■»-;■ Cornell University Library The original of this book is in the Cornell University Library. There are no known copyright restrictions in the United States on the use of the text. http://www.archive.org/details/cu31924003113523 Cornell University Library QM 23.G77 1870 Ariatomy, descriptive and surgical. 3 1924 003 113 523 CORNELL UNIVERSITY LIBRARY ANATOMY, DESCKIPTIVE AKD SURGICAL. BY HENKY GRAY, F.R.S., FELLOW OF THE ROYAL COLLBSB OF SURGEONS AND LECTURER ON ANATOMY AT ST. George's hospital medical school. THE DRAWINGS BY H. V. CARTER, M.D., LATE DEMONSTBATOR OF ANATOMY AT 81*. QEOEGE's HOSPITAL, WITH ADDITIONAL DRAWINGS IN THE SECOND AND LATER EDITIONS BY DR. WBSTMACOTT. THE DISSECTIONS JOINTLY BY THE AUTHOR AND DE. CAETER. WITH AN INTRODUCTION ON GENERAL ANATOMY AND DEVELOPMENT, BY T. HOLMES, M.A. Cantab. SUESEON TO ST. GEORSE'S HOSPITAL ; MEM. COERESP. DE LA SOO. DB CHIR. DE PARIS. A NEW AMEEICAN PROM THE FIFTH AND ENLARGED ENGLISH EDITION. r FOUR HUNDRED AND SIXTY-TWO ENGRAVINGS ON WOOD. PHILADELPHIA: HEI^EY O. LEA. 1870. TO Sm BEKJAim COLLINS BRODIE, BAKT, RE.S, D.C.L, SERJEANT-SURGEON TO THE QUEEN, CORRESPONDING MEMBER OF THE INSTITUTE OF FRANCE, %\is Sioii is f jMtateJr, IN ADMIRATION OF HIS GREAT TALENTS, IN REMEMBRANCE OF MANY ACTS OF KINDNESS SHOWN TO THE AUTHOR, FROM AN EARLY PERIOD OF HIS PROFESSIONAL CAREER. ( iii) AMERICAN PUBLISHER'S NOTICE. The present edition, like the previous American reprints, has been passed through the press under the supervision of Dr. Richard J. Dunglison, who has carefully corrected whatever errors had escaped the attention of the author, and has made such changes in the typographical arrangement as seemed calculated to render the volume more convenient for consultation and reference. A few illustrations have also been introduced in the introductory section. They will be found distinguished by inclosure in brackets. March, 18t0. (iv ) PREFACE TO THE FIFTH EDITION. In this edition the plan of the .work has been so far altered that the portion on General Anatomy, which was previously scattered throughout the book, has been collected into an Introductory Chapter, and re- written, so as to fur- nish the Student with a very succinct, but it is hoped sufficient, introduction to the study of Microscopic Anatomy ; and to this has been added a short description of the chief processes of the development of the ovum, and of the structures characteristic of the fcetal state: a subject which, though undeni- ably an integral portion of Human Descriptive Anatomy, was passed over in previous editions. This Introduction is inserted in deference to the opinions of persons very competent to judge, and who believe that some such addition is necessary to the completion of Gray's 'Anatomy." It is not intended, however, to super- sede or to trench upon the Treatises on Physiology, nor to go minutely into the more recondite and more dubious parts of microscopic research. Nor, again, is it intended to give any account in this work of vital phenomena. Such phenomena are purely within the domain of the physiologist. Conse- quently all the ingenious and beautiful researches by which modern micro- scopists (as Strieker, Yon Eecklingshausen, Beale, and others) have attempted to investigate the living tissues, lie beyond the scope of such a treatise as this. The humble aim of the following pages is to provide the Student — in the smallest compass, and in the simplest language — with a plain account of things for the most part universally admitted, and which, with moderate pains, he can succeed in demonstrating for himself In order to make such verbal descriptions intelligible, figures are necessary : but it appeared useless to manufacture new drawings of things which are quite faithfully represented by authors who are in everybody's hands ; and therefore all the illustrations to (V) vi PREFACE TO THE FIFTH EDITION. the chapter on General Anatomy have been borrowed from the English trans- lation of Kolliker's " Manual of Human Microscopic Anatomy," from the "Entwicklangsgesohichte" of the same author, Todd and Bowman's "Physi- ology," Harley and Brown's " Demonstrations of Microscopic Anatomy," and other well-known works: the source of the drawings having been in each case acknowledged in the Table of Contents. The text has been further expurgated from errors of the press; and the Editor has to acknowledge his obligations in this particular to his friend Pro- fessor Darling, of New York, and to Mr. Matthews, of Kirkdale, who have been kind enough to point out several, and some of them important, clerical errors which had escaped notice in previous revisions. 31 Olarges Street : September, 1869. PREFACE TO THE FIRST EDITION This work is intended to furnish the Student and Practitioner with an accurate view of the Anatomy of the Human Body, and more especially the application of this Science to Practical Surgery. One of the chief objects of the Author has been, to induce the Student to apply his anatomical knowledge to the more practical points in Surgery, by introducing, in small type, under each subdivision of the work, such observa- tions as show the necessity of an accurate knowledge of the part under examination. Osteology. Much time and care have been devoted to this part of the work, the basis of anatomical knowledge. It contains a concise description of the anatomy of the bones, illustrated by numerous accurately-lettered engravings showing the various markings and processes on each bone. The attachments of each muscle are shown in dotted lines (after the plan recently adopted by Mr. Holden), copied from recent dissections. The articulations of each bone are shown on a new plan ; and a method has been adopted, by which the hitherto complicated account of the development of the bones is made more simple. The Articulations. In this section, the various structures forming the joint are described ; a classification of the joints is given ; and the anatomy of each carefully described : abundantly illustrated by engravings, all of which are taken from, or corrected by, recent dissections. The Muscles and Fascise. In this section, the muscles are described, in groups, as in ordinary anatomical works. A series of illustrations, showing the lines of incision necessary in the dissection of the muscles in each region, are intro- duced, and the muscles are shown in fifty-eight engravings. The Surgical Anatomy of the muscles in connection with fractures, of the tendons or muscles divided in operations, is also described and illustrated. The Arteries. The course, relations, and Surgical Anatomy of each artery are described in this section, together with the anatomy of the regions contain- ing the arteries more especially involved in surgical operations. This part of the work is illustrated by twenty-eight engravings. ( vii ) Tiii PREFACE TO THE PIRST EDITION. The Veins are described as in ordinary anatomical works ; and illustrated by a series of engravings, showing those in each region. The veins of the spine are described and illustrated from. the well-known work of Brescbet. The Lymphatics are described, and figured in a series of illustrations copied from the elaborate work of Mascagni. The Xervous System and Organs of Sense. A concise and accurate description of this important part of anatomy has been given, illustrated by sixty-six engravings, showing the spinal cord and its membranes ; the anatomy of the brain, in a series of sectional views ; the origin, course, and distribution of the cranial, spinal, and sympathetic nerves ; and the anatomy of the organs of sense. The Viscera. A detailed description of this essential part of anatomy has been given, illustrated by fifty-five large, accurately lettered engravings. Regional Anatomy. The anatomy of the perineum, of the ischio-rej3tal region, and of femoral and inguinal hernise, is described at the end of the work ; the region of the neck, the axilla, the bend of the elbow, Scarpa's triangle, and the popliteal space, in the section on the arteries ; the laryngo-tracheal region, with the anatomy of the trachea and larynx. The regions are illustrated by many engravings. Microscopical Anatomy. A brief account of the microscopical anatomy of some of the tissues, and of the various organs, has also been introduced. The Author gratefully acknowledges the great services he has derived in the execution of this work, from the assistance of his friend. Dr. H. V. Carter, late Demonstrator of Anatomy at St. George's Hospital. All the drawings from which the engravings were made, were executed by him. In the majority of cases, they have been copied from, or corrected by, recent dissections made jointly by the Author and Dr. Carter. The Author has also to thank his friend, !Mr. T. Holmes, for the able assist- ance afforded him in correcting the proof-sheets in their passage through the press. The engravings have been executed by Messrs. Butterworth and Heath ; and the Author cannot omit thanking these gentlemen for the great care and fidelity displayed in their execution. Wilton Street, Belgrave Square : August, 1858. OOlTTElSrTS. INTRODUCTION"; GENERAL ANATOMY. PAQE The Blood 33 Lympli and Chyle 37 Cellular and Fibrous Tissue ... 38 Adipose Tissue 40 Pigment 41 Cartilage 41 Pibro-cartilage .... 43 Yellow or Eeticular Cartilage . . 44 Bone 45 Development of Bone ... 49 Muscular Tissue 53 Nervous Tissue ..... 57 The Brain 60 The Spinal Cord .... 62 The Ganglia 64 The Nerves 65 The Sympathetic Nerve ... 66 Terminations of Nerves ... 66 The Vascular System .... 72 The Arteries 72 The Capillaries . . . . 74 The Veins 75 The Lymphatics .... 77 The Lymphatic Glands ... 78 The Skin and its Appendages . . 78 The Nails 81 The Hairs 82 The Sebaceous Glands ... 83 The Sudoriferous Glands ... 84 The Epithelium 85 Serous, Mucous, and Synovial Membranes 86 Secreting Glands 87 Growth and Development of the Body . 89 Fecundation of the Ovum . . 89 Formation of Germinal Area and Chorda Dorsalis . . . . 90 Division of Blastodermic Membraue 90 Parts formed from each layer of the Blastodermic Membrane . . 90 The Amnion 91 The Allantois 91 The Umbilical Vesicle ... 93 The Chorion 93 The Decidua .... 93 The Placenta 95 The Umbilical Cord .... 96 The Earliest Condition of the Embryo . 96 Development of the Various Parts . 97 The Spine 97 The Cranium and Face ... 97 The Palate 99 The Brain 99 The Spinal Marrow and Nerves . 99 The Eye 101 The Ear 102 The Nose 102 The Skin, Glands, and Soft Parts . 102 The Heart and Great Vessels . . 103 The Alimentary Canal and its Ap- pendages 106 The Respiratory Organs . . . 107 The Genito-urinary Organs . . 108 The WolfBan Body . . . .108 The Internal Genital Organs. Indifferent type .... 108 Female Organs .... 109 Male Organs .... 109 The External Genital Organs. Indifferent type .... 109 Female Organs .... Ill Male Organs .... Ill Chronolosjical Table of the Development of the Foetus 112 ANATOMY, DESCRIPTIVE AND SURGICAL. The Skeleton. The Skeleton . 115 Peculiar Dorsal Vertebrae 121 Number of Bones .... . 115 Characters of the Lumbar Vertebrae 123 Form of Bones .... . 115 Structure of the Vertebrae 124 Development of the Vertebrae 124 The Spine. Atlas 125 Axis 125 General Characters of a Vertebra . . 116 7th Cervical . 125 Characters of the Cervical Vertebras . 117 Lumbar Vertebrae . 125 Atlas . 118 Progress of Ossification in the Spine 125 Axis . 119 Sacrum 126 Vertebra Prominens . 120 Coccyx 130 Characters of the Dorsal Vertebrae . 121 Of the Spine in General . 131 CONTENTS. Tlie Skull. PAGE PAGfK Peculiar Ribs 196 Bones of the Cranium . 134 Costal Cartilages . . . . 198 Occipital Bone . . 134 Parietal Bones . . 138 The Upper Extremity. Frontal Bone . . 140 The Clavicle 199 Temporal Bones . 143 The Scapula 202 Sphenoid Bone . 140 The Humerus 207 Ethmoid Bone . . . . . 154 The Ulna 212 Development of the Cranium . 15G The Radius 217 The Pontanelles . 1.56 The Hand 219 Wormian Bones . 1.57 The Carpus 219 Congenital Fissures and Gaps . 157 Bones of Upper Row 219 Bones of the Face : Bones of Lower Eow 221 Nasal Bones . 158 The Metacarpus 224 Superior Maxillary Bones . 159 Peculiar Metacarpal Bones 225 Lachrymal Bones . 163 Phalanges ..... 226 Malar Bones . 164 Development of the Bones of the Hand . 226 Palate Bones . . 16G Inferior Turbinated Bones . 168 The Lower Extremity. Vomer .... . 169 Os Innominatum 227 Inferior Maxillary . 170 Ilium .... 22 y Changes produced in the Lowei ■ Jaw Ischium ..... 230 by age . . 174 Pubes 232 Sutures of the Skull . 174 Development of the Os Innominatum 233 Vertex of the Skull 176 The Pelvis 234 Base of the Skull, Internal Surface 176 Difference between the Male and Fe- Anterior Fossie . 176 male Pelvis ..... 236 iliddle FossiB . 178 The Femur .... 237 Posterior Fossa . . 179 The Leg 242 Base of Skull, External Surface . 179 Patella . 242 Lateral Region of the Skull . . 183 Tibia 243 Temporal Fosste . 183 Fibula 247 Zygomatic Fossie . . 184 The Foot . 249 Spheno-maxillary Fossae . . 184 Tarsus 249 Anterior Region of the Skull . . 184 Os Calois 249 Orbits 185 Cuboid 251 Nasal Fossae .... . 187 Astragalus 253 Os Hyoides .... . 189 Scaphoid 254 Cuneiform Bone 254 The Thorax. ^Metatarsal Bones 256 The Sternum . 190 Phalanges .... 257 The Ribs . 194 i Development of the Foot 358 Sesamoid Bones 259 The Articulations. Structures composing the Joints . . 260 Articular Lamella of Bone . . 260 Ligaments ..... 260 Synovial Membrane .... 260 Bursa3 260 Synovia ..... 260 Forms of Articulation Synarthrosis 262 Amphiarthrosis . . . 202 Diathrosis 262 Movements of Joints . . 265 Articulations of the Trunk. Articulations of the Vertebral Column . 265 Atlas with the Axis 269 Atlas with the Occi- pital Bone . . 271 Axis with the Occi- pital Bone . . 272 Temporo-maxillary Articulation . . 273 Articulation of the Ribs with the Vertcbrie 275 Articulations of the Cartilages of the Ribs with the Sternum and Fusiform Cartilage Intercostal Articulations Ligaments of the Sternum Articulation of the Pelvis with the Spine Articulation of the Sacrum and Ilium Ligaments between the Sacrum and Ischium ..... Articulation of the Sacrum and Coccyx Inter-pubic Symphysis Articulations of the Upper Extrem Sterno-clavioular .... Scapulo-clavicular .... Proper Ligaments of the Scapula . Shoulder-joint Elbow-joint Radio-ulnar Articulations "Wrist-joint .... Articulations of the Carpus . 278 279 280 2 si) 281 2S2 283 2a3 ty. 285 2S6 287 288 289 291 294 294 CONTENTS. XI PAGE Carpo-metacarpal Articulations . . 296 Metacarpo-plialangeal Articulations . 298 Articulation of the Phalanges . . 298 Articulations of the Lower Extremity. Hip-joint 299 Knee-joint 301 Articulations between the Tibia and Fibula 305 Ankle-joint 307 Articulations of the Tarsus . . . 309 Tarso-metatarsal Articulations . . 312 Articulations of the Metatarsus . . 312 Metatarao-phalangeal Articulations . 313 Articulations of the Phalanges . . 313 Muscles and Fasciaa, General Description of Muscle . . 314 Tendon . . 315 Aponeurosis . 315 Fascia . . 315 Muscles and PASciiE op the Head and Pace. Subdivision into Groups . Epicranial Region. Dissection .... Occipito-fron talis 316 317 317 Auricular Region. Dissection .... . 319 Attollens Aurem . 319 Attrahens Aurem . . 319 Eetrabens Aurem . . 319 Actions . 320 Palpebral Region. Dissection Orbicularis Palpebrarum Corrugator Supercilii Tensor Tarsi . Actions . . . . Orbital Region. Dissection Levator Palpebrje . . . . Kectus Superior, Inferior, Internus, and Externus Superior Oblique Inferior Oblique Actions : Surgical Anatomy . Nasal Region. Pyramidalis Nasi Levator Labii Superioris Alaeque Nasi . Dilatator Naris, Anterior and Posterior . Compressor Nasi Narium Minor Depressor Alse Nasi .... Actions Superior Maxillary Region. Levator Labii Superioris Proprius . Levator Anguli Oris .... Zygomatici Actions Inferior Maxillary Region. Dissection Levator Labii Inferioris .... Depressor Labii Inferioris Depressor Anguli Oris .... 320 320 320 321 321 321 321 321 322 323 323 324 324 324 324 324 324 324 325 325 325 325 325 326 326 326 Intermaxillary Region. Dissection 326 Orbicularis Oris 326 Buccinator 327 Risorius 327 Actions 327 Temporo-maxillary Region. Masseter 327 Temporal Fascia 328 Temporal 328 Ptery go-maxillary Region. Dissection 329 Internal Pterygoid 329 External Pterygoid 330 Actions 330 Muscles and Fasciae of the Neck. Subdivision into Groups .... 330 Superficial Region. Dissection 331 Superficial Cervical Fascia 331 Platysma Myoides 331 Deep Cervical Fascia . . . . 332 Sterno-cleido-mastoid 332 Boundaries of the Triangles of the Necls 333 Actions : Surgical Anatomy . 334 Infraliyoid Region. Dissection 334 Stern o-hyoid 334 Sterno-thyroid 335 Thyro-hyoid 335 Omo-hyoid 335 Actions 336 Suprahyoid Region. Dissection . 336 Digastric 336 Stylo-hyoid, Mylo-hyoid, Genio-hyoid . 337 Actions . 337 Lingual Region. Dissection . 338 Genio-hyo-glossus .... . 338 Hyo-glossus . 339 Lingualis, Stylo-glossus, Palato-glossus . 339 Actions . 339 340 Pharyngeal Region. Dissection Inferior Constrictor, Middle Constrictor 340 Superior Constrictor .... 341 Stylo-pharyngeus 341 Actions 341 CONTENTS. Palatal Region. PAGE Dissection 342 Levator Palati .... 342 Oircumflexus or Tensor Palati . . 342 Azygos UvuliE, Palato-glossus, Palato- pharyngeus 343 Actions : Surgical Anatomy . . . 344 Vertebral Region [Anterior). Eectus Capitis Anticus Major and ?iIinor 344 Rectus Lateralis 344 Longus Colli .... . 345 Vertebral Region [Lateral). Scalenus Anticus 34G Scalenus Medius, Scalenus Posticus . 34C Actions 346 Muscles and Pasoije of the Trunk. Subdivision into Groups .... 346 Muscles of the Bach. Subdivision into Layers .... 347 First Layer. Dissection 347 Trapezius 347 Ligamentum Nuchse .... .348 Latissimus Dorsi 348 Second Layer. Dissection 3.50 Levator Anguli Scapulae .... 350 Khomboideus Minor and Major . . 350 Actions . . . . 351 Third La.yer. Dissection 351 Serratus Posticus Superior and Inferior . 351 Vertebral Aponeurosis . . . 352 Splenius Capitis and Colli . . . 352 Actions 352 Fourth Layer. Dissection ... . . 354 Erector Spinas . . . . 354 Sacro-lumbalis 354 Musculus Accessorius ad Sacro-lumbalem 354 Cervicalis Ascendens .... 354 Longissimus Dorsi ..... 354 Transversalis Colli 355 Trachelo-mastoid 355 Spinalis Dorsi 355 Spinalis Colli 355 Complexus, Diventor Cerviois . . . 355 Fifth Layer. Dissection ...... 356 Semispinalis Dorsi and Colli . . . 35G Multifidus Spinaj 356 Eotatores Spina3 350 ijupraspinales ...... 357 Interspinales 357 Extensor Coccygis 357 Intertransversales ..... 357 Rectus Capitis Posticus Major and Minor 357 Obliquus Inferior 357 Obliquus Superior 35H Actions 358 Muscles of the Abdomen. PAfSB Dissection . . . . . .359 Obliquus Externus 359 Obliquus luternus 361 Transversalis .... . 362 Lumbar Fascia 303 Rectus ....... 364 Pyramidalis, Quadratus Lumborum . 365 Linea Alba, Lineas Semilunares . 365 Liuese Transversa} ..... 365 Actions 365 Muscles and Fascia of the Thokax. Intercostal Fasciae 366 Interoostales Interni et Externi . . 366 Infra^costales, Triangularis Sterni . 367 Levatores Costarum .... 367 Actions .... . . 367 Diaphragmatic Region. Diaphragm 368 Actions 370 Muscles AND Faciei: of the Upper Extremity. Subdivision into Groups .... Dissection of Pectoral Region and Axilla Fasoias of the Thorax 371 372 372 Anterior Thoracic Region. Peotoralis Major .... Oosto-coracoid Membrane Pectoralis Minor .... Subclavius . . ... Actions ....... 372 374 374 375 375 Latercd Thoracic Region. Serratus Magnus, Actions 376 Acromial Region. Deltoid, Actions 377 Anterior Scapular Region. Subscapular Aponeurosis . . . 377 Subscapularis, Actions .... 377 Posterior Scapular Region. Supraspinous Aponeurosis . . . 378 Supraspinatus 378 Infraspinous Aponeurosis . . . 378 Infraspinatus ...... 379 Teres Minor . . . 379 Teres Major 380 Actions 380 Anterior Humeral Region. Deep Fascia of Arm . . . 3S0 Coraco-braohialis, Biceps . . . 381 Brachialis Anticus 382 Actions 382 Posterior Humeral Region. Triceps 382 Sub-anconeus 383 Actions 383 Muscles of Forearm. Deep Fascia of Forearm .... 383 CONTENTS. Anterior Braclxial Region, Superficial Layer. PAGE Pronator Radii Teres .... 384 Plexor Carpi Radialis Palmaria Longus Flexor Carpi Ulnaris Flexor Digitorum Sublimis 384 385 385 385 Anterior Brachial Region, Deep Layer. Flexor Profundus Digitorum . . .386 Flexor Longus Pollicis .... 387 Pronator Quadratus .... 387 Actions 388 Radial Region. Dissection 388 Supinator Longus 388 Extensor Carpi Radialis Longior . . 388 Extensor Carpi Radialis Brevoir . . 389 Posterior Brachial Region, Superficial Layer. Extensor Communis Digitorum . . 390 Extensor Minimi Digiti .... 390 Extensor Carpi Ulnaris .... 390 Anconeus 390 Posterior Brachial Region, Deep Layer. Supinator Brevis 391 Extensor Ossis Metacarpi Pollicis . . 391 Extensor Primi Internodii Pollicis . . 391 Extensor Secundi Internodii Pollicis . 391 Extensor Indicis 392 Actions 392 Muscles and Fasciae of the Hand. Dissection 393 Anterior Annular Ligament . . . 393 Posterior Annular Ligament . . . 393 Palmar Fascia 394 Muscles of the Hand. Radial Group 394 Ulnar Group 396 Middle Palmar Group . . . .397 Actions 398 Surgical Anatomy of the Muscles of the Upper Extremity. Fractures of the Clavicle Acromion Process Coracoid Process Humerus Ulna . Olecranon Radius . 399 399 399 399 400 400 401 Muscles and Fasciae of the Lower ExTKEMITY. Subdivision into Groups .... 402 Iliac Region. Dissection 403 Iliac Fascia 403 Psoas Magnus ..... 403 Psoas Parvus 404 Iliacus 404 Actions 405 Anterior Femoral Region. Dissection Fasciaa of the Thigh, Superficial Fascia . Deep Fascia (Fascia Lata) Saphenous Opening Iliac and Pubic Portions of Fas- cia Lata Tensor Vaginas Femoris, Sartorius Quadriceps Extensor Cruris . Rectus Femoris, Vastus Externus Vastus Internus and Crurasus Sub-cruraeus .... Actions Internal Femoral Region. Dissection Gracilis .... Pectineus Adductor Longus, Brevis, and '. Actions .... Magnus PAOT. 405 405 405 406 407 407 408 408 408 409 409 410 410 410 411 412 Gluteal Region. Dissection 412 Gluteus Maximus 412 Gluteus Medius 414- Gluteus Minimus 414 Pyriformis 414 Obturator Membrane .... 415 Obturator Internus, Gemelli . . . 415 Quadratus Femoris, Obturator Externus 410 Actions 416 Posterior Femoral Region. Dissection 417 Biceps, Semitendinosus . . . .417 Semimembranosus 417 Actions 417 Surgical Anatomy of Hamstring Tendons 418 Muscles and Fasciae of the Leg. Dissection of Front of Leg . . . 418 Fascia of the Leg 418 Muscles of the Leg 419 Anterior Tibio-fibular Region. Tibialis Anticus 419 Extensor Proprius Pollicis . . . 419 Extensor Longus Digitorum . . . 420 Peroneus Tertius 420 Actions 420 Posterior Tibio-fibular Region, Superficial Layer. Dissection 421 Gastrocnemius 421 Soleus, Tendo Achillis, Plantaris . . 422 Actions 422 Posterior Tibiofibular Region, Deep Layer. Deep Fascia of Leg .... 423 Popliteus 423 Flexor Longus Pollicis .... 423 Plexor Longus Digitorum, Tibialis Posticus 424 Actions 425 Fibular Region. Peroneus Longus Peroneus Brevis 425 425 XIV Actions Surgical Anatomy of Tendons around Ankle Muscles and Fasciae of Foot. Anterior Annular Ligament . Internal Annular Ligament External Annular Ligament . Plantar Fascia Muscles of {lie Foot, Dorsal Region. Extensor Brevis Digitorum Plantar Region. Subdivision into Groups Subdivision into Layers . CONTENTS. PAGE PAOE . 426 First Layer . 428 nd Second Layer 430 . 426 Third Layer . 431 Fourth Layer 432 426 Surgical Anatomy of the Muscles cf tl e '. 4'27 Lower Extremity. 427 Fracture of the Neck of the Femur 433 . 427 the Femur below Trochanter Minor .... 433 on. the Femur above the Con- . 428 dyles .... 433 the Patella .... 434 the Tibia . . . . 434 . 428 the Fibula, witli Displace- . 428 ment of the Tibia 435 The Arteries. General Anatomy. Subdivision into Pulmonary and Systemic 436 Distribution of — Where found . . 436 Mode of Division — Anastomoses . . 436 Arch of Aorta. Dissection ... . . 437 Ascending Part of Arch . . . 438 Transverse Part of Arcli . . . 439 Descending Part of Arch . . . 440 Peculiarities, Surgical Anatomy . . 440 Branches 441 Peculiarities of Branches . . . 441 Coronary Arteries. Right Coronary Artery .... 441 Left Coronary Artery .... 442 Arteria Innominata. Eelations 442 Peculiarities 443 Surgical Anatomy ..... 443 Gomvion Carotid Arteries. Course and Relations .... 443 Peculiarities, Surgical Anatomy . . 446 External Carotid Artery. Course and Relations .... 447 Surgical Anatomy 448 Branches 448 "• Superior Tliyroid Artery. Course and Eelations .... 448 Branches 449 Surgical Anatomy 449 Lingual Artery. Course and Eelations .... 449 Branches 449 Surgical Anatomy 450 Facial Artery. Course and Relations .... 451 Branches 451 Peculiarities 452 Surgical Anatomy '. ( .- . . . 453 Occipital Artery. Course and Eelations .... 453 Branches 453 Posterior Auricxdar Artery, Course and Eelations .... 454 Ascending Pharyngeal Artery. Course and Eelations .... 454 Temporal Artery. Course and Eelations .... 454 Branches, Surgical Anatomy . . . 455 Internal Maxillary Artery. Course, Eelations 455 Peculiarities 456 Branches from First Portion . . . 456 Second Portion . . 457 Third Portion . . .458 Surgical Anatomy of the Triangles OF THE Neck. Anterior Triangular Space. Inferior Carotid Triangle . 459 Superior Carotid Triangle . 460 Submaxillary Triangle . 460 Posterior Triangular Space. Occipital Triangle . 461 Subclavian Triangle . 461 Internal Carotid Artery. Cervical Portion .... . 463 Petrous Portion .... . 463 Cavernous Portion . . 463 Cerebral Portion . 463 Peculiarities, Surgical Anatomy . 464 Branches . 464 Branches Ophthalmic Artery. 465 Cerebral Branches of Internal Carotid. Coarse and Relations .... 467 Subclavian Arteries. 468 469 First Part of Eight Subclavian Artery First Part of Left Subclavian Artery CONTENTS. PAGE Superficial Lymphatics of Penia . . 568 of Labia, Nymplise, and Clitoris 568 Deep Lymphatics of Pelvis and Abdomen 568 Lymphatics of Bladder .... 569 of Rectum .... 569 of Uterus . . . .569 of Testicle . . . -569 of Kidney .... 569 of Liver .... 569 Lymphatic Glands of Stomach . . 569 Lymphatics of Stomach .... 570 Lymphatic Glands of Spleen . . . 570 Lymphatics of Spleen .... 570 Lympliatic System of the Intestines. Lymphatic Glands of Small Intestines (Mesenteric Glands) .... Lymphatic Glands of Large Intestine 570 570 Lymphatics of Small Intestine (Lacteals) 570 of Large Intestine . . 570 Lymphatics of Thorax. Deep Lymphatic Glands of Thorax . 570 Intercostal Glands .... 570 Internal Mammary Glands . . 570 Anterior Mediastinal Glands . .570 Posterior Mediastinal Glands . 570 Superficial Lymphatics on Front of Thorax 571 Deep Lymphatics of Thorax Intercostal Lymphatics . . . 571 Internal Mammary Lymphatics . 571 Lymphatics of Diaphragm . . . 571 Bronchial Glands 571 Lymphatics of Lung .... 571 Cardiac Lymphatics .... 571 Thymic Lymphatics .... 571 Thyroid Lymphatics .... 571 Lymphatics of (Esophagus . . . 571 Nervous System. General Anatomy. Subdivision into Cerebro-spinal Axis, Ganglia, and Nerves .... Tlie Spinal Cord and its Membranes. Dissection Membranes of the Cord Dura Mater Arachnoid Pia Mater Ligamentum Denticulatum Spinal Cord .... Fissures of Cord Columns of Cord Structures of the Cord The Brain and its Membranes. Membranes of the Brain Dura Mater. Structure Arteries, Veins, Nerves .... Glandulte Pacchioni .... Processes of the Dura Mater Falx Cerebri Tentorium Cerebelli .... Falx Cerebelli .... Arachnoid Membrane. Sub-arachnoid Space .... Cerebro-spinal Fluid .... Pia Mater. Vessels of The Beain. Subdivision into Cerebrum, Cerebellum, Pons Varolii, Medulla Oblongata Weight of Brain Medulla Oblongata. Anterior Pyramids Lateral Tract, and Olivary Body . Kestiform Bodies 2 572 572 572 573 573 574 574 575 575 575 576 577 577 577 578 578 578 578 579 579 579 580 580 581 581 Posterior Pyramids . 581 Posterior Surface of Medulla Oblongata 582 Structure of Medulla Oblongata . 582 of Anterior Pyramid . 582 of Lateral Tract . 582 of Olivary Body . 582 of Restiform Body . . 582 Septum of JfeduUa Oblongata . 582 Gray Matter of Medulla Oblongata . 583 Pons Varolii. Structure .... . 584 Transverse Fibres . . 584 Longitudinal Fibres . 584 Septum . 584 Oeeebrum. Upper Surface of Cerebrum . 585 Convolutions .... . 585 Sulci . 586 Base of the Brain . . 587 General Arrangements of the Parts com- posing the Cerebrum . . 590 Interior of the Cerebrum . 590 Corpus Callosum . 590 Lateral Ventricle . 592 Corpus Striatum . 593 Taenia Semicircularis . 593 Choroid Plexus . 593 Corpus Fimbriatum . . 593 Hippocampus . . 594 Transverse Fissure . . 595 Septum Lucidum . 595 Fifth Ventricle . 595 Fornix .... . 595 Foramen of Monro . . 596 Velum Interpositum . 596 Thalamus Opticus . . 596 Third Ventricle . 597 Commissure of Third Ven tricles 597 Gray Matter of Third Ven tricles 598 Pineal Gland . . 598 Corpora Quadrigemina . 598 Valve of Vieussens . . 599 CONTENTS. Corpora Geniculata . Structure of Cerebrum . Oeeebelldm. Its Position, Size, Weight, &o. Upper Surface . Under Surface . Lobes of the Cerebellum Structure of the Cerebellum Its Larainaj Corpus Dentatum Peduncles of Cerebellum Fourth Ventricle Lining Membrane, Choroid Plexus Gray Matter . PAGE 599 599 600 600 601 601 602 602 602 602 603 603 604 Cranial Nerves. Subdivision into Groups . Olfactory Nerve Optic Nerve .... Tracts .... Commissure Auditory Nerve Third Nerve .... Fourth Nerve .... Sixth Nerve .... Kelations of the Orbital Nerves in the Cavernous Sinus in the Sphenoidal Fissure in the Orbit Facial Nerve .... Branches of Facial Nerve Ninth or Hypoglossal Nerve . Fifth Nerve .... Casserian Ganglion . Ophthalmic Nerve . Lachrymal and Frontal Nasal .... Ophthalmic Ganglion Superior Maxillary Nerve Spheno-palatine Ganglion Inferior Maxillary Nerve Auriculo-temporal, Gustatory, and Inferior Dental Branches Otic Ganglion . Submaxillary Ganglion Eighth Pair .... (j-losso-pharyngeal . Spinal Accessory Pneumogastric (Vagus) . Spinal Nerves. Hoots of the Spinal Nerves Origin of Anterior .... of Posterior .... Ganglia of the Spinal Nerves Anterior Branches of the Spinal Nerves Posterior Branches of the Spinal Nerves Cervical Nerves. Roots of the Cervical Nerves . . . 633 Anterior Branches of the Cervical Nerves 633 Cervical Plexus. Superficial Branches of the Cervical Plexus 634 Deep Branches of the Cervical Plexus . 635 Posterior Branches of the Cervical Nerves 636 605 605 606 606 607 607 608 608 609 610 610 610 610 611 614 615 616 616 616 617 618 618 620 622 623 624 625 625 625 627 628 632 632 6:i2 633 633 633 Brachial Plexus. PASE Branches above the Clavicle. Posterior Thoracic, Suprascapular . . 639 Branches helow the Clavicle. Anterior Thoracic 639 Subscapular Nerves .... 640 Circumflex, and Musculo-cutaneous Nerves 640 Internal and Lesser Internal Cutaneous Nerves 641 . 642 . 644 645 . 646 . 646 Median Nerve . Ulnar Nerve . Musculo-spiral Nerve Radial Nerve . Posterior Interosseous Nerve Dorsal Nerves. Roots of the Dorsal Nerves . . . 647 Posterior Branches of the Dorsal Nerves 647 Intercostal Nerves .... 047 Upper Intercostal Nerves . . . 647 Intercosto-humeral Nerve . . . 648 Lower Intercostal Nerves . . . 648 Peculiar Dorsal Nerves First Dorsal Nerve . . . .648 Last Dorsal Nerve .... 648 LtrjiBAR Nerves. Roots of Lumbar Nerves . . 649 Posterior Branches of Lumbar Nerves . 649 Anterior Branches of Lumbar Nerves . 649 Lumbar Plexus. Branches of Lumbar Plexus . . . 650 Ilio-hypogastric Nerve .... 650 Ilio-ioguinal and Genito-crural Nerves . 651 External Cutaneous, and Obturator Nerves 651 653 653 654 654 654 655 Accessory Obturator Nerve Anterior Crural Nerve .... Branches of Anterior Crural . Middle Cutaneous .... Internal ('utaneons. Long Saphenous Muscular and Articular Branches . Sacral and Cocctobal Nerves. Boots of 055 Posterior Sacral Nerves . . . 656 Anterior Sacral Nerves .... 656 Coccygeal Nerve . . . 656 Sacral Plexus. Superior Gluteal Nerve .... 657 Pudic and Small Sciatic Nerves . . 057 Great Sciatic Nerve .... 659 Internal Popliteal Nerve . . . 659 Short Saphenous Nerve .... 660 Posterior Tibial Nerve .... 660 Plantar Nerves 660 External Popliteal or Peroneal Nerve . 661 Anterior Tibial Nerve .... 661 Musculo-cutaneous Nerve . . 662 Sympathetic Nerve. Subdivision of, into Parts . . . 663 Branches of the Ganglia, General De- scription of 663 CONTENTS. Six Cervical Portion op the Sympathetic. PAQE Superior Cervical Ganglion . . . 665 Middle Cervical Ganglion . . . 666 Inferior Cervical GanglioQ . . . 666 Carotid and Cavernous Plexuses. Carotid Plexus 665 Cavernous Plexus 665 Cardiac Nerves. Superior, Middle, and Inferior Cardiac Nerves 667 Deep Cardiac Plexus .... 667 Superficial Cardiac Plexus . . . 668 Anterior and Posterior Coronary Plexus 668 Thoracic Part of the Sympathetic. Great Splanchnic Nerve .... 669 Lesser Splanchnic Nerve . . . 669 PAQB Smaller Splanchnic Nerve . . . 669 Epigastric or Solar Plexus . . . 669 Semilunar Ganglia 669 Phrenic and Suprarenal Plexuses . . 669 Renal Plexus 670 Spermatic, Coaliac, and Gastric Plexuses 670 Hepatic, Splenic, and Superior Mesen- teric Plexuses 670 Aortic, and Inferior Mesenteric Plexuses 670 Lumbar Portion of Sympathetic. Pelvic Portion of Sympathetic . . 671 Hypogastric Plexus .... 671 Inferior Hypogastric or Pelvic Plexus . 671 Inferior Hasmorrhoidal Plexus . . 673 Vesical Plexus 673 Prostatic Plexus ....'. 673 Vaginal Plexus 673 Uterine Nerves 673 Organs of Sense. TONOUE. PapilliBof 674 Follicles, and Mucous Glands . . . 676 Fibrous Septum of 676 Muscular Fibres of 67G Arteries and Nerves of . . . . 677 Nose. Cartilages of. Muscles .... 678 Skin, Mucous Membrane .... 679 Arteries, Veins, and Nerves . . . 679 Nasal Fossce. Mucous Membrane of ... . 679 Peculiarities of, in Superior, Middle, and Inferior Meatuses . . 679 Arteries, Veins, and Nerves of Nasal Fossae . ^ -680 Eye. Situation, Form of 680 Sclerotic 681 Cornea 682 Choroid 683 Ciliary Processes 684 Iris 685 Membrana Pupillaris, Ciliary Ligament . 686 Ciliary Muscle 686 Retina 686 Structure of Retina Jacob's Membrane . . . -687 Granular Layer .... 687 Nervous Layer .... 687 Radiating Fibres of the Retina . 688 Arteria Centralis Retinae . . . 688 Structure of Retina, at Yellow Spot . 688 Humors op the Eye. Aqueous Humor 688 Anterior Chamber . . . 688 Posterior Chamber . . . 689 Vitreous Body 689 I Crystalline Lens and its Capsule Changes produced in the Lens by Age Suspensory Ligament of Lens . Canal of Petit Vessels of the Globe of the Eye Nerves of Eyeball .... Appendages of the Eye. Eyebrows Eyelids Structure Tarsal Cartilages Meibomian Gland Eyelashes Conjunctiva Caruncula Lachrymalis Lachrymal Appabatus. Lachrymal Gland .... Canals .... Sac .... Nasal Duct Ear. External Ear, Pinna, or Auricle Structure of Auricle .... Ligaments of the Pinna .... Muscles of the Pinna .... Arteries, Veins, and Nerves of the Pinna Auditory Canal Middle Ear, or Tympanum. Cavity of Tympanum Eustachian Tube Membrana Tympani Structure of . Ossicles of the Tympanum Ligaments of the Ossioula Muscles of the Tympanum Mucous Membrane of Tympanum Arteries, Veins, and Nerves of Tym- panum 689 690 690 690 690 691 691 691 691 691 692 692 692 693 693 694 694 694 694 695 695 695 696 697 698 700 700 700 700 701 702 702 702 XX CONTENTS. Internal Ear or Labyrinth. PAGE Vestibule . .... 703 Semicircular Canals .... 704 Cochlea Central Axis of, or Modiolus . 705 Spiral Canal of ... . 705 Lamina Spiralis of . . . 706 Scala Tympani, Scala Vestibuli . . 706 Cochlearis Muscle 706 Perilymph .... Membranous Labyrinth . Utricle and Saccule Membranous Semicircular Canals Budolymph-Otoliths Vessels of the Labyrinth . Auditory Nerve, Vestibular Nerve, Coch- lear Nerve .... PAnR 70G 706 706 707 707 708 708 VISCERA. Organs of Digestion and theii; Appendages. Subdivisions of the Alimentary Canal 709 AbDOiMEN. The Mouth ... 709 Boundaries 723 The Lips . ... 709 Apertures of . . 723 The Cheeks .... 710 Eegions . . 724 The Gums 710 Peritoneum. Teeth. Reflections traced . 725 General Characters of Permanent Teeth . Incisors . Canine, Bicuspid, Molars Temporary or iSlilk Teeth Structure of the Teeth Ivory or Dentine, Chemical Composition 711 711 711 712 713 713 713 Foramen of Winslow Lesser Omentum Great Omentum Gastro-splenio Omentum . ^Mesentery ..... Mesocaecum, Mesocolon, Mesorectum, Ap- pendices Epiploic^ 727 727 728 728 728 728 Enamel 714 Stomach. Cortical Substance .... 714 Situation Splenic end. Pyloric end . Cardiac and Pyloric Orifices . Greater and Lesser Curvatures 7'^S Development of the Teeth of the Permanent Teeth 715 715 729 729 Growth of the Teeth 716 729 Eruption of the Teeth 717 Surfaces ...... 729 Palate. Ligaments of . . . 730 Alterations in Position . 730 Hard Palate .... 718 Pylorus .... 730 Soft Palate 718 Structure of Stomach 730 Uvula, Pillars of the Soft Palate . 718 Serous and Muscular Coats 730 Mucous Membrane, Aponeurosis, anc Mucous Membrane . 731 Jluscles of Soft Palate 718 Gastric Follicles .... 731 Tonsils . . ... 718 Vessels and Nerves of Stomach 732 Arteries, Veins, and Nerves . 718 Small Intestines. Salivary Glands. Duodenum 732 Parotid Gland. Vessels and Nerves 734 Steno's Duct ..... Vessels and Nerves .... 719 . 720 Jejunum Ileum Structure of Small Intestines . 734 734 734 Suhmaxillary Oland. Serous, Muscular, and Cellular Coats 734 Mucous Membrane .... 734 Wharton's Duct .... 720 Epithelium and Valvulae Conniventes 734 Vessels and Nerves of Submaxillary T Villi — their Structure 735 Gland 720 Simple Follicles, Duodenal Glands . 735 Sublingual Oland. Solitary Glands .... Aggregate, or Peyer's, Glands 735 736 Vessels and Nerves of . . . Structure of Salivary Glands . . 720 721 Large Intestine. Gsecwm . 737 PlIARYKX. Appendix Vermiformis . . 737 Ueo-cajcal Valve . 737 Structure . 721 Colon . 738 Ascending .... . 73s OSSOPHAGUS. Transverse .... . 738 Relations, Surgical Anatomy, and Struc Descending . . 738 ture .... . 722 Sigmoid Flexure . . 738 CONTENTS. PAQE 739 739 739 740 740 740 Rectum .... Structure of Large Intestine Serous and Muscular Coats Cellular and Mucous Coats Epithelium, Simple Follicles Solitary Glands LiVEK. Size, "Weight, Position of . . . 741 Its Surfaces and Borders . . . 741 Changes of Position 741 Ligaments 742 Longitudinal 742 Lateral, Coronary . . . 742 Round Ligament .... 742 Fissures. Longitudinal ..... 743 Fissure of Ductus Venosus . . 743 Portal Fissure 743 Fissures for Gall Bladder and Vena Cava 743 Lobes. Bight 744 Left 744 Quadratus, Spigelii, Caudatus . . 744 Vessels and Nerves of Liver . . 744 Structure of Liver . . ' . . 744 Serous Coat, Fibrous Coat . . 745 Lobules 745 Hepatic Cells 746 Biliary Ducts, Portal Vein . . 746 Hepatic Artery .... 746 Hepatic Veins .... 747 Gall Bladder. Structure 747 Biliary Ducts 747 Hepatic Duct 748 Common Choledooh and Cystic Ducts 748 Structure of Biliary Ducts . . 748 Pancreas. Dissection 749 Relations 749 Duct . . .... 750 Structure, Vessels, and Nerves . . 750 Spleen. Relations 750 Size and Weight 750 Structure of Serous and Fibrous Coats . 751 Proper Substance 752 Malpighian Corpuscles .... 753 Splenic Artery, Distribution . . . 754 Capillaries of Spleen .... 754 Veins of Spleen Lymphatics and Nerves 754 754 THORAX. Boundaries of 755 Superior Opening, Base .... 755 Parts passing through Upper Opening . 755 Pbrioabdium. Structure Fibrous Layer, Serous Layer . Heart. Position, Size Subdivision into Four Cavities Circulation of Blood in Adult Aui-iculo-ventricular, and Ventricular Grooves RigM Auricle. Openings Valves Relics of Foetal Structure Musculi Pectinati Right Ventricle. Openings Tricuspid Valve Semilunar Chordae Tendineae and Columnce Carnese Left Auricle. Sinus and Appendix Openings, Musculi Pectinati Left Ventricle. Openings Mitral and Semilunar Valves Endocardium. Characters 755 756 757 757 757 757 758 759 759 759 760 760 761 761 761 762 762 763 763 Structure of Heart. Fibrous Rings 764 Muscular Structure 764 of Auricles .... 764 of Ventricles .... 764 Vessels and Nerves of Heart . . . 765 Peculiarities in Vascular System of Foetus 765 Foramen Ovale, Eustachian Valve . . 765 Ductus Arteriosus 765 Umbilical or Hypogastric Arteries . . 767 Fffital Circulation 767 Changes in Vascular System at Birth . 768 Organs of Voice and Respiration. The Larynx. Cartilages of the Larynx Thyroid Cartilage Cricoid ... Arytenoid Cartilages 769 769 770 770 Cartilages of Santorini, and Wrisberg 771 Epiglottis 771 Ligaments of the Larynx . . . 771 Ligaments connecting the Thyroid Car- tilage with the Os Hyoides . Ligaments connecting the Thyroid Car- tilage with the Cricoid Ligaments connecting the Arytenoid Car- tilages to the Cricoid . . . . Ligaments of the Epiglottis . Upper Aperture of the Larynx 772 772 772 772 772 CONTENTS. PAfJK Cavity of the Larynx .... 773 Glottis 773 False Vocal Cords 773 True Vocal Cords 774 Ventricle of Larynx, Sacculus Laryngis 774 Muscles of Larynx 774 Muscles of Vocal Cords, and Eima Glot- tidis ....... 774 Muscles of Epiglottis .... 774 Actions of Muscles of Larynx . . 776 Mucous Membrane of Larynx . . 776 Glands, Vessels, and Nerves of Larynx . 776 Trachea. Relations 778 Bronchi ....... 778 Structure of Trachea .... 778 Surgical Anatomy of Laryngo-tracheal Region 779 The Pleura. Reflections 780 Vessels and Nerves .... 782 Mediastinum. Anterior Mediastinum .... 782 Middle Mediastinum . . . 782 Posterior Mediastinum .... 782 The Lungs. Surfaces, Lobes Root of Lung ...... Weight, Color, and Properties of Sub- stance of Lung Structure of Lung ..... Serous Coat, and Subserous Areolar Tissue Parenchyma and Lobules of Lung . Bronchi, Arrangement of in Substance of Lung Structure of Smaller Bronchial Tubes . The Air-cells Pulmonary Artery ..... Pulmonary Capillaries and Veins . Bronchial Arteries and Veins Lymphatics and Nerves of Lung Tliyroid Gland. Structure ..... Vessels and Nerves Chemical Composition Thymus Gland. Structure . ... Vessels and Nerves Chemical Composition PAnn 782 784 785 785 785 785 785 786 786 786 786 787 787 787 788 788 789 The Urinary Organs. Kidneys. Structure 794 Relations 790 Vessels and Nerves . . . .794 Dimensions, Weight 790 Cortical Substance . 790 The Pelvis. Medullary Substance 791 Boundaries and Contents . . . 794 Minute Structure .... 791 Malpighian Bodies . 792 Bladder. Pelvis, Infundibula .... 792 Shape, Position, Relations . . . 795 Renal Artery, Renal Veins 792 Urachus . 796 Lymphatics and Nerves . 793 Subdivisions 796 Ureters. Ligaments Structure 790 797 Situation, Course, Relations . 793 Interior of Bladder . 797 Structure 793 Vessels and Nerves 798 Supra-renal Capsules. Male Urethra. Relations 793 Structure 798 Male Grenerative Organs. Prostate Gland 800 Structure 800 Vessels and Nerves . . . . 801 Prostatic Secretion 801 Cowper's Glands .... 801 Penis. Root 801 Glans Penis 801 Body 801 Corpora Cavernosa 802 Corpus Spongiosum 802 The Bulb . . . . 802 Structure of Corpus Spongiosum 803 Erectile Tissue .... 803 Arteries of the Penis .... 803 Lymphatics of the Penis . . . 803 Nerves of the Penis .... 804 The Testes and their Coverings. Scrotum 804 Other Coverings of the Testis . . 804 Vessels and Nerves of the Coverings of the Testis 805 Spermatic Cord. Its Composition 805 Relations of, in Inguinal Canal . . 805 Arteries of the Cord .... 805 Veins of the Cord . . . . 8i)5 Lymphatics and Nerves of the Cord . 805 Testes. Form and Situation Size and Weight Coverings Tunica Vaginalis Tunica Albuginea Mediastinum Testis Tunica Vasculosa Structure of the Testis Lobules of the Testis Tubuli Seminiferi . Arrangement in Lobuli in Mediastinum Testis CONTENTS. xxiii PAOE PAGE Arrangement in Epididymis . . 807 . 805 Vasculum Aberrans . 808 . 806 Vas Deferens, Course, Eelationa . 808 . 806 Structure .... . 808 . 806 Vesiculaj Seminales . 809 . 806 Form and Size . 809 . 807 Relations .... . 809 . 807 Structure .... . 809 . 807 Ejaculatory Ducts . . 809 . 807 The Semen .... . 809 . 807 Descent of the Testes . 810 . 807 Gubernaoulum Testis . 810 . 807 Canal of Nuck . 810 Female Organs of Generatio.n. Mons Veneris, Labia Majora . Labia Minora, Clitoris, Meatus Urinarius Hymen, Glands of Bartholine Bladder Urethra Rectum Vagina. Eelationa Structure Uterus. Situation, Form, Dimensions Fundus, Body, and Cervix Ligaments Cavity of the Uterus Structure Vessels and Nerves Its Form, Size, and Situation 811 812 812 813 813 814 814 814 815 815 815 815 816 816 817 in the Foetus . 817 at Puberty 817 during and after Menstruation 817 after Parturition 817 in Old Age 817 Appendages of the Uterus. Fallopian Tubes 817 Structure 818 Ovaries .... 818 Structure . 818 Graafian Vesicles 818 Discharge of the Ovum . 819 Corpus Luteum 819 Ligament of the Ovary . 820 Round Ligament 820 Vessels and Nerves of Appendages 820 Mammary Glands. Structure of Mamma . . . . 820 Vessels and Nerves 821 Surgical Anatomy of Inguinal Hernia. Coverings of Inguinal Hernia. Dissection 822 Superficial Fascia 822 Superficial Vessels and Nerves . . 822 Deep Layer of Superficial Fascia . . 823 Aponeurosis of External Oblique . . 823 External Abdominal Ring . . . 824 Pillars of the Ring 824 Intercolumnar Fibres .... 824 Fascia . . . .824 Poupart's Ligament .... 825 Gimbernat's Ligament .... 825 Triangular Ligament .... 825 Internal Oblique Muscle . . . .825 Cremaster . 825 Transversalis Muscle .... 826 Spermatic Canal 826 Fascia Transversalis .... 827 Internal Abdominal Ring . . .827 Subserous Areolar Tissue . . .827 Epigastric Artery Peritoneum Inguinal Hernia. Oblique Inguinal Hernia . . . . Course and Coverings of Oblique Hernia Seat of Stricture Scrotal Hernia Bubonocele Congenital Hernia Infantile Hernia Direct Inguinal Hernia. * Course and Coverings of the Hernia Seat of Stricture Incomplete Direct Hernia Comparative Frequency of Oblique and Direct Hernia ..... Diagnosis of Oblique and Direct Hernia 828 828 828 828 828 828 829 829 829 829 829 829 829 829 CONTENTS. Surgical Anatomy of Femoral Hernia. Dissection .... PAGE . 830 Superficial Fascia . Cutaneous Vessels . . 830 . 830 Internal Saphenous Vein Superficial Inguinal Glands Cutaneous Nerves . . 830 . 830 . 831 Deep Layer of Superficial Fascia Cribriform Fascia . . 831 . 831 Fascia Lata .... . 8-32 Iliac Portion . . 832 Pubic Portion . . 833 Saphenous Opening . 833 Crural Arch Gimbernat's Ligament Crural Sheath . Deep Crural Arch . Crural Canal . Femoral or Crural Ring Position of Parts around the Ring Septum Crurale Descent of Femoral Hernia Coverings of Femoral Hernia . Varieties of Femoral Hernia . Seat of Stricture PAGE 833 834 834 8:;5 83.0 83G 836 836 837 837 838 838 Surgical Anatomy of Perineum and Ischio-Rectal Eegion. Ischio-Rectal Eegion. Dissection of . Boundaries of . Superficial Fascia . E.xternal Sphincter Internal Sphincter . Ischio-rectal Fossa . Position of Parts contained in Perineimi. Boundaries, and Extent . . . . Superficial Layer of Superficial Fascia . Deep Layer of Superficial Fascia . Course taken by the Urine in Rupture of the Urethra Muscles of the Perineum (Male) . Accelerator Urinse Erector Penis Transversus Perinei . . . . Muscles of the Perineum (Female) Sphincter Vagince . . . . . Erector Clitoridis Transversus Perinei . . . . 839 839 839 840 840 840 840 841 841 841 841 841 842 843 843 844 844 844 844 Deep Perineal Fascia Anterior Layer Posterior Layer .... Parts between the two Layers Compressor Urethras Cowper's Glands .... Pudic Vessels and Nerves Artery of the Bulb Levator Ani ..... Relations, Actions . Cocoygeus, Relations, Actions Position of Viscera at Outlet of Pelvis Prostate Gland .... Parts concerned in the Operation of Lithotomy Parts Divided in the Operation Parts to be avoided in the Operation Abnormal Course of Arteries in the Perineum ..... Pelvic Fascia Obturator Fascia Recto-vesical Fascia 844 84.T 84.5 845 845 845 845 845 845 846 846 846 846 847 847 848 849 849 850 jical A] Qatomy of the Triangles of the Neck . . 