^f^MH • it*:- ^^m^ i 5.,*^V.,N~ ' "«i*Aj ^^xi^ '• y?a.ff' „v".:j^^ r* #^ in tfje Citp of i^eto Horfe College of ^fjpgictans! anb ^urgcohii l^eference l^iftrarp ■;?v;JS:: ;^n*gv; R^/-' ..i^ i>si>w4*; ITS VsT <■ ' vr"' MM W^^ '>^^^ •I^^S^ :lS^a^' -^Si^ i^MiliM^iMi '^r l^f', TEXT-BOOK OF ANATOMY EDITED BY D. J. CUNNINGHAM, F.R.S. M.D. fEDIN. ET DUEL.), D.SC, LL.D. (gLASG. ET ST. AND.), D.C.L. (OXON.) PROFESSOR OF ANATOMY, UNIVERSITY OF EDINBURGH ILLUSTRATED WITH 936 WOOD ENGRAVINGS FROM ORIGINAL DRAWINGS, 406 OF WHICH ARE PRINTED IN COLORS THIRD EDITION NEW YORK WILLIAM WOOD AND COMPANY MDCCCCIX TO 5ir SHilUam ^Turner, M,€M. K.R.S., M.B., LL.D., D.C.L., D.SC, IX RECOGNITION OF HIS EMINENCE AS AN ANATOMIST AND HIS INFLUENCE AS A TEACHER THIS VOLUME IS DEDICATED BY THOSE OF HIS FORMER PUPILS AND ASSISTANTS WHO HAVE CONTRIBUTED TO ITS PAGES PRINTED FOR HEXRY FKOWDE, OXFORD CXIVERSITV PRESS, AND HODDER & STOCGHTON, WARWICK SQUARE, E.C., BY R. & R. CLARK, LTD., EDINBURGH. All rights resen-ed PREFACE TO THE THIRD EDITION. The very gratifying reception which this work continues to receive, not only in this country but abroad, has necessitated the production of a third edition. Tlie co-operation of the Authors of the sections on the Bony Skeleton and the Muscular System has therefore been obtained, and the Editor has received every assistance in carrying out all the suggestions made by him with the view of im- proving the work in many ways. The section on Osteology has been mainly re-written, and many useful illustra- tions have been added by the Author, while the addition of illustrations in several colours throughout the section will, it is hoped, largely add to its usefulness to students. The interesting notes on the architecture of Bone, the variations in the Skeleton, Craniology, and the Morphology of the Limbs, are now brought together in appendices to the section, and it is hoped that this will prove a convenience to the student. The section on the Muscular System has been very largely altered, the text has been freely revised, but the chief change will be found in the illustrations. The greater number of the old figures have now been replaced with illustra- tions of new dissections modelled on a different plan. The majority of these new illustrations have been prepared in the Anatomical Department of the University of Edinburgh, under my own personal supervision, but those of the lower limbs, head, and neck, have been carried out under the supervision of the author. Professor A. M. Paterson. In these illustrations the Editor has again had the advantage of Mr. J. T. Murray's assistance, and it will, doubtless, be admitted that he shows all his accustomed vigour and power of anatomical delineation in carry- ing out the work. The new figures represent a great deal of labour on every side and the Editor trusts that the result will justify him. The question of anatomical terminology would appear at the present time to be a difficult one. Of late strong attempts have been made to discard the old British terminology, and to adopt, in its entirety, the B.N.A. nomenclature. It will be remembered that the Editor was one of the original members of the B.N.A. Com- mission, and has naturally been desirous from the first to replace the old by the new nomenclature where possible. In this connection he feels compelled to emphasise the fact that in the first edition of this work the B.N.A. terms were introduced, in all cases of difference, in brackets ; thus the present work has been from the beginning the first Text-book written in the English language which recognised the Basle nomenclature. At the same time, it is the Editor's deliberate opinion that no terminology, however superior or desirable it may be, can ever be forced either on teachers or pupils, and that it can only be a matter of gradual growth. Again it cannot be PEEFACE. V too fully recognised that the labours of the Basle Commission were conducted, not to ensure the adoption of a Latin terminology in every country, but rather a uniform system of nomenclature, and the abolition of many different terms. As a result of long thought and some experience, the Editor has been forced to regard the adoption of a rigid framework of terminology as by no means an un- qualified advantage, and he cannot doubt for a moment that, at any rate in those departments of anatomy where growth of knowledge is more amply evident, any such limitation may act even as a stumbling-block. So far as the Editor is aware the B.N. A. nomenclature has not as yet been entirely adopted among the English-speaking races. He recognises, however, that more may be done to assure its adoption, without imposing undue burdens on the student of the present day. For these reasons, in the re-written sections which comprise the ground -work of the subject, all old nomenclature which could be altered without undue confusion has been so arranged that in most cases, while the older terminology has been given, all alternative nomenclature has been abolished. In many instances (as, for example, the bones of the Carpus or Tarsus) the step has been boldly taken. Eeferences have been given as footnotes in the case of Vessels, Nerves, or other Structures where alteration in name occurs. In relative terms the terms " Medial " and " Lateral " have been employed throughout instead of " Inner " and " Outer." Through illness the Editor has not been able to undertake the full work of revision, and he owes a deep debt of gratitude for the help given him by Mr. J. Keogh Murphy, F.E.C.S., throughout the work. At his suggestion the Publishers have prepared a Glossary of the terms adopted by the Basle Commission to show the student at a glance the essential differences. For the whole he would wish to acknowledge the indebtedness of anatomists throughout the world to Professor His and his colleagues on the Commission. A new and exhaustive Index has been prepared for the present edition by the Editor's own demonstrators in the University of Edinburgh, to whom he tenders his grateful thanks. 18 Grosvenor Crescent, Edinburgh, June 1909. (This edition of the Text-book is the last work that Professor Cunningham undertook ; in spite of failing health he laboured up to the end at the plan and revision of the new edition, and the above Preface was drafted a few days only before he died on 23rd June.) PREFACE TO THE SECOND EDITION. The gratifying reception given to the Text-look of Anatomy, not only in this country but also in America, has rendered it necessary to prepare a new edition. In carrying out this work the whole book has been carefully revised, and a large number of new illustrations have been added. The sections in which the chief changes and additions have been made are those upon Embryology, the Joints, the Muscles, the Brain and Spinal Cord, the Genito- Urinary Organs, the Lymphatics, and Applied Anatomy. By pruning down in various directions, it has been found possible to incorporate a considerable amount of new matter in these and other sections without materially increasing the bulk of the book. The lamented death of Professor Birmingham was felt by all the contributors to be not only a personal loss, but one which materially affected an important section of the book. Although in very bad health, Professor Birmingham was desirous to undertake his share of the work, and he had the sheets on the Digestive System in his possession for this purpose when he died. There was probably no part of the book which required less revision than his, and the Editor has taken upon himself the duty of making the alterations which seemed essential. In doing this he has been careful to avoid unnecessary changes and to preserve throughout the original character of the article. In the section upon the Muscular System, a series of illustrations has been added in which the areas of muscle attachment are delineated upon the bones. Eor the preparation of the specimens, and for assistance in the mapping out of these areas, the Editor is indebted to Dr. E. B. Jamieson. Those who have attempted work of this kind will appreciate the amount of labour and judgment entailed, as it is only by taking the average condition in many specimens, and by the close study of the bones selected for the delineations, that a sufficiently accurate result can be attained. With the exception of the figures which have been added to the sections of the book dealing with Embryology, Osteology, and the Genito-Urinary Organs, the many new illustrations which appear in this edition have been prepared in the Anatomical Department of the University of Edinburgh. In carrying out this work, the Editor has again had the good fortune to secure the co-operation of Mr. J. T. Murray, an artist whose ability in the rendering of anatomical subjects is recognised on all hands. Wherever it was felt that colour would increase the artistic effect or the general usefulness of an illustration, it has been freely employed, both in the case of the old and of the new figures. The Editor cannot conclude this preface to the second edition of the Text-book without expressing his grateful acknowledgment of the assistance which has been so freely extended to him by his fellow-contributors at every stage of the work. He has also to thank many readers of the first edition for calling his attention to typographical errors and other imperfections which had escaped his notice in passing the sheets through the press. 18 Grosvenor Crescent, Edinburgh, August 1905. vi PREFACE TO THE FIRST EDITION. The form which this book has taken expresses the desire of those who have contributed the various sections to produce something which they might dedicate to their former teacher and master, Sir William Turner. With one exception, all the contributors have studied under Sir William Turner, and all but two have for longer or shorter periods acted as his Assistants. Bound together by this common tie, and animated by affection and reverence for their great master, they have sought to produce a book worthy of him whose teaching it so largely reflects, and if this object has not been attained it is not for want of will, but of power, on the part of the writers. In the preparation of a work such as this it is no easy matter to prevent over- lapping of the different articles and to keep the various sections in harmony with each other. Yet in this direction it is believed that a fair amount of success has been attained. Differences of opinion on particular points were bound to arise, but the Editor found in those concerned the greatest readiness to come to a mutual understanding, and he is deeply grateful to his colleagues for the manner in which they endeavoured to lighten his work and assist him in his task. Of course when totally different views were held by two authors on a matter which had to be dealt with in two sections, no serious attempt was made to urge these writers to qualify their statements so as to produce an apparent agreement. It was felt that if this were done the individuality of the author, which forms a characteristic feature of each article as it stands, would thereby be damaged ; and further, it was believed that the same question discussed from two different points of view could not fail to be of advantage to the reader. At the same time it is right to state that the places in which a divergence of opinion appears are very few, and taking into account that nine writers have co-operated with the Editor, a remarkable degree of harmony in the treatment of the different sections has been obtained. The recent introduction of Formalin as a hardening and preserving reagent imposed an especially arduous duty upon those writers who had undertaken the chapters dealing with the thoracic and abdominal viscera. The possibilities for establishing a more accurate topography and of improving our conception of the forms assumed by the viscera under different conditions have by this means been greatly extended ; and in preparing the sections which treat of these organs the writers have taken full advantage of the new method. Much, therefore, which appears in this book on the topographical relations of the viscera departs con- siderably from the older and more conventional descriptions hitherto in vogue. The arrangement of the matter treated in the following pages is very much the same as that adopted in the various courses of lectures delivered in the schools from which the different sections of the work have emanated. The first chapter is vii viii PEEFACE. devoted to the general principles and elementary facts of Embryology. Then follow, in an order best suited for the student, the chapters dealing with the various systems of organs ; whilst the last seventy-five pages are used for the purpose of applying the information conveyed in the preceding part of the book to the practice of medicine and surgery. Each chapter is more or less complete in itself, although an effort has been made to weld them all into one consistent whole. The numerous illustrations which appear in the text are all new in the sense that in no case has an old drawing or an old block been used. Further, the vast majority of the illustrations are new in the sense that they are original. The very few that are not have been taken from monographs dealing with the subjects so illustrated, and in every case the source from which these have been obtained is acknowledged in the text. The drawings for each section were prepared under the personal supervision of its author, and, with the exception of the figures in two chapters, they are the work of Mr. J. T. Murray. This talented artist has devoted much time to the undertaking, and the reader can judge for himself the success which has attended his efforts. The Editor cannot suf&ciently express his indebtedness to Mr. Murray for the great technical skill and the patience which he brought to bear upon this extremely trying and difficult work. The chapter on Osteology has been illustrated by Mr. W. C. Stevens ; that upon Embryology by the authors themselves ; whilst the microscopical drawings in the section on the Brain and Cord were executed by Mr. Wm. Cathie. It is also necessary to mention that the coloured outlines representing the attachments of the muscles on the figures of the bones were mapped in by Professor A. M. Paterson. The Editor has to thank his former Assistant, Professor A. F. Dixon of Cardiff, for much help in the correction of the proofs. Teinity College, Dublin, June 1902. LIST OF CONTRIBUTORS AMBROSE BIRMINGHAM, M.D., F.R.C.S.I., Formerly Professor of Anatomy, Catholic University School of Medicine, Duljlin. {Tlu Digestive System.) D. J. CUNNINGHAM, M.D., F.R.S., Professor of Anatomy, University of Edinburgh. (The Brain and Spinal Cord, The Respiratory System, The Ductless Glands.) A. FRANCIS DIXON, M.B., D.Sc. (Dubl.), Professor of Anatomy, Trinity College, Dublin. {The Urinogenital System.) DAVID HEPBURN, M.D., F.R.S.E., Professor of Anatomy, University College, Cardiff. (Arthrology.) ROBERT HOWDEN, M.A., M.B., Professor of Anatomy, University of Durham. (The Organs of Sense and the Integument.) A. M. PATERSON, M.D., Professor of Anatomy, University of Liverpool. (Myology, The Spinal and Cranial Nerves, Tfie Sympathetic Nervous System.) ARTHUR ROBINSON, M.D., Professor of Anatomy, University of Birmingham. (General Embryology, The Vascular System.) HAROLD J. STILES, M.B., F.R.C.S. Ed., Surgeon to the Royal Hospital for Sick Children, Edinburgh. (Surface and Surgical Anatomy.) ARTHUR THOMSON, M.A., M.B., Professor of Human Anatomy, University of Oxford. (Osteology.) A. H. YOUNG, M.B., F.R.C.S., till recently Professor of Anatomy, Victoria University, Manchester. (General Embryology, The Vascular System.) The New Index is the work of Dr. E. B. Jamieson, M.D. Ed., Mr. T. B. Johnston, M.B., Ch.B., and Mr. R. B. Thomson, M.B., Ch.B., Demonstrators of Anatomy in the University of Edinburgh. CONTENTS. INTEODUCTION. GENERAL EMBEYOLOGY. The Animal Cell PAGE 8 Mouth and Nose PAGE 38 Eeproduction of Cells 9 External Ear, Tympanic Cavity, and The Ovum 10 Eustachian Tube .... 43 Its Structure .... 10 Hind-gut, Anal Passage, and Post-anal Its Maturation .... 12 Gut 45 The Spermatozoon .... 14 The Limbs 46 Fertilisation of the Ovum 16 Nutrition and Protection of Embryo Segmentation of Ovum 17 during Intrauterine Existence 47 Formation of Blastodermic Vesicle 18 Festal Membranes and Appendages 48 Ectoderm and Entoderm . 19 Yolk-Sac 48 Embryonic Area 19 Amnion ...... 48 Neural Groove and Tube . 21 Body-Stalk 50 Formation of Notochord . 24 Allantois ...... 51 Formation of Ccelom 24 Umbilical Cord .... 51 Mesodermic Somites . 26 Chorion 52 Folding off of the Embryo 26 The Placenta 52 The Embryo 28 Primitive Vascular System and Foetal Primitive Alimentary Canal . 32 Circulation 60 Pharynx and Stomatodseum . 34 External Features of Human Embryo Visceral Clefts and Arches 35 at dijBferent periods 65 OSTEOLOGY. The Skeleton 69 The Lacrimal Bones . 131 Composition of Bone 70 The Vomer . . 131 Structure of Bone 71 Nasal Bones 132 Ossification and Growth of Bones 73 Wormian Bones . 133 The Vertebral Column . 75 Bones of the Face . . 133 A Typical Vertebra 76 Maxillae . . . . . 133 Cervical Vertebrae . 78 Palate Bones . . 138 Thoracic Vertebrse . 81 Zygomatic Bones 140 Lumbar Vertebrae . 83 Mandible . . . . . 142 False or Fixed Vertebrae 84 The Hyoid Bone . . 145 Sacrum . . . ... 84 The Skull as a whole . 146 Coccyx 87 Norma Frontalis .• 146 The Verteljral Column as a whole 88 Norma Lateralis 151 The Cartilaginous Verteljral Column 90 Norma Occipitalis . . 157 Ossification of tlie Vertel»r;e . 92 Norma Verticalis 158 The Stenium 94 Norma Basalis . 159 Tlie Ribs 97 The Skull in Section . . 166 The Costal Cartilages 100 Up])er Surface of tlie B ase of the The Thorax as a whole . 101 Skull . 166 The Bones of the Skull . 103 Medial Sagittal Section ol the Skull 170 Frontal Bone .... 103 Nasal Fossa? . 170 Paiietal Bones .... 106 Nasal Septum . . 172 Occipital Bone .... 108 Air-sinuses in connexion a villi Nasal Temporal Bones 112 Fosste 172 Sphenoid Bone. Ethmoid Bone .... 121 Coronal Sections . 173 127 Horizontal Section of the Skull . 179 Inferior Turbinated Bones 130 Sexual Differences in Skull . 180 CONTENTS. xi PAOB PAGE Differences due to Age . 181 Tarsus 238 Bones of Upper Extremity 181 Talus or Astragalus . 238 Clavicle 181 Calcaneus . 243 Scapula 183 Navicular Bone 245 Humerus 188 Cuneiform Bones 245 Ulna 194 Cuboid Bone 247 Radius 198 The Tarsus as a whole 248 Carpal Bones .... 201 Metatarsal Bones 249 Carpus as a whole 206 Phalanges . 251 Metacarpal Bones 207 Sesamoid Bones 253 Phalangeal Bones 210 Appendix — Sesamoid Bones 212 Architecture of the Bones of tht Bones of the Lower Limb 212 Skeleton .... i Pelvic Girdle and Lower Extremity 212 Variations in the Skeleton vi Innominate Bone 212 Serial Homologies of the Vertebrae xiii Pelvis 219 Measurements and Indices inPhysica L Femur 223 Anthropology . . XV Patella 229 Developmentof the Chondro-crauiun Tibia 230 and Morphology of the Skull XX Fibula 234 Morphology of the Limbs xxiii THE AETICULATIONS OR JOINTS. Arthrology Spiarthroses .... Movable Joints .... Structures which enter into th Formation of Joints Different Kinds of Movement at Joints . Development of Joints Morphology of Ligaments Ligaments of the Vertebral Column and Skull Articulation of Atlas with Axis Articulation of Spine with Cranium Temporo-mandibular Joint . Cranial Ligaments not directly asso ciated with Articulations Joints of Thorax Costo-central Joints . Costo-transverse Joints Articulations between the Ribs and their Cartilages Interchondral Joints Costo-sternal Joints . Sternal Articulations Articulations of the Superior Extremity Articulations of the Clavicle Sterno-clavicular Joint 255 j 255 I 256 i 257 I 259 j 259 I 261 ! 261 265 266 267 269 269 269 270 271 271 271 272 273 273 273 Acromio - clavicular or Scapulo clavicular Joint 274 Ligaments of Scapula . 275 Shoulder-joint .... 276 Elbow-joint 279 Radio-ulnar Joints 281 Radio-carpal Joint 283 Carjjal Joints .... 284 Intermetacarpal Joints . 287 Carpo-metacarjjal Joints 287 Metacarpo-phalangeal Joints 288 Interphalangeal Joints . 288 Articulations and Ligaments of Pelvis 289 Lumbo-sacral Joints 289 Sacro-iliac Joint . . . . 290 Symphysis Pubis .... 292 Articulations of Lower Extremity 293 Hip-joint 293 Knee-joint .... 297 Tibio-fibular Joints . 304 Joints of Foot .... 306 Ankle-joint .... 306 Intertarsal Joints 308 Tarso-metatarsal Joints 313 Intermetatarsal Joints 314 Metatarso-phalangeal Joints 314 Interphalangeal Joints 314 THE MUSCULAR SYSTEM. The Muscular System . Fascite ...... Description of the Muscles Appendicular Muscles . Fasci* and Superficial Muscles of the Back Fascise ...... The Superficial Muscles of the Back The Fasciae and Muscles of the Pectoral Region ..... Fasciae ...... Muscles of the Pectoral Region Fasciae and Muscles of the Shoulder 317 318 319 319 319 319 319 322 322 323 327 Muscles Fasciae and Muscles of the Arm Fasciae and Muscles of the Forearm and Hand Fasciae The Muscles of the Front and Media Aspect of the Forearm . Superficial Muscles Intermediate Layer Deep Layer ..... Short Muscles of the Hand . Muscles of the Thumb . Muscles of the Little Finger . 327 332 336 336 338 338 341 341 343 343 345 Xll CONTENTS. Tlie Interosseous Muscles The Muscles on tlie Back of tlie Forearm Superficial Muscles . Deep Muscles . The Lower Limb . Fascife and Muscles of the Thigh and Buttock Fasciag Muscles of the Thigh and Buttock The Muscles of the^Front of the Thigh The Muscles on the Medial Side of the Thigh The Muscles of the Buttock . The Muscles on the Back of the Thigh The Hamstring Muscles The Fasciae and Muscles of the Leg and Foot Fascice ...... The Muscles of the Leg and Foot . The Muscles on the Front of the Leg and Dor-sum of the Foot The Muscles on the Lateral Side of the Leg The Muscles on the Back of the Leg The Muscles in the Sole of the Foot Axial Muscles .... The Fascife and Muscles of the Back The Fasciae of the Back . The Muscles of the Back First Group . Second Group Third Group . PAGE 346 347 348 349 353 353 353 356 356 361 364 368 368 371 371 373 373 375 376 380 385 385 385 386 386 387 389 Fourth Group The Fasciae and Muscles of the Head and Neck .... Fasciae ...... The Muscles of the Head Superficial Muscles The Muscles of the Scalp The Muscles of the Face The Fascias and Muscles of the Orbit Muscles of Mastication . The Muscles of the Neck The Muscles of the Hyoid Bone The Muscles of the Tongue . The Muscles of the Pharynx . The Muscles of the Soft Palate Deep Lateral and Praevertebral Muscles of the Neck . . ' . The Muscles of the Thorax . Muscles of Eespiration . Fasciae and Muscles of the Abdominal WaU Fasciae ...... The Muscles of the Abdominal Wall Fasciae and Muscles of the Periiieum and Pelvis .... Fasciae of the Perineum . The Muscles of the Perineum The Fasciae of the Pelvis Muscles of the Pelvis The Development and MorjDhology of the Skeletal Muscles PAGE 391 394 394 395 395 395 397 399 401 404 405 408 410 412 413 415 415 419 420 421 430 430 431 433 438 439 THE NEEVOUS SYSTEM. Cerebrospinal Nervous System Nerve-fibres ..... Nerve-cells ..... Neuroglia ..... Spinal Cord Internal Structure of Sj)inal Cord Characters presented by Cord in its Different Eegions . Component Parts of Gray Matter of Spinal Cord .... Component Parts of the White Matter of the Sjjinal Cord Development of Spinal Cord . Brain or Encephalon . General Outline of Development of Brain Parts of Encephalon derived from the Hind-brain .... Medulla Oblongata or Bulb Pons Varolii .... Internal Structure of Medulla . Internal Structure of Pons A^'arolii Cerebellum Minute Structure of a Cerebellar Folium Deep Connexions of Cranial Nerves attached to Medulla and Pons Development of Parts derived from Ilhombencephalon . Mesencephalon .... Internal Structure of Mesencephalon Deep Origin of Cranial Nerves which arise within the Mesencephalon . Development of Mesencephalon Fore-brain ...... Parts derived from the Diencephalon 443 444 445 451 452 456 460 461 465 471 474 476 481 481 486 489 499 505 512 514 526 531 533 540 542 542 542 Optic Thalamus Subthalamic Tegmental Region Pineal Body Trigonum Habenulae Corpora Mammillaria Pituitary Body . Third Ventricle Cerebral Connexions of Optic Tract Parts derived from the Telencephalon Cerebral Hemisj)heres Olfactory Lobe .... Corpus Callosum, Septum Lucidum and Fornix .... Lateral Ventricle Basal Ganglia of Cerebral Hemi sphere Intimate Structure of Cerebral Hemi sphere Cerebral Cortex Olfactory Tract and Bulb . White Medullary Centre of Cerebral Hemisjjhere . Develoj^ment of Parts derived from Fore-brain .... Weight of Brain Meninges of Brain and Spinal Cord Dura Mater .... Arachnoidea .... Pia Mater Spinal Nerves .... Posterior Primary Divisions of Spinal Nerves . Cervical Nerves Thoracic Nerves Lumbar Nerves Sacral and Coccygeal Nerves 542 546 547 547 548 549 550 551 553 553 569 570 573 579 584 584 587 588 594 597 597 597 600 603 607 610 611 613 613 613 CONTENTS. xiu Morphology of Posterior Primary Divisions . . . . . Anterior Primary Divisions of Spinal Nerves ..... Cervical Nerves .... Cervical Plexus .... Phrenic Nerve .... Morphology of Cervical Ple.\us Brachial Plexus .... Branches of Brachial Plexus Anterior Thoracic Nerves Musculo-cutaneous Nerve Median Nerve .... Uhiar Nerve .... Internal Cutaneous Nerve Lesser Internal Cutaneous Nerve Circumflex Nerve Musculo-spiral Nerve Eadial Nerve .... Posterior Interosseous Nerve . Subscapular Nerves . Thoracic Nerves .... Lumbo-sacral Plexus Lumbar Plexus .... Obturator Nerve Anterior Crural Nerve Sacral or Sciatic Plexus Great Sciatic Nerve . Nerves of Distribution from the Sacral Plexus Peroneal Nerve .... Anterior Tibial Nerve Musculo-cutaneous Nerve . Tibial Nerve .... Internal Plantar Nerve External Plantar Nerve . 614 615 617 617 621 622 622 624 626 627 627 629 631 632 632 632 634 634 635 635 639 641 643 645 647 648 649 650 651 651 652 654 654 Pudendal Plexus .... Pudic Nerve .... Development of Spinal Nerves Morphology of Limb-plexuses Distribution of Spinal Nerves to Muscles and Skin of Limbs Variations in Position of Limb-plexuses Significance of Limb-plexuses Cranial Nerves .... First or Olfactory Nerve . Second or Optic Nerve Third or Oculo-motor Nerve . Fourth or Trochlear Nerve Fifth, Trigeminal or Trifacial Nerve Sixth or Abducent Nerve Seventh or Facial Nerve . Eighth or Auditory Nerve Ninth or Glosso-pharyngeal Nerve Tenth or Pneumogastric Nerve Thoracic Plexuses .... Eleventh or Spinal Accessory Nerve Twelfth or Hypoglossal Nerve . Development of Cranial Nerves Morphology of Cranial Nerves Sympathetic Nervous System . Cervical Part of Sympathetic Cord Superior Cervical Ganglion Middle Cervical Ganglion Inferior Cervical Ganglion Thoracic Part of Sympathetic Coi-d Lumbar Part of Sympathetic Cord Sacral Part of Gangliated Cord Sympathetic Plexuses . Solar and Pelvic Plexuses Development of Sympathetic System Morphology of Sympathetic System PAOB 655 658 660 662 665 673 674 674 675 675 676 677 678 686 686 688 689 690 693 695 696 698 700 703 706 706 708 708 708 710 711 712 712 715 716 THE OEGANS OF SENSE AND THE INTEGUMENT. Nose 717 Pinna . 743 Cartilages of Nose . 717 External Auditory Meatus 746 Nasal Fosste ..... 719 Middle Ear or Tympanic Cavity . 748 Eye 723 Mastoid Antrum and Mastoid A Lir- Eyeball 724 cells ..... . 752 Sclera 725 Eustachian Tube . 753 Cornea 726 Tympanic Ossicles . 754 Vascular and Pigmented Tunic 727 Internal Ear ..... . 759 Retina 731 Osseous Labyrinth .... . 759 Refracting Media of Eyeball . 735 Membranous Labyrinth . . 762 Eyelids 738 Development of Labyrinth . 769 Lacrimal Apparatus 740 Organs op Taste .... 770 Development of Eye 741 Skin or Integument . . 772 Ear 743 Appendages of Skin . 775 External Ear 743 Development of Skin and its Appenda ges 778 THE VASCULAE SYSTEM. Structure of Blood-vesse s 780 Heart .... 783 Chambers of Heart 786 Structure of the Heart 791 Pericardium . 793 Arteries 795 Pulmonary Artery . 795 Systemic Arteries . 797 Aorta 797 Thoracic Aorta 797 Abdominal Aorta . 798 Branches of Ascending Aorta . . 800 Coronary Ai-teries .... 800 Branches of Arch of Aorta . . . 800 Innominate Artery .... 801 Arteries of Head and Neck . . . 801 Common Carotid Arteries . . . 801 External Carotid Artery . . . 803 Branches of External Carotid Artery 804 Internal Carotid Artery . . . 813 Branches of Internal Carotid Artery 814 Vertebral Artery . . . . 818 XIV CONTENTS. Arteries of Upper Extremity Subclavian Arteries ... Branclies of Subclavian Artery Axillarj^ Artery .... Brandies of Axillary Artery Brachial Artery .... Brandies of Brachial Artery Radial Ai-tery .... Ulnar Artery .... Arterial Ai'ches of Wrist and Hand Branches of Descending Thoracic Aorta Parietal Branches of Descending Thoracic Aorta . . . . Visceral Brandies of Descending Thoracic Aorta Branches of Abdominal Aorta Parietal Branches of Abdominal Aorta Common Iliac Arteries . . ' Paired Visceral Branches of Abdomi nal Aorta .... Unpaired or Single Visceral Branches of Abdominal Aorta Internal Iliac Artery Branches of Posterior Division Branches of Anterior Division of In ternal Iliac Artery Visceral Branches Parietal Branches of Anterior Divi- sion of Internal Iliac Arteries of Lower Extremity External Iliac Artery Femoral Artery Popliteal Artery Posterior Tibial Artery Plantar Arteries Anterior Tibial Artery Veixs Pulmonary Veins . Systemic Veins Coronary Sinus and Veins of Heart Superior Vena Cava and its Tribu taries ..... Azygos Veins .... Innominate Veins Veins of Head and Neck Veins of Scalj) .... Veins of Orbit, Nose, and Pterygo maxillary Region . Venous Sinuses and Veins of Cranium and of its Contents Dijjloic and Meningeal Veins . Veins of Brain .... Blood Sinuses of Cranium Spinal Veins .... Veins of Upper Extremity Deep Veins of Upper Extremity Axillary Vein .... Suj^erficial Veins of U2)2Jer Extre inity PAGE 821 821 823 827 828 830 831 831 834 835 837 837 838 839 839 841 842 843 848 850 851 851 852 856 856 858 863 864 865 867 870 870 870 871 871 872 873 875 879 879 881 883 887 PAGE Inferior Vena Cava and its Tributaries 892 Iliac Veins 895 Veins of Lower Extremity . . . 897 Deep Veins of Lower Extremity . 897 Superficial Veins of Lower Extre- mity 900 Portal System 901 Mesenteric and Splenic Veins . . 903 Lymph Vascular System . . . 904 Terminal Lymph Vessels . . . 906 Lymphatic Vessels and Glands of Head and Neck 909 Lymphatic Glands and Vessels of Upper Extremity 913 Lymphatic Glands and Vessels of Lower Extremity 916 Lymphatic Glands and Vessels of Ab- domen and Pelvis . . . . 918 Lymphatic Glands and Lymphatic Vessels of Thorax .... 923 Development of Blood Vascular System 925 Pericardium, the Primitive Aortse, and Heart 925 Development of Heart, of first part of Aorta, and of Pulmonary Artery 928 Division of Heart into its different Chambers, and Division of Aortic Bulb 929 Aortic Arches — Formation of Chief Arteries 932 Primitive Dorsal Aortse — Formation of Descending Aorta . . . 933 Branches of Primitive Dorsal Aortse 933 Arteries of Limbs . . . . 933 Development of Veins . . . . 934 Veins of Limbs 938 Pulmonary Veins .... 938 Morphology of Vascular System . 938 Segmental Arteries and their Ana- stomoses 939 Aorta, Pulmonary Artery, and other Chief Stem Vessels . . .942 Limb Arteries ..... 943 Morphology of Veins . . . 943 Abnormalities of Vascular System . 946 Abnormalities of Heart .... 946 Abnormalities of Arteries . . . 947 Branches of Aorta .... 947 Arteries of Head and Neck . . 950 Arteries of Upper Limb . . .951 Iliac Arteries and their Branches . 952 Arteries of Lower Limb . . . 953 Abnormalities of Veins .... 954 Superior Vena Cava .... 954 Veins of Upper Extremity . . 955 Inferior Vena Cava .... 955 Veins of Lower Extremity . . 955 Abnormalities of Lymphatics . . 955 THE RESPIEATOKY SYSTEM. Organs of Respiration and Voice . . 957 Larynx or Organ of Voice . . .957 Caitiiages of Larynx .... 958 Joints, Ligaments, and Membranes of Larynx 961 Interior of Larynx 964 Laryngeal Muscles 968 Trachea 972 Bronchi Thoracic Cavity Pleural Memljranes Mediastinal or Intei'pleural Space Lungs Root of Lung Structure of Lung Develoj)ment of Respiratory Apparatus 975 976 977 982 983 989 990 992 CONTENTS. XV THE DIGESTIVE SYSTEM. Mouth Palate and Isthmus Faucium Tongue ...... Glands Salivary Glands ... Development of Salivary Glands Palate, and Tongue Teeth Permanent Teeth Milk Teeth .... Structure of Teeth ... Develojjment of Teeth Morphology of Teeth Pharynx ...... Development of Pharynx and Tonsil CEsophagus Development of CEsophagus Abdominal Cavity .... Subdivision of Abdominal Cavity Peritoneum ..... Stomach ...... PAOK 995 998 1000 1007 1009 1013 1014 1016 1022 1023 1025 1029 1029 1037 1038 1042 1043 1045 1048 1050 Structure of Stomach PAOE . 1058 Intestines . 1060 Structure of Intestines . 1061 Small Intestine . 1064 Duodenum .... . 1065 Jejunum and Ileum . 1071 Large Intestine . 1074 Ciecum and Appendix . . 1076 Colon ..... . 1082 Kectum ..... . 1087 Anal Canal .... . 1091 Peritoneum .... . 1097 Development of Intestinal Cana , and Peritoneum . . 1105 Liver ..... . 1108 Gail-Bladder and Bile Passages . 1118 Vessels of Liver . 1120 Structure of Liver . . 1121 Development of Liver . 1122 Pancreas. .... . 1124 Development of Pancreas . . 1129 THE UEINOGENITAL SYSTEM. Urinary Organs . Kidneys Bladder ..... Urethra .... Male Reproductive Organs Testis . Vas Deferens . Descent of Testis . Spermatic Cord Scrotum . Penis Prostate . 1130 1130 1144 1157 1159 1159 1162 1167 1168 1169 1170 1173 Cowper's Glands .... Male Urethra .... Female Reproductive Organs . Ovary ...... Fallopian Tubes .... Uterus ...... Vagina ...... Female External Genital Organs . Glands of Bartholin . Development of Urinogenital Organs Mammary Glands .... Development of Mammae 1176 1177 1181 1182 1185 1187 1192 1195 1198 1198 1207 1209 THE DUCTLESS GLANDS. Spleen . Suprarenal Capsules Thyreoid Body 1210 1213 1216 Parathyreoids . Thymus Gland Carotid and Coccygeal Bodies 1218 1218 1220 SUKFACE AND SUKGICAL ANATOMY. Head and Neck Cranium Face . Neck Thorax . Lungs Heart and Great Vessels Abdomen Anterior Abdominal Wall Abdominal Cavity Male Perineum Prostate . Female Pelvis Back 1222 1222 1236 1246 1253 1255 1262 1264 1264 1267 1277 1278 1282 1284 Upper Extremity . Shoulder . Axilla Upper Arm Elbow Forearm and Hand Lower Extremity . Buttock Back of the Thigh Popliteal Space. Front of Thigh . Knee . Leg . Foot and Ankle 1291 1291 1293 1295 1296 1298 1302 1302 1303 1305 1305 1307 1308 1310 INDEX 1313 LIST OF ILLUSTRATIONS. GENEEAL EMBRYOLOGY. FIG. 1. 2. 3. 4. 5. 9. 10. 11. 12. 13. 14. 15. 16. 17. 18. 19. 20. 21. 22. 23. 24. 25. 26. 27. 28. 29. Horizontal Section through Trunk at Level of First Lumbar Vertebra . Diagram of an Animal Cell Cell-Division The Ovum and its Coverings . Maturation of the Ovum : Extrusion of the "Polar Bodies". Diagram illustrating the Maturation of the Ovum .... Diagram illustrating the Process of Cell-Division resulting in the Formation of Spermatids which are afterwards modified into Sper- matozoa ..... Human Spermatozoa Structure of a Human Spermatozoon Fertilisation of the Ovum Segmentation of the Fertilised Ovum in the Rabbit .... Conversion of the Morula to the Blastula ..... Surface View of the Blastodermic Vesicle The Upper Pole of the Blastodermic Vesicle ...... Transverse Section of a Ferret Embryo Transverse Section of a Ferret Embiyo Surface Areas of the Blastoderm Sections showing the different Areas of the Blastodermic Vesicle Extension of Mesoderm and Forma- tion of Ccelom .... Surface View of an Early Embryo . Early Stages in the Folding-oflf of the Embryo The Relative Positions of the Blastodermic Layers in the Body of the Embryo when the " Fold- ing-off " is completed Transverse Section of a Ferret Embryo Further Differentiation of the Meso- derm ...... Coronal Section of a Rat Embryo . Tiansverse Section of a Rat Embryo Diagram of a Developing Ovum, .seen in Longitudinal Section Diagram representing the Condition of the Alimentaiy Canal in a Human Emljryo about fifteen days old (modified from His) Further Development of the Aliment- ary Canal, as seen in a Human Embryo about five weeks old PAGE 4 8 9 11 FIG. 30. 31. 12 32. 13 33. 34. 14 15 15 16 35. 36. 37. 17 18 38. 19 39. 20 20 40. 21 23 41. 24 42. 25 25 43. 27 44. 45. 28 46. 29 47. 29 30 31 48. 49. 32 50. 51. 33 52 34 Stages in the Formation of the Tongue and Upper Aperture of the Larynx in the Human Embryo (after His) Head of Human Embryo (four views ; two after His) .... Head of Human Embryo (four views ; two after His) .... Head of Human Embryo (two views ; one after His) .... Vertical Section through Head of Rat Embryo .... Transverse Section through the Head of a Rat Embryo Figures, modified from His, illustrat- ing the Formation of the Pinna . Diagrams showing the Separation of the Cloacal Part of the Hind-gut into Geni to - urinary Tract and Rectum Transverse Sections of the Uterus and Developing Ovum of a Ferret Very young Human Ovum almost immediately after its entrance into the Decidua .... Relation of the young Human Ovum to the Decidua .... Further Stage of Development of the Human Ovum and its Relation to the Decidual Tissues . Completion of the Decidua Capsu- laris, etc Enlargement of the Blood Sinuses in the Maternal Part of the Placenta and the Closure of the Amnion . Fcetal Ectoderm surrounding the Maternal Blood Sinuses, etc. Further Growth of the Placental Sinuses and Villi, etc. Later Stage in the Development of the Placenta .... Development of Blood -Vessels in the Vascular Area of the Rat The Primitive Blood-Vessels of the Embryo Blood - Vessels of a Mammalian Embryo after the Formation of the Heart Diagram of the Foetal Circulation . Human Embryo at the end of the 12th, 13th, and 14th days of De- velopment (after His) . Human Embrvo at the 21st, 23rd, and 27th days of Development (after His) 36 39 40 41 42 43 44 46 49 53 53 54 54 55 55 56 58 61 62 63 64 65 66 LIST OF ILLUSTEATIONS. xvii 53. Human Embryo at the 29th and 32nd days of Development (after His) . 64. Human Foetus at the sixth week of Development (after His) 55. Human Fojtus six and a half weeks 67 old (after His) .... 67 ' 56. Human Foetus eight and a half 67 weeks old (after His) ... 68 OSTEOLOGY. 57 a. Fifth Thoracic Vertebra from the Right Side 77 51 h. Fifth Thoracic Vertebra from Above 77 58. Fourth Cervical Vertebra, (A) from Above, (B) from the Eight Side . 78 59. Tlie Atlas from Above ... 79 60 a. Axis from Behind and Above . 80 60 b. Axis from the Left Side . . 80 61. First, Ninth, Tenth, Eleventh, and Twelfth Thoracic Vertebrte from the Left Side .... 82 62. Third Lumbar Vertebra, (A) from Above, and (B) from the Left Side 83 63. The Sacrum (anterior view) . . 85 64. The Sacrum (posterior view) . . 86 65. The Coccyx 87 66. Vertebral Column from the Left Side 89 67. Vertebral Column as seen from Behind 90 68. The Development of the Membranous Basis of a Vertebra . . . 91 69 a. Ossification of Vertebrae . . 92 69 b. Ossification of Vertebrae . . 93 70. Ossification of the Sacrum . . 94 71. The Sternum (anterior view) . . 95 72. Ossification of the Sternum . . 96 73. Fifth Right Rib as seen from Below 98 74. Fifth Right Rib as seen from Behind 99 75. First and Second Right Ribs as seen from Above ... 99 76. The Thorax as seen from the Front . 100 77. The Thorax as seen from the Right Side 101 78. The Frontal Bone (anterior view) . 104 79. The Frontal Bone as seen from Below 105 80. Ossification of the Frontal Bone . 106 81. The Right Parietal Bone (jiarietal surface) 106 82. The Right Parietal Bone (cerebral surface) ..... 107 83. The Occipital Bone as seen from Below 110 84. Occipital Bone (cerebral surface) . Ill 85. Ossification of the Occipital Bone . 112 86. The Right Temporal Bone seen from the Parietal Side . . .114 87. The Right Temporal Bone (cerebral aspect) 115 88. The Right Temporal Bone seen from Below 117 89. A Preparation to show the Position and Relations of the Mastoid Antrum 118 90 a. Vertical Transverse Section through the Left Temporal Bone (anterior half of sectioia) . . . .119 90 b. Vertical Transverse Section through the Left Temporal Bone (pos- terior half of section) . . 119 90 c. Horizontal Section through the Left Temporal Bone (lower half of section) 120 97. 98. 99. 100 101. 91. The Parietal and Cerebral Surfaces of the Right Temporal Bone at Birth 121 92. The Sphenoid seen from Behind . 122 93. The Sphenoid seen from the Fi'ont 122 94. Ossification of the Sphenoid . . 126 95. The Ethmoid seen from Behind . 127 96. The Ethmoid seen from the Right Side 128 Section showing the Nasal Aspect of the Left Lateral Mass of the Ethmoid 128 Showing the Articulation of the Inferior Turbinated Bone with the Ethmoid . . . .129 The Ethmoid seen from Above . 129 Right Inferior Turbinated Bone, (A) Medial Surface, (B) Lateral Surface 130 The Right Lacrimal Bone . . 131 102. The Vomer seen from the Right Side 132 103. The Vomer at Birth . . .132 104. The Right Nasal Bone, (A) Lateral Side, (B) Medial Side . . 133 105 a. The Right Maxilla (lateral aspect) 134 105 6. The Right Maxilla (medial aspect) 134 106. Ossification of the Maxilla . . 137 107. The Right Palate Bone, (A) from the Lateral Side, (B) from the Medial Side 138 108. The Right Palate Bone from Behind 139 109. The Right Zygomatic Bone, (A) Lateral Side, (B) Medial Side . 141 110. Medial Surface of the Zygomatic Bone at Birth .... 141 Ilia. The Mandible from the Left Side 142 1116. Medial Side of the Right Half of the Mandible .... 143 112. The Mandible at Birth, (A) from Above, (B) Lateral Side, (C) Medial Side .... 144 113. The Hyoid Bone as seen from the Front 145 Norma Frontalis of the Skull . 148 Norma Lateralis of the Skull . 152 Coronal Section through the Spheno - maxillary (Pterygo - palatine) Fossa of the Right Side 157 Norma Basalis of the Skull . . 160 Base of the Skull seen from Above 167 1 19. Medial Aspect of Left Half of Skull sagittally divided . . . 171 120. Nasal Septum seen from the Left Side 173 121. Part of the Frontal, Nasal, and Maxillary Bones removed in order to disj^lay the relation of the various cavities exposed . 174 122. Coronal Section passing inferiorly through the interval between the First and Second Molar Teeth 175 114 115, 116 117 118 LIST OF ILLUSTKATIONS. FIG. PAGE 123. Coronal Section passing througli tlie Splieno-maxillaiy Fossa . 176 124. Coronal Sectionof the Skull passing through the Glenoid Fossa just behind the Articular Eminence 177 125. Anterior Surface of the Section of the Skull immediately behind the preceding Section . . 178 126. Vertical Section through the Skull immediately in front of the Root of the Styloid Process . . 179 127. Horizontal Section of the Skull a little below the level of the Inferior Orbital Margin . . 180 128 a. The Right Clavicle seen from Above 181 128 b. The Upper Surface of the Right Clavicle with Muscle Attach- ments niajDj^ed out . . . 182 129 a. The Right Clavicle seen from Below 182 129 b. The Under Surface of the Right Clavicle with the Muscular Attachments majjjJed out . . 182 130. Ossification of the Clavicle . . 183 131 a. The Right Scapula seen from Behind 184 131 b. The Dorsum of the Right Scapula ^vith the Muscular Attachments majjped out . . . .185 132 a. The Right Scapula seen from the Front 186 132 b. Ventral Aspect of the Right Scapula with Muscular Attach- ments map23ed out . . .186 133. Ossification of the Scapula . . 188 134 a. Anterior View of the Right Humerus 189 134 b. The Anterior Aspect of the Right Humerus Avith Muscular Attach- ments majDped out . . .189 135 a. Posterior View of the Right Humerus 190 135 b. Posterior Asjsect of the Right Humerus with Attachments of Muscles mapped out . . 191 136. The Head of the Right Humerus seen from Above . . . .192 137. The Lower Extremity of the Right Humerus seen from Below . . 192 138. The Lower End of the Right Humerus seen from the Lateral Side 192 139. Ossification of the Humerus . . 193 140. The Right Ulna viewed from the Lateral Side 194 141 a. The Right Radius and Ulna seen from the Front .... 195 141 b. Anterior Aspect of Bones of the Forearm with Muscular Attach- ments mapped out . . . 196 142. The Ossification of tlie Ulna . . 197 143 a. Tlie Radius and Ulna seen from Behind 198 143 b. Posterior Aspect of Bones of Rigli t Forearm witli Attachments of Muscles mapped out . . . 199 144. The Ossification of the Radius . 201 145 a. The Bones of tlie Right Wrist and Hand seen from the Front . . 201 145 b. Palmar Aspect of Bones of the Right Carpus and Metacarpus with Muscular Attachments majDped out .... 145 c. Dorsal Aspect of Bones of the Right Carpus and Metacarpus with Muscular Attachments maj)2)ed out .... 145 fZ. Tlie Bones of the Right Wrist and Hand seen from Behind 146. The Right Navicular Bone . 147. The Right Os Lunatum . 148. The Right Os Triquetrum . 149. The Right Pisiform Bone 150. The Right Large Multangular Bone ...... 151. The Right Small Multangular Bone ...... 152. The Right Capitate Bone 153. The Right Os Hamatum 154. Radiograph of the Hand at Birth . 155. The First Right Metacarpal Bone . 156 a. The Second Right Metacarjaal Bone 156 b. The Third Right Metacarpal Bone 156 c. The Fourth Right Metacarpal Bone 156 d. The Fifth Right Metacarpal Bone 157. The Phalanges of the Fingers 158. Radiographs of Foetal Hands . 159 a. The Right Innominate Bone seen from the Lateral Side 159 b. Lateral Aspect of the Right In- nominate Bone with the Attach- ments of the Muscles mapped out 160. The Right Innominate Bone (medial aspect) 161. Muscle-Attachments to the Lateral Surface of the Pubis and Ischium 162. Ossification of the Innominate Bone 163 a. The Male Pelvis seen from the Front 163 b. The Female Pelvis seen from the Front 164 a. The Right Femur seen from the Front 164 b. Front Aspect of Upper Portion of the Right Femur with Attach- ments of Muscles mapped out . 165 a. The Right Femur seen from Behind 165 b. Posterior Aspect of the Upj)er Portion of the Right Femur with Attachments of Muscles mapped out 165 c. Posterior View of the Upper End of the Right Femur . 166. Posterior Aspect of Lower Portion of the Right Femur with Attach- ments of Muscles mapped out . 167. Lower End of the Right Femur (lateral side) 168. Lower End of the Right Femur seen from Below 169. Ossification of the Femur 170. The Right Patella .... 