter nerve may be altogether absent. The Genitofemoral Nerve {n. genitofevioralis; genitocrural nerve) arises from the first and second lumbar nerves. It passes obliquely through the substance of the Psoas major, and emerges from its medial border, close to the vertebral column, opposite the fibrocartilage between the third and fourth lumbar vertebrae; it then descends on the surface of the Psoas major, under cover of the peritoneum, and divides into the external spermatic and lumboinguinal nerves. Occasionally these two nerves emerge separatelj^ through the substance of the Psoas. The external spermatic nerve (n. spermaticus externus; genital branch of genito- femoral) passes outward on the Psoas major, and pierces the fascia transversalis, or passes through the abdominal inguinal ring; it then descends behind the spermatic cord to the scrotum, supplies the Cremaster, and gives a few filaments to the skin of the scrotum. In the female, it accompanies the round ligament of the uterus, and is lost upon it. The lumboinguinal nerve [n. lumboinguinalis ; femoral or crural branch of genito- femoral) descends on the external iliac artery, sending a few filaments around it, and, passing beneath the inguinal ligament, enters the sheath of the femoral vessels, lying superficial and lateral to the femoral artery. It pierces the anterior layer of the sheath of the vessels and the fascia lata, and supplies the skin of the anterior surface of the upper part of the thigh (Fig. 814). On the front of the thigh it communicates with the anterior cutaneous branches of the femoral nerve. A. few filaments from the lumboinguinal nerve may be traced to the femoral artery. The Lateral Femoral Cutaneous Nerve (?r. cutaneus femoralis lateralis; external cutaneous nerve) arises from the dorsal divisions of the second and third lumbar nerves. It emerges from the lateral border of the Psoas major about its middle, and crosses the Iliacus obliquely, toward the anterior superior iliac spine. It then 62 978 NEUROLOGY passes under the inguinal ligament and over the Sartorius muscle into the thigh, where it divides into two branches, an anterior and a posterior (Fig. 814). Sural- Deep fcronceal Fig. 814. — Cutaneous nerves of right lower extremity. Front view. Fig. 815. — Diagram of segmental distribution of the cutaneous nerves of the right lower extremity. Front view. THE LUMBAR NERVES 979 The anterior branch becomes superficiiil al)out 10 cm. below the inguinal ligament, and divides into branches which are distributed to the skin of the anterior and lateral parts of the thigh, as far , , , * " Laleral femoral culuiicuus as the knee. The terminal fila- ments of this nerve frequently communicate with the anterior cutaneous branches of the femoral nerve, and with the infrapatellar branch of the saphenous nerve, forming with them the patellar plexus. The posterior branch pierces the fascia lata, and subdivides into filaments which pass backward across the lateral and posterior surfaces of the thigh, supplying the skin from the level of the greater trochanter to the middle of the thigh. The Obturator Nerve (?i. obtura- torius) arises from the ventral divisions of the second, third, and fourth lumbar nerves; the branch from the third is the largest, while that from the sec- ond is often very small. It de- scends through the fibres of the Psoas major, and emerges from its medial border near the brim of the pelvis; it then passes behind the common iliac vessels, and on the lateral side of the hypogastric vessels and ureter, which separate it from the ureter, and runs along the lateral wall of the 'lesser pel- vis, above and in front of the obturator vessels, to the upper part of the obturator foramen. Here it enters the thigh, and divides into an anterior and a posterior branch, which are sepa- rated at first by some of the fibres of the Obturator externus, and lower down by the Adductor brevis. The anterior branch (ramus anterior) (Fig. 816) leaves the pelvis in front of the Obturator externus and descends in front of the Adductor brevis, and behind the Pectineus and Adductor longus; at the lower border of the latter muscle it communi- cates with the anterior cutaneous Iliacui) rcmoiul Psoas major A nterior d ivis ion of obturator Med. hr. of ant. cutaneou-s Saphenous Fig. 816. — Nerves of the right lower extremity. Front view. 980 NEUROLOGY and saphenous branches of the femoral nerve, forming a kind of plexus. It then descends upon the femoral artery, to which it is finally distributed. Near the obturator foramen the nerve gives off an articular branch to the hip-joint. Behind the Pectineus, it distributes branches to the Adductor longus and Gracilis, and usually to the Adductor brevis, and in rare cases to the Pectineus; it receives a communicating branch from the accessory obturator nerve when that nerve is present. Occasionally the communicating branch to the anterior cutaneous and saphenous branches of the femoral is continued down, as a cutaneous branch, to the thigh and leg. When this is so, it emerges from beneath the lower border of the Adductor longus, descends along the posterior margin of the Sartorius to the medial side of the knee, where it pierces the deep fascia, communicates with the saphenous nerve, and is distributed to the skin of the tibial side of the leg as low down as its middle. The posterior branch (rarmis posterior) pierces the anterior part of the Obturator externus, and supplies this muscle; it then passes behind the Adductor brevis on the front of the Adductor magnus, where it divides into numerous muscular branches which are distributed to the Adductor magnus and the Adductor brevis when the latter does not receive a branch from the anterior division of the nerve. It usually gives off an articular filament to the knee-joint. The articular branch for the knee-joint is sometimes absent; it either perforates the lower part of the Adductor magnus, or passes through the opening which trans- mits the femoral artery, and enters the popliteal fossa; it then descends upon the popliteal artery, as far as the back part of the knee-joint, where it perforates the oblique popliteal. ligament, and is distributed to the synovial membrane. It gives filaments to the popliteal artery. The Accessory Obturator Nerve {n. ohturatoriiis accessorius) (Fig. 813) is present in about 29 per cent, of cases. It is of small size, and arises from the ventral divi- sions of the third and fourth lumbar nerves. It descends along the medial border of the Psoas major, crosses the superior ramus of the pubis, and passes under the Pectineus, where it divides into numerous branches. One of these supplies the Pectineus, penetrating its deep surface, another is distributed to the hip-joint; while a third communicates with the anterior branch of the obturator nerve. Occasionally the accessory obturator nerve is very small and is lost in the capsule of the hip-joint. When it is absent, the hip-joint receives two branches from the obturator nerve. The Femoral Nerve {n. femoralis; anterior crural nerve) (Fig. 816), the largest branch of the lumbar plexus, arises from the dorsal divisions of the second, third, and fourth lumbar nerves. It descends through the fibres of the Psoas major, emerging from the muscle at the lower part of its lateral border, and passes down between it and the Iliacus, behind the iliac fascia; it then runs beneath the inguinal ligament, into the thigh, and splits into an anterior and a posterior division. Under the inguinal ligament, it is separated from the femoral artery by a portion of the Psoas major. Within the abdomen the femoral nerve gives off small branches to the Iliacus, and a branch which is distributed upon the upper part of the femoral artery; the latter branch may arise in the thigh. In the thigh the anterior division of the femoral nerve gives off anterior cuta- neous and muscular branches. The anterior cutaneous branches comprise the intermediate and medial cutaneous nerves (Fig. 814). The intermediate cutaneous nerve (ramus cutaneus anterior: middle cutaneous nerve) pierces the fascia lata (and generally the Sartorius) about 7.5 cm. below^ the inguinal ligament, and divides into two branches which descend in immediate proximity along the forepart of the thigh, to supply the skin as low^ as the front of the knee. Here they communicate with the medial cutaneous nerve and the THE LUMBAR XERVES 981 infrapatellar branch of the saphenous, to form the patellar plexus. In the upper part of the thigh the lateral branch of the intermediate cutaneous communicates with the lumboinguinal branch of the genitofemoral nerve. The medial cutaneous nerve (ramus cutaneus anterior; internal cutaneous nerve) passes obliquely across the upper part of the sheath of the femoral artery, and divides in front, or at the nunlial side of that^ vessel, into two branches, an anterior and a posterior. The anterior branch runs downward on the Sartorius, perforates the fascia lata at the lower third of the thigh, and divides into two branches: one supplies the integument as low down as the medial side of the knee; the other crosses to the lateral side of the patella, communicating in its course with the infra-^ patellar branch of the saphenous nerve. The posterior branch descends along the medial border of the Sartorius muscle to the knee, where it pierces the fascia lata, communicates with the saphenous nerve, and gives off several cutaneous branches. It then passes down to supply the integument of the medial side of the leg. Beneath the fascia lata, at the lower border of the Adductor longus, it joins to form a plexi- form net-work (subsartorial plexus) with branches of the saphenous and^obturator nerves. ^Mien the communicating branch from the obturator nerve is large and continued to the integument of the leg, the posterior branch of the medial cutaneous is small, and terminates in the plexus, occasionally giving off a few cutaneous filaments. The medial cutaneous nerve, before dividing, gives off a few filaments, which pierce the fascia lata, to supply the integument of the medial side of the thigh, accompanying the long saphenous vein. One of these filaments passes through the saphenous opening; a second becomes subcutaneous about the middle of the thigh; a third pierces the fascia at its lower third. MuscuL-iE Bran'CHES (rami musculares). — Tlie nerve to the Pectineus arises immediately below the inguinal ligament, and passes behind the femoral sheath to enter the anterior surface of the muscle; it is often duplicated. The nerve to the Sartorius arises in common with the intermediate cutaneous. The posterior division of the femoral nerve gives oft' the saphenous nerve, and muscular and articular branches. The Saphenous Nerve (n. sapherius; long or internal saphenous nerve) (Fig. 816) is the largest cutaneous branch of the femoral nerve. It approaches the femoral artery where this vessel passes beneath the Sartorius, and lies in front of it, behind the aponeurotic covering of the adductor canal, as far as the opening