459 li u Axilla . 478 ii a Bend of Elbow . 484 a (i: Scarpa's Triangle , . 518 u u Popliteal Space . 524 a a Laryngo-tracheal Eegion . 779 LIST OF ILLUSTRATIONS. [t^ Tli3 Illustrations, when copied from any other work, have the author's name affixed; when no auch acknowledgment is made, the drawing is to be considered original. Introduction. FIQ. [1. Corpuscles of Frog's Blood 2. Human Blood Globules 3. White Corpuscles 4. Blood Crystals 5. Chyle from the Lacteals [6. Areolar Tissue 7. AVhite Fibrous Tissue 8. Yellow Elastic Tissue 9. Formative Cells of Yellow Elastic Tissue 10. Formative Cells of Areolar Tissue [11. Bloodvessels of Fat 12. Adipose Tissue • 13. Human Cartilage Cells . 14. Costal Cartilage in Old Age 15. Fibro-cartilage 16. Yellow Cartilage . 17. Transverse Section of Bone 18. Longitudinal Section of Bone 19. Section of Bone after Eemoval of Earthy Portion 20. Ossification of Foetal Cartilage 21. Transverse Section of Muscle 22. Human Muscular Fibres . 23. Elementary Structure of Voluntary Muscle 24. Non-striated Muscular Fibres 2,5. Muscular Fibre Cells 26. Nerve Vesicles from Casserian Ganglion 27. Nerve Vesicles from Brain 28. Human Nerve Tubes 29. Nerve Tubes of Bel 30. Transverse Section of Spinal Cord 31. Transverse Section of Spinal Cord 32. Longitudinal Section of Spinal Cord 33. Tactile Corpuscles of Wagner . 34. Pacinian Corpuscle 35. Termination of Nerves of Voluntary Muscle, "Motorial End 36. Terminations of Nerves of Voluntary Muscle 37. Section of Small Artery and Vein 38. Capillary Vessels 39. Section of Small Artery and Vein 40. Section of Thoracic Duct 41. Sectional View of the Skin and its Appendages [42. Structure of Hair, Hair-follicles, &c 43. Pavement Epithelium 44. Columnar Epithelium 45. Spheroidal Epithelium 46. Ciliated Epithelium [47. Oonoidal Ciliated Epithelium . [48. Plans of Secreting Membranes . 49. Ovum of Sow 50. Human Ovum 51. Diagram of the Division of the Yelk 52. Diagram of the Division of the Blastodermic Membrane FKOM Wagner] Kolliher PAGE 34 34 Hurley 35 do. 35 do. 37 . Todd ^ Boiurjian] 38 Harley 38 do. 39 Kolliher 39 do. 39 . Todd §■ Boioman] . 40 Harley 41 Kolliher 42 Harley 43 do. 43 do. 44 Kolliher 47 do. 47 Harley 48 Rollett 50 Kolliher 54 do. 54 . Todd and Bowmai 54 Harley 56 Kolliher 56 . Todd and Bowman 58 Harley 58 Kolliher 58 . Todd and Bowmai 58 L. Clarhe 62 do. 63 do. 64 Kiilliker 68 . Todd and Bowmai 68 Plates" Kiihiie 70. Beale 71 Kolliher 72 do. 75 do. 75 do. 77 do. 79 do.] 83 Harley 85 Kolliher 85 Harley 85 Kolliher 86 Carpenter] 86 Sharpey] 88 M. Barry 89 Kolliher 89 do. 90 Bischoff 91 { XXV ) LIST OF ILLUSTRATIONS. 53. Diasrams of the Development of the Three Layers of the 1 Blastodermic Membrane . . . . | 54. Similar Diagrams — Antero-posterior Sections . 55. Diagram of the Membranes of the Ovum 56. Human Ovum, 12 to 13 days 57. Human Ovum, 15 days . 58. Embryo from the preceding Ovum 59. Human Ovum in the Fourth Week 60. Face of an Embryo of 25 to 28 days 61. Longittidinal Section of Head of Embryo at Four Weeks 62. Section of the Medulla of Embryo at Six Weeks 63. Diagram of Development of Lens .... 64. Heart of Embryo, Fifth Week . .... 65. Diagram of Formation of the Aortic Arches and Large Arteries 66. Diagram of Formation of the Main Systematic Veins . 67. Development of External Genital Organs FROM PAOE Benunis and Uoachard 92 do. 04 Wagner. 95 A. Tiwmson 96 do. 96 do. 9i; do. 97 Code 98 Kollikcr 90 do. 101) ItriiiaTc 101 Brier 103 Kolliker 104 do. 106 Ecker 110 Osteology. 68. A Cervical Vertebra 69. Atlas 70. Axis 71. Seventh Cervical Vertebra 72. A Dorsal Vertebra 73. Peculiar Dorsal Vertebrse 74. A Lumbar Vertebra 75 to 80. Development of a Vertebra 81. Sacrum, anterior surface 82. Vertical Section of the Sacrum 83. Sacrum, posterior surface 84 to 86. Development of Sacrum 87. Coccyx, anterior and posterior surfaces 88. Lateral View of Spine . 89. Occipital Bone, outer surface £0. Occipital Bone, inner surface 91. Occipital Bone, development of 92. Parietal Bone, external surface 93. Parietal Bone, internal surface 94. Frontal Bone, outer surface 95. Frontal Bone, inner surface 96. Frontal Bone at Birth . 97. Tcmpo.-al Bone, outer surface 98. Temporal Bone, inner surface 99. Temporal Bone, petrous portion 100. Temporal Bone, development of 101. Sphenoid Bone, superior surface 102. Sphenoid Bone, anterior surface 103. Sphenoid Bone, posterior surface 104. Plan of the Development of Sphenoid 105. Ethmoid Bone, outer surface . 100. Pcipendicular Plate of Ethmoid, enlarged 107. Ethmoid Bone, inner surface of right lateral mass, enlnriod 108. Skull at birth, showing the anterior and posterior Fontanelles 109. Lateral Fontanelles 110. Nasal Bone, outer surface 111. Nasal Bone, inner surface 112. Superior Maxillary Bone, outer surface 113. Superior Maxillary Bone, inner surface 114. Development of Superior Maxillary Bone 115. Lachrymal Bone, outer surface 116. Malar Bone, outer surface 117. Malar Bone, inner surface 118. Palate Bone, interior view, enlarged . 119. Palate Bone, posterior view, enlarged 120. Inferior Turbinated Bone, inner surface 121. Inferior Turbinated Bone, outer surface 122. Vomer ..... 123. Lower Jaw, outer surface 124. Lower Jaw, inner surface (juain Qiiain Qnavii Qnain LIST OF ILLUSTRATIONS. XXVll PT&. 125. Side-view of the Lower Jaw, at Birth 126. Side-view of the Lower Jaw, at Puberty 127. Side-view of the Lower Jaw, in the Adult 128. Side-view of tlie Lower Jaw, iu Old Age 129. Base of Skull, inner surface 130. Base of Skull, outer surface 131. Side-view of the Skull . 132. Anterior Region of Skull 133. Nasal Fossas, outer wall 134. Nasal Fossae, inner wall or septum 13,5. Hyoid Bone, anterior surface . 136. Sternum and Costal Cartilages, anterior surface 137. Sternum, posterior surface 138 to 141. Development of Sternum 142. A Rib . 143. Vertebral Extremity of a Rib . 144 to 148. Peculiar Ribs . 149. Left Clavicle, anterior surface . 1,50. Left Clavicle, inferior surface . 151. Left Scapula, anterior surface, or venter 152. Left Scapula, posterior surface, or dorsum 153. Plan of the Development of the Scapula 154. Left Humerus, anterior surface 155. Left Humerus, posterior surface 156. Plan of the Development of the Humerus 157. Bones of the Left Forearm, anterior surface 158. Bones of the Left Forearm, posterior surface 159. Plan of the Development of the Ulna . 160. Plan of the Development of the Radius 161. Bones of the Left Hand, dorsal surface 162. Bones of the Left Hand, palmar surface 163. Plan of the Development of the Hand 164. Os Innominatum, external surface 165. Os Innominatum, internal surface 166. Plan of the Development of the Os Innominatum 167. Male Pelvis (adult) 168. Female Pelvis (adult) . 169. Vertical Section of the Pelvis, with lines indicating the Axes 170. Bight Femur, anterior surface . 171. Right Femur, posterior surface . 172. Diagram showing the Structure of the Neck of the Femur 173. Plan of the Development of the Femur 174. Right Patella, anterior surface . 175. Right Patella, posterior surface 176. Tibia and Fibula, anterior surface 177. Tibia and Fibula, posterior surface 178. Plan of the Development of the Tibia 179. Plan of the Development of the Fibula 180. Bones of the Right Foot, dorsal surface 181. Bones of the Right Foot, plantar surface 182. Plan of the Development of the Foot . Articulat Quain of the Pelvis Ward ions. 183. Vertical Section of Two Vertebrae and their Ligaments, front view . 184. Occipito-atloid and Atlo-axoid Ligament, front view . 185. Occipito-atloid and Atlo-axoid Ligaments, posterior view 186. Articulation between Odoiitoid Process and Atlas 187. Ocoipito-axoid aud Atlo-axoid Ligaments .... 188. Temporo-maxillary Articulation, external view 189. Temporo-maxillary Articulation, internal view 190. Temporo-maxillary Articulation, vertical section 191. Oosto-vertebral and Costo-trans verse Articulations, anterior view 192. Costo-transverse Articulations ...... 193. Costo-sternal, Oosto-xiphoid, and Intercostal Articulations, anterior view 194. Articulations of Pelvis and Hip, anterior view 195. Articulations of Pelvis and Hip, posterior view 196. Vertical Section of the Symphysis Pubis .... 197. Sterno-clavicular Articulation ...... Arnold Arnold PAGE 173 17;! 173 173 177 180 183 186 188 189 190 191 191 193 195 196 198 200 200 202 203 206 208 210 211 213 215 216 218 220 222 227 228 230 233 235 235 236 237 239 241 242 243 243 244 246 247 249 250 252 2,58 2Ga 270 270 271 272 273 274 275 276 277 279 280 281 2K4 285 XXVUl LIST OP ILLUSTRATIONS. 198. Shoulder-joint, Scapulo-olavicular Articulations, and proper Ligaments of Scapula 199. Left Elbow-joint, showing anterior and internal Ligaments 200. Left Elbow-joint, showing posterior and external Ligaments 201. Ligaments of Wrist and Hand, anterior view . . . Arnold 202. Ligaments of Wrist and Pland, posterior view . . . do. 203. Vertical Section of Wrist, showing the Synovial Membranes 204. Articulations of the Phalanges 20.5. Left Hip-joint, laid open .... 206. Eight Knee-joint, anterior view 207. Right Knee-joint, posterior view 208. Right Knee-joiut, showing internal Ligaments 209. Head of Tibia, with Semilunar Cartilages, seen from above . 210. Ankle-joint, Tarsal and Tarso-metatarsal Articulations, internal view 211. Ankle-joint, Tarsal and Tarso-metatarsal Articulations, external view 212. Ligaments of Plantar Surface of the Foot .... 213. Synovial Membranes of the Tarsus and Metatarsus . . Arnold Muscles and Fascia, 214. Plan of Dissection of the Head, Pace, and Neck 215. ^Muscles of the Head, Face, and Neck 216. Muscles of the Right Orbit ..... 217. The relative position and attachment of the Muscles of the Left Ey 218. The Temporal Muscle ...... 219. The Pterygoid ^Muscles . . . . 220. Muscles of the Neck, and Boundaries of the Triangles 221. Muscles of the Neck, anterior view .... 222. Muscles of the Tongue, left side 223. Muscles of the Pharynx, external view 224. Muscles of the Soft Palate 225. The Prevertebral Muscles .... 226. Plan of Dissection of the Muscles of the Back 227. Muscles of the Back — first, second, and part of the third layers 228. Muscles of the Back — deep layers .... 229. Plan of Dissection of Abdomen .... 230. The External Oblique Muscle ... 231. The Internal Oblique Muscle ..... 232. The Transversalis, Rectus, and Pyramidalis . 233. Transverse Section of Abdomen in Lumbar Region . 234. The Diaphragm, under Surface .... 235. Dissection of Upper Extremity .... 236. Muscles of the Chest and Front of the Arm, superficial view 237. Muscles of the Chest and Front of the Arm, with the boundaries of 238. Muscles on the Dorsum of the Scapula and the Triceps 239. Front of the Left Forearm, superficial muscles 240. Front of the Left Forearm, deep muscles 241. Posterior surface of Forearm, superficial muscles 242. Posterior surface of Forearm, deep muscles . 243. Transverse Section through the AVrist, showing the Canals for the passage of the Tendons 244. Muscles of the Left Hand, palmar surface 245. Dorsal Interossei of Left Hand 246. Palmar Interossei of Left Hand 247. Fracture of the Middle of the Clavicle 248. Fracture of the Surgical Neck of the Humerus 249. Fracture of the Humerus above the Condyles 250. Fracture of the Olecranon 251. Fracture of Shaft of the Radius 252. Fracture of the lower end of the Radius 253. Plan of Dissection of Lower Extremity, front view 254. Muscles of the Iliac and Anterior Femoral Regions 255. Muscles of the Internal Femoral Region 256. Plan of Dissection of Lower Extremity, posterior view 257. Muscles of the Hip and Thigh . 258. Muscles of the Front of the Leg 259. Muscles of the Back of the Leg, superficial layer 260. Muscles of the Back of the Leg, deep layer . 2G1. jMuscles of the Sole of the Foot, first layer . 262. Muscles of the Sole of the Foot, second layer eball Annular Ligaments the Axilla Qaain Quain Quain Quain and the Hind do. do. do. do. do. Quain LIST OF ILLUSTRATIONS. XXIX 263. Muscles of the Sole of the Foot, third layer . 264. Dorsal Interossei . . .... 265. Plantar Interossei ...... 266. Fracture of the Neck of the Femur within the Capsular Ligament . Hind 267. Fracture of the Femur below the Trochanters . . . do. Fracture of the Femur above the Condyles .... do. Fracture of the Patella ...... do. Oblique Fracture of the Shaft of the Tibia .' '. '. '. do. Fracture of the Fibula, with displacement of the Tibia (Pott's fracture) do. 268, 269, 270, 271, Arteries. 272. The Arch of the Aorta and its branches 273. Plan of the branches of the Arch of the Aorta 274. Surgical Anatomy of the Arteries of the Necli 275. Plan of the branches of the External Carotid 276. The Arteries of the Face and Scalp . 277. The Internal Maxillary Artery and its branches 278. Plan of the branches of the Internal Maxillary Artery 279. The Internal Carotid and Vertebral Arteries . 280. The Ophthalmic Artery and its branches 281. The Arteries of the base of the Brain 282. Plan of the branches of the Eight Subclavian Artery 283. The Scapular and Circumflex Arteries 284. The Axillary Artery and its branches . 285. The Surgical Anatomy of the Brachial Artery 286. The Surgical Anatomy of the Radial and Ulnar Arteries 287. Ulnar and Radial Arteries, deep view . 288. Arteries of the Back of the Forearm and Hand 289. The Abdominal Aorta and its branches 290. The Coeliac Axis and its branches, the Liver having been raised, and the Omentum removed ........ 291. The Coeliac Axis and its branches, the Stomach having been raised, and the verse Meso-colon removed . . . 292. The Superior Mesenteric Artery and its branches 293. The Inferior Mesenteric Artery and its branches 294. Arteries of the Pelvis ..... 295. Variations in Origin and Course of Obturator Artery 296. The Internal Pudic Artery and its branches . 297. The Arteries of the Gluteal and Posterior Femoral Regions 298. Surgical Anatomy of the Femoral Artery 299. The Popliteal, Posterior Tibial, and Peroneal Arteries 300. Surgical Anatomy of the Anterior Tibial and Dorsalis Pedis Arteries 301. The Plantar Arteries, superficial view . 302. The Plantar Arteries, deep view Lesser Trans- PAOE 431 432 432 433 433 434 434 434 435 438 438 445 445 450 456 456 462 465 466 472 476 478 483 487 490 493 496 499 500 502 503 508 512 512 514 519 528 528 533 533 Veins. 303. Veins of the Head and Neck ........ 537 304. Veins of the Diploe, as displayed by the removal of the outer table 1 Brescliet 540 of the Skull ....... J 305. Vertical Section of the Skull, showing the Sinuses of the Dura Mater . . 542 306. The Sinuses of the Base of the Skull ....... 544 307. The Superficial Veins of the Upper Extremity ..... 545 308. The Venae Cavae and Azygos Veins, with their Formative Branches . . 548 309. Transverse Section of a Dorsal Vertebra, showing the Spinal Veins Breschet 550 310. Vertical Section of two Dorsal Vertebrae, showing the Spinal Veins do. 551 311 . The Internal, or Long Saphenous Vein and its Branches .... 552 312. The External, or Short Saphenous Vein ...... 553 313. The Portal Vein and its Branches ..... Quain 557 Lymphatics. 314. The Thoracic and Right Lymphatic Ducts ...... 560 315. The Superficial Lymphatics and Glands of the Head, Face, and Neck Mascagni 662 316. The Deep Lymphatics and Glands of the Neck and Thorax . . do. 563 317. The Superficial Lymphatics and Glands of the Upper Extremity . do. 564 318. The Superficial Lymphatics and Glands of the Lower Extremity . do. 566 319. The Deep Lymphatic Vessels and Glands of the Abdomen and Pelvis do. 568 LIST OF ILLUSTRATIONS. Nervous System. FIG. 320. The Spinal Cord and its IVIembranes .... 321. Transverse iSection of tlie Spinal Cord and its Membranes 322. Spinal Cord, side view. Plan of the Fissures and Columns . 323. Transverse Sections of the Cord .... 324. Medulla Oblongata and Pons Varolii, anterior surface 325. Posterior Surface of Medulla Oblongata 326. Transverse Section of Medulla Oblongata 327. The Columns of the Medulla Oblongata, and their Connection with the Cerebrum and Cerebellum 328. Upper Surface of the. Brain, the Pia Mater having been removed 329. Base of the Brain ... . . 330 Section of the Brain, made on a level with the Corpus Callosura 331. 'J'he Lateral Ventricles of the Brain .... 332. The Fornix, Velum Interpositum, and middle or descending Cornu Ventricle .... 333. The Third and Fourth Ventricles 334. Upper Surface of the Cerebellum 335. Under Surface of the Cerebellum 336. Vertical Section of the Cerebellum PAGE . . 573 Arnold 573 Quain 5i5 Arnold 576 . 581 . 581 Arnold 582 Altered from 583 Arnold 585 588 591 592 of the Lateral 594 597 600 601 Arnold 602 Cranial Nerves. 337. The Optic Nerves and Optic Tracts . . . . . . 338. Course of the Fibres in the Optic Commissure . . . Bowman 339. Nerves of the Orbit, seen from above .... After Aniohl 340. Nerves of the Orbit and Ophthalmic Ganglion, side view . . do. 341. The Course and Connections ofthe Facial Nerve in the Temporal Bone j4/'sriJ■ to the abundance of the molecular base. These molecules are almost or entirely absent in @ r^ ®' ^ymph. _ _ '^ %i^ In other respects lymph and chyle are indis- ^ ^ /^ tinguishable by microscopic examination, but in -^'Viisf. ^^ ® external appearance they are very different. Is^M^-- @ /Si @ Chyle is a milk-white fluid, which coagulates %'^:'0'i;yyWr\ spontaneously, and then on standing separates S.pt.Jj: ^i' -^ more or less completely into a clear part, the /&|^Vi;;'"'^f i- liguor chyli^ which is identical with the liquor 'Si^.^--:^;.|?;':! sanguinis, and a thinnish jelly-like clot, consist- /'°."'.\ ing of fibrin in which chyle-corpuscles and the '^'^iy-'S^^'yi^:;j^;;if!^isJ^ fatty molecules are entangled. Its analysis, as chyie from the lacteais. given by Dr. Gr. 0. Eees,^ from the chyle of a criminal examined shortly after his execution, and in whom the thoracic duct was found distended with chyle, is as follows : — Water 90.48 Albumen, with traces of fibrinous matter 7.08 Aqueous extractive .56 Alcoholic extractive or osmazome .52 Alkaline chloride, carbonate and sulphate, with traces of alkaline phos- phate and oxide of iron .44 Fatty matters 92 100.00 Lymph, as its name implies, is a watery fluid. In the lymph the molecular base is absent, and the lymph-corpuscles are very few in number, and indeed are said by Kdlliker to be absent in the smaller vessels. According to the same author, the size of the lymph-globules increases as the fluid ascends higher in the course of the circulation. In this view the lymph is at first a mere albuminous fluid, and the chyle at first a mere albumino-fatty fluid, the cells in both being produced during the passage of the fluid through the glands (lymphatic or mesenteric, as the case may be), and being further elaborated, and even new cells produced by the division of the old ones, in the course of the circulation. The presence of blood-globules in the lymph or in the chyle ' It may not be amiss to remind the student that the lacteal or chyliferous vessels only convey a portion of the nutritious matter from the food, and this only during digestion. At other times they seem to act precisely as ordinary lymphatics. 2 Phil. Trans. 1842, p. 82. 38 GENERAL ANATOMY. is regarded by most authors as accidental, i. e., produced by the manipulations of the dissector. The lymph-corpuscles, as seen in the above figure, are in all essential respects the same in the chyle, the lymph and the blood, where they have been described above as the colorless blood-corpuscles. In the chyle and lymph, however, they vary much in size. In some cases several younger cells have been seen inclosed in the original corpuscles. CELLULAE AND FIBROUS TISSUE. The Cellular or Areolar Tissue is so called because its meshes are easily dis- tended, and thus separated into cells or spaces which all open freely into each other, and are consequently easily blown up with [Fig. 6. air (Fig. 6), or permeated by fluid, when injected into any part of the tissue. Such spaces, however, do not exist in the natural condition of the body, but the whole tissue forms one unbroken mem- brane composed of a number of interlacing fibres, variously superimposed. Hence the old term "the cellular membrane" is in many parts of the body more appropriate than its more modern equivalents. The chief use of the cellular 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 inflam- matory and other effused fluids. It is consequently often denominated connective tissue, and this term is still more appropriate to the fibrous tissue which forms the bond of connection between the intimate elements of solid organs ; in which more restricted sense the term is often used in modern works. The areolar tissue consists essentially of two forms of fibrous tissue, the white and yellow, intermixed in varying proportions, together with a great quan- tity of capillary vessels, nerves and lymphatics, and in most situations it contains fat. The cellular tissue is continuous over the whole body ; so that fluid, and especially air, when injected forcibly into it — as from a wound of the lung or bowel — may be diffused into the remotest parts. The White Fibrous Tissue consists of bundles of wavy fibres, interlacing with each other, each composed of minute filaments, ov fihrillse, which appear homo- geneous, and measure from sjiln-i) Fig- ■?• to 5^Jj55 of an inch in diameter. (Fig. 7.) The larger fibres have no definite size, but are supposed to be solid masses formed by an agglutination as it were of the ultimate fibrillse. Acted upon by acetic acid, the white fibrous tissue swells up into an indis- tinct uniform mass, which gradu- ally becomes indistinguishable; and thus in the areolar tissue the yellow elastic element comes alone into view. The Yellow Elastic Fibrous Tissue is an aggregation of fibres which are con- siderably larger in size than the fibrillse of the white fibrous element, varying Portion of areolar tissue, infloted and dried, showing the general cha- racter of its larger meshes. Each lamina and filiment here repre- sented contains numerous smaller ones, matted together by the mode of preparation. (Magnified twenty diameters.)] White fibrous tissue. FIBROUS TISSUE. 39 from j^Jc^ to ^^igg of an inch in diameter (Harley). The fibres branch and anastomose freely with one another. They are homogeneous in appearance, with dark borders, and are usually seen curled up at their broken ends. They remain unaltered by acetic acid. Each of these elements of the connective tissue is developed from cells. Kolliker describes the yellow elastic fibres as developed from the stellate branching corpuscles, which may sometimes be found free in the areolar tissue, and which Virchow has denominated " connective-tissue-corpuscles" (Fig. 9) ; while the white fibrous tissue is formed from the coalescence of fusiform cells, which elongate into fibrillse as shown by Fig. 10. Fig. 8. Pig. 9. Fig. 10. Stellate formative cells of fine elastic fibres, from the ten- do Achillis of a new- born cbild. (Mag- nified 350 times.) Yellow elastic tissue. (High power.) FormatiTe cells of areo- lar tissue from sheep's embryo. (Magnified 350 times.) a, Cell without any indication of fibrils ; hf with commencing, and e, with distinct fibrils. The two tissues just described are very widely distributed in the body, espe- cially the white fibrous tissue. This latter forms nearly the whole of all the firm investing membranes, viz., the muscular fasciae, the periosteum, the invest- ments of the various glands (such as the tunica albuginea testis, the capsule of the kidney, &c.), the investing sheath of the nerves (neurilemma), and of va- rious organs, as the penis, and the eye (sheath of the corpora cavernosa and corpus spongiosum, sclerotic, and choroid). Into all these parts, however, the elastic tissue enters in greater or less proportion. The tendons and most of the ligaments are also formed almost entirely of the white fibrous tissue, but with some elastic fibres intermixed. The basis of the serous and mucous mem- branes is formed of connective tissue, disposed in a layer. The common sub- cutaneous cellular or cellulo-adipose tissue has been taken above as the typical form from which to describe connective tissue. Connective tissue also enters largely into the formation of the bloodvessels, glands, and, in fact, almost every organ in the body. The organs which are formed almost exclusively of the yellow elastic tissue are the ligamenta subflava of the vertebrae, the elastic 40 GENERAL ANATOMY. ligaments of the larynx, the longitudinal elastic fibres of the trachea, the elastic layer of the middle coat of the arteries, and in quadrupeds the ligamentum nuchse. Free cells are found in the areolar tissue, as indicated above. The chief forms are the spindle-shaped and the stellate, but numerous intermediate forms are described by recent observers ; and of late much interest has been excited by Von Eecklingshausen's discovery in the cellular tissue of cold-blooded ani- mals of " wandering cells," or cells endowed with the power of automatic mo- tion, and of changing their shape. These cells appear identical with the white globules of the blood ; and it would seem from the researches of Strieker, Cohn- heim, and others, that the walls of the capillary vessels are permeable to the latter bodies, which are thus allowed to escape into the cellular tissue, there to undergo development, normally into the natural cells and cellular tissue, or abnormally into the corpuscular forms of lymph and pus, according to circum- stances.' ADIPOSE TISSUE. The common cellular membrane contains a variable quantity of Adipose Tissue. The tissue is found also in various parts of the viscera — as the mesen- tery, the surface of the heart, &c., and fat enters largely into the formation of the marrow of the bones. There is, however, a difference which should be attended to between mere fat and adipose tissue. Adipose tissue consists of a number of vesicles formed by an extremely delicate structureless membrane, round or spherical where they have not been subject to pressure ; otherwise, variously flattened. They are supplied and held together by capillary blood- vessels (Eig. 11), and fine connective tissue, and each vesicle is filled with fat. [Fig. 11. Bloodvessels of fat. 1. Minute flnttened fat-lobule, in which the vessels only are represented. 3. Terminal artery. 4. Primitive vein. 6. Fat-cells of one border of the globule separately represented. (Magnified 100 diameters.) 2. Plan of arrangement of capillaries on exterior of fat-ceils, more highly magnified.] Fat is an unorganized substance, consisting of liquid oily matter (glycerine) in combination with certain fatty acids, stearic, margaric, and elaic. Sometimes the acids separate spontaneously before the fat is examined, and are seen under the microscope in a crystalline form, as in the figure. By boiling the tissue in ' On this subject reference may be made to Von Recklingshausen, in "Virchow's Arcliiv. Bd. xxviii., and RoUett in Strieker's Lehre von den Gcwehen, chap, ii., where the reader will find references to Strieker, Cohnheim, Kuhne, and others. CARTILAGE. 41 ether or strong alcohol, the fat may be extracted from the vesicle, which is then seen empty and shrunken. Besides the fully-formed fat-cells above described, others may occasionally be found in the course of formation, especially in cases of sudden death during robust health. They are described by Eollett as, in the first stage, small round granular cells, provided with a roundish nucleus, into the interior of which a Fiff. 12. Adipose tissue. «. Starlike appearance, from crystallization of fatty acids. (High power.) strongly refracting drop of fat is then secreted, which is at first surrounded by a ring of the granular matter, and gradually increases so as to fill the cell. As the granular matter becomes less and less, the nucleus, which can at first be easily recognized, becomes less perceptible, but according to this author can always be brought into view by appropriate reagents. Fat is said to be first detected in the human embryo about the fourteenth week. In various parts of the body pigment is found, viz., in the hairs, in the iris and choroid coat of the eye, in the lungs, in the nerve-cells, in the rete mucosum in the dark races, and in some parts of the body — such as the areola of the nipple — which are of dark color even in the fair races, except Albinoes, in whom pigment is absent. Pigment-cells are also found in the blood, according to Virchow. In many situations the color is produced simply by the presence of dark granules scattered about without any definite arrangement ; in the -choroid coat the pigment forms a regular layer of hexagonal nucleated cells filled with pigment granules ; in other parts the pigment is contained in branching cells, probably the connective-tissue-corpuscles filled with pigment granules ; and in most situations, such as the nerve-cells and the epidermis, the pigment-granules form a greater or less element in the contents of the nucleated cells of the part. In the dark races the color of the skin is due to the accumulation of pigment in the deeper layers of the epidermis — the rete mucosum. 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 air-passages, nostrils, and ear, which are to be kept permanently open. In the foetus at an early period the greater part of the skeleton is cartilaginous. As this cartilage is afterwards replaced by bone, it is called temporary^ in opposition to that which remains unossified during the whole of life, and which is called permanent. 42 GENERAL ANATOMY. Cartilage is divided according to its minute anatomy into true or hyaline cartilage, fibrous, or fibro- cartilage, and yellow, or elastic, or reticular cartilage. The various cartilages in the body are also classified according to their function and position, into articular, interarticular, costal, and membraniform. True Cartilage, which may be taken as the type of this tissue, consists of a gristly mass, of a pearly bluish color, enveloped in a fibrous membrane, the perichondrium, from the vessels of ^^' _ which it imbibes its nutritive fluids, being itself destitute of bloodvessels ; nor have nerves been traced into it. 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 an- gular shape, with nucleus and nucleo- lus, lying in groups, surrounded by a granular or almost homogeneous matrix. By boiling the cartilage for some hours, and treating it with Human eartilage cells, from the cricoid cartilage. (Magnified 350 times.) acetic acid, the cell membrane which lines the cavity in the matrix may be made visible. The matrix is often arranged in the form of a concentric ring around the cartilage-cell, forming what is described by some &,uthors as the cartilage-capsule. The articular cartilages, the temporary cartilages, and the costal cartilages, are all of the hyaline variety. They present minute differences in the size and shape of their cells, and in the arrangement of the matrix. In the articular cartilages, which show no tendency to ossification, the matrix is finely granular under a high power; the cells and nuclei are small, and are disposed parallel to the surface in the superficial part, while nearer to the bone they become vertical. Articular cartilages have a -tendency to split in a vertical direction, probably from some peculiarity in the intimate structure, or arrangement of the component parts, of the matrix. In disease this tendency to a fibrous splitting becomes very manifest. Articular cartilage in the adult is not covered by peri- chondrium, at least on its free surface, where it is exposed to friction, though an epithelial layer can be traced in the foetus over the whole surface of the car- tilage, and in the adult over a small part of its circumference, continuous with the epithelium of the synovial membrane. This is probably the remains of an investing membrane which is worn away in after-life by the action of the joint. Articular cartilage forms a thin incrustation upon the joint-surfaces of the bones, and its elasticity enables it to break the force of any concussion, whilst its smoothness affords ease and freedom of movement. It varies in thickness according to the shape of the bone on which it lies ; where this is convex, the cartilage is thickest over the convexity where the greatest pressure is received, and the reverse is the case in the concavities of the joints. Articular cartilage appears to imbibe its nutriment partly from the vessels of the neighboring synovial membrane, partly from those of the bone upon which it is implanted. Mr. Toynbee has shown that the minute vessels of the cancellous tissue, as they approach the articular lamella, dilate, and, forming arches, return into the substances of the bone. Temporary cartilage, and the process of its ossification, will be described with bone. In the costal cartilages the cells and nuclei are large, and the matrix has a tendency to fibrous striation, especially in old age. These cartilages also are very prone to ossify. In the thickest parts of the costal cartilages a few large vascular channels may be detected. This appears at first sight an exception to the statement that cartilage is a non-vascular tissue, but it is not so really, for the vessels give no branches to the cartilage-substance itself, and the channels CARTILAGE. 43 Fig. 14. may rather be looked upon as involations of the pprichondrium. The ensiform cartilage may be regarded as one of the costal cartilages, and the cartilage of the nose and of the larynx and trachea resemble them in microscopical charac- ters, except the epiglottis and cornicula laryngis, which are of the reticular variety. The hyaline cartilages, especially in adult and advanced life, are prone to calcify — ^that is to say, to have their matrix permeated by the salts of lime, without any appearance of true bone. This process of calcification occurs also, and still more frequently according to Eollett, in such cartilages as those of the trachea, which are prone afterwards to conversion into true bone. It is on the confines of true ossification that this cal- cerous change or degeneration is most liable to occur, so that it is rare to find true bone and true cartilage in juxtapo- sition at the confines of the normal ossi- fication, as for instance at the joint ends, at the ends of the ribs, in the symphysis pubis and intervertebral cartilages. Fihro-cariilage consists of a mixture of white fibrous and cartilaginous tissues in various proportions ; it is to the first of these two constituents that its flexi- Costal cartilage from a man seventy-six years of age, showing the development of fibrous struo. tare in the matrix. In several portions of the specimen, two or three generations of cells are seen inclosed in a parent cell-wall. (High power.) Fig. 15. White fibrous cartilages from the semilunar disk of the patella joint of an ox. (Magnified 100 times.) bility and toughness is chiefly owing, and to the latter its elasticity. The fibro-cartilages admit of arrangement into four groups — interarticular, connect- ing, circumferential, and stratiform. The interarticular fibro-cartilages (menisci) are flattened fibro-cartilaginous plates, of a round, oval, or sickle-like form, interposed between the articular cartilages of certain joints. They are free on both surfaces, thinner toward their centre than at their circumference, and held in position by their extremi- ties being connected to the surrounding ligaments. The synovial membrane of the joint is prolonged over them a short distance from their attached margin. They are found in the temporo-maxillary, sterno-clavicular, acromio-clavicular, wrist and knee-joints. These cartilages are usually found in those joints most exposed to violent concussions, and subject to frequent movement. Their use 44 GENERAL ANATOMY. is — to maintain tbe apposition of the opposed surfaces in their various motions-, to increase the depth of the articular surface, and give ease to the gliding movement; to moderate the effects of great pressure, and deaden the intensity of the shocks to which the parts may be submitted. Virchow describes in the semilunar cartilages of the knee a system of anastomosing tubes, formed by cells which communicate with each other, and by means of which the nutritious fluids are conveyed into the interior of the mass. The semilunar disks, accord- ing to this author, are wrongly denominated cartilages, since they yield no chondrine on boiling ; and he appears to regard tliem as a modification of ten- dinous structure, which, however, agrees with the cartilages in the important particular of being non- vascular. (See Virchow's "Cellular Pathology," by Chance, pp. 87-89.) The connecting fihro-cartilages are interposed between the bony surfaces of those joints which admit of only slight mobility, as between the bodies of the verte- brae and the pubic symphyses ; they form disks, which adhere closely to both of the opposed bones, and are composed of concentric rings of fibrous tissue, with cartilaginous laminae interposed, the former tissue predominating towards the circumference, the latter towards the centre. The circumferential fibro-cartilages consist of a rim of fibro-cartilage, which surrounds the margin of some of the articular cavities, as the cotyloid cavity of the hip, and the glenoid cavity of the shoulder; they serve to deepen the articular surface and to protect the edges of the bone. The stratiform filro-cartilages are those which form a thin layer in the osseous grooves, through which the tendons of certain muscles glide. Fiff. IG. Tellow cartilage, ear of horse. (High power. ) The Yellow or Reticular Cartilages found in the human body are the epiglot- tis, cornicula laryngis, and the cartilaginous parts of the ear (auricle and Eustachian tube). In this variety the cartilage cells lie in the meshes of a network of yellow elastic fibres, with a double outline, branching and anasto- mosing in all directions. The fibres resemble those of the yellow elastic fibrous tissue, both in appearance and in being unaffected by acetic acid, and according to Rollett their continuity with the elastic fibres of the neighboring cellular tissue admits of being demonstrated. The distinguishing feature of cartilage as to its chemical composition is that it yields on boiling a substance called chondrine, very similar to gelatine, but differing from it in not being precipitated by tannin. BONE. 45 BONE. Structure and Physical Properties of Bone. Bone is one of the hardest struc- tures of the animal body ; it possesses also a certain degree of toughness and elasticity. Its color, in a fresh state, is of a pinkish white externally, and deep red within. On examining a section of any bone, it is seen to be composed of two kinds of tissue, one of which is dense and compact in texture, like ivory ; the other consisting of slender fibres and lamellae, which join to form a reticu- lar structure ; this, from its resemblance to lattice-work, is called cancellous. The compact tissue is always placed on the exterior of a bone ; the cancellous tissue is always internal. The relative quantity of these two kinds of tissue varies in different bones, and in different parts of the same bone, as strength or lightness is requisite. Close examination of the compact tissue shows it to be extremely porous, so that the difference in structure between it and the cancel- lous tissue depends merely upon the different amount of solid matter, and the size and number of the spaces in each ; the cavities being small in the compact tissue, and the solid matter between them being abundant ; whilst in the can- cellous tissue the spaces are large, and the solid matter in smaller quantity. Bone during life is permeated by vessels, and is inclosed in a fibrous mem- brane, the periosteum, by means of which most of these vessels reach the hard tissue. If the periosteum be stripped from the surface of the living bone, small bleeding points are seen, which mark the entrance of the periosteal ves- sels ; and on section during life every part of the bone will be seen to exude blood, from the minute vessels which ramify in the Haversian canals. The interior of the bones of the limbs presents a cylindrical cavity filled with mar- row, and lined by a highly vascular areolar membrane, the medullary mem- brane or internal periosteum. The larger Haversian canals are also filled with marrow. The periosteum adheres to the surface of the bones in nearly every part, ex- cepting at their cartilaginous extremities. Where strong tendons or ligaments are attached to the bone, the periosteum is incorporated witii them. It consists of two layers closely united together; the outer one formed chiefly of con- nective tissue, containing occasionally a few fat-cells ; the inner one, of elastic fibres of the finer kind, forming dense membranous networks, which can be again separated into several layers (Kolliker). In young bones the periosteum is thick, and very vascular, and is intimately connected at either end of the bone with the epiphysial cartilage, but less closely with the shaft, from which it is separated by a layer of soft blastema, in which ossification proceeds on the ex- terior of the young bone. Later in life the periosteum is thinner, less vascular, and more closely connected with the adjacent bone, this adhesion growing stronger as age advances. The periosteum serves as a nidus for the ramifica- tion of the vessels previous to their distribution in the bone ; hence the liability of bone to exfoliation or necrosis, when, from injury, it is denuded of this membrane. The marrow differs in composition at different periods of life, and in different bones. In young bones, it is a transparent reddish fluid, of tenacious consist- ence, free from fat ; and contains numerous minute roundish cells with many nuclei. In the shafts of adult long bones, the marrow is of a yellow color, and contains, in 100 parts, 96 fat, 1 areolar tissue and vessels, and three of fluid with extractive matters ; whilst, in the flat and short bones, in the articular ends of the long bones, in the bodies of the vertebrae, in the base of the cranium, and in the sternum and ribs, it is of a red color, and contains, in 100 parts, 75 water and 25 solid matter, consisting of albumen, fibrin, extractive matter, salts, and a mere trace of fat. The red marrow is said by Kolliker to consist of a small quantity of areolar tissue and numerous medullary cells, and fat-cells with a large quantity of fluid. 46 GENERAL ANATOMY. Vessels of Bone. The bloodvessels of bone are very numerous. Those of the compact tissue are derived from a close and dense network of vessels, ramifying in the periosteum. From this membrane, vessels pass into the minute orifices in the compact tissue, running through the canals which traverse its substance. The cancellous tissue is supplied in a similar way, but by a less numerous set of larger vessels, which, perforating the outer compact tissue, are distributed to the cavities of the spongy portion of the bone. In the long bones, numerous apertures may be seen at the ends near the articular surfaces, some of which give passage to the arteries referred to ; but the most numerous and largest apertures are for the veins of the cancellous tissue which run separately from the arteries. The medullary canal in the shafts of the long bones is supplied by one large artery (or sometimes more), which enters the bone at the nutrient foramen (situated in most cases, near the centre of the shaft), and perforates obliquely the compact substance. This medullary or nutrient artery, usually accompanied by one or two veins, sends branches upwards and downwards, to supply the medullary membrane, which lines the central cavity and the adjoin- ing canals. The ramifications of this vessel anastomose with the arteries both of the cancellous and compact tissues. In most of the flat, and in many of the shart spongy bones, one or more large apertures are observed, which transmit, to the central parts of the bone, vessels corresponding to the medullary arteries and veins. The veins emerge from the long bones in three places (Kdlliker). 1. By a large vein which accompanies the nutrient artery ; 2. By numerous large and small veins at the articular extremities ; 3. By many small veins wMcb arise in the compact substance. In the flat cranial bones, the veins are large, very numerous, and run in tortuous canals in the diploic tissue, the sides of the canals being formed of a thin lamella of bone, perforated here and there for the passage of branches from the adjacent cancelli. The veins tbus inclosed and supported by the osseous structure, have exceedingly thin coats ; and when the bony structure is divided, they remain patulous, and do not contract in the canals in which they are contained. Hence the constant occurrence of purulent absorption after amputation, in those cases where the stump becomes inflamed, and the cancellous tissue is infiltrated and bathed in pus. Lymphatic vessels have been traced, by Cruikshank, into the substance of bone, but Kolliker doubts their existence. Nerves are distributed freely to the periosteum, and accompany the nutrient arteries into tbe interior of the bone. They are said, by Kolliker, to be most numerous in the articular ex- tremities of the long bones, in the vertebrae, and the larger flat bones. Minute Anatomy. The intimate structure of bone whicb in all essential par- ticulars is identical in the compact and cancellous tissue, is most easily studied in a transverse section from the compact wall of one of the long bones after maceration, such as is shown in Fig. 17. Tbe large round spaces seen ■ in the figure are the Haversian canals, and in these canals the larger vessels of the bone ramify. The fine lines leading out of (or into) these canals are called canaliculi, and the irregular dark spaces, which may be noticed to have a gene- ral circular arrangement round the Haversian canals, are called the lacunse. The canaliculi which originate in one lacuna most frequently run into a neigh- boring lacuna, or else into a neighboring Haversian canal ; some of them, how- ever, anastomose with others in their neighborhood, and a few appear to termi- nate in blind extremities or to bend backwards. The concentric rings of lacunae round each Haversian canal are called lamellse. The irregular intervals which would be left by the juxtaposition of these lamellae, are seen in the figure to be filled up by lacunse and canaliculi which communicate with the systems composing the adjacent lamellaa. The interspaces between the lacunse and canaliculi are filled with a granular homogeneous solid material, the ultimate mineral base of the bone. If a longitudinal section be taken, as in Fig. 18, the appearances are BONE. 47 identical. The lamellated or concentric arrangement is indeed lost, and the Haversian canals appear like half-tubes instead of circular spaces, and these Fig. 17. •w ■^"^Sa^K.* *^-^'^ ♦^ *< j^. >.