171. The Upper Surface of the Superior Extremity of the Right Tibia . 172 a. The Right Tibia and Fibula seen from the Front .... 172 6. Front Aspect of the Upper Portion of the Bones of the Right Leg with Attachments of Muscles mapped out .... 173. Ossification of the Tibia 174 a. The Right Tibia and Fibula seen from Behind .... 202 202 203 204 204 205 205 205 206 206 207 207 208 208 209 209 209 211 211 213 224 215 217 219 220 220 223 223 224 225 225 227 227 228 229 230 230 231 232 234 235 LIST OF ILLUSTKATIONS. XIX 175. 176. 177. 178 ( j-IG. PAGE FIG. 174 b. Posterior Aspect of the Bones of 186 the Right Leg Avith Attachments of Muscles mapped out . . 235 186 Right Fibula seen from the Medial Side 236 187. Ossification of the Fibula . . 238 188. Bones of the Right Foot seen from 189 Above 239 189 . Bones of the Right Foot seen 190. from Below .... 240 178 b. Plantar Aspect of the Left Tarsus 191. and Metatarsus with Attach- ments of Muscles mapped out . 241 179 ((. The Right Talus, (A) Upper Sur- I 192. face, (B) Under Surface . . 242 ' 193. 179 6. The Right Talus, (C) from Lateral 194. Side, (D) from Medial Side . 242 195. 180 rt. The Right Calcaneus, (A) from Above, (B) from Below . . 243 196. 180 b. The Right Calcaneus, (C) from the Lateral Side, (D) from the 197. Medial Side .... 244 The Right Navicular Bone . . 245 198. Anterior Yiew of the three Cunei- form Bones of the Right 199. Foot 246 The Right First Cuneiform Bone 200. (medial side) .... 246 The Right First Cuneiform Bone 201 (lateral side) .... 246 185 a. The Right Second Cuneiform (medial side) .... 246 202 The Right Second Cuneiform (lateral side) .... 246 181. 182. 183. 184. 185 6. a. The Right Third Cuneiform (medial side) .... b. The Right Third Cuneiform (lateral side) .... The Right Cuboid Bone . Radiographs of the Fcetal Foot a. Radiograph of the Hand at Birth b. Radiograph of the Foot at Birth . . The First Metatarsal Bone of the Right Foot . View of the Bases and Shafts of the Second, Third, and Fourth Meta- tarsal Bones of the Right Foot . The Fifth Right Metatarsal Bone . The Phalanges of the Toes . Radiographs of the Fcetal Foot Dissection showing the Calcar Femorale ..... Section through Head and Neck of Femur to show Calcar Femorale Diagram to illustrate the Homolo- gous parts of the Vertebrae Diagram to illustrate the chief points used in Craniometry View of the Chondro-cranium of a Human Foetus 5 cm. in length Diagram to illustrate the Homolo- gies of the Bones of the Limbs . Diagram to illustrate the Homolo- gous parts of the Scapula and Ilium, according to Flower Diagram to illustrate the Homolo- gous Parts of the Scapula and Ilium according to Humphry . 247 247 248 248 249 249 250 250 251 252 252 iv iv xiv xvi xxi xxiv THE AETICULATIONS OR JOINTS. 203. Vertical Section through a Suture . 204. Section through the Occipito- sphenoid Synchondrosis 205. Sutura Serrata .... 206. Diagram of a Diarthrodial Joint . 207. Diagram of a Diarthrodial Joint . 208. Medial Section through a portion of the Lumbar part of the Spine 209. Anterior Common Ligament of the Vertebral Column, and the Costo- vertebral Joints as seen from Front 210. Posterior Common Ligament of the Vertebral Column 211. Ligamenta Subflava 212. Medial Section through the Occi- pito-atloid and Atlo-axoid Joints 213. Dissection from Behind of the Ligaments connecting the Occipi- tal Bone, the Atlas, and the Axis with each other .... 214. Temporo-mandibular Joint . 215. Section through Temporo-mandi- bular Joint 216. Internal Lateral Ligament of the Temporo-maxillary Joint . 217. Sterno-clavicular and Costo-sternal Joints ...... 218. Capsule of the Shoulder-Joint and Coraco-acromial Ligament . 219. Capsular Ligament of Shoulder- Joint cut across and Humerus removed ..... 220. Vertical Section through the Shoulder-Joint .... 255 256 256 257 258 262 262 263 264 265 221. 222. 223. 224. 225. 226. 227. 228. 266 267 229. 230. 268 231. 268 232. 272 233. 276 234. 235. 277 236. 278 237 Anterior View of Elbow-Joint Elbow-Joint (inner aspect) Vertical Section through the Trochlear part of the Elbow- Joint ..... Orbicular Ligament of the Radius . Carpal Articular Surface of the Radius, and Triangular Fibro- Cartilage of the Wrist Ligaments on Anterior Aspect of Radio-carpal, Carpal, and Carpo- metacarpal Joints Coronal Section through the Radio- carpal, Carpal, Carpo-metacarpal, and Intermetacarpal Joints to show Joint Cavities and Inter- osseous Ligaments (diagram - matic) Metacarpo-phalangeal and Inter- phalangeal Joints Coronal Section of Pelvis Posterior View of the Pelvic Liga- ments and of the Hip-Joint Dissection of the Hip-Joint . Dissection of the Hip-Joint from the Front Dissection of the Knee-Joint from the Front ..... The Knee-Joint (posterior view) . The Knee- Jointopened from behind by the removal of the Posterior Ligament ..... Upper End of Tibia . . . , Ankle- Joint dissected from Behind 279 280 281 282 282 284 286 288 290 291 294 296 298 299 301 302 305 XX LIST OF ILLUSTEATIONS. 238. Articular Surfaces of Tibia and Fibula wliicli are opposed to tlie Astragalus 239. Ankle and Tarsal Joints from the Tibial Aspect .... 240. Ligaments on the Outer Aspect of PAGE I FIG. 306 307 241. 242. the Ankle - Joint and on the Dorsum of the Tarsus . The Composite Articular Socket for the Head of the Astragalus . Plantar Aspect of Tarsal and Tarso- metatarsal Joints .... THE MUSCULAE SYSTEM. 243. 245. 246. 247. 251. 252. 253. 254. Muscle-Attachments to the Eight 274. Clavicle (upper surface) . . 320 244. Superficial Muscles of the Back 275. and Vertebro-scapular Muscles . 321 Muscle-Attachments to the Right 276. Scapula (posterior surface) . . 322 Muscle-Attachments to the Front of 277. the Sternum . . . .323 The Muscles of the Front of the Chest 324 248. Muscle-Attachments to the Right 278. Clavicle (under surface) . . 325 249. The Left Serratus Anterior (Ser- 279. ratus Magnus) Muscle . . . 326 250. Muscle-Attachments to the Right Scapula (anterior aspect) . . 326 280. Left Scapular Muscles and Tricejjs 328 Muscles of Posterior Wall of Left Axilla and Front of the Arm . 329 Muscle-Attachments to the Front 281. of the Right Humerus . . 330 Muscle-Attachments to the Right Scajiula (posterior surface) . . 330 282. 255. Superficial Muscles on the Front of the Right Arm and Forearm . 333 256. The Muscles on the Back of the 283. Left Arm, Forearm, and Hand . 333 257 a. Muscle-Attachments to the Front 284. of the Right Humerus . . 334 Muscle-Attachments to the Back 285. of the Right Humerus . . 334 The Left Palmar Fascia . . .336 286. Superficial Muscles and Tendons in the Palm of the Left Hand . 337 Section Across the Forearm in the 287. Middle Third .... 339 288. The Superficial Muscles of the Left Forearm 340 289. 262. Deeper Muscles of the Left Forearm 340 263. The Tendons attached to the Index- Finger 341 290. 264. Muscle-Attachments to the Right Radius and Ulna (anterior aspect) 342 265. Deepest Muscles in the Front of the 291. Left Forearm . . ... 343 The Palmar Muscles, Right Side . 344 292. Muscle-Attachments to the Palmar Aspect of the Right Carpus and Metacarpus 345 293. The Right Palmar Interosseous Muscles 346 294. Muscle-Attachments to the Dorsal 295. Aspect of tlie Right Metacarpus . 346 Dorsal Interosseous Muscles of the 296. Right Hand (seenfrom the palmar aspect) 347 297. Muscle -Attachments to the Right Radius and Ulna (jjosterior aspects) 349 298. 272. The Superficial Muscles of the Back 299. of the Left Forearm . . . 350 273. Deep Muscles on the Back of the 300. Left Forearm .... 350 257 6. 258. 259. 260. 261. 266 267, 268. 269. 270. 27 L Superficial Anatomy of the Left Groin ...... The Dissection of the Left Inguinal Canal ...... The Muscles on the Front of the Right Thigh .... Muscle - Attachments to the An- terior Surface of the Upper Part of the Left Femur Transverse Section of the Thigh (Hunter's Canal) .... Muscle-Attachments to the Medial side of the Upper Part of the Left Tibia View of the Posterior Abdominal Wall, to show the Muscles and the Nerves of the Lumbo- sacral Plexus Muscle- Attachments to the Posterior Aspect of the Upper Part of the Left Femur Muscle -Attachments to the Outer Surface of the Right Pubis and Ischium ..... Scheme of the Course and Distribu- tion of the Right Obturator Nerve Deep Muscles on the Back of the Right Thigh .... Muscle -Attachments to the Right Dorsum Iliiand Tuber Ischiadicum Muscle-Attachments to the Posterior Aspect of the Upper Part of the Left Femur ..... The Right GlutseusMaximus Muscle The Muscles and Nerves of the Right Buttock .... Muscle-Attachments to the Upper Aspect of the Greater Trochanter of the Left Femur Muscle-Attachments to the Right Dorsum Ilii and Tuber Ischii (Ischiadicum) .... The Muscles on the Back of the Right Thigh .... Muscle-Attachments to the Medial Side of the Upper Part of the Right Tibia ..... Coronal Section through the Left Ankle- Joint, Talus, and Calcaneus The Left Plantar Fascia Muscle-Attachments to Left Tarsus and Metatarsus (plantar aspect) . Muscles of the Front of the Right Leg and Dorsum of the Right Foot The Insertions of the Tibialis Posterior and Peronteus Longus in the Sole of the Left Foot The Right Soleus Muscle The Deep Muscles on the Back of the Right Leg . . . . Muscle- Attachments to the Posterior Surface of the Right Tibia . 308 309 310 354 355 357 358 358 359 360 361 362 363 364 365 366 366 367 367 368 369 369 372 373 374 375 376 376 377 377 LIST OF ILLUSTEATIONS. XXI FIG. PAfiE 301. The Muscles of the Right Foot (second layer) .... 378 302. Muscle-Attachments to Left Tarsus and Metatarsus (jjlantar asjiect) . 380 303. The Superficial Muscles of the Right Foot 381 304. The Deep Muscles of the Sole of the Right Foot .... 382 305. Interosseous Muscles of the Right Foot 383 306. Transvei-se Section through the Abdomen, opposite the Second Lumbar Vertebra . . . 385 307. Schematic Representation of the parts of the Left Sacro-sjiinalis (Erector Spinae) Muscle . . 386 308. Scheme of Muscular -Attachments to the Transverse Processes of the Cervical Vertebrae . . . 387 309. The Deep Muscles of the Back . 388 310. The Suboccipital Triangle of the Left Side 390 311. Muscle-Attachments to the Sacrum 390 312. Muscle-Attachments to the Occipi- tal Bone (parietal surface) . . 391 313. Transverse Section in the Cervical Region 394 314. The Muscles of the Face and Scalp 396 315. Transverse Vertical Section through the Left Orbit behind the Eye- ball to show the arrangement of Muscles 399 316. The Muscles of the Right Orbit (from above) .... 400 317. The Muscles of the Right Orbit (from without) .... 400 318. Schematic Representation of the Nerves which traverse the Cavity of the Right Orbit . . .401 319 a. Muscle-Attachments to the Lateral Aspect of the Lower Jaw . . 402 319 h. Muscle - Attachments on the Medial Side of the Lower Jaw . 402 320. Muscles of Mastication (superficial view) 403 321. The Right Temporal Muscle . . 403 322. The Pterygoid Muscles of the Right Side 404 323. Muscle -Attachments to the Occipi- tal Bone (parietal surface) . . 405 324. The Muscles of the Tongue and Hyoid Bone (right side) . . 406 325. The Muscles of the Side of the Neck (anterior and posterior triangles) 407 326. Muscle - Attachments on the Medial Side of the Lower Jaw . 408 327. Transverse and Longitudinal Vertical Sections through the Tongue 408 328. Posterior View of the Pharynx and Constrictor Muscles . . . 411 FIO. 329. 330. 331. 332. 335. 336. 337 a. 337 h. 338. Lateral View of the Wall of the Pharynx 412 Muscle-Attachments to the Upper Surface of tlie First Rib and the Lateral Surface of the Second Rib 413 The Prsevertebral Muscles of the Neck 414 Sclieme of Muscular-Attachments to Cervical Vertebrae . . .414 333. Muscle-Attachments to the Occipi- tal Bone (inferior surface) . . 415 334. The Muscles of the Right Thoracic Wall 416 The Diaphragm (from below) . 417 View of the Posterior Abdominal Wall, to show the Muscles and the Nerves of the Lumbo-sacral Plexus 418 Superficial Anatomy of the Groin 420 The Dissection of the Inguinal Canal 421 Transverse Section through the Abdomen 422 339. The Left Obliquus Externus Ab- dominis ..... 423 340. The Right Obliquus Internus Ab- dominis ..... 424 341 a. The Left Inguinal Canal on Re- flection of the External Oblique 425 341 h. The Dissection of the Inguinal Canal 426 342. Deep Dissection of the Abdominal Wall 427 343. Sheath of the Rectus Abdominis Muscle 428 View of the Posterior Abdominal Wall to show the Muscles and the Nerves of the Lumbo - sacral Plexus 429 The Muscles and Nerves of the Male Perineum . . . .431 346. The Muscles of the Female Peri- neum (after Peter Thompson) . 432 The Triangular Ligament of the Perineum, and the Termination of the Pudic Nerve . . . 433 Relations of the Pelvic Fascia to the Rectum and Prostate . . 435 Relations of the Pelvic Fascia to the Rectum and Prostate (medial section) 436 Relations of the Pelvic Fascia to the Rectum, Urethra, and Vagina (medial section) .... 437 351. Fascial and Muscular Wall of the Pelvis after removal of i:)art of the Left Innominate Bone . . 439 Scheme to illustrate the disj^osition of the Myotomes in the Embryo in relation to the Head, Trunk, and Limbs 440 344. 345. 34 348. 349. 350. 352. THE NEEVOUS SYSTEM. 353. Nerve-Fibre from a Frog (after V. Kolliker) 354. Three Nerve-Cells from the An- terior Horn of Gray Matter of the Human Spinal Cord . 355. Two Multipolar Nerve-Cells . 444 445 446 356. Nerve-Cell from Cerebellum (Pro- fessor Symington) . . . 446 357. Transverse Section through the early Neiu-al Tube (Alfred H. Young) 447 358. Developmental Stages exhibited by LIST OF ILLUSTEATIONS. a Pyramidal Cell of the Brain (after Ramon j Cajal) . . . 447 359. Diagi-am of the Connexion estab- lished by a Ganglionic and a Motor Neuron (Eam6n j Cajal) . 449 360. Three Stages in the development of a Cell from a Spinal Ganglion 449 361. Nerve-Cells as depicted by Bethe . 450 362. Section through the Central Canal of the Sjjinal Cord of a Human Embryo (after v. Lenhossek) . 451 363. Human Foetus in the third month of Development, with the Brain and Spinal Cord exposed from behind 452 364. The Conns Medullaris and the Filuni Terminale exposed within the Spinal Canal .... 453 365. The Roots of Origin of the Seventh Dorsal Nerve .... 453 366. Section through the Conus Medul- laris and the Cauda Equina as they lie in the Sjsinal Canal . 453 367. Diagram of the Spinal Cord as seen from behind .... 455 368. Transverse Section through the Upper Part of the Cervical Region of the Cord of an Orang . . 456 369. Section through each of the Four Regions of the Cord . . . 458 370. Section through the Fifth Cervical Segment of the Cord . . .462 371. Section through the eighth Dorsal Segment of the Spinal Cord . 463 372. Section through the Third Lumbar Segment of the Spinal Cord to show the grouping of the Motor Cells 463 373. Section through the first Sacral Segment of the Spinal Cord . 464 374. Transverse Section through the White Matter of the Cord . . 465 375. Diagram to show the Arrangement of the Fibres of the Posterior Nerve -Roots in the Posterior Columns of the Cord . . . 467 376. Diagram to show the manner in which the Fibres of the Posterior Nerve-Roots enter and ascend in the Posterior Column of the Cord (from Edinger) .... 377. Diagrammatic Representation of a Transver.se Section through the SpinaJ4&ord .... 378. Schema of a Transverse Section through the Early Neural Tube (Young) ..... 379. Three Stages in the Develoi^ment of the Spinal Cord (His) 380. The Base of the Brain with Cranial Nerves attached .... 381. Schema showing the Connexions of the several parts of the Brain 382. Two Stages in the Development of the Human Brain (after His) . 383. Two Cross Sections through the Fore-Brain 384. The Brain of a Human Embryo in tlie Fifth Week (after His) . 385. Profile View of the Brain of a Human Embryo of Ten Weeks (His) .479 402. 403. 467 404. 469 405. 471 472 406. 474 476 407. 477 477 478 408. 409. 410. FIQ. PAGE 386. Diagrams to illustrate the Alar and Basal Laminae . , . 480 387. Front View of the Medulla, Pons, and Mesencei^halon of a full-time Human Foetus . . . .481 388. Back View of the Medulla, Pons, and Mesencephalon of a full-time Human Foetus .... 482 389. Diagram of the Decussation of the Pyramids (modified from van Gehuchten) 483 390. Lateral View of the Medulla, Pons, and Mesencephalon of a full-time Human Foetus .... 484 391. Floor of the Fourth Ventricle . 487 392. Section through the Lower End of the Medulla Oblongata of a Chim- panzee to show the Decussation of the Pyramids .... 489 393. Transverse Section through Lower End of the Medulla of a full-time Foetus 491 394. Section through the Closed Part of Human Medulla immediately above the Decussation of the Pyramids 492 395. Section through the Lower Part of the Medulla of the Orang . . 492 396. Transverse Section through the Closed Part of a Foetal Medulla . 493 397. Transverse Section through the Human Medulla in the Lower Olivary Region .... 493 398. Transverse Section through the Middle of the Olivary Region of the Human Medulla . . . 495 399. Inferior Olivary Nucleus as recon- structed and figured by Miss Florence R. Sabin . . . 495 400. Diagram which shows in part the Fibres which enter into the Constitution of the Restiform Body 496 401. Section through the Junction be- tween the Cord and Medulla of the Orang 496 Diagram of the Cerebello-olivary Fibres 497 Section through the Lower Part of the Human Pons Varolii imme- diately above the Medulla . . 500 Diagram to show Connexions of the Direct Cerebellar and the Olivo- cerebellar Tracts . . . .501 Transverse Section through the Pons Varolii at the Level of the Nuclei of the Trigeminal Nerve (Orang) 503 Section through the Upper Part of the Pons Varolii of the Orang, above the Level of the Trigeminal Nuclei 504 Two Sections through the Tegmen- tum of the Pons at its Upper Part, close to the Mesencephalon 605 Upper Surface of the Cerebellum . 505 Lower Surface of the Cerebellum . 508 Sagittal Section through the Left Lateral Hemisphere of the Cere- bellum 509 411. From a Dissection by Dr. E. B. Jamieson, showing Corpus Den- LIST OF ILLUSTEATIONS. XXlll tatum and Superior Cerebellar Peduncle, etc 509 412. IVIedial Section through the Corpus Callosuni, the Mesencephalon, the Pons, Medulla, and Cerebellum . 512 413. Transverse Section through a Cere- bellar Folium (after Kolliker) . 513 414. Section through the Moleculai- and Granular Layers in the Long Axis of a Cerebellar Folium (after Kolliker) . . . .514 415. Diagram of the Spinal Origin of the Spinal Accessory Nerve (after Bruce) ...... 416. Section through the Upper Part of the Cervical Kegiorf of the Cord (Orang) . . ... 417. Diagram showing the Brain Con- nexions of the Vagus, Glosso- pharyngeal, Auditory, Facial, Abducent, and Trigeminal Nerves 418. Central Connexions of the Cochlear and Vestibular Divisions of the Auditory Nerve .... 419. Section through the Pons Varolii of the Orang 420. Diagram of the Intrapontine Course pursued by the Facial Nerve 421. Section through the Pons Varolii of the Orang at the Level of the Nuclei of the Trigeminal Nerve 422. Three Stages in' the Development of the Medulla Oblongata (His — slightly modified) 423. Drawings to illustrate the Develop- ment of the Cerebellum (from Kuithan) ..... 424. Brain of an Embryo of Eleven Weeks 425. Sections through Cerebellum of Human Foetus .... 426. Under Surface of the Cerebellum of a Human Foetus .... 427. Cerebellum of a Human Foetus 428. Diagram of the Roots of the Oj^tic Nerve 429. Transverse Section through the Upper Part of the Mesencephalon 430. Transverse Section through the Human Mesencephalon at the Level of the Inferior Quadri- geminal Body .... 431. Transverse Section through the Human Mesencephalon at the Level of the Superior Quadri- geminal Body .... 536 432. Section tlirough the Inferior Quadri- geminal Body and the Tegmentum of the Mesencephalon below the Level of the Nucleus of the Fourth Nerve in the Orang . . . 537 433. Section through the Inferior Quad- rigeminal Body and the Tegmen- tum of the Mesencephalon . . 538 434. Diagram of the Connexions of the Posterior Longitudinal Bundle (after Held— modified) . . 538 435. Diagram of the Connexions of the Medial FiUet and also of certain of the Thalamo-Cortical Fibres . 539 436. Section through the Inferior Quad- rigeminal Body and the Teg- 437. 438. 439. 440. 441. 516 442. 443. 516 444. 445. 518 446. 520 522 523 447. 448. 449. 450. 525 451 527 452. 529 453. 454 529 455. 530 456 530 530 532 457. 458 459. 533 460. 535 461 462 463. 464. 465. 466. 467. 468. 469. mentum of the Mesencephalon (Orang) 540 Section through the Inferior Quad- rigeminal Body and the Tegmen- tum of the Mesencephalon (Orang) 541 Tlie Two Optic Thalami . . 543 Schema 546 Coronal Section through the Cere- brum of an Orang . . . 547 Medial Section through the Pituitary Region in a Cliild of Twelve Months old 549 Medial Section through the Pituitary Region in the Adult . . . 549 Medial Section through the Corpus Callosum, Diencephalon, etc. . 550 Ca.^ of the Ventricles of the Brain (from Retzius) . . . .551 Diagram of the Central Connexions of the Optic Nerve and Optic Tract 552 Gyri and Sulci on the Outer Surface of the Cerebral Hemisphere . 555 Three Stages in the Development of the Insula and the Insular Opercula 557 Development of the Opercula which cover the Insula .... 557 Fissure of Rolando fully ojjened up 558 Left Cerebral Hemisphere from a Foetus 559 The Gyri and Sulci on the Medial Aspect ofthe Cerebral Hemisphere 559 Gyri and Sulci on the Tentorial and Orbital Aspects of the Cerebral Hemispheres 562 Intraparietal Sulcus fully opened up 564 Internal Parieto-occipital and the Calcarine Fissures fully opened up 565 Development of the Parieto-occi- pital and the Calcarine Fissures . 566 Coronal Section through the Left Side of the Cerebrum, Mesen- cephalon, and Pons (Chimpanzee) 569 The Cor^jus CaUosum . . .570 Profile View of the Fornix . . 572 Cast of the Ventricular System of the Brain (after Retzius) . . 574 Coronal Section through the Frontal Lobes and the Anterior Horns of the Lateral Ventricles . . . 574 Dissection to show the Fornix and Lateral Ventricles . . .575 Coronal Section through the Posterior Horns of the Lateral Ventricles 576 Dissection to show the Fornix and the Posterior and Descending Cornua of the Lateral Ventricle of the Left Side .... 677 Dissection to show the Posterior and Descending Cornua of the Lateral Ventricle . . . 578 Horizontal Section through the Right Cerebral Hemisphere . 579 Coronal Section through the Cere- bral Hemispheres . . . 580 Coronal Section through the Cere- brum ...... 581 Coronal Section through the Left Side of the Cerebrum of an Orang 582 Diagram to illustrate Minute Structure of the Cerebral Cortex 586 XXIV LIST OF ILLUSTEATIONS. FIO. 470. Diagram of tlie Minute Structure of the Olfactory Bulb . 471. Two Coronal Sections through the Cerebral Hemispheres of an Orang 472. Diagram of the Leading Association Bundles ofthe Cerebral Hemisphere 473. Coronal Section through the Left Side of the Cerebrum, Mesen- cephalon and Pons (Chimpanzee) 474. Diagrams to show Flechsig's Sensory and Association Areas on the sur- face of the Cerebral Hemisphere 475. Two Drawings of the Embryonic Brain (by His) .... 476. Two Drawings by His illustrating the Development ofthe Human Brain 477. Sagittal Section through the Skull 478. Diagram to show the Eelations of the Membranes of the Brain to the Cranial Wall, etc. . 479. Membranes of the Spinal Cord, and the Mode of Origin of the Spinal Nerves 480. Medial Section through the Cranial Vault in the Frontal Eegion 481. Dissection to show the Velum In- terpositum ..... 482. Diagrammatic Coronal Section through the Optic Thalami 483. Membranes of the Spinal Cord, and the Mode of Origin of the Spinal Nerves ..... 484. Scheme of the Arrangement of the Membranes of the Spinal Cord and the Roots of the Spinal Nerves 485. Diagrammatic Representation of the Origin of the Spinal Nerves . 486. Scheme of the Distribution of a Typical Spinal Nerve . 487. Distribution of Cutaneous Nerves on the Back of the Trunk . 488. Posterior Cervical Plexus 489. Distribution of Cutaneous Nerves on the Front of the Trunk . 490. The Cervical Plexus 491. Distribution of Cutaneous Nerves to the Head and Neck 492. The Triangles of the Neck . 493. Muscles of the Hyoid Bone and Styloid Process, and the Extrinsic Muscles of the Tongue, with their Nerves 494. Nerves of the Brachial Plexus 495. Diagram of the Origin and Distri- bution of the Nerves to the Pectoral Muscles .... 496. The Posterior Wall of the Axilla and the Front of the Arm . 497. The Distribution of Cutaneous Nerves on the Front of the Arm and Hand 498. The Distribution of Cutaneous Nerves on the Back of the Arm and Hand 499. Deltoid Region and Back of Arm . 500. Diagrammatic Representation of the Brandies of the Musculo- spiral Nerve .... 501. The Muscles of the Back of the Forearm 502. Scheme of the Distribution of a Typical Spinal Nerve . 587 589 590 592 593 595 596 598 601 602 603 604 605 605 607 608 609 611 612 615 616 618 619 620 623 625 626 628 630 631 633 634 636 FIO. 503. The Distribution of Cutaneous Nerves on the Front of the Trunk 504. Nerves of the L;imbo-sacral Plexus 505. View of the Posterior Abdominal Wall, to show the Muscles and the Nerves of the Lumbo-Sacral Plexiis 506. Scheme of the Course and Distri- bution of the Obturator Nerve . 507. Distribution of Cutaneous Nerves on the Front of the Lower Limb . 508. Distribution of Cutaneous Nerves on the Dorsum of the Foot . 509. Distribution of Cutaneous Nerves on the Back of the Lower Limb . 510. Scheme of Distribution of the Plantar Nerves .... 654 511. Nerves of the Lumbo-sacral Plexus 656 512. The Muscles and Nerves of the Male Perineum .... 658 513. The Triangular Ligament of the Perineum 659 514. Scheme of the Innervation of the Hinder Portion of the Trunk and of the Perineum .... 660 515. Development of the Spinal Nerves 661 516. Scheme ofthe Segmental Distribu- tion of the Muscular Nerves of the Upper and Lower Limbs . . 671 517. View of the Under Surface of the Brain 675 518. Innervation of the Nasal Cavity . 676 519. Diagram of the Central Connexions of the Optic Nerve and Optic Tract 676 520. Relations of Structures in the Cav- ernous Sinus and Sphenoidal Fissure 677 521. Dorsal Surface of the Mid-Brain . 677 522. The Base of the Skull . . .678 523. Distribution of Sensory Nerves to the Head and Neck . . .679 524. Scheme of the Distribution of the Ophthalmic Nerve . . . 680 525. Schematic Representation of the Nerves which traverse the Cavity of the Orbit 681 526. Scheme, of the Course and Distri- bution of the Superior Maxillary Nerve 682 527. Scheme of the Distribution of the Inferior Maxillary Nerve . . 684 528. The Facial Nerve with its Branches and Communications in the Aque- duct of Fallopius .... 687 529. Distribution of Facial Nerve out- side the Skull, and Communica- tions with Trigeminal Nerve on the Face 688 530. Scheme of the Origin and Distribu- tion of the Auditory Nerve . . 689 531. Scheme of the Distribution of the Glosso-pharyngeal Nerve . . 690 532. The Distribution of the Pneumo- gastric Nerve .... 691 533. The Constitution of the Cardiac Plexuses 694 534. The Distribution of the Pneumo- gastric Nerve .... 695 535. Scheme of the Origin, Connexions, and Distribution of the Spinal Accessory Nerve .... 696 536. The Muscles of the Hyoid Bone and Styloid Process, and the Extrinsic LIST OF ILLUSTKATIONS. XXV Muscles of the Tongue with their Nerves 537. Comparison of Origins of Nerve- Roots from Spinal Cord and Hind- Brain (after His) .... 538. Scheme to illustrate the Disposition of the Myotonies in the Embryo in relation to the Head, Trunk, and Limbs 539. Scheme to illustrate the Embryo- logical Arrangement of the Cranial Nerves 540. Scheme of the Constitution of tlie White Ramus Communicans of the Sympathetic .... 541. Scheme of the Constitution and Connexions of the Gangliated Cord of the Sympathetic PAGE 697 700 702 703 704 705 FIO. PAGE 542. The Distribution of the Sym- pathetic Gangliated Cord in the Neck 707 543. The Constitution of the Cardiac Plexuses 708 544. The Arrangement of the Sym- jmthetic System in the Thorax, Abdomen, and Pelvis . . . 709 545. The Lumbar Portion of the Sym- pathetic Gangliated Cord and Lumbar Plexus . . . . 711 546. The Arrangement of the Sym- pathetic System in the Thorax, Abdomen, and Pelvis . . . 713 547. The Development of the Sym- pathetic Gangliated Cord . . 715 548. Section through the Sympathetic Gangliated Cord of an Embryo . 716 THE OKGANS OF SENSE AND THE INTEGUMENT. 549. Lateral View of Nasal Septum 550. Profile View of the Bony and Carti- laginous Skeleton of the Nose 551. Front View of the Bony and Carti- laginous Skeleton of the Nose 552. Cartilages of Nose from Below 553. Coronal Section through Nasal Fossfe ; Anterior Half of Section viewed from Behind . 554. Section through Nose of Kitten, showing position of Jacobson's Organ 555. View of the Outer Wall of the Nose 556. Section through the Olfactory Mucous Membrane 557. Olfactory and Supporting Cells 558. Diagram of a Horizontal Section through Left Eyeball and Optic Nerve 559. Vertical Section of Cornea 560. Vertical Section of Chorioid and Inner Part of Sclera 561. Diagram of the Circulation in the Eye (Leber) 562. Section through Ciliary Region of Eyeball 563. Blood-Vessels of Iris and Anterior Part of Chorioid (Arnold) . 564. Diagrammatic Section of the Human Retina (modified from Schultze) 565. Perpendicular Sections of ]\Iam- malian Retina (Cajal) . 566. Cone and two Rods from the Human Retina . . . 567. Pigmented Epithelium ofj Human Retina . . . • J • 568. Section through Outer Layers of Retina . . . • I • 569. Blood-Vessels of the Retina . 570. Canal of Petit distenfled and viewed from the Front [ 571. Lens hardened in Fornialiu and dissected to show its (Joncentric Laminse . . .1 . . 572. Diagrammatic Represedtatidn of the Radii Lentis of flie Fcetal Lens •••/•. 573. Section through the Eqifctor of the Lens . . . I . 718 574. 719 575. 719 576. 720 577. 720 578. 579. 721 580. 721 58L 722 582. 722 583. 584. 724 726 585. 586. 727 587. 728 588. 729 589. 590. 730 591. 592. 732 593. 733 594. 733 595. 734 734 596. 735 736 597. 598. 736 599. 600. 737 601. 737 Vertical Section through Upper Eyelid 738 Sections through Portions of the Heads of Foetal Rabbits . . 741 Optic Cup and Lens viewed from Behind and Below . . . 742 Diagrammatic View of the Organ of Hearing ..... 744 View of Outer Surface of Left Pinna 744 Outer Surface of Cartilage of Pinna 745 Inner Surface of Cartilage of Pinna 745 Vertical Transverse Section of Right Ear 747 Horizontal Section through Right Ear 747 Section through Left Temporal Bone 749 Left Membrana Tympani and Re- cessus Epitympanicus . . . 749 Left Tympanic Membrane . . 751 Transverse Section of the Cartilag- inous Part of the Eustachian Tube 753 Tympanic Ossicles of Left Ear . 755 Left Membrana Tympani and Chain of Tympanic Ossicles . . . 755 Left Bony Labyrinth . . . 759 Interior of Left Bony Labyrinth . 759 Section of Bony Cochlea . . 761 Diagrammatic Representation of the Different Parts of the Mem- branous Labyrinth . . . 762 Transverse Section of Human Semi- circular Canal (Riidinger) . . 763 Section across the Ductus Cochlearis (Retzius) 764 Transverse Section through Outer Wall of Ductus Cochlearis (Schwalbe) .... 765 Transverse Section of Corti's Organ from the Central Coil of Cochlea (Retzius) 766 Membranous Labyrinth of a Five Months' Foetus (Retzius) . . 768 Part of Cochlear Nerve (Henle) . 768 Sections through the Region of the Hind-Brain of Foetal Rabbits . 769 Left Labyrinth of Human Embryo 770 Section through Papilla Vallata (A) of Human Tongue and (B) of Rabbit 770 LIST OF ILLUSTRATIONS. 602. Three-quarter Surface View and Vertical Section of Taste Bud from the Pajjilla Foliata of a Eabbit 771 603. Isolated Cells from Taste Bud of Eabbit (Engelmann) . . .771 604. Vertical Section of the Skin . . 772 605. Vertical Section of E]Didermis and Pai^illse of Corium . . .773 606. Tactile Corpuscles .... 775 607. Transverse Section of a Nail . . 776 608. Longitudinal Section through Eoot of Nail 776 609. Transverse Section of Haif Follicle witli Contained Hair . . .777 THE VASCULAR SYSTEM. 610. Structure of Blood- Vessels 611. Transverse Section through Wall of a Large Artery 612. Transverse Section of the Wall of a Vein ...... 613. The Base and Inferior Surface of the Heart 614. The Antero-superior Surface of the Heart 615. The Eelation of the Heart to the Anterior Wall of the Thorax 616. The Cavities of the Eight Auricle and Eight Ventricle of the Heart 617. The Bases of the Ventricles of the Heart 618. The Eelations of the Heart and the Auriculo-ventricular, Aortic, and Pulmonary Orifices to the Anterior Thoracic Wall 619. Posterior Wall of the Pericardium after Eemoval of the Heart . 620. The Pulmonary Arteries and Veins and their Eelations 621. The Abdominal Aorta and its Branches 622. TheCarotidand Subclavian Arteries and their Branches 623. The External Carotid, Internal Maxillary, and Meningeal Ar- teries ...... 624. The Carotid, Subclavian, and Verte- bral Arteries and their Main Branches 625. Distribution of the Cerebral Arteries on the Medial, Tentorial, and Inferior Surfaces of the Cere- bral Hemispheres 626. Distribution of Cerebral Arteries on the Outer Surface of the Cerebrum 627. The Arteries of the Base of the Brain 628. Dissection of the Back of the Shoulder and Ui^per Arm . 629. The Axillary Artery and its Branches and Eelations 630. The Bi-acliial Artery and its Branches 631. Superficial Dissection of the Front of the Forearm and Hand . 632. Deep Dissection of the Front of the Forearm and Hand 633. The Posterior Interosseous Artery and the Second Part of the Eadial Artery, with tlieir Branches 634. The Abdominal Aorta and its Branches 635. The Coeliac Axis and its Branches 636. The Superior Mesenteric Artery and its Branches .... 637. The Internal Iliac Artery and its Branches in the Female 781 638. 781 639. 782 640. 784 641. 785 642. 786 643. 787 644. 788 645. 646. 789 647. 794 648. 796 799 649. 650. 803 651. 810 652. 813 653. 654. 815 816 819 655. 656. 657. 824 658. 827 830 832 833 659. 660. 661. 662. 835 840 844 846 849 663. 664. 665. The Perineal Distribution of the In- ternal Pudic Artery in the Male . 853 The Arteries of the Buttock and the Back of the Thigh and Knee . 855 The Iliac Arteries and Veins in the Female 857 The Femoral Artery and its Branches ..... 858 The Femoral Vessels in Scarpa's Triangle 860 The Arteries of the Buttock and the Back of the Thigh and Knee . 862 The Popliteal and Posterior Tibial Arteries and their Branches . 864 The Plantar Arteries and their Branches 866 The Anterior Tibial Artery and its Branches 867 The Dorsalis Pedis Artery and its Branches ..... 869 Superficial Veins of the Head and Neck 878 The Veins of the Diploe . . 881 Dissection of the Head and Neck, showing the Cranial Blood Sinuses and the Upper Part of the Internal Jugular Vein .... 884 Basal Blood Sinuses of the Dura Mater 885 Superficial Veins on the Dorsum of the Hand and Digits . . 889 Superficial Veins on the Flexor Aspect of the Upper Extremity . 890 Superficial Veins at the Bend of the Elbow 891 The Inferior Vena Cava and its Tributaries 893 The Femoral Vessels in Scarpa's Triangle 898 The Internal or Long Saphenous Vein and its Tributaries . . 899 Tlie External or Short Saphenous Vein and its Tribiitaries . . 901 The Portal Vein and its Tributaries 902 The Thoracic Duct and its Tribu- taries 907 Lymjjhatic Vessels and Glands of the Head and Neck . . . 910 Superficial Lymphatic Vessels of the Trunk, and the Lymphatic Glands and Vessels Superficial and Deep of the Limbs . . . 912 Superficial Lymphatics of the Digits and of tlie Dorsal Aspect of the Hand . \ 915 Deep Lymj'iihatic Glands and Vessels of tlie Th prax and Abdomen . 919 Diagram of the Primitive Vascular System b«fore the Formation of the Heart 926 LIST OF ILLUSTKATIONS. xxvn TIO. 666. Diagram of the Primitive Blood- vessels after the Formation of the Heart ..... 667. Diagram of the Primitive Blood- vessels after the Formation of the Heart, but before its Sub- division by Septa into Auricles and Ventricles .... 668. Development of the Heart 669. Development of the Heart and the Main Arteries .... 670. Diagram of the Course of the Foetal Circulation 671. Development of the Venous System (Stage I.) 672. Development of the Venoiis System (Stage II.) 935 673. Development of the Venous System (Stage III.) 936 674. Develojjment of the Venous System (Stage IV.) 937 92"; 927 928 930 931 934 675. Diagram of the Cejihalic Aortic Arches, and of the Segmental and Intersegmental Arteries in the Eegion in front of the Umbilicus 939 676. Diagram of the Caudal Aortic Arch, and of the Segmental and Inter- segmental Arteries in the Region behind the Umbilicus . . . 939 677. Diagram showing the Arrangement and Communications of the Seg- mental and Intersegmental Ar- teries at an Early Stage of De- velopment 940 Diagram of the Segmental and Intersegmental Arteries at a Later Period of Development than in Fig. 677 . . . .941 Diagram showing the Arrangement and Communications of the Seg- mental Arteries in the Region of the Cephalic Aortic Arches . . 941 678. 679. THE KESPIEATOEY SYSTEM. 680. The Cartilages and Ligaments of the Larynx viewed from the Front ...... 681. Profile View of the Cartilages and Ligaments of the Larynx 682. Cartilages and Ligaments of Larynx from Behind . . . . 683. Dissection to show the Lateral Part of the Crico-thyreoid Membrane . 684. Superior Aperture of Larynx 685. Coronal Section through Larynx . 686. Mesial Section through LarjTix 687. Diagram of Rima Glottidis . 688. Specimen showing a Great tension of the Saccule of Larynx .... 689. The Crico-thyreoid Muscle . 690. Dissection of the Muscles in Lateral Wall of the Larynx 691. Dissection of the Muscles on the Posterior Aspect of the Lar}Tix . 692. Cavitv of the Larvnx 693. The Trachea and Bronchi 694. Transverse Sections through the Trachea and its Immediate Sur- roundings Ex- the the 959 959 960 963 964 965 966 966 967 968 969 970 972 973 974 695. Diagram showing Arrangement of Pleural Sacs .... 977 696. Dissection of a Subject hardened by Formalin-Injection, to show the Relations of the two Pleural Sacs 978 697. Lateral View of the Right Pleural Sac in a Subject hardened by Formalin-Injection . . . 979 698. Left Pleural Sac in a Subject hardened by Formalin-Injection . 980 699. Dissection of the Pleural Sacs from Behind 981 700. Dissection of Thorax and Root of the Neck from the Front to show the Relations of the Lungs, Peri- cardium, and Thymus Gland . 984 701. Mediastinal Surfaces of the two Lungs of a Subject hardened by Formalin-Injection . . . 985 702. Outer or Costal Surfaces of the two Lungs 986 703. Sagittal Section through Left Shoulder and Left Lung . . 987 704. Sagittal Section through the Left Shoulder, Lung, and Apex of the Heart 988 THE DIGESTIVE SYSTEM. 705. General View of the Digestive System ...... 706. Coronal Section through the Closed Mouth 707. Open Mouth showing Palate and Tonsils 708. Sagittal Section through Mouth, Tongue, Larjnix, Pharj-nx, and Nasal Cavity .... 709. Horizontal Section through Mouth and Pharynx at the Level of the Tonsils 710. The Anterior Wall of the Pharynx with its Orifices, seen from Behind 711. The Papilla3 of the Tongue . 712. Open Mouth with Tongue raised. 994 996 999 1001 1002 1003 1004 and the Sublingual and A2:)ical Glands exposed .... 1005 713. Sections through the Tongue (Krause) ; and Lymphoid Follicle from Back Part of Tongiie (Mac- alister) 1006 714. Section of a Serous Gland and a Mucous Gland (Bohm and v. Davidoff) 1008 715. Horizontal Section through Mouth and Pharynx at the Level of the Tonsils 1009 716. The Salivary Glands and their Ducts 1010 717. Teeth of a Child over seven years old (modified from Testut) . . 1014 XXVlll LIST OF ILLUSTKATIONS. FIG. PAGE 718. Vertical Section of Canine Tootli . 1015 719. The Permanent Teeth of the Right Side, Outer or Labial Aspect . 1017 720. The Permanent Teeth of the Right Side, Inner or Lingual Aspect . 1018 721. Tlie Upper Permanent Teeth . 1018 722. The Lower Permanent Teeth . 1020 723. Horizontal Sections through both the Upper and Lower Jaws to show the Roots of the Teeth . 1021 724. To show the Relation of the Upper to the Lower Teeth when the Mouth is Closed .... 1022 725. The Milk Teeth of the Left Side . 1023 726. Vertical Section of Canine Tooth . 1024 727. Diagram to illustrate the Develoj)- ment of a Dermal Tooth in the Shark 1025 728. Diagram to illustrate DevelojDment of a Tooth 1026 729. The Anterior Wall of the Pharynx with its Orifices, seen from Behind 1030 730. Sagittal Section through Mouth, Tongue, Larynx, Pharynx, and Nasal Cavity .... 1031 731. The Naso-Pharynx from the Front 1032 732. Open Mouth showing Palate and Tonsils 1034 733. Horizontal Section through Mouth and Pharynx at the Level of the Tonsils 1035 734. Diagram to show the Course of the CEsophagus 1038 735. Tracings from Frozen Sections to show the Relations of the Oeso- phagus 1039 736. Dissection to show the Arrangement of the Muscular Fibres on the Back of the Q^lsopliagus and Pharynx 1041 737. The Lower Part of the Pharynx and the Upper Part of the Qllsophagus 1042 738. Structure of the CEsophagus . . 1042 739. The Abdominal Viscera in situ . 1044 740. The Front of the Body . . . 1046 741. Diagrammatic Medial Section of Female Body .... 1048 742. Diagrammatic Transverse Sections of Abdomen 1049 743. Moderately distended Stomach . 1050 744. The Abdominal Viscera after the Removal of the Jejunum and Ileum 1051 745. The Stomach Chamberand Stomach Bed 1053 746. The Viscera and Vessels on the Posterior Abdominal Wall . . 1054 747. Longitudinal Section through the Pyloric Canal and Commence- ment of the Duodenum in a New- bom Child 1056 748. Abdomen of Female, showing Dis- placements resulting from Tight Lacing 1057 749. Section through Wall of Stomach, Cardiac Portion (slightly modi- fied from Stijhr) .... 1058 750. The Three Layers of the Muscular Coat of the Stomach . . . 1059 751. Diagram to show Formation of Pylorus 1060 752. The Mucous Membrane of Stomach 1060 FIG. PAGE 753. A Portion of Small Intestine, with Mesentery and Vessels . . . 1061 754. Diagram to show the Structure of the Small and Large Intestine and the Duodenum . . . 1062 755. Valvules Conniventes . . . 1063 756. Peyer's Patch and Solitary Glands from Intestine of Child . . 1064 757. The Viscera and Vessels on the Posterior Abdominal Wall . . 1066 758. The Peritoneal Relations of the Duodenum, Pancreas, Spleen, Kidneys, etc 1067 759. The Duodenal Fossse and Folds . 1069 760. The Bile Papilla in the Interior of the Duodenum .... 1069 761. The Abdominal Viscera after the Re- moval of the Jejunum and Ileum 1071 762. Large Intestine .... 1074 763. Caecum showing Ileo-csecal Valve . 1076 764. Three Forms of Ileo-csecal Valve . 1077 765. Diagrammatic Section through the Junction of Ileum with Caecum, to show the Formation of the Ileo-caecal Valve .... 1078 766. The Blood-Supply of the Csecum and Vermiform Appendix . . 1079 767. Structure of the Vermiform Ap- pendix 1080 768. The Cascal Folds and Fossae . . 1081 769. The Abdominal Viscera after the Re- moval of the Jejunum and Ileum 1084 770. The Iliac and Pelvic Colons . . 1085 771. The Rectum from Behind . . 1087 772. Distended Rectum in situ . . 1088 773. The Peritoneum of the Pelvic Cavity 1090 774. Diagram of Rectum . . . 1093 775. The Interior of the Anal Canal and Lower Part of Rectum . . 1094 776. The Anal Canal and Lower Part of Rectum in the Foetus . . . 1094 777. Diagrammatic Medial Section of Female Body .... 1098 778. The Peritoneum of the Pelvic Cavity 1100 779. Diagrammatic Transverse Sections of Abdomen .... 1101 780. The Peritoneal Relations of the Duodenum, Pancreas, Spleen, Kidneys, etc. .... 1103 781. Two Diagrams to illustrate the Development of the Intestinal Canal 1106 782. Two Diagrams to illustrate the Development of the Mesenteries . 1107 783. Diagrams to illustrate the Develop- ment of the Great Omentum (after Hertwig) 1107 784. The Abdominal Viscera in situ . 1109 785. The Liver from the Front . . 1111 786. The Liver from Below and Behind 1112 787. The Abdominal and Thoracic Viscera of a Five Months' Foetus . 1117 788. Structures between the Layers of the Lesser Omentum . . .1119 789. Diagram showing the Bile and Pancreatic Ducts piercing the Wall of the Duodenum obliqixely 1120 790. Liver of a Pig injected from the Hepatic Vein by T. A. Carter . 1122 791 . Diagrams illustrating the Structure of Liver 1122 LIST OF ILLUSTEATIONS. Flo. 792. 793. Diagram illustrating the Arrange- ment of the Blood-Vessels and of the Hepatic Cells and Bile Ducts within a Lobule of the Liver . 1123 Two Diagrams to illustrate the Development of the Intestinal Canal 1123 794. The Viscera and Vessels on the Posterior Abdominal Wall . . 1125 795. The Peritoneal Relations of the Duodenum, Pancreas, Spleen, Kidneys, etc. .... 1126 796. The Pancreas and Duodenum from Behind 1128 THE UEINOGENITAL SYSTEM. 797. Dissection to show the Position and Relationships of the Kidneys 798. Transverse Section through the Abdomen at the Level of the Second Lumbar Vertebra . 799. The Posterior Relationships of the Kidneys 800. The Kidneys viewed from Behind . 801. Right Kidney and Duodenum 802. Left Kidney, the Pancreas, the Spleen, and the Descending Colon 803. The Kidneys and Great Vessels viewed from the Front 804. Longitudinal Section through the Kidney 805. Section through a Portion of the Kidney 806. Diagrammatic Representation of the Structures forming a Kidney Lobe 807. Longitudinal Section of the Kidney ojjening up the Kidney Sinus 808. Medial Section of an Adult Male Pelvis 809. Medial Section through the Male Pelvis 810. Medial Section of the Male Pelvis . 811. Under Aspect of the Empty Male Bladder 812. The Bladder, Prostate, and Seminal Vesicles, viewed from Below 813. The Bladder, Prostate, and Seminal Vesicle, from the Outer Side 814. The Bladder and the Structures traversed by the Urethra in the Male 815. Lateral Aspect of Bladder contain- ing Ten Ounces of Fluid 816. View looking into the Pelvis from Above and somewhat Behind 817. View of the Interior of the Bladder in the Region of the Urethral Orifice 818. Medial Section of the Pelvis in an Adult Female .... 