in the lower part of the Adductor magnus. Here it quits the artery, and emerges from behind the lower edge of the aponeurotic covering of the canal; it descends vertically along the medial side of the knee behind the Sartorius, pierces the fascia lata, between the tendons of the Sartorius and Gracilis, and becomes subcutaneous. The nerve then passes along the tibial side of the leg, accompanied by the great saphenous vein, descends behind the medial border of the tibia, and, at the lower third of the leg, divides into two branches: one continues its course along the margin of the tibia, and ends at the ankle; the other passes in front of the ankle, and is distributed to the skin on the medial side of the foot, as far as the ball of the great toe, com^municating with the medial branch of the superficial peroneal nerve. Bk^xches. — The saphenous nerve, about the middle of the thigh, gives oft' a branch which joins the subsartorial plexus. At the medial side of the knee it gives oft' a large infrapatellar branch, which pierces the Sartorius and fascia lata, and is distributed to the skin in front of the patella. This nerve communicates above the knee with the anterior cutaneous branches of the femoral nerve; below the knee, with other branches of the saphenous; and, on the lateral side of the joint, with branches of the lateral femoral cutaneous nerve, forming a plexiform net-work, the plexus patellae. The infrapatellar branch is occasionally small, and ends by joining the anterior cutaneous branches of the femoral, which supply its place in front of the knee. 982 NEUROLOGY Below the knee, the branches of the saphenous nerve are distributed to the skin of the front and medial side of the leg, communicating with the cutaneous branches of the femoral, or with filaments from the obturator nerve. The muscular branches supply the four parts of the Quadriceps femoris. The branch to the Rectus femoris enters the upper part of the deep surface of the muscle, and supplies a filament to the hip-joint. The branch to the Vastus lateralis, of large size, accompanies the descending branch of the lateral femoral circumflex artery to the lower part of the muscle. It gives off an articular filament to the knee-joint. The branch to the Vastus medialis descends lateral to the femoral vessels in company with the saphenous nerve. It enters the muscle about its middle, and gives oft' a filament, which can usually be traced downward, on the surface of the muscle, to the knee-joint. The branches to the Vastus intermedins, two or three in number, enter the anterior surface of the muscle about the middle of the thigh; a filament from one of these descends through the muscle to the Articularis genu and the knee-joint. The articular branch to the hip-joint is derived from the nerve to the Rectus femoris. The articular branches to the knee-joint are three in number. One, a long slender filament, is derived from the nerve to the Vastus lateralis; it penetrates the capsule of the joint on its anterior aspect. Another, derived from the nerve to the Vastus medialis, can usually be traced downward on the surface of this muscle to near the joint ; it then penetrates the muscular fibres, and accompanies the articular branch of the highest genicular artery, pierces the medial side of the articular capsule, and supplies the synovial membrane. The third branch is derived from the nerve to the Vastus intermedins. The Sacral and Coccygeal Nerves (Nn. Sacrales et Coccygeus). The anterior divisions of the sacral and coccygeal nerves {rami anteriores) form the sacral and pudendal plexuses. The anterior divisions of the upper four sacral nerves enter the pelvis through the anterior sacral foramina, that of the fifth between the sacrum and coccyx, while that of the coccygeal nerve curves forward below the rudimentary transverse process of the first piece of the coccyx. The first and second sacral nerves are large; the third, fourth, and fifth diminish pro- gressively from above downward. Each receives a gray ramus communicans from the corresponding ganglion of the sympathetic trunk, while from the third, and frequently from the second and the fourth sacral nerves, a white ramus com- municans is given to the pelvic plexuses of the sympathetic. The Sacral Plexus {plexus sacralis) (Fig. 817). — The sacral plexus is formed by the lumbosacral trunk, the anterior division of the first, and portions of the anterior divisions of the second and third sacral nerves. The lumbosacral trunk comprises the whole of the anterior division of the fifth and a part of that of the fourth lumbar nerve; it appears at the medial margin of the Psoas major and runs downward over the pelvic brim to join the first sacral nerve. The anterior division of the third sacral nerve divides into an upper and a lower branch, the former entering the sacral and the latter the pudendal plexus. The nerves forming the sacral plexus converge toward the lower part of the greater sciatic foramen, and unite to form a flattened band, from the anterior and posterior surfaces of w^hich several branches arise. The band itself is continued as the sciatic nerve, which splits on the back of the thigh into the tibial and common peroneal nerves; these two nerves sometimes arise separatel}'^ from the plexus, and in all cases their independence can be shown by dissection. Relations. — The sacral plexus lies on the back of the pelvis between the Piriformis and the pelvic fascia (Fig. 818); in front of it are the hypogastric vessels, the ureter and the sigmoid colon. The superior gluteal vessels run between the lumbosacral trunk and the first sacral nerve, and the inferior gluteal vessels between the second and third sacral nerves. All the nerves entering the plexus, with the exception of the third sacral, split into ventral and dorsal divisions, and the nerves arising from these are as foUows: THE SACRAL AND COCCYGEAL NERVES 983 Ventral divisions. Nerve to Quadratus femoris and Gemellus inferior Nerve to Obturator internus and Gemellus superior Nerve to Piriformis Superior gluteal Inferior gluteal Posterior femoral cutaneous f Tibial |4, 5L, 1 S. I i 5L, 1,2S. Sciatic 2, 3 S . 4, 5 L, 1, 2, 3 S. \ Common peroneal Superior gluteal Inferior gluteal To Piriformis Sciatic J Coynmon Xieroneat Dorsal divisions. (1) 2 S. 4, 5 L, 1 S. 5 L, 1, 2 S. 1, 2 S. 4, 5 L, 1, 2 S. 'ah Lumbar To Quadratus femoris and Inferior gemellus To Obturator internus and ■ Superior gemellus Post. fern, cutaneous ' Perforating cutaneous' Pudendal ; To Levator ani, Coccygeus audi Sphincter ani externus Fig. 817. — Plan of sacral and pudendal plexuses. olh Lumbar \st Sacral Coccygeal 984 NEUROLOGY The Nerve to the Quadratus Femoris and Gemellus Inferior arises from the ventral divisions of the fourth and fifth knnbar and first sacral nerves: it leaves the pelvis through the greater sciatic foramen, below the Piriformis, and runs down in front of the sciatic nerve, the Gemelli, and the tendon of tlie Obturator internus, and enters the anterior surfaces of the muscles; it gives an articular branch to the hip-joint. The Nerve to the Obturator Internus and Gemellus Superior arises from the ventral divisions of the fifth lumbar and first and second sacral nerves. It leaves the pelvis through the greater sciatic foramen below the Piriformis, and gives off the branch to the Gemellus superior, which enters the upper part of the posterior surface of the muscle. It then crosses the ischial spine, reenters the pelvis through the lesser sciatic foramen, and pierces the pelvic surface of the Obturator internus. flortq^ Sympathetic trunk Fig. 818. — Dissection of side wall of pelvis showing sacral and pudendal plexuses. The Nerve to the Piriformis arises from the dorsal division of the second sacral nerve, or the dorsal divisions of the first and second sacral nerves, and enters the anterior surface of the muscle; this nerve may be double. The Superior Gluteal Nerve {ji. ghdaetis superior) arises from the dorsal divisions of the fourth and fifth lumbar and first sacral nerves: it leaves the pelvis through the greater sciatic foramen above the Piriformis, accompanied by the superior gluteal vessels, and divides into a superior and an inferior branch. The superior branch accompanies the upper branch of the deep division of the superior gluteal artery and ends in the Glutaeus minimus. The inferior branch runs with the lower branch of the deep division of the superior gluteal artery across the Glutaeus THE SACRAL AND COCCYGEAL NERVES . 985 minimus; it gives filaments to the Glutaei medius and minimus, and ends in the Tensor fasciae latae. The Inferior Gluteal Nerve (n. glidaeus inferior) arises from the dorsal divisions of the fifth luml)ar and first and second sacral nerves: it leaves the pelvis through the greater sciatic foramen, below the Piriformis, and divides into branches which enter the deep surface of the Glutaeus maximus. The Posterior Femoral Cutaneous Nerve (n. cutaneus femoralis posterior; small sciatic nerve) is distributed to the skin of the perineum and posterior surface of the thigh and leg. It arises partly from the dorsal divisions of the first and second, and from the ventral divisions of the second and third sacral nerves, and issues from the pelvis through the greater sciatic foramen below the Piriformis. It then descends beneath the Glutaeus maximus with the inferior gluteal artery, and runs down the back of the thigh beneath the fascia lata, and over the long head of the Biceps femoris to the back of the knee; here it pierces the deep fascia and accompanies the small saphenous vein to about the middle of the back of the leg, its terminal twigs communicating with the sural nerve. Its branches are all cutaneous, and are distributed to the gluteal region, the peri- neum, and the back of the thigh and leg. The gluteal branches {mi. chmium infer lores) , three or four in number, turn upward around the lower border of the Glutaeus maximus, and supply the skin covering the lower and lateral part of that muscle. The perineal branches (rami yerineales) are distributed to the skin at the upper and medial side of the thigh. One long perineal branch, inferior pudendal {long scrotal nerve) , curves forward below and in front of the ischial tuberosity, pierces the fascia lata, and runs forward beneath the superficial fascia of the perineum to the skin of the scrotum in the male, and of the labium majus in the female. It communicates with the inferior hemorrhoidal and posterior scrotal nerves. The branches to the back of the thigh and leg consist of numerous filaments derived from both sides of the nerve, and distributed to the skin covering the back and medial side of the thigh, the popliteal fossa, and the upper part of the back of the leg (Fig. 819). ■ The Sciatic {n. ischiadicus; great sciatic nerve) (Fig. 821) supplies nearly the whole of the skin of the leg, the muscles of the back of the thigh, and those of the leg and foot. It is the largest nerve in the body, measuring 2 cm. in breadth, and is the continuation