*■ u# A transverse eectinn of the diaphysis of the hume- rus. (Magnified 350 times.) a, Haversian canals ; b, lacunse with their canalicull in the lamellse of these canals ; c, lacunae of the interstitial lamellse j d, others at the surface of the Haversian systems, with canalicull going off from one side. Section parallel to the surface from the shaft of the femur. (Mngnified 100 times.) a, Ha- versian cannls ; i, lacunae seen from the side ; c, others seen from the surface in lamellse which are cut horizontally. tubes are seen to branch and communicate (so that each separate Haversian canal runs only a short distance), but in other respects the structure has much the same appearance as in transverse sections. In sections of thin plates of bone (as in the walls of the cells which form the cancellous tissue), the Haversian canals are absent, whenever the thickness of bone is not too great to allow of its nutritious juices being absorbed from the fibrous membrane coating either side by means of the lacunse and canalicull only ; but when the thickness becomes at all considerable, Haversian systems begin to appear. Thus the spaces of the cancellous tissue (medullary spaces) have the same function there that the Haversian canals have in the more compact tissue. In the long bones, by maceration in dilute mineral acid, it may easily be shown that besides these microscopic lamellse surrounding each Haversian canal, the whole bone is composed of distinct laminse, concentrically disposed around the medullary tube. These laminse are crossed and pinned together, as it were, by the fibres of bone running obliquely through them, which were first described by Dr. Sharpey, and named by him perforating fibres. In the flat bones parallel or superimposed plates can be demonstrated similarly held together by perforating fibres, which a*e more numerous than in the long bones.' Besides the Haversian canals larger and irregularly shaped spaces are found — Havernan spaces — which are as it were a transition from the Haversian canals to the medullary spaces of the cancellous tissue. It seems as if both the medullary spaces and the Haversian spaces are formed by absorption, as we Sharpey, in Quain's Anatomy, 7th edit., p. xcvii. 48 GENERAL ANATOMY. shall try to explain in speaking of the development and growth of bone. These Haversian spaces are found chiefly in growing bones; but they occur also, though in less number, in the adult bones. They have irregular jagged out- lines, and the adjoining systems of lacunse and eanaliculi are seen to be eaten away by them. When the microscopic structure of bone was first demonstrated, it was believed that the lacuna were solid cells, and their eanaliculi solid processes from those cells. Subsequently, when it was seen that the Haversian canals are channels, which lodge the vessels of the part, and the eanaliculi and lacunas spaces by which the plasma of the blood, or the blood itself, circulates through the tissue, it was taught that the lacunse were hollow spaces filled during life with that fluid, and only lined (if lined at all) by a delicate membrane. Bat this view appears also to be delusive. Examination of the structure of the bone, when recent, has led Virchow to believe that the so-called lacunas are really filled up during life with a nucleated cell, the processes from which pass down the eanaliculi. It is by means of these cells that the fluids necessary for nutrition are brought into contact with the ultimate tissue of the bone. The animal part of a bone may be obtained by immersing the bone for a considerable time in dilute mineral acid, after which process the bone comes out exactly the same size and shape as before, but perfectly flexible — so that a long bone (one of the ribs is the usual example) can easily be tied in a knot. If now a transverse section be made, the same general arrangement of the Haversian canals, lamellae, lacunae, and eanaliculi is seen, though not so plainly as in the macerated specimen. If the individual lamellae are examined, they are found to be composed of fibres, most of which are nearly parallel ; but which interlace together, and anastomose or communicate with the fibres of the neigh- boring lamellae. The organic or animal constituents of a bone is only incompletely removed by maceration, leaving the bone for an indefinite period perfectly tough and coherent; but after being long kept in a warm dry atmosphere, or by incine- ration in a furnace, the animal part may be entirely removed, and then the earthy constituent will retain the form of the original bone, but on the slightest force it will crumble down. The animal base is often called cartilage, but differs from it in the following respects, viz., that it is softer and more flexible, and when boiled under a high pressure is almost entirely resolved into gelatine. Carti- lage does, however, form the animal basis of bone in certain parts of the skeleton. Thus, according to Tomes and De Morgan, it occurs in the petrous part of the temporal bone, and, according to Dr. Sharpey, on the articular ends of adult bones, lying underneath the natural cartilage of the joint. Chemical Analysis. The organic constituent of bone forms about one-third or 33.3 per cent.; the inorganic matter, two-thirds, or 66.7 per cent.: as is seen in the subjoined analysis by Berzelius : — Fig. 19. Section of bone after the removal of the earthy matter by the action of acids. Organic matter, Gelatine and bloodvessels . 33.30 ' Phosphate of lime .... . 51.04 Inorganic, Carbonate of lime .... . 11.30 or Fluoride of calcium . 2.00 Earthy Matter, Phosphate of magnesia . . 1.16 Soda and chloride of sodium . . 1.20 100.00 Some chemists add to this about one per cent, of fat. The relative proportions of the two constituents of bone are found to differ BONE. 49 in different hones of the skeleton, as shown by Dr. Owen Eees. Thus, the bones of the head, and the long bones of the extremities, contain more earthy matter than those of the trunk; and those of the upper extremity somewhat more than the corresponding bones of the lower extremity. The humerus contains more earthy matter than the bones of the forearm; and the femur more than the tibia and fibula. The vertebrae, ribs, and clavicle, contain nearly the same proportion of earthy matter. The metacarpal and metatarsal bones contain about the same proportion as those of the trunk. Much difference exists in the analyses given by chemists as to the proportion between the two constituents of bone at different periods of life. According to Schreger and others, there is a considerable increase in the earthy constituents of the bones with advancing years. Dr. Eees states, that this is especially marked in the long bones, and the bones of the head, which, in the foetus, do not contain the excess of earthy matter found in those of the adult. But the bones of the trunk in the foetus, according to this analyst, contain as much earthy matter as those of the adult. On the other hand, the analyses of Stark and Von Bibra show, that the proportions of animal and earthy matter are almost precisely the same at different periods of life. According to the analyses of Von Bibra, Valentin, and Dr. Eees, the compact substance contains more earthy matter than the cancellous. The comparative analysis of the same bones in both sexes shows no essential difference between them. There are facts of some practical interest, bearing upon the difference which seems to exist in the amount of the two constituents of bone at different periods of life. Thus, in the child, where the animal matter predominates, it is not uncommon to find, after an injury to the bones, that they become bent, or only partially broken, from the large amount of flexible animal matter which they contain. Again, in aged people, where the bones contain a large proportion of earthy matter, the animal matter at the same time being deficient in quantity and quality, the bones are more brittle, their elasticity is destroyed; and, hence, fracture takes place more- readily. Some of the diseases, also, to which bones are liable, mainly depend on the disproportion between the two constituents of bone. Thus, in the disease called rickets, so common in the children of scrofulous parents, the bones become bent and curved, either from the super- incumbent weight of the body, or under the action of certain muscles. This depends upon some defect of nutrition, by which bone becomes deprived of its normal proportion of earthy matter, whilst the animal matter is of unhealthy quality. In the vertebra of a rickety subject. Dr. Bostock found in 100 parts 79.75 animal and 20.25 earthy matter. Development of Bone. In the fcetal skeleton some bones, such as the long bones of the limbs, are cartilaginous, others, as the cranial bones, are mem- branous.* Hence two kinds of ossification are described — the intra-cartilaginous and the intra-memhranous ; and to these a third is sometimes added, the sub- periosteal, which is a variety of the second. In the intra-cartilaginous ossification the first step is that the cartilage cells increase rapidly in number, and arrange themselves in rows, with the long axis of the cell transverse to that of the future bone. The cells are closely packed, and in some places are even wedged together, an appearance which is supposed to be due to their cleavage horizontally. The accompanying illustration, taken i'rom EoUett's article in Strieker's "Handbuch der Lehre von den Geweben." p. 95, will save much of minute detail, and make the accompanying description intelligible. The intra-cellular matrix of the cartilage a is still semi-transparent, though ' The bones -wliich are developed entirely in membrane are the occipital, as far as it enters into the formation of the vault of the skull, the parietal and frontal bones, the squamous portion of the temporal with the tympanitic ring, the Wormian bones, the nasal, lachrymal, malar, palate, upper and lower maxillary, and vomer; also, apparently, the internal pterygoid plate and the sphenoidal turbinated bones. 4 50 GENERAL ANATOMY. somewhat granular. Lying below this cartilaginous layer (i.e., nearer to the centre of ossification), is a layer, b, consisting of large round clear cells (the Fig. 20. Lnngitndinal section tTiroiigh the ossifying portion of a lon(t bone in the humitn embryo, a. Cartilnginons region, i. Kegion of the round cle.ar cells, g. Region of the dark graoular cells. "osteoblasts" of some anatomists), with granular contents, also arranged in somewhat parallel rows, each row and each pair of superimposed cells being separated by a transparent cartilaginous matrix — the arrangement being com- pared by Eollett to a ladder. In the lower part of this region the matrix is encroached upon by calcareous matter, so that if a transverse section be made here, rings of dark granular calcareous deposit are seen inclosing the large round clear cells. As the section is taken deeper and deeper into the ossifying part, the calcified rings or areolaa are seen to inclose numerous smaller granular masses ("primitive marrow" of some authors) which have replaced the siogle clear cells, and may be formed by the proliferation of those cells. This, how- ever, is doabted by Eollett and others, who believe that these masses are fur- nished by the underlying periosteal vessels. In the longitudinal section (Fig. 20) these masses are seen at g to succeed very suddenly to the separate clear cells. If they are detached from the surface, they are found to have one or more processes. Deeper down in the ossifying or ossified portion, bloodvessels are met with, which proceed from the periosteum. The next step in the process is that the above-described areolae ("primary areolas") break into each other, so as to give rise to the " secondary areolae," or medullary spaces of H. Muller. These spaces are filled with the red or foetal marrow above described. The cells of this marrow appeared to be furnished directly from the bloodvessels which are abundantly supplied to these spaces BONE. 51 from the underlying vessels proceeding from the periosteal tissue. It is to these vessels, and to the cavities or tubes which they form for themselves as they proceed inwards, that the origin of the Haversian canals is due. The origin of the lacunae and of the bone-cells which fill them is still a matter of dispute. KoUiker, Virchow, and many other anatomists, maintain that in the intra-cartilaginous ossification they are developed directly from the cartilage-cells, the investing membrane of which ossifies and forms the bony lacuna, while its nucleus is developed into the bone-cell. Others, as Dr. Sharpey, H. Miiller, and Rollett, believe that the cartilage-cells, after becoming developed into the " osteoblasts," above described, and shown at b, Fig. 20, become dissolved, and shed their granular contents to form the bony matrix, while the lacunas and bone corpuscles are developed from the granular masses, which are seen below g in the figure, and which are furnished, according to these authors, from the vessels of the periosteum or perichondrium. If this view be correct, the intimate process is the same in all forms of ossification. Thus far, then, we have followed the steps of a process by which a solid bony mass, is produced, having vessels running into it from the periosteum, Haversian canals in which those vessels run, medullary spaces filled with foetal marrow, lacunje with their contained bone-cells, and canaliculi growing out of those lacunae. This process of ossification, however, is not the origin of the whole of the skeleton, for even in those bones in which the ossification proceeds in a great measure from a single centre, situated in the cartilaginous diaphysis, a con- siderable part of the original bone is formed by inira-memhranous ossification beneath the perichondrium or periosteum. Kolliker (following H. Miiller, and referring to an observation of Howship to the same effect, made so long ago as 1819), describes the first rudiment of a long bone as having the form of a tube, surrounding the primordial cartilage; thus showing that the intra- membranous ossification of the outer part of the bone from the periosteum even precedes the intra-cartilaginous development of its interior from the "ossifio centre." Also, a great part of the increase in girth of the bone takes place by bony deposit from the deeper laj^er of the periosteum. This process is now acknowledged to belong to the intra-membranous form of ossification. Thus even in long bones only a portion of their tissue is formed by intra-carti- laginous ossification. The shaft of the bone is at first solid, but a tube is gradually hollowed out in it by absorption around the vessels passing into it, which becomes the medullary canal; and as more and more bone is deposited from the periosteum, so more and more is removed from around the medullary membrane, until at length the bone has attained the shape and size which it is destined to retain during adult life. As the ossification of the cartilaginous diaphysis extends towards the articular ends it carries with it, as it were, a layer of cartilage, or the cartilage grows as it ossifies. During this period of growth the articular end, or epiphysis, remains for some time entirely cartilaginous, then a bony centre appears in it, and it commences the same process of intra-cartilaginous ossification, but this process never extends to any very great distance. The epiphyses remain separated from the shaft by a narrow cartilaginous layer for a definite time. This layer ultimately ossifies, the distinction between shaft and epiphysis is obliterated, and the bone has assumed its completed form and shape. The same remarks also apply to the processes of bone which are sepa- rately ossified, and called apophyses. The intra-cartilaginous ossification, and the growth by means of epiphyses, are usually described from the long bones; but almost all the bones of the body are primarily laid down in cartilage (see note, p. 49); and a great many of the flat and short bones grow by means of epiphyses, as will be seen in the de- tailed description of each, given in the body of the work. The medullary spaces which characterize the cancellous tissue are produced 52 GENERAL ANATOMY. by the absorption of the original foetal bone in the same way as the medullary tube is formed, and the same is the case with the Haversian spaces above re- i'erred to as a sort of intermediate step between the Haversian canals and the medullary spaces. Thus the distinction between the cancellous and compact tissue appears to depend essentially upon the extent to which this process of absorption has been carried, and we may perhaps remind the reader that in morbid states of the bone inflammatory absorption effects exactly the same change, and converts portions of bone naturally compact, into cancellous tissue. The intra- membranous ossification is that by which the bones of the vertex of the skull are entirely formed. In the bones which are so developed no cartilaginous mould precedes the appearance of the bony tissue. The process, though pointed out originally by Dr. Nesbitt, in the year 1736, was first accu- rately described by Dr. Sharpey; .and it does not appear that subsequent ob- servers have been able to add anything essential to his description. This is, substantially, as follows: In the membrane which occupies the place of the future bone a little network of bony spiculas is first noticed, radiating from the point of ossification. When these rays of growing bone are examined by the microscope, there is found a network of fine clear fibres (osteogenic fibres), which become dark and granular from calcification, and as they calcify they are found to inclose in their interior large granular corpuscles (the so-called "osteoblasts" described above in the account of the intra-cartilaginous ossifi- cation). These corpuscles at first lie upon the osteogenic fibres, so that the corpuscles must be removed by brushing the specimen with a hair pencil in order to render the fibres clear; but they gradually sink into areolae developed among the fibres. The areolae appear to be the rudiments of the lacunse, the passages between the fibres form the canaliculi, and the osteoblasts are the rudiments of the bone cells. As the tissue increases in thickness vessels shoot into it, grooving for themselves spaces or channels, which become the Haver- sian canals. The subperiosteal is in all essential respects identical with the intra-membran- ous process of ossification. The Period of Ossification is different in different bones. The order of succes- sion may be thus arranged (Kolliker): — In the second month, first, in the clavicle, and lower jaw (fifth to seventh week); then, in the vertebrae, humerus, femur, the ribs, and the cartilaginous portion of the occipital bone. At the end of the second, and commencement of the third month, the frontal bone, the scapula, the bones of the forearm and leg, and upper jaw, make their appearance. In the third month, the remaining cranial bones, with few exceptions, the metatarsus, the metacarpus, and the phalanges, begin to ossify. In the fourth month, the iliac bones, and the ossicula auditus. In the fourth or fifth month, the ethmoid, sternum, os pubis, and ischium. . From the sixth to the seventh month, the calcaueum, and astragalus. In the eighth month, the hyoid bone. At birth, the epiphyses of all the cylindrical bones, with the exception of the lower epiphysis of the femur, and occasionally the upper epiphysis of the tibia; all the bones of the carpus; the five smaller ones of the tarsus; the patella; the sesamoid bones; and the coccyx,' are still ossified. From the time of birth to the fourth year, osseous nuclei make their appear- ance also in these parts. At twelve years, in the pisiform bone. The number of ossific centres is different in different bones. In most of the short bones, ossification commences by a single point in the centre, and pro- I On the development of the coccyx, vide Coccyx. MUSCULAR TISSUE. 63 ceeds towards the circumference. In the long bones, there is a central point of ossification for the shaft or diaphysis ; and one or more for each extremity, the epiphyses. That for the shaft is the first to appear; those for the extremi- ties appear later. The union of the epiphyses with the shaft takes place in the inverse order to that in which their ossification began; for, although ossification commences latest in those epiphyses towards which the nutrient artery in the several bones is directed, they become joined to the diaphyses sooner than the epiphyses at the opposite extremity, with the exception of the fibula, the lower end of which commences to ossify at an earlier period than the upper end, but, nevertheless, is joined to the shaft earliest. The order in which the epiphyses become united to the shaft, appears to be regulated by the direction of the nutrient artery of the bone. Thus the arteries of the bones of the arm and forearm are directed towards the elbow, and the epiphyses of the bones forming this joint become united to the shaft before those at the opposite extremity. In the lower extremities, on the contrary, the nutrient arteries pass in a direction from the knee; that is, upwards in the femur, downwards 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, become first united to the shaft. Where there is only one epiphysis, the medullary artery is directed towards that end of the bone where there is no additional centre: as, towards the acro- mial end in the clavicle; towards the distal end of the metacarpal bone of the thumb and great toe; and towards the proximal end of the other metacarpal and metatarsal bones. Besides these epiphyses for the articular ends, there are others (more com- monly called apophyses) for projecting parts, or processes, which are formed separately from the bulk of the bone. For an account of these the reader must be referred to the descriptions of the individual bones in the sequel. A knowledge of the exact periods when the epiphyses become joined to the shaft, is often of great importance in medico-legal inquiries. It also aids the surgeon in the diagnosis of many of the injuries to which the joints are liable; for it not unfrequently happens, that on the application of severe force to a joint, the epiphyses become separated from the shaft, and such injuries may be mistaken for fracture or dislocation. MUSGULAE TISSUE. The Muscles are formed of bundles of reddish fibres, endowed with the pro- perty of contractilit3'. Two kinds of muscular tissue are found in the animal body, viz., that of voluntary or animal life, and that of involuntary or organic life. The Muscles of Animal Life (striped muscles) are capable of being put in action and controlled by the will. They are composed of bundles of fibres inclosed in a delicate web of areolar tissue, called in the figure the "perimy- sium." Each bundle consists of numerous smaller bundles, inclosed in a similar fibro-areolar covering, and these again of primitive fasciculi. The fibres are of no great length — not extending, it is said, further than an inch and a half. They end either by blending with the tendon or aponeurosis, or else by becoming drawn out into a tapering extremity which is connected to the neighboring fibre by means of the sarcolemma. The precise mode in which the muscular fibre joins the tendon has been variously described by different observers. It may, perhaps, be sufficient here to say that the sarco- lemma, or membranous investment of the muscular fibre, appears to become blended with the tissue of the tendon, and that the muscular fibre appears to be prolonged more or less into the tendon, so that the latter forms a kind of sheath around the fibre for a longer or shorter distance. When muscular 54 GENERAL ANATOMY. fibres are attached to the skin or mucous membranes, the fibres are described by Salter as becoming continuous with those of the areolar tissue. The primitive fasciculi consist of a number of filaments, inclosed in a tubular sheath of transparent, elastic, and apparently homo- geneous membrane, named by Bowman the "sar- colemma." The primitive fasciculi are cylindriform or prismatic. Their breadth varies in man from ,J„ to 5J5 of an inch, the average of the majority ■Veing about ^|\^; their length is not always in proportion to the length of the muscle, but depends on the arrangement of the tendons. This form of muscular fibre is especially characterized by being apparently marked with very fine, dark lines or strise, which pass transversely round the fibre, in curved or wavy parallel directions, from tttt^t to T^nuti of ail inch apart. Other strise pass longitu- dinally over the fibres, indicating the direction of the primitive fibrils of which the primitive fasci- culus is composed. They are less distinct than the former. The primitive fihrils constitute the proper con- tractile tissue of the muscle. Each fibril is cylin- driform, somewhat flattened, about ygj;!^ an inch in thickness, and marked by transverse stride placed at the same distance from each other as the strise on the surface of the fasciculus. Each fibril apparently consists of a single row of minute particles (named " sarcous elements" by Transverse section from the ster- no-raastoid in man (50 times mag- nified), ii. External perimysium. b. Internal perimysium, t. Primi- tive and secondary fasciculi. Fig. 22. Fig. 23. Two human muscular fibres (magnified 350 times) . In the one, the bundle of fibrillae (4) is torn, and the parco- lemma (a) is seen as an empty tube. Fragments of striped elementary fibres, showing a cleavage in op- posite directions (magnified 300 diameters). A. Longitudinal cleavage. The longitudinal and transverse lines are both seen. Some longitudinal lines are darker and wider than the rest, and are not continuous from end to end. This results from partial separation of the fibrillae. c. Fibrillse separated from one another by violence at the broken end of the fibre, and marked by transverse lines equal in width to those on the fibre. «/ c" represent two appearances commonly presented by the separated single fibrillse (more highly magnified). At r' the borders and transverse lines are all perfectly rectilinear, and the in- cluded spaces perfectly rectangular. At c" the borders are scalloped, and the spaces bead-like. When most distinct and definite, the fibrilla presents the former of these appearances. B. T»-ansverse cleavage. The longitudinal lines are scarcely visible, a. Incomplete fracture following the opposite surfaces of a disk, which stretches across the in- terval, and retains the two fragments in connection. The edge and surfaces of this disk are seen to be minutely granular, the granules corresponding in size to the thickness of the disk, and to the distance between the faint longitudinal lines, b. Another disk nearly detached. (/. Detached disk, more highly magnified, showing the sarcous elements. MUSCULAR TISSUE. 55 Bowman), connected together like a string of beads. Closer examination, however, shows that the elementary particles are little masses of pellucid substance, having a rectangular outline, and appearing dark in the centre. These appeara^nces would favor the suggestion that the elementary particles of which the fibrils are composed are possibly nucleated cells, cohering in a linear series, the transverse marks between them corresponding to their line of junction. Kdlliker, however, considers " the sarcous elements as artificial products, occasioned by the breaking up of the fibril at the parts where they are thinner." This form of muscular fibre composes the whole of the voluntary muscles, all the muscles of the ear, those of the larynx, pharynx, tongue, the upper half of the oesophagus, the heart, and the walls of the large veins at the point where they open into it. The fibres of the heart, however, differ in several particulars from those of other striped muscles. They are smaller by about one -third, and their trans- verse striae are by no means so distinct. Fat-cells are also often found in them to a large extent, even apart from any obvious disease of the organ. They break up much more readily into their smallest elements. There is also much less (if any) connective tissue separating the bundles of fibres ; and Kdlliker has described and figured the ultimate fibres as anastomosing with each other. The Unstriped Muscle, or Muscle of Inorganic Life, is found in the walls of the hollow viscera, viz., the lower half of the oesophagus and the whole of the remainder of the gastro-intestinal tube ; in the trachea and bronchi ; in the gall-bladder and ductus communis choledochus ; in the pelvis and calices of the kidney, the ureters, bladder, and urethra; in the female sexual organs, viz., the Fallopian tubes, the uterus (enormously developed in pregnancy), the vagina, the broad ligaments, and the erectile tissue of the clitoris ; in the male sexual organs, viz., the dartos scroti, the vas deferens, and epididymis, the vesiculae seminales, the prostate gland and the corpora cavernosa;' in the ducts of certain glands, as in Wharton's duct; in the capsule and trabeculse of the spleen ; in the arteries, veins, and lymphatics ; in the iris ; and in the skin. The fibres of inorganic muscle form flattened bands, interlacing in various directions, and which when viewed without reagents appear nearly homo- geneous, though if the organ from which the fibres are taken has been mace- rated previously for some time in dilute acid, the nuclei can be perceived. Even in fresh fibres the nuclei are occasionally visible. In many situations these fibres, by prolonged immersion in chromic or nitric acid, can be resolved into the elementary contractile fibre-cells, of which Kdlliker has shown that they really consist; and in some parts, as in the arteries and in the skin, such fibre-cells are found single. They are elongated, their length about ten to fifteen times their breadth (.02'" to 0.4'" in length, .002'" to .003'" in breadth, according to Kdlliker), consisting of a spindle- shaped, homogeneous-looking, fibre-cell, in which a rod shaped nucleus is faintly visible. Acetic acid dissolves out the granular contents of the cell, and brings the nucleus clearly into view. The unstriped muscle, as a rule, is not under the influence of the will, nor is the contraction rapid and involving the whole muscle, as is the case with the muscles of animal life. The membranes which are composed of the un- striped muscle slowly contract in a part of their extent, generally under the influence of 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 contraction. This peculiarity of action is most strongly marked in the intestines, constituting their vermicular motion. In chemical composition, the muscular fibres of both forms consist mainly of ' Kolliker describes muscular fibres also in the tunica vaginalis testis. 56 GENERAL ANATOMY. a substance called syntonin, nearly identical with the fibrine of the blood ; but, unlike the latter, not dissolved by nitrate of potash. Muscle after death ex- hibits an acid reaction ; but this appears to be due to post-mortem changes. Fiff. 25. Non-striated elementary fibres from the human colon, a. Treated with acetic acid, showing the corpuscles, b. Fragment of a detached fibre, not touched with acid. Muscular fibre cells from human arteries. 1. From the popliteal artery : a, without ; d, with acetic ncid. 2. From a branch of the anterior tibial : a, nuclei of the fibres. (Magnified 350 times.) The capillaries of muscle are very abundant, and form a series of rectangular areolae, the branches, which run longitudinally between the muscular fibres, being united at short intervals by transverse anastomosing branches. Nerves are profusely distributed to the muscular tissue, more especially to the voluntary muscles. The mode of their termination will be described on a subsequent page. The distribution and the mode of origin of the lymphatic vessels of muscle has not yet been ascertained. The muscles during life, and for some time after death, respond to the appro- priate stimulus by contracting in the manner peculiar to the class to which they belong. Thus, for some time after a limb has been amputated, its muscles can be set in motion by scratching, pinching, or galvanizing them ; and even after the irritability of the muscular tissue has been exhausted by the prolonged suspension of the circulation, it can be at first temporarily restored by injecting fresh arterial blood through it (Brown-Sdquard). The time at which muscular irritability ceases after death depends on the vitality of the- subject ; thus it ceases in birds, whose circulation and vital heat are of a very high degree, sooner than in man and quadrupeds ; in these sooner than in fishes, &c. Dr. Sharpey says that it lasts long in hybernating animals killed during their winter sleep. It is also affected by the mode of dying, being e.'vtinguished in- stantaneously (as is asserted) in some cases of lightning-stroke, and much di- minished by certain gaseous poisons, particularly sulphuretted hydrogen. As the muscles die they become stiff, and it is to this cause that the rigidity so characteristic of recent death (" rigor mortis") is due. The ultimate cause of the phenomenon is not well understood, beyond the obvious fact that it must be due to the change from partial fluidity to a solid condition of the contents of the sarcolemma. The periods of its occurrence and of its disappearance are very variable, and the causes of those variations are of extreme interest and importance, especially in medico-legal inquiries, but the subject is too compli- NERVOUS TISSUE. 67 cated to be adequately treated bere. All that need be said in this place is that, as might be expected, the rigor is stronger the more powerful and more healthy the muscles are, and, consequently, is both more powerful and more lasting in cases of sudden or violent death. It also sets in later in such cases, while in emaciated and exhausted subjects it is more rapid and transient : as is also the case, according to Hunter, in animals which have been hunted to death. In some instances of violent death in persons of robust frame, the rigor mortis has not entirely disappeared till the end of the first week after death. In rare cases, as in some instances of death from lightning, the muscles are found rigid immediately, and in other cases rigor commences in a few minutes, but usually not till six or seven hours after death. The cessation of rigidity in the muscles must be regarded as the commencement of putrefactive changes. NEEVOUS TISSUE. The Nervous Tissue is composed chiefly of two different structures, the gray or vesicular, and the white or fibrous. It is in the former, as is generally sup- posed, that nervous impressions and impulses originate, and by the latter that they are conducted. Hence the gray matter forms the essential constituent of all the ganglionic centres, both those separated in the ganglia, and those aggre- gated in the cerebro-spinal axis ; while the white matter is found in all the commissural portions of the nerve centres, and in all the cerebro-spinal nerves. Besides these two principal kinds of nervous matter, there is found a third structure — chiefly in the sympathetic system — called the gelatinous nerve-tissue. The nervous substance is again divided into two different systems. The first is connected directly with the great central mass inclosed in the skull and spine. This is called the cerebrospinal system, and is divided into the brain (in- cluding the medulla oblongata), the spinal cord, the cranial nerves, the spinal nerves, and the ganglia connected with both those classes of nerves. The second, called the sympathetic system, is not directly connected with the brain or spinal cord, though it is so indirectly by means of its numerous communi- cations with the cranial and spinal nerves. It consists of a double chain of ganglia, with the branches which go to and come from them. A third method of division of the nervous system is based upon \\ie functions which it performs. On this principle it is divided into the nervous system of animal life and the nervous system of organic life — the former subserving the higher functions of volition, sensation, &c., the latter those of growth and nu- trition. It is clear that the former qualities reside mainly in the cerebro-spinal system, while the intimate connection between the sympathetic nerve and the great viscera renders it highly probable that the sympathetic system has mainly to do with the organic functions. Consequently the cerebro-spinal system was designated the system of animal life, and the sympathetic the system of organic life. But the distinction, though true to a certain extent, is by no means com- plete, as the student may easily see by consulting the works of modern phy- siologists. The gray or vesicular nervous substance is distinguished by its dark reddish- gray color and soft consistence. It is found in the brain, spinal cord, and various ganglia, intermingled with the fibrous nervous substance, but is never found in the nerves. It is composed, as its name implies, of vesicles, or cor- puscles, commonly called nerve-corpuscles or ganglion-corpuscles, containing nuclei and nucleoli; the vesicles being imbedded either in a fine granular sub- stance, as in the brain, or in a capsule of nucleated cells, as in the ganglia. Each vesicle consists of an exceedingly delicate membranous wall, inclosing a finely granular material, part of which is occasionally of a coarser kind, and of a reddish or yellowish-brown color. The nucleus is vesicular, much smaller than the vesicle, and adherent to some part of its interior. The nucleolus, which is inclosed within the nucleus, is vesicular in form, of minute size, and 58 GENERAL ANATOMY. peculiarly clear and brilliant. The nerve-corpuscles vary in shape and size; some are small, spherical, or ovoidal, with an uninterrupted outline. These Fig. 26. Pig. 27. Nerve-vesicles from the Caeserian gan- glion of the human subject, a. A globu- lar one with defined border ; ^, its nucleus ; f, its nucleolus. ^.Caudate reside ; e. Elongated vesicle, with two groups of pig- ment particles,-/. Vesicle surrounded by its sheath or capsule of nucleated parti- cles ; g. The same, the sheath only being in focus. (Magnified 300 diameters.) Nerve-vesicles from the inner parts of the gray matter of the convolutions of the human brain (magnified .350 times). Nerve cells: «, larger; ^, smaller, c. Nerve fibre, with axis-cylinder. forms are most numerous in the ganglia of the sympathetic. Others, called caudate or stellate nerve-corpuscles, are characterized by their larger size, and Fiff. 28. Fig. 29. Human nerve-tubes (magnified 350 times). Three of them are fine, one of which is varicose, one of middling thickness, and with a simple contour; and three thick, two of which are double contoured, and one with grumous con- tents. Nerve-tube of the common eel in water. The delicate line on its exterior indicates the tubu- lar membrane. The dark double-edged inner one is the white substance of Schwann, slightly wrinkled, b. The same in ether. Several oil globules have coalesced in the interior, and others have accumulated around the exterior of the tube. The white substance has in part disappeared. (Magnified 300 diameters.) from having one or more tail-like processes issuing from them, which occasion- ally divide and subdivide into numerous branches. These processes are very NERVOUS TISSUE. 59 delicate, apparently tubular, and contain a similar granular material to that found within the corpuscle. Some of the processes terminate in fine transparent fibres, which become lost among the other elements of the nervous tissue ; others may be traced until, after losing their granular appearance, they become continuous with an ordinary nerve-fibre. The white, otherwise called tubular or fibrous nervous substance^ is found con- stituting a great part of the brain and spinal cord, almost the whole of the cerebro-spinal nerves, and a great part of the sympathetic. The tubes, when perfectly fresh, appear to be homogeneous, but they soon separate into two parts, the white substance of Schwann and the axis-cylinder of Purkinje, the whole being inclosed in a structureless membrane — the tubular membrane} The white substance is regarded as being a fatty matter in a fluid state, which isolates and protects the essential part of the nerve — the axis-cylin- der. The partial coagulation of this white substance which follows on cooling gives the nerve-tube, when examined after death, a double contour — the darker part seen on the outside of the axis-cylinder being the white substance of Schwann. In consequence of the extreme delicacy of the tubular membrane, even slight pressure will often give nerve-tubes a varicose outline, and drops of oil, from the transudation of the fatty matter, often form outside the tubular membrane. This is, of course, promoted by the action of ether. The axis-cylinder constitutes about one-half or one-third of the nerve tube, the white substance being greater in proportion in the nerves than in the cen- tral organs. The axis-cylinder is perfectly transparent, and is therefore indis- tinguishable in a perfectly fresh and natural state of the nerve. It is described by Kdlliker as being distinguished from the white substance by the fact that though soft and flexible it is not fluid and viscid, but firm and elastic, some- what like coagulated albumen, with which it appears for the most part also to agree in its chemical characters. In appearance it is pale and homogeneous, or more rarely finely granular or striated. Besides these nerve-fibres which consist of two distinct parts, others are found in which only the axis-cylinder can be recognized, surrounded by its medullary membrane, whilst there are again mere primitive fibrils found in various parts, which are perfectly destitute of any visible structure, and only recognized as nerves by their connection with ganglionic cells, or with obvious nerve-tubes.^ They display a great tendency to become varicose on manipula- tion. The finely-striated appearance of those nerves, which consist only of the axis-cylinder and its membranous investment, renders it probable that these also are formed of an aggregation of the primitive fibrillae. Thus three different kinds of white nerve-fibres are described by recent authorities — viz., 1. Those which consist of the axis-cylinder, ensheathed in the white substance of Schwann, the whole being invested by the tubular mem- brane; 2. Those which consist of the axis-cylinder and medullary membrane only; and 3. The primitive fibrils, of which it is believed that the axis-cylinder of the more composite nerves is made up.^ Most of the nerves of the sympathetic system, and some of the cerebro-spinal (see especially the description of the olfactory nerve), consist of a fourth de- scription of nervous fibres,^ which are called the gray or gelatinous nerve-fibres ' Dr. Beale describes and figures cases in which several fibres, some with, others without the white substance, are inclosed in a common tubular membrane. See Phil. Trans., 1862. 2 Schultze (Strieker's Handbuch, fi^. 17, p. 109) represents these primitive fibrils, both in their connection with ganglion-cells and with large nerves. See also below. Fig. 36. ' Schultze believes that the primitive fibrils are the essential elements of all nerves ; thus, according to him, the essential difference between the gelatinous and the ordinary nerve fibrils consists in the absence from the former of the white substance (medulla) of Schwann, while the tubular membrane is present. The small nerve-fibres, on the other hand, described as primitive fibrils or naked axis-cylinders, are either destitute of any investment, or surrounded merely by a structureless basement membrane. * The real nature of these fibres has been doubted by several authors. It seems better, how- ever, and more consonant with the prevalent opinion, to describe them as truly nervous. 60 GENERAL ANATOMY. (fibres of Eemak). These consist of a bundle of finely granular fibrillse, in- closed in a sheath. Nuclei niay be detected at intervals in each fibre, which Schultze believes to be situated in the sheath of the nerve. In external ap- pearance the gelatinous nerves are semi-transparent, and gray or yellowish- gray. The individual fibres vary in size — most of them being of smaller size than in the cerebro-spinal nerves, so that the average size of the latter is given ^t 5T)V"i!" to 3B0!i of an inch, and of the former at only half that size; but on the one hand the smallest fibrils of the cerebro-spinal system are, as we have seen, of hardly appreciable thickness; while on the other some of the gelatinous fibres (especially those in the olfactory bulb), are said to be three or four times as thick as those of the cerebro-spinal nerves. Chemical composition. The following analysis, by Lassaigne, represents the relative proportion of the different constituents composing the gray and white matter of the brain. Gray. White. Water 85.2 73.0 Albuminous matter 7.5 9.9 Colorless tat 1.0 13.9 Eed fat 3.7 0.9 Osmazome and lactates 1.4 1.0 Phosphates 1.2 1.3 100.0 100.0 It appears from this analysis, that the cerebral substance consists of albumen dissolved in water, combined with fatty matters and salts. The fatty matters, according to Fremy, consist of cerebric acid, which is most abundant, choleste- rin, oleophosphoric acid, and olein, margarin, and traces of their acids. The same analyst states, that the fat contained in the brain is confined almost ex- clusively to the white substance, and that its color becomes lost when the fatty matters are removed. According to Vauquelin, the cord contains a larger pro- portion of fat than the brain; and, according to L'H^ritier, the nerves contain more albumen and more soft fat than the brain. With regard to the constitution of the different portions of the nervous sys- tem, the cerebro-spinal axis is composed of the two above-described kinds of nervous structure, intermingled in various proportions, and having in the brain a very intricate arrangement, which can only be fully understood by a careful study of the details of its descriptive anatomy in the sequel. The gray or vesicular nervous matter is found partly on the surface of the brain, forming the convolutions of the cerebrum, which are in the most direct relation to the mental faculties, and the laminae of the cerebellum, the functions of which are still a matter of dispute. Again, gray matter is found in the interior of the brain, collected into large and distinct masses or ganglionic bodies, such as the corpus striatum, optic thalamus, and corpora quadrigemina; the functions of which bodies, so far as they have been ascertained, have been found to be con- nected with some of the main organic endowments of the body, such as volun- tary motion, sensation, sight. Finally, gray matter is found intermingled inti- mately with the white, and without definite arrangement, as in the corpora dentata of the medulla and cerebellum, or the gray matter in the pons and the floor of the fourth ventricle. Such scattered masses of gray matter are, in many instances at any rate, connected to all appearance with the origin of par- ticular nerves. In other situations their use is as yet unknown. The proper nervous matter, both in the brain and spinal cord, is traversed and supported by a network of fine connective tissue. This has been termed by Virchow the neuroglia, and is supposed to be the source of one of the forms of tumor recently described by that author under the name of glioma. The white matter of the brain is divisible into four distinct classes of fibres. There are, in the first place, the nerves which arise in the gray matter, and pass out through the cranial foramina. Next the fibres which connect the brain BRAIN. 