819. The Bladder of a Newly-born Male Child 820. Medial Section through the Pelvis of Newly-born Child . 821. View looking from Above into the Pelvis and Lower Part of the Abdominal Cavity in a Fcstus of about the Seventh Month . 822. View looking into the Male Pelvis seen from Above and somewhat Behind 823. Medial Section of the Pelvis in an Adult Male 824. Medial Section through the Female Pelvis 1131 1132 1133 1134 828 1135 829 1135 830. 1136 831. 1137 832. 1138 833. 1139 834. 1141 1142 835. 1145 1146 836. 1147 1147 837. 1148 838. 1149 839. 1150 1150 840. 841. 1151 842. 1152 843. 1152 844. 1153 845. 846. 1154 847. 1154 1155 848. 1158 825. 826. 827. The Right Testis and Epididymis . 1159 Right Testis within Tunica Vaginalis 1160 Transverse Section of Testis and Epididymis and of Spermatic Cord below External Al)dominal Ring 1161 Diagram to illustrate the Structure of the Testis and Eijididymis . 1162 The Peritoneum of the Pelvic Cavity 1163 Horizontal Section through the Rectum and Bladder . . . 1164 View of the Base of the Bladder, Prostate, Seminal Vesicles, and Vasa Deferentia from Behind . 1165 The Bladder, Prostate, and Seminal Vesicle viewed from the Side . 1166 The Seminal Vesicle and the Ampulla of Vas Deferens . . 1166 View looking from Above into the Pelvis and Lower Part of the Abdominal Cavity in a Foetus of about the Seventh Month . . 1167 Diagram to illustrate the Descent of the Testis and the manner in which the Tunica Vaginalis is derived 1168 Transverse Sections of Testis and Epididymis and of Spermatic Cord below External Abdominal Ring 1169 Deep Dissection of the Inguinal Region 1169 Dissection to illustrate the Com- ponent Parts of the Penis . . 1171 A Longitudinal Section of the Terminal Portion of the Penis, and a Transverse Section through the Body of the Organ . .1172 Bladder, Prostate, and Seminal Vesicles, from the Outer Side . 1173 Prostate, Bladder, and Seminal Vesicles, seen from Below . . 1174 Transverse Section through the Prostate 1175 Transverse Section through the Prostate 1176 The Bladder and the Structures traversed by the Urethra . . 1177 Medial Section of an Adult Male Pelvis 1178 The Prostatic, Membranous, and the Upper Portion of the Spongv Urethra . . . . '.1178 A Longitudinal Section of the Ter- minal Portion of the Penis, and a Transverse Section through the Body of the Organ . . .1180 Medial Section through the Female Pelvis 1181 XXX LIST OF ILLUSTEATIONS. FIO. PAGE 849. Side Wall of tlie Female Pelvis . 1183 850. The Uterus and Broad Ligament, and Diagrammatic Representa- tion of the Uterine Cavity . . 1183 Graafian Follicle .... 1185 The Uterus and Broad Ligament, and Diagrammatic Representa- tion of the Uterine Cavity . . 1188 Medial Section of the Pelvis in an Adult Female . . . .1193 Tlie Vagina, the Base of the Bladder, and the Recto-vaginal Pouch of Peritoneum .... 1194 Female External Genital Organs . 1196 Dissection of the Female External Genital Organs . . . .1197 Dissection of Female Perineum to show the Clitoris, the Bulb of the Vestibule, and Bartholin's Glands 1198 851 852 853. 854. 855. 856. 857. FIG. 858. Development of the Bladder, Ureter, and Kidney 859. Transverse Section through the Body of a Fowl Embryo 860. Diagram to illustrate the manner in which, the Ureter, the Vas Deferens, and the Bladder arise in the Embryo 861. Diagrammatic Representation and Comparison of the manner in which the Urinogenital Passages arise in the two Sexes . 862. Transverse Section through the Body of a Rat Embryo 863. Development of the External Genital Organs .... 864. External Genital Organs in a Male Embryo 865. Dissection of the Mammary Gland 866. Section through a Mammary Gland 1199 1200 1201 1202 1203 1205 1206 1207 1208 THE DUCTLESS GLANDS. 867. Dissection of the Spleen, Liver, and Kidneys from Behind . 868. The Spleen 869. Anterior Surfaces of Suprarenal Capsules ..... 870. Posterior Surfaces of Suprarenal Cai^sules 871. Transverse Section through the Suprarenal Capsule of a New- born Child in situ 872. Dissection of the Thyreoid Body 1211 1212 1214 1214 1215 and of the Parts in immediate re- lation to it . 873. Thymus Gland ina Full-time Foetus hardened by Formalin-Injection. 874. Dissection to show the Thymus Gland in an Adult Female . 875. Deep Surface of Thymus Gland 876. Section through Carotid Body 877. Schema of the relation presented by the Carotid Gland and its ac- cessory Outlying Parts to Branches of Middle Sacral Artery 1216 1218 1219 1220 1221 •1221 SURFACE AND SUEGICAL ANATOMY. the tlie 878. Diagrammatic Representation of a Coronal Section through the Scalp, Cranium, Meninges, and Cortex Cerebri .... Cranio-cerebral Topography . Scheme showing Relative Topo- graphy of the Chief Subdivi- sions of the Motor Area (adapted from Griinbaum and Sherring- ton) Cranio-cerebral Topography . View of the Outer Wall of Middle Ear Left Tympanic Membrane View of tlie Inner Wall of Middle Ear .... Section through Left Temporal Bone, showing Outer Wall of Tympanic Cavity, etc. . 886. Section through Petrous Portion of Temporal Bone of Adult 887. Frontal Sinuses of average dimen- sions, with a Medial Sei^tum (Logan Turner) .... 888. A Large Right Frontal Sinus with Septum oblique to the Left (Logan Turner) .... Right Frontal Sinus of very large dimensions; Left Sinus unopened (Logan Turner) .... 879, 880, 881. 882. 883. 884. 885. 889. 1223 1226 1227 1228 1230 1230 1231 1231 1232 1234 1234 1235 890. Vertical Coronal Section through the Nose and Frontal Sinuses . 1236 891. Head of Human Embryo about 29 days old 1240 892. Coronal Section through the Face of a Human Embryo at the Seventh Week 1241 893. From a Photograph showingDouble Complete Hare -Lip and Cleft Palate 1241 894. Shows Arrangement of Bones in Double Cleft Palate . . . 1242 895. Coronal Section through the Tongue and Submaxillary Region in a Plane behind the Molar Teeth . 1243 896. Open Mouth with Tongue raised and the Sublingual and Apical Glands exposed .... 1243 897. Horizontal Section through Mouth and Pharynx at the Level of the Tonsils 1245 898. Anterior Aspect of Neck and Shoulders 1247 899. Dissection of the Front of the Neck 1248 900. Lateral Aspect of Neck . . .1250 901. Anterior Aspect of Trunk, showing Surface Topography of Viscera . 1254 902. Dissection of a Subject to show the relations of the two Pleural Sacs viewed from the Front . . 1256 LIST OF ILLUSTKATIONS. FIG. 903. 904. 905. 906. 907. 908. 909. 910. 911.. 912. 913. 914. 915. 916. 917. 918. 919. Anterior Aspect of Trunk, sliowing Surface Tojiography of Viscera . 1257 Lateral Viewof the Right Pleural Sac 1258 Dissection of the Pleural Sacs from Behind 1259 Dissection from Behind to show the relation of the two Pleural Sacs to the Kidneys .... 1260 Posterior Aspect of Trunk, showing Surface Topography of Viscera . 1261 I Relations of the Cavities and Valves - of the Heart to Anterior Wall of I Thorax 1263 The Groin 1265 Anterior Aspect of Trunk, showing Surface Topography of Viscera . 1268 Lateral Aspect of Trunk, showing Surface Topography of Viscera . 1269 The Ctecal Folds and Fosste . . 1273 The Blood-Supply of the Csecum and Vermiform Appendix . . 1274 Anterior Aspect of Trunk, showing Surface Topography of Viscera . 1275 Dissection of the Perineum . . 1277 Tlie Interior of the Anal Canal and Lower Part of Rectum . . . 1280 *"I0- PAOE 920. The Rectum from Behind . .1282 921. Dissection of the Spleen, Liver, and Kidneys from Behind . . . 1286 922. Posterior Aspect of Trunk, show- ing Surface Topogi'aphy of Viscera 1287 923. Dissection of the Left Hypochon- driuni 1288 924. Axilla, Inner Aspect of Upper Arm and Elbow 1294 925. Extensor Aspect of Upper Limb . 1295 926. Transverse Section through the Bend of the Elbow . . .1297 927. Bend of Elbow, Front of Forearm, and Palm of Hand . . . 1298 928. Palm of Hand .... 1299 929. Dorsal Aspect of Hand . . . 1300 930. Section through Thigh at the Level of the Upper Part of Hunter's Canal 1303 931. Section through the Thigh immedi- ately above the Patella . . 1304 932. The Thigh and Groin . . . 1305 933. Anterior Aspect of Knee . . 1307 934. Outer Aspect of Knee and Leg . 1309 935. Outer Aspect of Foot and Ankle . 1310 936. Inner Aspect of Foot and Ankle . 1311 GLOSSARY OF ANATOMICAL TERMINOLOGY. Introduction. The question of the introduction of the B.N. A. (Basle Nomina Anatomica) into English Text-Books is discussed in the Editor's Preface, but it may be of interest to add a few words here as to the origin and objects of this nomenclature. The Terminology of Anatomy has been for many years in a chaotic condition. This fact has long been recognised not only by anatomists, but by teachers and students of other branches of medical and allied sciences. The Anatomical World must ever remain indebted to Professor W. His of Leipzig and his distinguished countrymen for their energy and perseverance in initiating successfully the gigantic task of forming an international Anatomical Nomenclature, otherwise known as the "B.N. A." (Basle Nomina Anatomica). Historical. The first step towards the revision of anatomical nomenclature with the view of making it internationally uniform was taken by Professor W. His, who introduced the subject at the meeting of the Anatomical Society at Leipzig in 1887. Professor His admitted that he owed the conception to the example given in Henle's work on Anatomy. The matter was taken up and as a result an International Commission was formed in 1891, con- sisting of von Bardeleben, Henle, Hertwig, His, Kolliker (as President), Kollmann, Kliptter, Leboucq, Merkel, von Mikalkovics, Romiti, Schwalbe, Toldt, Waldeyer, Duval, and Testut ; and as representatives of the English-speaking Anatomists : the dis- tinguished Editor of the present work — Professor Cunningham, Professor Thane, and Sir William Turner, to whom this volume is dedicated by the Editor and the contributors. For this Commission Professor W. Krause of Berlin acted as Editor. From the very constitution of the Committee it will be seen that its success was assured ; it only remained to go through the work — " periculosse plenum opus alese." The Method of the Commission. As a basis for comparison anatomical names were taken as they appeared in Gegenbauer's Text-Book of Human Anatomy, which was at that time the most recent text-book ; to these the various synonyms which had appeared from time to time were appended, and the individual members of the Commission were asked to record their choice of each name. After many alterations in arrangement, and after six years' strenuous work, the result of their labours was presented by the Commission to a meeting of the Anatomical Society in Basle in 1895, and there adopted — hence the name. The Objects held in View by the Commission. These are of the greatest importance, and their excellence must be admitted by all. They may be given in the words of the Editor, Professor Krause : — 1. Every part of the body shall have one single Latin name only ; there shall be no synonyms separated by a " sive " or " seu " as in most text-books. Each nation using the Latin names can translate them in the way that seems best to it. 2. The name shall be short and distinctive and should recall some point of description or distinctive charactei*. 3. No part of the body shall have an unnecessarily long Latin name. 4. No two parts of the body shall have the same name unless they are truly homologous parts. xxxiii XXXIV GLOSSAEY. 5. The names given shall be consistent with Latin grammar and orthography. 6. Names of observers shall, as far as possible, be removed from anatomical terms except where they actually mark historical observation. 7. In the whole work the Commission shall endeavour to be as conservative as possible. 8. The same names shall be used for arteries, veins, and nerves, where they run together — at least where possible ; e.g. femoral artery and femoral nerve (anterior crural). 9. The same names shall be given to foramina and to the vessels or other structures which pass through them. 10. Adjectives shall, as far as possible, be used as opposites — Scf. profundus and superficialis. 11. Ligaments shall be named according to their attachments, the final part of the name indicating the proximal attachment {i.e. sacro-iliac, not ilio-sacral). 12. There shall be no hybrid names. It might at first sight appear that all these conditions were easy to fulfil ; such a conclusion, howeA'er, would be far from the truth. The laboiirs of the Commission occupied a space of no less than six years, and even at their conclusion many names remained which could not be brought into harmony with the conditions laid down ; in retaining these, many of the above conditions were violated at times ; in all such cases, however, there were strong grounds for retaining the old nomenclature. For these and other details in connection with the International Nomenclature we would refer those interested to the original papers by Professors Krause and His ; Die anatomische Nomen- clatur by Professor W. Krause, Leipzig, George Thieme and Co., 1893; and Die anatomische Nomendatur by Wilhelm His, Leipzig, von Vert and Co., 1895. In conclusion, we wish to emphasise the fact that the Latin names are the essential and international. Each country may, does, and will continue, no doubt, to translate these names as seems best to it. In the form of a Glossary we append a list of the B.N. A. terms which differ in any important detail from those originally used in this work or from the terms in common use in the English language. It is our hope that the student may readily find in the Glossary any name he may require at once, and if the name is not to be found in the Glossary he may rest assured that it has not been altered. THE BONY SKELETON. Or.D Tbrminoloqy. Vertebrae Incomplete facet for head of rib, upper lucoiajilete facet for head of rib, lower Facet for transverse process Pedicle (This word is retained in use, the Latin term being unwieldy) Atlas Facet for odontoid process Axis Odontoid process Sternum Gladiolus Eusiform process Supra-sternal notch B.N.A. Terminology. Fovea costalis superior Fovea costalis inferior Fovea costalis trans- versalis Radix arcus vertebrae Fovea dentis Epistropheus Dens Corpus sterni Xipiioid process Incisura jugularis Bones of Skull. Frontal Nasal spine Lateral angulaiy ])rocess (Use retained) Internal surface External surface Parietal Temporal ridges Si)ina frontalis Processus zygomaticus Cerebral surface Parietal surface Temporal lines Old Terminology. Groove for lateral sinus Occipital Anterior condyloid foramen Posterior condyloid foramen Supeiior longitudinal groove Sphenoid Pterygoid ridge Optic groove Ethmoidal crest Spinous process Internal pterygoid process Pjxternal pterygoid l)rocess Vidian canal Pterygo - palatine canal Temporal Bone A(jueduct of Fal- lopius Hiatus Fallojiii Vaginal process of tympanic bone Digastric fossa B.N.A. Terminology. Sulcus transversus Canalis hypoglossi Canalis condjdoideus Sulcus sagittalis Ci'ista infratemporalis Sulcus chiasmatis Crista sphenoidalis Spina angularis Lamina niedialis pro- cessus pterygoidei Lamina lateralis pro- cessus pterygoidei Canalis pterygo id eus [Vidii] Canalis i)haryiigeus Canalis facialis [Fal- lopii] Hiatus canalis facialis Vagina processus sty- loidei Incisura mastoidea GLOSSARY. XXXV Old Terminology. Glaserian fissure (Still retained) Glenoid cavity (Still retained) Ethmoid Lateral mass Os plaiiuin Lacrimal Bone Haiuular process Lacrimal crest Nasal Bone Groove for nasal nerve Maxilla Facial or external surface Antrum of Higlimore Nasal process ]\Ialar process Malar Bone Zygomatic process Frontal process Temporo-malar canal Malar foramen Mandible Genial tubercle or spine External oblique line Internal oblique line Sigmoid notch Inferior dental fora- men Inferior dental canal B.N. A. Tekminology. Fissura petrotympanica Fissura mandibularis Labyrinthus etlimoiil- alis Lamina papyracea Hamulus lacrimalis Crista lacrimalis pon- terior Sulcus etlimoidalis Facies anterior Sinus maxillaris Processus frontalis Processus zygomaticus Os zygomaticum Processus temporalis Processus fronto-sphen- oidalis Foramen zygomatico- orbitale Foramen zygomatico- faciale Spina mentalis Linea ohliqua Linea myloliyoidea Incisura mandibularis Foramen mandibulare Canalis mandibulie The Skull as a Whole. Wormian bones Pacchionian depressions Spheno-maxillary fossa Posterior palatine canal Foramen lacerum medium Posterior nares Ossa suturaruin Foveohe granulares (Pacchioni) Fossa pterygo-palatina Canalis pterygo-palat- inus Foramen lacerum Choanse Upper Extremity. Clavicle Impression for conoid ligament Impression for rhom- boid ligament Scapula Anterior or lateral angle Superior angle Humerus Bicipital groove External lip Internal lip Internal surface External surface Tuberositas coracoidea Tubei'ositas costalis Margo lateralis Margo medialis Sulcus intertubercularis Crista tuberculi majoris Crista tuberculi niinoris Facies anterior medialis Facies anterior lateralis Old Terminology. Musculo-spiral groove Capitellum Intei'iial condyle Lateral condyle Ulna Greater sigmoid cavity Lesser sigmoid cavity Radius Bicipital tuberosity Sigmoid cavity Carpus Scaphoid Semilunar Cuneiform Trapezium Trapezoid Os magnum Unciform B.N. A. Terminology. Sulcus nervi radialis Cajiitulum Epicondylus medialis Epicondylus lateralis Incisura semilunaris Incisura radialis Tuberositas radii Incisura ulnaris Navicular Os lunatum Os triquetrum Os multangulum majus Os multangulum minus Os capitatum Os hamatum Lower Extremity, Innominate Bone Inferior curved line Superior curved line Spine of the ischium Great sacro-sciatic notch Lesser sacro-sciatic notch Spine of pubis Descending ramus of pubis Pelvis False pelvis True pelvis Pelvic inlet Linea glirtrea anterior Linea glutfea posterior Spina ischiadica Incisura ischiadica major Incisura ischiadica minor Tuberculum pubicum Ramus inferior pubis Pelvic outlet Femur Digital fossa Spiral line Intertrochanteric line Inner tuberosity Outer tuberosity Tibia Internal tuberosity External tuberosity Spine Tubercle Bones of the Foot Astragalus Os calcis Tuberosity of Inner Outer Inner cuneiform Middle cuneiform Outer cuneiform Pelvis major Pelvis minor Apertura pelvis minoris suijerior Apertura pelvis minoris inferior Fossa trochanterica Linea intertrochanterica Crista intertrochan- terica Epicondylus medialis Epicondylus lateralis Condylus medialis Condylus lateralis Eminentia intercondy- loidea Tuberositas tibife Talus Calcaneus Tuber calcauei Processus medialis tuber calcanei Processus lateralis tuber calcanei Os cuneiforme primum Os cuneiforme secun- dum Os cuneiforme tertium XXXVl GLOSSAKY. SYNDESMOLOGY. Old Terminology. Posterior occipito- axial ligament Joint between the atlas and the axis Odontoid ligament Suspensorj' ligament External lateral liga- ment of the jaw Internal lateral liga- ment of the jaw Khomboid ligament Accessory ligament of the shoulder -joint Superior radio - irlnar joint Internal lateral liga- ment of elbow-joint External lateral liga- ment Orbicular ligament Oblique ligament of the superior radio - ulnar joint Inferior radio - ulnar joint Anterior ligament of the radio-carpal joint Posterior ligament of the radio - carpal joint B.N. A. Terminology. Membrana tectoria Articulatio atlauto-epis- trophica Lig. alaria Lig. apicis dentis Lig. temporo-iuandibu- lare Lig. spheno-mandibu- lare Lig. costo-elaviculare Lig. coraco-humerale Articulatio radio-ulnaris proximalis Lig. collaterale ulnare Lig. collaterale radiale Lig. annulare radii Chorda obliqua Articulatio radio-ulnaris distalis Lig. radio-carpeum vo- lare Lig. radio-carpeum dor- sale Old Terminology. Palmar ligaments of the metacarpo - phalan - geal joints Transverse metacarpal ligament Lateral phalangeal liga- ments Great sacro-sciatic liga- ment Small sacro-sciatic liga- ment Posterior ligament of knee-joint Arcuate popliteal liga- ment External semilunar car- tilage Internal semilunar car- tilage Superior tibio - fibular articulation Inferior tibio - fibular articulation Superior astragalo-sca- phoid ligament Superior calcaneo - sca- phoid ligament Internal calcaneo-cuboid ligament B.N. A. Terminology. Lig. accessoria volaria Lig. capitulorum (oss. metacarpalium) trans- versa Lig. collateralia Lig. sacro-tuberosum Lig. sacro-spinosum Lig. popliteum obli- quum Lig. popliteum arcua- tum Meniscus lateralis Meniscus medialis Articulatio tibiofibularis Syndesmosis tibiofibu- laris Lig. talo-naviculare Pars calcaneo - navicu- laris Pars calcaneo-cuboidea NEUROLOGY. Spinal Cord. Clark's column Nucleus dorsalis Dorsal part of spinal Pars thoracalis cord Paramedian furrow Sulcus intermedins pos- terior Direct pyramidal tract Fasciculus cerebro-spin- alis anterior Crossed pyramidal tract Fasciculus cerebro-spin- alis lateralis Direct cerebellar tract Fasciculus cerebello - spinalis Gower's tract Fasciculus antero-later- alis supcrficialis Brain. Cerebello-olivary fibres Fibne eerebello-olivares Corpus Trapezoid es Posterior crescentic lo- bule Postero-infeiior lobule Great horizontal fissure Crus cerebri Iter e tertio ad ipiartuni ventriculum Foranicn of Monro Sulcus of Monro Middle commissure Bundle of Vicq d'Azyr Pars basilaris Cori)US Trapezoideum Lobulus semilunaris su- perior Lobulus semilunaris in- ferior Sulcus horizontalis cerc- belli Pcdunculus cerebri Aqueductus cerebri Foramen interventricu- lare Sulcus hypothahimicus Massa intermedia Fasciculus thalanio- mammillaris Pars opercularis Fissure of Sylvius First temporal gyrus Second temporal gyrus Third temporal gyrus Fissure of Rolando Parallel sulcus Second temporal sulcus Occipito -temporal sul- cus Occipito-temporal con- volution Intraparietal sulcus Callosal sulcus Calloso-niarginal fissure Dentate fissure Callosal convolution Ticnia semicircularis 'i'rigonum ventriculi Jlippocampus major Pes liippocam[)i Gyrus dcntatus Lenticular nucleus Anterior limb (of inter- nal capsule) Posterior limb (of inter- nal cap.sule) 0[)tic radiation Fissura cerebri lateralis Gyrus temporalis su- perior Gyrus temporalis medius Gyrus temporalis in- ferior Sulcus centralis Sulcus temporalis su- perior Sulcus temporalis me- dius Sulcus temporalis in- ferior Gyrus fusiforniis Sulcus inter[)arietalis Sulcus corporis callosi Sulcus cinguli Fissura hippocampi Gyrus cinguli Stria tcnuinalis Trigonum collaterale Hippocampus Digitationes hippo - campi Fascia dentata hippo- campi Nucleus lentiformis Pars frontalis capsulfe internae Pars occipitalis capsulae internas Radiatio occipito-thal- amica GLOSSAKY XXXVll Membranes of Brain. Old Terminology. Cistenia magna Cisterna basalis Pacchionian bodies Cranial Superior maxillarj' nerve Inferior maxillary nerve Great superficial petro- sal nerve Deep petrosal nerve Lenticular ganglion External palatine nerve Pars intermedia of Wrisberg Auditory nerve .Jugular ganglion Recurrent laryngeal nerve Ganglion of root Ganglion of trunk Plexus gulii? Accessory portion of spinal accessory nerve Spinal portion B.N. A. TEHMINOLOdV. Cisterna cerebello- niedullaris Cisterna interpeduncu- laris Granulationes araclinoi- deales Nerves. N. maxillaris N. niandibularis N. petrosus superlicialis major N. petrosus profundus G. ciliare N. palatinus niedius N. intermedins N. acusticus G. sujierius N. recurrens Ganglion jugulare Ganglion nodcEum r Plexus oesopliageus I anterior "j Plexus cesophageus I posterior Ramus internus Ramus externus Posterior primary divi- sions Superficial cervical nerve Suprasternal nerves Supraclavicular nerves Supra-acromial nerves Nerve to the rhomboids Cutaneous branch of the musculo- cutaneous nerve Nerve of Bell Long subscapular nerve Lesser internal cutane- ous nerve Spinal Nerves. Rami posteriores N. cutaneus colli Nn. supraclaviculares anteriores Nn. supraclaviculares niedii Nn. siipraclaviculares posteriores N. dorsalis scapulte N. cutaneus antibrachii lateralis N. thoracalis longus N. thoraco-dorsalis N. cutaneus brachii medialis Or,n Tkuminology. I nteriKil cutaneous nerve Anterior branch Internal branch Circumflex nerve Anterior interosseous Palmar cutaneous branch of the median nerve Collateral palmar digi- tal branches of median nerve Dorsal cutaneous branch of ulnar nerve Palmar cutaneous branch of ulnar nerve Musculo-sj)iral nerve Upper external cutane- ous branch of mus- culo-spiral nerve LoAver external cutane- ous branch of mus- culo-si)iral nerve Radial nerve Posterior interosseous nerve Dorsal digital nerves I n tercosto- h umeral nerve Iliac branch of ilio-hypo- gastric nerve Hypogastric branch of ilio-hy}»ogastric nerve Genito-crural nerve Crural branch of genito- crural nerve Genital branch of genito- crural nerve External cutaneous nerve Anterior crural nerve Long saphenous nerve Patellar branch of long saphenous nerve Great sciatic nerve External popliteal nerve Musculo - cutaneous nerve Anterior tibial nerve Internal ]»opliteal nerve Short saphenous nerve Pudic nerve B.N. A. Terminology. N. cutaneus antibrachii medialis Ramus volaris Rannis ulnaris N. axillaris N. interosseus volai'is Ramus palmaris N. median! Nn. digitales volares proprii Ramus dorsalis manus Ramus cutaneus iial- maris N. radialis N. cutaneus brachii posterior N. cutaneus antibrachii dorsalis Ramus superficialis N. interosseus dorsalis Nn. digitales dorsales Nn. intercosto-brachi- ales Ramus cutaneus lateralis Ramus cutaneus an- terior N. genito-femoralis N. lumbo-ingninalis N. spermaticus externus N. cutaneus femoris la- teralis N. femoral is N. saphenus R. infrapatellaris N. ischiadicus N. peronseus communis N. peronseus superfi- cialis N. peroniTeus profundus N. tibialis N. suralis N. pudendus MYOLOGY. Muscles of the Back. Superficial. Levator angulae scapulfe Levator scapulre Muscles of the Chest. Serratus magnus Serratus anterior Muscles of Upper Extremity. Biceps Bicipital fascia Brachialis anticus Triceps Inner head Outer head Biceps brachii Lacertus tibrosus Brachialis Triceps brachii Caput mediale Caput laterale Pronator radii teres Coronoid head Supinator longus Supinator brevis Extensor car})! radialis longior Extensor carpi radialis brevior Extensor indicis Extensor minimi digiti Extensor ossis meta- carpi pollicis Abductor pollicis Pronator teres Caput ulnare Brachio-radialis M. supinator Extensor carpi radialis longus Extensor carpi radialis brevis Extensor indicis pro- prius Extensor digiti quinti proprius Abductor pollicis longus Abductor pollicis brevis XXXVlll GLOSSAEY. Old Terminology. B.N. A. Terminology. Extensor primi inter- Extensor pollieis brevis nodii pollieis Extensor secundi inter- Extensor pollieis longus nodii pollieis Anterior annular liga- Lig. carpi transversuni ment Posterior annular liga- Lig. carpi dorsale ment Muscles of Lower Extremity. Tensor fascia? femoris Hunter's canal Scarpa's triangle Crui'al canal Crural ring Quadriceps — Vastus externus Crureus Internus SuLcrureus Tibialis anticus Tendo Achillis Tibialis posticus Accessorius Upper annular ligament Internal annular liga- ment Lower annular ligament Tensor fascite latae Canalis adductorius (Hunteri) Trigonum femorale (fossa ScarpEE major) Canalis femoralis Annulus femoralis Vastus lateralis A''astus intermedins Vastus medialis M. articularis genu Tibialis anterior Tendo calcaneus Tibialis posterior Quadratus jJantge Lig. transversuni cruris Lig. laciniatum Lig. cruciatum cruris Axial Muscles. Muscles of the Back. Serratus posticus superior Serratus posticus in- ferior Splenius colli Erector spinse Ilio-costalis — Sacro-lumbalis Accessorius Cervicalis ascendens Longissimus — Dorsi Transversalis cervicis Trachelo-mastoid Spinalis — Dorsi Colli Caj)itis Semispinalis — Dorsi Colli Complexus Multifidus spinae Serratus posterior superior Serratus posterior in- ferior Splenius cervicis M. sacro-spinalis Ilio-costalis — Lumborum Dorsi Cervicis Longissimus — Dorsi Cervicis Capitis Spinalis — Dorsi Cervicis Capitis Semispinalis — Dorsi Cervicis Capitis Multifidus Muscles of Head and Neck. Platysma inyoidcs Occipito-frontalis Epicranial aponeurosis Attrahens aurein Retrahens aurem Attollens aurem Orbicularis palpebrarum Tensor tarsi Pyramidalis nasi Compressor naris Dilatores naris Platysma M. eiiicranius Galea aj ion euro tica M. auricularis anterior M. auricularis posterior M. auricularis suijerioi' Orbicularis oculi Orbicularis - pars lacri- malis M. }jroeerus M. nasalis Pars alaris Old Terminology. Depressor alaj nasi Depressor anguli oris Quadratus labii superi- oris — Z3^gomaticus minor ;_ Levator labii superi- " ., oris Lev^r labii superi- oris alfeque nasi Zygomaticus major Levator anguli oris Depressor labii inferioris B.N. A. Terminology Depressor septi M. triangularis Caput zygomaticum Caput infraorbitale Caput angulare M. zygomaticus M. caninus M. quadratus labii in- ferioris M. mentalis Depi-essor menti Muscles and Fascia of the Orhit. Capsule of Tenon Fascia bulbi Palpebral ligaments Rectus externus Rectus internus Septum orbitale Rectus lateralis Rectus medialis Muscles of the Tongue. Genio-hyo-glossus Superior lingualis Inferior lingualis Transverse fibres Vertical fibres Genio-glossus M. longitudinalis superior M. longitudinalis inferior M. transversus linguae M. verticalis linguae Muscles of the Pharynx. Palato-iaharyngeus Pharyngo-palatinus Azygos-uvulse M. uvulae Levator palati Lerator veli palatini Tensor jjalati • Tensor veli palatini Palato-glossus M. glosso-palatinus Deep Lateral Muscles of Neck. Scalenus anticus Scalenus posticus Rectus capitis anticus major Rectus capitis anticus minor Muscles of Thorax, Scalenus anterior Scalenus jjosterior Longus capitis Rectus capitis anterior Triangularis sterni Diaphragm, lumbar part — Internal arcuate liga- ment Ligamentum arcu- atum internum Ligamentum arcu- atum externum M. transversus thoracis Cms mediale Crus intermedium Crus lateral e Arcus lumbo-costalis medialis (Halleri) Arcus lumbo-costalis lateralis (Halleri) Muscles of the Abdomen. Poupart's ligament Gimbernat's ligament Intercolumnar fi))res Triangular fascia External abdominal ring Internal pillar External pillar Ligamentum inguinale Pouparti Ligamentum lacunare (Gimbernati) FibrsB intercrurales Ligamentum inguinale rcdexum (Collesi) Annulus inguiualis sub- cutaneus Crus superius Crus inferius GLOSSAKY. XXXIX Old Teiiminology. Conjoined tendon Transversalis muscle Fold of Douglas Internal abdominal rinj Hesselbach's liijament B.N. A. Tkuminology. Falx aponeurotica in- guinalis M. transversns abdom- inis Linea semicircularis (I)ouglasi) Annulns inguinalis ab- dominalis Ligamentum interfoveo- lare (Hesselbachi) Perineum. Ol.l) TKKMINOUKiY. Traiisversus perinei Compressor urethrae Triangular ligament Deep layer of triangular ligament White line of pelvis B.N. A. Tekminology. Transversns perinei superficialis M. sjihincter uretlirfe membranaceae Diaphragma urogenitale Fascia diaphragmatis iirogenitalis superior Arcus tendineus m. levatoris ani SPLANCHNOLOGY. Digestive Apparatus. Anterior palatine arch Posterior palatine arch Gland of Nuhn Wharton's duct Circumvallate papilhie Pharyngeal recess of Rosenmiiller Pharyngeal aponeurosis Valvulae conniventes Crypts of Lieberkuhn Ileo-crecal valve Columns of Morgagni Valves of Houston Valve of Heister Arcus glosso-palatinus Arcus pharyngo - pala- tinus Gl. lingualis anterior Ductus submaxillaris PapilliE vallatje Recessus i)haryngeus Tela submucosa Plicfe circulares Gl. intestinales Valvula coli Columnae rectales Pliciie transversales recti Valvula spiralis Respiratory Apparatus. Adam's apple Superior thyroid notch Aryteno - epiglottidean muscle Internal thy ro - ary- tenoid muscle Thyro- epiglottidean muscle Laryngeal sac Prominentia laryngea Incisura thyreoidea su- perior M. ary-epiglotticus M. vocalis M. thyreo-epiglottieus Appendix ventriculi laryngis True vocal cord False vocal cord Superior thyro - ary - tenoid ligament Inferior thyro - ary - tenoid ligament Glottis vera Glottis spuria Plica vocalis Plica ventricularis Ligamentum ventricu- lare Ligamentum vocale Glottis Rima vestibuli Urogenital Apparatus. Malpighian corpuscles Organ of Giraldes Hydatid of Morgagni Vas deferens Glands of Littre Graaliau follicles Discus proligerus Fallo]>ian tube Hydatids of Morgagni Gartner's duct Parovarium Lesser peritoneal sac Foramen of Winslow Costo-colic ligament Douglas' pouch Corpuscula renis Paradidymis Appendix testis Ductus deferens Gl. urethrales Folliculi oophori vesi- culosi Cumulus oophorus Tuba uterina Appendices vesiculosi Ductus epoophori longi- tudinalis Epoophoron Peritoneum. Bursa omentalis Foramen epiploicum Lig. phrenico-colicum Excavatio recto-uterina (cavum Douglasi) ANGIOLOGY. Heart. Auricle Auricular appendix Notch at ai)ex of heart Columufe carnepe Intervenous tubercle of Lower Atrium Auricula cordis Incisura cordis Trabeculae caruepe Tuberculum interveno - sum Arteries. Sinuses of Valsalva Innominate artery Ranine artery Facial artery Inferior dental artery Small meningeal artery Buccal artery Posterior dental artery Anterior superior dental arteries Sinus aortse A. anonyma A. profunila lingufe A. maxillaris externa A. alveolaris inferior Ramus meningeus ac- cessorius A. buccinatoria A. alveolaris superior postei'ior Aa. alveolares superiores anteriores Anterior chorioidal ar- A. chorioidea tery Auditory artery Transverse arteries (branches of Basilar artery) Arteria comes nervi phrenici Anterior intercostal ar- teries Thyreoid axis Suprascapular artery Superior intercostal ar- tery Superior intercostal proper Transversalis colli Superior thoracic artery Long thoracic artery Dorsalis scapulae Superior profunda A. auditiva interna Rami ad pontem A. pericardiaco-phrenica Rami intercostales Truncus thyreo-cervi- calis A. transvei'sa scapulte Truncus costo-cervicalis A. intercostalis suprema A. transversa colli A. thoracalis suprema A. thoracalis lateralis A. circumflexa scapulae A. 2^1'ofunda brachii xl GLOSS AEY. Old Terminology. Articular branch of su- perior profunda Inferior profunda Anastomotica magna Anterior radial carpal Posterior radial carpal Dorsal interosseous ar- teries Kadialis indicis Deep palmar arch Posterior interosseous artery Posterior interosseous recurrent artery Anterior interosseous artery Posterior ulnar carjial Anterior ulnar carpal Superficial palmar arch Palmar digital arteries Collateral digital ar- teries Rami intestini tenuis iliddle capsular artery Internal iliac artery Deep epigastric artery Cremasteric artery Superficial and deep ex- ternal pudic arteries Internal circumflex ar- tery External circumflex ar- tery Anastomotica magna Superior external arti- cular artery Inferior external arti- cular artery Superior internal arti- cular artery Inferior internal arti- cular ai'tery Azygos articular artery B.N. A. Terminology. A. collateralis radialis A. collateralis ulnaris superior A. collateralis ulnaris inferior Ramus carpeus volaris Ramus carpeus dorsalis Aa. metacarpeae dorsales A. volaris indicis radi- alis Arcus volaris profundus A. interossea dorsalis A. interossea recurrens A. interossea volaris Ramus carpeus dorsalis Ramus carpeus volaris Arcus volaris superfici- alis Aa. digitales volares communes Aa. digitales volares proprise Aa. ilefe A. suprarenalis media A. hypogastrica A. epigastrica inferior A. spermatica externa Aa. pudendse externa A. circumflexa femoris medialis A. circumflexa femoris lateralis A. genu suprema A. genu sujierior later- alis A. genu inferior lateralis A. genu superior me- dialis A. genu inferior medialis A. genu media Old Terminology. External malleolar ar- tery Internal malleolar ar- teiy Anterior peroneal artery Posteri or peroneal artery Internal malleolar ar- tery External calcaneal! ar- tery Internal calcanean ar- tery Internal plantar artery External plantar artery Digital branches Collateral digital branches B.N. A. Terminology. A. malleolaris anterior lateralis A. malleolaris anterior medialis Ramus perforans A. malleolaris posterior lateralis A. malleolaris posterior medialis Rami calcanei laterales Rami calcanei mediales A. plantai'is medialis A. plantaris lateralis Aa. metatarsaj plantares Aa. digitales plantares Veins. Great cardiac vein Oblique vein of Marshall Vestigial fold of Mar- shall Veins of Thebesius Lateral sinus Torcular Herophili Basilar sinus Superior longitudinal sinus Inferior longitudinal sinus Veins of Galen Vena magna Galeni Vein of the corpus stria- tum Basilar vein Suprascapular vein Vena azygos major Vena azygos minor in- ferior Vena azygos minor su- perior Internal saphenous vein External saphenous vein V. cordis magna V. obliqua atrii sinistri Lig. V. cavaj sinistra Vv. cordis minimte Sinus transversus Confluens sinuum Plexus basilaris Sinus sagittalis sui^erior Sinus sagittalis inferior V. cerebri internae V. cerebri magna V. terminalis V. basalis V. transversa scajjulre V. azygos V. hemiazygos V. hemiazygos acces- soria V. saphena magna V. saphena parva Lymphatics. Receptaculum chyli Cisterna chyli TEXT-BOOK OF ANATOMY. INTRODUCTION. Anatomy is a comprehensive term, which includes several closely related branches of study. Primarily it is employed to indicate the study of the several parts which build up the body, and the relationship which these present to each other. But during the period of its existence the individual exhibits many structural changes : its structure is not the same at all stages of its life. The ovum or starting-point of every individual is very different from the finished organism as represented by the adult, and the series of changes through which the organism passes until its structure is perfected and full growth is attained constitute the study of development. The general term " development " includes not only the various and striking structural changes which occur during the intrauterine life of the individual, to the study of which the term embryology is more specially applied, but also many growth processes which occur after birth, such as the later stages in the ossification and growth of the bones, the eruption of the two series of teeth, the adjustment of the vascular system to its new requirements, etc. The actual obser- vation of the processes by which the parts of the body are gradually formed, and of the structural arrangements by means of which a temporary connexion is estab- lished between the ovum and the mother, through which an interchange of nutritive and other matters between the two takes place, renders embryology one of the most interesting of all the departments of anatomy. The term ontogeny is also used to denote the development of the individual. There is, however, another form of development, slower, but just as certain in its processes, which affects not only the individual, but every member of the animal group collectively to which it belongs. The theory of descent or evolution leads us to believe that between man of the present day and his remote ancestors there is a wide structural gap, which, if the geological record were perfect, would be seen to be completely occupied by long-lost intermediate forms. In the process of evolution, therefore, structural changes have gradually taken place which have modified the entire race. A more or less close or remote blood-relationship links together all the members of the animal kingdom. These evolutionary phases constitute the ancestral history or phylogeny of the individual. Ontogeny and phylogeny are intertwined in a remarkable manner, and present certain extraordinary relationships. In other words, the ancestral evolutionary development appears to be so stamped upon an individual that it repeats certain of the phylogenetic stages with more or less clearness during the process of its own individual development. Thus at an early period in the embryology of man we recognise evanescent gill-slits comparable with those of a fish, whilst a study of the development of his heart shows that it passes 1 2 TEXT-BOOK OF ANATOMY. through transitory structural conditions in many respects similar to the permanent condition of the heart in certain of the lower animals. It is in connexion with this that the phrase has arisen that every animal in its individual development or ontogeny climbs up its own genealogical tree — a saying which, taking it even in the broadest sense, is only partially true. The higher conceptions of anatomy, which are obtained by taking a general survey of the structural aspects of the entire animal kingdom, constitute morphology. The morphologist investigates the laws of form and structure, and in his generalisa- tions he gives attention to detail only in so far as this is necessary for the proper establishment of his views. The knowledge of anatomy which is required by the student of medicine is different. It is essentially one of detail, and often details important from the practical and utilitarian points of view have little or no morphological value. This want of balance in the interest attached to anatomical facts, according to the aspect from which they are examined, so far from being unfortunate, affords the teacher the means of making the study of anatomy at once fascinating and attractive. Almost every fact which is brought under the notice of the student can be accompanied by a morphological or a practical application. This it is that lightens a study which, presented to the student of medicine in any other way, would be at once dry and tedious. Certain terms employed in morphology require early and definite explanation. These are homology, serial homology, and homoplasy. The same organ repeated in two different animals is said to present a case of homology. But this morphological identity between these two organs must be proved beyond dispute before the homology between them can be allowed. In deciding this identity the great and essential test is that the two organs in question should have a similar develop- mental origin. Thus the fore-limb of a quadruped is homologous with the upper limb of man ; the puny collar-bone of a tiger, the fibrous thread which is the only representative of this bone in the horse, and the strongly marked clavicle of the ape or man, are aU, strictly speaking, homologous with each other. Homologous oro'ans in different animals usually present a similar position and a similar structure, but not invariably so. It is not uncommon for a muscle to wander somewhat from its original position, and many cases could be quoted in which parts have become completely transformed in structure, either from disuse or for the purpose of meeting some special demand in the animal economy. In the study of the muscles and ligaments instances of this will be brought under the notice of the reader. Identity or correspondence in the function performed by two organs in two different animals is not taken into consideration in deciding questions of homology. The gills of a fish and the lungs of a higher vertebrate perform very much the same physiological office, and yet they are not homologous. The term analogy is often used to express functional correspondence of this kind. Often orcrans which perform totally different functions are yet perfectly homologous. Thus the wing of a bat or the wing of a bird, both of which are subservient to flight, are homologous with the upper limb of man, the office of which is the different one of prehension. In the construction of vertebrates and certain other animal groups a series of similar parts are repeated along a longitudinal axis, one after the other. Thus the series of vertebra? which build up the backbone, the series of ribs which gird round either side of the chest, the series of intercostal muscles which fill up the intervals between the ribs, the series of nerves which arise from the brain and spinal cord, are all examples of this. An animal exhibiting such a condition of parts is said to present the segmental type of organisation, and in the early stages of development this segmentation is much more strongly marked, and is to be seen in parts which INTEODUCTION. 3 subsequently lose all trace of such a subdivision. The parts thus repeated are said to be serially homologous. But there are other instances of serial homology besides those which are manifestly produced by segmentation. The upper limb is serially homologous with the lower limb : each is composed of parts which, to a large extent, are repeated in the other, and the correct adjustment of this comparison between the several parts of the upper and lower limbs constitutes one of the most difficult and yet interesting problems of morphology. Homoplasy is a term which has been introduced to express a form of corre- spondence between organs in different animals which cannot be included under the term homology. Two animal groups, which originally have sprung from the same stem-form, may independently develop a similar structural character which is altogether absent in the ancestor common to both. Thus the common ancestor of man and the carnivora in all probability possessed a smooth brain, and yet the human brain and the carnivore brain are both richly convoluted. Not only this, but certain anatomists seek to reconcile the convolutionary pattern of the one with the convolutionary pattern of the other. What correspondence there is does not, in every instance, constitute a case of homology, because there is not in every case a community of origin. Correspondence of this kind is included under the term " homoplasy." Another example is afforded by the heart of the mammal and that of the bird. In both of these groups the ventricular portion of the heart consists of a right and a left chamber, and yet the ventricular septum in the one is not homologous with the corresponding septum in the other, because the common ancestor from which both have sprung possessed a heart with a single ventricular cavity, and the double-chambered condition has been a subsequent and independent development in the two groups. Systematic Anatomy. — The human body is composed of a combination of several systems of organs, and the several parts of each system not only present a certain similarity in structure, but also fulfil special functions. Thus we have — 1. The skeletal system, composed of the bones and certain cartilaginous and membranous parts associated with them, the study of which is known as osteology. 