of the flattened band of the sacral plexus. It passes out of the pelvis through the greater sciatic foramen, below the Piriformis muscle. It descends between the greater trochanter of the femur and the tuberosity of the ischium, and along the back of the thigh to about its lower third, where it divides into two large branches, the tibial and common peroneal nerves. This division may take place at any point between the sacral plexus and the lower third of the thigh. When it occurs at the plexus, the common peroneal nerve usually pierces the Piriformis. In the upper part of its course the nerve rests upon the posterior surface of the ischium, the nerve to the Quadratus femoris, the Obturator internus and Gemelli, and the Quadratus femoris; it is accompanied by the posterior femoral cutaneous nerve and the inferior gluteal artery, and is covered by the Glutaeus maximus. Lower down, it lies upon the Adductor magnus, and is crossed obliquely by the long head of the Biceps femoris. The nerve gives off articular and muscular branches. The articular branches (rami articulares) arise from the upper part of the nerve and supply the hip-joint, perforating the posterior part of its capsule; they are sometimes derived from the sacral plexus. The muscular branches (rami musculares) are distributed to the Biceps femoris, Semitendinosus, Semimembranosus, and iVdductor magnus. The nerve to the short head of the Biceps femoris comes from the common peroneal part of the sciatic, 986 NEUROLOGY while the other muscuhir branches arise from the tibial portion, as may be seen in those cases where there is a high division of the sciatic nerve. \ Fig. 819. — Cutaneous nerves of right lower extremity. Posterior view. Fig. 820. — Diagram of the segmental distribution of the cutaneous nerves of the right lower extremity. Posterior view. THE SACRAL AND COCCYGEAL NERVES 987 Tlu> Tibial Nerve {n. tibialis: inicrnal popliteal iicnr) (Fig. S21) the larger of the two terminal branches of the sci- atic, arises from the anterior branches of the fourth and fifth lumbar and first, second, and third sacral nerves. It descends along the back of the thigh and through the middle of the poj)liteal fossa, to the lower part of the Popliteus muscle, where it passes with the pop- liteal artery beneath the arch of the Soleus. It then runs along the back of the leg with the posterior tibial vessels to the interval between the medial malleolus and the heel, where it divides beneath the laciniate liga- ment into the medial and lateral plantar nerves. In the thigh it is overlapped by the hamstring muscles above, and then becomes more super- ficial, and lies lateral to, and some distance from, the popliteal vessels; opposite the knee-joint, it is in close relation with these vessels, and crosses to the medial side of the artery. In the leg it is covered in the upper part of its course by the muscles of the calf; lower down by the skin, the superficial and deep fasciae. It is placed on the deep muscles, and lies at first to the medial side of the posterior tibial artery, but soon crosses that vessel and descends on its lateral side as far as the ankle. In the lower third of the leg it runs parallel with the medial margin of the tendo calcaneus. The branches of this nerve are : artic- ular, muscular, medial sural cutaneous, medial calcaneal, medial and lateral plantar. Articular branches (rami articulares) , usually three in number, supply the knee-joint; two of these accompany the superior and inferior medial genic- ular arteries; and a third, the middle genicular artery. Just above the bi- furcation of the nerve an articular branch is given off to the ankle-joint. Muscular branches {rami musculares) , four or five in number, arise from the nerve as it lies between the two heads of the Gastrocnemius muscle; thev Superior gluteal Pudendal Kervp to obturator interims Po^t. fern. ^ cutaneous Perineal branch Medial calcaneal Fig. 821. -Nerves of the right lower extremity.' Posterior view. 1 N. B. — In this diagram the medial sural cutaneous and peroneal anastomotic are not in their normal position. They have been displaced by the removal of the superficial muscles. 988 NEUROLOGY supply that muscle, and the Plantaris, Soleus, and Popliteus. The branch for the Popliteus turns around the lower border and is distributed to the deep surface of the muscle. Lower down, muscular branches arise separately or by a common trunk and supply the Soleus, Tibialis posterior. Flexor digitorum longus, and Flexor hallucis longus; the branch to the last muscle accompanies the peroneal artery; that to the Soleus enters the deep surface of the muscle. The medial sural cutaneous nerve (71. cutaneus surae medialis; n. communicans tibialis) descends bet^veen the two heads of the Gastrocnemius, and, about the middle of the back of the leg, pierces the deep fascia, and unites with the anasto- motic ramus of the common peroneal to form the sural nerve (Fig. 819). The sural nerve {n. suralis; short saphenous nerve), formed by the junction of the medial sural cutaneous with the peroneal anastomotic branch, passes downward near the lateral margin of the tendo calcaneus, lying close to the small saphenous vein, to the interval between the lateral malleolus and the calcaneus. It runs forward below the lateral malleolus, and is continued as the lateral dorsal cutaneous nerve along the lateral side of the foot and little toe, communicating on the dorsum of the foot with the intermediate dorsal cutaneous nerve, a branch of the superficial peroneal. In the leg, its branches communicate with those of the posterior femoral cutaneous. The medial calcaneal branches {rami calcanei mediales; internal calcaneal branches) perforate the laciniate ligament, and supply the skin of the heel and medial side of the sole of the foot. The medial plantar nerve (?i. plantaris medialis; internal plantar nerve) (Fig. 822), the larger of the two terminal divisions of the tibial nerve, accompanies the medial plantar artery. From its origin under the laciniate ligament it passes under cover of the Abductor hallucis, and, appearing between this muscle and the Flexor digi- torum brevis, gives of! a proper digital plantar nerve and finally divides opposite the bases of the metatarsal bones into three common digital plantar nerves. Branches. — The branches of the medial plantar nerve are: (1) cutaneous, (2) muscular, (3) articular, (4) a proper digital nerve to the medial side of the great toe, and (5) three common digital nerves. The cutaneous branches pierce the plantar aponeurosis between the Abductor hallucis and the Flexor digitorum brevis and are distributed to the skin of the sole of the foot. The muscular branches supply the Abductor hallucis, the Flexor digitorum brevis, the Flexor hallucis brevis, and the first Lumbricalis; these for the Abductor hallucis and Flexor digitorum brevis arise from the trunk of the nerve near its origin and enter the deep surfaces of the muscles; the branch of the Flexor hallucis brevis springs from the proper digital nerve to the medial side of the great toe, and that for the first Lumbricalis from the first common digital nerve. The articular branches supply the articulations of the tarsus and metatarsus. The proper digital nerve of the great toe (nn. digitales plantares proprii; plantar digital branches) supplies the Flexor hallucis brevis and the skin on the medial side of the great toe. The three common digital nerves {nn. digitales plantares communes) pass betw^een the divisions of the plantar aponeurosis, and each splits into two proper digital nerves — those of the first common digital nerve supply the adjacent sides of the great and second toes; those of the second, the adjacent sides of the second and third toes; and those of the third, the adjacent sides of the third and fourth toes. The third common digital nerve receives a communicating branch from the lateral plantar nerve; the first gives a twig to the first Lumbricalis. Each proper digital nerve gives off cutaneous and articular filaments; and opposite the last phalanx sends upward a dorsal branch, which supplies the structures around the nail, the continuation of the nerve being distributed to the ball of the toe. It will be THE SACRAL AXD COCCYGEAL NERVES 989 observed that these digital nerves are similar in their distribution to those of the median nerve in the hand. The Lateral Plantar Nerve (n. plwitaris lateralis; external lolantar nerve) (Fig. 822) supphes the skin of the fifth toe and lateral half of the fourth, as well as most of the deep muscles, its distribution being similar to that of the ulnar nerve in the hand. It passes obliquely forward with the lateral plantar artery to the lateral side of the foot, lying between the Flexor digitorum brevis and Quadratus plantae; and, in the interval between the former muscle and the abductor digiti quinti, divides into a superficial and a deep branch. Before its division, it supplies the Quadratus plantae and Abductor digiti quinti. The superficial branch {ramus superficial is) splits into a proper and a common digital nerve; the proper digital nerve supplies the lateral side of the little toe, the Flexor digiti quinti brevis, and the two Interossei of the fourth intermetatarsal space; the common digital nerve communicates with the third common digital branch of the medial plantar nerve and divides into two proper Avv-^^^^^^"^'! ''W\ mar digital nerves which supply the adjoining vlania'- ^Vv ''^CAw^A^'f 1 sides of the fourth and fifth toes. Deep - branch Fig. 822. — The plantar nerves. Fig. 823. — Diagram of the segmental distribution of the cutaneous nerves, of the sole of the foot. The deep branch (ramus profundus; muscular hranch) accompanies the lateral plantar artery on the deep surface of the tendons of the Flexor muscles and the Adductor hallucis, and supplies all the Interossei (except those in the fourth metatarsal space), the second, third, and fourth Lumbricales, and the Adductor hallucis. The Common Peroneal Nerve {n. peronaeus communis; external popliteal nerve; peroneal nerve) (Fig. 821), about one-half the size of the tibial, is derived from the dorsal branches of the fourth and fifth lumbar and the first and second sacral nerves. It descends obliquely along the lateral side of the popliteal fossa to the head of the fibula, close to the medial margin of the Biceps femoris muscle. It lies between the tendon of the Biceps femoris and lateral head of the Gastrocnemius muscle, winds around the neck of the fibula, between the Peronaeus longus and the bone, and divides beneath the muscle into the superficial and deep peronealnerves. Previous to its division it gives off articular and lateral sural cutaneous nerves. 