61 with the spinal cord; that is to say, those which are usually traced upwards from the columns of the spinal cord, through the medulla oblongata into the cerebrum, chiefly by means of the anterior pyramids, fasciculi teretes, and restiform bodies, passing through the pons and crura cerebri, to expand into the corpora striata, optic thalami and convolutions (corona radiata), and by means of the restiform bodies, into the cerebellum. The other two classes of white fibres in the brain are commissural ; some of the commissures serving to connect different parts of the same hemisphere together (as the fornix, the processus e cerebello ad testes, &c.), or even different parts of the same section or organ, as the'arciform fibres of the medulla. Most of these commissures are longitudinal ; while others — as the corpus callosum and the transverse fibres of the pons Yarolii — are transverse, serving to con- nect opposite hemispheres together, and thus probably securing the single action of a double organ. The following is Mr. Lockhart Clarke's account of the intimate structure of the cerebral convolutions : — " Most of the convolutions, when properly examined, may be seen to consist of at least seven distinct and concentric layers of nervous substance, which are alternately paler and darker from the circumference to the centre. The lami- nated structure is most strongly marked at the extremity of the posterior lobe. In this situation all the nerve-cells are small, but differ considerably in shape, and are much more abundant in some layers than in others. In the superficial layer, which is pale, they are round, oval, fusiform, and angular, but not nume- rous. The second and darker layer is densely crowded with cells of a similar kind, in company with others that are pyriform and pyramidal, and lie with their tapering ends either towards the surface or parallel with it, in connection with fibres which run in corresponding directions. The broader ends of the pyramidal cells give off two, three, four, or more processes, which run partly through the white axis of the convolution, and in part horizontally along the plane of the layer, to be continuous like those at the opposite ends of the cells, with nerve-fibres running in different directions. The third layer is of a much paler color. It is crossed, however, at right angles by narrow and elongated groups of small cells and nuclei of the same general appearance as those of the preceding layer. These groups are separated from each other by bundles of fibres, radiating towards the surface from the central white axis of the convolu- tions, and together with them form a beautiful fanlike structure. The/owrt/j layer also contains elongated groups of small cells and nuclei, radiating at right angles to its plane ; but the groups are broader, more regular, and, together with the bundles of fibres between them, present a more distinctly fanlike structure. The fifth layer is again paler and somewhat white. It contains, however, cells and nuclei which have a general resemblance to those of the preceding layers, but they exhibit only a faintly radiating arrangement. The sixth and most internal layer is reddish-gray. It not only abounds in cells like those already described but contains others that are rather larger. It is only here and there that the cells are collected into elongated groups, which give the appearance of radiations. On its under side it gradually blends with the central white axis of the convolution, into which its cells are scattered for some distance. " The seventh layer is this central white stem or axis of the convolution. On every side it gives off bundles of fibres, which diverge in all directions, and in a fanlike manner towards the surface, through the several gray layers. As they pass between the elongated and radiating groups of cells in the i'nner gray layers, some of them become continuous with the processes of the cells in the same section or plane, but others bend round and run horizontally, both in a transverse and longitudinal direction (in reference to the course of the entire convolution), and with various degrees of obliquity. While the bundles them- selves are by this means reduced in size, their component fibres become finer 62 GENERAL ANATOMY. in proportion as they traverse the layers towards the surface, in consequence, apparently, of branches which they give ofi' to be connected with cells in their course. Those which reach the outer gray layer are reduced to the finest dimensions, and form a close network, with which the nuclei and cells are in connection. " Besides these fibres which' diverge from the central white axis of the con- volution, another set, springing from the same source, converge or rather curve inwards from opposite sides, to form arches along some of the gray layers. These arciform fibres nin in different planes — transversely, obliquely, and longitudinally — and appear to be partly continuous with those of the divergent set which bend round, as already stated, to follow a similar course. All these fibres establish an infinite number of communications in every direction, be- tween different parts of each convolution, between different convolutions, and between these and the central white substance." Mr. Clarke then goes on to describe in detail the minuter diiferences which exist between the structure of the convolutions in dift'erent parts of the brain.' Spinal Cord. In the spinal cord, on the other hand, the gray matter is entirely in the interior of the organ, and is collected together into one central mass, while the whole of the white matter is external, and is arranged into various columns and commissures. [See Spinal Cord.) We shall here merely give an account of the intimate structure of the cord, which is condensed from the researches of Mr. Lockhart Clarke.* The white substance of the cord consists of transverse, oblique, and longitudinal fibres, with bloodvessels and connective tissue. The transverse fibres, proceed from the gray substance, and form with each other a kind of plexus between the bundles of longitudinal fibres, with which many are continuous; while others reach the surface of the cord through fissures containing connective tissue. Within the gray substance they are continuous with the roots of the nerves, with the processes of the nerve-cells, and with the anterior and posterior Fig- 30. commissures. ^\iq oblique fibres ^vo- ceed from the gray substance both upwards and downwards: they form the deep strata of the white columns, and, after running a variable length, become superficial. The longitudinal fibres are more superficial, run nearly parallel with each other, and form the greater portion of the white columns. The gray substance of the cord consists of, 1. Nerve fibres of varia- ble, bat smaller average diameter than those of thelcolumns. 2. Nerve- cells of various shapes and sizes, witli from two to eight processes. 3. Bloodvessels and connective tissue. Each lateral half of the gray sub- stance is divided into an anterior and posterior horn, and the tractus intermedio-lateralis, or lateral part of the gray substance between the anterior and posterior cornua. ' See Mr. Clarke's Bummary of his researches on this subject in Maudsley on the Pathology and Physiology of Mind, pp. 60-6:^. '' Phil. Trans., 1851-1853, part iii.; 1858 part i. ; 1859 part i. ; 1882 part ii. (/'>^{-^. Transverse section of the gray substance of the spinal cord, near the middle of the dorsal region. (Magnified 1.3 diameters.) SPINAL CORD. 63 The posterior horn consists of two parts, the caput cornu, or expanded ex- tremity of the horn (Fig. 30), round which is the lighter space or lamina, the gelatinous substance; and the cervix cornu, or remaining narrow portion of the horn, as far forwards as the central canal. The gelatinous substance contains along its border a series of large nerve- cells; but more internally consists of a stratum of small cells traversed by transverse, oblique, and longitudinal fibres (Figs. 31, 32). Fig. 31. TrnnsTerse section of the gray substance of the spinal cord through the middle of the lumber enlargement. On the left side the groups of large cells are seen ; on the right side the course of the fibres without the cells. (Magnified 13 diameters.) Nearly the whole inner half of the cervix is occupied by a remarkable and important column of nerve-cells, called the posterior vesicular column (Fig. 30), which varies in size and appearance in different regions of the cord, and is intimately connected with the posterior roots of the nerves. "Within, and along the outer border of the cervix, are several thick bundles of longitudinal fibres, represented in Fig. 30 by the dark spots ; other bundles of the same kind may be seen in the gray substance along the line of junction of the caput with the cervix cornu (Fig. 31). The anterior horn of the gray substance in the cervical and lumbar swellings, where it gives origin to the nerves of the extremities, is much larger than in any other region, and contains several distinct groups of large and variously shaped cells. This is well shown on comparing the above figures. The tractus intermedio-lateralis (Fig. 80) extends from the upper part of the lumbar to the lower part of the cervical enlargement, and consists of variously shaped cells, which are smaller than those of the anterior cornu. In the neck above the cervical enlargement, a similar tract reappears, and is traversed by the lower part of the spinal accessory nerve. Origin of the Spinal Nerves in the Cord. The posterior roots are larger than the anterior; but their component filaments are finer and more delicate. They are all attached immediately to the posterior columns only, and decussate each other in all directions thro-ugh the columns; but some of them pass through 64 GENERAL ANATOMY. Fig. 32. J'ojst^ Jtaol?s SuIfslciTice 'Grey the gray substance into both the lateral and anterior columns. Within the gray substance, they run longitudinally upwards and downwards ; transversely through the posterior commissure to the oppo- site side; and into the anterior cornu of their own side (Figs. 31, 82). The anterior roots are attached exclusively to the anterior column, or rather to the anterior part of the antero-lateral columns ; for tbere is no antero-lateral fissure dividing the anterior from the lateral column. Within the gray substance, the fibrils cross each other, and di- verge in all directions, like the expanded hairs of a brush (Figs. 31, 32), some of them run- ning more or less longitudinally upwards and downwards ; and others decussating those of the opposite side through the anterior com- missure in front of the central canal. All the fibres of both roots of the nerves proceed through the white columns into the gray substance, with, perhaps, the exception of some which appear to run longitudinally in the posterior columns; but whether these latter fibres of the posterior roots ultimatelv enter the gray substance of the cord after a very oblique course, or whether they proceed upwards to the brain, is uncertain. The Central Canal of the Spinal Cord. In the foetus, until after the sixth month, a canal, continuous with the general ventricular cavity of the brain, extends throughout the entire length of the spinal cord, formed by the clos- ing-in of a previously open groove. In the adult, this canal can only be seen at the upper part of the cord, extending from the point of the calamus scriptorius, in the floor of the fourth ventricle, for about half an inch down the centre of the cord, where it terminates in a cul-de-sac; the remnant of the canal being just visible in a section of the cord, as a small, pale spot, corresponding to the centre of the gray commissure; its cavity is lined with a layer of cylindrical ciliated epithelium. In some cases, this canal remains pervious throughout the whole length of the cord. The Ganglia may be regarded as separate and independent nervous centres, of smaller size and less complex structure than the brain, connected with each other, with the cerebro-spinal axis, and with the nerves in various situations. They are found on the posterior root of each of the spinal nerves ; on the pos- terior or sensory root of the fifth cranial nerve ; on the facial nerve ; on the glosso-pharyngeal and pneumogastric nerves; in a connected series along each side of the vertebral column, forming the trunk of the sympathetic ; on the branches of that nerve, and at the point of junction of those branches with the cerebro-spinal nerves. On section, they are seen to consist of a reddish-gray substance, traversed by numerous white nerve-fibres : they vary considerably in form and size ; the largest are found in the cavity of the abdomen ; the smallest, not visible with the naked eye, exist in considerable numbers upon the nerves distributed to the different viscera. The ganglia are invested by a smooth and firm closely-adhering membranous envelope, consisting of dense areolar tissue ; this sheath is continuous with the neurilemma of the nerves, Ant; ' A/U-" Jiools Longitudinal section of the white and gray substance of the spinal cord, through the middle of the lumbar enlargement. (Magnified 34 diameters.) THE NERVES. 65 and sends numerous processes into the interior of the ganglia, which support the bloodvessels supplying its substance. In structure, all ganglia are essentially similar ; consisting of the same struc- tural elements as the other nervous centres, viz., a collection of vesicular nervous matter, traversed by tubular and gelatinous nerve-fibres. The vesicular nervous matter consists of nerve-cells or ganglion globules, most of which appear free, and of a round or oval form: these are more especially seated near the surface of the ganglion ; others have caudate processes, and give origin to nerve-fibres. In the ganglia, the nerve-cells are usually inclosed in a capsule of granular corpuscles and fibres. The tubular nerve-fibres run through the ganglion, some being collected into bundles, while others, separating from each other, take a circuitous course among the nerve-cells before leaving the ganglia. The Nerves are round or flattened cords, which are connected at one end with the cerebro-spinal centre or the ganglia, and are distributed, at the other, to the various textures of the body : they are subdivided into two great classes, the Cerebro-spinal, which proceed from the cerebro-spinal axis, and the Sym- pathetic or Ganglionic nerves, which proceed from the ganglia of the sympa- thetic. The cerebrospinal nerves consist of numerous nerve-fibres, collected together and inclosed in a membranous sheath. A small bundle of primitive fibres, inclosed 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 ; and are bound together in a common membranous investment, termed the sheath. In structure, the common sheath investing the whole nerve, as well as the septa given off from the sheath, and which separate the fasciculi, consist of areolar tissue, composed of white and yellow elastic fibres, the latter existing in greatest abundance. The tubular sheath of the funiculi, or neurilemma, consists of a fine, smooth, transparent membrane, which may be easily separated, in the form of a tulse, from the fibres it incloses ; in structure, it is, for the most part, a simple and homo- geneous transparent film, occasionally composed of numerous minute reticular fibres. The cerebro-spinal nerves consist almost exclusively of the tubular nerve- fibres, the gelatinous fibres existing in very small proportion. The bloodvessels supplying a nerve terminate in a minute capillary plexus, the vessels composing which run, for the most part, parallel with the funiculi; they are connected together by short transverse vessels, forming narrow oblong meshes, similar to the capillary system of muscle. The nerve-fibres, as far as is at present known, do not coalesce, but pursue an uninterrupted course from the centre to the periphery. In separating a nerve, however, into its component funiculi, it may be seen that they do not pursue a perfectly insulated course, but occasionally join at a very acute angle with other funiculi proceeding in the same direction ; from which, again, branches are given off, to join again in like manner with other funiculi. It must be remembered, however, that in these communications the 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 become blended with the nerve-fibres in some adjoining fasciculus. Nerves, in their course, subdivide into branches, and these frequently com- municate with branches of a neighboring nerve. In the subdivision of a nerve, the filaments of which it is composed are continued from the trunk into the branches, and at their junction with the branches or neighboring nerves, the filaments pass to become intermixed with those of the other nerve in their fur- ther progress; in no instance, however, have the separate nerve-fibres been shown to inosculate. The communications which take place between two or more nerves, form 5 66 GENERAL ANATOMY. 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 plex- uses, and occasionally by the terminal fasciculi, as in the plexuses formed at the periphery of the body. In the formation of a plexus, the component nerves divide, then join, and again subdivide in such a complex manner that the indi- ^vidual fasciculi become interlaced most intricately; so that each branch leav- ing a plexus may contain filaments from each of the primary nervous trunks which form it. In the formation also of the smaller plexuses at the periphery of the body, there is a free interchange of the fasciculi and primitive fibrils. In each case, however, the individual filaments remain separate and distinct, and do not inosculate with each other. It is probable that, through this interchange of fibres, the different branches passing off from a plexus have a more extensive connection with the spinal cord than if they each had proceeded to be distributed without such connection with other nerves. Consequently, the parts supplied by these nerves have more extended relations with the nervous centres ; by this means, also, groups of muscles may be associated for combined action. The sympathetic nerve consists of tubular and gelatinous fibres, intermixed with a varying proportion of filamentous areolar tissue, and inclosed in a sheath formed of fibro-areolar tissue. The tubular fibres are, for the most part, smaller than those composing the cerebro-spinal nerves ; their double contour is less distinct, and, according to Remak, they present nuclei similar to those found in the gelatinous nerve-fibres. Those branches of the sym- pathetic which present a well-marked gray color, are composed more especially of gelatinous nerve-fibres, intermixed with a few tubular fibres ; whilst those of a white color contain more of the tubular fibres, and few gelatinous. Occasionally the gray and white cords run together in a single nerve, without any intermixture, as in the branches of communication between the sym- pathetic ganglia and the spinal nerves, or in the communicating cords between the ganglia. The nerve-fibres, both of the cerebro-spinal and sympathetic system, convey impressions of a twofold kind. The sensory nerves, called also centripetal or afferent nerves, transmit to the nervous centres impressions made upon the peripheral extremities of the nerves, and in this way the mind, through the medium of the brain, becomes conscious of external objects. The motor nerves, called also centrifugal or efferent nerves, transmit impressions from the nervous centres to the parts to which the nerves are distributed, these impres- sions either exciting muscular contractions, or influencing the processes of nutrition, growth, and secretion. Terminations of Nerves. By the expression "the termination of nerve-fibres" is signified their connections with the nerve centres, and with the parts which they supply. The former are called their central, the latter their peripheral terminations. "With regard to the central terminations of the nerves, little is as yet certainly known.' The nerve-cells, or nerve-corpuscles, above figured, have been regarded as the central origin of the fibres with which they are connected ; and it is very probable that in many cases they are so. There are instances, however, in which such cells occur as mere nucleated swellings in the course of a nerve, and in these cases they obviously cannot be regarded as being in any sense the origins of the nerves. In other cases, as in the nerve- cells in the anterior horn of the gray matter of the cord, there are numerous processes springing out of the cell ; one of these (and according to Deiters one only) is jecognized as an axis-cylinder; the others are fibril Ise, which are con- ' The most recent author, and one of the most distinguished observers on this subject, Max Schultze, speaks thus : " In the present state of our knowledge, we are not in a position to assign its central origin to any single primitive fibril of the nervous system, however certainly we may have discovered the peripheral terminations of a great part of them." (Schultze, in Strieker's Handhuch, 1868, p. 134) THE NERVES. 67 tinuous with similar fibrillEe, of whicb, under high powers, the apparently granular contents of the cell are found to be composed, and which appear therefore simply to run through the cell. The fibrillte may be, and probably are, primitive nervous fibrils, but they are so delicate, that it has not as yet been found possible to ascertain their destination. With regard also to the axis-cylinder which is seen proceeding out of the ganglionic corpuscle, although it is highly probable that it originates in that corpuscle, the fact has not been proved — nor has its relation to the nucleus of the corpuscle been demonstrated. In fine, all that is known on the subject is, that many of the fibrill^ and axis- cylinders can be shown either to originate in or to pass through ganglionic corpuscles (or nerve-cells), and other nerves can be shown to contain such nerve-cells in their anterior at certain parts of their course. But whether in the case of such connection in one of the central organs the cell is to be regarded as the origin of the nervous fibril, or whether the fibril merely passes through the cell (as some observers believe), just in the same manner as nerves pass through ganglia, has not been determined. If the latter view be correct, it may be that nerves have really no central termination, but that their fibrils start from their peripheral distribution, travel to the nervous centre, are there brought into connection with the nerve-cells, and thence return to their distri- bution. However, in the present state of anatomical knowledge, the more probable opinion seems to be that which is usually entertained, viz., that each nerve-fibre is connected somewhere with a ganglionic corpuscle, which is to be regarded as its central termination or origin. Dr. Beale asserts, that even in those ganglion-cells, which appear either altogether destitute of processes, or unipolar, numerous fibres can be seen proceeding out of them if the proper reagents be used and very high powers employed. The peripheral connections, or terminations of the nerve-fibres, are some- what more easy to ascertain, though even as to these a great difierence exists with respect to minute details. They are usually and naturally studied in the sensory and motor nerves separately. Sensory nerves sometimes terminate in minute plexuses in the subcutaneous or submucous areolar tissue. Dr. Sharpey says that he has seen the ultimate fibres of these minute plexuses come into close contact with the connective- tissue corpuscles, but has not been able to trace any distinct connection between them. The white substance of Schwann and the tubular sheath usually disappear as the nerve approaches its termination, leaving only the axis-cylinder invested by its proper basement- membrane, on which nuclei can be seen at intervals, and in many cases the axis-cylinder itself breaks up into the primitive fibrils. In some parts, however, the fibres appear to be inclosed up to their termination in a sheath, which is either a prolongatiou of the neurilemma, or a continuation of the tubular membrane. The differences of opinion prevailing on the ques- tion of the ultimate distribution of the nerve-fibres depend on their extreme delicacy and the consequent great difficulty of following individual fibres in continuity. Hence what some observers describe as a free end, in which the nerve terminates, others regard as merely a bending of the fibre where it be- comes lost to sight, or a spot where it is lost sight of in consequence of the power used being too low, or from difficulty in focussing. These ultimate fibres, it should be remembered, are structureless, and can therefore only be recognized positively as nervous by their continuity with a nerve of more complex structure. In the papillae of the skin, or mucous membrane, and on the surface of various membranes (conjunctiva, mesentery, &c.), three different kinds of terminal organs have been found connected with the nerves, viz., the end-bulbs of Krause, the tactile corpuscles of Rudolph Wagner, and the Pacinian corpuscles. The end-bulbs of Krause are small capsules of connective tissue, in which nuclei can be detected by reagents, and in which one or more nerve-fibrils 68 GENERAL ANATOMY. terminate either in a coiled plexiform mass or in a bulbous extremity. They have been described as occurring in the conjunctiva, the mucous membrane of the mouth, and the surface of the glans penis and glans clitoridis.^ The tactile corpuscles of Wagner (Fig. 33) are described by him as oval- shaped bodies, made up of superimposed saccular laminae, presenting some resemblance to a miniature iir-cone, and he regarded them as directly concerned in the sense of touch. Kolliker considers that the central part of the papillaa generally consists of a connective tissue more homogeneous than that of the outer part, surrounded by a sort of sheath of elastic fibres, and he believes that these corpuscles are merely a variety of this structure. The nerve-fibres, 33. Fiff. 34. A. Side view of a papilla of the hand. a. Cortical layer; b, tactile corpuscle, with transverse nuclei; c^ small nerve of the papilla, -with neurilemma; d, its two nervous fibres runningwith spiral coils around the tactile corpuscle ; e, apparent termination of one of these fibres. B. A tactile papilla seen from above, so as to show its transverse section, a. Cortical layer; h, nerve fibre ; 0, outer layer of the tactile body, with nuclei; d, clear interior substance. From the human subject, treated with acetic acid. (Magnified 350 times.) Pacinian corpuscle with its system of capsiiles and central cavity, u. Arterial twig, ending in capillaries, whicli form loops in some of the intercapsular spaces, and one penetrates to the central capsule ; 5, lh3 fibrous tissue of the .«talk prolonged from the neurilemma; m, nerve-tube advancing to the central capsule, there losing its white substance, and stretching along the a.via to the opposite end, where it is fixed by a tubercular enlargement. according to this observer, run up in a waving course to the corpuscle, not penetrating it, but forming. two or three coils round it, and finally join together in loops. These bodies are not found in all the papillae; but from their exist- ence in those parts in which the skin is highly sensitive, it is probable that they are especially concerned in the sense of touch, though their absence from the papillae of other tactile parts shows that they are not essential to this sense. The Pacinian corpuscles^ (Fig. 34) are found in the human subject chiefly on the nerves of the fingers and toes, lying in the subcutaneous cellular tissue;' but ' Krause, Die terminalen Korperchen, 18G0. Anatomische Unter^nchungen, 1861. ' Often called in German anatomical works " corpuscles of Vater." THE NERVES. 69 they have also been described by Eauber as connected with the nerves of the joints, and with the nerves lying between many of the muscles of the trunk and limbs. Each of these corpuscles is attached to and incloses the termination of a single nerve. The corpuscle, which is perfectly visible to the naked eye (and which can be most easily demonstrated in the mesentery of a cat), consists of a number of concentric layers of cellulur tissue, between which Todd and Bowman have figured capillary vessels as running. The nerve, at its entrance into this body, parts with its white substance, and the axis-cylinder runs forwards in a kind of cavity in the centre of the corpuscle to terminate in a rounded end or knob, sometimes bifurcating previously, in which case each branch has a similar termination. Grandry, who has examined these corpus- cles with very high magnifying powers, describes the axis-cylinder as exhibit- • ing a very well marked fibrillar structure, and the bulbous end as consisting of a mass of granules into which the fibrils run, diverging as they approach it. The investing capsules are from thirty to sixty in number, the outer being more separated from each other, as if by a clear fluid, while the inner are closely applied together. Schultz calls attention to the striking resemblance in all essential particulars between these corpuscles and Krause's end-bulbs above described.' In the special organs the nerves end in various ways, which hitherto are not perfectly known. Hoyer and Cohnheim have described the nerves of the cornea as terminating in primitive fibrillse, which run between the cells forming the pavement-epithe- lium of that membrane, and end on its free surface. This, however, is doubted by Hulke,^ who has only succeeded in tracing them as far as the middle tier of the epithelial cells. Schultze discovers in the olfactory mucous membrane, lying between the cells of its epithelium, spindle-shaped cells, each possessing a central and a peripheral process — the central process being, according to him, continuous with a primitive fibril of the olfactory nerve, and the peripheral process either ending on the free surface of the epithelium, as is the case in men, mammals, and fishes, or in some other animals prolonged into a long stiff hair. These cells he has denominated "olfactory cells;" and similar cells have been described by Axel Key, Schwalbe, and Loven, in the papillae circumvallatas of men, and the fungiform papillse of the frog ("taste-cells"). The fibres also of the optic nerve have, according to Schultze, a similar connection with the cells ("sight-cells") of the retina; and cells somewhat similar, and connected with processes that pass through the epithelium, are to be found on the nerve fibrils of the auditory nerve, in the membranous labyrinth ("hearing-cells"). The terminations of the nerves in the hair-bulbs are probably to be found in the papillae at their root, as is also the case in the teeth. In glands the nerves, according to Pfliiger, are connected with the caecal commencements of the gland tubes — -at least he has described this arrangement in the salivary glands, and thus he is led to regard the nuclei of these caecal pouches as the termina- tions of the nerves. Motor nerves are to be traced either into unstriped or striped fibres. In the unstriped fibres it appears from the researches of Beale, Franken> haiiser, and Julius Arnold, that the ultimate fibrils of the nerves form plexuses at the junctions of the branches of which small nuclear bodies are situated. These nuclei are regarded by Arnold as the real terminations of the nerves, for although he agrees with Frankenhaiiser in stating that the nervous filaments penetrate the muscular fibres, and enter into relation with the granular con- tents of their nuclei, he traces the filaments back again from that point to the nuclei situated at the junctions of the nervous plexuses, in the connective tissue of the muscular fibres. ' Strieker's Hmdbuch, p. 123. * Lectures on the Histology of the Eye, at the Eoyal College of Surgeons, June, 1869. TO GENERAL ANATOMY, In the voluntary muscles Beale and Kolliker have described the nerve-fibres as terminating either in a plexiform arrangement, or (according to the latter author), sometimes in free ends between the muscular fibres external to the sarcolemma. Lately another method of termination, which had been formerly described, has received the support of numerous eminent authorities — viz., the " motorial end-plates" of Kiihne, or "nerve-hillocks" (nerve-tufts) of Doyere. The latter author had described, nearly thirty years ago, a connection between the nervous and muscular fibres in some of the lower animals, consisting in an elevation at the point of junction of the two, where the sarcolemma of the muscular fibre became blended with the tubular membrane of the nerve. This has been since so far confirmed by subsequent researches, that it seems well to figure, from the most recent author, Kiihne, what he supposes to be the termi- nation of all motor nerves of voluntary muscles. The following is Kiihne's description of the method of connection. "In all striped muscles the nerve terminates below the sarcolemma — the tubular membrane being blended with th6 sarcolemma. The white substance accompanies the axis-cylinder as far as this point. The ending of the axis- cylinder always represents an expansion with a considerably increased surface, and this is constantly formed by its branching out on a flat plate. This nerve- end-plate is sometimes more like a membrane, at others like a system of fibres. In most cases the plate rests upon a base of granules and finely-granular proto- plasm; in other cases there is no such support, and the nerve-plates then possess the so-called nerve-end-bulbs. The ends of the nerves never penetrate the in- terior of the contractile cylinder, nor does the plate ever embrace the whole Fior. 3.5. Mupcular fibres of Lacerta Viridis with the terminatiotis of Derves. a. Seen in profile ; p p, the nerre end-plates ; s s, the base of the plate, consisting of a granular mass "with nuclei, b. The same as seen in looking at a perfectly fresh fibre, the nervous ends being probably still excitable. (The forms of the variously- divided plate can hardly be represented in a wood-cut by sufficiently delicate and pale contours to reproduce correctly what is seen in nature.) e. The same as seen two hours after death from poisoning by curare. circumference of the cylinder. Short muscular fibres generally have only one nerve-end, while longer fibres have several." It is right, however, to state that the most eminent English authority on this subject entirely denies the description above given, and explains the appear- ances, figured by Kiihne and others, in a different manner. In a very interest- ing paper by Dr. Beale, published in 1867,' he endeavors to show that the nerve-hillocks of Doyere are merely accidental elevations produced by the sarco- lemma being drawn up in a cone, as the nerve which is attached to it is stretched by the manipulation of the observer; and with reference to the end-plates of ' On Anatomical Controversy. Seal's Archives, iv. 161. THE NERVES. 71 Klihne, he asserts that by his own method of examination he is able to follow the nerve-fibrils much beyond the point at which that author describes theni as terminating. The appearance of their penetrating the sarcolemma he regards as an optical illusion, and the nuclei shown in the above figures are, according to him, situated outside of the muscular fibres on the points of junction of the fibrils which form the intricate and extensive plexus in which the nerves terminate, so that the nerves nowhere terminate in free ends, not at any definite part of the fibre; but, on the contrary, surround every point of the latter with a very close interlacement. Terminations of motor nerves, according to Beale. 1. Nerve-tuft on the sarcolemma of a muscular fibre ; chameleon. Nerve-fibres are seen passing out of as well as into the tuft. 2. Nerve-fibres distributed to elementary muscular fibre; chameleon, x 3000, and reduced half. This is a very simple form of "nerve tuft," clearly external to the sarcolemma. 3. The intimate structure of a very simple " nerve tuft" on a muscular fibre of the chameleon. It will be observed that the nerve fibres are continuous throughout, nnX that the whole is on the surface of the sarcolemma, x 3000. This " nerve tuft" is, as it were, but a com- pound network. By the kindness of Dr. Beale we are enabled to reproduce some of the figures representing preparations which he exhibited to the British Medical Associa- tion at Oxford, in 1868, in illustration of this view. T2 GENERAL ANATOMY. THE VASCULAR SYSTEM. The Vascular System, exclusive of its central organ, the Heart, is divided into four classes of vessels — the Arteries, Capillaries, Veins, and Lymphatics — the minute structure of which we will now proceed briefly to describe, referring the reader to the body of the work for all that is necessary in the details of their ordinary anatomy. The Arteries. The arteries are composed of three coats — internal serous, or epithelial coat (tunica intima of Kolliker), middle fibrous or circular coat, and external cellular coat or tunica adveniitia. The two inner coats together are very easily separated from the external, as by the ordinary operation of tying a ligature on the artery. If a fine string be tied forcibly upon an artery, either before or after death, and then taken off, the external coat will be found uninjured, but the internal coats are divided in the track of the ligature, and can easily be further dissected from the outer coat. The inner coat can be separated from the middle by a little maceration. The inner coat consists of: 1. A layer of pavement epithelium, the cells of which are oval or fusiform, and have very distinct nuclei. 2. This epithelium rests upon a layer of longitudinal elastic fibres, in which, under the microscope, small elongated apertures are seen, and which was therefore called by Henle the fenestrated membrane. This layer is marked with numerous reticulations; it is perfectly smooth when the artery is distended ; but when empty, presents longitudinal and transverse folds. The fenestrated membrane can often be separated into more than one layer. An artery from the mesentery of a child, .nC2"', nnd i, vein .067'", in di.imoter ((rented with acetie iieid and magnified 350 times), a. Tunica ndventitia, with elongated nuclei. /?. Nuclei of the contractile fibie- cells of the tunica media, seen partly from the surface, partly apparent in transverse section, y. Nuclei of the epithelial cells. S'. Elastic longitudinal fibrous coat. In arteries of less than a line in diameter, the internal coat consists of two layers, as above described; but in middle-sized arteries, several lamella composed of elastic fibres and connective tissue, are interposed between the epithelial and elastic coats. In the largest arteries, the inner coat is usually much thickened, especially in the aorta ; and consists of a homogeneous sub- stance, occasionally striated or fibrillated, transversed by longitudinal elastic networks, which are very fine in the lamellae immediately beneath the epithe- THE ARTERIES. 73 lium, but increase in ttickness from within outwards. The internal and middle coats are separated, by either a dense elastic reticulated coat, or a true fenes- trated membrane. The middle coat is distinguished from the inner by its color, and by the trans- verse arrarUgement of its fibres, in contradistinction to the longitudinal direction of those of the inner coat. In the largest arteries, this coat is of great thick- ness, of a yellow color, and highly elastic; it diminishes in thickness, and becomes redder in color as the arteries become smaller ; becomes very thin, and finally disappears. In small arteries, this coat is purely muscular, consisting of muscular fibre-cells united to form lamellae which vary in number according to the size of the artery, the very small arteries having only a single layer, and those not larger than the -j^th of a line in diameter, three or four layers. In arteries of medium size, this coat becomes thicker in proportion to the size of the vessel ; its layers of muscular tissue are more numerous, and intermixed with numerous fine elastic fibres which unite to form broad-meshed networks: In the larger vessels, as the femoral, superior mesenteric, coeliac, external iliac, brachial, and popliteal arteries, the elastic fibres unite to form lamellse, Avhich alternate with the layers of muscular fibre. In the largest arteries, the muscTilar tissue is only slightly developed, and forms about one-third or one-fourth of the whole substance of the middle coat ; this is especially the case in the aorta, and trunk of the pulmonary artery, in which the individual cells of the muscular layer are imperfectly formed ; while, in the carotid, axillary, iliac, and subclavian arteries, the muscular tissue of the middle coat is more developed. The elastic lamellsB are well marked, may amount to fifty or sixty in number, and alternate regularly with the layers of muscular fibre. They are most distinct, and arranged with most regularity in the abdominal aorta, innominate artery, and common carotid. The external coat consists mainly of connective tissue, and contains elastic fibres in all but the smallest arteries. In the largest vessels, the external coat is- relatively thin; but in small arteries, it is as thick, or thicker, than the mid- dle coat. In arteries of the medium size, and above it, the external coat is formed of two layers, the outer of which consists of connective tissue, con- taining an irregular elastic network, while the inner is composed of elastic tissue only. The inner elastic layer is very distinct in the carotid, femoral, brachial, profunda, mesenteric and coeliac arteries, the elastic fibres being often arranged in lamellK!. In the smaller arteries, the former layer of mixed connective tis- sue and elastic fibres composes the whole of the external tunic ; 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 homoge- neous the nearer it approaches the capillaries, and is gradually reduced to a thin membranous envelope, which finally disappears. Some arteries have extremely thin coats in proportion to their size ; this is especially the case in those situated in the cavity of the cranium and spinal canal, the difference depending upon the greater thinness of the external and middle coats. The arteries, in their distribution throughout the body, are included in a thin areolo-fibrous investment, which forms what is called their sheath. In the limbs, this is usually formed by a prolongation of the deep fascia ; in the upper part of the thigh, it consists of a continuation downwards of the transversalis and iliac fasciae of the abdomen; in the neck, of a prolongation of the deep cervical fascia. The included vessel is loosely connected with its sheath by a delicate areolar tissue ; and the sheath usually incloses the accompanying veins, and sometimes a nerve. Some arteries, as those in the cranium, are not included in sheaths. All the larger arteries are supplied with bloodvessels like the other organs of the body ; they are called vasa vasorum. These nutrient vessels arise from a branch of the artery or from a neighboring vessel, at some considerable dis- 74 GENERAL ANATOMY, tance from the point at which they are distributed; they ramify in the loose areolar tissue connecting the artery with its sheath, and are distributed to the external and middle coats, and, according to Arnold and others, supply the in- ternal coat. Minute veins serve to return the blood from these vessels ; they empty themselves into the vense comites in connection with the artery. Arteries are also provided with nerves, which are derived chiefly from the sympathetic, but partly from the cerebro-spinal system. They form intricate plexuses upon the surface of the largest trunks, the smaller branches being usually accompanied by single filaments ; their exact mode of distribution is unknown. According to Kolliker, the majority of the arteries of the brain and spinal cord, those of the choroid and of the placenta, as well as many arte- ries of muscles, glands, and membranes, are unprovided with nerves. The Capillaries. The smaller arterial branches (excepting those of the caver- nous structures of the sexual organs, and in the uterine placenta) terminate in a network of vessels which pervade nearly every tissue of the body. These vessels, from their minute size, are termed capillaries {capillus, "a hair"). They are "interposed between the smallest branches of the arteries and the commencing veins, constituting a network, the branches of which maintain the same diame- ter throughout, the meshes of the network being more uniform in shape and size than those formed by the anastomoses of the small arteries and veins. The diameter of the capillaries varies in the different tissues of the body, their usual size being about ^5^55 of an inch. The smallest are those of the brain, and the mucous membrane of the intestines ; the largest, those of the skin, and the marrow of bones. The form of the capillar}^ net varies in the different tissues, being modifica- tions chiefly of rounded or elongated meshes. 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 being more or less angular, sometimes nearly quadrangular, or polygonal ; more frequently, ir- regular. Ehngated meshes are observed in the bundles of fibres and tubes com- posing muscles and nerves, the meshes being usually of a parallelogram form, the long axis of the mesh running parallel with the long axis of the nerve or fibre. Sometimes, the capillaries have a looped arrangement, a single vessel projecting from the common network, and returning after forming one or more loops, as in the papillje of the tongue and skm. The number of the capillaries, and the size of the meshes, determines the degree of vascularity of a part. The closest network, and the smallest inter- spaces are found in the lungs and in the choroid coat of the eye. In the liver and lung, the interspaces are smaller than the capillary vessels themselves. In 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 diameter, and from four to six times as large in their transverse diameter. In the cellular coat of the arteries, the width of the meshes is ten times that of the capillary vessels. As a general rule, the more active the function of an organ is, the closer is its capillary net, and the larger its supply of blood, the network being very nar- row in all growing parts, in the glands, and in the mucous membranes; wider in bones and ligaments, which are comparatively inactive; and nearly alto- gether absent in tendons and cartilages, in which very little organic change occurs after their formation. Structure. The walls of the capillaries consist of a fine, transparent, homo- geneous membrane, in which are imbedded, at intervals, minute oval corpuscles, probably the remains of the nuclei of the cells from which the vessel was originally formed. In the largest capillaries (which ought perhaps to be described rather as the THE VEINS. 