2. The articulatory system, which includes the joints or articulations, the study of which is termed arbhrology. 3. The muscular system, comprising the muscles, the study of which constitutes myology. 4. The nervous system, in which are included the brain, the spinal cord, the spinal and cranial ganglia, the sympathetic ganglia, and the various nerves proceeding from and entering these. The study of these parts is expressed by the term neurology. In this system the organs of sense may also be included. 5. The vascular and lymphatic system, including the heart, blood-vessels, the lymphatic vessels, and the lymphatic glands. Angeiology is the term applied to the study of this system. 6. The respiratory system, in which we place the lungs, windpipe, and larynx. 7. The digestive system, which consists of the alimentary canal and its associated glands, and parts such as the tongue, teeth, liver, pancreas, etc. 8. The urogenital system, composed of the urinary organs and the reproductive organs — the latter difiering in the two sexes. The term splanchnology denotes the study of the organs included in the respiratory, digestive, and genito-urinary systems. 9. The integumentary system, consisting of the skin, nails, hair, etc. These numerous organs which form the various systems are themselves built up of tissues, the ultimate elements of which can only be studied by the aid of the 4 TEXT-BOOK OF ANATOMY. microscope. The study of these elements and the manner in which they are grouped together to form the various tissues of the body forms an important branch of anatomy, which is termed histology. The structure of the human body may be studied in two different ways. The several parts may be considered with reference to their relative positions, either as they are met with in the course of an ordinary dissection, or as they are seen on the surface of a section through the body. This is the topographical method. On the other hand, the several systems of organs may be treated separately and in sequence. This constitutes the systematic method, and it is the plan which is adhered to in this treatise. Descriptive Terms. — Anatomy is a descriptive science founded on observation, and in order that precision and accuracy may be attained it is absolutely necessary that we should be provided with a series of well-defined descriptive terms. It must be clearly understood that all descriptions are framed on the supposition that the body is in the erect position, with the arms by the side, and the hands held so that Fig. 1. — Horizontal Section through the Trunk at the Level of the First Lumbar Vertebra. the palms look forwards and the thumbs outwards. An imaginary plane of section, passing longitudinally through the body so as to divide it accurately into a right and left half, is called the medial plane. Fig. 1 (M.P.). When the right and left halves of the body are studied it will be found that both are to a large extent formed of similar parts. The right and left limbs are alike ; the right and left halves of the brain are the same ; there are a right and left kidney and a right and left lung, and so on. So far tlie organs are said to be symmetrically arranged. But still a large amount of asymmetry may be observed. Thus the chief bulk of the liver lies to the right side of the medial plane, and the spleen is an organ which belongs wholly to the left half of the body. Indeed, it is well to state that perfect symmetry never does exist. There always will be, and always must be, a certain want of balance between symmetrically placed parts of the body. Thus the right upper limb is, as a rule, constructed upon a heavier and more massive plan than the left, and even in those organs where the symmetry appears most perfect, as for instance the brain and spinal cord, it only requires a closer study to reveal many points of difference between the right and left halves. The line on the front of the body along which the medial plane reaches the surface is INTEODUCTION. 5 termed the anterior median line ; whilst the corresponding line behind is called the posterior median line. It is convenient to employ other terms to indicate other imaginary planes of section through the body. The term sagittal is, therefore, used to denote any plane which cuts through the body along a path which is parallel to the medial plane (S S') ; and the term coronal or frontal is given to any vertical plane which passes through the body in a path which cuts the medial plane at right angles (C C). The term horizontal as applied to a plane of section requires no explanation. Any structure which lies nearer to the medial plane than another is said to be medial or internal to it ; and any structure placed further from the medial plane than another is said to lie lateral or external to it. Thus in Fig. 1, A is lateral to B ; whilst B is medial to A. The terms anterior and ventral are synonymous, and are used to indicate a structure (D) which lies nearer to the front or ventral surface of the body than another structure (E) which is placed nearer to the back or dorsal surface of the body, and which is thus said to be posterior or dorsal. In some respects it would be well to discard the terms " anterior " and " posterior " in favour of " ventral " and " dorsal," seeing that the former are only applicable to man in the erect attitude, and cannot be applied to an animal in the prone or quadrupedal position. They have, however, become so deeply ingrained into the descriptive language of the human anatomist that it would hardly be advisable at the present moment to adopt this course throughout. A similar objection may be raised to the terms superior and inferior, which are employed to indicate the relative levels at which two structures lie with reference to the upper and lower ends of the body. The equivalent terms of cephalic and preaxial are, therefore, frequently used in place of " superior," and caudal and postaxial in place of " inferior." The terms proximal and distal should only be applied in the description of the limbs. They denote relative nearness to or distance from the trunk. Thus the hand is distal to the fore-arm, whilst the upper arm or brachium is proximal to the fore-arm. GENERAL EMBRYOLOGY. By Alfeed H. Young and Arthur Kobinson. Although Llie tissues and organs of the body when fully formed differ greatly not only in respect of their functional characteristics, but also with regard to their structural features, they are developed from cell elements so similar in appear- ance at first that they cannot be distinguished from one another. They are all the offspring of parent cells — the female cell or ovum, and the male cell or spermatozoon. Developmental processes apparently take place in the female cell alone, but they cannot occur unless tlie essential elements of a sperm or male cell previously unite with it. Like all animal cells, the ovum is a mass of protoplasm (cytoplasm) containing a nucleus. In many cells the cytoplasm or cell body is itself enclosed by an ex- ternal investing membrane, the cell wall, and such a membrane is present in the ovum. Speaking generally, animal cells are minute structures, those of the human body rarely attaining a diameter of more than about '083 mm., but they vary somewhat in size, they assume different forms, and they acquire characteristic peculiarities associated with their positions and functions ; thus, whilst the majority of the constituent cells of an individual form the various tissues and organs of the body, others are reproductive or germinal cells. Ova are simply specialised cells modified and adapted for the purpose of repro- duction and the continuance of the species. They are enclosed, and partially or entirely matured, in the ovaries, or female generative glands, in the cell-lined spaces known as Graafian follicles. When an ovum has reached a certain stage of development it is discharged from the ovary, and passing along the oviduct or Fallopian tube it eventually reaches the cavity of the uterus. Though mature and capable of being fertilised it may not be impregnated, in which case it does not remain in the uterus, but is cast out from .that organ. If, however, it becomes fertilised, l»y union with the male germinal element, it is retained in the uterus, and develops into an embryo which possesses all the characteristic features of the species to which it belongs and most of the special peculiarities of its parents. When the embryo, or the foetus as it is termed after it has assumed definite form, is capable of independent existence, its intrauterine life terminates, and it is separated from the rest of the ovum and is born. The development of the individual, however, is not complete, nor does it become complete until the new being reaches the adult condition. The term embryology is sometimes used to include the consideration of all the developmental changes and processes which take place in the ovum from the begin- ning up to the final adult stage. It is more convenient, however, to restrict its application to the study of those changes which take place during the development and growth of the organism before the fcetus is separated from the rest of the ovum, or, in other words, during its intrauterine existence. Briefly epitomised, the sequence of changes is as follows : — Impregnation of the mature ovum is followed by segmentation or cleavage. By a series of successive divisions the egg-cell is divided into two, four, eight, and ultimately into a large 7 8 GENEEAL EMBEYOLOGY. number of cells, and so is transformed into a multicellular mass, the morula. The majority of the " segmentation masses " or cells, or blastomeres, as they are termed, are differentiated into tissue elements, but a certain number retain the characters of the original germ-cells and become ova or sperm-cells, which form the " points of departure " of succeeding generations. Every germ-cell is derived, therefore, " by a continuous and unbroken series of cell-divisions " which have extended through the past from the most primitive ancestor, and it forms a point from which, under ordinary circumstances, all future generations will commence. It is in this sense that the changes through which a living being passes in the course of its life "may, in their completest form, be considered as constituting a morpho- logical cycle, beginning with the ovum and ending with the ovum again." To follow these changes it is necessary that the characters and capabilities of the constructive elements should be clearly understood. The animal cell, which plays an all-important part in the life-history of the individual, and the modified germ-cells must be carefully studied, and as far as possible the exact nature of their constituent parts ascertained. The phenomena of impregnation and segmentation, and the subsequent develop- mental processes and morphological changes which result in the formation of the embryo, and, finally, the arrangements for the nutrition and protection of the ovum during its intrauterine existence, will then be considered. THE ANIMAL CELL. Nucleolus Nucleus Nuclear ^ membrane Spongioplasm (cyto-reticulum) Hyaloplasm Attraction sphere Ceutrosome Cells are the structural units of the body. Each cell has an individual life- history within the tissue or organ to which it belongs, it is produced by a pre- existing cell, it develops and grows, is modified by circumstances, reproduces other cells similar to itself, or it dies. A cell possesses a body and a nucleus. An external investing membrane or cell waU may or may not be differentiated. The cell body consists of proto- plasm — an unstable, highly complex organic substance, the constitution of which is approximately repre- sented by the formula C^QH^QQK^gO^Q. It is colourless, semi-fluid, viscous, insoluble in water, capable of osmosis, and it is contractile and irritable. In the living condition it always contains a certain amount of water and various inorganic matters. It is to be observed, how- ever, that there are many varieties of protoplasm, differing somewhat in nature and qualities. The protoplasm of the cell body is called cytoplasm. Under low powers of the microscope it is homogeneous or slightly granular, but with higher magnification, and especially after the application of staining agents, it is possible to distinguish — (1) A highly refractile, elastic, and extensile network — the cyto-reticulum or spongioplasm — the meshes of which are filled with (2) A clear, semi-fluid substance — the cytolymph or hyaloplasm. The fibres of the reticulum present some few minute rounded bodies of doubtful nature, which are termed microsomes. The nucleus is a spherical vesicle embedded in the cell body. It is surrounded by a distinct nuclear membrane, and usually contains nucleoli. It consists of modified protoplasm, which is termed karyoplasm, the precise rela- tion of which to the cytoplasm is not clear. Structurally it resembles cytoplasm in that it presents a fine reticulum, the fibres of which seem to be continuous with the cyto-reticulum through the nuclear membrane, whilst its meshes are occupied by nuclear juice. Fig. 2.— Diagram of an Animal Cell. THE ANIMAL CELL. 9 The reticulum forms a line network composed of linin fibres (achromatic substance). There is also a coarser network, more readily stainable, consisting of chromatin, granular portions of which may also be embedded in the linin. Instead of forming a coarse network the chromatin may be arranged in the form of a con- voluted cord, or as a number of separate filaments, and in certain cases it constitutes a series of loops from which secondary branches are projected, the apices of the loops being grouped together at one pole of the nucleus round a clear area known as the " polar field." The nuclear membrane consists of both chromatin and linin. Nucleoli are of two kinds, true and false. A true nucleolus is a small, refractile particle, of spherical outline, embedded in the reticulum. It stains deeply, and is said to consist of a special modification of the karyoplasm which is called pyrenin. False nucleoli are simply the nodes of the chromatin reticulum. The nucleus is capable of motion ; it has been seen to alter its shape in the living cell, and it undoubtedly plays an active part in the process of cell reproduction. In addition to the nucleus many cells contain one or more small rounded bodies called centrosomes. The centrosomes are modified portions of the protoplasm, and they lie, as a rule, in a modified, clear-looking area of the cytoplasm, which is known as the attraction sphere. This is generally situated close to the nucleus, and from its surface a number of fine radiating lines project into the adjacent cytoplasm. Centrosomes become very evident when reproduction commences, but are not so distinct at other times. The attraction sphere also becomes more evident when cell-division commences, and the radii which project from it, as well as the contained centrosome, appear to play important parts in the reproductive process. Reproduction of Cells. — Cell division or reproduction may take place either — 1. By direct division — amitosis ; 2. By indirect division— mitosis or karyokinesis. In the amitotic or direct form of division the nucleus, and then the cell body, are equatorially constricted, the constrictions deepen until both are completely divided, and so two daughter cells are produced. Apparently the attraction sphere Fig. 3. — Cell Division. Huccessive stages of mitosis or karyokinesis (diagrammatic, modified from Heuneguy). A, B, C, D, and E illustrate the phenomena of the prophase ; F those of the metaphase ; G and H those of the anajihase ; J, K, and L those of the telophase. and centrosome play some part in this process, but whether their influence is initiative or directive is unknown. Mitosis, the process of indirect division, is by far the most common mode of 10 GENERAL EMBRYOLOGY. cell-division. It is a complex process, and the phenomena observable during its progress are classified into four groups : (1) the j^Tophase, (2) the metaphase, (3) the anaphase, and (4) the telophase. The phenomena of the prophase commence with the division of the centrosome and attraction sphere into two parts which travel to opposite poles of the nucleus. At the same time the reticulum of the nucleus disappears, and in its place a con- voluted cord of chromatin, the skein or spirem, is formed (Fig. 3, A, B, and C) ; this is afterwards broken up into a number of segments which may be mere rods, but which more frequently have the form of V-shaped loops (Fig. 3, D). The nucleoli disappear, and some of the filaments which radiate from the newly-formed attraction spheres seem to penetrate the nuclear membrane at the poles of the nucleus. The nuclear membrane subsequently disappears, and the filaments passing from the attraction spheres into the nucleus form two cones, the bases of which meet at the equator of the nucleus, where they fuse together, forming an achromatic spindle which extends between the two attraction spheres (Fig. 3, E). The loops, or rods, of chromatin are gradually grouped at the equator of the spindle, each rod, or chromosome, being apparently connected with one of the achromatic fibrils ; and the prophase is completed. In the metaphase each chromosome is split longitudinally into two halves — daughter chromosomes — which separate from one another ; the separation com- mences at the apex of each V-shaped chromosome, which appears to be attached to an achromatic fibril (Fig. 3, F). In the anapihase the daughter chromosomes pass to the opposite poles of the spindle. It is suggested that this movement is brought about by the contraction of the spindle fibrils, but this is doubtful, though it is noteworthy that in some cases fine achromatic fibrils connecting the separated daughter chromosomes are present (Fig. 3, G and H). Slightly before, or simultaneously with, the completion of the anaphase the cell body is equatorial ly constricted. During the telophase the constriction deepens and the cell is divided into two daughter cells. Whilst this division is taking place the daughter chromosomes, which are grouped in the neighbourhood of each attraction sphere at opposite ends of the spindle, unite into a convoluted cord, round which a nuclear membrane is formed, whilst the cord is converted into a reticulum, and nucleoli appear (Fig. 3, J, K, L). Therefore when the separation of the daughter cells is completed, at the end of the telophase, each possesses all the characteristic features of the mother cell. Reproductive Cells. — The germinal elements, the union of which is essential to the formation of a new being, are the ovum or female element, and the sperma- tozoon or male element. THE OVUM. Structurally an ovum presents all the characteristic features of a typical cell. It is peculiar because of the large size of the nucleus and nucleolus and in the possession of two investing membranes, an inner one, tlie vitelline membrane, which corresponds to tlie cell wall, and an outer one, the oolemma or zona pellucida. Moreover, the nucleus always occupies an excentric position in the cytoplasm, and the cell body contains nutritive material in the form of yolk granules. The constituent parts of an ovum have received distinctive names, however ; thus the cell body is known as the yolk or vitellus, the nucleus is termed the germinal vesicle, and the true nucleolus is called the germinal spot. Vitellus or Yolk. — The body of the ovum, consisting as in an ordinary cell of cytoplasm resolvable into reticulum and cytolymph, contains also numerous granules of small but varying size called yolk granules. These are highly retractile, fatty, and albuminoid bodies containing phosphorus and mineral salts ; collectively they constitute the deutoplasm or nutritive yolk, in contradistinction to the cytoplasm or formative yolk. Xutritive or food yolk plays an important part in development. In some animals it is the only means of support for the embryo in the early stages of development ; in most mammals, on the other hand, the embryo is supplied almost from the first with food not from the egg itself, but directly from the mother THE OVUM. 11 through the placenta. The amount of deutoplasm present in the ova of different animals therefore varies greatly. Ova in which there is no deutoplasm are spoken of as alecithal. Such ova, if they exist, are very rare ; most of those usually classed under this head undoubtedly contain a certain amount of deutoplasm granules scattered throughout the cyto- plasm, and are better described by the . term oligolecithal. The size of an ovum is determined by the amount of food yolk present, and all oligolecithal ova are small; the human ovum, which may be taken as a type of the class, is about '2 mm., or T^^tli of an inch in diameter. As the deutoplasm is increased m amount the ovum is^ increased in size. The deutoplasm also tends to accumulate in certain situations ; if the accumulation is at one extremity of the cell the ovum is described as telolecithal ; such ova are naturally divisible into two areas or poles, a cytoplasmic or formative pole, and a deutoplasmic or nutritive pole. In eutelolecithal ova the deutoplasm almost entirely displaces the cytoplasm from one pole, as in the egg of the fowl, in which the cytoplasm is represented b}' a disc spread over one pole of a large deutoplasmic mass. In many of the arthropoda the deutoplasm accumulates at the centre of the ovum, which is there- fore termed centrolecithal. The germinal vesicle or nucleus of the human ovum is about "05 mm. or ; diameter of the whole ovum. It lies excentrically in the yolk, and has the usual characters of a cell nucleus, i.e. it possesses a nuclear membrane within which is the karyoplasm, divisible into reticulum or nucleoplasm, and nuclear juice. The nucleoplasm consists of chromatin and achromatic filjres (linin), and the nuclear juice contains one or more spherical and highly refractile true nucleoli or geruunal spots ; the nodes of the reticulum constitute false nucleoli. In addition to the nucleus, the vitelhis, at certain periods, also contains a structure known as the vitelline body, body of Balbiani, or accessory nucleus. It is readily seen in young ova lying near the nucleus. It contains one or more centrosomes, and probably represents an attraction sphere. Vitelline Membrane. — The viteUine membrane is simply the peripheral portion of the vitellus, modified and transformed into a fine structureless envelope which covers the outer surface of the yolk. It is usually closely appUed to the inner aspect of the outer membrane, the zona pellucida, and is best seen in the dead ovum and after treatment by reagents. It is therefore thought by some to be merely a condensation of the outer part of the vitellus produced by the action of the reacrents. There is evidence, however, to show that it is present in the normal living ovum. Zona Pellucida or Oolemma.— This membrane is thick, tough, and refractile. It serves as a protective covering for the ovum, and persists for a considerable time after fertilisation, only disappearing when the ovum becomes attached to the uterus. It is perforated by numerous fine canals, which give to the broad clear membrane a finely striated appearance, from which circumstance it has been called the " zona striata." The zona pellucida is not formed by the ovum, but is secreted by the cells of the Graafian follicle in which the ovum lies ; it is consequently regarded as a secondary membrane, and is altogether different from the vitelline Pn;. 4. — The Ovum and its Cuverings ( Diagrammatic). The corona radiata, which completely surroimds the ovum, is only represented in the lower part of the figure. 5. Vitellus or Yolk, (i. (ierniinal vesicle (nucleus). GenniuHl spot (nucleolus). 1. Corona radiata 2. Granular layer 3. Vitelline menil)ran 4. Zona pcUuciila ((joleiiiina). S. Nuclear membrane. L^th of an inch in diameter, i.e. \ the 12 GENEKAL EMBEYOLOGY. membrane. The perforations in the zona serve for the passage of nutritive material to the ovum. When the ovum leaves the Graafian follicle it is surrounded by several layers of cells, the innermost of which are columnar. They are derived from the cells of the follicle, and collectively constitute the corona radiata ; the cells gradually diminish in size, and ultimately disappear. Their function is unknown, but between them and the zona pellucida there is a layer of granular matter, probably formed by the cells of the corona radiata, which rapidly swells up when the ovum is liberated from the follicle, and forms a gelatinous elastic layer called the albumen ; this increases in thickness as the ovum passes along the oviduct, and persists for some time after it enters the uterine cavity. The function of the albumen has not been definitely ascertained ; it may act merely as a protective covering against undue pressure, possibly it may be nutritive, whilst in the dog it apparently helps to fix the ovum to the wall of the uterus. It has not been found in all mammalian ova, and it has not been seen round the human ovum ; still it may be present, for human ova at the stage when it might be expected to develop have not yet been observed. Special Characters of the Ovum. — The ovum as it lies in the Graafian follicle presents no obvious structural modifications when compared with an ordinary animal cell, but undoubtedly differs greatly in its capabilities and life history. Unlike an ordinary cell, it has no inherent power of division into two equal parts, but before it is capable of fertilisation it twice undergoes unequal division during the period of ripening or maturation ; again, its history is different from that of ordinary tissue cells, though it corresponds closely with that of the male germinal elements or spermatozoa. Maturation of the Ovum. — As it lies in the Graafian follicle before matura- FiG. 5. IJ E !■' -The Matukation of thk Ovum: Extrusion of the "Polar i:ioDiE.s " (Diagrammatic). A, An ovum at the commeucement of the process ; B, After the formation of the .spindle. The chromosomes are gathered at the equator of the spindle. C, One apex of the spindle has projected into a bud on the surface, and half of the divideS^ m^-. Scleratogenous layer" Muscle plate 'Blood-vessel _ „Spinal cord Ectoderm — Coronal Section of a Rat Embryo. Showing the relationship of the extending scleratogenous tissue to the spinal cord and to the muscle plates. notochord, and passing both be- neath the neural tube and up- wards along its lateral walls to its dorsal aspect ; they intermingle above and below with the cells of the corresponding layer of the opposite side, and in front and behind with the cells of the sclerato- genous layers of adjacent somites. In this way the neural tube and the notochord are gradually en- veloped by a continuous sheath of mesodermal tissue, which forms the membranous vertebral column. This is perforated at regular in- tervals by the nerve-roots issuing from the spinal cord and brain, and by the vessels of supply to those structures. From its sub- stance the vertebrae and ligaments, the greater part of the interverte- bral discs, and the investing mem- branes of the brain and cord are afterwards developed. Muscle Plates. — The cells of the muscle plate layer lose their original epithelial-like characters; they elongate antero-posteriorly, become spindle-shaped and striated, and they give rise to the striped muscles of the body. For a long time the fibres developed from each muscle plate remain localised and quite distinct from the fibres developed from neighbouring segments ; the masses they form are called myotomes. After a time, however, the fibres of neighbouring myotomes are more or less intermingled, and in the adult, except in certain situa- tions, the intermyotomic intervals are no longer recognisable. The main portions of the myotomes are converted into the muscle masses situated in the dorsal part of the body wall, that is, into the erectores spinse and their main subdivisions, and the other muscles which occupy the vertebral grooves. In the lower vertebrates the ventral ends of the myotomes descend in the somatojjleure almost to the mid- ventral line, and are transformed into the muscles of the ventro-lateral walls of the body. A similar descent of the ventral ends of the myotomes into the lateral walls of the body has not been proved in the highest vertebrates. In mammals, including man, the ventral ends of the myotomes only descend for a short distance in the somatopleure, and then all trace of their char- acteristic structure is lost. It is presumed, however, that cells budded off from the THE EMBEYO. 31 myotomes descend to a lower level, and that they take part in the formation of the ventro-lateral muscles. In lower vertebrates bud-like projections pass from the myotomes in the thoracic and peMc regions into the limb rudiments, and from these the muscles of the limbs are developed. In the highest vertebrates distinct buds from the myo- tomes have not been observed, but it is said that outgrowths of ceUs pass from the myotomes into the limb buds, where they proliferate and form the limb-muscles. The occurrence of these outgrowths into the limbs, like the descent of the lower ends of the myotomes into the ventral part of the body-wall, has not been jjroved in mammals; possibly it occurs, but if not, the ventral and limb-muscles of mammals must be develijped from the somatopleural mesoderm. Cutaneous Lamellae of the Mesodennic Somites. — The cells which form Hind-btain Auditory ganglion , Rudiment of otic vesicle Paraxial mesoharyngeal niembrane Fk;. 27. — Diagram ok a Developing Ovum, seen in Longitudinal Section. The folding off of the embryo has commenced, and the downward bend of the head fold in front lias invagi- nated the amniotic area. The tail fold i.s partly formed, and the primitive alimentary canal, closed in front by the Imcco-pharyngeal membrane and behind V;y the cloacal membrane, i.s distinguishable ; it communicates freely with the yolk sac by a wide umbilical aperture. C. Ccelom. EN. Entoderm. SoM. Somatic mesoderm. EC. Ectoderm. M. Mesoderm. SpM. Splanchnic mesoderm. anterior and posterior extremities are easily recognisable, and, as the embryo is folded off from the surface of the blastodermic vesicle, a portion of the blastodermic cavity is enclosed within it ; this is the primitive alimentary canal. It is simply an incomplete tubular cavity, situated beneath the notochord, which is bounded in THE PEIMITIVE ALIMENTARY CANAL. o3 otic vesicle front by the head fold, l^ehind bv the tail fold, and laterally by the lateral folds, but is widely open telow and continuous \s"ith the cayity of the yolk-sac. As the head of the embryo grows more rapidly than any other part, the head fold is more marked than the other folds, and with its formation the pericardial area is bent round until it Ijecomes yentral in position, its original upper and lower surfaces being reyersed (Fig. 27}. It is owing to this change of relatiye position that the yentral wall of the alimentary canal is completed in front, and it is obyious that its anterior limit, corresponds to the bucco-pharyngeal area of the blastoderm. The part of the blastodermic cavity enclosed in the head fold con- stitutes the fore-gnt. The tail fold at this period is smaU, but it limits the primitive gut behind. The yentral closing of the posterior end of the primitive alimentary canal to form a Mnd-gut is produced, as in the case of the fore-gut, by tending of the embryonic area. This takes place in the region of the tail fold; but the posterior part of the em- bryonic area retains for a con- siderable time it? original position, and forms a connect- ing stalk, termed the body- stalk, between the embryo and the chorionic area of the blastoderm. Ultimately, how- ever, this terminal section of the eml>ryonic area is re- versed in position, its posterior end being carried forwards till it forms the posterior boundary of the umbihcal orifice, and the yentral wall of the hind-gut is thus completed. The rest of the primitive alimentary canal constitutes the mid -gut. It remains for some time in free communica- tion with the cavity of the yolk-sac, and this communica- tion between the alimentary canal and the yolk-sac at a later stage forms a tubular passage, the vitello - intestinal duct. The entoderm forms the lining epithelium of the ali- mentary canal., but this is invested by the splanchnic layer of the mesoderm, which is separated from the somatopleure or body wall by the coelom or body cavity. As the splanchnic mesoderm passes on each side to its continuity with the somatic mesoderm it forms a fold, by which the gut is suspended from the under surface of the primitive vertebral column ; this fold is the mesentery. "When the diaphragm is formed at a later period it separates the thorax from the abdomen, and divides the ci.'elom into pleural and peritoneal portions. The primitive alimentary canal is almost a straight tube, bhnd at both its extremities, and communicating only with the cavity of the yolk-sac. As yet there is no mouth and no anal passage or aperture. The simple tubular canal is divisible into fore-gut, mid-gut, and hind-gut, parts which are conveniently associated developmentally with definite portions of the fully-formed alimentary canal. o Yolk-sac Cloacal membraue Body stalk Fig. 2S. — Diagram represkxtisc. the Cosditios of the Ali- MEXTART CaXAL IX A HCJIAX EMBRYO ABOUT FlFTEEM DaTS Old (modified from His). The visceral clefts are formed, and the subtlivisions of the fore-gut, together with the rudiments of the bronchi and liver, are distinct. 34 GENEEAL EMBRYOLOGY. Thus the fore-gut is converted into the pharynx, cesophagus, stomach, and the , greater part of the duodenum ; whilst from the mid-gut and the hind-gut the rest of the small intestine (jejunum and ileum), and the whole length of the large intestine (cfecum, colon, and rectum), are formed. There is no sharp limit between the mid-gut and the hind-gut, or between the portions of the intestinal canal which develop from them. Diverticular outgrowths from the entoderm of the primitive alimentary canal form the rudiments of the intestinal glands, including the liver and pancreas ; of the respu'atory apparatus ; and of the thyroid and thymus glands. Details of the formation of these structures are given in the special description of the develop- ment of the system to which each belongs. Fig. 29. — Further Development of the Alimentary Canal, as seen in a Human Embryo ABOUT Five Weeks Old (Diagrammatic). The tongue is well formed, the trachea and ojsophagus are separated, the bronchi have comnieiiced to branch ; the duodenal curve is well formed, and the CEecum has appeared in the loop of the mid-gut. The cloaca is partially separated into genito-urinary and rectal portions. 1. Hind-brain. 2. Mouth. 3. Tongue. 4. Pericardium. 5. Pharynx. 6. Heart. 7. Trachea. 8. (Esophagus. 9. Lung. 10. Liver. 11. Bile duct. 12. Stomach. 13. Pancreas. 14. Small intestine. 15. C'secum. 16. Intestinal loop. 17. Large intestine. 18. Notochord. 19. Vertebra. 20. Spinal cord. 21. Bladder. 22. Wolffian duct. 23. Kidney. 24. Ureter. 25. Rectum. 26. ProetodiEum. 27. Allantoic diverticulum. 28. Vitello-intestiual duct. 29. Fore-brain. 30. Mid-brain. Except with respect to the anterior part of the fore-gut, the changes in shape and position which the originally simple alimentary tube undergoes during its conversion into its final or adult form are described in the account of the development of the digestive organs ; Ijut the development of the pharynx and the structures associated with it, and the formation of the mouth and anus, may be considered now. Development of the Pharynx and Stomatodseum. — The development of the anterior x^art of the fore-gut into the pharynx and the floor of the mouth is so inti- mately associated with the formation of a primitive mouth, the stomatodseum, that the two must to a certain extent be considered simultaneously. The stomatodaeum first ajjpears as a depression between the head and the peri- VISCERAL CLEFTS AND VISCERAL ARCHES. 35 cardial region. It is produced by the downward growth of the fore-part of the head in front and the bulging forward of the pericardium behind, and it is separated* from the anterior end of the fore-gut by the bilaminar bucco-pharyngeal membrane. When the stomatodreum first appears it is not enclosed laterally ; but at a later period side boundaries are formed, and the space is developed into the upper part of the mouth and the nasal cavities. The fore-gut, a relatively wide space, continuous posteriorly with the mid-gut, is at first closed anteriorly by the bucco-pharyngeal membrane, which separates it from the stomatodaeum. About the fifteenth day, in the human embryo, the bucco- pharyngeal membrane disappears, the fore -gut is then thrown into continuity with the stomatodseal space, and the anterior opening of the alimentary canal is formed. As development proceeds the cavity of the fore-gut is gradually compressed dorso-ventrally until its transverse section assumes a triangular outline ; but in the earliest stages there are no indications of the various organs which are ulti- mately developed from its walls. After a short interval, however, two elevations appear in its ventral wall. The anterior of these is a rounded elevation, termed the tuberculum impar. It is situated directly behind the lower ends of two raised bars or arches, called the mandibular arches, which are growing down into the floor of the fore-gut from the anterior parts of its lateral walls. The tuberculum impar is the rudiment of the anterior two-thirds of the tongue, which is thus formed in the floor of the entodermal portion of the alimentary canal. The more posterior elevation, termed the furcula, is a curved ridge, which bounds a mesial longitudinal depression. It is separated from the lateral walls of the fore-gut and from the tuberculum impar by a groove, the sinus arcuatus. The anterior part of the furcula is transformed into the epiglottis and the margins of the upper aperture of the larynx ; the median depression becomes the cavity of the larynx and of the trachea, and from its posterior end hollow outgrowths extend and form the rudiments of the epithelial lining of the bronchi and lungs. Still more posteriorly, behind the region of the furcula, a dilatation of the fore-gvit is formed, which projects forwards and downwards towards the pericardium. This is the first indication of the stomach. Visceral Clefts and Visceral Arches. — In the lateral wall of the anterior part of the fore-gut, on each side, four incomplete and more or less transverse clefts, the visceral clefts, appear. They are due to outward linear pouchings of the entoderm, and corresponding, but less marked, inward depressions of the ectoderm. The anterior cleft is the best marked, and the rest diminish in size from before back- wards. At the bottoms of the clefts the ectoderm and the entoderm are in contact, but the thin membranes thus formed, which intervene between the cavity of the fore-gut and the exterior, are only exceptionally and abnormally perforated in the human subject, though in lower vertebrates they invariably disappear, and the pharyngeal or anterior part of the fore-gut is thrown into continuity, laterally, with the exterior by a number of narrow slits, the gill slits, which are used for respiratory purposes. In man and other mammals, however, the floors of the second, third, and fourth clefts are utilised in the formation of the sides of the neck ; that of the first cleft is transformed into the tympanic membrane, which separates the external auditory meatus from the cavity of the tympanum. In the further consideration of the fate of the visceral clefts, it must be borne in mind that each consists of an inner or entodermal portion and an outer or ecto- dermal portion. The inner part of the first cleft is converted into the tympanum and the Eustachian tube, and the outer part becomes the external auditory meatus. No traces of the outer part of the second cleft are left, but a portion of the inner part can be recognised as a slight depression above the tonsil in the lateral wall of the pharynx and in a recess, the fossa of Rosenmuller, behind the pharyngeal end of the Eustachian tube. Both the outer and inner portions of the third and fourth clefts disappear, but from their inner parts diverticula are given off which form the rudiments of the thymus and the lateral lobes of the thyroid body. The diverticula from which the thymus is developed are derived from the third clefts, whilst each lateral lobe of the thyroid body, in the majority of mammals, is formed by a diverticulum from the fourth cleft, but in some mammals the lateral lobes are 36 GENEKAL EMBEYOLOGY. derived from the median diverticulum, and the outgrowths from the posterior parts of the fourth clefts constitute the post-branchial bodies. The margins of the visceral clefts are thickened Ijy the growth of the mesoderm between the entodermal and ectodermal layers, and they are moulded into a series of five rounded bars, the visceral arches, of which the fifth is not recognisable externally, though it is easily seen internally. The dorsal extremities of the arches terminate at the sides of the head below the level of the neural tube, and in the early stages the ventral ends rest upon the pericardial region. When the neck is formed, it grows forwards from the pericardial region and carries with it the lower ends of the visceral arches, which henceforth terminate in its ventral wall. As the visceral arches are carried forwards the head is strongly curved towards the ventral aspect, and the lower ends of the visceral arches are pushed backwards over each other till the ^ fourth is over- lapped by the third, and the third by the second. The first arch is the mandi- bular, the second the hyoid, the third the thyro- hyoid; the fourth and fifth have no special designa- tions. Each arch is covered — ex- ternally by ecto- derm, internally by entoderm, and its core is formed of mesoderm, in which there is developed a bar of cartilage and a blood - vessel Fig. 30. — Stages in the Formation of the Tongue and Uppek Aperture of the Larynx in the Human Embryo (after His). Embryo 14 days old. II. Embryo 23 days old. III. Embryo 28 to 30 days old. Embryo 2 months old. Cojlom. G. Glottis. Epiglottis. HA. Sinus arcuatus. Furcula. T. Tongue. Foramen crecum. TI. Tuberculum impar. Visceral arches. IV. C. E. F. FC. called a cephalic aortic arch. At first each arch is limited to the side wall of the fore-gut ; but after a time it is prolonged into the ventral wall, encroaching, with the exception of the first, upon the sinus arcuatus. The first, or mandibular arch, is ibrmed between the first visceral cleft and the bucco-pharyngeal membrane. As it develops it forms the lateral and lower boundaries of the stomatodseal space, and it grows downwards till it meets its fellow of the opposite side in the ventral middle line, immediately in front of the tuberculum impar. The greater part of this arch is converted into the lower jaw and the soft tissues which invest it. From its upper part a process grows forwards, the maxillary process, from which the upper lateral part of the face, between the orbit and the mouth, is developed, and in which the superior maxillary, the malar, and the palate bones, and possibly the internal pterygoid plate also, are developed and ossified. From the posterior border of the outer aspect of the mandibular arch the tragus and a portion of the helix of the pinna of the external ear are formed. The carti- laginous bar in its interior is known as Meckel's cartilage. It forms the primitive VENTEAL WALL OF THE FOEE-GUT. 37 skeleton of the arch. Its upper and lower extremities are ossified and remain in the adult, the former as the malleus, and possibly the incus, and the latter as the symphysial part of the lower jaw. Tlie remainder of the cartilaginous bar dis- appears, but the hbrous membrane which surrounds the lower section of the inter- mediate part is ossified and converted into the main part of the lower jaw, whilst that round the upper section of the intermediate portion persists as the spheno- mandibular hgameut. The blood-vessel developed in the mandibular arch is, for the main part, a transitory structure, but its ventral section is converted into the internal maxillary, superficial temporal, facial and lingual arteries. The second and third arches are continued downwards into the floor of the pharyngeal portion of the fore-gut. There, converging, they insinuate themselves between the tuberculum impar and the furcula, across the anterior part of the sinus arcuatus, and uniting together form a transverse bar. This rapidly changes into a semilunar ridge which first embraces, and afterwards fuses with the posterior part of the tuberculum impar, and it forms the posterior third of the tongue. The second arch takes part in the formation of the side and anterior part of the neck. From its anterior border externally a part of the helix, the antihelix, the antitragus, and the lobule of the pinna of the external ear are developed. The lower and upper portions of its cartilaginous bar — the hyoid bar — are ossified : the lower portion forms part of the body and the small cornu of the hyoid bone on its own side, and the upper portion is converted into the intra- and extra- temporal sections of the styloid process (the tympano-hyal and stylo-hyal portions of the styloid process of the temporal bone). The fibrous tissue of the intermediate imrt of the hyoidean bar persists in the adult as the stylo-hyoid ligament. The blood- vessel of the hyoid arch, the second cephalic aortic arch, almost entirely disappears, but from its ventral extremity the ascending pharyngeal, occipital, and posterior auricular arteries are probably developed. The third visceral arch forms part of the neck posterior to the region of the second arch, and, as already pointed out, its lower end takes part in the formation of the posterior part of the tongue. The upper and middle parts of its cartilaginous bar disappear, but the lower part persists, and is converted into the posterior part of the