990 NEUROLOGY The articular branches ^rami articidares) are three in number; two of these accom- pany the superior and inferior lateral genicular arteries to the knee ; the upper one occasionally arises from the trunk of the sciatic nerve. The third {recurrent) articular nerve is given off at the point of division of the common peroneal nerve; it ascends with the anterior recurrent tibial artery through the Tibialis anterior to the front of the knee. The lateral sural cutaneous nerve (n. cutaneus surae lateralis; lateral cutaneous branch) supplies the skin on the posterior and lateral surfaces of the leg; one branch, the peroneal anastomotic (m. comimmicans fibularis), arises near the head of the fibula, crosses the lateral head of the Gastrocnemius to the middle of the leg, and joins with the medial sural cutaneous to form the sural nerve. The peroneal anastomotic is occasionally continued down as a separate branch as far as the heel. The Deep Peroneal Nerve {n. peronaeus projundus ; anterior tibial nerve) (Fig. 816) begins at the bifurcation of the common peroneal nerve, between the fibula and upper part of the Peronaeus longus, passes obliquely forward beneath the Extensor digitorum longus to the front of the interosseous membrane, and comes into relation with the anterior tibial artery above the middle of the leg; it then descends with the artery to the front of the ankle-joint, where it divides into a lateral and a medial terminal branch. It lies at first on the lateral side of the anterior tibial artery, then in front of it, and again on its lateral side at the ankle-joint. In the leg, the deep peroneal nerve supplies muscular branches to the Tibialis anterior. Extensor digitorum longus, Peronaeus tertius, and Extensor hallucis proprius, and an articular branch to the ankle-joint. The lateral terminal branch {external or tarsal branch) passes across the tarsus, beneath the Extensor digitorum brevis, and, having become enlarged like the dorsal interosseous nerve at the wrist, supplies the Extensor digitorum brevis. From the enlargement three minute interosseous branches are given off, which supply the tarsal joints and the metatarsophalangeal joints of the second, third, and fourth toes. The first of these sends a filament to the second Interosseus dorsalis muscle. The medial terminal branch {internal branch) accompanies the dorsalis pedis artery along the dorsum of the foot, and, at the first interosseous space, divides into two dorsal digital nerves {iin. digitales dor sales hallucis lateralis et digiti secundi medialis) which supply the adjacent sides of the great and second toes, communicat- ing with the medial dorsal cutaneous branch of the superficial peroneal nerve. Before it divides it gives off to the first space an interosseous branch which supplies the metatarsophalangeal joint of the great toe and sends a filament to the first Interosseous dorsalis muscle. The Superficial Peroneal Nerve {n. perojiaeus superficialis; musculocutaneous nerve) (Fig. 816) supplies the Peronei longus and brevis and the skin over the greater part of the dorsum of the foot. It passes forward between the Peronaei and the Extensor digitorum longus, pierces the deep fascia at the lower third of the leg, and divides into a medial and an intermediate dorsal cutaneous nerve. In its course between the muscles, the nerve- gives off muscular branches to the Peronaei longus and brevis, and cutaneous filaments to the integument of the lower part of the leg. The medial dorsal cutaneous nerve {n. cutaneus dorsalis medialis; internal dorsal cutaneous branch) passes in front of the ankle-joint, and divides into two dorsal digital branches, one of which supplies the medial side of the great tOe, the other, the adjacent side of the second and third toes. It also supplies the integument of the medial side of the foot and ankle, and communicates with the saphenous nerve, and with the deep peroneal nerve (Fig. 814). The intermediate dorsal cutaneous nerve {n. cutaneus dorsalis intermedius; external dorsal cutaneous branch), the smaller, passes along the lateral part of the dorsum of the foot, and divides into dorsal digital branches, which supply the contiguous THE SACRAL AXD COCCYGEAL NERVES 991 sides of the third and fourth, and of the fourth and fifth toes. It also supplies the skin of the lateral side of the foot and ankle, and communicates with the sural nerve (Fig. 814). The branches of the superficial peroneal nerve supply the skin of the dorsal surfaces of all the toes excepting the lateral side of the little toe, and the adjoining sides of the great and second toes, the former being supplied by the lateral dorsal cutaneous nerve from the sural nerve, and the latter by the medial branch of the deep peroneal nerve. Frequently some of the lateral branches of the superficial peroneal are absent, and their places are then taken by branches of the sural nerve. The Pudendal Plexus {plc.vus pudendus) (Fig. 817). — The pudendal plexus is not sharply marked off from the sacral plexus, and as a consequence some of the branches which spring from it may arise in conjunction with those of the sacral plexus. It lies on the posterior w^all of the pelvis, and is usually formed by branches from the anterior divisions of the second and third sacral nerves, the whole of the anterior divisions of the fourth and fifth sacral nerves, and the coccygeal nerve. It gives off' the follow:ing branches: Perforating cutaneous 2, 3 S. Pudendal 2, 3, 4 S. Visceral 3, 4 S. Muscular 4 S. Anococcygeal 4, 5 S. and Cocc. The Perforating Cutaneous Nerve (n. dunium inferior viedialis) usually arises from the posterior surface of the second and third sacral nerves. It pierces the lower part of the sacrotuberous ligament, and winding around the inferior border of the Glutaeus maximus supplies the skin covering the medial and lower parts of that muscle. The perforating cutaneous nerve may arise from the pudendal or it may be absent; in the latter case its place may be taken by a branch from the posterior femoral cutaneous nerve or by a branch from the third and fourth, or fourth and fifth, sacral nerves. The Pudendal Nerve (n. pudendiis; internal pudic rierve) derives its fibres from the ventral branches of the second, third, and fourth sacral nerves. It passes between the Piriformis and Coccygeus muscles and leaves the pelvis through the lower part of the greater sciatic foramen. It then crosses the spine of the ischium, and reenters the pelvis through the lesser sciatic foramen. It accompanies the internal pudendal vessels upward and forward along the lateral wall of the ischiorectal fossa, being contained in a sheath of the obturator fascia termed Alcock's canal, and divides into two terminal branches, viz., the perineal nerve, and the dorsal nerve of the penis or clitoris. Before its division it gives off. the inferior hemorrhoidal nerve. The inferior hemorrhoidal nerve (?i. haemorrhoidalis inferior) occasionally arises directly from the sacral plexus; it crosses the ischiorectal fossa, wdth the inferior hemorrhoidal vessels, toward the anal canal and the lower end of the rectum, and is distributed to the Sphincter ani externus and to the integument around the anus. Branches of this nerve communicate with the perineal branch of the posterior femoral cutaneous and with the posterior scrotal nerves at the forepart of the perineum. The perineal nerve {n. perinei), the inferior and larger of the tw^o terminal branches of the pudendal, is situated below the internal pudendal artery. It accompanies the perineal artery and divides into posterior scrotal (or labial) and muscular branches. The posterior scrotal (or labial) branches {nn. scrotales (or lahiales) posteriores; superficial peroneal nerves) are two in number, medial and lateral. Thej' pierce the fascia of the urogenital diaphragm, and run forward along the lateral part of the urethral triangle in company with the posterior scrotal branches of the perineal 992 NEUROLOGY artery; the}' are distributed to the skin of the scrotum and communicate with the perineal branch of the posterior femoral cutaneous nerve. These nerves supply the labium majus in the female. The muscular branches are distributed to the Transversus perinaei superficialis, Bulbocavernous, Ischiocavernosus, and Constrictor urethrae. A branch, the nerve to the bulb, given off from the nerve to the Bulbocavernosus, pierces this muscle, and supplies the corpus cavernosum urethrae, ending in the mucous membrane of the urethra. The dorsal nerve of the penis {71. dorsalis penis) is the deepest division of the puden- dal nerve; it accompanies the internal pudendal artery along the ramus of the ischium; it then runs forward along the margin of the inferior ramus of the pubis, between the superior and inferior layers of the fascia of the urogenital diaphragm. Piercing the inferior layer it gives a branch to the corpus cavernosum penis, and passes forward, in company with the dorsal artery of the penis, between the layers of the suspensory ligament, on to the dorsum of the penis, and ends on the glans penis. In the female this nerve is very small, and supplies the clitoris (n. dorsalis clitoridis). The Visceral Branches arise from the third and fourth, and sometimes from the second, sacral nerves, and are distributed to the bladder and rectum and, in the female, to the vagina; they communicate with the pelvic plexuses of the sympathetic. The Muscular Branches are derived from the fourth sacral, and supply the Levator ani, Coccygeus, and Sphincter ani externus. The branches to the Levator ani and Coccygeus enter their pelvic surfaces; that to the Sphincter ani externus (perineal branch) reaches the ischiorectal fossa by piercing the Coccygeus or by passing between it and the Levator ani. Cutaneous filaments from this branch supply the skin between the anus and the coccyx. Anococcygeal Nerves (nn. anococcygei) . — The fifth sacral nerve receives a com- municating filament from the fourth, and unites with the coccygeal nerve to form the coccygeal plexus. From this plexus the anococcygeal nerves take origin; they consist of a few fine filaments which pierce the sacrotuberous ligament to supply the skin in the region of the coccyx. Applied Anatomy. — The lumbar plexus passes through the Psoas major, and therefore in psoas abscess any or all of its branches may be irritated, causing severe pain in the part to which the irritated nerves are distributed. The genitofemoral nerve is the one which is most frequently imphcated. This nerve is also of importance as it is concerned in one of the principal superficial reflexes employed in the investigation of diseases of the medulla spinahs. If the skin over the medial side of the thigh just below the inguinal Ugament (the part supphed by the liunboinguinal nerve) be gently tickled in a male chUd, the testes will be drawn upward, through the action of the Cremaster muscle, supplied by the lumboinguinal nerve. The same result may sometimes be noticed in adults, and can almost always be produced by severe stimulation. This reflex, when present, shows that the portion of the cord from which the first and second lumbar nerves are derived is in a normal condition. The femoral nerve is in danger of being injured in fractures of the lesser pelvis, since the frac- ture most commonly takes place through the