15 smallest arteries) traces of an epithelial lining, and of circular transverse fibres, are to be seen. The Veins are composed of three coats, internal, middle, and external, as the arteries are; and these coats are, with the necessary modifications, analogous Fiff. 38. Fig. 39. Finest vessels un the iirterial side. 1. Smallest artery. 2. Transition vessel. 3. Coarser capillaries. 4. Finer capillaries. u. Structureless membrane still with some nuclei, representative of the tunica adventitia ; b, nuclei of the muscular fibre-cells ; c, nuclei within the small artery, perhaps appertaining to nn epithelium ; d, nuclei in the transition vessels. From the human brain. (M.ignifled 300 times.) An artery, .01'", and h, a vein, .015", from the mesentery of a child (mag- nified 350 times and treated with acetic acid). The letters as in Fig. 37. 6. The tunica media of the vein, consisting of nucleated connective tissue. to the coats of the arteries — ^the internal being the epithelial, the middle the fibrous, and the external the connective or areolar. The main difference be- tween the veins and the arteries is in the comparative weakness of the middle coat of the former; and to this it is due that the veins do not stand open when divided, as the arteries do ; and that they are passive rather than active organs of the circulation. In the veins immediately above the capillaries, the three coats are hardly to be distinguished. The epithelium is supported on an outer membrane of nu- cleated connective tissue, separable into two layers, the outer of which is the thicker, the fibres of both being longitudinal. The interior thinner layer of nucleated tissue is regarded by Kdlliker as the analogue of the middle coat. In the veins next above these in size (one-fifth of a line, according to Kolliker) a muscular layer and a layer of circular fibres can be traced, forming the middle coat, while the elastic and connective elements of the outer coat become more distinctly perceptible. In the middle-sized veins, the typical structure of these vessels becomes clear. The epithelium is of the same character as in the arteries, but its cells are more oval, less fusiform. It is supported by one or more layers of nucle- ated fibrous tissue, arranged longitudinally, and external to this is a layer of elastic fibrous tissue. This constitutes the internal coat. The middle coat is :6 GENERAL ANATOMY. composed of a thick inner layer of connective tissue with elastic fibres, having intermixed in some veins a transverse layer of muscular fibres; and an outer layer consisting of longitudinal elastic lamellae, varying from five to ten in number, alternating with layers of transverse muscular fibres and connective tissue, which resembles somewhat in structure the middle coat of large arteries. The outer coat is similar in all essential respects to that of the arteries. In the large veins, as in the commencement of the vena portse, in the upper part of the abdominal portion of the inferior vena cava, and in the large hepatic trunks within the liver, the middle coat is thick, and its structure similar to that of the middle coat in medium-sized veins; but its muscular tissue is scanty, and the longitudinal elastic networks less distinctly lamellated. The muscular tissue of this coat is best marked in the splenic and portal veins; it is absent in certain parts of the vena cava below the liver, and wanting in the subcla- vian vein and terminal parts of the two cavte. In the largest veins, the outer coat is from two to five times thicker than the middle coat, and contains a larger number of longitudinal muscular fibres. This is most distinct in the hepatic part of the inferior vena cava, and at the termination of this vein in the heart; in the trunks of the hepatic veins; in all the large trunks of the vena portee; in the splenic, superior mesenteric, external iliac, renal, and azygos veins. Where the middle coat is absent, this muscular layer extends as far as the inner coat. In the renal and portal veins, it extends through the whole thickness of the outer coat: but in the other veins mentioned, a layer of connective and elastic tissues is found external to the muscular fibres. All the large veins which open into the heart are covered for a short distance by a layer of muscular tissue continued on to them from the heart. Muscular tissue is wanting in the veins : 1. Of the maternal part of the placenta. 2. In most of the cerebral veins and sinuses of the dura mater. 3. In the veins of the retina. 4. In the veins of the cancellous tissue of bones. 6. In the venous spaces of the corpora cavernosa. The veins of the above- mentioned parts consist of an internal epithelial 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. They are formed by a reduplication of the middle and inner coats, and consist of connective tissue and elastic fibres, covered on both surfaces by epithelium; their form is semilunar. They are attached by their convex edge to the wall of the vein; the concave margin is free, directed in the course of the venous current, and lies in close apposition with the wall of the vein as long as the current of blood takes its natural course ; if, however, any regurgi- tation takes place, the valves become distended, their opposed edges are brought into contact, and the current is intercepted. 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 small branches ; occasionally there are three, and sometimes only one. The wall of the vein immediately above the point of attachment of each segment of the valve, is expanded into a pouch or sinus, which gives to the vessel, when in- jected 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 having to conduct the blood against the force of gravity. They are absent in the very small veins, also in the vense cavas, the hepatic vein, portal vein and its branches, the renal, uterine, and ovarian veins. A few valves are found in the spermatic veins, and one also at their point of junction with the renal vein and inferior cava in both sexes. 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. They are occasionally found, few in number, in the vense azygos and intercostal veins. The veins are supplied with nutrient vessels, vasa vasorum, like the arteries ; THE LYMPHATICS. 77 t)ut nerves are not generally found distributed upon them. The only vessels upon which they have at present been traced, are the sinuses of the dura mater; on the spinal veins; on the venae cavse ; on the common jugular, iliac, and crural veins ; and on the hepatic veins (Kolliker). The Lymphatic Vessels, like arteries and veins, are composed of three coats. The internal is an epithelial and elastic coat. It is thin, transparent, slightly elastic, and ruptures sooner than the other coats. It is composed of a layer of elongated epithelial cells, supported on a simple network of elastic fibres. The middle coat is composed of smooth muscular and fine elastic fibres, dis- posed in a transverse direction. The external, or areolar-fibrous coat, consists of filaments of the areolar tissue, intermixed with smooth muscular fibres, longitudinally or obliquely disposed. It forms a protective covering to the other coats, and serves to connect the vessel with the neighboring structures. The lymphatics are supplied by nutrient vessels, which are distributed to their outer and middle coats ; but no nerves have at present been traced into them. The lymphatics are very generally provided with valves, which assist ma- terially in effecting the circulation of the fluid they contain. These valves are formed of a thin layer of fibrous tissue, lined on both surfaces with scaly epithelium. Their form is semilunar ; they are attached by their convex edge to the sides of Fiff- 40. the vessel, the concave edge being free, and directed along the course of the contained cur- rent. Usually, two such valves, of equal size, are found opposite one another ; but occasionally exceptions occur, especially at or near the anastomoses of lymphatic vessels. Thus, one valve may be of very rudimentary size, and the other increased in proportion. In other cases, Transverse section through the coats the semilunar flaps have been found directed of the thoracioduotofman. (Magni- . ^ , ^ ■ , T o ^ fled 30 times) . a- Epithelium, striated transversely across the vessel, instead of ob- j^^^„^ ^„^ j^,,,^ ,,,,3ti„ „„^t. ^_ liquely, so as to impede the circulation in both longitudinal connective tissue of the directions, but not to completely arrest it in middle coat j c, transverse muscles of either; or the semilunar flaps, taking the same the same ; rf, tunica adventitia, withe, direction, have been found united on one side, the longitudinal muscular fibres, so as to form, by their union, a transverse sep- tum, having a partial transverse slit ; and sometimes the flap is constituted of a circular fold, attached to the entire circumference of the vessel, and having in its centre a circular or elliptical aperture, like the ileo-csecal valve. The valves in the lymphatic vessels are placed at much shorter intervals than in the veins. They are most numerous near the lymphatic glands, and they are found more frequently in the lymphatics of the neck and upper ex- tremity, than in the lower. The wall of the lymphatics, 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 which they present. Valves are wanting in the vessels composing the plexiform network, in which the lymphatics usually originate on the sur- face of the body. Besides this plexiform commencement, however, there are other modes of origin of the lymphatics, for those of the intestinal villi arise sometimes by closed extremities; and the lymphatics which arise in the in- terior of the" organs (as in the glands to be presently described) originate in irregular spaces, lymph- sinuses, or lacunse. There is no satisfactory evidence to prove that any natural communication exists between the lymphatics of glandular organs and their ducts, or between the lymphatics and the capillary vessels. 78 GENERAL ANATOMY. With respect to the structure of the Lymphatic Glands, there are some points which are certain, while others must be allowed to be doubtful. It is certain that a number of vessels enter them at various points of their circumference {afferent vessels), and that one or two vessels leave them {efferent vessels), usually at a definite spot, the hilum. Further, that the external coats of these vessels are continuous with an envelope of fibrous tissue, which constitutes the capsule of the gland, and that all parts of the gland are freely supplied with capillary bloodvessels. The intimate structure, however, of the gland, is a matter of some doubt. In former editions of this work, the description of Hewson was adopted, according to which the afferent vessels break up into a plexus of smaller vessels, and these reunite to form the efferent vessels, so that the afferent and efferent lymphatics are directly continuous. Some observers added to this description, that there were a number of minute dotted cor- puscles lying between the meshes of the network of vessels in the interior of the gland, and grouped in cells like the acini of secreting glands. But the description given by His and Kolliker, and which has been adopted by Dr. Sharpey, makes the structure more complex than this. It is, in brief, as follows: Passing inwards from the capsule of the gland are a number of septa or trabeculae, fibrous in man, muscular in some of the lower animals, which separate the outer or cortical portion of the gland into alveoli. The afferent vessels break up and open into these alveoli, much in the same way that the splenic capillaries open into the pulp of that organ. The alveoli contain a grayish-white pulp, consisting, according to Kolliker, of the minutest ramifica- tions of fibrous tissue, and of a juice, containing round cells identical with those of the chyle or lymph. The interior of the gland {medullary portion) is formed of a number of vascular channels (together with capillaries and connective tissue), which are the radi- cles of the efferent vessels, and converge to the hilum. The cortical portion is usually deficient at the hilum, where the medullary tissue of the gland passes directly into the efferent channels. The afferent lymphatics, after passing at various points through the capsule, break up in the septa between the alveoli into their terminal ramifications; and here, as Kolliker supposes, they open into those spaces just as the arteries of erectile tissue do into the cavernous spaces of which that tissue is composed. From the walls of the alveoli lymphatic channels can again be traced, which are the radicles of the efferent vessels, and accompany the arterial branches. The gland-pulp does not completely fill the alveoli of the cortical, nor the vascular channels of the medullary portion, but leaves a space, visible in sec- tions from which the lymph-corpuscles have been washed away. This space is called the lymph-simis ; but it seems to be distinguished from the rest of the alveolus merely by a less close arrangement of the connective tissue, through which the lymph circulates. Dr. Sharpey describes the lymph-sinus as lined throughout by a layer of pavement-epithelium similar to that of the lymphatic vessels with which it is continuous. The arteries and veins pass into and out of the gland at the hilum, and Kol- liker has described some fine nervous filaments, as accompanying them. THE SKIN AND ITS APPENDAGES. The Skin is the principal seat of the sense of touch, and may be regarded as a covering for the protection of the deeper tissues; it is also an important excretory and absorbing organ. It consists of two layers, the derma or cutis vera, and the epidermis or cuticle. On the surface of the former layer are the sensitive papillae; and within, or imbedded beneath it, are the sweat-glands, hair-follicles, and sebaceous glands. The derma, or true skin, is tough, flexible, and highly elastic, in order to de- fend the internal parts from violence. It consists of fibro-areolar tissue, inter- THE SKIN. 79 mixed with numerous bloodvessels, lymphatics, and nerves. The flbro-areolar tissue form's the framework of the cutis; it is composed of firm interlacing bundles of white fibrous tissue, intermixed with a much smaller proportion of yellow elastic fibres, the amount of which varies in different parts. The fibro- areolar tissue is more abundant in the deeper layers of the cutis, where it is Fig. 41. S^,^i. A sectional view of the skin (mngnified). dense and firm, the meshes being large, and graduall}' becoming blended with the subcutaneous areolar tissue; towards the surface, the fibres become finer and more closely interlaced, the most superficial layer being covered with numerous small conical vascular eminences, the papillae. From these differ- ences in the structure of the cutis at different parts, it is usual to describe it as consisting of two layers ; the deeper layer or corium, and the superficial or papillary layer. The corium consists of strong interlacing fibrous bands, composed chiefly of the white variety of fibrous tissue; but containing, also, some fibres of the .yellow elastic tissue, which vary in amount in different parts. Towards the attached surface, the fasciculi are large and coarse ; and the areolae which are left by their interlacement are large, and occupied by adipose tissue and the sweat-glands. This element of the skin becomes gradually blended with the subcutaneous areolar tissue. Towards the free surface, the fasciculi are much finer, and they have a closer interlacing, the most superficial layers consisting of a transparent, homogeneous matrix, with imbedded nuclei. The corium varies in thickness, from a quarter of a line to a line and a half, in different parts of the body. Thus, it is thicker in the more exposed regions, as the palm of the hand and sole of the foot; on the posterior aspect of the body, than the front ; and on the outer, than the inner side of the limbs. In 80 GENERAL ANATOMY. the eyelids, scrotum, and penis, it is exceedingly thin and delicate. The skin generally is thicker in the male than in the female. The areolse are occupied by adipose tissue, hair-follicles, and the sudoriferous and sebaceous glands ; they are the channels by which the vessels and nerves are distributed to the more superficial strata of the corium, and to the papillary layer. Uhstriped muscular fibres are found in the superficial layers of Ihe corium, wherever hairs are found ; and in the subcutaneous areolar tissue of the scro- tum, penis, perineum, and areolse of the nipple. In the latter situations the fibres are arranged in bands, closely reticulated, and disposed in superimposed laminae. The papillary layer is situated upon the free surface of the corium : it con- sists of numerous small, highly sensitive, and vascular eminences, the papillae, which rise perpendicularly from its surface, and form the essential element of the organ of touch. The papillae are conical-shaped eminences, having a round or blunted extremity, occasionally divided into two or more parts, and con- nected by their base with the free surface of the corium. Their average length is about y^uth of an inch, and they measure at their base about jlijth of an inch in diameter. On the general surface of the body, more especially in those parts which are endowed with slight sensibility, they are few in number, short, exceedingly minute, and irregularly scattered over the surface; but in other situations, as upon the palmar surface of the hands and fingers, upon the plan- tar surface of the feet and toes, and around the nipple, they are long, of large size, closely aggregated together, and arranged in parallel curved lines, forming the elevated ridges seen on the free surface of the epidermis. In these ridges, the larger papillae are arranged in a double row, with smaller papillae between them ; and these rows are subdivided into small square-shaped masses by short transverse furrows, regularly disposed, in the centre of each of which is the minute orifice of the duct of a sweat-gland. No papillae exist in the grooves between the ridges. In structure, the papillae resemble the superficial layer of the cutis ; consisting of a homogeneous tissue, faintly fibrillated, and contain- ing a few fine elastic fibres. The smaller papillse contain a single capillary loop : but in the larger the vessels are convoluted to a greater or less degree ; each papilla also contains one or more nerve-fibres, but the mode in which these terminate is uncertain. In those parts in which the sense of touch is highly developed, as in the lips and palm of the hand, the nerve-fibres are con- nected with the "tactile corpuscles." Kolliker considers that the central part of the papillae generally consists of a connective tissue more homogeneous than that of the outer part, surrounded by a sort of sheath of elastic fibres, and he believes that these corpuscles are merely a variety of this structure. The cor- puscles, and their connection with the nerves, have been described above. The epidermis, or cuticle (scarfskin), is an epithelial structure, accurately moulded on the papillary layer of the derma. It forms a defensive covering to the surface of the true skin, and limits the evaporation of watery vapor from its free surface. It varies in thickness in different parts. Where it is exposed to pressure and the influence of the atmosphere, as upon the palms of the hands and soles of the feet, it is thick, hard, and horny in texture ; whilst that which lies in contact with the rest of the body, is soft and cellular in structure. The deeper and softer layers have been called the rete mticosum, the term reie being used from the deepest layers presenting, when isolated, numerous depressions, or coTnplete apertures, which have been occupied by the projecting papillae. The free surface of the epidermis is marked by a network of linear furrows of variable size, marking out the surface into a number of spaces of polygonal or lozenge-shaped form. Some of these furrows are large, as opposite the flex- ures of the joints, and correspond to the folds in the derma produced by their movements. In other situations, as upon the back of the hand, they are ex- ceedingly fine, and intersect one another at various angles: upon the palmar APPENDAGES OF THE SKIN. 81 surface of tlie hand and fingers, and upon the sole, these lines are very distinct, and are disposed in curves. They depend upon the large size and peculiar arrangement of the papillaa upon which the epidermis is placed. The deep surface of the. epidermis is accurately moulded upon the papillary layer of the derma, each papilla being invested by its epidermic sheath ; so that when this layer is removed by maceration, it presents a number of pits or depressions corresponding to the elevations of the papillte, as well as the furrows left in the intervals between them. Fine tubular prolongations from this layer are continued into the ducts of the sudoriferous and sebaceous glands. In struc- ture, the epidermis consists of flattened cells, agglutinated together, and having a laminated arrangement. In the deeper layers the cells are large, rounded, or columnar, and filled with soft opaque contents. In the superficial layers the cells are flattened, transparent, dry, and firm, and their contents converted into a kind of horny matter. The difference in the structure of these layers is dependent upon the mode of growth of the epidermis. As the external layers desquamate, from their being constantly subjected to attrition, they are repro- duced from beneath, successive layers gradually approaching towards the free surface, which, in their turn, die and are cast off. These cells are developed in the liquor sanguinis, which is poured out on the free surface of the derma ; they contain nuclei, and form a thin stratum of closely-aggregated nucleated cells, which cover the entire extent of the papil- lary layer. The deepest layer of cells, according to Kdlliker, are of a columnar form, and are arranged perpendicularly to the free surface of the derma, form- ing either a single or a double, or even triple, layer; the laminae succeeding these are composed of cells of a more rounded form, the contents of which are soft, opaque, granular, and soluble in acetic acid. As these cells successively approach the surface by the development of fresh layers from beneath, they assume a flattened form from the evaporation of their fluid contents, and finally form a transparent, dry, membranous scale, lose their nuclei, and apparently become changed in their chemical composition, as they are unaffected now by acetic acid. The black color of the skin in the negro, and the tawny color among some of the white races, is due to the presence of pigment in the cells of the cuticle. This pigment is more especially distinct in the cells of tiie deeper layer, or rete mucosum, and is similar to that found in the choroid. As the cells approach the surface and desiccate, the color becomes partially lost. The arteries which supply the skin divide into numerous brandies in the subcutaneous tissue; they then pass through the areolae of the corium, and divide into a dense capillary plexus, which supplies the sudoriferous and seba- ceous glands and the hair-follicles, terminating in the superficial layers of the corium, by forming a capillary network, from which numerous fine branches ascend to the papillae. The lymphatic vessels are arranged in a minute plexiform network in the superficial layers of the corium, where they become interwoven with the capil- lary and nervous plexuses; they are especially abundant in the scrotum and round the nipple. The nerves which supply the skin ascend with the vessels through the areolaa of the deep layers of the corium to the more superficial layers, where they form a minute plexiform mesh. From this plexus the primitive nerve-fibres pass to be distributed to the papillae. The nerves are most- numerous in those parts which are provided with the greatest sensibility. The appendages of the skin are, the Nails, the Hairs, the Sudoriferous and Sebaceous Glands, and their ducts. The nails and hairs are peculiar modifications of the epidermis, consisting essentially of the same cellular structure as that membrane. The Nails are flattened, elastic structures, of a horny texture, placed upon 6 82 GENERAL ANATOMY. the dorsal surface of the terminal phalanges of the fingers and toes. Bach nail is convex on its outer surface, concave within, and is implanted by a portion called the root into a groove of the skin; the exposed portion is called the body, and the anterior extremity the free edge. The nail has a very firm adhesion to the cutis, being accurately moulded upon its surface, as the epidermis is in other parts. The part of the cutis beneath the body and root of the nail is called the matrix, because it is the part from which the nail is produced. Correspond- ing to the body of the nail, the matrix is thick, and covered with large, highly vascular papillae, arranged in longitudinal rows, the color of which is seen through the transparent tissue. Behind this, near the root of the nail, the papillae are small, less vascular, and have no regular arrangement; hence, the portion of the nail corresponding to this part is of a whiter color, and called lunula, from its form. The cuticle, as it passes forwards on the dorsal surface of the finger, is at- tached to the surface of the nail, a little in advance of its root. At the ex- tremity of the finger it is connected with the under surface of the nail, a little behind its free edge. The cuticle and horny structure of the nail (both epi- dermic structures), are thus directly continuous with each other. The nails, in structure, consist of cells having a laminated arrangement, and these are essen- tially similar to those composing the epidermis. The deepest layer of cells which lie in contact with the papillae at the root and under surface of the nail, are of elongated form, arranged perpendicularly to the surface, and provided with nuclei; those which succeed these are of a rounded or polygonal form, the more superficial ones becoming broad, thin, and flattened, and so closely com- pacted together as to make the limits of each cell very indistinct. It is by the successive growth of new cells at the root and under surface of the body of the nail, that it advances forwards, and maintains a due thickness, whilst, at the same time, the growth of the nail in the proper direction is secured. As these cells in their turn become displaced by the growth of new cells, they assume a flattened form, lose their nuclei, and finally become closely compacted together into a firm, dense, horny texture. In chemical composition, the nails resemble the epidermis. According to Mulder, they contain a some- what larger proportion of carbon and sulphur. The Hairs are peculiar modifications of the epidermis, and consist essentially of the same structure as that membrane. They are found on nearly every part of the surface of the body, excepting the palms of the hands and soles of the feet, and vary much in length, thickness, and color, in difi^erent parts of the body, and in difierent races of mankind. In some parts they are so short as not to project beyond the follicles containing them; in other parts, as upon the scalp, they are of considerable length; along the margin of the eyelids and upon the face, they are remarkaljle for their thickness. A hair consists of a root, the part implanted in the skin; the shaft, the portion projecting from its surface, and the point. They generally present a cylindrical or more or less flattened form, and a reniforin outline upon a transverse section (Fig. 42). The root of the hair presents at its extremity a bulbous enlargement, which is whiter in color, and softer in texture than the stem, and is lodged in a follicular involution of the epidermis, called the hair-foUivle. When the hair is of con- siderable length, the follicle extends into the subcutaneous cellular tissue. The hair-follicle is bulbous at its deep extremity, like the hair which it contains, and has opening into it, near its free extremity, the orifices of the ducts of one or more sebaceous glands. In structure, the hair-follicle consists of two coats — an outer or dermic, and an inner or cuticular. The outer coat is formed mainly of areolar tissue; it is continuous with the corium, is highly vascular, and supplied by numerous minute nervous filaments. The inner or cuticular lining is continuous with the epidermis, and, at the bottom of the hair-follicle, with the root of the hair; this cuticular lining resembles the epidermis in the peculiar rounded form and soft character of those cells which lie in contact SEBACEOUS GLANDS. 83 •witli the outer coat of the hair-follicle, and the thin, dry, and scaly character of those which lie near the surface of the hair, to which they are closely adhe- rent. When the hair is plucked from its follicle, this cuticular lining most commonly adheres to it, and forms what is called the root-sheath. At the bottom of each hair- follicle is a small conical vascular eminence or papilla, similar in every respect to those found upon the surface of the skin ; it is continuous with the dermic layer of the follicle, is highly vascular, and probably supplied with nervous fibrils. This is the part through which material is supplied for the production and constant growth of the hair. The root of the hair rests upon this conical-shaped eminence, and is con- tinuous with the cuticular lining of the follicle at this part. It consists of nucleated cells, simi- lar in every respect to those which in other situations form the epidermis. These cells gradually enlarge as they are pushed upwards into the soft bulb, and some of them contain pigment granules, which either exist in separate cells, or are separate, or aggregated round the nucleus ; it is these granules which give rise to the color of the hair. It occasionally happens that these pigment-granules completely fill the cells in the centre of the bulb, which gives rise to the dark track of pigment often found, of greater or less length, in the axis of the hair. The shaft of the hair consists of a central part or medulla, the fibrous part of the hair, and the cortex externally. The medulla occupies the centre of the shaft, and ceases toward the point of the hair. It is usually wanting in the fine hairs covering the surface of the body, and com- monly in those of the head. It is more opaque and deeper colored than the fibrous part, and consists of cells containing pigment or fat-gran- ules. The fibrous portion of the hair constitutes the chief part of the stem ; its cells are elongated, and unite to form flattened fusiform fibres. These also contain pigment granules, which assume a linear arrangement. The cells which form the cortex of the hair consist of a single layer which surrounds those of the fibrous layer; they are converted into thin flat scales, having an imbricated arrangement. The Sebaceous Glands are small, sacculated, glandular organs, lodged in the substance of the corium, or subdermoid tissue. They are found in most parts of the skin, but are most abundant in the scalp and face; they are also very numerous around the apertures of the anus, nose, mouth, and external ear; but are wantiog in the palms of the hands and soles of the feet. Bach gland con- sists of a single duct, more or less capacious, which terminates in a lobulated pouch-like extremity. ' The basement membrane forming the wall of the sac, as well as the duct, is lined by epithelium, which is filled with particles of se- baceous matter ; and this becoming detached into the cavity of the sac, as its growth is renewed, constitutes the secretion. The sacculi connected with each duct varv in number from two to five, or even twenty. The orifices of the ducts open most frequently into the hair-follicles, but occasionally upon the general surface. On the nose and face, the glands are of large size, distinctly lobulatedj^and often become much enlarged from the accumulation of pent-up Diagram of straoture of hair, hair follicle, and sebaceous glands (Kolliker). a. Root of hair, in its follicle. 1. Outer dry layer of cuticle. 2. Malpighian or mucous layer, both dipping into hair sac. 3. Cutis, or true Bkin. 4. Sebaceous glands, opening into hair sac. 5. Root of hair. 6. Walls of hair sac. 7. Papilla, on which hair grows, b. Larger view of lower end of root of hair, and bottom of hair sac. 6. Hair sac, showing outer and inner root-sheath, latter adhering to hair. 7. Vascular papilla on which hair grows. The hair itself shows its fibrous structure, its dark medulla, and transverse lines of its scaly covering, c. Transverse section of a hair, showing its outer covering, its fibrous part, and central softer medulla or pith.] 84 GENERAL ANATOMY. secretion. The largest sebaceous glands are those found in the eyelids, the Meibomian glands. The Sudoriferous or Sweat- Glands are the organs by which a large portion of the aqueous and gaseous materials are excreted by the skin. They are found in almost every part of the skin, and are situated in small pits in the deep parts of the corium, or in the subcutaneous areolar tissue, surrounded by a quantity of adipose tissue. They are small, lobular, reddish bodies, consisting of one or more convoluted tubuli, from which the efferent duct proceeds upwards through the corium and cuticle, and opens upon the surface by a slightly en- larged orifice. The efferent duct, as it passes through the corium, pursues, for a short distance, a spiral course, becoming straight in the more superficial part of this layer, and opens on the surface of the cuticle by an oblique valve-like aperture. In the parts where the epidermis is thin, the ducts are finer and al- most straight in their course; but where the epidermis is thicker, they assume again a spiral arrangement, the separate windings of the tube being as close and as regular as those of a common screw. The spiral course of these ducts is especially distinct in the thick cuticle of the palm of the hand and sole of the foot. The size of these glands varies. They are especially large in those regions where the amount of perspiration is great, as in the axillas, where they form a thin mammillated layer of a reddish color, which corresponds exactly to the situation of the hair in this region ; they are large, also, in the groin. Their ijumber varies. They are most numerous on the palm of the hand, pre- senting, according to Krause, 2800 orifices on a square inch of the integument, and are rather less numerous on the sole of the foot. In both of these situa- tions, the orifices of the ducts are exceedingly regular, and correspond to the small transverse grooves which intersect the ridges of papillae. In other situations they are more irregularly scattered, but in nearly equal numbers over parts in- cluding the same extent of surface. In the neck and back they are least nume- rous, their number amounting to 417 on the square inch (Krause). Their total number is estimated by the same writer at 2,381,248 ; and supposing the aperture of each gland to represent a surface of g'g of a line in diameter, he calculates that the whole of these glands would present an evaporating surface of about eight square inches. Each gland consists of a single tube intricately convoluted, terminating at one end by a blind extremity, and opening at the other end upon the surface of the skin. In the larger glands this single duct usually divides and subdivides dichotomously ; the smaller ducts ultimately terminating in short CEecal pouches, rarely anastomosing. The wall of the duct is thick; the width of the canal rarely exceeding one-third of its diameter. The tube, both in the gland and where it forms the excretory duct, consists of two layers ; an outer, formed by fine areolar tissue; and an inner layer of epithelium. The external, or fibro-cellular coat, is thin, continuous with the superficial layer of the corium, and extends only as high as the surface of the true skin. The epithelial lining is much thicker, continuous with the epidermis, and alone forms the spiral portion of the tube. When the cuticle is carefully removed from the surface of the cutis, these convoluted tubes of epidermis may be drawn out, and form nipple-shaped projections on its under surface. According to Kdlliker, a layer of non-striated muscular fibres, arranged longitudinally, is found between the areolar and epithelial coats of the ducts of the larger sweat-glands, as in the axilla, root of the penis, on the labia majora, and round the anus. The contents of the smaller sweat-glands are quite fluid; but in the larger !:rlands, the contents are semi-fluid and opaque, and contain a number of col- ored granules, and cells which appear analogous to epithelial cells. EPITHELIUM. 85 THE EPITHELIUM. All the surfaces of the body, the external surface of the skin, the internal surface of the digestive and respiratory tracts, the closed serous cavities, and the ducts of all glands, are covered by one or more layers of simple cells, called Epithelium or Epithelial Cells, which serve various purposes, both as a protec- tive layer, and as an agent in secretion. Thus, in the skin, the main purpose served by the epithelium (here called the epidermis) is that of protection. As the surface is worn away by the agency of friction or change of temperature, new cells are supplied, and thus the surface of the true skin, and the vessels and nerves which it contains, are defended from damage. In the gastro-intestinal mucous membrane and in the glands, the epithelial cells appear to be the prin- cipal agents in separating the secretion from the blood or from the alimentary fluids. In other situations (as the nose, fauces, and respiratory passages) the chief office of the epithelial cells appears to be to maintain an equable tempera- ture by the moisture with which they keep the surface always slightly lubri- cated. 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 insure a perfectly smooth surface. The epithelium is usually spoken of as tessellated or pavement, columnar, spheroidal or glandular, and ciliated. Fig. 43. Epithelial cells in the oral cavity of man. a. Large, i. Middle-sized, e. The same with two nuclei, (Magnified 350 times.) Ihe pavement epithelium is composed of flat nucleated scales of various shapes, usually polygonal, and varying in size. These scales often contain granules, as Fig. 44. Fig. 45. Epithelium of the intestinal villi of the rabhit. a. Base- ment-membrane. (Magnified 300 times.) Spheroidal epithelium from the human bladder. (Magnified 350 times.) in Fig. 43. This kind of epithelium is found on the surface of the skin (the epidermis), on all the serous surfaces (unless the ventricles of the brain be aa 86 GENERAL ANATOMY. exception), on the lining membranes of the bloodvessels, on many of the mucous membranes, and in the ducts. The nails, hairs, and in animals the horns, are a variety of this kind of epithelium. The columnar epithelium (Fig. 44) is formed of cylindrical or rod-shaped cells, each containing a nucleus, and set together, so as to form a complete membrane. This form of epithelium covers the mucous membrane of the whole gastro- intestinal tract and the glands of that part, the greater part of the urethra, the vas deferens, the prostate, Cowper's glands, Bartholine's glands, and a portion of the uterine mucous membrane. The spheroidal or glandular epithelium (Fig. 45) is composed of circular cells, "with granular contents and a small nucleus. This form is found in the kidney, ureters, and bladder, and in the secreting glands. Ciliated epithelium (Fig. 46) may be of any of the preceding forms, but usually inclines to the columnar shape. It is distinguished by the presence of minute Fig. 46. Simple conoidal ciliated epithelium. h. Cilia and their free extremities.] a. Nucleated cells. processes, like hairs or eyelashes (cilia), standing up from the free surface (Fig. 47). If the cells be examined during life, or imme- diately on removal from the living body (for which in the human subject the removal of a nasal polypus offers a frequent opportunity), in tepid water, the cilia will be seen in active lashing motion, and if the cells be separate, they will often be moved about in the field by that motion. The situations in which ciliated epithelium is found in the human body are : the respiratory tract from the nose downwards, the tympanum and Eu.stachian tube, the Fallopian tube and upper portion of the uterus, and the ventricles of the brain. Ciliated epithelium, from the humau tra- chea. (Mngnified .S50 times.) u. Innermost layers of the elastic longitudinal fibres, b. Homogeneous innermost layers of the mu- cous membrane, c. Deepest round cells, d. Middle, elongated, c. Superficial, hearing cilia. SEEOUS, SYNOVIAL, AND MUCOUS MEMBRANES. These membranes consist of a layer of epithelium supported on a structure- less membrane, called the basement membrane, beneath which lies a tract of connective or areolar tissue, which in the mucous membranes lodges glands of various kinds, and contains unstriped muscle, or contractile muscular fibre- cells, and in both serous and mucous membranes conveys the bloodvessels out of which the secretion is to be eliminated. The Serous Membranes are the simplest of the three, and will tljerefore be first described. They form shut sacs, sometimes arranged quite simply, as the tunica vaginalis testis, at others with numerous involutions and recesses, as the peritoneum, but which can always be traced continuously around the whole circumference. The sac is completely closed, so that no communication exists between the serous cavity and the parts in its neighborhood. An apparent exception exists in the peritoneum of the female; for the Fallopian tube opens freely into the perito- neal cavity in the dead subject, so that a bristle can be passed from the one into SECRETING GLANDS. SI the other. But this communication is closed during life, except at the moment of the passage of the ovum out of the ovary into the tube, as is proved by the fact that no interchange of fluids ever takes place between the two cavities in dropsy of the peritoneum, or in accumulation of fluid in the Fallopian tubes. The serous membrane is often supported by a firm fibrous layer, as is the case with the pericardium, and such membranes are sometimes spoken of as "fibro- serous." In the parietal portion of the arachnoid there is, according to many anatomists, no serous membrane in the proper sense of the term; but the dura mater is merely lined with a layer of epithelium, the basement-membrane being here indistinguishable. In other situations, the following parts may be recog- nized as constituting a serous membrane. 1. The epithelium, a single layer of polygonal or pavement-epithelial cells. 2. A structureless basement-membrane. 