body and the great cornu of the hyoid bone on its own side. Its blood- vessel, the third cephalic aortic arch, becomes the lower part of the stem of the internal carotid artery. The fourth and fifth visceral arches also enter into the formation of the neck, but their exact limits in the adult cannot be defined. Of the upper sections of their cartilaginous bars no trace remains in the adult, but their lower portions are believed to enter into the formation of the thyroid cartilage of the larynx. The blood-vessel of the fourth arch on the right side becomes part of the right sub- clavian artery, that on the left side is converted into the arch of the aorta. The vessels of the fifth arches form portions of the pulmonary arteries, and that on the left side forms also the ductus arteriosus. Further Development of the Ventral Wall of the Fore-gut in the Region of the Furcula. — The sinus arcuatus which surrounds the furcula disappears to a great extent as development proceeds, but certain parts of it remain and are recog- nisable in the adult. The anterior portion immediately in front of the furcula is divided into two parts as the lower ends of the second and third arches of the two sides converge and fuse in the ventral wall of the pharyngeal portion of the fore-gut ; the middle portion of the sinus, in front of the transverse bar formed by this fusion, persists in the adult as the foramen caecum of the tongue, and at a very early period a diverticulum grows backwards from it in the floor of the pharynx, dorsal to the cartilage bars which form the hyoid bone, but ventral to the rudi- ments of the thyroid cartilage. This diverticulum is the thyro-glossal duct. As soon as it reaches the level of the fourth visceral clefts it enlarges, unites with the diverticula from those clefts which form the lateral lobes of the thyroid body, and is itself converted into the isthmus of the thyroid, its pyramidal process and the thyro-glossal duct or the fibrous cord into which that duct becomes converted in the adult. Occasionally the thyro-glossal duct is not wholly transformed into a fibrous cord, but portions of it remain in the form of isolated vesicles, hned with 38 GENERAL EMBEYOLOGY. columnar or cubical epithelium, or as cords of cells, and these occasionally undergo abnormal development, forming tumours at the base of the tongue or in the upper part of the neck. The portion of the sinus arcuatus which lies behind the conjoined lower extremities of the second and third arches of opposite sides, and in front of the farcula, persists in a modified form in the adult, and is recognisable as glosso- epiglottidean pouches or valleculce at the base of the tongue. The furcula and the groove in the ventral wall of the fore-gut, which it embraces antero-laterallj, are both of considerable importance. The anterior part of the furcula is situated in the ventral wall of the pharyngeal portion of the fore-gut, but its backward prolongations and the furrow between them lie in what may be termed the intermediate part of the fore-gut, that is, in that part of the fore-gut which intervenes between the pharyngeal and stomach regions. Gradually the furrow deepens, and its posterior extremity dilates on each side. Afterwards the margins of the furrow coalesce from behind forwards, and in this manner the cavity of the furrow is separated from the fore-gut, its walls are converted into the trachea and the lower part of the larynx, whilst the diverticula which are projected from its posterior end form the rudiments of the bronchi. The fusion of the margin of the furrow ceases a short distance behind its anterior extremity, which latter persists as the superior aperture of the larynx. The anterior part of the furcula, which bounds this aperture in front, becomes the epiglottis, and its lateral extensions, which form the margins of the aperture, are converted into the aryteno- epiglottidean folds in the substance of which the arytenoid cartilages and the cartilages of Santorini and Wrisberg (cuneiform cartilages) are formed. DEVELOPMENT OF THE MOUTH AND THE NOSE. The nose is formed entirely from the stomatodseum. The mouth has a double origin ; the roof and fore-part, including the teeth, are developed from the stomato- dceum, whilst the floor and the tongue are developed from the pharyngeal portion of the fore-gut. It has already been pointed out (p. 34) that the stomatodccal depression lies between the anterior part of the head {i.e. the tissues forming the base of the primary fore-brain) and the pericardial region, and that it is separated posteriorly from the fore-gut by the bucco-pharyngeal membrane. At first it has no distinct lateral boundaries, but subsequently the mandibular arches, which are developed at the sides of the bucco-pharyngeal membrane, project forward beyond the membrane and form lateral limits of the depression. If the stomatodseal space is examined from the front at this period the following boundaries are recognisable : — Above and in front is the projecting anterior part of the head which is termed the fronto-nasal process, laterally are the mandibular arches, and below and posteriorly is the anterior part of the pericardial region. After a short time the lower ends of the mandibular arches meet in front of the pericardial region, and, fusing together, form the posterior or lower margin of the aperture ; simultaneously the lateral boundaries of the space are still further completed by the forward growth of a nodular projection, the maxillary process, from the upper end of each mandibular arch. About the fifteenth day the bucco-pharyngeal membrane disappears, and the stomatodseal space and pharynx are thenceforth continuous. No trace of the bucco-pharyngeal mem- brane is recognisable in the adult, but its position may be represented by an imaginary plane extending from the anterior parb of the basi-sphenoid above to the base of the alveolar process of the lower jaw, on its lingual surface, below. Whilst the boundaries of the stomatodajal space are being defined, two oval depressions, lined with thickened epithelium, appear in its upper boundary on the lower and anterior surfaces of the fronto-nasal process ; these are the olfactory pits or depressions. A portion of the epithelium of their walls is separated off and takes part in the formation of the olfactory bulbs, whilst the remainder is transformed into the olfactory epithelium, from which the olfactory nerve-fibres grow inwards to the olfactory bulbs. As the olfactory pits deepen they grow backwards into the roof of the stomatodseal space, and at the same time they separate the lower portion THE MOUTH AND NOSE. 39 of the fronto-nasal process into three parts, constituting a median and two lateral nasal processes. At each lateral angle of the median nasal process a spheroidal elevation, the globular process, appears. The part of the median nasal process which intervenes between the two globular processes is divided into two areas, an upper triangular and a lower quadrilateral, by the appearance of a transverse ridge, which is afterwards moulded into the tip of the nose. The upper triangular area becomes the dorsum of the nose, and the lower quadrilateral area forms the columella, i.e. the lower and anterior part of the septum between the anterior Mesencephalon Maxillary Eye process Mandibular arch Prosencephalon Olfactory pit Prosencephalon Mesial nasal process Stomatodceum. Fig. 31. I. Side view of the head of human embryo about 27 days old, showiug the olfactory pit and the visceral arches aud clefts (from His). II. Transverse section through the head of an emliryo, showiug the relation of the olfactory pits to the fore- brain and to the roof of the stomatodajal space. III. Head of human embryo about 29 days old, showing the division of the lower part of the mesial frontal process into the two globular processes, the intervention of the olfactory pits between the mesial and lateral nasal processes, and the approximation of the maxillary and lateral nasal processes, which, however, are separated by the oculo-nasal sulcus (from His). IV. Transverse section of head of embryo, showiug the deepening of the olfactory pits and their relation to the hemisphere vesicles of the fore-brain. nasal apertures. The globular processes are utilised in the formation of the philtrum or middle part of the upper lip, and the lateral nasal processes form the alse of the nose or lateral boundaries of the anterior nasal apertures. As the olfactory pits deepen and grow backwards into the roof of the stomatod^eum the maxillary pro- cesses grow forwards from the lateral boundaries of that space, that is from the upper ends of the mandibular arches, and pass beneath the eyes, which now form distinct prominences on the sides of the head. The upper borders of the maxillary processes come into contact with the lateral nasal processes from which they are temporarily separated by grooves, the oculo-nasal sulci. These latter pass from the depressions round the eyeballs, the rudimentary conjunctival sacs, to the margins of the nasal pits. The anterior extremities of the maxillary processes impinge 40 GENEEAL EMBEYOLOGY. upon the globular processes, and ultimately their upper borders and anterior ex- tremities fuse with the lateral nasal and globular processes, completing the lower boundaries of the anterior nasal orifices and the lateral parts of the primitive upper lip. At the same time the oculo-nasal sulci are converted first into solid cords of cells, and afterwards into the lachrymal sacs and the nasal ducts, which henceforth constitute the channels of communication between the conjunctival sacs and the nose. The result of the ingrowth of the maxillary processes and their fusion with the Cerebral liemisi)he!es Olfactory pit Globular proces-- Maxillary process Pituitary depression Aiit. nasal orifice "^ Globular process Maxillary proces'- Lower jaw Olfactory pit Maxillary process Globular process Moutli Cerebral hemisphere Nasal cavity Jacobson's organ Globular process Maxillary process Lower jaw Mouth Fig. 32. I. Portiou of the head and neck of a human embryo 32 days old. The fioor of the month and pharynx and the ventral part of the anterior portion of the body have been removed. By the approximation of the globular and maxillary processes the boundaries of the anterior nares are almost complete, but the olfactory pits still open in the whole of their lengths into the roof of the mouth (from His). II. Transverse section of the head oi an embryo, showing the close apposition of the globular and maxillary processes. III. Head of human embryo about 2 months old, showing the union of the globular processes and their fusion with the maxillary processes. The anterior nasal apertures are now completely defined (from His). IV. Transverse section of the head of an embryo, showing tlie fusion of the maxillary processes with the globular processes, and the separation anteriorly of the nose from the mouth. lateral nasal and globular processes is the division of the large orifice which led into the stomatodccal space into three parts — a large lower, and two smaller upper aper- tures. The lower opening is the aperture of the mouth ; it is bounded below by the united mandibular arches, and above by the fused mesial nasal and maxillary processes. The smaller upper openings are the anterior nares, which on their first Ibrmation are merely foramina of communication between the exterior and the upper part of the stomatod^eal sjjace ; the latter is not yet separated into nasal and oral chambers. Formation of the Palate and the Separation of the Nasal and Buccal Cavities. — This separation is effected by the formation of the palate, which is developed to a slight extent by the backward growth of the globular processes FOKMATION OF THE PALATE. 41 along the roof of the space as a pair of ridges, termed the nasal laminae, which fuse together to form a small anterior portion of the palate, viz. the intermaxillary pro- cess, in which the intermaxillary parts of the superior maxilhe are formed. The remaining and greater part of the palate is formed by two ledge-like ingrowths, one from the inner surface of each maxillary process, which meet and fuse anteriorly with the intermaxillary process, and behind this with each other. In these pro- jections the palatal processes of the superior maxillae and the horizontal plates of the palate bones are formed, and by their fusion the upper part of the stomatodieal space is separated off from the remainder as a common nasal chamber which com- municates in front with the exterior by the anterior narial orifices, and behind with the pharyngeal portion of the fore-gut by the choanal apertures or posterior nares. The lower part of the stomatodteal space and the front part of the fore-gut together form the mouth or buccal cavity ; this opens anteriorly by a transverse aperture, the boundaries of which have already been described, and posteriorly it is in direct continuity w^ith the pharynx. The division of the common nasal chamber into two parts commences before its separation from the mouth is completed, and it is brought about by the development Anterior nasal orifice Etlimo-vomerine plate Xasal cavity Palatal process Pituitary depression Fig, Mediel's cartilage I. Portion of the head of a human embryo about 2^ months old (His). The lips are separated from the gums, and the line of the common dental germ is visible in the latter. The palatal processes are growing inwards from the maxillary processes. II. Transverse section of the head of an embryo after the fusion of the palatal processes of the maxillary pro- cesses with the nasal septum, which grows backwards from the fused globular processes. of a septum which is continuous anteriorly with the fused nasal laminte, and which grows downwards and backwards from the mesial part of the under aspect of the fronto-nasal process. This septum fuses below with the conjoined margins of the palatal ledges of the maxillary processes, and a vertical plate of cartilage soon develops in its interior, which is continuous above with the cartilaginous base of the cranium (basi-cranial axis). A portion of this septal cartilage remains in the adult as the septal cartilage of the nose, and the remainder is more or less completely replaced by the vertical plate of the ethmoid bone and by the vomer. The lateral wall of each nasal chamber is formed, in' the lower part of its extent, by the maxillary process of the mandibular arch, in which the superior maxillary, malar, and palate bones, and possibly the internal pterygoid plate, are developed, and in the upper part by the outer boundary of the original nasal pit, which now forms only the upper part of the nasal cavity. In this upper section of the outer wall an outgrowth of the basi-cranial axis projects downwards, and is developed into the lateral mass of the ethmoid bone ; probably it also takes part in the formation of the inferior turbinal bone. The fusion of the three segments of the palate commences anteriorly at the eighth week by the union of the maxillary and globular processes ; it passes back- wards and is completed by the fusion of the posterior parts of the palatal ledges of the maxillary processes about the tenth week. To the non-completion of this fusion the various cases of hare-Hp and cleft palate are due. Organ of Jacobson. — The organs of Jacobsou are rudimentary structures in man. 4:2 G ENSEAL EMBKYOLOGY. They lie in the lower and anterior part of the nasal septum, one upon each side. They are developed as small diverticula which grow backwards and upwards in the substance of the septum, and their points of commencement are situated immediately above the intermaxillary segment of the palate. Each diverticulum is partially sur- rounded, on its inner side, by a cartilaginous capsule, it ends blindly behind, and it opens anteriorly close to the floor of the nose in the region of Stenson's foramen — a small aperture left between the premaxillary and maxillary sections of the bony palate. TH Pituitary Body. — The pituitary body is formed partly from the floor of the first primary cerebral vesicle, and partly from the roof of the stomatodseal space. The stomatodfeal portion appears as a small pouch, Eathke's pouch, which grows upwards into the base of the head immediately in front of the dorsal margin of the bucco-pharyngeal membrane and the anterior end of the notochord, and behind the fore-brain. It is lined by ectoderm, and soon becomes a conical vesicle which lies beneath the base of the fore-brain. Its orifice of communica- tion with the stomatodseal space is gradu- ally constricted until the lumen dis- appears, and then for a time the vesicle is connected with the surface by a solid cord of ectodermal cells. This also dis- appears, and the vesicle is embedded in the base of the head in a region above and between those parts of the basal axis which afterwards are transformed into the basi- and pre-sphenoid elements of the sphenoid bone. During the period of its formation and separation the ingrowth from the stomatodseum comes into relation pos- teriorly with a small diverticulum from the floor of the fore-brain, which dilates at its lower end to form the posterior or cerebral lobe of the pituitary body, whilst its upper part remains as the Showing the formation of the two parts of the pituitary jnfundibulum, the Connecting stalk be- body (diagrammatic). '=' Fig. 34. -Vertical Section through Head of Rat Embryo. (Ectoderm is represented in black, entoderm in blue, and mesoderm in red.) At. Ax B. Atlas. Axis. Cartilaginous basi- cranial axis. Heart. HB. Hind-brain. .MB. Mid-brain. Part of nasal cavity. H N. P. Pineal body. PR. Cerebral hemisphere. body. SG. Spinal ganglion. T. Tongue. Th. Tlialameiicci^halon. tween the pituitary body and the floor of the third ventricle of the brain. The anterior or stomatodeeal lobe of the pituitary body is much larger than the Pfi. Cerebral part of pituit- posterior lobe, which it surrounds and Pt2. Buccli'part'of pituitary conceals both in front and at the sides. It is evident that in the early stages the pituitary body consists of two ecto- dermal vesicles, the cavity of the pos- terior vesicle is continuous with the cerebral tube, and that of the anterior vesicle with the cavity of the primitive mouth. The cavity of the posterior vesicle is generally obliterated, and though nervous structures are for a time developed in its walls they entirely disappear in man and are replaced by vascular connective tissue. Occasionally a small part of tlie cavity remains as a minute vesicle lined with columnar ciliated epithelium. The cavity of the anterior vesicle persists, it sends out numerous diverticula, and is gradually converted into a number of tubular spaces, lined with cubical or columnar cells, united together by vascular connective tissue which has grown amidst the tubules from the surrounding mesoderm. THE EXTERNAL EAR AND EUSTACHIAN TUBE. 43 THE EXTERNAL EAR, THE TYMPANIC CAVITY, AND THE EUSTACHIAN TUBE. The external ear, the tympanic cavity, and the Eustachian tube are all developed from the first visceral cleft and its boundaries. The cleft lies between the mandibular (first) and the hyoid (second) visceral arch in the side wall of the pharyngeal portion of the fore-gut, and, before a neck is developed, it extends from just ventral to the otic vesicle, which lies at the side of the hind-brain, above, to the pericardial region below. The membrane which lies at the bottom of the cleft consists in the early stages of ectoderm and entoderm, but in a short time a thin layer of mesoderm grows between the two primary layers, and the trilaminar septum is ultimately converted into hb the tympanic membrane which separates the external from the middle ear. The differentiation of the outer part of the cleft is initi- ated by the appearance of six tubercles round its margins, which are afterwards trans- formed into the several parts of the pinna. Two tubercles are formed anteriorly on the mandibular arch, one at the dorsal end of the cleft and three posteriorly on the hyoid arch. The two tubercles on the mandibular arch are a small lower, the tuberculum tragicum, and a larger upper, the tuberculum anterius helicis. The tubercle at the upper end of the cleft is the tuberculum intermedium helicis. The upper tubercle on the hyoid arch is the tuber- culum anthelicis, the middle is the tuberculum antitragicum, and the lowest is the tuber- culum lobulare. Shortly after the appearance of the tubercles a process, the caudal process, grows backwards and downwards, from the posterior part of the tuberculum intermedium helicis, behind the tuberculum anthelicis and the tuberculum anti- tragicum to the tuberculum lobulare, with which it fuses. The tuberculum tragicum remains more or less distinct, and it forms the prominence called the tragus which lies in front of the concha and external auditory meatus. The two tubercles of the helix and the caudal process unite to form the helix or marginal portion of the pinna ; this terminates below in the lobule which is developed from the tuberculum lobulare. The tuberculum anthelicis and the tuberculum antitragicum are the rudiments respectively of the antihelix and the antitragus, and the latter unites below the lower part of the cleft with the rudiment of the tragus, forming the lower boundary of the outer part of the external meatus. It should be noted that in the early stages the tuberculum anterius helicis lies in front of the outer part of the first visceral cleft, but it does not retain this position in the later stages during which the cleft is relatively reduced in size, and when development is completed and the outer part of the cleft is transformed into the external auditory meatus the commencement of the helix, which is developed from the tuberculum anterius helicis, is situated just above the outer extremity of the external meatus. Fig. 35. -Transverse Section throdgh the Head OF A Rat Embryo. Showing the rudiments of the three parts of the ear and their relation to the hyo-mandibular cleft. BV. Blood-vessels. C. Cochlea. EM. Ext. auditory meatus. ET. Eustachian tube. HB. Hind-brain. HM. Hyo-mandibular cleft. N. Notochord. OV. Otic vesicle. P. Pharynx. RL. Recessus labyrinthii. SC. Semicircular canal. T. Tympanum. 44 GENEKAL EMBEYOLOaY. The outer part of the cleft is moulded into the external auditory passage. It remains relatively shallow and devoid of bony boundaries till after birth, but in the subcutaneous tissue round the lower margin of the tympanic membrane an incomplete ring of bone is formed during the third month, and at an earlier period, above the upper part of that membrane, the rudiment of the squamous loart of the temporal bone appears. To the outer side of the tympanic ring in the subcutaneous tissue of the pinna and the outer part of the external auditory passage three pieces of cartilage appear, and they afterwards join to form the cartilage of the pinna and the external auditory meatus. After birth the external meatus is deepened by the outgrowth of the tympanic ring below and of the squamous part of the temporal bone above, together with a coincident in- crease of the outer part of the canal. The tympanic cavity and the Eustachian tube are both formed from the inner part of the first visceral cleft, and consequently they are both lined by entoderm. The tympanic cavity is developed from the dorsal or upper end of this portion of the cleft, and it is prolonged upwards on the outer side of the otic vesicle which simultaneously descends in the tissuesof the head. Thus the upper end of the inner portion of the cleft, which is somewhat dilated, comes to lie between the otic vesicle, which is developed into the internal ear on the inner side, and the tympanic membrane which separates it from the external auditory meatus on the outer side, and it remains in the adult as a laterally compressed space, the tympanic cavity, which is continuous through the Eustachian tube with the upper part of the pharynx. In the mesoderm round the inner, upper, and back part of the cavity the petrous part of the temporal bone is developed and ossified, and in the lower and anterior part the tympanic ossification extends outwards during the formation of the tympanic plate. The upper part of the tympanic space is prolonged backwards between the ossifying petrous and squamous parts of the temporal bone, where it forms a recess known in the adult as the mastoid antrum, from which at a later period diverticula are projected into the mastoid portion of the temporal bone, forming the mastoid air cells. The lower portion of the inner part of the cleft is moved obliquely forwards. As development proceeds it is contracted and carried downwards and forwards in front of the developing otic vesicle. It is the rudiment of the Eustachian tube, and, as the septum which separates the nasal chambers from the mouth is formed. Fig. 36.- HM -FiGUUKS, MODIFIED FROM HiS, ILLUSTRATING THE FORMATION OF THE Pinna. 1. Tuberculuiu tragicum = Tragus. 2. ,, anterius helicis \ 3. ,, intermedium helicis p 4. Cauda helicis j 5. Tuberculum anthelicis = Antihelix. 6. Tuberculum antitragicum = Anti- tragus. 7. Tuberculum lobulare = Lobule. HM. Hj'o-mandibular cleft. OV. Otic vesicle. THE HIND-aUT AND ANAL PASSAGE. 45 itsilower end attains a position just behind and at the side of the posterior narial orifice in the upper and lateral part of the pharynx. Apparently, therefore, the lower end of the Eustachian tube has a much higher position than that originally occupied by the lower end of the cleft from which it is formed, for it will be rememljered that the lower end of the first visceral cleft is situated, in the early stages, at the side of the tuberculum impar from which the anterior two-thirds of the tongue is formed. This alteration in relative position is due, however, not to elevation of the lower end of the first visceral cleft during its transformation into the Eustachian passage, l3ut to the enormous downgrowth of the mandibular arches, which carry with them the tongue, as they enlarge to form the lower jaw. THE HIND-GUT, THE ANAL PASSAGE, AND THE POST-ANAL OE TAIL-GUT. By the formation of the mouth the primitive alimentary canal opens anteriorly ; it remains closed posteriorly until a later date, when the anal passage and orifice are developed. The posterior end of the hind-gut which is enclosed in the tail-fold is termed the cloaca. The cloaca is dilated, and, assuming a conical form, receives the terminations of the genito-urinary ducts. It is bounded postero-inferiorly by the cloacal membrane which extends from the root of the tail to the body stalk by which the embryo is attached to the chorion. The cloacal membrane is modified from the posterior part of the primitive streak ; this remains on the surface of the body after the anterior part has been separated and enclosed during the completion of the posterior part of the neural canal, and it forms a septum between the cavity of the cloaca and the exterior. It consists at first of ectoderm and entoderm alone, and it is only at its lower and anterior part that it is subsequently invaded to a slight extent by mesoderm. During the second month of intrauterine Life the cloaca is divided into a ventral or genito-urinary, and a dorsal or rectal section, by the formation and fusion of lateral folds, which gradually unite, from before backwards, till finally the posterior end of the septum approaches and fuses with the cloacal membrane, and the rectum is separated from the genito-urinary chaml^er. Before this separation is completed an eminence appears in the region of the anterior part of the cloacal membrane at the junction of the ventral surface with the posterior extremity of the body, i.e. in that part which afterwards becomes the region of the symphysis pubis. This eminence is the genital eminence, and from it are formed the penis in the male and the clitoris in the female. The genital eminence is surrounded by an oval fold of skin, genital fold, which extends from the front of the eminence to the root of the tail and encloses a shallow fossa, the cloacal fossa, at the bottom of which is the cloacal membrane. The posterior part of the cloacal fossa is afterwards separated from the anterior part by a transverse fold, the perineal fold, which crosses the external surface of the cloacal membrane in a position which corresponds internally J with that occupied by the lower end of the septum separating the genito-urinary from the rectal portions of the cloacal. The posterior part of the cloacal fossa, ]jehind the transverse fold, is the proctodeeal depression or proctodaeum ; at first its long axis lies transversely, afterwards it assumes a triangular and then a circular form, the sphincter ani muscle develops in its walls, and it is transformed into the greater part, if not the whole, of the anal canal of the adult. It is separated from the rectum by the posterior part of the cloacal membrane, but when that disappears, at a date which has not yet been definitely ascertained, but probably about the third month, the anal passage forms the canal by which the rectum communicates with the exterior of the body. The orifices of the alimentary canal are thus completed. The Post-anal or Tail-Gut. — When the hind-gut is first enclosed there is no tail, but a rudimentary tail is subsequently developed as an outgrowth from the dorsal end of the tail-fold, i.e. from the posterior extremity of the body of the embryo. As the tail is formed, a narrow tube, which communicates in front with the hind-gut, is developed within it. This is called the post-anal or tail-gut. As a rule it only exists for a short 46 GENEEAL EMBRYOLOGY. time, disappearing from before backwards about the period when cartilage begins to be formed in the body and limbs, and before the cloaca is divided into its rectal and genito- urinary portions. In the few cases in which it persists it retains its continuity with the rectum, which is formed from the dorsal part of the cloaca. The tail-gut appears in the human subject when the embryo is 3 mm. long, and the rudimentary tail is just visible as a small nodule. When the embryo attains the length of 4-8 mm. the anterior part of the tail-gut begins to degenerate, its cavity disappears, and it is converted into a solid cord of cells which is still attached in front to the hind-gut. In embryos 11-5 mm. long, when the tail has been enclosed in the posterior part of the body, the connexion of the tail- gut with the hind -gut is lost, and the tail -gut is represented by a small vesicle with a short cord of degenerating cells attached to its anterior part. In larger embryos the tail-gut entirely disappears. When, as in the human subject, the rudimentary tail is eventually embedded in the posterior end of the body, any rudiments of the tail -gut which persist will be found in this situation ; it is stated that such rudi- ments occasionally develop into tumour formations. In mammals with free tails, rudiments of the tail-gut may be met with in any part of the tail, and apparently the anterior portion occasionally persists and maintains its connexion with the rectum, from which it extends backwards as a narrow and blind diverticulum. THE LIMBS. Though the body of the embryo begins to assume definite form as soon as it is folded and nipped off from the rest of the ovum, it does not present any distinguishable human characteristics until the anterior and posterior limbs are formed. There are no traces of these before the third week of in- trauterine life when two longitudinal ridges, the _. Wolffian ridges, are developed, one on each lateral tioii'of the cioacai part "of tiie hind- surfacc of the body, just external to the outer gut into genito- urinary tract and margins of the mesodcrmic somitcs, and opposite the line of the intermediate cell mass. The rudi- ments of the fore- and hind -limbs are discernible, vs.' vtsicuin"mi- almost from the first, as slight prominences of the WT. w"^]!"- , . Wolffian ridg-es, and in the fourth week they project WD. Wolffian cluct. -, -, ^ t • t t • i i • as bud-like outgrowths m the thoracic and pelvic regions respectively. The development of the fore-limb or arm is throughout slightly in advance of that of the hind-limb or leg. At the fourth week each limb-bud is a flattened semilunar projection, as long as it is broad, with a dorsal and a ventral surface and an anterior or preaxial, and a posterior or postaxial border. As growth proceeds the elongating limb-buds are bent ventrally, and in the fifth week two transverse furrows, on the ventral aspect of each, indicate the positions of the joints and the division of each limb into three segments — distal, middle, and proximal — representing the hand, fore-arm, and arm in the upper limb, and the foot, leg, and thigh in the lower limb. The terminal or distal segments are broad, flat x^lates with rounded margins, but each is soon divided into a some- what enlarged basal part, and a thinner and more flattened marginal part. It is where these two parts are continuous that the rudiments of the digits appear. They become distinguishable about the end of the fifth week as small lobes which gradually extend outwards. In the fore-limb the fingers project beyond the margin of the hand-segments in the sixth week, but the toes do not reach the margins of CM Fig. 37. — Diagrams showing the separa- rectum. A. Allantoic stalk. B. Bladder. C. Cloaca. CM. Cloacal membrane K. Kidney. R. Rectum. U. Ur. Ureter. Uretlira. THE LIMBS. 47 the foot till the early part of the seventh week. The nails appear at the third month, and reach the ends of the digits at the sixth month. In the primary position of the limljs the elbow and the knee appear alike to be directed outwards, but this is soon altered. At the end of the sixth week each limb undergoes a partial rotation, the direction of which is different in the fore- and hind-limbs respectively. In the former the elbow is turned backwards, the ventral surface therefore becomes anterior, and the preaxial (thumb) margin is directed outwards ; in the hind-hmb the knee is turned forwards, and the ventral surface of the limb becomes posterior, whilst the preaxial (great toe) margin is directed inwards ; thus in the adult the anterior surface and outer border of the upper extremity correspond with the posterior surface and inner border of the lower extremity, whilst obviously the posterior surface and inner border of the former are homologous with the anterior surface and outer border of the latter. Each limb-bud may be regarded as an extension from a definite number of the segments of the body ; it contains a core of mesoderm, and the anterior or ventral primary divisions of the corresponding spinal nerve segments are apparently prolonged into it. The central part of the mesoderm, except in the regions of the joints where cavities appear, is condensed and then converted first into cartilage, and afterwards into bone. The proximal part of the bony skeleton of each liml), the limb girdle, is not, however, developed in the limb-bud, but in the body-wall at its base. The more superficially situated mesoderm is transformed into muscles and subcutaneous tissues, the extensor muscles appearing on the dorsal and the flexor muscles on the ventral aspect. As the nerve trunks pass into the free portion of the limb they bifurcate, the branches passing respectively to the dorsal or extensor aspect of the limb, and to the ventral or flexor aspect. Apparently in mammals the whole of the mesodermal core of each limb-bud is formed from the somatic mesoderm of the lateral plates. If this is the case the muscles of the limbs differ in origin from those of the back, for the latter are developed from the muscle plates of the protovertebral somites. In lower verte- brates (cartilaginous fishes) buds are given off to the limbs from the muscle plates and cutaneous lamellee in the thoracic and pelvic regions, and as the muscle plates pass downwards in the somatopleure towards the ventral aspect of the body, these buds grow outwards into the limb-rudiments and develop into the muscles of the limbs. Presumably this is the more primitive arrangement, and that met with in man and other mammals is secondary, and it is stated that although no distinct buds from the muscle plates pass into the limbs of mammals, nevertheless the limb-muscles are formed by cells, proliferated from the muscle plates, which have migrated into the somatopleural mesoderm of the limbs. THE NUTKITION AND PROTECTION OF THE EMBRYO DURING ITS INTRAUTERINE EXISTENCE. The impregnated ovum during its passage down the Fallopian tube, and for a brief period also after it enters the uterus, lives either on the yolk granules (deuto- plasm) embedded in its own cytoplasm, or upon material absorbed from the fluids by which it is surrounded. The human ovum is very small, and consequently it is almost from the first dependent for its nutrition upon sources of supply outside itself. The urgent necessity for adequate arrangements whereby this may be effected leads to that early establishment of an intimate vascular connexion between the embryo and the mother which is so characteristic a feature in the development of the human ovum. At the end of the second week, after fertilisa- tion of the ovum, the embryo is separated by a slight constriction from the rest of the blastodermic vesicle, and already a primitive heart and rudimentary blood- vessels are distinguishable. The development of the vascular system, and the establishment of the fcetal 48 GENERAL EMBRYOLOGY. circulation, however, cannot well be understood until the formation and structural features of the group of closely associated extra-embrj^onic organs or appendages have been considered. This group includes the yolk-sac, the chorion, the amnion, the allantois, and the placenta. THE ECETAL MEMBRANES AND APPENDAGES. Yolk-Sac or Umbilical Vesicle. — That portion of the blastodermic cavity and its wall which is not included in the body of the embryo to form the primitive alimentary canal constitutes the umbilical vesicle or yolk-sac. Its walls, like its cavity, are continuous with the corresponding parts of the intestine, and their structural features are identical, there being an inner layer of entodermal cells and an outer layer which is formed by the splanchnic layer of the mesoderm. In the human embryo the yolk-sac is a small flask-like body, suspended from the ventral wall of the alimentary canal by a hollow stalk, the vitello-intestinal duct, which passes through the umbilical orifice. It lies in the extra-embryonic continuation of the body-cavity (ccelom), and is filled with fluid. Possibly the contents of the yolk-sac are utilised in the nutrition of the embryo in its earliest stages, and the first rudiments of the blood vascular system, viz. blood corpuscles and vessels, appear in its walls. In the human embryo, however, it is of little nutritional importance ; it soon atrophies and almost entirely disappears, but leaves traces of its existence in the umbilical cord. Amnion. — The amnion is a protective sac which surrounds the embryo. It is formed, after the development of the coelom, from the amniotic area of the blastoderm, and its wall is continuous, at the margins of the umbilical orifice, with the body-wall of the embryo. Both walls consist of a layer of ectoderm and a layer of somatic mesoderm, but whilst in the body-wall the ectoderm is external and the mesoderm internal, the relative positions of the layers are reversed in the amnion, the mesoderm being external and the ectoderm internal. The cavity enclosed between the amnion and the embryo, the amniotic cavity, is filled with fluid, the amniotic fluid, in which the embryo floats. The amniotic cavity is quite shut off for some time from all the neighbouring spaces, but after the disappearance of the bucco-pharyngeal and cloacal membranes it communicates, both anteriorly and posteriorly, with the alimentary canal of the embryo. The development of the amnion in mammals is closely associated with the attachment of the ovum to the uterine wall and with the subsequent formation of the placenta. Thus in the carnivora, before the coelom is formed, the ectoderm in the chorionic area becomes attached to the uterine tissues by small villous out- grow"ths which invade the uterine mucous membrane. This attachment is most complete in the placental region, that is, around the margins of the amniotic area. As the embryo is folded off from the blastoderm and the coelom develops, both the embryo and the amniotic area remain quite free from the uterine tissues, indeed, it may be said that, at this period, the embryo is suspended from the margins of the placental area hj the amniotic membrane. As development proceeds the amniotic area increases in extent by interstitial growth, and thereupon the emljryo, the membrane which suspends it being relaxed, sinks more and more into the interior of the ovum, or, to be more precise, into the coelomic space, which, in the meantime, has considerably increased. At the same time the growth of the placental area causes all parts of its inner margin to converge, and as the inner margins of the placental area are continuous with the outer margins of tlie amniotic membrane, the amnion is gradually carried over the dorsal surface of the embryo till its margins meet and fuse. After the fusion of its margins the amnion separates entirely from the chorionic area, henceforth known as the chorion, and forms a closed sac which completely surrounds the embryo. On reference to Figs. 21 and 27 it will be seen that as the wall of the blasto- dermic vesicle is carried inwards over the dorsal surface of the embryo it is folded ; the outer part of the fold consists of the chorionic portion, and the inner part of the THE FCETAL MEMBEANES AND APPENDAGES. 49 amniotic portion of the blastoderm. The fold is called the amnion fold ; it is quite continuous round the whole margin of the embryo, but some parts of it are more advanced than others, or in other words the convergence of the inner margin of the placental area of the blastoderm over the dorsal surface of the embryo does not take place at the same rate or to the same extent in all parts. For convenience of description it is usual to divide the amnion fold into four parts — the cephalic, the caudal, and the two lateral amnion folds ; these, however, are all continuous with one another. The inner part of the fold, which is formed from the amniotic area, is termed the true amnion, and the outer part, formed from the chorionic area, the false amnion. The latter term is, however, synonymous with chorion, and as it is misleading, it should be avoided. As the amnion is formed from the amniotic area of the blastoderm after the extension of the coelom, it must consist, as previously mentioned, of ectoderm and somatic mesoderm, 'and as the sur- face of the amniotic area reversed during the 18 formation of the amnion folds, it is obvious that in the fully-formed amnion the ectodermal layer is internal and the somatic mesoderm external. In the case of the human ovum the phe- nomena of amnion forma- tion are probably practi- cally similar, except that the ovum develops not in the cavity of the uterus, but in the substance of the mucous membrane into which it has penetrated. It is therefore surrounded by the mucous membrane on all sides, and the chorionic part of the surface of the ovum is closely attached to the surrounding tissue, but the amniotic and embryonic areas are free. If this is the case the process of amnion folding can take place in the human ovum exactly as in the ovum of a carnivorous animal, the inner margin of the chorionic area growing inwards over the amniotic and embryonic areas, the only difference being that the process takes place in a cavity in the mucous membrane and not on its surface. This conclusion is supported by Spec's observations on human ova and by those of Selenka on the ova of monkeys and apes, but it is, however, possible that, as in some rodents and insectivora, the amnion cavity appears in a mass of ectoderm which lies at the embryonic pole of the ovum, the mass being cleft by the appearance of the cavity into embryonic and amniotic sections. The two parts are then continuous at the 4 -Transverse Sections of the Uterus and Developing Ovum of a Ferret. Showing the formation and closure of the amnion folds, the completion of the amnion, and the coincident ingrowth of the inner margins of the placental area of the blastoderm. Amnion. EN. Entoderm. Amnion fold. M. Muscular wall A. AF. C. Ch. EC. Ccelom. Chorion. Ectoderm . NG. PV. of uterus. Neural groove. Placental villus SC. SS. SoM. Stratum compactum. Stratum spongiosum. Somatic mesoderm. Sp.M. Splanchnic mesoderm. UL. Unchanged layer of uterine mucosa. 