superior ramus of the pubis, at or near the point where this nerve crosses the bone. It is also liable to be pressed upon, and its functions impaired, by some tumors growing in the pelvis. Moreover, on account of its superficial position, it is exposed to injury in wounds and stabs in the groin. Its central origin is often affected in cases of infantile paralysis. When this nerve is paralyzed, the patient is unable to flex his hip com- pletely, on account of the paralysis of the Iliacus; or to extend the knee on the thigh, on account of paralysis of the Quadriceps femoris; there is complete paralysis of the Sartorius, and partial paralysis of the Pectineus. There is loss of sensation down the front and medial side of the thigh, except in that part supphed by the lumboinguinal and ilioinguinal nerves. There is also loss of sensation down the medial side of the leg and foot as far as the ball of the great toe. The obturator nerve is rarely paralyzed alone, but occasionally in association with the femoral. The principal interest attached to it is in connection with its supply to the knee; pain in the knee being symptomatic of many diseases in which the trunk of this nerve, or one of its branches, is irritated. Thus it is well known that in the earher stages of hip-joint disease the patient does not always complain of pain in that articulation, but on the medial side of the knee, or in the knee-joint itseK, both of these articulations being supplied by the obturator nerve, the final THE SACRAL AND COCCYGEAL NERVES 993 distribution of the nerve being to the knee-joint. Again, the same thing occurs in sacroiliac disease; pain is complained of in the. knee-joint, or on its medial side. The obturator nerve is in close relationship with the sacroiliac articulation, passing over it, and, according to some anatomists, distributing filaments to it. Further, in cancer of the sigmoid colon, and even in cases where masses of hardened feces are impacted in this portion of the gut, pain is complained of in the knee. The left obtui-ator nerve hes beneath the sigmoid colon, and is readily pressed upon and irritated when disease exists in this part of the intestine. Finally, pain in the knee forms an important diagnostic sign in obturator hernia. The hernial protrusion as it passes out through the opening in the obturator membrane presses upon the nerve and causes pain in the parts suppHed by its peripheral filaments. When the obturator nerve is paralyzed, the patient is unable to press his knees together or to cross one leg over the other, on account of paralysis of the Adductor muscles. Rotation outward of the thigh is impaired from paralysis of the Obturator externus. Sometimes there is loss of sensation in the upper half of the medial side of the thigh. The sciatic nerve is liable to be pressed upon by various forms of pelvic tumor, giving rise to pain along its trunk, to which the term sciatica is appUed. Tumors growing from the pelvic viscera, especially advanced cancer of the rectum, aneurisms of some of the branches of the hypogastric artery, calculus in the bladder when of large size, accumulation of feces in the rectum, may all cause pressure on the nerve inside the pelvis, and give rise to sciatica. Outside the pelvis violent movements of the hip-joint, exostoses or other tumors j^rowing from the margin of the greater sciatic foramen, may also give rise to the same condition. ' Most cases of sciatica, however, are due to neuritis of the sciatic nerve from exposure to cold, and it occurs more often in men than in women, in the latter half of life, and often in association with rheumatism, gout, or diabetes mellitus. The inflamed nerve is often sensitive to pressure, particularly in certain "tender spots," e. g., near the posterior iliac spine, at the sciatic notch, about the middle of the back of the thigh, in the popliteal fossa, below the head of the fibula, behind the malleoli, on the dorsum of the foot, and pain is felt whenever extension of the leg is attempted, and the nerve is stretched. Paralysis of the sciatic nerve is rarely complete; when the lesion occurs high up there is palsy of the Biceps femoris, Semimembranosus, and Semitendinosus, and of the muscles below the knee. If the lesion be lower down, there is loss of motion in all the muscles below the knee, and loss of sensation in the same situation, except the upper half of the back of the leg, which is sup- pUed by the posterior femoral cutaneous, and in the upper half of the medial side of the leg, when the communicating branch of the obturator is large (see p. 980) . Lesions of the common peroneal nerve cause paralysis of the Tibialis anterior, the Peronaei, the long Extensors of the toes, and the short Extensor on the dorsum of the foot. "Foot drop" follows, dorsal flexion of the toes and abduction of the foot becoming impossible. Later on tahpes results, largely by the action of gravity or by the weight of the superincmnbent bedclothes when the patient lies in bed, aided by the contracture of the unopposed posterior crural group of muscles. The sciatic nerve has been frequently cut down upon and stretched, or has been acupunctm-ed, for the reUef of sciatica. In order to define it on the surface, a point is taken at the junction of the middle and lower thirds of a line stretching from the posterior superior spine of the ilium to the lateral part of the ischial tuberosity, and a line drawn from this to the middle of the upper part of the popUteal fossa. The hue must be sUghtly curved with its convexity outward, and as it passes downward to the lower border of the Glutaeus maximus is sHghtly nearer to the ischial tuberosity than to the greater trochanter, as it crosses a fine drawn between these two points. The operation of stretching the sciatic nerve is performed by making an incision over the course of the nerve beneath the fold of the buttock. The skin, superficial structures, and deep fascia having been divided, the hamstrings are defined, and pulled apart with retractors. The nerve will be found lying on the Adductor magnus and covered by the Biceps femoris. It is to be separated from the surrounding structm-es, hooked up with the finger, and stretched by steady and continuous traction for two or thi'ee minutes. The sciatic nerve may also be stretched by what is known as the "dry" plan. The patient is laid on his back, the foot is extended, the leg flexed on the thigh, and the thigh strongly flexed on the abdomen. While the thigh is maintained in this position, the leg is forcibly extended to its full extent, and the foot as fully flexed on the leg. The position of the common peroneal nerve, close behind the tendon of the Biceps femoris, on the lateral side of the popliteal fossa, should be remembered in subcutaneous division of the tendon. After the tendon is divided, the common peroneal nerve rises up as a cord and might be mistaken for a small undivided portion of the tendon. Where this nerve wmds around the neck of the fibula, it is also liable to be severed accidentally if its exact situation is not kept in mind, and especial care must be used when deahng with sinuses leading down to carious bone in this situation. Section of the nerve results in complete "foot drop" from paralysis of the anterior tibial group of muscles and inversion of the foot from the unopposed action of the Tibiahs posterior, the Peronaei being paralyzed, together with anesthesia of the parts suppUedby the nerve, and, owing to loss of nutrition, the limb frequently becomes blue and cold, and may develop "trophic" sores. 63 994 NEUROLOGY THE SYMPATHETIC NERVES. The sympathetic nerves (Fig. 824), sometimes grouped under the term sympathetic system, are distributed to the viscera and bloodvessels, and are intimately connected with the spinal and certain of the cerebral nerves. They are characterized by the spmf Maxillary nerve Ciliary ganglion Sphenopalatine ganglion Superior cerricai, ganglion of sympathetic Cervical jdexus Brachial plexus Greater splanchnic nerve Lesser splanchnic nerve Lumbar plexus Sacral plexus Pharyngeal plexus Middle cervical ganglion of Hympathetic Inferior cervical ganglion nf sympathetic Recurrent nerve Bronchial plexus ■ Cardiac plexus Oesophageal plexus Coronary plexuses Left vagus nerve Gastric plexus C celiac plexus ■ Superior mesenteric plexus Aortic plexxis Inferior mesenteric plexus Hypogastric plexus Pelvic plexus Bladder Vesical plexus Fig 824 —The right sympathetic chain and its connections with the thoracic, abdominal, and pelvis plexuses. (After Schwalbe.) THE CEPHALIC PORTION OF THE SYMPATHETIC SYSTEM 995 presence of niiraeroiis ganglia wliich may be divided into three groups, central, collateral, and terminal ganglia. The central ganglia are arranged in two vertical rows, one on either side of the middle line, situated i)artly in front and partly at the sides of the vertebral column. Each ganglion is joined by intervening nervous cords to adjacent ganglia so that two chains, the sympathetic trunks, are formed. The collateral ganglia are found in connection with three great prevertebral plexuses, placed within the thorax, abdomen, and pelvis respectively, while the terminal ganglia are located in the walls of the viscera.^ The sympathetic trunks (tnoicus sym path tens; gamjliated cord) extend from the base of the skull to the coccyx. The cephalic end of each is continued upward through the carotid canal into the skull, and forms a plexus on the internal carotid artery; the caudal ends of the trunks converge and end in a single ganglion, the ganglion impar, placed in front of the coccyx. The ganglia of each trunk are dis- tinguished as cervical, thoracic, lumbar, and sacral and, except in the neck, they closely correspond in number to the vertebrae. They are arranged thus: Cervical portion . ... 3 ganglia Thoracic " 12 Lumbar " 4 " Sacral " 4 or 5 " In the neck the ganglia lie in front of the transverse processes of the vertebrae; in the thoracic region in front of the heads of the ribs; in the lumbar region on the sides of the vertebral bodies ; and in the sacral region in front of the sacrum. Connections with the Spinal Nerves. — Communications are established between the sympathetic and spinal nerves through what are known as the gray and white rami communicantes (Fig. 798); the gray rami convey sympathetic fibres into the spinal nerves and the white rami transmit spinal fibres into the sympathetic. Each spinal nerve receives a gray ramus communicans from the sympathetic trunk, but white rami are not supplied by all the spinal nerves. White rami are derived from the first thoracic to the first lumbar nerves inclusive, while the visceral branches which run from the second, third, and fourth sacral nerves directly to the pelvic plexuses of the sympathetic belong to this category. The fibres which reach the sympathetic through the white rami communicantes are medullated; those which spring from the cells of the sympathetic ganglia are almost entirely non-medullated. The sympathetic nerves consist of efferent and afferent fibres, the origin and course of which are described on page 950) . The three great gangliated plexuses {collateral ganglia) are situated in front of the vertebral column in the thoracic, abdominal, and pelvic regions, and are named, respectively, the cardiac, the solar or epigastric, and the hypogastric plexuses. They consist of collections of nerves and ganglia; the nerves being derived from the sympathetic trunks and from the cerebrospinal nerves. They distribute branches to the viscera. THE CEPHALIC PORTION OF THE SYMPATHETIC SYSTEM (PARS CEPHALICA S. SYMPATHICI). The cephalic portion of the sympathetic system begins as the internal carotid nerve, which appears to be a direct prolongation of the superior cervical ganglion. It is soft in texture, and of a reddish color. It ascends by the side of the internal carotid artery, and, entering the carotid canal in the temporal bone, divides into 1 The ciliary, sphenopalatine, otic, and submaxiUarj' ganglia, already described in connection with the trigeminal nerve, may be regarded as belonging to the sjTnpathetic. 