3. The connective tissue and vessels which support the latter, connect it with the parts below, and supply blood to its deep surface. Some of the serous portion of the blood is secreted, or transudes, through the basement-membrane to furnish the special secretion. This latter is, in most cases, only in sufficient quantity to moisten the membrane, but not to furnish any appreciable quantity of fluid. "When a small quantity can be collected, it appears to resemble in many respects the lymph, and like that fluid coagulates spontaneously, but when secreted in large quantities, as in dropsy, it is a watery fluid containing usually sufB.cient albumen to gelatinize with heat.' The Mucous Membranes are more complex in their structure than the serous. Their epithelium is of various forms, including the spheroidal, columnar, and ciliated, and is often arranged in several layers (see Fig. 46). This epithelial layer is supported by the corium, which is analogous to the derma of the skin; and is in fact continuous with it at the orifices of the body. The corium con- sists, as it is usually described, of a transparent structureless basementrmem- brane next to the epithelium, supported by a fibre- vascular layer of variable thickness below it, and this merging into the submucous areolar tissue. It is only in some situations that the basement-membrane can be demonstrated. The fibro-vascular layer of the corium contains, beside the white and yellow fibrous tissue and the vessels, muscular fibre-cells, nerves, and lymphatics, in various proportions. Imbedded in it are found numerous glands, and project- ing out of it are processes (villi and papillas) analogous to the papillse of the skin. These glands and processes, however, exist only at certain parts, and it will be more convenient to refer for their description to the sequel, where the parts are described in which they occur. Thus the mucous glands are described in the account of the mouth, the stomach, the intestines, &c., the papillae and villi with that of the tongue and the small intestine. The Synovial Membranes are analogous in structure to the serous, but differ from them in the nature of their secretion, which rather resembles mucus. They are described in connection with the Articulations. SECEBTIJSrG GLANDS. The Secreting Glands are organs in which the blood circulating in capillary vessels is brought into contact with the epithelial cells of a mucous membrane, whereby certain elements are separated ("secreted") out of the blood, and are poured into the mucous cavity. This cavity is arranged in the form of a rami- fying duet, the secreting cells lying in, or touching, the terminal ramifications (or more correctly the commencing radicles) of the duct. In size these glands vary extremely: thus the liver weighs nearly four pounds, while many of the mucous glands are only visible to the naked eye when distended with secretion ; and they vary not less in structure. Thus the ' The resemblance, between lymph and serum led Hewson to the belief that the serous cavities are sacs into which the lymphatics open. 88 GENERAL ANATOMY, [Fig. 48. structure of tbe liver is so complex that it can hardly yet be regarded as known with absolute certainty, while there are a great many glands which consist either of a single tube lined with epithelium, on the outer side of which the blood circulates, or even a simple closed sac which opens when it becomes charged with secretion. The great majority of glands, however, can be reduced ideally to a very simple form, viz., to an involution more or less complex of the basement- membrane, carrying of course its epithelium with it, and having the capillary vessels distributed on its attached surface (Fig. 48). If this involution be perfectly simple, an open tube results, as in the stomach (see Fig. 400), or the common mucous crypts of the urethra (Figs. 404, 406); and should the mouth of such a tube become closed, a simple follicle is formed, as in the intestine. Branches projecting out from the bottom of this tube con- stitute the simplest form of racemose gland. The most rudimentary condition of such a gland is shown in the branched tubes of the gastric mu- Three plans, a, I, c, of supposed sec- qqus membrane in Figure 400. If such a tube be t;onsof.ecretinginemi,raiies, to show gonceived of as divided into branches as well as general arraogement of their compo- ^^v^nohm^ OUt at its extremity, We have a COm- Dent structures, and the way m which -, -, -, . *^, . p . , ^, . r ■ 1 T 11 pound racemose gland consisting oi a single their surfaces are incre.iFerl. In all r . . °. . . ° 6 three plans, the broad shaded line re- lobule terminating lu its duct (such Es Bruuner's presents the areoio-vascniar layer, the glauds), and an aggregation of such lobules may thin solid line is the basement or limit- all Open into a common duct, or may have a great ing membrane, and the dotted line the number of Separate ducts. Instances of such epithelial or covering layer. «, shows glands will be fouud in the salivary glands, the pancreas, &c. Or the necessary extent of epithe- lial surface may be obtained by the duct being coiled on itself, as in the sweat-glands (Fig. 41, page 79), or the extremity of the duct only may be thus arranged (Fig. 370). In other glands, as in the kidney, the mucous duct is undivided from the beginning, and the capillaries from which the secretion is to be eliminated are dis- tributed upon its walls or project into its ampul- lated commencement (Fig. 335). an increase by simple plaited or fringed projections; h, fiye modes of increase by recesses, forming five kinds of sim- ple glands, viz., 1, a tubular follicle or crypt; 2, u saccular follicle or sac; .S, a coiled tube ; 4, a muUiloctilar tithe, that is, a tube with depressions in it ; 6, a tnultiloc^tlar sac. c, shows two forms of compound glands ; 6, branch- ed tubes forming a ctympoitnd tiibnlar gland; 7, briincbed tubes ending in little recesses or vesicles, forming a compoiiiid raceTnose or conglomerate gland. (After Sharpey.)] For the description of the Ductless or Blood Glands, we must refer to the sections in the text relating to the Anatomy of the Spleen, Suprarenal Capsules, Thyroid, and Thymus. Growth and Development of the Body. Fig. 49. Jto, Cermoial\ CtrmirLol spat'^ -J)itEUS^n^ Ovum of the sow. The whole body grows out of the fecundated ovum, and it is accordingly necessary to follow, in as few words as possible, the various stages in which the ovum is found in the uterus, from the earliest moment at which conception can be recognized as having taken place, down to the birth of the complete foetus. The ovum is a small spherical body, situated in immature Graafian vesicles near their centre, but in the mature ones in contact with the membrana granulosa (see Ovum in body of the work), at that part of the vesicle which projects from the surface of the ovary. The cells of the membrana granulosa are accumulated round the ovum in greater number than at any other part of the vesicle, forming a kind of granular zone, the discus proligerus (Fig. 49). The human ovum (Fig. 50) is extremely minute, measuring from ^j^ith to ^l^th of an inch in diameter. It is a cell, consisting externally of a transparent envelope, the zona pellucida or vitel- line membrane. Within this, and in close contact with it, is the yelk or vitellus ; imbedded in the substance of the yelk is a small vesicular body, the germinal vesicle (vesicle of Purkinje) — the nucleus of the cell ; and this contains as its nucle- olus a small spot — the macula germinativa, or the spot of Wagner. The zona pellucida, or vitelline membrane, is a thick, colorless, transparent membrane, which appears under the microscope as a bright ring, bounded externally and internally by a dark outline. It corresponds to the chorion of the impregnated ovum. The yelk consists of granules and globules of various sizes, imbedded in a more or less viscid fluid. The snialler granules resemble pigment; the larger granules, which are in greatest number at the periphery of the yelk, resemble fat-globules. In the human ovum, the number of granules is comparatively small. The germinal vesicle consists of a fine, trans- parent, structureless membrane, containing a watery fiuid, in which are occasionally found a few granules. It is about ,^5 of an inch in diameter, and in immature ova lies nearly in the centre of the yelk ; but, as the ovum be- comes developed, it approaches the surface, and enlarges much less rapidly than the yelk. The germinal spot occupies that part of the periphery of the germinal vesicle which is nearest to the periphery of the yelk. It is opaque, of a yellow color, and finely-granular in structure, measuring from jg'55 to j^'jg of an inch. The phenomena attending the discharge of the ova from the Graafian vesicles, since they belong as much or more to the ordinary functions of the ovary than to the general subject of the growth of the body, are described with the anatomy of the ovaries in the body of the work. 89 Fig. 50. Hurann ovum, from a middle-sized fol- licle (magnified 250 times), o. Vitelline membrane. Zo)m pelliicida. b. External border of the yelk and internal border of the vitelline membrane, c. Germinal vesi- cle and germinal spot. 90 GENERAL ANATOMY. The first changes in the ovum which take place upon conception, appear to be as follows: The spermatozoon penetrates the ovum/ the effect of which is to bring it into contact with the yelk, and with the germinal vesicle contained in the yelk. It seems as if this normally occurs in the Fallopian tube,^ and abnormally it may even take place in the peritoneal cavity. The first effect is to produce a cleavage and multiplication of the yelk, which becomes first cleft Fig. 51. Four diagrams to show the division of the yelk. The ovum is surrounded by spermatozoa, corpuscles (polar globules of Robin) are seen in the first two. The clear into two masses, then into four, and so on, until at length a mulberry-like agglomeration of nucleated cells results (Fig. 51). It appears probable that this proliferation is due to some change in the germinal vesicle and its nucleolus, but the nature of such change has not been made out. Some observers describe it as consisting simply in the cleavage of the vesicle and nucleolus, others in their disappearance and replacement by a fresh cell, or nucleus, the embryo-cell, around which the yelk gathers. In this view the fer- tilization of the yelk is due to the solution of the germinal vesicle under the action of the spermatozoon. There are also found within the vitelline membrane one or more clear globules, called "polar globules," by Eobin, because they lie near one of the poles of segmentation. The nature, origin, and uses of these bodies are not known. They seem to be usually regarded as produced by the liquefaction of the yelk, and as not being essential to the process of fructification. The globules of which the yelk is now composed soon arrange themselves into the form of a membrane lined with pavement-epithelium. As the yelk- mass softens, fluid accumulates in the interior of this membrane, spreading it out on the internal surface of the vitelline membrane. The latter (external) membrane (Fig. 53) soon becomes covered with granulations or vegetations, giving it a shaggy appearance, and then takes the name of the "primitive chorion," whilst the internal membrane is called the " blastodermic vesicle." The blastodermic membrane soon afterwards splits into two layers, the division proceeding from the point where the thickening or aggregation next to be described as the germinal area occurs, and extending gradually over the whole circumference of the ovum, which now consists of three concentric layers of membrane — the external, the primitive chorion, the middle, the external layer of the blastodermic vesicle, and the inner, its internal layer. The annexed figure shows this division commencing. It is said that the ovum is in this condition at about eight days, but no observations of the human ovum at so early a period exist. The internal layer of the blastodermic mem- brane next separates into two at the situation of the area germinativa. The membrane which results from this separation is called the middle layer of the germinal or blastodermic membrane, and is distinguished from the others in not being coextensive with the embryo, but existing only at the germinal area. ' See Newport Phil. Trans. 1853, vol. ii. p. 233. This has been since confirmed by other observers on various lower animals, and may be assumed to be generally true. 2 Many physiologists, as Bischoff and Dr. M. Barry, believe that the ovum is fecundated in the ovary, but the reasoning of Dr. Allen Thomson appears very cogent in proving that the usual spot at which the spermatozoon meets with the ovum is in the tube. THE AMNION, 91 Germinal area. — In the mass of nucleated cells into which the yelk becomes converted during the formation of the blastodermic vesicle, a small agglome- ration is formed, which then spreads out into an area of nucleated cells, from which the em- ^ig- 62. bryo is to be formed, and which has accord- ingly received the name of germinal disk or area germinativa. In this portion of the ovum the first trace of the embryo appears as a faint streak, which is called the primitive trace or primitive groove. This groove first deepens into a furrow, bounded by two plates — the laminse dorsales, beneath which a delicate fibril appears — the chorda dorsalis or notochord — in which cartilage can very early be recognized, and which forms the future spinal column. The germinal disk is found to consist on a transverse section of three layers; an upper «-- with the germinal area .een in ^ , T, 1 /. t\ profile to show the division of the blag- (external), or serous; a lower (internal), or todermb membrane, l. Vitelline mem- mucous ; and a middle layer, which is formed brane. 2. Blastoderm. Germinal area. from the mucous lamina, as above shown. i. Plaoe where the blastoderm is just di- The chorda dorsalis and the laminae dorsales vided into its two layers. are the rudiments of the vertebral column and canal. The upper or serous layer of the embryo gives origin to the cere- bro-spinal nervous centres, and to the organs of the senses, including the cuticle and its appendages, as also to the mammary glands. From the middle layer are developed the locomotive organs, the spinal and sympathetic nerves, the vascular system, the ductless glands, the sexual organs, the cutis, where the middle layer touches on the external, and the muscular and submucous coats of the intestines, where it touches on the internal layer. The latter fur- nishes the lining of the alimentary canal and its various appendages, liver, pancreas, &c., the respiratory organs, and the urinary organs. Besides this, however, there are three appendages to the ovum, which must now be described as the amnion, the umbilical vesicle, and the allantois. Formation of the Amnion. — The amnion is formed from the external germinal layer, which is drawn in on all sides by the changes of shape of the embryo. The embryo as it grows becomes curved at its anterior and posterior end, so as to form the cephalic and caudal Jlexures (Fig. 54, B); it also curves on itself laterally towards the umbilicus (Fig. 53, 7), and as it does so, it draws the ex- ternal germinal layer with it, forming double folds which meet at the umbili- cus, and at a point opposite to the umbilicus on the dorsal aspect of the embryo, sometimes called "the posterior umbilicus" (Fig. 54, 8'), and finally communi- cate so as to form a delicate closed sac, into which a serous fluid — the liquor amnii — is secreted. This fluid increases in quantity up to about the end of the fifth or the sixth month, when it reaches the amount of about two pints. Thence it diminishes, and at the end of pregnancy is about half its maximum quantity. The outer layer of the amnion incloses all the parts of which the embryo consists, and is in contact externally with the chorion. The portion of the external germinal layer which does not take part in the formation of the amnion is called the vesicula serosa (Fig. 54, 2'). When the sac of the amnion is completely closed, the vesicula serosa becomes detached from it, and then forms an envelope to the ovum, lining the primitive chorion. Its future destination appears to be to form the epithelial layer of the secondary or permanent chorion. The allantois (Fig. 54, at) is a projection from near the hinder part of the embryo, formed by the middle and internal germinal layers, and therefore con- tinuous with the intestinal cavity. The lower part of this cavity becomes the GENERAL ANATOMY. Fig. 53.' Diagrams to show the deyelopment of the three layers of the hlastodermio membrane on transverse sec- tions. A. Portion of the ovum with the zona pellucida and the germinal area. B C D E F G-. Different stages of development, o. Umbilical vesicle. «.. Amnion, i. Intestine, p. Peritoneal cavity. 1. Vitelline membrane. 2. External blastodermic layer. 3. Middle layer. 4. Internal layer. 5. Medullary laminse and groove. 6'. Medullary canal. 6. Epidermic laminse. 7. Lateral flexures of the amnion. 7'. The same almost in contact. 8. Ini-ernal epithelial layer of the amnion. 9. Epidermis of the embryo. 10. Chorda dorsalis. 11. Vertebral laminse. 12. Protovertebras proper. 13. Muscular laminae. 14. Lateral laminse. 15. Fibro-intestinal laminae. 16. Cutaneous lamina. 17. Internal fibrous layer of the umbilical vesicle. 18. Muscular laminse extending to meet the cutaneous. 19. External layer Af the cutaneous laminae. 20. Internal layer of the same. 21. Mesentery. 22. Fibrous layer of the intestine. ' The dotted lines indicate the parts belonging to the internal blastodermic layer ; the plain lines those belon"-ing to the middle ; the interrupted lines those belonging to the external. THE CHORION— THE DECIDUA. 93 UTO-geniial sinus, and it is to the urinary tract that the allantois mainly belongs. It projects out from the embryo through the same opening as the vitelline or umbilical duct. The Ipwer part of the allantois which is contained within the embryo becomes the bladder ; the upper part of its intra-embryonic portion is denominated the urachus; the extra-embryonic portion is divided into two parts, called the allantoic vesicle, or the epithelial portion of the allantois, and the fibrous or vascular portion. The allantois, which is at first a simple serous membrane, becomes vascular over its whole extent about the fifth week, and its vessels communicate, as will be described presently, with those of the cho- rion, forming the vascular connection between the mother and foetus. In the human foetus the allantoic vesicle is small, soon withers and disappears, and its vessels are soon limited to the two umbilical arteries and one vein. The allantoic fluid is alkaline, and contains from one to four per cent, of solid matters — uric acid, urea, allantoin, sugar, and saline matters. Umbilical Vesicle (Figs. 53, 54, o). — The embryo itself in the earliest recog- nizable condition is, above stated, a mere streak, but it soon becomes curved at either end, corresponding to the head and lower extremity of the future animal (the tail of animals, the buttocks and lower limbs in man); the lower part is, however, open, and from this a body projects which at first consists of the matter into which the yelk has been developed (yelk-sac), and later on is con- verted into a vesicular body filled with clear fluid (the umbilical vesicle), and communicating with the body of the embryo by a constriction, the umbilical duct, opening at first into the intestinal cavity. As the development of the intestine proceeds, this canal is closed, and the umbilical vesicle is then a closed sac, lying external to the amnion. It is formed mainly by the internal germi- nal layer, but has a lining derived from the middle layer. As the arteries developed in the middle layer grow they cover the umbilical vesicle, forming th(s vascular area, the chief vessels of which are the omphalo-mesenteric, two in number. The vessels of this area appear to absorb the fluid of the umbilical vesicle, whicb dries up into a disk-like body attached to the amnion, and hav- ing no further function. The activity of the umbilical vesicle ceases about the same time (fifth or sixth week) as the allantois is formed. In fact, the umbilical vesicle provides nutrition to the foetus from the ovum itself, while the allantois is the channel whereby nutrition is conveyed to it from the uterine tissues. The \imbilical vesicle, however, is visible, containing fluid up to the fourth or fifth month, between the amnion and the chorion, with its pedicle and the omphalo-mesenteric vessels. The latter vessels then become atrophied, as the functional activity of the body with which they are connected ceases. The Chorion (Figs. 55, k, and 56). — The jmmitive chorion has already been described. It is formed by the vitelline membrane, which becomes covered with shaggy villous processes, and disappears about the fifteenth day, to give place to the secondary or permanent chorion. The latter is composed of two lamellas, the external one of which is furnished by the vesicula serosa (or false amnion), and the internal by the fibrous layer of the allantois. This latter furnishes a vascular membrane, which is applied to the epithelial layer of the chorion (vesicula serosa) (Fig. 54, 13, 14, 15). As the latter becomes villous by the development of tufts upon it (shaggy chorion), the bloodvessels of the internal layer pass into those tufts, forming the foetal portion of the placenta, and dipping through the decidua into the uterine sinuses of the maternal placenta. The Decidua (Figs. 54, 55) is formed from the mucous membrane of the uterus. Even before the arrival of the fecundated ovum in the uterus, the mucous membrane of the latter becomes vascular and tumid, and when the ovum has reached the uterus, it is imbedded in the folds of the mucous membrane, which overlap, and finally completely encircle the ovum. Thus two portions of the uterine mucous membrane (decidua) are formed — viz., that which coats 94 GENERAL ANATOMY Mg. 54.' Diagrams to phow the development of the threa blastodermic layers on antero-posterior sections. A. por- tion of ovum with the vitelline membrane and germinal area. B C D E F. Various stages of development. G. Ovum in the uterus and formation of decidua. 1. Vitelline membrane. 2. External blastodermic layer. 2'. Vesicula serosa. 3. Middle blastodermic layer. 4. Internal layer. 5. Vestige of the future embryo. B. Cephalic flexure of the amnion. 7. Caudal flexure. 8. Spot where the amnion and vesicula serosa are continuous. 8'. Posterior umbilicus. 9. Cardiac canity. 10. External fibrous layer of the umbilical vesicle. 11. External fibrous layer of the atnnion. 12. Internal layer of the blastoderm forming the intestine. IH. 14. External liiyer of the allantois, e.xtending to the inner surface of the vesicula serosa. 15. The same now completely applied to the inner surface of the vesicula serosa. 16. Umbilieal cord. 17. Umbilical vessels^ 18. Amnion. 19. Chorion. 20. Foetal placenta. 21. Mucous membrane of uterus. 22. Maternal pla. centa. 28 Decidua reflexa. 24 Muscular wnli of uterus. The same note applies to this as to the preceding diagram. THE PLACENTA. 95 the muscular wall of the uterus, decidna vera, and that which is in contact with the ovum, dccidua reflexa. The decidua does not extend into the neck of the uterus, which after conception is closed by a plug of mucus. The decidua vera is perforated by the openings formed by the enlarged uterine glands, which become much hypertrophied and de- veloped into tortuous tubes. It con- tains at a later period numerous arteries and venous channels, continuous with the uterine sinuses, and it is from it that the uterine part of the placenta is developed. The portion of the de- cidua vera which takes part in the for- mation of the placenta is called "de- cidua serotina." The decidua reflexa is shaggy on its outer aspect, but smooth within. The vessels which it contains at first dis- appear after about the third month; about the fifth or sixth month the space between the two layers of the decidua disappears, and towards the end of pregnancy the decidua is trans- formed into a thin yellowish mem- brane, which constitutes the external envelope of the ovum. The Placenta is the organ by which the connection between the foetus and mother is maintained, and through which blood reaches the foetus and is returned to the uterus. It therefore subserves the purposes both of circu- lation and respiration. It is formed of two parts, as already shown, viz., the maternal portion which is devel- oped out of the decidua vera (sero- tina), and the fcetal placenta formed by the villous chorion. Its shape in the human subject is that of a disk, one side of which adheres to the uterine walls, while the other is covered by the amnion. The villi of the chorion (or foetal placenta) gradually enlarge, forming large projections — '■'■cotyledons'^ — which each contain the ramifications of vessels communicating with the umbi- lical arteries and veins of the foetus. Tliese vascular tufts are covered with epithelium, and project into corresponding depressions in the mucous mem- brane of the uterine walls. The maternal portion of the placenta consists of a large number of cells formed by an enlargement of the vessels of the uterine wall, and conveying the uterine blood into close proximity to the villi of the foetal placenta, which dip into these cells. The interchange of fluids, necessary for the growth of the foetus, and the depuration of the blood, take place through the walls of these villi, but there is no direct continuity between the maternal and foetal vessels. The arteries open into the placental cells somewhat after the manner of the erectile tissue. The veins anastomose freely with one another, and give rise at the edge of the placenta to a venous channel which runs aroun'J it.s whole circumference — the placental sinus. Sectional plan of the gravid uterus, from Wagner, in the third and fourth month, u. Plug of mucus in necli of uterus, b. Fallopian tube. c. The decidua vera ; c\ The decidua vera passing into, the right Fallopian tube. The cavity of the uterus ia almost completely occupied by the ovum, e e. Points of the reflection of the decidua reflexa (in nature the united deciduse do not stop here, but pass over the whole uterine surface of the placenta), g. Supposed allan- tois. h. Umbilical vesicle, i. Amnion. Jc. Chorion, covered with the decidua reflexa. d. Cavity of the decidu.a. f, Decidua serotina, or placental decidua. 9G GENERAL ANATOMY. The umbilical cord appears about the end of the fifth month after pregnancy. It consists of the coils of two arteries (umbilical) and a single vein, united to- gether by a gelatinous mass (gelatin of Wharton) contained in the cells of an areolar structure. There are originally two umbilical veins, but one of these vessels becomes obliterated, as do also the two omphalo-mesenteric arteries and veins, and the duct of the umbilical vesicle, all of which are originally con- tained in the rudimentary cord. The permanent structures of the cord are therefore those furnished by the allantois. Oroivth of the Embryo. — The youngest human embryos which have been met with are two described by Dr. A. Thomson, in the "Edinb. Med. and Surgical Journal, 1839," and in his paper references to the other extant descriptions of early ova will be found. The ova in question were believed to be of the ages re- spectively of twelve to fourteen days, and about fifteen days.' The figures are here reproduced. The earliest ovum (Fig. 56) was -^^ of an inch in diameter, when freed from some adherent decidua. The chorion presented a slightly villous ap- Fig. 57. Kg. 58. Human ovum, 12 to 14 days. 1. Natural size. 2 Enlarged. Human ovum, 15 days. Embryo from the preceding ovum. 1. Umbilical vesicle. 2. Medullary groove. 3. Cephalic por- tion of the embryo. 4. Caudal portion. 5. Frag- ment of membrane (amnion?). pearance, and consisted only of one layer of membrane. On opening it the um- bilical vesicle and embryo were found not to fill its cavity completely. The embryo was a line in length, and nearly ^\ of an inch in thickness. The chorion was united to the embryo and umbilical vesicle by a thin tenacious web of albu- minous filaments, formed probably by coagulation in the spirit in which it had been kept. There were no vessels on the umbilical vesicle. The abdomen of the embryo presented no appearance of intestine, but merely a long shallow groove, forming a common cavity with the yelk-sac. Around this intestinal groove the germinal membrane was continuous with that on the surface of the yelk-sac. One extremity of the embryo, probably the cephalic, was enlarged, but this the author believed to be accidental. A more opaque and expanded portion be- tween the cephalic extremity and the surface of the yelk-sac appeared to him to indicate the rudimentary heart. The second embryo (Figs. 57, 58) was in a slightly more advanced condition. In it, as in the former, the amnion and allantois were not found, though the adhesion of the embryo by its dorsal aspect to the inner side of the chorion renders it probable that the amnion was formed. The cephalic and caudal extremities could be easily distinguished ; the vertebral groove appeared to be open in its whole extent; there was a more perfect intestinal groove than in the former case, and there was an irregular shaped mass between the yelk and the cephalic extremity of the embryo, which Professor Thompson believed to ' For the data on which these calculations are founded, the reader is referred to the original paper. GROWTH or THE EMBRYO. 97 No distinct trace of the omphalo-mesenteric be the rudiment of the heart vessels could be observed.' In an embryo of fifteen to eighteen days, described by Coste, the villi of the chorion were well formed, the umbilical vesicle communicated largely with the intestine, and the allantois was present, united to the inner surface of the chorion, and communicat- ing by a large pedicle with the intestine. Both the allantois and umbilical vesicle were vascular. The amnion was not yet closed. In ova of the third and fourth week the amnion has been found closed, the . rudiments of the eye, ear, maxillary projections, pharyngeal arches, cere- bral vesicles, anterior and posterior extremities, liver and umbilical cord are observed (Fig. 59). The further development of the embryo will perhaps be better understood if we follow as briefly as possible the principal facts relating to the chief the cranium, the pharyngeaLcavity, mouth, &c., the nervous centres, the organs of the senses, the circu- latory system, the alimentary canal and its append- ages, the organs of respiration, and the genito- parts of which the body consists, viz., the spine, urinary organs.^ The reader is also referred to the table of the development of the fcetus on page 112. Hutnan embryo in the fourth week. 1. Amnion removed in part of the dorsjil region. 2. Umbilical vesicle. 3. Omphalo-mesenteric duct. 4. In- ferior maxillary tubercle of first pha- ryngeal arch. 5. Superior maxillary tubercle from the same arch. 6. Second pharyngeal arch. 7. Third. 8. Fourth. 9. Eye. 10. Primitive auditory vesicle. 11. Anterior ex tremity. 12. Posterior extremity. 13. Umbilical cord. li. Heart, la. Liver. Development of the Spine. — The first trace of the future spinal column is found at a very early period of foetal life, constituting the chorda dorsalis or notochord (Fig. 53). This is a cylindrical tube, composed of a transparent sheath, containing em- bryonic cells, and extending from the cephalic to the caudal extremity of the fcetus below the spinal canal. The proio-veriebree or primitive vertebrae appear early, as dark spots, which soon enlarge and form quadrangular laminae, one on either side of the chorda dorsalis, commencing in the cervical region, These spread out and bend towards each other, so as to come into contact around the spinal canal and inclose it, forming the rudiment of the future bodies and arches of the vertebrae, as well as of the vertebral and other muscles. This primitive vertebral column is, however, entirely mem- branous until about the sixth or seventh week, when cartilage begins to be deposited in it. The proto-vertebr« do not coincide with the permanent verte- brae. On the contrary, each primitive vertebra separates into two parts, the upper part belonging to the permanent vertebra, which lies above the point of separation, and the lower one to that below. The chorda dorsalis becomes gradually atrophied, except at the part corresponding to the intervals between the permanent vertebrae, where it forms the intervertebral disks. (The particular facts relating to the ossification of the spinal column will be found under the description of the Vertebrae.) Development of the Cranium in general, mid of the Face. — The foetal cranium is developed from the primitive vertebral disks surrounding the upper extremity ' A third early embryo is figured and described in this paper, but the author is more uncertain as to its date. ^ The scope of this work only permits the briefest possible reference to these subjects. Those who wish to study the subject of embryology in more detail are referred to KiiUiker's Entwicke- lungsgeschichte, to the chapters on the development of the various organs in the 7th edition of Quain's Anatomy, or to Beaunis et Bouchard, Nouvf.aux Elements d'Anatomie descriptive et d'Embryologie ; to the latter of which works especially the editor must express his obligations. GENERAL ANATOMY. of the chorda dorsalis. These advance in the form of a membranous capsule, which covers the end of the chorda dorsalis, forming the rudiment of the base of the skull, and moulds itself on the cerebral vesicles, so as to constitute the membrane in which the vault of the skull is developed. The membranous capsule presents at the base of the skull two thickenings (lateral trabeculae of Eathke) directed forwards, and inclosing an opening (pituitary opening) which is partly closed by a thinner membrane— the middle trabecula. The upper end of the chorda dorsalis terminates in a pointed extremity, which extends about as far forwards as the body of the sphenoid bone, where it becomes lost about the situation of the pituitary body. The membrane becomes replaced by carti- lage in the part corresponding to the base of the skull and the trabeculse. A portion of this primitive cartilaginous cranium becomes atrophied and disap- pears, a portion persists — forming the cartilages of the nose and those of the articulations; the rest forms the cartilaginous nidus of the basilar part of the occipital, the greater part of the sphenoid, the petrous and mastoid portions of the temporal, the ethmoid bone, and the septum nasi. As the cerebral extremity of the foetus grows it becomes twice bent forwards on its own axis (Fig. 61). The upper or posterior curvature is called the cere- bral ; the lower or anterior, the frontal pro- tuberance. From the anterior end of the chorda dorsalis four prolongations proceed on either side, and meet in the middle line (Fig. 60, 4, 7, 8, 9). These are the pharyn- geal arches, and in them, and in the frontal protuberance, certain bones are developed, which are called secondary bones, to distin- guish them from those above enumerated, which are formed from the primitive cra- nium itself. Between the first pharyngeal arch and the frontal protuberance is situated the buccal depression, which afterwards be- comes the cavity of the mouth. The frontal protuberance next gives off two lateral parts (lateral frontal protuberances), on each of which a depression is formed, the olfactory fossa, bounded on either side by the internal and external nasal processes. There is a groove external to the external nasal pro- cess, which afterwards is transformed into the lachrymal canal, and another groove leading from the olfactory fossa to the buc- cal cavity — the nasal groove. The first pharyngeal arch divides at its anterior extremity into two parts — a superior and inferior maxillary protuberance. The latter unites very early to its fellow of the opposite side to form the lower jaw. The superior maxillary protuberances are displaced outwards and unite to the ex- ternal nasal process; from this part are developed the internal plate of the pterygoid process, the palate bone, the superior maxillary, and the malar. The lateral masses of the ethmoid, the os unguis, and nasal bones are furnished by the internal nasal process. The rest of these processes on either side are united into a single protuberance, the incisive tubercle, from which the intermaxillary bone and the middle of the upper lip are formed, and, according to some, the vomer. Besides the lower jaw, the inferior maxillary protuberance furnishes a transi- tory cartilaginous mass — the cartilage of Meckel — from which the malleus and F.ioe of an embryo of 25 to 2S d.iy.s. fMag- nified 15 tioies.) 1. Frontal prominence. 2, 3. Right and left olfactory fossae. 4. Infe- rior maxillary tubercles, united in the middle line. 6. Superior maxillary tubercles. 6. Mouth. 7. Second pharyngeal arch. 8. Third. 9. Fourth. 10. Primitive ocular ■vesicle. 11. Primitive auditory vesicle. DEVELOPMENT OF THE NERVOUS CENTRES. 09 incus are formed. The remains of Mediel's cartilage persist as long as till the end of the seventh or the eighth month of foetal life, in the form of a rod of cartilage lying inside the lower jaw. From the second pharyngeal arch are formed the stapes and stapedius muscle, the pyramid, the styloid process, the stylohyoid ligament, and the small cornu of the hyoid bone. The great cornu and body of the hyoid bone are developed from the third arch, while the fourth pharyngeal arch enters merely into the formation of the soft parts of the neck, and does not give origin to any special organ. The pharyngeal or branchial fissures are four in number, the fourth being situated behind or belo.w the fourth arch ; the first persists, though only in a portion of its extent, forming the Eustachian tube, the meatus auditorius, and the tympanic cavity. The other fissures are wholly closed by the sixth week. Development of the Palate. — The buccal cavity is at first common to the mouth and nose. Then a lamella is given off from the superior maxillary tuberosity on either side, which is directed horizontally inwards. These two palatine lamellae meet in the median line, in front, about the eighth week, and by the ninth week the septum should be complete. The superior maxillary bones proper, and the soft parts covering them, unite at an early period with the in- cisive bone, and the median portion of the lower lip. The olfactory fossae open into the upper (respiratory) portion of the cavity, forming the nostrils. The student will notice that the various forms of harelip correspond to various interruptions of the process of union; thus the ordinary single harelip on one side of the median line results from the mere absence of union on that side, between the soft parts which cover the incisive bone and those connected with the proper superior maxillary; if this occurs on both sides, we have the sim- plest form of double harelip ; if besides this the intermaxillary bone remains ununited, it usually is carried forward at the end of the vomer, forming the double harelip, complicated with projection of the intermaxillary bone; if, added to this, the palatine lamellae also remain unu- nited, we have the complete degree of fissured palate Fig. 61. and harelip. Fissure of the soft palate only, or of -^b^ r; 6 the soft and a portion of the hard, represent various degrees of non-union of the palatine lamellae. J' -^Z^MM^9Mfji^'i Development of the Nervous Centres. — The medullary groove above described (page 91 ) presents about the third week three dilatations at its upper part, separated by two constrictions, and at its posterior part another dilatation called the rhomboidal sinus. Soon afterwards the groove becomes a closed canal (medullary canal), and a soft blastema is deposited in it which lines it, corresponding to its dilatations, and, like it, assuming a tubular form. This is the rudiment of the cerebro- spinal axis. As the embryo grows, its cephalic part becomes more curved, and the three dilatations in the anterior end of the primi- tive cerebro-spiual axis become vesicles distinctly separated from each other -(Fig. 61). These are the cerebral vesicles — anterior, middle, and posterior; The anterior cerebral vesicle (situated at this period quite below the middle vesicle) is the rudiment of the lateral and third ventricles, and of the parts sur- rounding them — viz., the cerebral hemispheres, optic thalami, corpora striata, corpus oallosum, fornix, and all the parts which form the floor of the third ventricle. The middle vesicle represents the aqueduct of Sylvius, with the corpora quadrigemina, and the crura cerebri. The posterior vesicle is deve- liongltudinal section of the head of an embryo four ■weeks old seen from the inside. 1. Ocular vesi- cle. 2. Optic nerve flattened out. 3. Fore brain. 4. Intermediary brain. 6, Middle brain. 6. Hind- er brain. 7. After-brain. 8. An- terior portion of the tentorium cerebelli. 9. Its lateral portion intervening between Nos. 4 and 5. 10. The pharyngeal curve, bent into a cul-de-sao. 11. The auditory vesicle. 100 GENERAL ANATOMY, loped into the fourth ventricle, and its walls form the cerebellum, pons Varolii, medulla oblongata, and parts in the floor of the fourth ventricle. 'I'he antero- posterior fissure which indicates the division of the brain into two halves appears early, and the primary anterior and posterior cerebral vesicles are also soon divided by a transverse fissure into two parts, so as to constitute five permanent rudiments of the brain and medulla oblongata. The middle pri- mary vesicle remains undivided. The anterior part of the anterior cerebral vesicle (Vorderhirn, fore brain) constitutes the cerebral hemispheres, corpus callosum, corpora striata, fornix, lateral ventricles, and olfactory nerves. These parts lie at first quite covered and concealed by those formed from the middle vesicle, and by the optic thalami, which, with the optic nerves, the third ventricle, and the parts in its floor,' are furnished by the posterior portion of the anterior vesicle (Zwis- chenhirn, intermediary brain). By the third month, however, the hemis- pheres have risen above the optic thalami, and by the sixth month above the cerebellum. Fissures are seen on the surface of the hemispheres at the third month, but all except one disappear. This one persists, and forms the fissure of Sylvius. The permanent fissures for the convolutions do not form till about the seventh or eighth month. The middle cerebral vesicle (Mittelhirn, middle brain) is at first situated at the summit of the angle shown on Fig. 61. Its sur- face, at first smooth, is soon divided by a median and transverse groove into four tubercles (tubercula quadrigemina), which are gradually covered in by the growth of the cerebral hemispheres. The cavity diminishes as its walls thick- en, and contracts to form the aqueduct of Sylvius. The crura cerebri are also formed from this vesicle. The third primary cerebral vesicle is divided at an early period (between the ninth and twelfth week) into two, the anterior part (Hinterhirn, hinder brain), forming the cerebellum, and a membrane (membrana obturatrix), which closes the upper part of the fourth ventricle, and which disap- pears as development progresses ; its posterior part (Nachhirn, after-brain) forms the medulla oblongata, with the restiform bodies and auditory nerves. When the medullary groove is closed, the fcetal spinal marrow at first occupies the whole of the canal so formed. It presents at first a large central canal, which gradually contracts, and in after life is no longer perceptible to the eye, though it is still visi- ble on microscopic sections (p. 64). After the fourth month the spinal column begins to grow in length more rapidly than the medulla, so that the latter no longer occupies the whole canal. The ganglia and anterior roots of the nerves are perceptible at the fourth week, the posterior roots at the sixth. The cord is composed at first entirely of uniform- looking cells, which soon separate into two layers, the inner of which forms the epithelium of the central canal, while the outer forms the central gray substance of the cord. The white columns are formed later ; their rudiments can be detected about the fourth week. rai column. 9. Posterior col- The Central caual of the Spinal cord is at first unclosed umn. 10. Anterior roots. 11. behind, exccpt by the epithelial layer, but at the age Posterior roots. of nine wceks the medullary substance is united hero also. The ganglia appear to be developed from the protovertebral disks, and it is possible that the posterior roots also are ; the anterior roots proceed from the medulla itself. The development of the nerves 7 5 Section of the medulla in the cervical region, at six iveeks (magnified 50 diameters). 1. Central canal. 2. Its epithe- lium. 3. Anterior gray matter 4. Posterior gray matter. 5. Anterior commissure. 6. Pos- terior portion of the canal, closed by the epithelium, only. 7. Anterior column. 8. Late- The development of tbe pituitary body is still a matter of question. DEVELOPMENT OP THE ORGANS OF SENSE. 101 has not yet been followed. The sympathetic can be seen as a knotted cord at the end of the second month. The cerebral and spinal membranes are also, according to Kolliker, a pro- duction from the protovertebral disks, and are recognizable about the sixth week. A-s the fissures separating the parts of the cerebro-spinal axis appear, the membranes extend down them, and the pia mater passes into the cerebral ventricles. Bischoff, however, describes the pia mater and arachnoid as deve- loped from the cerebral vesicles, and formed in the position which they perma- nently occupy. Development of the Eye. — The first rudiment of the eye is seen about the third week, in a vesicle (primitive ocular vesicle), which communicates with the first cerebral vesicle, and after the latter is divided into two, communicates with its posterior division — the Zwischenhirn or intermediary brain— by a hollow stalk, which afterwards becomes the optic nerve. This primitive ocular vesi- cle, derived from the cerebral mass, is invested by a layer from the epidermic lamina of the blastoderm; from the latter layer are derived the conjunctiva, the epithelium of the cornea, and the crystalline lens ; while the cephalic layer gives origin to the vitreous body, the fibrous coat of the eye (sclerotic and cornea), the choroid and iris, and the retina. The lens is formed by a thickening of the epidemic layer, opposite to the primitive ocular vesicle, by which that vesicle is at first depressed, and then reversed in the manner indicated by the annexed figures; so that the cavity of the primitive ocular vesicle is finally obliterated. As this process takes place, a secondary cavity (secondary ocular vesicle) is formed between the rudi- mentary lens and the coats of the reversed primitive vesicle, and in this space the vitreous humor is secreted. Diagram of deTelopment of the lens. A B C. Different stages of development. 1. Epidermic layer. 2. Thiclsening of this layer. 3. Crystalline depression. 4. Primitive ocuLar vesicle, its anterior part pushed back by the crystalline depression. 5. Posterior part of the primitive ocular vesicle, forming the externnl layer of the secondary ocular vesicle. 6. Point of separation between the lens and the epidermic layer. 7. Cavity of the secondary ocular vesicle, occupied by the vitreous. The lens is at first a mere depression in the epidermic layer. When this is closed the lens becomes a vesicle, formed of epithelial cells, which grow and fill its cavity, becoming gradually transformed into fibres. It is at first sur- rounded by a vascular membrane — the vascular capsule of the lens— which is connected with the termination of the temporary artery (hyaloid) that forms the continuation of the central artery of the retina through the vitreous chamber. This vascular capsule of the crystalline lens forms the membrane pupillaris (described under the Anatomy of the Eye), and attaches the borders of the iris to the capsule of the lens. It disappears about the seventh month. The sclerotic and cornea, except the epithelial layer of the latter, are formed from the outer layer of the reversed primitive ocular vesicle, the retina from the inner layer; the pigment of the choroid is also derived from the inner layer, its proper tissue from one of these layers, but which has not yet been deter- mined. The cavity of the primitive ocular vesicle 'disappears as that of the optic nerve does. • 102 GENERAL ANATOMY. The eyelids are formed at the end of third month, as small cutaneous folds, which come together in front of the globe and cohere. This union is broken up, and the eyelids separate before the end of foetal life. The lachrymal canal appears to result from the non-closure of a fissure which exists between the external nasal process and the maxillary process (p. 98). Devehjyment of the Ear. — The first rudiment of the ear appears about the same time as that of the eye, in the form of a vesicle (primitive auditory vesicle. Fig. 60, 11) situated close on the outside of the third cerebral vesicle, though not communicating with it. It is formed by a depression of the epithelium over the second pharyngeal arch, which becomes converted into a closed sac. From this vesicle the internal ear is developed. The auditory nerve is described either as a projection from the third cerebral vesicle, or as an independent formation which unites with both, and thus establishes a communication between the cerebral and the auditory vesicles. The middle ear and Eustachian tube con- stitute the remains of the first pharyngeal or branchial cleft. The formation of the ossicles of the tympanum has been already pointed out, viz., the incus and malleus from Meckel's cartilage, and the stapes, with its muscle, from the second pharyngeal arch. These parts project into the first pharyngeal cleft, which remains occupied by connective tissue during the whole of fcetal life, according to Kcilliker. The membrana tympani forms across the cleft, dividing it into an outer and inner portion. The pinna, or external ear, is developed from the soft parts covering the first pharyngeal arch. Development of the Nose. — Two fossae (olfactory fossse) have been already spoken of, which are found below and in front of the ocular vesicles and the upper maxillary projection (Fig. 60, 2, 3). They appear about the fourth week. Their borders become prominent, and the fossae deepen, except at the lower part, where they lead by a groove (olfactory groove) into the buccal cavity. This groove is bounded by the internal and external nasal process. As the superior maxillary projection increases, the olfactory groove is transformed into a deep canal, the rudiment of the two superior meatus of the nose. As the palatine septum is formed, the buccal cavity is divided into two parts, the upper of which represents the inferior meatus of the nose, while the lower forms the mouth. The soft parts of the nose are formed from the coverings of the frontal projection, and of the olfactory fossae. The nose is perceptible about the end of the second month. The nostrils are at first closed by epithelium, but this disappears about the fifth month. The olfactory nerve, as above pointed out, is a prolongation, at first in the form of a hollow stalk, from the anterior cerebral vesicle. The Development of the Teeth is spoken of in the body of the work. Development of the Skin, Glands, and Soft Parts. — The epidermis is produced from the external, the true skin from the middle blastodermic layer (Fig. 53, 19, 20). About the fifth week the epidermis presents two layers, the deeper one corresponding to the rete mucosum. The subcutaneous fat forms about the fourth month, and the papillae of the true skin about the sixth. A considerable desquamation of epidermis takes place during foetal life, and this desquamated epidermis mixed with a sebaceous secretion constitutes the vernix caseosa, with which the skin is smeared during the last three months of foetal 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 month in the form of a depression of the deeper layer of the epithelium, which then becomes inverted by a projection from the papillary layer of the skin. The papilla grows into the interior of the epithelial layer, and finally, about the fifth month, the foetal hairs (lanugo) 'appear first on the head and then on the other parts. DEVELOPMENT OP THE HEART AND VESSELS. 