50 GENEEAL EMBEYOLOGY. margin of the embryonic area, and the mesoderm growing round the amniotic ectoderm separates it from the chorionic ectoderm. After the amnion is completed its cavity is distended with fluid. As it expands it gradually obliterates the extra-embryonic part of the coelomic cavity, and finally its outer surface, of somatic mesoderm, comes into contact and fuses with the somatic mesoderm on the inner surface of the chorion. At this period the cavities in the ovum are the amniotic cavity, the remains of the yolk-sac, and those portions of the original blastodermic and ccelomic spaces which have been included in the embryo. In the human ovum, when the amnion folds unite and the true amnion separates from the chorion, the embryo and its enclosing amnion would be free within the cavity of the chorion, or extra-embryonic coelom, were it not that a very short cord of somatic mesoderm and ectoderm, the body-stalk, connects the posterior end of the embryo with the somatic mesoderm on the inner surface of the chorion. Body-Stalk. — To thoroughly understand how this union is effected in the human ovum, and to comprehend the nature of the body-stalk, it is necessary to refer to some striking peculiarities which are to be observed in the earlier stages in the development of the human embryo. When segmentation is completed, and the morula is converted into a blastula by the appearance of a cavity in its interior, the human ovum consists of an outer layer, the ectoderm, and an inner cell-mass (Figs. 12 and 39). The latter, however, which is attached to a small area of the ectoderm, does not, as in many mammals, extend itself by migration round the inner surface of that layer, and so transform the unilaminar into a bilaminar blastoderm and convert the cavity of the blastula into the blastodermic cavity. The sequence of events is different : a cavity or space appears in the inner cell-mass itself (Figs. 41, 42, and 44), and this expanding rapidly, is ultimately converted into the yolk- sac and the alimentary canal of the embryo ; it corresponds, therefore, with the blastodermic cavity of other mammals. Thus the entoderm, though derived from the inner cell-mass, never lines the inner surface of the ectoderm except in the embryonic area, for soon after the appearance of the cavity of the inner cell-mass the mesoderm grows rapidly from the primitive streak and extends, not in a single layer, as in the majority of mammals, but as two layers, one over the outer surface of the entoderm, the splanchnic layer, and the other, the somatic layer, over the inner surface of the ectoderm. The cavity of the blastula is thus ultimately enclosed between the somatic and splanchnic layers of the mesoderm, and so becomes converted into the coelomic space (Fig. 42). As the mesoderm extends, the several areas of the blastoderm are differentiated as in other mammals, but the embryonic and amniotic areas remain of relatively small size. The separation of the amnion from the chorion is effected at a very early period, Ijefore the folding off of the embryo has commenced, but the somatic mesoderm growing from the posterior end of the embryonic area still retains its connexion with the similar layer on the inner surface of the chorion, and it forms a short, and for a time a ])road stalk which unites the embryo, and consequently the amnion and the blastodermic cavity, with which the embryo is connected, to the chorion (Fig. 42). In addition to forming a bond of union between the embryo and the chorion the mesodermal stalk conducts blood-vessels from the embryo to the chorion, and more especially to its placental part. At an early period a pouch -like diverticulum projects from the posterior part of the entodermal sac. This is the allantoic diverticulum ; it lies beneath the posterior part of the embryonic area, and the area is curved upon itself so that its convexity looks towards the entodermal sac, and its concavity towards the amnion. After the embryonic area has increased in extent, and when the folding off of the eml^ryo has commenced, the anterior end of the area and the posterior end of the primitive streak remain relatively stationary as in other mammals, the cephalic and caudal folds appear, and the curvature of the greater part of the area is reversed, but the most posterior part retains its original position, lying for a time parallel with the caudal fold ; afterwards, however, it assumes a more horizontal position. This posterior section of the embryonic area contains the diverticular process of the entodermal sac wliich is called the allantois ; it also contains the THE ALLANTOIS AND UMBILICAL COED. 51 blood-vessels, allantoic arteries and veins, which pass between the embryo and the placenta. It is in relation at first with the amnion, it appears to be entirely behind the embryo, and it is called the " body-stalk." At a later period, when the stalk of mesoderm — the allantoic stalk — which connects it with the inner surface of the chorion is elongated, this part of the embryonic area is reversed in position, its anterior end is carried forwards till it forms the posterior boundary of the umbilical orifice, and the area in question forms the ventral wall of the Ijody from the umbilical to the genital region. Allantois. — The allantois plays an important part in the formation of the placenta. It consists of two portions, an entodermic diverticulum Irom the ^■entral wall of the cloacal part of the hind-gut, and a mesodermal covering. The ento- dermic diverticulum appears in the human subject, before the hind-gut is defined, as a hollow blind protrusion from the blastodermic cavity ; it extends behind the primitive streak into the mesoderm of the body-stalk, but as the folding off of the embryo proceeds, and the body-stalk is carried forward into the ventral wall of the embryo, the position of the diverticulum is altered, and ultimately, when the folding off is completed, it springs from the ventral part of the cloaca, runs forward to the umbilical orifice, and passing through it, projects for a short distance still invested with the mesodermal covering primarily obtained from the body-stalk. The ventral part of the cloaca is afterwards converted into the bladder, while the rectum is formed from the dorsal part. The mesodermal sheath which surrounds the entodermic diverticulum extends beyond it to the inner surface of the chorion ; the part which extends beyond the diverticulum is at first extremely short, indeed it is only recognisable as a layer of mesoderm uniting the body-stalk and chorion, but as development proceeds and the body-stalk is folded forward to form the ventral wall of the body of the embryo, posterior to the umbilicus, this portion of the mesoderm is elongated, and it forms the allantoic stalk by which the embryo retains its connexion with the chorion, and along which pass the allantoic or umbilical arteries to, and the corresponding veins from, the chorionic villi. After the separation of the cloaca into bladder and rectum, that portion of the allantois which lies in the body of the embryo, between the apex of the bladder and the umbilical orifice, is gradually converted into a fibrous cord, the urachus. The entodermal diverticulum disappears, and after birth, when the placental circu- lation ceases, the umbilical arteries are transformed into fine fibrous strands. The remainder of the allantois which lies outside the body of the embryo, and which takes part in the formation of the umbilical cord and placenta, is separated from the embryo at birth. Umbilical Cord. — The umbilical cord is essentially a mesodermal structure which connects the embryo with the placenta, serving as a passage for the allantoic vessels to and from the fcetal portion of the latter organ. It replaces, functionally, the body-stalk and the allantoic stalk, which were earlier provisions for the same purpose, and it is formed by the fusion of the allantoic stalk with part of the vitello-intestinal duct and the remains of the yolk-sac. The vitello-intestinal duct is at first a relatively wide channel which connects the primitive gut with the yolk-sac ; it passes through the imibilical orifice. In later stages, as the body-stalk is swung round into the ventral wall of the body, the allantoic stalk, which projects from the end of the body-stalk, is brought into close relation with the distal end of the vitello-intestinal duct and the remains of the yolk-sac ; the mesodermal constituents of the three structures then fuse together, and the whole is surrounded by the expanding amnion. In this way the umbilical cord is formed. It includes, therefore, the allantoic stalk and its blood- vessels, together with the remains of the yolk-sac and its stalk, the vitello-intestinal duct, all of which are invested and bound together by the amnion. The mesodermal core of the cord forms a fibro-mucoid tissue known as " Wharton's jelly," which consists of stellate and irregular cells embedded in a gelatinous matrix. The blood-vessels of the cord are situated in the core, and include two allantoic or umbilical arteries which run spirally round a single umbilical vein. The terminal portion of the allantoic diverticulum projects into 52 GENEEAL EMBEYOLOaY. the embryonic end of the cord, and at first a loop of intestine protrudes into it for a short distance ; the gut, however, soon recedes into the abdominal cavity. The umbihcal cord, which extends from the umbilical orifice to the centre of the placenta, is at first short and straight. As the amnion expands the length of the umbilical cord increases until, at the time of birth it measures, on an average, about 20 inches. This increase in the length of the cord allows the foetus to float freely in the amniotic fluid, and prevents traction on the placenta. After the middle of the second month the umbilical cord is twisted spirally, usually from right to left. It is suggested that this is due either to the great elongation of the allantoic arteries or to muscular movements of the foetus, and it involves a rotation of the foetus in the amniotic fluid. Chorion. — The chorionic area, by far the largest of the areas into which the blastoderm is divisible, lies external to the amniotic area. In most mammals it consists at first of ectoderm and entoderm, but after the extension and cleavage of the mesoderm has taken place, it is formed by ectoderm and somatic mesoderm. In man, however, it consists in the earliest stages of ectoderm alone, but on the formation and extension of the mesoderm it also acquires an inner layer of somatic mesoderm. In all cases, therefore, it eventually consists of the same two layers. The ectoderm of the chorionic area which immediately surrounds the amniotic area thickens to form the annular placental area, and in this way the chorionic area becomes divisible into placental and non-placental regions. When the blastodermic vesicle enters the uterus numerous ectodermal villous processes grow from the surface of the chorionic area, both in its placental and non- placental parts, and attach themselves to the uterine mucous membrane. As already pointed out in the description of the formation of the amnion, the embryonic and amniotic areas do not become attached to the uterus, but remain free from it, whilst by the approximation and fusion of its inner margins, the rapidly growing ring-like placental area is converted into a disc which intervenes between the amnion and the uterine wall. The chorionic area after the separation of the amnion is known as the chorion or chorionic membrane. The chorion forms the outer wall of a vesicle, the chorionic vesicle, which is the modified remains of the blastodermic vesicle, and which contains the embryo, the yolk-sac, the amnion, and the allantois. It consists of an outer layer of ectoderm and an inner layer of somatic mesoderm. The cavity of the chorion is the extra-embryonic portion of the ccelom. Eor a time it remains distinct, and is traversed by the allantoic stalk which unites the embryo to the inner or mesodermal layer of the placental area. The cavity is ultimately obliterated by the growth of the amnion, the latter sac expanding rapidly till its outer surface is in contact and intimately blended with the inner surface of the chorion. Chorionic Villi. — The villous processes which begin to grow from the surface of the chorionic area before it is separated from the amnion continue to develop after the separation of the two membranes is completed. They penetrate the surrounding uterine tissues. At first each consists of ectoderm only, but a core of vascular mesoderm is soon acquired. The villi increase in size and in com- plexity also, but ultimately only those in the placental area persist and continue to grow ; the remainder atrophy and disappear. Thus the placental region of the chorion eventually constitutes the main bond of union between the ovum and the mother, and it forms the foetal part of the placenta. THE PLACENTA. The placenta is the organ of foetal nutrition and respiration. In it the blood-vessels of the foetus and those of the uterus are brought into such close relationship with one another that free interchanges readily take place between the blood of the mother and that of the fcetus. In the simplest form of placenta the foetal villi are merely embedded in the maternal mucous membrane, and the relationship between foetal and maternal blood is not very close. In other THE PLACENTA. 53 forms, e.(j. ihe huinau placenta, the relation of fcetal to maternal blood is much more intimate ; this involves marked complications in the elements of the placenta, and its strvicture becomes correspondingly more complex. In all forms, however, the placenta consists of fcetal and maternal portions. Before the impregnated ovum reaches the uterine cavity the mucous membrane of the uterus undergoes certain changes in preparation for its reception and reten- Decidua.basalis Dilated part\ l Unrhaiiged part liirlianged layer Stratum siioiigiosuiii i uterine .Stratum compactuin /'""f^o^a Ectoilf'rmal villus enclosing jiaee containing maternal blood mass (Entoderm) Gland- Unchanged Dilated Fig. 39. — Diagram reineseiitiug a very young human ovum almost immediately after its entrance into the decidua, and whilst the place of its entrance is still covered with a plug of tibrin. The ectoderm has already proliferated and embraced spaces which contain maternal bloo„„„..i lo,,.,. Decidnp. basaiis the part pushed into the cavity of the uterus around the growing ovum is the decidua capsularis ; and the remainder of the decidua is the decidua vera. The decidua cap- sularis is not formed, as was formerly be- lieved, by folds of the decidua which have grown up and sur- rounded an ovum merely attached to the surface of the decidua basalis. On the contrary it is merely the superficial part of that portion of the decidua into 41. — Diagram, sliowing a further stage of developnient of the human ovum and its relation to the decidual tissues. The entoderuial cavity or yolk-sac has appeared in the inner cell -mass, and the mesoderm has commenced to extend from the primitive streak in two layers, splanchnic on the yolk-sac and somatic on the ectoderm. Unchanged layer Stratum spongiosum Stratum compactu Placental villus Maternal \'essel Body-stalk Coelom Ectoderm Somatic mesoderm Entoderm Splanchnic mesoderm Decidua vera Decidua vera Fig. 42. — Diagram, showing the completion of the decidua capsularis, the enlargement of the maternal blood-vessels in the stratum compactum of the decidua basalLs, the increase of the placental villi, the formation of the amnion folds, and the appearance of the allantoic diverticulum. which the ovum has penetrated, theretbre it may contain glands or the remains of glands which open on its superficial surface into the uterine cavity, but no glands open on its inner surface. The decidua basalis lies in contact with the placental area of the chorion, i.e. the foetal part of the placenta, and it forms the maternal part of the organ. In the fully developed human placenta, the fcetal and maternal tissues of which it THE PLACENTA. 55 Unchanged layer Stratum spongiosum Stratum compactum Amnion Matprnal blood-vessel Fuetal ectoderm villus, enclosing space filled witli maternal blood Allantoic diverticulum Ectoderm Somatic mesoderm Splanchnic mesoderm Entoderm Decidua Decidua vera DiAGEAM, showing enlargement of the blood sinuses in the maternal part of the placenta and the closnre of the amnion. is formed are so intimately mingled and blended together that it is impossible to say where one ends and the other begins. By a careful study, however, of a series of placentae of different ages a fairly clear and satisfactory idea of the part })layed by the maternal and the fcetal elements respectively, as well as of their relations to each other, may be obtained. The structural char- acters of the completed organ will be best under- stood if the two con- stituent parts are first considered separately. Fcetal Part of the Placenta. — The villi of the placental portion of the chorion invade and penetrate the decidua basalis, whilst the villi of the non-placental chorionic area of the ovum enter the decidua capsularis. As previously ex- plained, in connexion fig. 43 with the formation both of the amnion and of the chorion, the annular placental area is converted into a circular disc. It consists, like the rest of the chorion, of ectoderm and mesoderm, and it contains ramificationsof the allantoic vessels ; but the ectoderm is thickened and increased, its villi are larger than those of the non- placental region of the chorion, and it is directly con- nected with the allantoic stalk. The early villi ■ i.entary canal g^j,g merely CCtO- Yoik-sac dermal buds which penetrate the sur- rounding decidual tissues, destroying and replacing the uterine elements. These villi grow and branch, and their Vjranches an- astomose together Fig. 44. — Diagram, showing the fcetal ectoderm surrounding the maternal blood Surrounding the sinuses, the commencement of secondary fcetal villi which project into the ])lood SpaceS of the sinuses, and the disappearance of the superficial portions of the glands. i • i i • i, decidua which are in the immediate neighbourhood of the ovum. As development proceeds every ectodermal villus is penetrated Ijy an outgrowth of the subjacent mesoderm Decidua basalis Unchanged layer Placental v Maternal blood sinus Maternal vessel Placental villus Allantoic stalk Foetal villus Allantoic diverticulum Primitive ali- Ectoderm Somatic mesoderm Splanchnic mesoderm Entoderm Decidua vera 56 GENEEAL EAIBEYOLOGY. Decidua basalis Unchanged layer Stratum spongiosum Stratum compactuin Maternal blood sinus Foetal villus Body-.stalk which carries branches of thf allantoic vessels, and so the villi become vascularised with foetal blood. ¥ov some time all the vilH, placental and non-placental, grow and absorb nutriment from the maternal tissues, probably utihsing as food the tissues which they destroy and replace : but when the decidua capsularis is thinned by the expansion of the growing ovum, the vilh of the non-placental region which have penetrated it are no longer able to obtain nutrient matter, and they con- sequently atrophy and disappear. The placental vilh, on the contrary, continue to increase ; they grow in size and become more complex, and secondary branches growing i'rom them project into the maternal blood spaces which they have surrounded and float in the maternal blood. When the formation of the placenta is completed, its foetal part consists of vilh, each of which possesses an external covering of two layers of ectodermal cells and a vascular mesodermal core ; the villi project into the interior of large blood spaces which are surrounded more dnertfcuium 01' Isss Completely by foetal ectoderm, and they are bathed by maternal bloo from which they ol tain the materiaJ necessary for the nutrition and growth of the em- bryo, and into which they trans- mit the effete ex- cretory matters from the embryo. Maternal Part of the Pla- centa and the Changes in the Decidua. — The occurrence of further changes in the decidua, after the developing ovum enters the uterus, is dependent upon the retention of the ovum in the substance of the decidua. These changes only occur, therefore, in what may be termed the decidua of pregnancy. They are intimately associated with and essential to the development of the maternal part of the placenta, and a more detailed and complete account of the decidua and the modifications of its several yjarts is therefore necessary. The decidua is formed by the mucous membrane of the uterus, which is a hollow, thick- walled muscular organ, situated in the pelvic cavity. The mucous membrane contains numerous tubular glands embedded in an interglandular tissue formed of round and irregular cells. The uterine glands are lined by a columnar or cubical epithelium, and they open into the cavity of the uterus on a surface which is also covered by columnar cells. The whole of the mucous membrane is plentifully supplied with blood-vessels which pass into it from the surrounding muscular walls, and it is transformed into the decidua by proliferation and hypertrophy of all its parts. The interglandular tissue increases in amount and its blood-vessels dilate, especially near the surface of the membrane : but the most striking of the early changes occur in the glands — they become longer, more tortuous, their Yolk-sac Cceloi Somatic mesodenn Splanclinie mesoderni Entoderm Decidua caijsularis Decidua vera Fio. 45. — Diagram, showing further growth of the placental .sinuses and villi ; the fusion of the decidua capsularis with the decidua vera, and the obliteratiou of the uterine cavity. THE PLACENTA. 57 apertures enlarge and assume a funnel-like appearance, and they dilate a short distance from their terminations into large irregular spaces. The increase of the interglandular tissue is most marked in the intervals between the dilated portions of the glands and their apertures, and when all the changes are fully- established it is possible to recognise three layers of the decidual tissue. (1) A sviperficial relatively thick layer in which the interglandular tissue preponderates, the stratum compactum ; (2) A layer formed principally by the dilated portions of the glands, the stratum spongiosum ; and (3) a thin deep part of the membrane which contains the outer extremities of the glands which are practically unchanged, the unchanged layer. The decidua capsularis differs from the other portions of the decidua in that it represents only the superficial portion of the other parts of the decidua, and therefore contains no spongy layer or deep unchanged layer. This is obviously the case, for after the ovum has penetrated through the surface epithelium it becomes embedded in the stratum compactum of that portion of the decidua which it has invaded, and consequently the portion of the stratum which closes over it cannot contain more than the outer parts of some of the uterine glands with their orifices and the intervening interglandular tissue. The changes which occur in the decidua capsularis are due, first, to its connexion with and invasion by the chorionic villi; and, secondly, to the pressure exerted upon it by the enlarging ovum. The former influence is brought to bear whilst the decidua is still increasing ; the latter after it has reached its full development. The changes which result from its union with the chorion are the destruction and absorption of some of the interglandular tissue ; they are due to the activity of the ectodermic cells of the chorion, which attack and invade the uterine tissues. The changes due to pressure exerted by the enlarging ovum are diminution of vascularity, disappearance of the lumina of such portions of the glands as remain in the decidua capsularis, and the removal of their epithelium, together with the co- incident atrophy of the fatal villi which have penetrated this portion of the placental decidua. All these changes result in the reduction of the decidua capsularis to a thin membrane in which no traces of the original structure are recognisable, in the fusion of the altered decidua capsularis with the decidua vera, and the consequent obliteration of the uterine cavity. After the fifth month the decidua vera also undergoes atrophic changes, but they do not proceed so far as in the decidua capsularis ; nevertheless the stratum com- pactum is greatly reduced, the superficial epithelium and the superficial parts of the glands entirely disappear from it, the interglandular tissue becomes less vascular, and it diminishes very considerably in thickness. The epithelium dis- appears from the spaces in the spongy layer, and the spaces themselves are flattened out into long slit -like clefts, in which condition they remain till the period of pregnancy is completed. The decidua vera is thus reduced to the condition of a relatively thin membrane, and its inner surface is fused with the remains of the decidua capsularis. Decidua Basalts. — This portion of the decidua is constituted by the deeper part of the stratum compactum in which the ovum is embedded together with the more externally situated spongy and unchanged layers, and, apart from the changes due to the invasion of the foetal villi, the most important transformations in this part of the decidua occur in the stratum compactum. The alterations in the spongy layer are similar to those which occur in the same layer of the decidua vera, viz. the lining epithelium disappears and the spaces are flattened out into a layer of cleft-like slits. In the stratum compactum, however, much more striking changes occur ; all traces of the glands disappear, Imt the blood-vessels become greatly dilated, and, consequently, the layer increases considerably in thickness. The small blood-vessels which lie in the immediate neighbourhood of the ovum become converted into enormous blood sinuses, but in the deeper part of the stratum a thin layer, which lies next the stratum spongiosum, remains relatively unchanged ; this deeper part is called the basal layer, and through it the blood-vessels pass to and from the 58 GENEEAL EMBRYOLOGY blood sinuses in the more superficial portion of the membrane. When it is completed, therefore, the maternal portion of the placenta, which is the transformed decidua basalis, no longer consists of the stratum compactum, the stratum spongiosum, and the unchanged layer, but it is formed from within outwards of — (1) a layer of blood sinuses, (2) the basal layer, (3) the modified spongy layer, and (4) the unchanged layer. The difference between the decidua basalis and the maternal part of the placenta may be tabulated as follows : — Decidua basalis. Deep part of stratum compactum Stratum spongiosum Unchanged layer Maternal placenta. Layer of blood sinuses. Basal layer. Modified stratum spongiosum. Unchanged layer. Placenta Unchanged layer stratum ■sponglo■^um Stratnra Placental \ illus It must not be forgotten, however, that whilst the changes which result in the formtvtion of the maternal placenta out of the decidua basalis are taking place the stratum compactum has been invaded by the placental villi. The first result of this invasion is the destruction of much of the decidual tissue by the ectoderm of the foetal villi. Gradually the ec- toderm of the villi, always in advance of the main body, reaches and sur- rounds the dilated decidual vessels, destroys the in- tervening tissues, and ultimately re- places the endo- thelial walls of the vessels, which by this time have dilated into enor- mous spaces. Into these spaces the ramifications of the villi project, and, as the endo- thelial walls are destroyed, they lie directly within the cavities of the spaces, and are surrounded on all sides by maternal blood. The most peculiar feature of this part of the placenta, when fully developed, is that the whole of the maternal por- tion of it, except the blood, has been removed and replaced hj fcetal tissues, so that, although the maternal blood continues to circulate in the same spaces wliich it has occupied from the first, viz. the blood sinuses in the more superficial part of the stratum compactum of the" maternal decidua, yet the walls of these spaces have been replaced more or less Yolk-sac Peri- cardium decidua cap- s and decidua Fused mesoderm of amnion and cliorion Fig. 46. — Diagha.m. Later stage in the developmeut of the placenta, showing the relations of the fcetal villi to the placental sinuses, the fusion of the amnion with the inner surface of the chorion, and the thinning of tlie fused deciduic (cap- sularis and vera). THE PLACENTA. 59 completely by fcetal ectoderm, and, consequently, the spaces now lie in the midst of the foetal tissues. The invasion of the maternal by the foetal part of the placenta proceeds as far as the basal layer, and in this region the foetal ectoderm is directly continuous with the walls of the maternal blood-vessels at the points where they enter the sinuses. Although the invasion of the decidua basalis is so complete, some portions of the maternal tissues persist ; thus the basal layer and many strands of the stratum compactum escape destruction. The latter extend from the basal layer to the outer surface of the chorion, and they are eventually converted into fibrous strands, which divide the superficial part of the completed placenta into lobular areas. The completed placenta consists, therefore, of closely intermingled and fused foetal and maternal tissues, through which both the fcetal and maternal blood streams circulate. It is well adapted, on account of its peculiarities of structure, to fulfil the nutritive and respiratory requirements of the embryo. The fcetal blood stream which flows through the placental villi and the maternal blood stream in the placental sinuses are only separated irom each other by two layers of fcetal ectodermal epithelium and a small amount of foetal mesoderm, the latter being practically reduced to the single layer of endothelial cells which form the walls of the fcetal vessels. Through these layers, by osmosis, and possibly by secretion, materials are passed ijoth from mother to embryo and from embryo to mother, the placenta ser\dng not only for purposes of nutrition and respiration, but also as an excretory organ. Whilst tlie placenta is attaining its full development the amnion is expanding, and finally its outer surface fuses with the inner surface of the chorion, consequently, the innermost portion of the placenta is provided with a covering of amnion. The full-time placenta is a discoid mass about 20 or 25 inches (50 to 60 cm.) in circumference and 1\ in thickness at its centre ; it is much thinner, however, at its margins, where it is continuous with the membranes formed by the fused chorion, decidua vera, and decidua capsularis. Its weight is about one pound, and it consists from within outwards of the following layers : — Fcetal , . f Ectoderm. Amnion . . . . . • i at ^ ( Mesoderm. Allantois with foetal vessels . . . Mesoderm. I Mesoderm. Chorion Ectoderm. Layer of maternal blood sinuses and remains of the intergiandular tissue of the stratum compactum. Maternal -{ Basal la^^er. Modifiecl spongy layer. Unchanged layer. When the period of intrauterine life is completed the muscular walls of the uterus contract and the lower orifice of the uterine cavity is dilated, the fused chorion and amnion, which close the upper part of the orifice, rupture and the amniotic fluid escapes, the foetus is then expelled, but it remains attached to the placenta by the umbilical cord. The cord is divided artificially, and after a short period the placenta and membranes are expelled. The membranes attached to the placenta consist of the fused amnion, chorion, decidua capsularis, and also the decidua vera internal to the altered spongy layer ; therefore both the placenta and the membranes consist of maternal and fcetal tissues. Before the placenta and membranes are expelled the uterine decidua is separated into two parts by a cleavage which takes place in the modified stratum spongiosum. The inner portion which inclucies the placenta and membranes is cast off. The outer portion remains in the uterus ; it consists almost entirely of the deep unchanged layer of the decidua, and from it the uterine mucous membrane is reconstructed. CO GENERAL EMBRYOLOGY. THE PRIMITIVE VASCULAR SYSTEM AND THE FffiTAL CIRCULATION. It has already been said that the ovum during its passage down the Fallopian tube lives either on its own yolk particles or upon substances absorbed from the tiuids by which it is surrounded. For a time after it enters the uterus its nutrition must be provided for in a similar manner, but as soon as the chorionic villi are formed it is probable that the ectodermal cells, of which in the earliest stages they entirely consist, and which cover their surfaces in the later stages, actually eat up the decidual tissues which they invade and use them for food. This source of nutrition, however, is only sufficient for the short period during which the ovum remains relatively small, and substances absorbed through the surface cells can be readily transmitted to all its parts. In addition to the solid decidual tissues devoured by the ectodermal cells it is evident that fluids from the mother are also absorbed, for the yolk-sac and coelom enlarge and are filled with fluid. The only sources from which this can have been derived are the uterine glands or the blood and lymph vessels of the decidua. In all probability the fluids absorbed into the ovum contain nutritive material, and so long as the embryo is constituted by the thin layers of the early blastoderm sufficient food material can easily be absorbed. When, however, the various parts of the embryo increase in thickness and become moulded into the form of organs they are no longer in such intimate relation with the surrounding nutritive fluids, whilst, further, as their development progresses they require a greater amount of food and oxygen than they can obtain from these fluids. There is, therefore, an imperative necessity for a further supply of nutritive material by which their re- quirements may be satisfied, failing which, development must cease and death ensue. To meet this necessity the vascular system is formed. It is essentially an irrigation system consisting of a propulsive organ, the heart, and of tubular vessels, the blood-vessels, all of which contain blood. The heart propels the blood through the blood-vessels to all parts of the embryo, but the blood which is at first formed from the mesoderm of the ovum must, at least so far as its fluid part is concerned, be supplemented largely from maternal sources. It is necessary, there- fore, that the foetal blood-vessels be brought into close relation with the maternal blood-vessels at an early period. It is for this purpose, amongst others, that the large blood sinuses are formed in the maternal portion of the placenta, and that they are surrounded and invaded by the fcetal villi, carrying in their interior branches of the foetal blood-vessels, and as previously shown, the foetal blood- vessels in the placenta are only separated from the maternal blood in the sinuses by their own thin mesodermal walls, and by one or two layers of ectodermal cells. When the placenta is fully formed fluids can readily pass from the maternal to the f(etal vessels, and there can be no doubt that both food and oxygen pass from the maternal blood to the foetal blood through and by the agency of the .intervening cells, whilst at the same time the waste products which are formed in the embryo pass outwards to the maternal blood. Ob\T.ously, however, a system of vessels filled with fluid would be of little use in the general economy unless there were some means by which the fluid could be kept in constant movement. In the first instance this is accomplished by rhythmical contractions of the vessel walls, but in a short time portions of the two primitive stem-vessels which appear in the embryo are modified into a single propulsive organ, the heart, which forces the fluid, or blood, in a definite direction both through the body of the embryo, along the body-stalk or umbilical cord, accord- ing to the age of the embryo, and through the vessels in the placental villi. We have now to consider how the blood-vessels and blood are formed. Where, or how, the first blood-vessels appear in the human subject is not definitely known, but in other mammals they are first seen outside the body of the embryo in the wall of the yolk-sac. The outer layer of the wall of the yolk- sac consists of splanchnic mesoderm, and in that part of this layer which lies nearest the j>rimitive alimentary canal a large num})er of the cells proliferate PEIMITIVE VASCULAR SYSTEM AND FGETAL CIRCULATION. 61 rapidly and, fusing together, form multi-nucleated masses of protoplasm, the " blood islands " of I'ander. Soon after their appearance the blood islands anastomose together by means of nucleated processes which they throw out on all sides, and thus a nucleated proto- plasmic reticulum is formed in the substance of the splanchnic mesoderm. The region in which this occurs is known as the vascular area. The solid nucleated reticulum is soon converted into a system of anastomosing canals, the primitive blood-vessels, by the ap- pearance within it of ^.^'Y^^iM^rvrTT'raTAC:,,,,, ^ numerous vacuoles w'hich ^v^/r^-avv^r-'A.^sieii^aurss^irsKr.j^fv'* ^.^t soon fuse together, whilst at the same time the nu- cleated protoplasm is trans- formed into cells. The cells which lie nearest the in- terior separate from each other and form the primi- tive blood -corpuscles, whilst those situated ex- ternally remain connected by their margins and form the endothelial walls of the embryonic vessels. The fluid which fills these first- formed vessels in the vas- cular area is probably de- rived either from thecoelom or from the yolk-sac. The primitive blood - corpuscles are nucleated cells of a reddish colour ; white or colourless blood- corpuscles appear later, and it is statecl that those first formed are developed in the thymus gland. Nucleated red cor- puscles persist and increase in number till the end of the second month of in- trauterine life ; they are then gradually replaced by non-nucleated red corpus- cles. The majority of the nucleated red corpuscles disappear long before birth, but a few can usually be found in the blood of the new-born child. There is some doubt about their ultimate fate, but it is generally believed that their nuclei disappear, and that they are converted into non-nucleated corpuscles. Directly after the appearance of the blood islands in the vascular area of the yolk-sac, and just as the folding off of the embryo commences, two short tubular vessels appear in the splanchnic layer of the pericardial mesoderm. These vessels at once extend forwards and outwards into the extra-embryonic region where they become .connected with the vessels of the vascular area ; they also extend back- wards in the body of the embryo beneath the protovertebral somites. In the majority of mammals they at first terminate behind, as in front, on the wall of the yolk-sac, but after a time the main stems appear to be continued along the allantoic stalk to the placenta, whilst they give off branches to the yolk-sac. It is probable that in the human embryo also, though this has not apparently been actually observed, these main stem vessels, the primitive aortse, end at first on the wall of BV2 Fig. 47. — Development of Blood-Vessels in the Yasculae Area op THE Rat. I. Entoderm and splaiichuic mesoderm. II. Proliferation of cells of mesoderm and formation of "blood islands." III. Commencing differentiation of islands to form blood-vessels and blood-corpuscles. IV. Completed vessels. BC Blood-corpuscles. BI Blood islands. BVj Blood islands being trans- formed into blood-vessels. BVo Blood-vessels. EN Entoderm. M Mesoderm. 62 GENEEAL EMBEYOLOGY. the yolk-sac, but on the fourteenth day of intrauterine life, before the heart is formed, the two primitive stem vessels pass backwards along the body-stalk to the chorion, their terminal branches entering the chorionic villi. As they pass back- wards the primitive aortiie give off branches to the wall of the yolk-sac. Thus, at this period the vascular system of the human embryo consists of two longitudinal vessels which run parallel vsdth each other, one on each side of the middle line, throughout the whole length of the embryo. They communicate anteriorly with the vessels on the yolk-sac, and terminate posteriorly in the chorion. When the circulation commences the blood flows from the anterior part of the vascular area into the anterior ends of the primitive aortse, and passes backwards through the embryo. Some of it is returned to the vascular area by the branches which are given off to the walls of the yolk-sac ; but the greater part is carried to the chorion, whence it returns by venous channels, the allantoic veins, which have been developed in the meantime, to the anterior ends of the primitive aortse. As the cephalic and caudal folds are developed the anterior and posterior parts of the primitive aortse are carried into the ventral wall of the body of the embryo, and thus each primitive vessel is divisible into three parts : (1) a dorsal part, the primitive dorsal aorta, which extends from the dorsal end of the mandibular arch to the cloaca, and runs beneath the protovertebral somites; (2) an anterior ventral part, situated in the dorsal wall of the pericardium and extending from the umbilicus to the ventral end of the man- dibular arch ; and (3) a posterior ventral part, which at first runs in the ventral wall at the side of the cloaca, and then turns backwards in the body -stalk to the placenta, but afterwards, when the posterior part of the ventral wall of the body is completed, it extends forwards from the pelvic region to the umbilical orifice, through which it passes to the umbilical cord. The three sections are united together by two arches — an anterior arch, the first cephalic aortic arch, which passes through the mandibular arch, and a posterior arch, the caudal arch, which lies at the side of the cloaca. In a short time four additional communica- tions are formed between the anterior ventral and the dorsal part of each primitive aorta; they are the second, third, fourth, and fifth cephalic aortic arches, each of which lies in the substance of the corresponding visceral arch. As soon as the last cephaUc aortic arch is developed the rudiments of the main vessels of the embryo are established ; and by a series of transformations, for a full account of which the chapter which deals with the Vascular System must be consulted, there are formed from the vessels which have been mentioned the heart, the aorta, the main vessels of the head and neck, the pulmonary artery and its primary branches, the common and internal iliac arteries, and the hypogastric arteries. The blood distributed by the various arteries is returned to the heart by vessels called veins, which are developed in the substance of the mesoderm in the same manner as the arteries. From the yolk-sac the blood returns by the vitelline veins ; from the alimentary canal and its appendages, through the portal and hepatic veins ; from the head and neck, by the jugular veins and the superior vena cava ; and from the body and lower limbs, first by the cardinal veins, and afterwards by the inferior vena cava and the azygos veins. The heart is formed by the fusion of portions of the anterior ventral sections of the primitive aorta behind the origins of the cephalic aortic arches, and, therefore, it is primitively a bilateral organ. Subsequently it possesses for a time a single chamber, but this is afterwards divided. During the greater part of foetal life the Poster or ventral aorta Primitive caudal arch Hypogastric artery .Chorionic vessels 3. — The Primitive Blood- Vessels OF THE Embryo. PEIMITIVE VASCULAR SYSTEM AND ECETAL CIRCULATION. 63 heart, as in the adult, possesses four chambers— two auricles or upper chambers, and two ventricles or lower chambers, right and left. The two auricles communicate with the corresponding ventricles through auriculo- ventricular apertures, and with each other through a foramen, the foramen ovale, in the septum between them. In the adult the blood enters the right auricle by the superior and inferior venae cavse and the coronary sinus ; from the right auricle it passes into the right ventricle, by which it is propelled through the pulmonary arteries and lungs ; re- turning to the heart by the pulmonary veins it passes into the left auricle, and then into the left ventricle, by the contraction of which it is forced into the systemic aorta. From the aorta, by various branches, it traverses the organs and tissues of the body, and is returned again to the right auricle. The course of the fcetal circulation differs from that of the adult ; the blood passes out of the body into the placenta, to be oxygenated and p\irified, the lungs of the fcetus remaining functionless until the time of birth. Very little of the blood which is ejected from the right ventricle at every contraction of that chamber reaches the lungs ; the greater part is transferred from the pulmonary Caudal arches Dorsal aortiv 7th pair of segmental arteries Vertebral arteries 1st pair of segmental arteries Umbilical vein Splanchnic arteries Hypogastric artery 1st cephalic aortic arch 2nd cephalic aortic arch 3rd cephalic aortic arch 4th cephalic aortic arch yth cephalic aortic arch Aortic bulb Sinus Vf*nosus Vitelline vein Fig. 49. — Diagram of the Blood-Vessels of a Mammalian Embryo after the formation of the Heart. artery to the aorta by an anastomosing channel, the ductus arteriosus, which disappears after the pulmonary circulation is established. During the later months of foetal life, blood enters the right auricle by the superior and inferior vense cavte and through the coronary sinus ; only a small amount of blood, viz. that returning from the walls of the heart, enters the right auricle through the coronary sinus. The blood poured into the right auricle by the superior vena cava is returned from the head, neck, upper extremities, and the thoracic walls ; passing from the auricle by the right auriculo-ventricular opening it enters the right ventricle ; from the right ventricle it is forced into the pulmonary artery, and a small part of it traverses the lungs and returns to the left auricle by the pulmonary veins ; the main part, however, is conducted by the ductus arteriosus into the aorta at a point beyond where the main vessel of supply to the left upper extremity, the left subclavian artery, rises. The blood which enters the right auricle by the inferior vena cava is mixed ; it consists partly of purified blood from the placenta, and partly of impure blood returning from the abdomen and lower extremities. The blood from the placenta is returned to the embryo by the umbihcal vein. From the umbilical vein it passes along a channel called the ductus venosus, which terminates in the upper part of the inferior vena cava. The mixed blood from the inferior vena cava passes through the right auricle, traverses the foramen ovale in the interauricular septum, and 64 GENEEAL EMBEYOLOGY. enters the left auricle ; from the left auricle it is transferred to the left ventricle through the left auriculo-ventricular opening, and the left ventricle ejects it into the aorta. From the first part of the aorta some of the blood passes into the vessels which supply the head and neck and upper extremities, the remainder Internal jugular vein External jugular vein Right vertebral artery- Right subclavian artery Right subclavian vein Innominate veins Pulmonary artery Superior vena cava Vena azygos major Right auricle Right ventricle Hepatic vein Inferior vena cava Intercostal veins 1st cephalic aortic arch Internal carotid artery 2ncl cephalic aortic arch External carotid artery 3rd cephalic aortic arch Vertebral artery Subclavian artery 4th cephalic aortic arch Superior intercostal vein 5th cephalic aortic arch Pulmonary artery Vena azygos minor superior Left auricle Vena azygos minor inferior Ductus venosus Atrophied cardinal vein j, /| Portal vein Renal vein Lumbar vein Common iliac artery External iliac artery Internal iliac artery Aorta Atrophied cardinal vein Placenta Hypogastric arteries Middle sacial vein Fig. 50. — Diagram of the Fcetal Circulation. mixes 'with the blood conveyed to the aorta by the ductus arteriosus, and the blood, thus further mixed, is in part distributed to the walls of the thorax and abdomen to the abdominal viscera and to the lower extremities, and in part it passes to the placenta. Before birth, therefore, there is no pure arterial or fully oxygenated blood in the arteries of the fretus. The blood entering the heart by the superior vena cava is venous blood from the head, neck, upper extremities, and thorax ; that entering by the inferior vena cava is mixed blood, consisting of venous blood from the lower PEIMITIVE VASCULAK SYSTEM AND FO^.TAL CIECULATION. 