996 NEUROLOGY two branches, -which lie one on the lateral and the other on the medial side of that vessel. The lateral branch, the larger of the two, distributes filaments to the internal carotid artery, and forms the internal carotid plexus. The medial branch also distributes filaments to the internal carotid artery, and, continuing onward, forms the cavernous plexus. The internal carotid plexus (plexus caroticus internus; carotid plexus) is situated on the lateral side of the internal carotid artery, and in the plexus there occasionally exists a small gangliform swelling, the carotid ganglion, on the under surface of the artery. The internal carotid plexus communicates with the semilunar gan- glion, the abducent nerve, and the sphenopalatine ganglion; it distributes filaments to the wall of the carotid artery, and also communicates with the tympanic branch of the glossopharyngeal nerve. The communicating branches with the abducent nerve consist of one or two filaments which join that nerve as it lies upon the lateral side of the internal carotid artery. The communication with the sphenopalatine ganglion is effected by a branch, the deep petrosal, given off from the plexus on the lateral side of the artery; this branch passes through the cartilage filling up the foramen lacerum, and joins the greater superficial petrosal to form the nerve of the pterygoid canal (Vidian nerve), which passes through the pterygoid canal to the sphenopalatine ganglion. The communication with the tympanic branch of the glossopharyngeal nerve is effected by the caroticotympanic, which may consist of two or three delicate filaments. The cavernous plexus (jjlexiis cavernosus) is situated below and medial to that part of the internal carotid artery which is placed by the side of the sella turcica in the cavernous sinus, and is formed chiefly by the medial division of the internal carotid nerve. It communicates with the oculomotor, the trochlear, the ophthalmic and the abducent nerves, and with the ciliary ganglion, and distributes filaments to the wall of the internal carotid artery. The branch of communication with the oculomotor nerve joins that nerve at its point of division; the branch to the troch- lear nerve joins it as it lies on the lateral wall of the cavernous sinus; other filaments are connected with the under surface of the ophthalmic nerve; and a second fila- ment joins the abducent nerve. The filaments of connection with the ciliar}- ganglion arise from the anterior part of the cavernous plexus and enter the orbit through the superior orbital fissure; they may join the nasociliary branch of the ophthalmic nerve, or be continued for- ward as a separate branch. The terminal filaments from the internal carotid and cavernous plexuses are prolonged as plexuses around the anterior and middle cerebral arteries and the ophthalmic artery; along the former vessels, they may be traced to the pia mater; along the latter, into the orbit, where they accompany each of the branches of the vessel. The filaments prolonged on to the anterior communicating artery connect the sympathetic nerves of the right and left sides. THE CERVICAL PORTION OF THE SYMPATHETIC SYSTEM (PARS CERVICALIS S. SYMPATHICI). The cervical portion of the sympathetic trunk consists of three ganglia, distin- guished, according to their positions, as the superior, middle, and inferior ganglia, connected by intervening cords. This portion receives no white rami communi- cantes from the cervical spinal nerves; its spinal fibres are derived from the white rami of the upper thoracic nerves, and enter the corresponding thoracic ganglia of the sympathetic trunk, through which they ascend into the neck. THE CERVICAL PORTION OF THE SYMPATHETIC SYSTEM 997 The superior cervical ganglion (ganglion cervicale superius), the largest of the three, is phuvd opijositc the second and third cervical vertebrae. It is of a reddish- gray color, and usuall.y fusiform in shape; sometimes broad and flattened, and occa- sionally constricted at intervals; it is believed to be formed by the coalescence of four ganglia, corresponding to the upper four cervical nerves. It is in relation, in front, with the sheath of the internal carotid artery and internal jugular vein; behind, with the Longus capitis muscle. Its branches may be divided into inferior, lateral, medial, and anterior. The Inferior Branch communicates with the middle cervical ganglion. The Lateral Branches (external branches) consist of gray rami communicantes to the upper four cervical nerves and to certain of the cerebral nerves. Sometimes the branch to the fourth cervical nerve may come from the trunk connecting the upper and middle cervical ganglia. The branches to the cerebral nerves consist of delicate filaments, which run to the ganglion nodosum of the vagus, and to the hypoglossal nerve. A filament, the jugular nerve, passes upward to the base of the skull, and divides to join the petrous ganglion of the glossopharyngeal, and the jugular ganglion of the vagus. The Medial Branches (internal branches) are peripheral, and are the lamygo- pharyngeal branches and the superior cardiac nerve. The laryngopharyngeal branches (rami laryngopharyngei) pass to the side of the pharynx, where they join with branches from the glossopharyngeal, vagus, and external laryngeal nerves to form the pharyngeal plexus. The superior cardiac nerve (n. cardiacus superior) arises by two or more branches from the superior cervical ganglion, and occasionally receives a filament from the trunk between the first and second cervical ganglia. It runs down the neck behind the common carotid artery, and in front of the Longus colli muscle; and crosses in front of the inferior thyroid artery, and recurrent nerve. The course of the nerves on the two sides then differ. The right nerve, at the root of the neck, passes either in front of or behind the subclavian artery, and along the innominate artery to the back of the arch of the aorta, where it joins the deep part of the cardiac plexus. It is connected with other branches of the sympathetic; about the middle of the neck it receives filaments from the external laryngeal nerve; lower down, one or two twigs from the vagus; and as it enters the thorax it is joined by a filament from the recurrent nerve. Filaments from the nerve communicate with the thyroid branches from the middle cervical ganglion. The left nerve, in the thorax, runs, in front of the left common carotid artery and across the left side of the arch of the aorta, to the superficial part of the cardiac plexus. The Anterior Branches (nn. carotid exierni) ramify upon the common carotid artery and upon the external carotid artery and its branches, forming around each a delicate plexus, on the nerves composing which small ganglia are occasionally found. The plexuses accompanying some of these arteries have important com- munications with other nerves. That surrounding the external maxillary artery communicates with the submaxillary ganglion by a filament; and that accompany- ing the middle meningeal artery sends an offset to the otic ganglion, and a second, the external petrosal nerve, to the genicular ganglion of the facial nerve. The middle cervical ganglion (ganglion cervicale medium) is the smallest of the three cervical ganglia, and is occasionally wanting. It is placed opposite the sixth cervical vertebra, usually in front of, or close to, the inferior thyroid artery. It is probably formed by the coalescence of two ganglia corresponding to the fifth and sixth cervical nerves. It sends gray rami communicantes to the fifth and sixth cervical nerves, and gives off the middle cardiac nerve. The Middle Cardiac Nerve (n. cardiacus 7nedius; great cardiac nerve), the largest of the three cardiac nerves, arises from the middle cervical ganglion, or from the 998 NEUROLOGY trunk between the middle and inferior ganglia. On the right side it descends behind the common carotid artery, and at the root of the neck runs either in front of or behind the subclavian artery; it then descends on the trachea, receives a few filaments from the recurrent nerve, and joins the right half of the deep part of the cardiac plexus. In the neck, it communicates with the superior cardiac and recur- rent nerves. On the left side, the middle cardiac nerve enters the chest between the left carotid and subclavian arteries, and joins the left half of the deep part of the caridac plexus. The inferior cervical ganglion (ganglioji cervicale inferius) is situated between the base of the transverse process of the last cervical vertebra and the neck of the first rib, on the medial side of the costocervical artery. Its form is irregular; it is larger in size than the preceding, and is frequently fused with the first thoracic ganglion. It is probably formed by the coalescence of two ganglia which corre- spond to the seventh and eighth cervical nerves. It is connected to the middle cervical ganglion by two or more cords, one of which forms a loop around the sub- clavian artery and supplies offsets to it. This loop is named the ansa subclavia {Vieussenii). The ganglion sends gray rami communicantes to the seventh and eighth cervical nerves. It gives off the inferior cardiac nerve, and offsets to bloodvessels. The inferior cardiac nerve {n. cardiacus inferior) arises from either the inferior cervical or the first thoracic ganglion. It descends behind the subclavian artery and along the front of the trachea, to join the deep part of the cardiac plexus. It communicates freely behind the subclavian artery with the recurrent nerve and the middle cardiac nerve. The offsets to bloodvessels form plexuses on the subclavian artery and its branches. The plexus on the vertebral artery is continued on to the basilar, posterior cerebral, and cerebellar arteries. The plexus on the inferior thyroid artery accompanies the artery to the thyroid gland, and communicates with the recurrent and external laryngeal