103 These hairs drop off after birth, and give place to the permanent hairs. The sudoriferous and sebaceous glands are also formed from the epithelial layer about the fifth and sixth month respectively. The mammary gland is also formed from the deeper layer of the epithelium. Its first rudiment is seen about the third month, in the form of a small projection, from which others radiate, and which then give rise to the glandular follicles and ducts. The development of the former, however, remains imperfect, except in the adult female, and especially after pregnancy. The muscles become visible about the seventh or eighth week. The source of their development is not completely determined, for the muscles of the limbs. The vertebral muscles appear to be developed from the " muscular laminse" of the primitive vertebral disks (Fig. 53, 13), and the muscles of the neck and jaws, as well as those which inclose the cavities of the thorax and abdomen, are also formed from the same source. They do not meet in the middle line of the body till about the fourth month. The cutaneous muscles are developed from the cutaneous portion of the middle blastodermic layer. Development of the Heart and Great Vessels. — The first trace of the heart is found about the tenth or twelfth day, in the form of a mass of cells proceeding from the middle layer of the blastodermic vesicle, and the anterior wall of the intestinal cavity. It soon forms a bent tube lying in front of the embryo, and only connected to it by its vessels (Fig. 59, 14). The heart is situated at first at the anterior end of the embryo, lying opposite the last two cerebral vesicles. As the head is developed, the heart falls as it were backwards to the lower part of the neck, and then to the thorax. It fills the whole thoracic cavity about the second month. As the lungs and thoracic parietes form, the heart assumes its permanent position. The tube is soon curved into the shape of the letter S, the arterial part being situated above, in front, and to the right, the venous below, behind, and to the left. Traces of the auricular appendages are early perceptible on the venous part. Then the walls of the ventricular portion begin to thicken in regard to the auricular part. The ventricle is separated by a con- striction from the dilated part above, which corresponds to the aortic siuus or bulb (Fig. 64, 1), and from the posterior or auricular dilatation. Then each of Fiff. 64. Heart at the fifth week. A. Opened from the abdominal aspect. 1. Arterial sinus. 2. Aortio arches uniting behind to form the descending aorta. 3. Auricle. 4. Aurioulo-rentrioular orifice. 5. Commencing septum ventricnlorum. 6. Ventricle. 7. Inferior vena cava. B. Posterior view of the same. 1. Tr.ichea. 2. Lungs. 3. Ventricles. 4, 5. Auricles. 6. Diaphragm. 7. Descending aorta. 8, 9, 10. Pneumogastrio nerves and their branches. these three parts becomes subdivided by a septum. After the completion of the ventricular septum the auricular is commenced. The septum ventricnlorum is at first almost transverse, and divides off a smaller portion (the right ven- tricle) from the common cavity. This septum is complete about the eighth week and then the interauricular begins to grow, commencing from above and behind and coalescing with the edge of the interventricular septum, so as to leave an orifice (auriculo-ventricular) on either side. The auricular septum, 104 GENERAL ANATOMY. however, is not complete during foetal life, but leaves an aperture (foramen ovale) by which the two auricles communicate. The heart is at first composed of a mass of foetal cells, but its rhythmic con- tractions can be observed even in this condition before the development of any muscular fibres, and even, according to some authors, before it is in connection with any vessels. The vessels which are in communication with the foetal heart are as follows: In its earliest state the circulation is external to the embryo. This primitive circulation appears about the fifteenth day, and lasts till the fifth week. It con- sists of two arteries, the first aortic arches, which unite into a single artery, running down in front of the primitive vertebrae and in the walls of the intes- tinal cavity, and joining in a single artery, which again divides into two primitive aortm or vertebral arteries, and these give o'ff five or six omphah-mesenteric arteries, which ramify in the germinal area, forming with their parent trunks a close network, terminating in veins, which converge towards a venous trunk, the terminal sinus. This vessel surrounds the vascular portion of the germinal area, but does not extend up to the anterior end of the embryo. It terminates on either side in a vein called omphalo-mesenteric. The two omphalo-mesen- teric veins open by a single trunk into the auricular extremity of the heart. This primitive circulation extends gradually from the germinal area over the whole of the umbilical vesicle, and disappears as the latter becomes atrophied. In a more advanced state of the embryo, the position of this first pair of aortic arches, corresponds to the first pharyngeal arch. Next in succession, other pairs of arches are formed behind the first' (Fig. 65). The total number is five, but the whole five pairs do not exist together, for the first two have disappeared before the others are formed. These two have no representatives in the per- manent structures. The third pair gives origin to the carotids, the fourth pair forms the innominata and subclavian on the right, the arch of the aorta and subclavian on the left. The fifth forms on the left side the pulmonary artery, the ductus arteriosus and the descending portion of the thoracic aorta. Its right branch disappears. The ascending portion of the arch of the aorta, and the root of the pulmo- nary artery, are at first blended together in the common dilatation (aortic sinus), which has been above spoken of as connected with the ventricular end of the rudimentary heart (Fig. 64, 1). The septum which divides this common artery into two begins to appear very early, even before the interventricular septum. The formation of the permanent vessels is shown by the following diagram : — Fig. 6o. Diagram of the formation of the aortic nrehes nnd the liirge arteries. I II. III. IV. V. First, Becond, third, fourth and fifth aortic arche.s. A. Common trunk from which the first pair spring ; the place ^%here the succeeding pairs are formed is indicated by dotted lines. B. Common trunk, with four arches and a trace of the fifth. C. Common trunk with the three last pairs, the first two haying been obliterated. D. The per- sistent arteries, those which have disappeared being indicated by dotted lines. 1. Common arterial trunk. 2. Thoracic aorta. 3. Right branch of the common trunk, irhich is only temporary. 4. Left branch, per- manent. 6. Axillary artery. 6. Vertebral. 7. 8. Subclavian. 9. Common carotid. 10. External; and H, Internal carotid. 12. Aorta. 1.3. Pulmonary artery. 14, 15. Right and left pulmonary arteries. I The position of the first four of these aortio arches is behind the corresponding pharyngeal arches, and that of the fifth behind the fourth pliaryngeal cleft. DEVELOPMENT OF THE VESSELS. 105 The descending aorta appears to be the remnant of the artery formed by the union of the two primitive aortse. The omphalo-mesenteric arteries, which spring from these latter, all disappear except one, which remains as the superior mesenteric artery. The umbilical arteries are at first the terminations of the two primitive aortse, but when these vessels are united into one, the umbilical arteries appear as branches, and the aorta itself ends in a caudal prolongation, which afterwards becomes the middle sacral. The common and internal iliac arteries are the only permanent remains of the umbilical arteries {see Internal Iliac Arteries.) Veins. — The primitive venous circulation has been described above, the two omphalo-mesenteric veins opening by a common trunk into the lower end of the tube, which represents the heart. The next state of the venous circulation is, that at about four weeks there is found a single vein lying behind the in- testinal cavity (not in front of it, as the temporary omphalo-mesenteric veins do), and receiving the trunk vein from the intestine (mesenteric). Two um- bilical veins are early formed, and open together into the common trunk of the omphalo-mesenteric vein. They receive branches from the allantois and anterior surface of the embryo. The right vein soon disappears ; the left um- bilical vein, on the contrary, grows till it becomes the trunk vessel into which the omphalo-mesenteric vein and its mesenteric branch appear to open. Next the liver begins to be formed around the umbilical vein, and then this vein sends branches into that gland (afferent veins) which afterwards become the portal veins in the interior of the liver, and which give origin to other veins (efferent), which return the blood from the liver, and form afterwards the hepatic veins. The portion of the umbilical vein between the giving off of the future portal vessels and the reception of the hepatic, forms the ductus venosus. The mesenteric vein communicates at first with the omphalo-mesen- teric r when the veins of the liver are formed, the omphalo-mesenteric is trans- ferred from the umbilical vein to the right afferent hepatic. A portion of it persists and forms the trunk of the portal vein. The systemic veins are developed from four trunk veins, two on either side, above and below, which appear before the formation of the allantois or the umbilical vessels. These unite into one canal on either side (canal of Cuvier), which open into the common trunk of the omphalo-mesenteric veins, and so into the auricular portion of the rudimentary heart. These four primitive veins lie, two of them in front, the anterior cardinal, or jugular veins, and the other two behind, the posterior cardinal veins. As the umbilical vein increases, and the omphalo-mesenteric diminishes in volume, the sinuses of Cuvier are transferred to the former vein, and when the inferior cava is formed and the umbilical vein becomes merely its tributary, the sinuses of Cuvier open into the inferior vena cava. At a later period the portion of the vena cava inferior, between the opening of the sinuses of Cuvier and the auricle, disappears, and then the auricle receives three veins — viz., the inferior cava, and the two sinuses of Cuvier, which are now called right and left superior vena cava (Fig. 66). The superior cardinal, or jugular veins, which form the upper branches of the sinuses of Cuvier on either side, unite about the second month by a transverse anastomosing branch. The left superior vena cava assumes an oblique posi- tion, and empties itself into the lower and left end of the auricle. Finally, its trunk disappears, while its orifice is transformed into the coronary sinus, in which the great cardiac vein opens. The right sinus of Cuvier, or superior vena cava, persists; the transverse anastomosing branch between the two jugu- lars becomes the left innominate vein, and the end of the right jugular the right innominate. The venous circulation in the lower part of the embryo is at first carried on by the inferior cardinal veins, which return the blood from the Wolffian bodies, and receives branches corresponding to the intercostal, lumbar, and crural veins. lOG GENERAL ANATOMY. Between the fourtli and fifth week, the inferior vena cava begins to appear in the form of a vessel which passes upwards behind the liver and between the Fig. 66. Diagram of the formation of the main systemic veins. A. Heart and venous pystem at the period when there are two vena? en vsB superiores, posterior view. 1. Left superior cava. 2. Right superior cava. 3. Inferior cava. 4. Left inferior cardinal. 6. Right inferior cardinal. 6. Right jugular. 7. Anastomosing branch between the jugulars (left innominate). 8. Subolavians. 9. Intern.il jugular. 10. External jugu- lar. 11. Middle obliterated portion of the posterior cardinal veins. 12. Newly formed posterior vertebral veins. 13. An.istomosis between the two vertebrals— trunk of small azygos. 14. Iliac veins, proceeding from anastomosis between the inferior cava and posterior cardinals. 15. Crural. 16. Hypogastric — origin- ally the distal ends of the cardinals. B. Heart and permanent vein, posterior view. 1. Obliterated left superior cava. 6. Right innominate, 7. Left innominate. 8. Subclavian. 10. Jugular. 13. Trunk of the small azygos. 17. Coronary sinus receiving the coronary vein. 18. Superior intercostal. 19. Superior small azygos. 20. Inferior small azygos. two "Wolffian bodies. It anastomoses below with the two cardinal veins, and with the crural veins, which gradually come to open into it. The middle part of the cardinal veins disappears ; their distal extremities persist as the hypogastric veins, which open along with the crural into the vena cava, forming the iliac and other veins of the lower extremities. The termination of each cardinal vein above, in the sinus of Cuvier, or superior cava, also persists. The central atrophied portion of the cardinal veins is re- placed by a vein on either side, called posterior vertebral, which receive the intercostal and lumbar veins, and are soon united by an oblique anastomosing branch. The right vertebral vein, together with the persistent termination of the right cardinal vein, forms the great azygos vein. The distal portion of the left vertebral vein with the oblique anastomosing branch, forms the small azygos ; and the upper part of the left vertebral, with the persistent termina- tion of the left cardinal, forms the left superior intercostal vein. The Fcetal Circulation is spoken of in the body of the work, under the subject of the Thorax. Development of the Alimentary Canal. — The development of the intestinal cavity is, as shown above, p. 97, one of the earliest phenomena of embryonic life. This original intestine is closed at either end, and is at first in free com- munication with the umbilical vesicle (Fig. 59, 3). It is divided into three parts: the anterior or cephalic portion of the primitive intestine; the middle, DEVELOPMENT OF THE ALIMENTARY CANAL. 107 and the posterior or pelvic. From tlie first is formed the pharynx and oeso- phagus ; from the second, the stomach, small intestine and large intestine, as far as the upper part of the rectum ; from the third, the middle third of the rec- tum. The buccal cavity, on the one hand, and the lower portion of the rectum on the other, are separate productions from the external layer of the blasto- dermic membrane, and do not communicate with the common cavity till a later period. The permanence of the foetal septum in either case constitutes a well known deformity — imperforate oesophagus or imperforate rectum, as the case niay be. The anal cavity is at first common to the urogenital, as well as to the digestive organs. The development of the palate has been spoken of above. The tongue appears about the fifth week as a small elevation, behind the inferior maxillary arch, to which is united another projection from the second pharyngeal arch. The epithelial layer is furnished by the external blastoder- mic membrane. The tonsils appear about the fourth month. The middle portion of the primitive intestine is at first a straight tube, com- municating freely with the umbilical vesicle. It then leaves the vertebral column in the middle, and forms a curve attached to that column by the mesen- tery. A portion of the intestine above this mesentery dilates into the stomach, which gradually also acquires a mesentery of its own ; the rest remains at- tached to the spine, and forms the duodenum. The curve of the intestine ap- pears as it were drawn out from the body by its attachment to the vitelline duct, and lies external to the parietes, and in the umbilical cord, until the end of the third month, when it passes back again into the abdomen. While still forming a portion of the cord, the intestine begins to be distinguished into large and small, for the anterior or upper part, corresponding to the small intestine, begins to assume a convoluted arrangement about the eighth week, whilst the lower part, which had been posterior, passes to the front and right side of the other, and becomes dilated at a short -distance from the insertion of the vitelline duct, to form the rudiment of the caecum. When the intestine lies wholly in the belly, the curve of the large intestine begins rapidly 'to form; but the caecum lies for some time in the middle line, and the ascending colon is not fully formed till the sixth month. The source of each layer of the intestine, and the closure of the omphalo- mesenteric or vitelline duct have been spoken of (above pp. 91, 94). The liver appears after the Wolffian bodies, about the third week, in the form of two depressions formed by the epithelial and fibro-intestinal layers of the blastodermic membrane, and projecting from the intestine at the part which afterwards forms the duodenum. These depressions are developed into the right and left lobes. They grow very rapidly around the omphalo-mesenteric vein, from which they receive the branches enumerated on p. 106, and about the third month the liver almost fills the abdominal cavity. From this period the relative development of the liver is less active, more especially that of the left lobe, which now becomes smaller than the right ; but the liver remains up to the end of foetal life relatively larger than in the adult. The gall-bladder appears about the second month, and bile is detected in the intestine in the third month. The pancreas is also an early formation, being far advanced in the second month. It, as well as the other salivary glands, which appear about the same period, originates in a projection from the epithelial layer, which afterwards forms a cavity, from the ramifications of which the lobules of the gland are formed. Development of the Respiratory Organs. — The lungs appear somewhat later than the liver. They are developed from a small cul-de-sac which is formed on either side as a projection from the epithelial and fibrous laminse of the in- 108 GENERAL ANATOMY. testine. During the fourth week these depressions are found on either side, opening freely into the pharynx, and from the original pouches other secondary pouches are given off, so that by the eighth week the form of the lobes of the lungs may be made out. The two primary pouches have a common pedicle of communication with the pharynx. This is developed into the trachea (Fig. 64), the cartilaginous rings of which are perceptible about the seventh week. The parts which afterwards form the larynx are recognized as early as in the sixth week, viz : a projection on either side of the pharyngeal opening, the rudiment of the arytenoid cartilages, and a transverse elevation from the third pharyngeal arch, which afterwards become the epiglottis : the vocal cords and ventricles of the larynx are seen about the fourth month. The traces of the diaphragm appear early, in the form of a fine membrane, separating the lungs from the Wolffian bodies, the stomach and liver, but the source of its formation has not been ascertained. The pleural and peritoneal cavities are then sepa- rated, having been common up to this time. The serous membrane of the pleura is formed about the tenth week ; but its development is also unknown. Development of the Genito-urinary Organs. — The allantois communicates at first with the lower part of the primitive intestine by a canal — -the urachus. After the second month the lower part of the urachus dilates, so as to form the bladder, which then communicates above with the cavity of the urachus, and below with the rectum, by a canal of communication which is afterwards trans- formed into the urethra. The urachus is obliterated before the termination of foetal life; but the cord formed by its obliteration is perceptible throughout life, passing from the upper part of the bladder to the umbilicus. The kidneys are also formed from the lower end of the urachus. They are at first hollow organs lying behind and below the Wolffian body. As their dis- tance from the bladder increases, the ureters become developed, and the simple cul-de-sacs in which the foetal kidneys commence, divide and subdivide so as to form lobulated organs provided with calices in their interior. This lobulation, is perceptible for some time after birth. The suprarenal bodies are formed independently both of the kidneys and Wolffian bodies. The Wolffian hody, or primordial kidney, is perceptible about the third week, forming a mass of cells which soon give rise to a hollow organ, situated on either side of the primitive vertebrae, and extending from the heart to the lower end of the embryo, terminating above in a cul-de-sac and opening below into the bladder. The structure of the Wolffian body is in many respects analogous to that of the permanent kidney. It is composed partly of an excretory canal into which open numerous "conduits," rectilinear at first, but afterwards tor- tuous, and partly of a cellular or glandular structure, in which Malpighian tufts are found. It is fixed to the diaphragm by a superior ligament, aind to the spinal column by an inferior or lumbar ligament. Its office is the same as that of the kidneys, viz., to secrete fluid containing urea, which accumulates in the bladder. When the permanent kidneys are formed, the greater part of the Wolffian body disappears. The rest takes part in the formation of the genital organs. The internal genital organs have at first no distinctive signs of sex. They are developed from the Wolffian body, the genital gland, and the conduit of Muller. The genital glands are masses of cells which are formed towards the sixth week of foetal life. They are produced from the middle blastodermic layer, and lie on the inside of the Wolffian body, to which they are attached by a mesenteric layer of peritoneum. The conduit of Muller, or genital duct, is formed at the same time as the genital gland, and like it from the middle blastodermic layer. It is at first a mere cellular cord, and then represents a canal, the upper part of which is closed; the lower opens into the bladder. It lies internal and anterior to the duct of the Wolffian body. DEVELOPMENT OF THE GENITAL ORGANS. 109 Up to this point no difference of sex is perceptible; but from this stage, towards the commencement of the third month, the internal organs of the female and male begin to assume a different appearance. Female Organs. — The genital gland, in its development into an ovary, becomes more lengthened and assumes an oblique position, by which characters it can be distinguished from the testicle, about the ninth or tenth week. The ovary is at first situated internal and anterior to the "Wolf&an body. As that body disappears the ovary descends towards the inguinal region. It passes into the pelvis towards the end of foetal life. The ovules and Graafian follicles are derived from the genital gland, but according to His the stroma of the ovary is furnished by the Wolffian body. The Fallopian tube is formed by the portion of the duct of Miiller, which lies above the lumbar ligament of the Wolffian body. This duct is at first com- pletely closed, and its closed extremity remains permanent, forming a small cystic body attached to the fimbriated end of the Fallopian tube, and called the " hydatid of Morgagni." Below this, a cleft forms in the duct, and is developed into the fimbriated opening of the Fallopian tube. Below this portion of the duct of Miiller, that body on either side, and the ducts of the Wolffian body, are united together in a structure called "the genital cord," in which the two Miillerian ducts approach each other, lying side by side and finally coalescing to form the cavity of the vagina and uterus. This coalescence commences in the middle, corresponding to the body of the uterus. The upper parts of the Miillerian ducts in the genital cord constitute the cornua of the uterus, little developed in the human species. The only remains of the Wolffian body consist in a structure (parovarium or organ of Eosenmiiller) which can usually be detected lying between the ovary and Fallopian tube, and consisting of a group of tubules converging to a single duct, which is some- times of considerable size and runs for some distance in the broad ligament. About the fifth month an annular constriction marks the position of the neck of the uterus, and after the sixth month the walls of the uterus begin to thicken. The round ligament is derived from the lumbar ligament of the Wolffian body, the superior ligament of the genital gland becomes the cord which attaches the ovary to the fimbriated extremity of the Fallopian tube, the peri- toneum constitutes the broad ligaments, the superior ligament of the Wolffian body disappears with that structure. Internal Organs in the Male. — 1. The genital gland, in its development into a testicle, becomes rounded and thick, and is more vertical than the ovary is in its early state. The tubuli seminiferi are early visible, being at first short and straight, and then gradually assume a coiled arrangement. The tunica albu- ginea is formed about the third month. 2. The Miillerian ducts disappear in the male sex, with the exception of their lower ends. These unite in the middle line, and open by a common orifice into the uro-genital sinus. This constitutes the utriculus hominis or sinus prostaticus. 3. The head of the epididymis, its canal, the vas deferens and ejaculatory duct, are formed from the canals and from the duct of the Wolffian body. The remains of the Wolffian bodies also form the vas aberrans, and a struc- ture described by Giraldfes' and called after him, "the organ of Girald^s," which bears a good deal of resemblance to the organ of Eosenmiiller in the other sex. It consists of a number of convoluted tubules lying in the cellular tissue in front of the cord and close to the head of the epididymis. The descent of the testis and the formation of the gubernaoulum are de- scribed under the Male Generative Organs, in the body of the work. The external organs of generation, like the internal, pass through a stage in which there is no distinction of sex (Fig. 67, I, II, III). We must therefore ' Journ. de Phys., 1861. 110 GENERAL ANATOMY. first describe this stage, and then follow the development of the female and male organs respectively. As stated above, the anal depression at an early period is formed by an in- volution of the external epithelium apart from the intestine, which is still Fig. 67. II Sis y' y^^^^ ^ P"^- 8 If; IS 3. c Derelopment of the external genital organs. Indifferent type, I. II. III. Female. A B. At the middle of the fifth month. C. At the beginning of the sixth. Male. A'. At the beginning of the fourth month. B', At the middle of the fourth month. C. At the end of the fourth month. 1. Cloaca. 2. Genital tur berole. 3. Slans penis or clitoridis. 4. Genital furrow. 6. External genital folds (labia majora or scrotum). 6. Umbilical cord. 7. Anus. 8. Caudal extremity and coccygeal tubercle. 9. Labia minora. TO. Uro- genital sinus. II. Frsenum olitoridis. 12. Preputium penis or oUtoridis. 13. Opening of the urethra. 14. Opening of the vagina. 15. Hymen. 16. Scrotal raph^. closed at its lower end. When the septum between the two opens, which is about the fourth week, the urachus in front and the intestine behind both com- municate with the cloaca. About the second month a transverse division (the DEVELOPMENT OF THE GENITAL ORGANS. Ill perineum) begins to form and divides the cloaca into the anal cavity behind, the urogenital sinus in front. In the sixth week a tubercle, the genital tubercle^ is formed in front of the cloaca, and this is soon surrounded by two folds of skin, the genital folds. Towards the end of the second month the tubercle pre- sents, on its lower aspect, a groove, the genital furrow, turned towards the cloaca. All these parts are well developed at the period shown by No. III. of the following diagrams, where the anus is separated from the urogenital sinus, yet no distinction of sex is possible. Female Organs (Fig. 67, A, B, C). — The female organs are developed by an easy transition from the above form. The urogenital sinus persists as the ves- tibule of the vagina, and forms a single tube with the upper part of the vagina, which we have already seen developed from the united Mullerian ducts. The genital tubercle forms the clitoris, the genital folds the labia majora, the lips of the genital furrow, the labia minora, the genital furrow remaining open, except below where it unites with the perineum, constituting the raph^. Male Organs. — In the male, the changes are greater from the indifferent type. The genital tubercle is developed into the penis, the glans appearing in the third month, the prepuce and corpora cavernosa in the fourth. The genital furrow closes, and thus forms a canal, the spongy portion of the urethra. The urogenital sinus becomes elongated, and forms the prostatic and membranous urethra. The genital folds unite in the middle line, to form the scrotum, at about the same time as the genital furrow closes, viz., between the third and fourth month. CHEOK"OLOGI0AL TABLE OF THE DEYELOPMEITT OF THE FCETUS. (The following table is translated from the work of Beaunis and Bouchard, with some very unimportant alterations.' It will serve to present a resume of the preceding facts in an easily accessible form.) End of second xueek. — Formation of the amnion and umbilical vesicle. Chorda dorsalis and medullary groove. Heart. Beginning of third week. — The vitelline membrane has entirely disappeared. Protovertebral disks. First pharyngeal arch. Buccal depression. Primitive circulation. End of third week. — The allantois and Wolffian body appear. The amnion is closed. Cerebral vesicles. Primitive ocular and auditory vesicles. Coalescence of the inferior maxillary protuberances. Liver. Formation of the three last pharyngeal arches. Fourth loeek. — The umbilical vesicle has attained its full development. Projection of the caudal extremity. Projection of the upper and lower limbs. Cloacal aperture. The heart sepa- rates into a right and left heart. Spinal ganglia and anterior roots. Olfactory foss». Lungs. Pancreas, Fifth week. — Vascularity of the allantois in its whole extent. First trace of hands and feet. The primitive aorta divides into primitive aorta and pulmonary artery. Conduit of Miiller and genital gland. Ossification of clavicle and lower jaw. Cartilage of Jleckel. Sixth week. — The activity of the umbilical vesicle ceases. The pharyngeal clefts disappear. The vertebral column, primitive cranium and ribs assume the cartilaginous condition. Posterior roots of the nerves. Membranes of the nervous centres. Bladder. Kidneys. Tongue. Larynx. Thyroid gland. Germs of teeth. Genital tubercle and folds. Seventh week. — ^The muscles begin to be perceptible. Points of ossification of the ribs, scapula, shafts of humerus, femur, tibia, intermaxillary bone, palate, upper jaw (its first four points). Eighth weeA.^Distinction of arm and forearm, and of thigh and leg. Appearance of the inter- digital clefts. Capsule of the lens and pupillary membrane. Completion of the interven- tricular and commencement of the interauricular septum. Salivary glands. Spleen. Su- prarenal capsules. 'I'he larynx begins to become cartilaginous. All the vertebral bodies are cartilaginous. Points of ossification for the ulna, radius, fibula, and ilium. The two halves of the bony palate unite. Sympathetic nerve. Ninth week. — Corpus striatum. Pericardium. Distinction between ovary and testicle. Forma- tion of the genital furrow. Osseous nuclei of vertebral bodies and arches, frontal, vomer, malar bone, shafts of metacarpal bones, metatarsal bones and phalanges. The union of the hard palate is completed. Gall-bladder. Third month. — Formation of the foetal placenta. The projection of the caudal extremity disap- pears. It is possible to distinguish the male and female organs at the commencement of the third month. The cloacal aperture divided into two pai-ts. The cartilaginous arches on the dorsal region of the spine close. Points of ossification for the occipital, sphenoid, os unguis, nasal bones, squamous portion of temporal and ischium. Orbital centre of superior maxillary bone. Commencement of formation of maxillary sinus. Pons Varolii. Fissure of Sylvius. Formation of eyelids and of hairs and nails INlammary gland. Epiglottis. Union of the testicle with the canals of the Wolffian body. Prostate. Fourth month. — The closure of the cartilaginous arches of the spine is complete. Osseous points for the first sacral vertebra and pubes. Ossification of the malleus and incus. Corpus callosum. Membranous lamina spiralis : cartilage of the Eustachian tube. Tym.- panic ring. Fat in subcutaneous cellular tissue. Tonsils. Closure of genital furrow and formation of scrotum and prepuce. ' It will be noticed that the time assigned in this table for the appearance of the first rudiment of some of the bones [e. g., the ilium) varies in some cases from that assigned on p. 52. 'J'his is ii point on which anatomists differ, and which probably varies in diiferont cases. 112 CHRONOLOGICAL TABLE, 113 Fifth month. — The two layers of decidua begin to coalesce. Osseous nuclei of axis and odontoid process. Lateral points of first sacral vertebra ; median points of second. Osseous points of lateral masses of ethmoid. Ossification of stapes and petrous bone. Ossification of germs of teeth. Appearance of germs of permanent teeth. Eruption of hair on head. Sudoriferous glands. Glands of Brunner. Follicles of tonsils and base of tongue. Lym- phatic glands. Commencement of limitation of uterus and vagina. Sixth month. — Points of ossification for the anterior root of the transverse process of the seventh cervical vertebra. Lateral points of second sacral vertebra ; median points of third. The sacro-vertebral angle forms. Osseous points of the manubrium sterni and of the os calcis. The cerebral hemisphere covers the cerebellum. Papillae of the skin. Sebaceous glands. The free border of the nail projects from the corium of the dermis. Peyer's patches. The walls of the uterus thicken. Seventh month. — Additional points of first sacral vertebra; lateral points of third, median point of fourth. First osseous point of body of sternum. Osseous point for astragalus. Disap- pearance of Meckel's cartilage. Cerebral convolutions. Insula of Reil. Separation of tubercula quadrigemina. Disappearance of pupillary membrane. The testicle passes into the vaginal process of the peritoneum. Eighth month. — Additional points for the second sacral vertebra; lateral points for the fourth; median points for the fifth. Ninth month.- — Additional points for the third sacral vertebra; lateral points for the fifth. Osseous point for the middle turbinated bone ; for the body and great cornu of the hyoid ; for the second and third pieces of the body of the sternum ; for the lower end of the femur. Ossification of the bony lamina spiralis and axis of the cochlea. Opening of the eyeUds. The testicles are in the scrotum. DESCRIPTIVE AND SURGICAL AMTOMY. The Skeleton. The entire skeleton in the adult consists of 200 distinct bones. These are— The Spine or vertebral column (sacrum and coccyx included, 26 Cranium 8 Face 14 Os hyoides, sternum, and ribs 26 Upper extremities 64 Lower extremities 62 200 In this enumeration, the patellae are included as separate bones, but the smaller sesamoid bones, and the ossicula auditus, are not reckoned. The teeth belong to the tegumentary system. These bones are divisible into four classes : Long, Short, Flat, and Irregular. The Long Bones are found in the limbs, where they form a system of levers, which have to sustain the weight of the trunk, and to confer the power of locomotion. A long bone consists of a lengthened cylinder or shaft, and two extremities. The shaft is a hollow cylinder, the walls consisting of dense com- pact tissue of great thickness in the middle, and becoming thinner towards the extremities; the spongy tissue is scanty, and the bone is hollowed out in its interior to form the 'medullary canal. The extremities are generally somewhat expanded for greater convenience of mutual connection, for the purposes of articulation, and to afford a broad surface for muscular attachment. Here the bone is made up of spongy tissue with only a thin coating of compact sub- stance. The long bones are, the humerus, radius, ulna, femur, tibia, fibula, metacarpal, and metatarsal bones, and the phalanges. .The clavicle is also usually reckoned as a long bone. Short Bones. Where a part of the skeleton is intended for strength and compactness, and its motion is at the same time slight and limited, it is divided into a number of small pieces, united together by ligaments, and the separate bones are short and compressed, such as the bones of the carpus and tarsus. These bones, in their structure, are spongy throughout, excepting at their sur- face, where there is a thin crust of compact substance. Flat Bones. Where the principal requirement is either extensive protection, or the provision of broad surfaces for muscular attachment, we find the osseous structure expanded into broad flat plates, as is seen in the bones of the skull and the shoulder-blade. These bones are composed of two thin layers of com- pact tissue inclosing between them a variable quantity of cancellous tissue. In the cranial bones, these layers of compact tissue are familiarly known as the tables of the skull ; the outer one is thick and tough ; the inner one thinner, denser, and more brittle, and hence termed the vitreous table. The intervening cancellous tissue is called the diploe. The flat bones are, the occipital, parietal, frontal, nasal, lachrymal, vomer, scapulse, ossa innominata, sternum, and ribs. 115 116 THE SKELETON. The Irregular or Mixed Bones are such as, from their peculiar form, cannot be grouped under either of the preceding heads. Their structure is similar to that of other bones, consisting of a layer of compact tissue externally, and of spongy, cancellous tissue within. The irregular bones are, the vertehree, sacrum, coccyx, temjMral, sjohenoid, ethmoid, superior maxillary, inferior maxillary, palate, inferior turbinated, and hyoid. Surfaces of Bones. If the surface of any bone is examined, certain eminences and depressions are seen, to which descriptive anatomists have given the fol- lowing names. A prominent process projecting from the surface of a bone, which it has never been separate from, or movable upon, is termed an apophysis (from dnofvai^, an excrescence') ; but if such process is developed as a separate piece from the rest of the bone, to which it is afterwards joined, it is termed an epiphysis (from irtl^vaif, an accretion). 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. Non-articular eminences are desig- nated according to their form. Thus, a broad, rough, uneven elevation is called a tuberosity; a small rough prominence, a tubercle; a sharp, slender, pointed eminence, a spine ; a narrow rough elevation, running some way along the sur- face, a ridge, or li7ie. The non-articular depressions are also of very variable form, and are de- scribed as fossje, grooves, furrows, fissures, notches, etc. These non-articular eminences and depressions serve to increase the extent of surface for the attach- ment of ligaments and muscles, and are usually well marked in proportion to the muscularity of the subject. THE SPINE. The Spine is a flexuous and flexible column, formed of a series of bones called Vertebras. The Vertebrae are thirty-three in number, exclusive of those which form the skull, and have received the names cervical, dorsal, lumbar, sacred, and coccygeal, according to the position which they occupy; seven being found in the cervical region, twelve in the dorsal, 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 the number may be diminished in one region, the deficiency being supplied by an additional vertebra in another. These observations do not apply to the cervical portion of the spine, the number of bones forming which is seldom increased or diminished. The vertebrae in the three uppermost regions of the spine are separate throughout the whole of life ; but those found in the sacral and coccygeal regions are, in the adult, firmly united, so as to form two bones — five entering into the formation of the upper bone or sacrum, and four into the terminal bone of the spine or coccyx. General Characters of a Vertebra. Each vertebra consists of two essential parts, an interior solid segment or body, and a posterior segment or arch. The arch is formed of two pedicles and two laminae, supporting seven processes, viz., four articular, two transverse, and one spinous process. The bodies of the vertebrse are piled one upon the other, forming a strong pillar, for the support of the cranium and trunk ; the arches forming a hollow cylinder behind for the protection of the spinal cord. The different vertebrae are connected together by means of the articular processes, and the interverte- CHARACTERS OF THE CERVICAL VERTEBRA. 117 bral cartilages ; while the transverse and spinous processes serve as levers for the attachment of muscles which move the different parts of the spine. Lastly, between each pair of vertebrae, apertures exist through which the spinal nerves pass from the cord. Each of these constituent parts must now be separately examined. The Body is the largest and most solid part of a vertebra. Above and below, it is slightly concave, presenting a rim around its circumference; and its upper and lower surfaces are rough, for the attachment of the intervertebral fibro- cartilages. In front, it is convex from side to side, concave from above down- wards. Behind, it is flat from above downwards and slightly concave from side to side. , Its anterior surface is perforated by a few small apertures, for the passage of nutrient vessels; whilst, on the posterior surface, is a single large irregular aperture, or occasionally more than one, for the exit of veins from the body of the vertebra, the vense basis vertebrss. The Pedicles project backwards, one on each side, from the upper part of the body of the vertebra, at the line of junction of its posterior and lateral surfaces. The concavities above and below the pedicles are the intervertebral notches ; they are four in number, two on each side, the inferior ones being generally the deeper. When the vertebrae are articulated, the notches of each contiguous pair of bones form the intervertebral foramina which communicate with the spinal canal and transmit the spinal nerves. The Laminse are two broad plates of bone, which complete the vertebral arch behind, inclosing a foramen which serves for the protection of the spinal cord ; they are connected to the body by means of the pedicles. Their upper and lower borders are rough, for the attachment of the ligamenta subflava. The Articular Processes, four in number, two on each side, spring from the junction of the pedicles with the laminae. The two superior project upwards, their articular surfaces being directed more or less backwards, the two inferior project downwards, their articular surfaces looking more or less forwards.' The Spinous Process projects backwards from the junction of the two laminae, and serves for the attachment of muscles. The Transverse Processes, two in number, project one at each side from the point where the articular processes join the pedicle. They also serve for the attachment of muscles. Chaeacters of the Cervical Vertebrae (Fig. 68). The Body is smaller than in any other region of the spine, and broader from side to side than from before backwards. The anterior and posterior surfaces Fiff. 68. — A Cervical Vertebra. AnUrurTiihTclt of TramTroc. i'aramen /«• Virtehral Ar-l^ BderurrTuicTde aflraas.Fw Transverse Praeiat. jSupe,rl,i ■ '^ —i for undo r sUT^fa^-A ^ body Fig. 78.— Atlas. By 3 ccTitres not -^^ — f f<^ anCe?: ctTV^ l^^'-v^) '-'^'^- vr^^ ■' ' ^ ^ stanl \,^ f for carJh ), , ,. ,, *' ^^ J Lateral, mass) •' Fin-. 79.— Axis. Btj centres \ ^ Jar ea^h Jatera I viatt '/Jbr lady (SA mo.) Fig. 80. — Lumbar Vertebra. >2 a^difiiynnl cc^jitre^ O a o '-^ &, O 'A far luherclcs an Sup.Artic.Rvc. DEVELOPMENT OF THE VERTEBRA. 