65 part of the body and the lower extremities, and arterial blood from the placenta. The two streams do not mix in the right auricle, but the mixed or more arterial stream passes directly through the right into the left auricle, thence into the left ventricle, and from the left ventricle into the aorta or main systemic vessel, which conveys it to all parts of the body. The different parts of the body do not, however, receive equally oxygenated blood, for the venous stream which enters the right auricle by the superior vena cava, passes througli that cavity into the right ventricle ; by the right ventricle it is forced into the pulmonary artery, from which some small part passes into the lungs, and so back to the left auricle by the pulmonary veins, but by far the greater part is carried by the ductus arteriosus to the aorta, which it enters beyond the origins of the vessels which supply the head, neck, and upper extremities ; therefore the blood in the lower part of the aorta, which is distributed to the abdomen, the abdominal viscera including the liver, the lower limbs, and the placenta, is much more mixed or impure (less oxygenated) than that which is dis- tributed to the head, neck, and upper extremities from the upper part of the aorta. SUMMARY OF THE EXTERNAL FEATURES OF THE HUMAN EMBRYO AT DIFFERENT PERIODS OF DEVELOPMENT. First week. — The phenomena of fertilisation and segmentation have not been observed in the human ovum, but there is no reason to believe that they differ in any essential respect from those met with in the ova of other mammals. Fertilisation probably occurs in the upper jjart of the Fallopian tube, and segmentation is completed in the lower part of the same canal by the sixth or eighth day, when, presumably, the ovum becomes a morula, and passes, either as such or as a blastula, into the cavity of the uterus. Second week. — At the twelfth day the ovum is embedded in the uterine wall ; it is a lenticular vesicle, which measures 5'5 mm. (i of an inch) in length and 3"3 mm. (^ of an inch) in breadth. Its upper and lower surfaces are smooth and convex, the latter being somewhat flatter than the former, and it is surrounded equatorially by a broad band of villi, some of which are slightly branched. The wall of the vesicle and the villous processes which project from it consist of ecto- dermal cells, and in the embryonic area, wliich is clearly marked on the upper surface, there is an inner layer of granular nucleated corpuscles. By the end of the twelfth or the beginning of the thirteenth day the length of the ovum has increased to 6 mm. {\ inch), and its breadth to 4 -.5 mm. (^V inch). The embryonic area is no longer on the surface of the ovum, for the amnion folds have closed. The yolk- sac is formed, and the rudiment of the allantoic duct projects backwards from the upper and posterior part of the embryonic area. Mesoderm has formed, and it has extended round the yolk-sac and over the inner surface of the chorion. The embryonic area, with the yolk-sac and the amnion, are enclosed within the blastoderm, but they remain attached to the inner surface of the chorion by a relatively thick stalk of ectodermal and mesodermal tissue, the body-stalk, which is subsequently replaced by the umbilical coid. The outer surface of the ovum, which now consists entirely of chorion, is covered with small villi into some of which mesodermal cores are projecting. Obviously the ovum of the latter part of the twelfth day differs considerably from that of the earlier part of the same day, but the transitional stages which intervene between the two have not yet been observed. Probably, however, the inner granular layer of cells in the embryonic area, which represent the entoderm, increase and form a solid mass in which a cavity soon appears. Directly after the foimation of the cavity in the entoderm the primitive streak appears, and the mesoderm, growing from it, rapidly 5 A. AM A B Fig. 51. Human embryo at the end of the 12th day of development ; B. At the end of the 13th day of development ; C. At the end of the 14th day of development. (After His.) . Amnion ; AS. Allantoic stalk ; BS. Body-stalk ; CV. Chorionic villi on a segment of the chorion ; E. Embryo ; H. Head of embryo ; PR. Peri- cardial region ; SS. Stomatodieal depression ; YS. Yolk-sac. 66 GENERAL EMBRYOLOGY. covers the entodermal sac and spreads over the inner surface of the chorionic area. At the same time tlie amniotic folds form and separate from the chorion, but this separation is not efiected till the mesoderm, extending backwards from the posterior end of the embryonic area, has reached and becomes connected with the inner surface of the chorion. Consequently, when the amniotic folds fuse together and separate from the remainder of the blastoderm, the embryonic area with the yolk-sac and amnion still remain attached to the inner surface of the chorion. Dnring the thirteenth day the embryonic area is elevated, the cephalic and caudal folds are developed, and the pericardial region becomes prominent between the head extremity of tlie embryo and the upper and anterior part of the yolk-sac. The neural groove and the neural folds appear ; the posterior ends of the folds embrace the anterior extremity of the primitive streak on which the primitive groove is formed. At the anterior end of the primitive groove a neurenteric canal appears, forming a communication between the neural groove and the posterior end of the primitive alimentary canal On the fourteenth day the embryo is more distinctly separated from the yolk-sac ; the head increases considerably in size, and its anterior part is bent downwards. The posterior part of the neural canal is completed, except at the extreme end, by the meeting and fusion of the neural folds, but it is still open anteriorly, where traces of the cerebral vesicles are present. The two halves of the heart fuse together ; the single tube thus formed is slightly bent upon itself, and its outline is visible from the exterior. The pericardial region increases in size, and a distinct stomatodfeal space appears between it and the anterior part of the head. The outlines of fourteen protovertebral somites are visible on the outer surface of the body. HA HL D D. AS. E F Fig. 52. Human embryo at tlie 21st day of development ; E. At the 23rd day nf development ; F. At the 27th day of development. (After His.) Allantoic stalk ; BS. Body-stalk ; CV. Chorionic villi on a segment of the chorion ; EY. Eye ; FL. Fore- limb ; H. Head; HA. Hyoid arch ; HL. Hind-limb; MA. Mandibular arch ; MB. Mid-brain; MP. Maxillary process ; OP. Olfactory pit ; OV. Otic vesicle ; PR. Pericardial region ; PS. Protovertebral somite ; SS. Stomatodseal space ; U(J. Umbilical cord ; VC. Visceral cleft ; WR. Wolffian ridge ; YS. Yolk-sac. Third week. — On the fifteenth day the auditory pits and two visceral clefts appear. Tlie head and pci-icavflial region enlarge, and the stomatodasal space, which increases simultaneously, becomes more defined laterally by tlie forward growth of the maxillary processes. ]>y the end of the third week Wolffian ridges appear below the ventral ends of the ])rotovertebral somites ; they are most marked in the thoracic and pelvic regions, where bud-like projections form the rudiments of the limbs. Four visceral clefts are visible, and there is ;i distinct tail. Fourth week. — The embryo is curved upon itself, and its outline is almost circular. 'I'he visceral arches begin to overlap each other. The rudiments of the external ear are just visible as small nodules. The limb rudiments are flat, oval buds. Fifth week. — The curvature is diminished, and tlie head and neck form about half the embryo. Tlie eye is recognisable externally. The nose begins to grow forwards, but it is still broad and flat, and the nostrils are widely apart. The nodular elements of the external ear fuse together. The segments of the limbs are defined, but the digits do not project beyond the ends of the limb-buds. The genital tubercle, the rudiment of the external generative organs, is formed. Sixth week. — During the sixth week the increase in size is less rapid than in previous stages, but the embryo begins to assume a more distinctly human form. The HUMAN EMBRYO AT DIFFERENT STAGES. 67 liead remains relatively large and it is bent at right angles to the body. Tlie neck is l)etter defined and appears as a constricted region between the head and trunk. The BE (I H Fig. 53. a. Human emliryo at tlie 29th day of development ; H. At the 32nd day of development. (After His.) EE. Rudiment of ear ; EY. Eye ; FL. Fore-limb; HA. Hyoid arch ; HL. Hind-limlp ; MA. Mandibular arch : MB. Mid-brain; MP. Maxillary process ; OP. Olfactory ])it ; PPi. Pericardial region ; UG. Umbilical cord. maxillary processes fuse with the lateral nasal processes, and the lips and eyelids begin to assume their characteristic foi-m. The outer parts of all the visceral clefts except the hyo-mandibular disappear. The external ear acquires its adult form. The rotation of Fig. 54. — Hdman F(etus at the sixth week Fig. 55. — Human F(etcs six and a OF Development. (After His.) half weeks old. (After His.) D. Digits ; EE. Rudiment of ear ; FL. Fore-limb ; HL. Hind-limb ; MP. Maxillary process ; N, Nose ; UC. Umbilical cord. the limbs commences, and the fingers reach the extremity of the hand ; the tail is beginning to disappear as an external projection. Seventh week. — The flexure of the head upon the body is reduced. The nose projects more than in the preceding stage, and the chin appears. The toes reach the margins of the feet, and the projecting portion of the tail is still further reduced in length. Eighth week. — The flexure of the head disappears. The forehead projects. 68 GENEEAL EMBKYOLOGY. The nose narrows and becomes more prominent, but the anterior nasal orifices are still directed forwards. Tlie upj)er lip is completed by the fusion of the globular processes. The tlnnnb is widely separated from the fingers, and the hand assumes a distinctly human appearance. The tail is reduced to a small nodule, and the umbilical cord is attached to the lower part of the abdominal wall. At the end of the second month the total length of the foetus, excluding the legs, is 28 mm. (1-| in.). Third month. — The head grows less rapidly and, though it is still large, it is relatively smaller in proportion to the whole body. The eyelids close, and their margins fuse together. The neck increases in length. The various parts of the limbsassume theirdefinite proportions, and nails appear on the fingers and toes. The procto- dseum is formed and the external generative organs are differentiated, so that the sex can be distin- guished on external examination. The skin is a rosy colour, thin and delicate, but more consistent than in the preceding stages. By the end of the third month the total length of the foetus, ex- cluding the legs, is 7 cm. (2 ^ in.), including the legs, 9-10 cm. (3|-4 in.), and it weighs from 100-125 grammes (3^-4| oz.). Fourth month. — In the fourth month the skin becomes firmer, and fine hairs are de- veloped. The disproportion between the fore and hind limbs disappears. If the foetus is born at this period it may live for a few hours. Its total length from vertex to heels is 16-20 cm. (6|-8 in.), from vertex to coccyx 12-13 cm. (4-i-5i in.), and it weighs from 230-260 grammes {8-^-91 oz.). Fifth month. — The skin becomes firmer, the hairs are more developed, and sebaceous matter appears on the siirface of the body. The legs are longer than the arms, and the umbilicus is farther from the pubis. At the end of the month the total length of the foetus, from vertex to heels, is 25-27 cm. (10-101 in.), from vertex to coccyx 20 cm. (8 in.), and its average weight is about half a kilogramme (Ijo ^bs.). Sixth month. — The skin is wrinkled and of a dirty reddish colour. The hairs are stronger and darker. The deposit of sebaceous matter is greater, especially in the axillte and groins. The eyelashes and eyebrows appear. At the end of the month the total length of the fcjetus, from vertex to heels, is from 30-32 cm. (12-12j in.), and its average weight is about one kilogramme (2i lbs.). Seventh month. — The skin is still a dirty red colour, but it is lighter than in the previous month. The body is more plump on account of a greater deposit of sub- cutaneous fat. The eyelids reopen, and the foetus is capable of living if born at this period. Its total length at the end of the month, measured from vertex to heels, is 35-36 cm. (14-1 4 J in.), and its weight is about one and a half kilogrammes (3)j lbs.). Eighth month. — The skin is completely covered with sebaceous deposit which is thickest on the head and in the axillsD and groins, and its colour changes to a bright flesh tint. The umbilicus is farther from the pubis, but it is not yet at the centre of the body. The total length of the foetus, from vertex to heels, is 40 cm. (16 in.), and its weight varies from 2 to 2^ kilogrammes (4|-5^ lbs.). Ninth month. — 'i'he hair begins to disappear from the body, but it remains long and abundant on the head. The skin becomes paler, the plumpness increases, and the umbilicus reaches the centre of the body. At the end of the ninth month, when the foetus is born, it measures about 50 cm. from vertex to heels (20 in.), and it weighs from 3-3^ kilogrammes (6yV*'^ro lbs.). The age of a foetus may he estimated approximately by Hasse's rule, viz. Up to the fifth month the length in centimeters, the lower limbs being included, equals the square of the age in months, and after the fifth month the length in centimeters equals the age multiplied by five. Fig. 56. — Human Fcetus eight and a half WEEKS OLD. (After His. ) GE. Genital eminence ; UC. Umliilical cord. OSTEOLOGY. THE SKELETON. By Arthue Thomson. The term skeleton (from the Greek, o-KeAero?, dried) is applied to the parts which remain after the softer tissues of the body have been disintegrated or removed, and includes not only the bones, but also the cartilages and ligaments which bind them together. In the restricted sense of the word the skeleton denotes the osseous framework of the body. It is in this sense that it is generally employed in human anatomy. The skeleton serves to support the softer structures which are grouped around it, and also affords protection to many of the delicate organs which are lodged within its cavities. By the articulation of its several parts, its segments are con- verted into levers which constitute the passive portion of the locomotory system. Eecent research has also proved that certain cells found in bone -marrow are intimately associated with the development and production of some of the corpuscles of the blood. Bone may be regarded as white fibrous tissue which, having become calcified, has undergone subsequent changes, so as to be converted into true osseous tissue. Most probably all bone is of membranous origin, but it may pass through a stage in which cartilage plays an important part in its development. In many instances the cartilage persists, and is not converted into bone, as in the case of the articular cartilage which clothes the joint surfaces, the nasal septum, the cartilages of the nose, and the cartilages of the ribs. A persistence of the membranous condition is met with in man in the case of the tentorium cerebelli, which in some groups of animals (Carnivora) is converted into a bony partition. Skeletal structures may be derived from each of the three layers of the trilaminar blastoderm. The exo-skeleton includes structures of ectodermal, and some of mesodermal origin in the shape of hair, nails, feathers, teeth, scales, armour- plates, etc., whilst the endo-skeleton, with which we are more particularly concerned, is largely derived from the mesoblastic tissue, but also includes the notochord, an entodermal structure which forms the primitive endo-skeleton, around which the axial skeleton is subsequently developed in the Vertebrata. The endo-skeleton is divisible into an axial portion, appertaining to the trunk and head, and an appen- dicular part associated with the limbs. It also includes the splanchnic skeleton, which comprises certain bones developed in the substance of some of the viscera, such as the os cordis and os penis of certain mammals. In man, perhaps, the cartilaginous framework of the trachea and bronchi may be referred to this system. The number of the bones of the skeleton of man varies according to age. Owing to a process of fusion taking place during growth, the number in the adult is less than the number in the child. The following table does not include the sesamoid bones which are frequently developed in tendons, the most constant ossicles of this description being those in relation to the metacarpo-phalangeal joint of the thumb, and the metatarso-phalangeal joint of the great toe. 69 5 70 OSTEOLOGY. life The table represents the number of bones distinct and separable during adult Axial skeleton Appendicular skeleton The ossicles of the ear Single Bones. Pairs. Total 'The vertebral column 26 26 The skull . 6 8 22 The sternum 1 1 The ribs . 12 24 The hyoid bone 1 1 /The upper limbs . 32 64 I^The lower limbs . 31 62 ... 3 6 34 86 206 Bones are often classified according to their shape. Thus long bones, that is to say, bones of elongated cylindrical form, are more or less characteristic of the limbs. Broad or flat bones are plate-like, and serve as protective coverings to the structures they overlie ; the bones of the cranial vault display this particular form. Other bones, such as the carpus and tarsus, are termed short bones ; whilst the bones of the cranial base, the face, and the vertebrae, are frequently referred to as irregular bones. Various descriptive terms are applied to the prominences commonly met with on a bone, such as tuberosity, eminence, iJrotuberance, 'process, tuhercle, spine, ridge, crest, and line. These may be articular in their nature, or may serve as points or lines of muscular and ligamentous attachment. The surface of the bone may be excavated into pits, depressions, fossae, cavities, furrows, grooves, and notches. These may be articular or non-articular, the latter serving for the recep- tion of organs, tendons, ligaments, vessels, and nerves. In some instances the substance of the bone is hollowed out to form an air space, sinus, or antrum. Bones are traversed hj foramina and canals ; these may be for the entrance and exit of nutrient vessels, or for the transmission of vessels and nerves from one region to another. A cleft, hiatus, or fissure serves the same purpose. Channels of this kind are usually placed in the line of a suture, or correspond to the line of fusion of the primitive portions of the bone which they pierce. Composition of Bone.' — Bone is composed of a combination of organic and inorganic substances in about the proportion of one to two. Organic matter (Fat, etc., Collagen) . . . 31 "04 Mineral matter — Calcic phosphate .... 58"23' Calcic carbonate Calcic fluoride Magnesic phosphate Sodic chloride 7-32 1-41 1-32 •69 68-97 100-00 The animal matter may be removed by boiling or charring. According to the completeness with which the fibrous elements have been withdrawn, so the brittle- ness of the bone increases. When subjected to high temperatures the earthy matter alone remains. By soaking a bone in acid the salts may be dissolved out, leaving only the organic part. The shape of the bone is still retained, though it has now become soft, and can be bent about in any direction. The touglmess and elasticity of bone depends therefore on its organic constituents, whilst its hardness is due to its mineral matter. Bone may be examined either in the fresh or dry condition. In the former state it retains all its organic parts, which include the fibrous tissue in and around it, the blood-vessels and their contents, together with the cellular elements found within the substance of the bone itself, and the marrow which occupies the lacunar spaces and marrow cavity. In the dried or macerated bone most of these have disappeared, though a considerable portion of the organic matter still remains, even in bones of great antiquity and in a more or less fossil condition. Con- sidering its nature and the amount of material employed, bone possesses a remark- STKUCTUEE OF BONE. 71 able strength, equal to nearly twice that of oak, whilst it is capable of resisting a greater crushing strain ; it is stated that a cubic inch of bone will support a weight of over two tons. Its elasticity is remarkable, and is of the greatest service in enabling it to withstand the shocks to which it is so frequently subjected. In regions where wood is scarce the natives use the ribs of large mammals as a sub- stitute in the construction of their bows. Its hardness and density vary in different parts of the skeleton, and its permanency and durability exceed that of any other tissue of the body, except the enamel and dentine of the teeth. The osseous remains of a race over eighty centuries old are now being excavated in Egypt. Structure of Bone (Macroscopic). — To obtain an idea of the structure of a bone it is necessary to examine it both in the fresh or recent condition and in the macerated state. In the former the bone is covered by a membrane which is with difficulty torn off, owing to the abundance of tine fibrils which enter the substance of the bone from its deep surface. This membrane, called the periosteum, overlies the bone, except where the bone is coated with cartilage. This cartilage may form a bond of union between contiguous bones or, in the case of bones united to each other by movable joints, may be moulded into smooth articular surfaces called the articular cartilages. The attachment of the various ligaments and muscles can also be studied, and it will be noticed that where tendon or ligament is attached, the bone is often roughened to form a ridge or eminence ; where fleshy muscular fibres are attached, the bone is, as a rule, smooth. In the macerated condition, when the cartilage and fibrous elements have been destroyed, it is possible, however, to determine with considerable accuracy the parts of the bone covered with articular cartilage, since the bone here is smooth and conforms generally to the curves of the articular areas of the joint ; these areas are referred to as the articular surfaces of the bone. The bone now stripped of its periosteal covering displays a dense surface finely pitted for the entrance of the processes derived from the periosteum, which thus establish a connexion between the bony substance and that vascular layer ; here and there, more particularly in the neighbourhood of the articular extremities, these pits increase in size and number and allow of the trans- mission of small blood-vessels. If careful examination be made, one or two foramina of larger size will usually be noticed. These allow the passage of arteries of con- siderable size into the interior of the bone, and are called the vascular foramina or canals of the bone. There are also corresponding channels for the escape of veins from the interior. In order more fully to ascertain the structure of bone it will be necessary to study it in section. Taking first a long bone, such as one meets with in the extremities, one notices on longitudinal section, that the bone is not of the same density throughout, for, whilst the external layers are solid and compact, the interior is made up of loose spongy bone called cancellous tissue. Further, it will be observed that in certain situations this cancellous tissue is absent, so that there is a hollow in the interior of the bone called the medullary cavity. In the recent condition this cavity is filled with the marrow and is hence often called the marrow cavity. This marrow, which fills not only the marrow cavity but also the interstices between the cancellous fibres, consists largely of fat cells together with some marrow cells proper supported by a kind of retiform tissue. The appearance and con- stituents of this marrow differ in different situations. In the medullary cavity of long bones the marrow, as above described, is known as yellow marrow. In other situations, viz. in the diploe of the cranial bones (to be hereafter described), in the cancellated tissue of such bones as the vertebrae, the sternum, and the ribs, the marrow is more fluid, less fatty, and is characterised by the presence of marrow- cells proper, which resemble in some respects colourless blood corpuscles. In addition to these, however, there are small reddish - coloured cells, akin to the nucleated red corpuscles of the blood of the embryo. These cells (erythroblasts) are concerned in the formation of the coloured corpuscles of the blood. Marrow which displays these characteristic appearances is distinguished from the yellow variety, already described, by being called the red marrow. The marrow met with in the cancellous tissue of the cranial bones of aged individuals often undergoes degenerative changes and is sometimes referred to as gelatinous marrow. 72 OSTEOLOGY. A better idea of the disposition of the bony framework of a long bone can be obtained by the examination of a section of a macerated specimen. Here the marrow has been destroyed and the osseous architecture of the bone is consequently better displayed. AVithin the shaft is seen the marrow cavity extending towards, but not reaching, either extremity of the bone. This cavity is surrounded on all sides by a loose spicular network of bone, which gradually increases in compactness until it reaches the circumference of the shaft, where it forms a dense surrounding wall. In the shaft of a long bone the thickness of this outer layer is not the same throughout, but tends to diminish as we approach the extremities, nor is it of uniform thickness on all sides of the bone. All the long bones display curves in varying degree, and it is a uniform rule that the thicker dense bone is found along the concave surface of the curve, thus assisting in materially strengthening the bone. Towards the extremities of the long bone the structure and arrangement of the bone undergoes a change. There is no marrow cavity, the cancellated tissue is not so open and irregular, and the external wall is much thinner than in the shaft, indeed in many instances it is little thicker than stout paper. A closer examination of the arrange- ment of this cancellous tissue throughout the bone suggests a- regularity in its arrangement which might escape notice, and if in place of one bone only being examined sections of other bones be also inspected, it will be observed that the spicules of this tissue are so arranged as best to withstand the strains and stresses to which the bone is habitually subjected. From what has been said it will be obvious that the arrangements above described are those best adapted to secure the maximum of strength with the minimum of material, and a consequent reduction in the weight of the skeleton. The same description applies, with some modification, to bones of flattened form. Taking as an example the expanded plate-like bones of the cranial vault, their structure as displayed on section exhibits the following appearance : The outer and inner surfaces are formed by two compact and dense layers, having sandwiched between them a layer of cancellous tissue called the diploe, containing red marrow. Note that there is no medullary cavity, though in certain situations and at certain periods of life the substance of the diploe may become absorbed and converted by the evagination of the mucous membrane of the respiratory tract into air-spaces or air-sinuses. Microscopic. — True bone differs from calcified cartilage or membrane in that it not merely consists of the deposition of earthy salts within its matrix, but displays a definite arrangement of its organic and inorganic parts. Dense bone merely differs from loose or cancellous bone in the compactness of its tissue, the character- istic feature of which is the arrangement of the osseous lamellae to form what are called Haversian systems. These consist of a central or Haversian canal which contains the vessels of the bone. Around this the osseous lamellae are arranged concentrically, separated here and there by interspaces called lacunae, in which the bone corpuscles are lodged. Passing from these lacunae are many fine channels called canaliculi. These are disposed radially to the Haversian canal, and pass through the osseous lamellae. They are occupied by the slender processes of the bone corpuscles. Each Haversian system consists of from three to ten concentric rings of osseous lamellae. In addition to the lamellae of the Haversian systems there are others which are termed the interstitial lamellae ; these occupy the intervals between adjoining Haversian systems, and consist of Haversian systems which have undergone a process of partial absorption. Towards the surface of the bone, and subjacent to the peri- osteal membrane which surrounds the shaft, there are lamellae arranged circum- ferentially ; these are sometimes referred to as the outer fundamental lamellae. The periosteal membrane which surrounds the bone, and which plays so important a part in its development, sends in processes through the various Haversian systems, which carry with them vessels and cells, thus forming an organic meshwork around which the earthy salts are deposited. Ossification of Bone. — For an account of the earlier development of the skeleton the reader is referred to the section on Embryology, Concerning the OSSIFICATION AND GEOWTH OF BONES. 73 subsequent changes which take place, these are dependent on the conversion of the scleratogenous tissue into membrane and cartilage. A characteristic of this tissue is that it contains elements which become formed into bone-producing cells, called osteoblasts. These are met with in the connective tissue from which the membrane bones are formed, whilst they also appear in the deeper layers of the investing tissue of the cartilage (perichondrium), and so lead to its conversion into the bone- producing layer or periosteum. All true bone, therefore, may probably be regarded as of membranous origin, though its appearance is preceded in some instances by the deposition of cartilage ; in this case calcification of the cartilage is an essential stage in the process of bone formation, but the ultimate conversion into true bone, with characteristic Haversian systems, leads to the absorption and disappearance of this primitive calcified cartilage. In considering the development of bone an inspection of the skeleton of a foetus will enable the student to realise that much of what is bone in the adult is preformed in cartilage, whilst a part of the fully- developed skeleton is represented only by memltrane: hence, in regard to this ossification, bones have been described as of cartilaginous and membranous origin. If the development of a long bone be traced through successive stages from the cartilaginous condition in which it is preformed, it will be noticed that ossification first begins in the shaft. This ossific centre is referred to as the diaphysis, and, since it is the first to appear, is also spoken of as the primary centre of ossification. As yet, the extremities of the shaft are cartilaginous knobs, but at a later stage one or more ossific centres appear in these cartilaginous extremities. These centres, which are independent of the diaphysis and appear much later, at variable periods, are termed epiphyses or secondary centres. If there be more than one such centre at the extremity of a bone, these associated centres unite, and at a later stage the osseous mass so formed joins with the shaft or diaphysis, and in this way the formation of the bone is completed. Complete fusion by osseous union of the epiphyses with the diaphyses occurs at variable periods in the life of the individual. Prior to this taking place, the two are bonded together by a cartilaginous layer which marks the position of the epiphyseal line. If the bone be macerated at this stage of growth, the epiphysis falls away from the diaphysis. In the case of the articular ends of ])one it will be noticed that the surfaces exposed by the separation of the epiphysis from the diaphysis are not plane and smooth, but often irregular, notched, and deeply pitted, so that when the two are brought together they interlock, and, as it were, dovetail into each other. In this way the extremities of the bone as yet ununited by osseous growth are during youth and adolescence able to withstand the shocks and jars to which during life they are habitually subjected. A long bone has been taken as the simplest example, but it by no means follows that these secondary centres or epiphyses are confined to the articular extremities of long bones. They are met with not only in relation to the articular surfaces of bones of varied form, but also occur where bones may be subjected to unusual pressure or to the strain of particular muscles. For this reason epiphyses of this nature have been called pressure and traction epiphyses (Parsons). There occur, however, secondary independent centres of ossification, which cannot be so accounted for. Possibly these are of phylogenetic interest only, and may accord- ingly be classed as Atavistic. Ossification in Membrane. — Membrane bones are such as have developed from fibrous tissue without having passed through a cartilaginous stage. Of this nature are the bones of the cranial vault and the majority of the bones of the face, viz. the maxillte, malars, nasals, lacrimals, and palate bones, as well as the vomer. The internal pterygoid plate (medial layer of the pterygoid process) is also of mem- branous origin. In the course of the development of a bone from membrane, as, for example, the parietal bone, the fibrous tissue corresponding to the position of the primary centre becomes osteogenetic, because here appear the bone-forming cells (osteoblasts), which rapidly surround themselves with a bony deposit more or less spicular in arrangement. As growth goes on these osteoblasts become embedded in the ossifying matrix, and remain as the corpuscles of the future bone, the spaces in which they are lodged corresponding to the lacunae and canaliculi of the fully developed osseous tissue. From the primary centre ossification spreads eccentrically 74 OSTEOLOGY. towards the margins of the bone, where ultimately the sutures are formed. Here the growth rendered necessary by the expansion of the cranium takes place through the agency of an intervening layer of vascular connective tissue rich in osteoblasts ; but in course of time the activity of this is reduced until only a thin layer of intermediate tissue persists along the line of the suture ; this may eventu- ally become absorbed, leading to uhe obliteration of the suture by the osseous union of the contiguous bones. Whilst the expansion of the bone in all directions is thus provided for, its increase in thickness is determined by the activity of the underlying and overlying strata. These form the periosteum, and furnish the lamella which constitute the inner and outer compact osseous layers. Ossification in Cartilage. — Cartilage bones are those which are preformed in cartilage, and include most of the bones of the skeleton. Their growth is often described as endochondral and ectochondral, the former term implying the deposition of membrane bone in the centre of the cartilage, while the latter signifies a deposit of membrane bone on the surface of the cartilage, the osteo- genetic layer on the surface of the cartilage being named the perichondrium till once bone has been formed, when it is called the periosteum. In a cartilage bone changes of a similar nature occur. The cartilage, which may be regarded histologically as white fibrous tissue + chondro-sulphuric acid and a certain amount of lime salts, undergoes the following changes : — First, the cartilage cells being arranged in rows, become enlarged ; secondly, the matrix between the cartilage cells becomes calcified by the deposition of an additional amount of lime salts ; thirdly, the rows of cells become confluent ; and, fourthly, into the spaces so formed extend the blood-vessels derived from the vascular layer of the periosteum. Accompanying these vessels are osteoblasts and osteoclasts, the former building up true bone at the expense of the calcified cartilage, the latter causing an absorption of the newly-formed bone, and leading to its conversion into a marrow cavity, so that in due course all the cartilage or its products disappear. At the same time that this is taking place within the cartilage, the perichondrium is undergoing conversion into the periosteum, an investing membrane, the deeper stratum of which, highly vascular, furnishes a layer of osteoblast cells which serve to develop the circumferential lamellae of the bone. It is by the accrescence of these layers externally, and their absorption internally through the action of the osteoclast cells, that growth takes place transversely. A transverse section of the shaft of a long bone shows this very clearly. Centrally there is the marrow cavity, formed primarily by the absorption of the calcified cartilage; around this the cancellous tissue produced by the partial erosion of the primary periosteal bone is disposed, whilst externally there is the dense envelope made up of the more recent periosteal growth. Growth of Bone. — The above description, whilst explaining the growth of bone circumferentially, fails to account for its growth in length ; hence the necessity in long bones for some arrangement whereby ossification may take place at one or both extremities of the shaft. This zone of growth is situated where the ossified shaft becomes continuous with the cartilaginous epiphysis. In addition, within these epiphysial cartilages calcification of the cartilage takes place centrally, just as in the diaphysis. The two parts of the bone, viz. the diaphysis and epiphysis, are thus separated by a layer of cartilage, sometimes called the cartilage of conjuga- tion, as yet uncalcified, but extremely active in growth owing to the invasion of vessels and cells from a vascular zone which surrounds the epiphysis. The nucleus of the epiphysis becomes converted into true bone, which grows eccentrically. This arrangement provides for the growth of the shaft towards the epiphysis, and the growth of the epiphysis towards the shaft ; so that as long as the active intervening layer of cartilage persists, extension of growth in a longitudinal direction is possible. As might be expected, experience proves that growth takes place more actively, and is continued for a longer time, at the end of the bone where the epiphysis is the last to unite. In consequence, surgeons sometimes term this the " growing end of the bone." Subsequently, however, at variable periods the intervening layer of cartilage becomes calcified, and true bony growth occurs within it, thus leading to complete osseous union between the shaft and epiphysis. When this has taken place all further growth in a longitudinal THE VERTEBRAL COLUMN. 75 direction ceases. In cases where the epiphysis enters into the formation of a joint, the cartilage over the articular area persists and undergoes neither calcification nor ossification. Vascular, Lymphatic, and Nervous Supply. — From what has been said it will be gathered that the vascular supply of the bone is derived from the vessels of the periosteum. These consist of fine arteries which enter the surface of the shaft and epiphysis; but in addition there is a larger trunk which enters the diaphysis and reaches the medullary cavity. This is called the nutrient artery of the bone. The direction taken by this vessel varies in ditlerent bones. In the upper limb the artery runs downwards in the case of the humerus and upwards in the radius and ulna ; in the lower limb the nutrient vessel of the femur is directed towards the upper extremity of the shaft, whilst in the tibia and fibula it follows a downward course. The direction of the nutrient artery in the bone is a mechanical result of the unequal growth of the two extremities of the bone. During the greater part of intra-uterine life the principal nutrient arteries of the loug bones are directed towards the distal extremity of the limb. In the process of development the point of entrance of the artery is turned away from the epiphysis which furnishes the greatest amount of bone, and thus, together with the nutrient canal, acquires an obliquity directed towards the extremity of the bone which develops last (Pioliet, J. de VAnat. et de la Phys., 1905, p. 57). It may assist the memory to point out that when all the joints are flexed, as in the position occupied by the fcetus in utero, the direction taken by the vessels is the same, and corresponds to a line passing from the head towards the tail-end of the embryo. Consequently, in the upper limb the vessels run towards the elbow, whilst in the lower Umb they pass from the knee. The veins which permeate the cancellous texture of the bone are large and thin- walled. They do not accompany the arteries, and, as a rule, in long bones they escape through large openings near the articular surfaces. In flat bones they occupy channels within the diploe, and drain into an adjacent sinus, or form communica- tions with the superficial veins of the scalp. The lymphatics are mainly periosteal, but enter the bone along with the vessels and become perivascular. The nerves which accompany the arteries are probably destined for the supply of the coats of these vessels. Whether they end in the bony tissue or not is unknown. The attention of anatomists has long been directed to the elucidation of the laws which regulate bone-growth. Our present knowledge of the subject may be briefly summarised in the following generalisations : — 1. In bones with a shaft and two epiphyses, the epiphysis towards which the nutrient artery is directed is the first to unite with the shaft. 2. In bones with a shaft and two epiphyses, as a rule the epiphysis which com- mences to ossify latest unites soonest with the shaft. (The fibula is a notable exception to this rule.) 3. In bones with a shaft and one epiphysis the nutrient artery is directed towards the end of the bone which has no epiphysis. (This arrangement holds good in the case of the clavicle, the metacarpus, metatarsus, and phalanges.) 4. When an epiphysis is ossified from more than one centre, coalescence takes place between the separate ossific nuclei before the epiphysis unites with the shaft. Highly suggestive, too, are the following propositions — That ossification first commences in the epiphysis which ultimately acquires the largest relative propor- tion to the rest of the bone, and that the ossification of the epiphysis is also correlated with its functional importance. In cases of long bones with only one epiphysis, the epiphysis is placed at the end of the bone where there is most movement. THE VERTEBRAL COLUIVIN. The vertebral column (columna vertebralis) of man consists of thirty-three superposed segments or vertebrae. In the adult, certain of these vertebrae have become fused together in the process of growth to form bones, the segmental 76 OSTEOLOGY. arrangement of which is somewhat obscured, though even in their fully- developed condition sufficient evidence remains to demonstrate their com- pound nature. The vertebrse so blended are termed the fixed or false vertebrae, whilst those between which osseous union has not taken place are described as the movable or true vertebrae. This fusion of the vertebral segments is met with at either extremity of the vertebral column, more particularly below, where the column is modified to adapt it for union with the girdle of the lower limb, and also in the region of man's degenerated caudal appendage. But a partial union of the vertebral segments also takes place above, between the two highest vertebrae, in association with the mechanism necessary to provide for the movements of the head on the column. For descriptive purposes the vertebral column is subdivided according to the regions through which it passes. Thus the vertebrse are described as cervical (vertebrae cervicales), dorsal or thoracic (vertebrse thoracales), lumbar (vertebrse lumbales), sacral (vertebrae sacrales), and coccygeal (vertebrae caudales), according as they lie in the regions of the neck, back, loins, pelvis, and tail. The number of vertebrae met with in these regions is fairly constant, though, as will be hereafter pointed out, ^'ariations may occur in the number of the members of the different series. The vertebrae in man are thus apportioned — 7 cervical, 12 thoracic, 5 lumbar, 5 sacral, and 4 or 5 coccygeal ; the three former groups comprise the true or mov- able vertebrae, the two latter the false or fixed vertebrae. The vertebral formula may be thus expressed : — Movable or True Vertebrae. Fixed or False Vertebrae. Cervical. Thoracic. Lumbar. Sacral. Coccygeal. 