nerves, with the superior cardiac nerve, and with the plexus on the common carotid artery. THE THORACIC PORTION OF THE SYMPATHETIC SYSTEM (PARS THORACALIS S. SMYPATHICI) (Fig. 825). The thoracic portion of the sympathetic trunk consists of a series of ganglia, which usually correspond in number to that of the vertebrae; but, on account of the occasional coalescence of two ganglia, their number is uncertain. The thoracic ganglia rest against the heads of the ribs, and are covered by the costal pleura; the last two, however, are more anterior than the rest, and are placed on the sides of the bodies of the eleventh and twelfth thoracic vertebrae. The ganglia are small in size, and of a grayish color. The first, larger than the others, is of an elongated form, and frequently blended with the inferior cervical ganglion. They are connected together by the intervening portions of the trunk. Two rami communicantes, a white and a gray, connect each ganglion with its corresponding spinal nerve. The branches from the up-per five ganglia are very small; they supply filaments to the thoracic aorta and its branches. Twigs from the second, third, and fourth ganglia enter the posterior pulmonary plexus. The branches from the lower seven ganglia are large, and white in color; they distribute filaments to the aorta, and unite to form the greater, the lesser, and the lowest splanchnic nerves. The greater splanchnic nerve {n. splanchnicus major; great splanchnic nerve) is white in color, firm in texture, and of a considerable size; it is formed by branches V THE THORACIC PORTiOS OF THE SYMPATHETIC SYSTEM 999 from the fifth to the iiintli or tenth thoracic ganglia, hut tlie fibres in the higher roots may be traced upward in the synii)athetic trunk as far as the first or second thoracic ganghon. It descends obHquely on the IxxHes of the vertebrse, perforates the cms of the Diaphragma, and ends in the ccehac ganghon. A ganglion (ganglion splanchnicum) exists on this ner\^e opposite the eleventh or twelfth thoracic vertebra. Highest intercostal artery Highest intercostal vein Fig. 825. — Thoracic portion of the sympathetic trunk. The lesser splanchnic nerve (?i. splanchiiciis minor) is formed by filaments from the ninth and tenth, and sometimes the eleventh thoracic ganglia, and from the cord between them. It pierces the Diaphragma with the preceding nerve, and joins the aorticorenal ganglion. The lowest splanchnic nerve (?i. splanchnicus imus; least splanchnic nerve) arises from the last thoracic ganglion, and, piercing the Diaphragma, ends in the renal plexus. 1000 NEUROLOGY A striking analogy exists between the splanchnic and the cardiac nerves. The cardiac nerves are three in number; they arise from all three cervical ganglia, DiaphrayiiMt ic (jaiKjlion Swprareiuil gh Aorticorejuil ganglion- — _ \ \ \ Lowest spanchnic nerve Hepatic ariuy ,Lcft codiac ganglion — v <*fBsr-:f unyi'w Superior mesenteric ^1^!^^ , %^^ ^y^ Greater splanchnic nerve -^ ^.^-J^ -^ jg^^ gi gawjlwu Hi iial artery Lesser splanchnic nerve ~\ Svperior tnesenteric ganglion Blanch to aortic plexus Branch to aortic plexus JllWi"i 'T Sympathetic trunk — Inferior mesenteric artery \ Inferior mesenteric ganglion Sacrovertehral angle Common iliac vein Cmnmon iliac artery Fig. 826. — Abdominal portion of the sympathetic trunk, -nith the cceliac and hypogastric plexuses. (After Henle.) THE CARDIAC PLEXUS 1001 and are distributed to a large and important organ in the thoracic cavity. The splanchnic nerves, also three in number, are connected probably with all the thoracic ganglia, and are distributed to important organs in the abdominal cavity. THE ABDOMINAL PORTION OP THE SYMPATHETIC SYSTEM (PARS ABDOMINALIS S. SYMPATHICI; LUMBAR PORTION OF GANGLIATED CORD) (Fig. 826). The abdominal portion of the sympathetic trunk is situated in front of the ver- tebral column, along the medial margin of the Psoas major. It consists usually of four lumbar ganglia, connected together by interganglionic cords. It is continuous above with the thoracic portion beneath the medial lumbocostal arch, and below with the pelvic portion behind the common iliac artery. The ganglia are of small size, and placed much nearer the median line than are the thoracic ganglia. Gray rami communicantes pass from all the ganglia to the lumbar spinal nerves. The first and second, and sometimes the third, lumbar nerves send white rami communicantes to the corresponding ganglia. The rami communicantes are of considerable length, and accompany the lumbar arteries around the sides of the bodies of the vertebrae, passing beneath the fibrous arches from which some of the fibres of the Psoas major arise. Of the branches of distribution, some pass in front of the aorta, and join the aortic plexus; others descend in front of the common iliac arteries, and assist in forming the hypogastric plexus. THE PELVIC PORTION OF THE SYMPATHETIC SYSTEM (PARS PELVINA S. SYMPATHICI). The pelvic portion of each sympathetic trunk is situated in front of the sacrum, medial to the anterior sacral foramina. It consists of four or five small sacral ganglia, connected together by interganglionic cords, and continuous above with the abdominal portion. Below, the two pelvic sympathetic trunks converge, and end on the front of the coccyx in a small ganglion, the ganglion impar. Gray rami communicantes pass from the ganglia to the sacral and coccygeal nerves. No white rami communicantes are given to this part of the gangliated cord, but the visceral branches which arise from the third and fourth, and sometimes from the second, sacral, and run directly to the pelvic plexuses, are regarded as white rami communicantes. The branches of distribution communicate on the front of the sacrum with the corresponding branches from the opposite side; some, from the first two ganglia, pass to join the pelvic plexus, and others form a plexus, which accompanies the middle sacral artery and sends filaments to the glomus coccygeum (coccygeal body). THE GREAT PLEXUSES OF THE SYMPATHETIC SYSTEM. The great plexuses of the sympathetic are aggregations of nerves and ganglia, situated in the thoracic, abdominal, and pelvic cavities, and -named the cardiac, coeliac, and hypogastric plexuses. They consist not only of sympathetic fibres derived from the ganglia, but of fibres from the medulla spinalis, which are con- veyed through the white rami communicantes. From the plexuses branches are given to the thoracic, abdominal, and pelvic viscera. The Cardiac Plexus (Plexus Cardiacus) (Fig. 824). The cardiac plexus is situated at the base of the heart, and is divided into a super- ficial part, which lies in the concavity of the aortic arch, and a deep part, between the aortic arch and the trachea. The two parts are, however, closely connected. 1002 XEUROLOGY The superficial part of the cardiac plexus lies beneath the arch of the aorta, in front of the right pulmonary artery. It is formed by the superior cardiac branch of the left sympathetic and the lower superior cervical cardiac branch of the left vagus. A small ganglion, the cardiac ganglion of Wrisberg, is occasionally found connected with these nerves at their point of junction. This ganglion, when present, is situated immediately beneath the arch of the aorta, on the right side of the ligamentum arteriosum. The superficial part of the cardiac plexus gives branches (a) to the deep part of the plexus; (6) to the anterior coronary plexus; and (c) to the left anterior pulmonary plexus. The deep part of the cardiac plexus is situated in front of the bifurcation of the trachea, above the point of di\-ision of the pulmonary artery, and behind the aortic arch. It is formed by the cardiac nerves derived from the cervical ganglia of the sympathetic, and the cardiac branches of the vagus and recurrent nerves. The only cardiac nerves which do not enter into the formation of the deep part of the cardiac plexus are the superior cardiac nerve of the left sympathetic, and the lower of the two superior cervical cardiac branches from the left vagus, which pass to the superficial part of the plexus. The branches from the right half of the deep part of the cardiac plexus pass, some in front of, and others behind, the right pulmonary artery; the former, the more numerous, transmit a few filaments to the anterior pulmonary plexus, and are then continued onward to form part of the anterior coronary plexus; those behind the pulmonary artery distribute a few filaments to the right atrium, and are then continued onward to form part of the posterior coronary plexus. The left half of the deep part of the plexus is connected with the superficial part of the cardiac plexus, and gives filaments to the left atrium, and to the anterior pulmonary plexus, and is then continued to form the greater part of the posterior coronary plexus. The Posterior Coronary Plexus (plei-us coronarius jxjsterior; left coronary plexus) is larger than the anterior, and accompanies the left coronary artery; it is chiefly formed by filaments prolonged from the left half of the deep part of the cardiac plexus, and by a few from the right half. It gives branches to the left atrium and ventricle. The Anterior Coronary Plexus (jjlexus coronarius anterior; right coronary plexus) is formed partly from the superficial and partly from the deep parts of the cardiac plexus. It accompanies the right coronary artery, and gives branches to the right atrium and ventricle. The Coeliac Plexus (Plexus Coeliacus; Solar Plexus) fFigs. 