125 puberty, no other changes occur, excepting a gradual increase in the growth of these primary centres, the upper and under surface of the bodies, and the ends of the transverse and spinous processes, being tipped with cartilage, in which ossific granules are not as yet deposited. At sixteen years (Fig. 76), four secondary centres appear, one for the tip of each transverse process, and two (sometimes united into one) for the end of the spinous process. At twenty- one years (Fig. 77), a thin circular plate of bone is formed in the layer of car- tilage situated on the upper and under surface of the body, the former being the thicker of the two. All these become joined ; and the bone is completely formed about the thirtieth year of life. Exceptions to this mode of development occur in the first, second, and seventh cervical, and in the vertebrse of the lumbar region. The Atlas (Fig. 78) is developed by two primary centres, and by one or more epiphyses. The two primary centres are destined for the two lateral or neural masses, the ossification of which commences before birth, near the articular processes, and extends backwards : these portions of bone are separated from one another behind, at birth, by a narrow interval filled in with cartilage. Between the second and third years, they unite either directly or through the medium of an epiphysal centre, developed in the cartilage near their point of junction. The anterior arch, at birth, is altogether cartilaginous, and this portion of the atlas is completed by the gradual extension forwards and ulti- mate junction of the two neural processes. Occasionally, a separate nucleus is developed in the anterior arch, which, extending laterally, joins the neural pro- cesses in front of the pedicles; or, there are two nuclei developed in the anterior arch, one on either side of the median line, which join to form, a single mass, afterwards united to the lateral portions in front of the articulating processes. The Axis (Fig. 79) is developed by six centres. The body and arch of this bone are formed in the same manner as the corresponding parts in the other vertebrae : one centre for the lower part of the body, and one for each lamina. The odontoid process consists originally of an extension upwards of the cartila- ginous mass, in which the lower part of the body is formed. At about the sixth month of foetal life, two osseous nuclei make their appearance in the base of this process: they are placed laterally, and join before birth to form a conical bi-lobed mass deeply cleft above ; the interval between the cleft and the summit of the process, is formed by a wedge-shaped piece of cartilage ; the base of the process being separated from the body by a cartilaginous interval, which gradually becomes ossified, sometimes by a separate epiphysal nucleus. Finally, as D r. Hum- phry has demonstrated, the apex of the odontoid process has a separate nucleus. The Seventh Cervical. The anterior or costal part of the transverse process of the seventh cervical, is developed from a separate osseous centre at about the sixth month of foetal life, and joins the body and posterior division of the transverse process between the fifth and sixth years. Sometimes this process continues as a separate piece, and, becoming lengthened outwards, constitutes what is known as a cervical rib. The Lumbar Vertebrae (Fig. 80) have two additional centres (besides those pecu- liar to the vertebrae generally), for the tubercles, which project from the back part of the superior articular processes. The transverse process of the first lumbar is sometimes developed as a separate piece, which may remain perma- nently unconnected with the remaining portion of the bone; thus forming a lumbar rib, a peculiarity which is rarely met with. Progress of Ossification in the Spine generally. Ossification of the laminae of the vertebrae commences at the upper part of the spine, and proceeds gradually downwards; hence the frequent occurrence of spina bifida in the lower part of the spinal column. Ossification of the bodies, on the other hand, commences a little below the centre of the spinal column (about the ninth or tenth dorsal vertebrte), and extends both upwards and downwards. Although, however, the ossific nuclei make their first appearance in the lower dorsal vertebrae, the lumbar and first sacral are those in which these nuclei are largest at birth. 126 THE SKELETON, Attachment of Muscles. To the Atlas are attached the Longus Colli, Rectus Anticus Minor, Rectus Lateralis, Rectus Posticus Minor, Obliquus Superior and Inferior, Splenius Colli, Levator Anguli Soapulge, Interspinous, and Inter- transverse. To the Axis are attached the Longus Colli, Obliquus Inferior, Rectus Posticus Major, Semi-spinalis Colli, Multifidus Spinae, Levator Anguli Scapulas, Splenius Colli, Transversalis Colli, Scalenus Posticus, Intertransversales, Interspinales. 'To the remaining Vertebras generally are attached, anteriorly, the Rectus Anticus Major, Longus Colli, Scalenus Anticus and Posticus, Psoas Magnus, Psoas Parvus, Quadratus Lumborum, Diaphragm, Obliquus Internus and Trans- versalis ; posteriorly, the Trapezius, Latissimus Dorsi, Levator Anguli Scapulae, Rhomboideus Major and Minor, Serratus Posticus Superior and Inferior, Sple- nius, Sacro-lumbalis, Longissimus Dorsi, Spinalis Dorsi, Cervicalis Ascendens, Transversalis Collis, Trachelo-mastoid, Complexus, Semi-Spinalis Dorsi and Colli, Multifidus Spinas, Interspinales, Supraspinales, Intertransversales, Leva- tores Costarum. The Sacral and Coccygeal Vertebrae consist, at an early period of life, of nine separate pieces, 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. Occa- sionally, the coccyx consists of five bones.' The Sacrum. The Sacrum (Fig. 81) is a large triangular bone, situated at the lower part of the vertebral column, and at the upper and back part of the pelvic cavity. Fig. 81. — Sacrum, Anterior Surface. I*Tonu}iitoTtf 1 Dr. Humphry describes this as the usual composition of the Coccyx. — On the Skeleton, p. 45G. SACRUM. 127 Fig. 82. — Vertical Section of the Sacrum. where it is inserted like a wedge between the two ossa innominata; its upper part, or base, articulating with the last lumbar vertebra, its apex with the coccyx. The sacrum is curved upon itself, and placed very obliquely, its upper extremity projecting forwards, and forming, with the last lumbar verte- bra, a very prominent angle, called the promontory or sacro-vertehral angle, whilst its central part is directed backwards, so as to give increased capacity to the pelvic cavity. It presents for examination an anterior and posterior surface, two lateral surfaces, a base, an apex, and a central canal. The Anterior Surface is concave from above downwards, and slightly so from side to side. In the middle are seen four transverse ridges, indicating the original division of the bone into five separate pieces. The portions of bone intervening between the ridges correspond to the bodies of the vertebrae. The body of the first segment is of large size, and in form resembles that of a lum- bar vertebra ; the succeeding ones diminish in size from above downwards, are flattened from before backwards, and curved so as to accommodate themselves to the form of the sacrum, being concave in front, convex behind. At each end of the ridges above mentioned, are seen the anterior sacral foramina, analogous to the intervertebral foramina, four in number on each side, somewhat rounded in form, diminishing in size from above downwards, and directed outwards an-d forwards ; they transmit the anterior branches of the sacral nerves. External to these foramina is the lateral mass, consisting, at an early period of life, of separate segments, which correspond to the anterior transverse processes. These become blended, in the adult, with the bodies, with each other, and with the posterior transverse processes. Each lateral mass is traversed by four broad shallow grooves, which lodge the ante- rior sacral nerves as they pass outwards, the grooves being separated by promi- nent ridges of bone, which give attach- ment to the slips of the Pyriformis muscle. If a vertical section is made through the centre of the bone (Fig. 82), the bodies are seen to be united at their cirumference by bone, a wide interval being left centrally, which, in the recent state, is filled by intervertebral sub- stance. In some bones, this union is more complete between the lower segments, than between the upper ones. The Posterior Surface (Fig. 83) is convex and much narrower than the ante- rior. In the middle line, are three or four tubercles, which represent the rudi- mentary spinous processes of the sacral vertebrse. Of these tubercles, the first is usually prominent, and perfectly distinct from the rest; the second and third are either separate or united into a tubercular ridge, which diminishes in size from above downwards ; the fourth usually, and the fifth always, remain- ing undeveloped. External to the spinous processes on each side, are the laminae broad and well marked in the three first pieces ; sometimes the fourth, and generally the fifth, being undeveloped ; in this situation the lower end of 128 THE SKELETON. the sacral canal is exposed. External to the laminse are a linear series of in- distinct tubercles representing the articular processes; the upper pair are large, well developed, and correspond in shape and direction to the superior articu- lating processes of a lumbar vertebra; the second and third are small; the Fig. 83.— Sacrum, Posterior Surface. Jiost.sacraZJir, fourth and fifth (usually blended together) are situated on each side of the sacral canal. They are called the sacral cornua, and articulate with the cornua of the coccyx. External 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 branches of the sacral nerves. On the outer side of the posterior sacral foramina are a series of tubercles, the rudimentary posterior transverse processes of the sacral vertebrae. The first pair of transverse tubercles are of large size, very distinct, and correspond with each superior angle of the bone; the second, small in size, enter into the formation of the sacro-iliac articulation; the third give attachment to the oblique sacro-iliac ligaments; and the fourth and fifth to the great sacro-ischiatic ligaments. The interspace be- tween the spinous and transverse processes on the back of the sacrum, presents a wide shallow concavity, called the sacral groove; it is continuous above with the vertebral groove, and lodges the origin of the Erector Spinas. The Lateral Surface, broad above, becomes narrowed into a thin edge below. Its upper half presents in front a broad ear-shaped surface for articulation with the ilium. This is called the auricular surface, and in the fresh state is coated with cartilage. It is bounded posteriorly by deep and uneven impressions, for the attachment of the posterior sacro-iliac ligaments. The lower half is thin and sharp, and gives attachment to the greater and lesser sacro-ischiatic liga- ments, and to some fibres of the Gluteus Maximus ; below, it presents a deep notch, which is converted into a foramen by articulation with the transverse SACRUM. 129 -Development of the Sacrum. Jvdditlonal oefltTes for the Jti st 3 i Fig. 85. process of the upper piece of the coccyx, and transmits the anterior branch of the fifth sacral nerve. The Base of the sacrum, which is broad and expanded, is directed upwards and forwards. In the middle is seen an oval articular surface, which corres- ponds with the under surface of the body of the last lumbar vertebra, bound- ed behind by the large triangular orifice of the sacral canal. This orifice is formed behind by the spinous process and laminae of the first sacral vertebra, whilst projecting from it on each side are the superior articular processes ; they are oval, concave, directed backwards and inwards, like the superior articular processes of a lumbar vertebra ; and in front of each articular process is an in- tervertebral notch, which forms the lower half of the last intervertebral fora- men. Lastly, on each side of the articular surface is a broad and flat triangular Fig- 84-- surface of bone, which extends outwards, and is continuous on each side with the iliac fossa. The Apex^ directed downwards and forwards, presents a small oval concave ^t Im-th surface for articulation with the coccyx. The Sacral Canal runs throughout the greater part of the bone ; it is large and triangular in form above, small and flat- tened from before backwards below. In this situation, its posterior wall is incom- plete, from the non-development of the laminae and spinous processes. It lodges the sacral nerves, and is perforated by the anterior and posterior sacral fora- mina, through which these pass out. Structure. It consists of much loose spongy tissue within, invested externally by a thin layer of compact tissue. Differences in the Sacrum of the Male and Female. The sacrum in the female is usually wider than in the male ; and it is much less curved, the upper half of the bone being nearly straight, the lower half presenting the greatest amount of curvature. The bone is also directed Fig. 86. more obliquely backwards; which in- creases the size of the pelvic cavity, and 2 Epiph- forms a more prominent sacro-vertebral angle. In the male, the curvature is more evenly distributed over the whole length of the bone, and is altogether greater than in the female. Peculiarities of the Sacrum. This bone, in some cases, consists of six pieces; occasionally the number is reduced to four. Sometimes the bodies of the first and second segments are not, joined, or the laminse and spinous processes have not coalesced. Occasionally, the upper pair of transverse tubercles are not joined to the rest of the bone on one or both sides ; and lastly, the sacral canal may be open for nearly the lower half of the bone, in consequence of the imperfect development of the laminae and 9 At 4^ Years. tpiphyi %2 la for each lateral surface. at 25 7-. y- 130 THE SKELETON, spinous processes. The sacrum, also, varies considerably with respect to itg degree of curvature. From the examination of a large number of skeletons, it would appear that, in one set of cases, the anterior surface of this bone was nearly straight, the curvature, which was very slight, affecting only its lower end. In another set of cases, the bone was curved throughout its whole length, but especially towards its middle. In a third set the degree of curvature was less marked, and affected especially the lower third of the bone. Demhpnent (Fig 84). The sacrum, formed by the union of five vertebrse, has thirty-five centres of ossification. The bodies of the sacral vertebrje have each three osaific centres ; one for the central part, and one for the epiphysal plates on its upper and under surface. The laminse of the sacral vertebrae are each developed by two centres ; these meet behind to form the arch, and subsequently join the body. "The lateral masses have six additional centres, two for each of the first three vertebrse. These centres make their appearance above and to the outer side of the anterior sacral foramina (Fig. 84), and are developed into separate segments, which correspond with the anterior transverse processes (Fig. 85); they are subsequently blended with each other, and with the bodies and the posterior transverse processes to form the lateral mass. Lastly, each lateral surface of the sacrum is developed by two epiphysal plates (Fig. 86) ; one for the auricular surface, and one for the remaining part of the thin lateral edge of the bone. Period of Development. At about the eighth or ninth week of fcetal life, ossification of the central part of the bodies of the first three vertebras com- mences ; and, at a somewhat later period, that of the last two. Between the sixth and eighth months ossification of the laminse takes place, and, at about the same period, the characteristic osseous tubercles for the three first sacral vertebrse make their appearance. The laminse join to form the arch, and are united to the bodies, first, in the lowest vertebrae. This occurs about the second year, the uppermost segment appearing as a single piece about the fifth or sixth year. About the sixteenth year the epiphyses for the upper and under surfaces of the bodies are formed ; and, between the eighteenth and twentieth years, those for each lateral surface of the sacrum make their appearance. At about this period the last two segments are joined to one another; and this process gradually extending upwards, all the pieces become united, and the bone com- pletely formed from the twenty-fifth to the thirtieth year of life. Articulations. With four bones ; the last lumbar vertebra, coccyx, and the two ossa innominata. Attachment of Muscles. In front, the Pyriformis and Coccygeus ; behind, the Gluteus Maximus and Erector Spinae. The Coccyx. The Coccyx {x6xxv%, cuckoo), so called from having been compared to a cuckoo's beak (Fig. 87), is usually formed of four small segments of bone, the most rudimentary parts of the vertebral column. In each of the first three segments may be traced a rudimentary body, articular and transverse processes ; the last piece (sometimes the third) is a mere nodule of bone, without distinct processes. All the segments are destitute of laminse and spinous processes; and, conse- quently, of spinal canal and intervertebral foramina. The first segment is the largest ; it resembles the lowermost sacral vertebra, and often exists as a sepa- rate piece ; the last three, diminishing in size from above downwards, are usually blended together so as to form a single bone. The gradual diminution in the size of the pieces gives this bone a triangular form, the base of the triangle joining the end of the sacrum. It presents for examination an anterior and posterior surface, two borders, a base, and an apex. The anterior surface is slightly concave, and marked with three transverse grooves, indicating the THE SPINE IN GENERAL. 131 Fig;. 87. — Coccyx. Ctypnva Jl.Ttte'rioT ^'UJ^a^e points of junction of the different pieces. It has attached to it the anterior sacro-coccygeal ligament and Levator Ani muscle, and supports the lower end of the rectum. The posterior surface is convex, marked by transverse grooves similar to those on the anterior surface; and presents on each side a lineal row of tubercles, the rudimentary articular processes of the coccygeal vertebrae. Of these, the superior pair are very large; and are called the cornua of the coccyx; they project upwards, and articulate with the cornua of the sacrum, the junc- tion between these two bones completing the fifth sacral foramen for the transmission of the posterior branch of the fifth sacral nerve. The lateral borders are thin, and present a series of small eminences, which represent the transverse processes of the coccy- geal vertebrae. Of these, the first on each side is of large size, flattened from before backwards ; and often ascends to join the lower part of the thin lateral edge of the sacrum, thus completing the fifth sacral foramen: the others diminish in size from above downwards, and are often wanting. The borders of the coccyx are narrow, and give attachment on each side to the sacro-sciatio ligaments and Ooccygeus muscle. The base presents an oval surface for articu- lation with the sacrum. The apex is rounded, and has attached to it the tendon of the External Sphinc- ter muscle. It is occasionally bifid, and sometimes deflected to one or other side. Development. The coccyx is developed by four centres, one for each piece. Occasionally, one of the first three pieces of this bone is developed by two centres, placed side by side. The ossifii nuclei make their appearance in the following order : in the first segment, at birth ; in the second piece, at from five to ten years; in the third, from ten to fifteen years; in the fourth, from fifteen to twenty years. As age advances, these various segments become united in the following order : the first two pieces join; then the third and fourth ; and, lastly, the bone is completed by the union of the second and third. At a later period of life, especially in females, the coccyx often becomes joined to the end of the sacrum. Articulation. With the sacrum. Attachment of Muscles. On either side, the Ooccygeus ; behind, the Gluteus Maximus ; at the apex, the Sphincter Ani ; and in front, the Levator Ani. Of the Spine in Geneeal. The Spinal Column, formed by the junction of the vertebrte, is situated in the median line, at the posterior part of the trunk : its average length is about two feet two or three inches, measured along the curved anterior surface of the column. Of this length the cervical part measures about five, the dorsal about eleven, the lumbar about seven inches, and the sacrum and coccyx the remain- der. Viewed in front, it presents two pyramids joined together at their bases, the upper one being formed by all the vertebrae from the second cervical to the last lumbar ; the lower one by the sacrum and coccyx. When examined more closely, the upper pyramid is seen to be formed of three smaller pyramids. The uppermost of these consists of the six lower cervical vertebrae ; its apex being formed by the axis or second cervical; its base, by the first dorsal. The 132 THE SKELETON. Fig. 88.— Lateral View of the Spine. Ist Cervical or Atlas 2d Cervical or Axis. 1^ Dorsal. io~ "^t /s- '"•m ■<«;;; i^Lo N''(\'^ second pyramid, which is inverted, is formed by the four upper dorsal ver.tebrse, the base being at the first dorsal, the smaller end at the fourth. The third pyramid commences at the fourth dorsal, and gradually increases in size to the fifth lumbar. Viewed laterally (Fig. 88), the spinal column presents several curves, which correspond to the different regions of the column, and are called cervical, dorsal, lumbar, and pelvic. The cer- vical curve commences at the apex of the odon- toid process, and terminates at the middle of the second dorsal vertebra ; it is convex in front, and is the least marked of all the curves. The dorsal curve, which is concave forwards, com- mences at the middle of the second, and ter- minates at the middle of the twelfth dorsal. Its most prominent point behind corresponds to the body of the seventh or eighth vertebra. The lumbar curve commences at the middle of the last dorsal vertebra, and terminates at the sacro-vertebral angle. It is convex ante- riorly ; the convexity of the lower three ver- tebrae being much greater than that of the upper ones. The pelvic curve commences at the sacro-vertebral articulation, and terminates at the point of the coccyx. It is concave an- teriorly. These curves are partly due to the shape of the bodies of the vertebras, and partly to the intervertebral substances, as will be explained in the Articulations of the Spine. The spine has also a slight lateral curva- ture, the convexity of which is directed to- ward the right side. This is most probably produced, as Bichat first explained, chiefly by muscular action ; most persons using the right arm in preference to the left, especially in making long-continued efforts, when the body is curved to the right side. In support of this explanation, it has been found, by B^- clard, that in one or two individuals who were left-handed, the lateral curvature was directed to the left side. The spinal column presents for examina- tion an anterior, a posterior, and two lateral surfaces; a base, summit, and vertebral canal. The anterior surface present the bodies of the vertebrae separated in the recent state by the intervertebral disks. The bodies are broad in the cervical region, narrow in the upper part of the dorsal, and broadest in the lumbar region. The whole of this surface is convex transversely, concave from above downwards in the dorsal region, and convex in the same direction in the cervical and lumbar regions. The posterior surface presents in the median line the spinous processes. These are short, THE SKULL. 133 horizontal, with bifid extremities in the cervical region. In the dorsal region, they are directed obliquely above, assume almost a vertical direction in the middle, and are horizontal below, as are also the spines of the lumbar vertebrae. They are separated by considerable intervals in the loins, by narrower intervals in the neck, and are closely approximated in the middle of the dorsal region. Occasionally one of these processes deviates a little from the median line, a fact to be remembered in practice, as irregularities of this sort are attendant also on fractures or displacements of the spine. On either side of the spinous processes, extending the whole length of the column, is the vertebral groove, formed by the laminae in the cervical and lumbar regions, where it is shallow, and by the laminae and transverse processes in the dorsal region, where it is deep and broad. In the recent state, these grooves lodge the deep muscles of the back. External to the vertebral grooves are the articular processes, and still more externally the transverse processes. In the dorsal region, the latter processes stand back- wards, on a plane considerably posterior to the same processes in the cervical and lumbar regions. In the cervical region, the transverse processes are placed in front of the articular processes, and between the intervertebral foramina. In the lumbar, they are placed also in front of the articular processes, but behind the intervertebral foramina. In the dorsal region, they are posterior both to the articular processes and foramina. The lateral surfaces are separated from the posterior by the articular processes in the cervical and lumbar regions, and by the transverse processes in the dorsal. These surfaces present in front the sides of the bodies of the vertebrae, marked in the dorsal region by the facets for articulation with the heads of the ribs. More posteriorly are the intervertebral foramina, formed by the juxtaposition of the intervertebral notches, oval in shape, smallest in the cervical and upper part of the dorsal regions, and gradually increasing in size to the last lumbar. They are situated between the transverse processes in the neck, and in front of them in the back and loins, and transmit the spinal nerves. The hase of the vertical column is formed by the under surface of the body of the fifth lumbar vertebra ; and the summit by the upper surface of the atlas. The vertebral canal follows the different curves of the spine ; it is largest in those regions in which the spine enjoys the greatest freedom of movement, as in the neck and loins, where it is wide and triangular ; and narrow and rounded in the back, where motion is more limited. THE SKULL. The Skull, or superior expansion of the vertebral column, is composed of four vertebrae, the^elementary parts of which are specially modified in form and size, and almost immovably connected, for the reception of the brain, and special organs of the senses. These vertebrae are the occipital, parietal, frontal, and nasal. Descriptive anatomists, however, divide the skull into two parts, the Cranium and the Face. The Cranium (xpai/oj, a helmet) is composed of eight bones : viz., the occipital, two parietal, frontal, two temporal, sphenoid, and ethmoid. The Face is composed of fourteen bones : viz., the two nasal, two superior maxillary, two lachrymal, two malar, two palate, two inferior turbinated, vomer, and inferior maxillary. The ossicula auditiis, the teeth, and Wormian bones, are not included in this enumeration. "! 134 THE SKELETON. /Occipital. (Two Parietal. I ri ■ or. Frontal. ' Uranium, o hones, m m i ' jiwo Temporal. I Sphenoid. \ Ethmoid. Skull, 22 hones. ( /Two Nasal.^ I Two Superior Maxillary. \Two Lachrymal. ITwo Malar. Face, 14 bones. yTwo Palate. /Two Inferior Turbinated. j Yomer. \lnferior Maxillary. BONES OF THE CRANIUM. The Occipital Bone. The Occipital Bone (Fig. 89) is situated at the back part and base of the cranium, is trapezoid in form, curved upon itself, and presents for examination two surfaces, four borders, and four angles. The External Surface is convex. Midway between the summit of the bone and the posterior margin of the foramen magnum is a prominent tubercle, the external occipital protuberance, for the attachment of the Ligamentum Nuohse ; and descending from it as far as the foramen, a vertical ridge, the external occipital crest. This tubercle and crest vary in prominence in different skulls. Passing outwards from the occipital protuberance on each side are two semi- circular ridges, the superior curved lines ; and running parallel with these from the middle of the crest, are the two inferior curved lines. The surface of the bone above the superior curved lines is smooth on each side, and, in the recent state, is covered by the Occipito-frontalis muscle, whilst the ridges, as well as the surface of the bone between them, serve for the attachment of numerous muscles. The superior curved line gives attachment internally to the Trapezius, externally to the Occipito-frontalis and Sterno-cleido-mastoid, to the extent shown in Fig. 89 ; the depressions between the curved lines to the Complexus internally, the Splenius Capitis and Obliquus Capitis Superior externally. The inferior curved line, and the depressions below it, afford insertion to the Eectus Capitis Posticus Major and Rectus Capitis Posticus Minor muscles. The foramen magnum is a large oval aperture, its long diameter extending from before backwards. It transmits the spinal cord and its membranes, the spinal accessory nerves, and the vertebral arteries. Its back part is wide for the transmission of the cord, and the corresponding margin rough for the attachment of the dura mater inclosing the cord ; the forepart is narrower, being encroached upon by the condyles; it has projecting towards it from below the odontoid process, and its margins are smooth and bevelled internally to support the medulla oblongata. On each side of the foramen magnum are the condyles, for articulation with the atlas ; they are convex, oblong, or reniform in shape, and directed downwards and outwards ; they converge in front, and encroach slightly upon the anterior segment of the foramen. On the inner border of each condyle is a rough tubercle for the attachment of the ligaments (check) which connect this bone with the odontoid process of the axis ; whilst external to them is a rough tubercular prominence, the transverse or jugular process (the representative of the transverse process of a vertebra) channelled in front by a deep notch, which forms part of the jugular foramen. The under surface of this process affords attachment to "the Eectus Capitis Lateralis ; its upper or cerebral surface presents a deep groove which lodges part of the lateral sinus, OCCIPITAL BONE. 135 whilst its prominent extremity is marked by a quadrilateral rough surface, covered with cartilage in the fresh state, and articulating with a similar surface on the petrous portion of the temporal bone. On the outer side of each con- dyle, near its forepart, is a foramen, the anterior condyloid ; it is directed down- Fig. 89.— Occipital Bone. Outer Surface. wards, outwards, and forwards, and transmits the hypoglossal nerve. This foramen is sometimes double. Behind each condyle is a fossa,' sometimes perforated at the bottom by a foramen, the posterior condyloid, for the trans- mission of a vein to the lateral sinus. In front of the foramen magnum is a strong quadrilateral plate of bone, the basilar process, wider behind than in front ; its under surface, which is rough, presenting in the median line a tuber- cular ridge, the pharyngeal spine, for the attachment of the tendinous raph^ and Superior Constrictor of the pharynx ; and, on each side of it, rough depres- sions for the attachment of the Rectus Capitis Anticus Major and Eectus Capitis Anticus Minor muscles. The Internal or Cerebral Surface (Fig. 90) is deeply concave. The posterior or occipital part is divided by a crucial ridge into four fossae. The two supe- rior fossae receive the posterior lobes of the cerebrum, and present slight emi- nences and depressions corresponding to their convolutions. The two inferior, which receive the lateral lobes of the cerebellum, are larger than the former, and comparatively smooth ; both are marked by slight grooves for the lodg- ment of arteries. At the point of meeting of the four divisions of the crucial ridge is an eminence, the internal occipital protuberance. It nearly corresponds to that on the outer surface, and is perforated by one or more large vascular ' This fossa presents many variations in size. It is usually shallow ; and the foramen small ; occasionally wanting, on one, or both sides. Sometimes both fossa and foramen are large, but confined to one side only ; more rarely, the fossa and foramen are very large on both sides. 136 THE SKELETON. foramina. From this eminence, the superior division of the crucial ridge rung upward to the superior angle of the bone; it presents occasionally a deep groove for the superior longitudinal sinus, the margins of which give attachment to the falx cerebri. The inferior division, the internal occipital crest, runs to the Fig. 90. — Occipital Bone. Inner Surface. S u // Aryylg Jaiferiof AnaL posterior margin of the foramen magnum, on the edge of which it becomes gradually lost; this ridge, which is bifurcated below, serves for the attachment of the falx cerebelli. It is usually marked by two small grooves, which com- mence on either side of the posterior margin of the foramen magnum, join together above, and run into the depression for the Torcular Herophili. They lodge the occipital sinuses. The transverse grooves pass outwards to the lateral angles ; they are deeply channelled, for the lodgment of the lateral sinuses, their prominent margins affording attachment to the tentorium cerebelli.' At the point of meeting of these grooves is a depression, the " Torcular Hero- phili,"* placed a little to one or the other side of the internal occipital pro- tuberance. More anteriorly is the foramen magnum, and on each side of it, but nearer its anterior than its posterior part, the internal openings of the ante- ' Usually one of the transverse grooves is deeper and broader than the other; occasionally both grooves are of equal depth and breadth, or both equally indistinct. The broader of the two transverse grooves is nearly always continuous with the vertical groove for the superior longitudinal sinus, and occupies the corresponding side of the median line. 2 The columns of blood coming in different directions were supposed to be 'pre&sed together at this point. OCCIPITAL BONE. 137 rior condyloid foramina ; the internal openings of the posterior condyloid fora- mina being a little external and posterior to them, protected by a small arch of bone. At this part of the internal surface there is a very deep groove, in which the posterior condyloid foramen, when it exists, has its internal termination. This groove is continuous in the complete skull with that which separates the upper from the lower fossae, and lodges the end of the same sinus, the lateral. In front of the foramen magnum is the basilar process, presenting a shallow depression, the basilar groove, which slopes from behind, upwards and forwards, and supports the medulla oblongata ; and on each side of the basilar process is a narrow channel, which, when united with a similar channel on the petrous por- tion of the temporal bone, forms a groove, which lodges the inferior petrosal sinus. Angles. The superior angle is received into the interval between the poste- rior superior angles of the two parietal bones : it corresponds with that part of the skull in the foetus which is called the posterior fontaneUe. The inferior angle is represented by the square-shaped surface of the basilar process. At an early period of life, a layer of cartilage separates this part of the bone from the sphenoid; but in the adult, the union between them is osseous. The lateral angles correspond to the outer ends of the transverse grooves, and are received into the interval between the posterior inferior angles of the parietal and the mastoid portion of the temporal. Borders. The superior extends on each side from the superior to the lateral angle, is deeply serrated for articulation with the parietal bone, and forms, by this union, the lambdoid suture. The inferior border extends from the lateral to the inferior angle ; its upper half is rough, and articulates with the mastoid portion of the temporal, forming the masto-occipital suture: the inferior half articulates with the petrous portion of the temporal, forming the petro-occipital suture ; these two portions are separated from one another by the jugular process. In front of this process is a deep notch, which, with a similar one on the petrous portion of the temporal, forms the foramen lacerum posterius. This notch is occa- sionally subdivided into two parts by a small process of bone, and presents an aperture at its upper part, the internal opening of the posterior condyloid foramen. Structure. The occipital bone consists of two compact laminae, called the outer and inner tables, having between them the diploic tissue : this bone is espe- cially thick at the ridges, protuberances, condyles, and Fig. gi.-Pevelopment of Occipital Bone, anterior part of the basilar /?y SG by the ethmoidal notch. Each orbital vault consists of a smooth, concave, triangular plate of bone, marked at its anterior and external part (immediately beneath the external angular process) by a shallow depression; the lachrymal fossa, for lodging the lachrymal gland ; and at its anterior and internal part, by a depression (sometimes a small tubercle) for the attachment of the fibrous pulley of the Superior Oblique muscle. The ethmoidal notch separates the two orbital plates ; it is quadrilateral ; and filled up, when the bones are united, by the cribriform plate of the ethmoid. The margins of this notch present several half-cells, which, when united with corresponding half-cells on the upper surface of the ethmoid, complete the ethmoidal cells ; two grooves are also seen crossing these edges transversely ; they are converted into canals by articulation with the ethmoid, and are called the anterior and posterior ethmoidal canals ; they open on the inner walls of the orbit. The anterior one transmits the nasal nerve and anterior ethmoidal vessels, the posterior one the posterior ethmoidal vessels. In front of the ethmoidal notch is the nasal spine, a sharp- pointed eminence, which projects downwards and forwards, and articulates in front with the crest of the nasal bones ; behind, it is marked by two grooves, separated by a vertical ridge ; the ridge articulates with the perpendicular lamellee of the ethmoid, the grooves form part of the roof of the nasal fossae. On either side of the base of the nasal spine are the openings of the frontal sinuses. These are two irregular cavities, which extend upwards and outwards, a variable distance, between the two tables of the skull, and are separated from TEMPORAL BONES. 143 one another by a thin bony septum. They give rise to the prominences above the root of the nose, called the nasal eminences and superciliary ridges. In the child they are generally absent, and they become gradually developed as age advances. These cavities vary in size in different persons, are larger in men than in women, and are frequently of unequal size on the two sides, the left being commonly the larger. Occasionally they are subdivided by incomplete bony laminae. They are lined by mucous membrane, and communicate with the nose by the infundibulum, and occasionally with each other by apertures in their septum. The Internal Surface of the Horizontal Portion presents the convex upper surfaces of the orbital plates, separated from each other in the middle line by the ethmoidal notch, and marked by eminences and depressions for the con- volutions of the anterior lobes of the brain. Borders. The border of the vertical portion is thick, strongly serrated, bevelled at the expense of the internal table above, where it rests upon the parietal bones, and at the expense of the external table at each 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 border of the horizontal portion is thin, serrated, and articu- lates with the lesser wing of the sphenoid. Structure. The vertical portion and external angular processes are very thick, consisting of diploic tissue contained between two compact laminse. The horizontal portion is thin, translucent, and composed entirely of compact tissue ; hence the facility with which instruments can penetrate the cranium through this part of the orbit. Development (Fig. 96). The frontal bone is formed in membrane, being deve- loped by two centres, one for each lateral half, which make their appearance, at an early period of foetal life, in the situation of the orbital arches. From this point ossification extends, in a radi- ating manner, upwards into the forehead, and backwards over the orbit. At birth it consists of two pieces, which after- wards become united, along the middle line, by a suture which runs from the vertex to the root of the nose. This su- ture usually becomes obliterated within a few years after birth : but it occasion- ally remains throughout life. Artictilations. With twelve bones: two parietal, sphenoid, ethmoid; two nasal, two superior maxillary, two lach- rymal, and two malar. Attachment of Muscles. The Corrugator Supercilii, Orbicularis Palpebrarum, and Temporal, on each side. Fig. 96.— Frontal Bone at Birth. Developed by two lateral Halves. The Tempoeal Bones. The Temporal Bones are situated at the side and base of the skull, and present for examination a squamous, mastoid, and petrous portion. The Squamous Portion {squama, a scale), (Fig. 97), the anterior and upper part of the bone, is scale-like in form, and thin and translucent in texture. Its outer surface is smooth, convex, and grooved at its back part for the deep tem- poral arteries ; it affords attachment to the Temporal muscle, and forms part of the temporal fossa. At its back part may be seen a curved ridge — part of the temporal ridge ; it serves for the attachment of the temporal fascia, limits the origin of the Temporal mu'scle, and marks the boundary between the 144 THE SKELETON. squamous and mastoid portion of the bone. Projecting from the lower part of the squamous portion is a long arched outgrowth of bone, the zygomatic process. This process is at first directed outwards, its two surfaces looking upwards and downwards ; it then appears as if twisted upon itself, and runs Fi^. 97. — Left Temporal Bone. Outer Surface. 'astoicl foramen forwards, its surfaces now looking inwards and outwards. The superior border of the process 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 muscle. Its outer surface is convex and subcutaneous ; its inner is concave, and also affords attachment to the Masseter. The ex- tremity, broad and deeply serrated, articulates with the malar bone. The zygomatic process is connected to the temporal bone by three divisions, called its roots — an anterior, middle, and posterior. The anterior, which is short, but broad and strong, runs transversely inwards into a rounded eminence, the eminentia articularis. This eminence forms the front boundary of the glenoid fossa, and in the recent state is covered with cartilage. The middle root forms .the outer margin of the glenoid cavity ; running obliquely inwards, it termi- nates at the commencement of a well-marked fissure, the Glaserian fissure ; whilst the posterior root, which is strongly marked, runs from the upper border of the zygoma, in an arched direction, upwards and backwards, forming the posterior part of the temporal ridge. At the junction of the anterior root with the zygoma is a projection, called the tubercle^ for the attachment of the exter- nal lateral ligament of the lower jaw ; and between the anterior and middle roots is an oval depression, forming part of the glenoid fossa (yHi-ji, a socket), for the reception of the condyle of the lower jaw. This fossa is bounded, in front, by the eminentia articularis ; behind, by the vaginal process ; and, ex- ternally, by the auditory process and middle root of the zygoma ; and is di- vided into two parts by a narrow slit, the Glaserian fissure. The anterior part, formed by the squamous portion of the bone, is smooth, covered in the TEMPORAL BONES. 145 recent state with cartilage, and articulates with the condyle of the lower jaw. This part of the glenoid fossa is separated from the auditory process by a small tubercle, the post-glenoid process, the representative of a prominent tubercle which, in some of the mammalia, descends behind the condyle of the jaw, and prevents it being displaced backwards during mastication (Humphry). The posterior part of the glenoid fossa is formed chiefly by the vaginal process of the petrous portion, and lodges part of the parotid gland. The Glaserian fissure, which leads into the tympanum, lodges the processus gracilis of the malleus, and transmits the Laxator Tympani muscle and the tympanic branch of the internal maxillary artery. The chorda tympani nerve passes through a separate canal parallel to the Glaserian fissure (canal of Huguier), on the outer side of the Eustachian tube, in the retiring angle between the squamous and petrous portions of the temporal bone. The internal surface of the squamous portion (Fig. 98) is concave, presents numerous eminences and depressions for the convolutions of the cerebrum, and two well-marked grooves for the branches of the middle meningeal artery. Borders. The superior border is thin, bevelled at the expense of the inter- nal surface, so as to overlap the lower border of the parietal bone, forming the squamous suture. The anterior inferior border is thick, serrated, and bevelled, alternately at the expense of the inner and outer surfaces, for articulation with the great wing of the sphenoid. The Mastoid Portion {iJ-aatb;, a nipple or teat) is situated at the posterior part of the bone ; its outer surface is rough, and perforated by numerous foramina : one of these, of large size, situated at the posterior border of the bone, is termed the mastoid foramen ,■ it transmits a vein to the lateral sinus and a small artery. 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. This process serves for the attachment of the Sterno-mias- toid, Splenius Capitis, and Trachelo-mastoid muscles. On the inner side of the mastoid process is a deep groove, the digastric fossa, for the attachment of the Digastric muscle; and running parallel with it, but more internal, the occipital groove, which lodges the occipital artery. The internal surface of the mastoid portion presents a deep curved groove, which lodges part of the lateral sinus ; and into it may be seen opening the mastoid foramen. A section of the mastoid process shows it to be hollowed out into a number of cellular spaces, communicating with each other, called the mastoid cells ; they open by a single or double orifice into the back of the tympanum; are lined by a pro- longation of its lining membrane ; and, probably, form some secondary part of the organ of hearing. The mastoid cells, like the other sinuses of the cranium, are not developed until after puberty ; hence the prominence of this process in the adult. Borders. The superior border of the mastoid portion is broad and rough, its serrated edge sloping outwards, for articulation with the posterior inferior angle of the parietal bone. The posterior border, also uneven and serrated, articulates with the inferior border of the occipital bone between its lateral angle and jugular process. The Petrous Portion {nirpos, a stone), so named from its extreme density and hardness, is a pyramidal process of bone, wedged in at the base of the skull between the sphenoid and occipital bones. Its direction from without is in- wards, forwards, and a little downwards. It presents for examination a base, an apex, three surfaces, and three borders ; and contains, in its interior, the essential parts of the organ of hearing. The base is applied against the internal surface of the squamous and mastoid portions, its upper half being concealed; but its lower half is exposed by the divergence of those two portions of the 10 146 THE SKELETON, bone wbich brings into view the oval expanded orifice of a canal leading into the tympanum, the meatus auditorius externus. This canal is situated between the mastoid process and the posterior and middle roots of the zygoma; its upper margin is smooth and rounded, but the greater part of its circumference is surrounded by a curved plate of bone, the auditory process, the free margin of which is thick and rough, for the attachment of the cartilage of the external ear. The apex of the petrous portion, rough and uneven, is received into the angular interval between the spinous process of the sphenoid and the basilar process of the occipital ; it presents the anterior or internal orifice of the carotid canal, and forms the posterior and external boundary of the foramen lacerum medium. The anterior surface of the petrous portion (Fig. 98) forms the posterior bound- ary of the middle fossa of the skull. This surface is continuous with the squa- Fig. 98. — Left Temporal Bone. Inner Surface. fie ta/. Vcprcesufn for Vuraviate-r Hiatus fcbUopii ■Ojie^rty Jor Smaller Petrosal N',n>t BcnwssUm f^ Cassenan ga-nrflit^n, ■Bristle passed llrou