824, 827). The coeliac plexus, the largest of the three sympathetic plexuses, is situated at the level of the upper part of the first lumbar vertebra and is composed of two large ganglia, the coeliac ganglia, and a dense net-work of nerve fibres uniting them together. It surrounds the coeliac artery and the root of the superior mesenteric artery. It lies behind the stomach and the omental bursa, in front of the crura of the Diaphragma and the commencement of the abdominal aorta, and between the suprarenal glands. The plexus and the ganglia receive the greater and lesser splanchnic nerves of both sides and some filaments from the right vagus, and give off numerous secondary plexuses along the neighboring arteries. The Coehac Ganglia (ganglia coeliaca; semilunar ganglia) are two large irregularly- shaped masses having the appearance of lymph glands and placed one on either side of the middle line in front of the crura of the Diaphragma close to the supra- renal glands, that on the right side being placed behind the inferior vena cava. The upper part of each ganglion is joined by the greater splanchnic nerve, while the THE CCELIAC PLEXUS 1003 lower part, which is segmented oil' and named tlie aorticorenal ganglion, receives the lesser splanchnic nerve and gives ofi" the greater j)art of the renal plexus. C celiac Left Phrenic plexus vagus plexus vagus Hepatic plextis Common bile-ducf Superior mesenteric plexus Aortic plexu'' <>tric plexus P/irenic plexus Suprarenal plexus Lienal plexus Phrenic ganglicn Greater ^^^ splanchnic celiac nglion Renal plexus Superior mesenteric ganglion Spermatic plexus Lumbar ganglia Inferior \ mesenteric plexus Fig. 827. — The coeliac ganglia with the sympathetic plexuses of the abdominal viscera radiating from the ganglia. (Toldt.) The secondary plexuses springing from or connected with the coeliac plexus are the Phrenic. Renal. Hepatic. Spermatic. Lienal. Superior mesenteric. Superior gastric. Abdominal aortic. Suprarenal. Inferior mesenteric. The phrenic plexus {plexus jjhrenicus) accompanies the inferior phrenic artery to the Diaphragma, some filaments passing to the suprarenal gland. It. arises from the upper part of the coeliac ganglion, and is larger on the right than on the left side. It receives one or two branches from the phrenic nerve. At the point 1004 NEUROLOGY of junction of the right phrenic plexus with the phrenic nerve is a small ganglion (ganglion phrenicum). This plexus distributes branches to the inferior vena cava, and to the suprarenal and hepatic plexuses. The hepatic plexus {plexus hepaticvs), the largest offset from the coeliac plexus, receives filaments from the left vagus and right phrenic nerves. It accompanies the hepatic artery, ramifying upon its branches, and upon those of the portal vein in the substance of the liver. Branches from this plexus accompan}^ all the divisions of the hepatic artery. A considerable plexus accompanies the gastroduodenal artery and is continued as the inferior gastric plexus on the right gastroepiploic arter}'- along the greater curvature of the stomach, where it unites with offshoots from the lienal plexus. The lienal plexus (plexus lienalis; splenic plexus) is formed by branches from the coeliac plexus, the left coeliac ganglion, and from the right vagus nerve. It accom- panies the lienal artery to the spleen, giving off, in its course, subsidiary plexuses along the various branches of the artery. The superior gastric plexus {plexus gastricus superior; gastric or coronary plexus) accompanies the left gastric artery along the lesser curvature of the stomach, and joins with branches from the left vagus. The suprarenal plexus {plexus suprarenalis) is formed by branches from the coeliac plexus, from the coeliac ganglion, and from the phrenic and greater splanchnic nerves, a ganglion being formed at the point of junction with the latter nerve. The plexus supplies the suprarenal gland, being distributed chiefly to its medullary portion; its branches are remarkable for their large size in comparison with that of the organ they supply. The renal plexus {plexus renalis) is formed by filaments from the coeliac plexus, the aorticorenal ganglion, and the aortic plexus. It is joined also by the smallest splanchnic nerve. The nerves from these sources, fifteen or twenty in number, have a few ganglia developed upon them. They accompany the branches of the renal artery into the kidney; some filaments are distributed to the spermatic plexus and, on the right side, to the inferior vena cava. The spermatic plexus {plexus spermaticus) is derived from the renal plexus, receiving branches from the aortic plexus. It accompanies the internal spermatic artery to the testis. In the female, the ovarian plexus {plexus arteriae ovaricae) arises from the renal plexus, and is distributed to the ovary, and fundus of the uterus. Applied Anatomy. — The intimate connection which exists between the renal and spermatic plexuses serves to explain the very frequent symptom in renal calculus, of pain which is referred to the body of the testis. The superior mesenteric plexus {plexus mesentericus superior) is a continuation of the lower part of the coeliac plexus, receiving a branch from the junction of the right vagus nerve with the plexus. It surrounds the superior mesenteric artery, accompanies it into the mesentery, and divides into a number of secondary plexuses, which are distributed to all the parts supplied by the artery, viz., pancreatic branches to the pancreas; intestinal branches to the small intestine; and ileocolic, right colic, and middle colic branches, w^hich supply the corresponding parts of the great intestine. The nerves composing this plexus are white in color and firm in texture; in the upper part of the plexus close to the origin of the superior mesenteric artery is a ganglion (ganglion mesentericum superius) . The abdominal aortic plexus {plexus aorticus abdominalis; aortic plexus) is formed by branches derived, on either side, from the coeliac plexus and ganglia, and receives filaments from some of the lumbar ganglia. It is situated upon the sides and front of the aorta, between the origins of the superior and inferior mesenteric arteries. From this plexus arise part of the spermatic, the inferior mesenteric, and the hypogastric plexuses; it also distributes filaments to the inferior vena cava. THE HYPOGASTRIC PLEXUS 1005 The inferior mesenteric plexus {j)lexus mesentericus inferior) is derived chiefly from the aortic plexus. It surrounds the inferior mesenteric artery, and divides into a number of secondary plexuses, which are distributed to all the parts supplied by the artery, viz., the left colic and sigmoid plexuses, wliich supply the descending and sigmoid parts of the colon; and the superior hemorrhoidal plexus, which supplies the rectum and joins in the pelvis with branches from the pelvic plexuses. The Hypogastric Plexus (Plexus Hypogastricus) (Fig. 824). The hypogastric plexus is situated in front of the last lumbar vertebra and the promontory of the sacrum, between the two common iliac arteries, and is formed by the union of numerous filaments, which descend on either side from the aortic plexus, and from the lumbar ganglia; it divides, below, into two lateral portions which are named the pelvic plexuses. The Pelvic Plexuses (Fig. 824).- — The pelvic plexuses supply the viscera of the pelvic cavity, and are situated at the sides of the rectum in the male, and at the sides of the rectum and vagina in the female. They are formed on either side by a continuation of the hypogastric plexus, by the visceral branches from the second, third, and fourth sacral nerves, and by a few filaments from the first two sacral ganglia. At the points of junction of these nerves small ganglia are found. From these plexuses numerous branches are distributed to the viscera of the pelvis. They accompany the branches of the hypogastric artery. The Middle Hemorrhoidal Plexus (plexus haemorrhoidalis medius) arises from the upper part of the pelvic plexus. It supplies the rectum, and joins with branches of the superior hemorrhoidal plexus. The Vesical Plexus (plexus vesicalis) arises from the forepart of the pelvic plexus. The nerves composing it are numerous, and contain a large proportion of spinal nerve fibres. They accompany the vesical arteries, and are distributed to the sides and fundus of the bladder. Numerous filaments also pass to the vesiculae seminales and ductus deferentes; those accompanying the ductus deferens join, on the sper- matic cord, with branches from the spermatic plexus. The Prostatic Plexus (plexus prostaticus) is continued from the lower part of the pelvic plexus. The nerves composing it are of large size. They are distributed to the prostate vesiculae seminales and the corpora cavernosa of the penis and urethra. The nerves supplying the corpora cavernosa consist of two sets, the lesser and greater cavernous nerves, which arise from the forepart of the prostatic plexus, and, after joining with branches from the pudendal nerve, pass forward beneath the pubic arch. The lesser cavernous nerves (nn. cavernosi penis minores; small cavernous nerves) perforate the fibrous covering of the penis, near its root. The greater cavernous nerve (n. cavernosu^ penis major; large cavernous plexus) passes forward along the dorsum of the penis, joins with the dorsal nerve of the penis, and is distributed to the corpora cavernosa. The Vaginal Plexus arises from the lower part of the pelvic plexus. It is distributed to the walls of the vagina, to the erectile tissue of the vestibule, and to the clitoris. The nerves composing this plexus contain, like the vesical, a large proportion of spinal nerve fibres. The Uterine Plexus accompanies the uterine artery to the side of the uterus, between the layers of the broad ligament; it communicates with the ovarian plexus. Applied Anatomy. — Little is known as to the connection between the numerous microscopic alterations (pigmentation, atrophy, hemorrhage, fibrosis) that have been described in the sympa- thetic nervous system, and the fimctional changes that ensue therefrom. Grosser lesions due to stabs, bullet woimds, or the pressm-e of new growths, may cause either irritative or paralytic 1006 NEUROLOGY symptoms. In paralysis of the cervical sympathetic on one side, the pupil is small and does not dilate when shaded or on the instillation of cocaine, although it contracts still farther when brightly illumiaated; it also loses the cihospinal reflex, faihng to dilate when the skin of the neck is pinched. The palpebral fissure narrows from paralysis of the involuntary muscle of the eyelid, and the eyeball sinks backward into the orbit — enophthahnos — either from paralysis of Miiller's orbital muscle which closes the inferior orbital fissure, or from wasting of the intraorbital fat. The superficial vessels of the face and scalp are at first dilated, but later they contract. Anidrosis, or absence of sweating, is often noted on the afTected side. Irritation of the cervical sympathetic produces signs mainly the converse of those described above. We have no definite knowledge of the signs and symptoms that follow lesions of the thoracic or abdominal sympathetic systems. It is Ukely, however, that a number of nervous disorders characterized by persistent vascular disturbances, such as dilatation of the vessels with throbbing, flushing, sweating, and localized oedema, or contraction of the vessels with pallor, chilliness, pain, and malnutrition of the affected parts, are due to implication of the sympathetic nervous system. It is possible, too, that the rare condition of progressive facial hemiatro'phy, coming on between the ages of ten and twenty, and producing marked unilateral shrinkage of all the tissues of the face, is primarily an affection of the sympathetic. THE ORGANS OF THl^] SENSES AND THE COMMON INTEGUMENT. THE organs of the senses may be divided into (a) those of the special senses of taste, smell, sight, and hearing, and (6) those associated with the general sensa- tions of heat, cold, pain, pressure, etc. THE PERIPHERAL ORGANS OF THE SPECIAL SENSES. THE ORGAN OF TASTE (ORGANON GUSTUS). The periphery gustatory or taste organs consist of certain modified epithelial cells arranged in flask-shaped groups termed gustatory calyculi (taste-buds), which are found on the tongue and adjacent parts. They occupy nests in the stratified epithelium, and are present in large numbers on the sides of the papillae vallatae (Fig. 828), and to a less extent on their opposed walls. They are also found on the