7 12 5 5 4 =33. The vertebrae, though displaying great diversity of characters in the regions above enumerated, yet preserve certain features in common. All possess a solid part, centnim or body (corpus vertebrae) ; all have articular processes by which they articulate with their fellows ; most have muscular processes developed in connexion with them; whilst the majority display a vertebral or spinal foramen (foramen vertebrale) formed by the union of a bony arch (arcus vertebrae) with the body. These common characters may best be studied by selecting for description an intermediate member of the series. For this purpose one of the middle or lower thoracic vertebrae may be chosen. A typical vertebra may be described as consisting of a body or centrum (corpus vertebrae) composed of a mass of spongy bone, more or less cylindrical in form. The size and shape of the body is Hable to considerable variation according to the vertebra examined. The upper and lower surfaces of the body are very slightly concave from before backwards and from side to side, due to the thickening of the bone around its margins. In the recent condition these surfaces afford attachment for the intervertebral discs which are placed like pads between the bodies of the movable members of the series. The circumference of the body, formed as it is of more compact bone than the interior, is usually slightly concave from above downwards, though it becomes flat behind, where the body forms the anterior boundary of the spinal or vertebral foramen, at which point it is usually shghtly concave from side to side. The vertical surfaces of the body are pierced liere and there by foramina for the passage of nutrient vessels, more particularly on the posterior surface, where a depression of considerable size receives the openings of the canals through which some of the veins which drain the body of the bone escape. Connected with the body posteriorly there is a bony vertebral arch (arcus vertebrae), which, by its union with the body, encloses a foramen of variable size, the vertebral foramen (foramen vertebrale). When the vertebrse are placed on the top of each other these foramina form with the uniting ligaments a con- tinuous canal — spinal or neural canal — in which the spinal cord with its coverings is lodged. The vertebral arch, which is formed by the union of the pedicles ^ and laminae, besides enclosing the spinal foramen, also supports the spinous and trans- 1 I retaiu this term in place of the cumbrous radix arcus vertebrse or "root of the vertebral arch " of the B.N. A., classification." — A.T. THE VEETEBKAL COLUMN. 77 Superior articular process Pedicle Facet for tubercle of rib (Fovea co^talis transversalis) Transverse, process Demi-facet for head of rib (Fovea costalis superior) Body verse processes, which may be regarded as a series of levers to which muscles are attached, whilst others are articular and assist in uniting the different vertebrse together by means of a series of movable joints. The pedicles are the bars of bone which pass from the back of the body of the vertebra? on either side to the points where the articular processes are united to the arch. These roots are compressed laterally, and have rounded superior and in- ferior borders. Since the vertical breadth of the pedicles is not as great as the thickness of the body to which they are attached, it follows that when the vertebrae are placed one above the other a series of in- tervals is left between the pedicles of the different vertebrae. These spaces, enclosed in front by the bodies of the vertebras and their intervertebral discs, and behind by the coaptation of the articular pro- cesses, form a series of holes com- municating with the neural or spinal canal ; these are called the inter- vertebral foramina (foramina inter- vertebralia), and allow the trans- mission of spinal nerves and vessels. Demi-facet for head of rib (Fovea costalis inferior) Spinous process FticGt for As each intervertebral foramen is tubercle of rib cea cos- talis tran: versalis) Superior articular process Fig. 57. — Fifth Thoracic Vebtebra, (A) as viewed from the right side, (B) as viewed from above. bounded above and below by a (pove pedicle, the grooved surfaces in correspondence with the upper and lower borders of the pedicles are called the upper and lower inter- oemi-facet fJr'he'l vertebral grooves or notches (incisura of nb (Fovea cost Uw . . ... inferioi ) vertebralis superior et mferior). Posteriorly, the two pedicles are united by two somewhat flattened plates of bone — ^the laminae, which converge towards the middle line, and become fused with the root of the projecting spinous process (pro- cessus spinosus). The breadth of the laminge and their sloping arrangement are such, that when the vertebrae are articulated together they leave little space between them, thus enclosing fairly completely the neural canal, of which they form the posterior wall. The edges and inner surfaces of the laminae are rough for the attachment of the ligaments which bind them together. The muscular processes are three in number, viz. two transverse processes — one on either side — and one central or median, the spinous process. The former (processus transversus) project laterally on either side from the arch at the point where the pedicle joins the lamina. The latter (processus spinosus) extends back- wards in the middle line from the point of fusion of the lamina;. The spinous processes display much variety of length and form. The articular processes (zygapophyses), four in number, are arranged in pairs — one superior, the other inferior ; the former are placed on the upper surface of the arch where the pedicles and laminte join, the latter below the arch in correspondence with the superior. Whilst differing much in the direction of their articular surfaces, the upper have generally a backward tendency, whilst the lower incline forwards. 78 OSTEOLOaY. THE TRUE OR MOVABLE VERTEBR/E. The Cervical Vertebrae. The cervical vertebrae (vertebrae cervicales), seven in number, can be readily distinguished from all the other vertebras by the fact that their transverse pro- cesses are pierced by a foramen. The two highest, and the lowest, require special description ; the remaining four conform to a common type. Their bodies, the smallest of all the true vertebrse, are oblong in shape, the transverse diameter being much longer than the antero-posterior width. The upper surface, which slopes from behind forwards and downwards, is concave from side to side, owing to the marked projection of its lateral margins. Its anterior lip is rounded oS", whilst its posterior edge is sharply defined. The inferior surface, which is more or less saddle-shaped, is directed downwards and backwards. It is convex from side to side, and concave from before backwards, with a slight rounding off of the projecting anterior lip. The vertical diameter of the body is small in proportion to its width. The anterior surface is flat in the middle line, but furrowed laterally. The posterior surface, which is rough and pierced by many small foramina, is flat from side to side and above downwards ; it Bifid spine Superior articular process Superior notcli Vertebrarterial foramen Inferior notch Inferior articular process Vertebrarterial foramen Anterior tubercle A Spinous process Fig. 58.— Fourth Cervical Vertebra, (A) from above, and (B) from the right side. forms in its entire extent the anterior wall of the spinal foramen. The lateral aspects of the body, particularly in their upper parts, are fused with the costal parts of the transverse processes, and form the inner wall of the vertebrarterial or transverse foramen (foramen transversarium). The pedicles which spring from the posterior half of the lateral aspects of the body, about equidistant from their upper and lower margins, are directed horizontally backwards and outwards. The superior and inferior notches are nearly equal in depth. The laminse are long, and about as wide as the body of the bone is thick. The spinal foramen is larger than in the thoracic and lumbar regions ; its shape is triangular, or more nearly semilunar. The transverse processes, so called, are pierced by the vertebrarterial or transverse foramen fforamen transversarium). They consist of two parts — the part behind the foramen, which springs from the neural arch and is the true transverse process, and the part in front, which is homologous with the ribs in the thoracic portion of the column. These two processes, united externally by a bridge of bone, which thus converts the interval between them into a foramen, terminate in two tubercles, known respectively as the anterior and posterior tubercles (tuberculum anterius et posterius). The general direction of tliese processes is laterally, slightly forwards, and a little downwards, the anterior tubercles lying medial to the posterior. The two tubercles are se])arated above by a groove directed laterally, downwards, and forwards ; along this tlie s])inal nerve trunk passes. The vertebrarterial foramen (foramen transversarium), often subdivided by a spicule of bone, is traversed by the vertebral artery and vein in the upper six vertebrte. The spinous processes, which are directed downwards, are short, compressed vertically, and bifid. The articular processes are supported on cylindrical masses of bone fused with the arch where THE CERVICAL VERTEBRA.. 79 the pedicles and lamintB join. These cylinders are sliced away obliquely above and below, so that the superior articular facets, more or less circular in form, are directed upwards and backwards, whilst the corresponding inferior surfaces are turned downwards and forwards. First Cervical Vertebra or Atlas. — This bone may be readily recognised by the absence of the body and spinous process. It consists of two lateral masses (massae laterales), which support the articular and transverse processes. The lateral masses are themselves united by two curved bars of bone, the anterior and posterior arches, of which the former is the stouter and shorter. Each lateral mass is irregularly six- sided, and so placed that it lies closer to its fellow of the opposite side in front than behind. Its upper surface is excavated to form an elongated oval facet (fovea articularis superior), concave from before backwards, and inclined obliquely inwards; not infrequently this articular surface displays indications of division into two parts. These facets are for the reception of the condyles of the occipital bone. The inferior articular facets (fovese articulares inferiores) are placed on the under surfaces of the lateral masses. Of circular form, they display a slight side- to-side concavity, though g flat in the antero-posterior direction. Their disposi- tion is such that their sur- faces incline downwards and slightly inwards. They rest on the superior ar- ticular processes of the second cervical vertebra. Springing from the anterior and inner aspects of the lateral masses, and uniting them in .front, is a curved bar of bone, the anterior arch (arcus anterior) ; com- pressed on either side, this is thickened centrally so as to form on its anterior aspect the rounded anterior tubercle (tuberculum an- ^erius). In correspondence with this on the posterior surface of this arch is a circular facet (fovea dentis) for articulation with the odontoid process (dens) of the second cervical vertebra (axis). The inner surface of the lateral mass is rough and irregular, displaying a little tubercle for the attachment of the transverse ligament which passes across the space included between the two lateral masses and the anterior arch, thus holding the odontoid process of the axis in position. Behind each tubercle there is usually a deep pit, opening into the bottom of which are the canals for the nutrient vessels. Laterally to the lateral mass, and principally from its upper half, the transverse process arises by two roots which include between them the vertebrarterial foramen. The transverse process is long, obliquely compressed, and down-turned ; the anterior and posterior tubercles have fused to form one mass. The posterior arcb arises in part from the posterior surface of the lateral mass, and in part from the posterior root of the transverse process. Compressed from above downwards anteriorly, where it bounds a groove which curves around the posterior aspect of the superior articular process, which groove is also continuous externally with the vertebrarterial foramen, the posterior arch becomes thicker mesially, at which point it displays posteriorly a rough irregular projection — the posterior tubercle (tuberculum posterius), the feeble representative of the spinous process. A prominent little tubercle, arising from the posterior extremity of the superior articular process, overhangs the groove above mentioned, and not in- frequently becomes developed so as to form a bridge of bone across it, converting the groove into a canal through which the vertebral artery and the first cervical or Fig. 59.- Posterior arch. Transverse process. Tubercle for transverse ligament. Anterior arch. Anterior tubercle. -The Atlas from Above. 6. Surface for articulation with odontoid process. 7. Superior articular process. 8. Foramen for vertebral artery. 9. Groove for vertebral artery. 10. Posterior tubercle. 80 OSTEOLOGY. suboccipital ^ nerve pass — a condition normally met with in many animals. It is noteworthy that the grooves traversed by the two highest spinal nerves lie behind the articular processes, in place of in front, as in other parts of the column. The ring formed by the lateral masses and the anterior and posterior arches is of irregular outline. The anterior part, cut off from the rest by the transverse ligament, serves for the lodgment of the odontoid process of the axis ; the larger part behind corresponds to the upper part of the neural or spinal canal. Second Cervical Vertebra, Axis, or Epistropheus. — This is characterised by the presence of the tooth-like dens (odontoid process) which projects upwards from the superior surface of the body. Slightly constricted where it joins the body, the odontoid process tapers to a blunt point superiorly, on the sides of which there are surfaces for the attachment of the odontoid or check (alar) ligaments. When the atlas and axis are articulated this process lies behind the anterior arch of the atlas, and displays on its anterior surface an oval or circular facet which rests on that on the posterior surface of the anterior arch of the atlas. On the posterior aspect of the neck of the odontoid process there is a shallow groove in which lies the transverse ligament which holds it in position. The anterior surface of the body has a raised triangular surface, which ends Odontoid process (dens) Groove for transverse ligament Superior articular surface Odontoid process (dens) Articular surface for anterior arch of atlas Foiamen foi vertebral artery Inferior pre articular ^ )cess m spine A Foramen for verte' Inferior articular process bral artery Transverse process B Fig. 60.— Axis or Epistkopheus, (A) from behind and ahove, (B) from the left side. superiorly in a ridge passing upwards to the neck of the odontoid process. The pedicles are concealed above by the superior articular processes ; inferiorly, they are deeply grooved. The laminae — prismatic on section — are thick and strong, ending in a stout, broad, and bifid spinous process, the under surface of which is deeply grooved, whilst its sides meet superiorly in a ridge. Placed over the pedicles and the anterior root of the transverse processes are the superior articular surfaces. These are more or less circular in shape, shghtly convex from before backwards, flat from side to side, and are directed upwards and a little outwards. They are channelled inferiorly by the vertebrarterial foramina which turn outwards beneath them. The grooves by which the second cervical nerves (great occipital) leave the neural canal cross the laminee immediately behind the superior articular processes. The inferior articular processes agree in form and position with those of the remaining members of the series, and are placed behind the inferior inter- vertebral notches. The transverse process is markedly down-turned, with a single pointed extremity. The sixth cervical vertebra often displays an enlargement of the anterior tubercle on the transverse ])rocess, called the carotid tubercle (tuberculum caroticum) from the circumstance that the carotid artery maybe conveniently compressed against it. It is necessary to add, however, that tbe tubercle is not always well developed. The seventh cervical vertebra (vertebra prominens) receives the latter name from the outstanding nature of its spinous process, which ends in a single broad tubercle. ' Under the B.N. A. nomenclature the name is given to the whole of the first cervical nerve. THORACIC VERTEBR-^. 81 This forms a well-marked surface projection at the back of the root of the neck. The transverse processes are broad, being flattened from above downwards ; they project considerably beyond those of the sixth. The maximum width between their extremities agrees with that between the transverse processes of the atlas, these two constituting the widest members of the cervical series. The anterior tubercle is very small and is placed near the body. The vertebrarterial foramen is small and does not as a rule transmit the vertebral artery. Usually a small vein passes through it. Not infrequently the costal element is separate from the true transverse process, thus constituting a cervical rib. Thoracic Vertebrae. The thoracic or dorsal vertebrae (vertebrae thoracales), twelve in number, are distinguished by having facets on the sides of their bodies for the heads of the ribs, and in most instances also articular surfaces on their transverse processes for the tubercles of the ribs (Fig. 57, p. 77). The body is described as characteristically heart-shaped, though in the upper and lower members of the series it undergoes transition to the typical forms of the cervical and lumbar vertebrae, respectively. Its antero- posterior and transverse widths are nearly equal ; the latter is greatest in line with the facets for the heads of the rib. The bodies are slightly thicker behind than in front, thus adapting themselves to the anterior concavity which the column displays in this region. The bodies of the second to the ninth thoracic vertebrae inclusive, each possess four costal demi-facets (fovea costalis superior et inferior) a superior pair placed on the upper margin of the body, close to the junction of the pedicle with the centrum, and an inferior pair situated on the lower edge, close to and in front of the inferior intervertebral grooves. When contiguous vertebrae are articulated, the upper pair of demi-facets of the lower vertebra coincide with the lower demi-facets of the higher vertebra, and, together with the intervening intervertebral disc, form an articular cup for the reception of the head of a rib. Of these facets on the body the upper pair are the primary articular surfaces for the head of the rib ; the lower are only acquired secondai'ily. Moreover, these facets, though apparently placed on the body, are in reality developed on the sides of the pedicles behind the line of union of the pedicles with the centrum (neuro-central synchondrosis), as will be explained hereafter. • The pedicles are short and thick, and directed backwards and slightly upwards. The superior vertebral notch is faintly marked ; the inferior is deep. The laminae are broad, flat, and sloping, having sharp upper and lower margins. When the vertebrae are superposed the latter overlap the former in an imbricated manner. The spinal foramen is smaller than in the cervical and lumbar regions, and nearly circular in shape. The spinous processes vary in length and direction, being shorter and more horizontal in the upper and lower members of the series, longest and most oblique in direction towards the middle of this part of the column. Nearly all have a down- ward inclination, and are so arranged that they overlap one another. Triangular in section where they spring from the neural arch, they become laterally compressed towards their extremities, which are capped by more or less distinct tubercles. The transverse processes are directed backwards and outwards, and a little upwards. They gradually decrease in size and length from above downwards. Each has a somewhat expanded extremity, the anterior surface of which, in the case of the upper ten vertebrae, is hollowed out in the form of a circular facet for articulation with the tubercle of the rib which rests in the upper demi-facet of the vertebra to which the transverse process belongs. The superior articular processes are vertical, and have their surfaces directed backwards, slightly upwards, and a little outwards; the inferior, correspondingly forwards, downwards, and inwards. Certain of the thoracic vertebrae display characters by which they can readily be recognised. These are the first, tenth, eleventh, and twelfth, and sometimes the ninth. The first thoracic vertebra resembles the seventh cervical in the shape of its 82 OSTEOLOGIY. body, and the length and direction of its spine. There is an entire facet on either side of the body for the head of the first rib, and one demi- facet on each side at the lower border of its body, to complete the socket for the head of the second rib. Its transverse processes are long, and the superior interverte- bral notch is better marked than in other members of the thoracic series. The superior articular surfaces are directed backwards and upwards, not outwards as in the lower members of the series. The ninth thoracic vertebra occasionally has only the upper pair of demi- facets on its body ; at other times it conforms to the usual type. The tenth thoracic ver- tebra may have only one complete costal facet on each side for the X. rib, though sometimes the articular socket may be completed by the ninth dorsal vertebra. The facet on the transverse pro- cess is generally small, and sometimes absent. The eleventh thoracic vertebra has a complete circular facet on the outer side of each pedicle for ar- ticulation with the XI. rib. Its transverse processes are short and stunted, and have no facets. The twelfth thoracic vertebra has a single facet on the pedicle on each side for the XII. rib. Its trans- verse processes, short and stunted, have no facets, and are broken up into smaller tubercles, called respectively the external, superior, and inferior tubercles. These are homologous with the Fig. 61. — First, Ninth, Tenth, Eleventh, and Twelfth Thoracic Vertebra fhom the Left Side. 1. Inferior articular process with out-turned facet. 2. Single facet for head of XII. rib ; no facet on transverse process. 3. Single facet for head of XI. rib ; no facet on transverse process. 4. Single or demi-facet for head of X. rib. .5. Occasional demi-facet for head of X. rib. 6. Demi - facet for head of IX. rib. 7. Demi-facet for head of II. ril). 10. Single facet for head of I. rib. Facet on transverse process for tuberosity of I. rib. Facet on transverse process for tuberosity of IX. rib. Facet ou transverse process for transvcrsc, mammillary, and tuberosity of X rib, in this acccssory proccsses of the particular instance well , , , ^ t t marked. lumbar vertebrse. indica- iiperior'^ Tuberclus f M.-uiiniillary. tioUS of tllCSC uferior I '■'°'\'^- M«:'=«««o'-y. J^r:"r:n:rar. the tenth and eleventh thoracic vertebrse. The twelfth thoracic vertebra may usually be distinguished from the eleventh by the arrangement of its inferior articular processes, which resemble those of 11. processes may also be met with in E. External LUMBAR VP]RTEBE^. 83 Inferior articular process Maminillary process Accessoiv process y fiaiisverse process Superior articular process the lumbar series in being out-turned ; but the eleventh occasionally displays the same arrangement, in which case it is not always easy to distinguish between them. Lumbar Vertebrae. The lumbar vertebrae (vertebrae lumbales), five in number, are the largest of the movable vertebrse. They have no costal articular facets, nor are their trans- verse processes pierced by a foramen. In this way they can be readily dis- tinguished from the mem- bers of the cervical and ' '"'"^ thoracic series. The body is kidney- shaped in outline, and of large size, exhibiting a gradual transition from the thoracic form in the higher segments. The transverse diameter is usually about a half greater than the antero- posterior width. The anterior vertical thickness is slightly greater than the posterior, being thus adapted to the anterior convex curve of the column in this region. The pedicles, directed horizontally backwards, are short and stout ; the superior notches are shallow, but deeper than in the thoracic region ; the inferior grooves are deep. The laminae are broad and nearly vertical, sloping but little. They support on their lower margins the inferior articular processes. The spinal foramen is large and triangular. The spinous processes, spatula shaped, with a thickened posterior mar- gin, project backwards and slightly downwards. The transverse processes, more slender than in the thor- acic region, pass horizon- tally outwards, with a slight backward inclination and usually with an upward tilt. Arising from the junction of the pedicles with the laminae in the higher members of the series, they tend to advance so as to become fused with the outer side of the pedicle and back of the body in the two lower lumbar vertebrae. In these latter vertebrae the superior intervertebral grooves are carried obliquely across the upper surfaces of the bases of the transverse processes. The transverse processes lie in line with the lateral tubercles of the lower thoracic vertebrae, with which they are serially homologous, and are to be regarded as representing the costal element. Placed on their base posteriorly, and just external to and below the superior articular processes, are the Body Superior articular process Mammillary process Tians verse process Fig. 62.- Iiiferior articular process -Third Lumbar Vertebra, (A) from aliove, and (B) from the left side. 84 OSTEOLOGY. small accessory tubercles (processus accessorii) which are in series with the inferior tubercles of the lower thoracic vertebrae. The superior articular processes are stout, oval, curved plates of bone, fused in front with the pedicles and laminae, and having their concave articular surfaces vertical and in-turned. Externally, and on their posterior edge, the bone rises in the form of an elongated oval tubercle, the mam- millary process (processus mammillaris) ; these are in correspondence with the superior tubercles of the lower thoracic transverse processes. The inferior articular processes lie on either side of the root of the spinous process, supported on the inferior margin of the laminse. Their articular surfaces, oval in outline, convex from side to side, and plane from above downwards, are out-turned. The inferior articular processes are much closer together than the superior ; so that when the vertebrae are articulated the superior articular processes of the lower vertebra embrace the inferior articular processes of the higher vertebra. The fifth lumbar vertebra is characterised by the size of its body, which is the largest of all the vertebrae. Further, the under surface of the body is cut away at the expense of its posterior part : hence the thickness of the centrum in front much exceeds that of the vertical diameter behind. By its articulation with the first sacral segment the lower border of the body of this bone assists in the formation of the sacro-vertebral angle. The transverse process is pyra- midal in form, and stouter than those of the other lumbar vertebrae. It arises by a broad base from the side of the back of the body, as well as from the pedicle, and is directed outwards and a little backwards and upwards. Its upper surface is slightly grooved by the superior intervertebral notch. A deep notch separates it posteriorly from the superior articular processes, which are less in-turned than in the other members of the series, their articular surfaces being directed more backwards than inwards, and displaying less concavity. The inferior articular processes are further apart than is the case with the other members of the series, they lie in line with the superior. The spinous process is shorter and narrower than the other lumbar spines, particularly so in the female. The neural canal is somewhat compressed at its external angles. THE FALSE OR FIXED VERTEBRAE. The Sacrum. The sacrum (os sacrum), of roughly triangular shape, is formed normally by the fusion of five vertebrae. The anterior surface of the bone is slightly hollow from side to side and concave from above downwards, the curve being usually most pronounced opposite the third sacral segment. The central part corresponds to the l^odies of the sacral vertebrae, the lines of fusion of which are indicated by a series of four parallel ridges which cross the median part of the bone at gradually diminishing intervals from above downwards; externally, these ridges disappear on either side on the inner walls of the four anterior sacral foramina (foramina sacralia anteriora). The size of these holes decreases from above downwards. The upper and under border of each foramen is formed by a stout bar of bone, of which there are five on each side, corresponding in number with the vertebrae present. These unite externally so as to form the lateral mass (pars lateralis), thus en- closing the foramina to the outer side, though here the edge is not abrupt, but sloped so as to pass gradually into the canal. The large anterior divisions of the sacral nerves pass through these foramina and occupy the shallow grooves. The bone is broadest across the first sacral vertebra, tends to narrow opposite the second, and again usually increases in width opposite the third. When this condition is well marked, the edge has a notched appearance (sacral notch) which assists in the interlocking of the sacro-iliac joint ; this feature is common in the Simiidae and some of the lower races of mankind (Paterson). The surface of bone between and external to the first, second, third, and fourth foramina affords THE SAOKUM. 85 attachment to the fibres of origin of the piriformis, which may in some instances extend on to the bodies of the second and third segments (Adolphi), whilst on the edge lateral to and Ijelow the fourth foramen the coccygeus is inserted. The posterior surface is rough and irregular. Convex from aljove downwards it displays medially a crest (crista sacralis media) whereon are seen four elongated tubercles — the spines of the upper four sacral vertebrte. External to these the bone forms a groove — the sacral groove — the floor of which is made up of the con- Huent lamiiue of the corresponding vertebrae. In line with the intervals between the spines, and wider apart above than below, another series of tubercles is to be seen. These are due to the fusion of the articular processes of the sacral vertebrie, which thus form faint interrupted ridges on either side of the bone (cristas sacrales articulares). Normally, the spine of the lowest sacral segment is absent, and the Superior articular processes Transverse process of first sacral vertebra Anterior sacra foramen Inferior lateral anirlp. Groove for fifth sacral nerve Coccygeal articular surface Fig. 63. — The Sacrum (anterior view). laminse do not coalesce medially, thus leaving a gap in which the spinal canal is exposed (hiatus sacralis) ; whilst inferiorly the tubercles corresponding to the inferior articular processes of the last sacral vertebra form little down-projecting processes — the sacral cornua (cornua sacralia) — by means of which the sacrum is in part united to the coccyx. Just wide of the articular tubercles are the posterior sacral foramina (foramina sacralia posteriora), for the transmission of the posterior divisions of the sacral nerves. These are in correspondence with the anterior foramina, so that a probe can be passed directly through both openings ; but be it noted that the posterior are much smaller, and their margins much sharper, than is the case with the anterior. The surface of the lateral mass lateral to the posterior sacral foramina is rough and irregular, owing to the presence of four more or less elevated tubercles, which constitute the lateral ridges on either side of the bone (cristse sacrales laterales), and which are serially homologous with the true transverse processes of the lumbar vertebrae. The posterior surface of the bone furnishes an extensive surface for the origin of the erector spinse (sacro- spinalis), whilst the 6 86 OSTEOLOGY. edge of the bone lateral to the third and fourth foramen gives attachment to the glutaius maximns. The base of the bone displays features more in accordance with a typical vertebra. Centrally, and in front, is placed the body, the upper surface of which articulates with the last lumbar vertebra through the medium of an intervertebral disc. The anterior margin is thin and projecting, overhanging the general con- cavity of the front of the bone, and forming what is called the promontory (promon- torium). Behind the body, the spinal canal, of triangular form with slightly appressed sides, is seen, whilst posteriorly is the short spinous process forming the highest tubercle of the median crest. Spreading out from the sides, and partly from the back of the body on either side, is a fan-shaped mass of bone, the upper surface of which is slightly concave from side to side, and convex from above and behind Superior aperture of hacral canal Superior articular process Transverse process \ Posterior sacral foramen-^'''^ V Inferior lateral angle Sacial cornu nferior aperture of sacral canal Groove for fifth sacral nerve Coccygeal articular surface Fig. 64. — The Saceum (posterior view). downwards and forwards. This, the ala (ala sacralis), corresponds to the thick upper border of the lateral mass, and is formed, as will be explained hereafter, by elements which correspond to the pedicles and transverse processes of the sacral vertebrae, together with superadded structures— the sacral ribs. The lateral margin of the lateral mass, as seen i'rom aljove, is sharp and laterally convex, terminating behind in a x^rominent tubercle — the highest of the series of elevations seen on the posterior surface of the bone, which have been already described as serially homologous with the true transverse processes of the lumbar vertebrae. Fused with the back of each lateral mass, and separated from it laterally by a narrow but deep notch, is the superior articular process. This supports a vertical articular surface, which is of circular or oval form, and concave from side to side, having a general direction backwards and a little medially. The borders of the bone are thick above, where they articulate with the ilia, thin and tapering below, where they furnish attachments for the powerful sacro-sciatic (sacro-tuberous) ligaments. The iliac articular surfaces are described as auricular in COCCYX. 87 shape (fades auricularis), and overlie tlie lateral masses formed by the first three sacral vertebne, though this arrangement is liable to considerable variation. Behind the auricular surface the bone is rough and pitted by three distinct depressions for the attachment of the strong sacro- iliac ligaments. Inferiorly, the edge formed by the lateral masses of the fourth and fifth sacral vertebrae becomes gradually thinner, and at the inferior lateral angle changes its direction and sweeps inwards towards the body of the fifth sacral segment. The apex, or lower end of the sacrum, is formed by the small oval body of the fifth sacral vertebra, which articulates with the coccyx. The sacral canal follows the curve of the bone ; more or less triangular in shape above, it becomes appressed and flattened below. Inferiorly, its posterior wall is deficient owing to the imperfect ossification of the lamina3 of the fifth, and, it may be, of the fourth sacral segments. Passing obUquely downwards and laterally from this canal into the lateral masses on either side are the four pairs of intervertebral foramina, each of which is connected laterally with a V-shaped canal which terminates in front and behind in the anterior and posterior sacral foramina. The hinder limb of the V is shorter and narrower than the anterior. The female sacrum is proportionately broader than the male, its curves are liable to great individual variation, usually it is flattened above, and somewhat abruptly curved below as contrasted with the male sacrum in which the curve is more uniformly distributed throughout the bone. In the female the absolute depth of the curve is less than in the male. The variation in the proportions of the breadth to the length of the sacrum is expressed by the formula breadth x 100 = Sacral Index. Sacra with an index above length 100 are platyhieric and are generally characteristic of the higher races, those with an index below 100 are dolichohieric and are more commonly met with in the lower races of man. The average European index is 112"-4 for males and 116"8 for females Coccyx. The coccyx consists of four — sometimes five, less frequently three — rudimentary vertebrae, which tend to become fused. The first piece is larger than the others ; it has an oval hollow facet on its upper sur- face, which articulates with the body of the last sacral segment. Pos- teriorly, two processes, comua coccygea, which he in series with the articular processes of the sacrum, extend upwards and unite with the sacral comua, thus bridging over the notch for the exit of the fifth sacral nerve, and converting it into a foramen, the last of the intervertebral series. From the outer sides of the body project rudimentary transverse processes which may, or may not, unite with the sacrum close to the lower lateral angles; in the latter case the fifth anterior sacral foramina are enclosed. Inferiorly, the body of the bone articulates with the succeeding vertebra. The second coccygeal vertebra displays slight traces of a transverse process and the rudiments of pedicles. The succeeding segments are mere rounded or oval-shaped nodules of bone. Fusion between the lower elements occurs normally in middle life, whilst imion between the first and second segments occurs somewhat later. It is not unusual, however, to find 1. Transverse process 2. Transverse process Fig. 65. — The Coccyx. A. Posterior Surface. B. Anterior Surface. 5. Sacrum 6. Cornu. 3. Sacrum. 4. Cornu. 7. Transverse process. 8. Transverse process. 88 OSTEOLOGY. that the first coccygeal vertebra i*emains separate from the others. Though very variable, as a rule, fusion occurs more commonly in the male, and at an earlier age, than in the female. Szawlowski has recorded a case in which a curved process arose from the ventral surface of the first coccygeal segment. He regards this as possibly the homologue of a ventral arch {Anat. Anz. Jena, vol. xx. p. 320). From the posterior surface of the coccyx the glutseus maximns arises, whilst to it is attached the filum terminale of the spinal cord. To its lateral borders are attached the coccygei and levatores ani muscles, and from its tip spring the fibres of the sphincter ani. THE VERTEBRAL COLUIYIN AS A WHOLE. When all the vertebrse are articulated together, the resulting column displays certain characteristic features. The division of the column into a true or movable part, comprising the members of the cervical, thoracic, and lumbar series, and a false or fixed portion, including the sacrum and coccyx, can now be readily recognised. The vertebrae are so disposed that the centra or bodies form an interrupted column of solid parts in front, which constitutes the axis of support for the head and trunk ; whilst the neural arches behind provide a canal for the lodgment and protection of the spinal cord and its membranes. In the movable part of the column both the anterior supporting axis and the neural canal are liable to changes in their disposition owing to the movements of the head and trunk. Like the bodies and neural arches, the spinous and transverse processes are also superposed, and fall in line, forming three series of interrupted ridges — one (the spinous) placed centrally and behind, the others (the transverse) placed laterally. In this way two vertebral grooves are formed which lie between the central and lateral ridges. The floor of each groove is formed by the laminae and articular processes, and in these grooves are lodged the muscles which serve to support and control the movements of the column. Further, the column so constituted is seen to display certain curves in an antero- posterior direction. These curves are, of course, subject to very great variation according to the position of the trunk and head, and can only be satis- factorily studied in a fresh specimen ; but if care be exercised in the articulation of the vertebrae, the following characteristic features may be observed, assuming, of course, that the column is erect and the head so placed that the axis of vision is directed towards the horizon. There is a forward curve in the cervical region, which gradually merges with the backward thoracic curve ; this becomes con- tinuous below with an anterior convexity in the lumbar region, which ends more or less abruptly at the union of the fifth lumbar with the first sacral vertebra, where the sacrum slopes suddenly backwards, causing the column to form a marked projection — the sacro-vertebral angle. Below this, the anterior concavity of the front of the sacrum is directed downwards as well as forwards. Of these four curves, two — the thoracic and sacral — are primary, they alone exist during fcetal life ; whilst the cervical and lumbar forward curves only make their appearance after birth — the former being associated with the extension and elevation of the head, whilst the latter is developed in connexion with the use of the hind limb in the hyper-extended position, which in man is correlated with the assumption of the erect posture ; this curve, therefore, only appears after the child has begun to walk. For these reasons the cervical and lumbar curves are described as secondary and compensatory. Not infrequently there is a slight lateral curvature in the thoracic region, the convexity of the curve being usually directed towards the right side. This may be associated with a greater use of the muscles of the right upper limb, or may depend on the pressure exercised by the upper part of the thoracic aorta on the vertebne of the thoracic region, thus causing a slight lateral displacement, together with a flattening of the side of the fifth thoracic vertebra (impressio aortica) as was first pointed out by Wood (Journ. Anat. and Physiol, vol. iii.). Above and below this curve there are slight compensatory curves in the opposite direction. VERTEBEAL COLUMN AS A WHOLE. 89 •^ < The line which unites the tips of the spines is not a repetition of the curves formed by the bodies. This is due to the fact that the length and direction of the spines vary much in different regions ; thus in the neck, with the exception of the second, sixth, and seventh, the spines are all short (absent in the case of the atlas). In the thoracic region the spines, though long, are obliquely placed — a circumstance which much reduces their prominence ; that of the seventh thoracic vertebra is usually the longest and most slanting. Below this point the length of the spines gradually decreases, and their position more nearly approaches the horizontal. In the loins the spines have all a slight downward direction. The spines of the upper three or four sacral vertebrae form an osseous ridge with interrupted tubercles. Tlie ridge formed by the vertebral spines is an important determinant of the surface form, as it corresponds to the median furrow of the back, and here the indi\'idual spines may be felt and counted from the seventh cervical down to the sacral region. This is best done when the back is well bent forwards. Taken as a whole, the spines of the movable vertebrae in man have a downward inclination — a character which he shares with the anthropoid apes and a few other animals. This character serves to distinguish his column from tho.se of lower mammals in which the spines of the lumbar vertebrae are directed headwards towards the " centre of motion," which is usually situated near the hinder extremity of the thorax, where a vertebra is placed the direction of whose spine is vertical to the horizontally disposed column ; this vertebra is often referred to as the anticlinal vertebra. As viewed from the front, the vertebral bodies increase in width from the second cervical to the first thoracic ; thence a reduction in breadth takes place to the level of the fourth thoracic, below which there is a gradual increase in their transverse dia- meters until the sacrum is reached. Here a rapid reduction in width takes place, terminating inferiorly in the nodules of the coccyx. The transverse processes of the atlas are wide and outstanding. The succeeding four cervical vertebrae have transverse processes of nearly equal width ; the seventh, however, displays a marked increase in its transverse diameter, and is about equal in width to the first thoracic vertebra. Below this a gradual and regular diminution in width characterises the trans- verse processes of the thoracic vertebrae, until ia the case of the eleventh and twelfth they are merely represented by the small lateral tubercles. In the lumbar region the transverse processes again appear outstanding, and of nearly equal length. The transverse diameter of the lateral mass of gi J the first sacral vertebra forms the widest part of the 5 |, I column. Below this, a decrease in width occurs until Fig. 66. the level of the third sacral segment is reached, at which point the transverse diameter is somewhat abruptly diminished, a reduction in width which is further suddenly accentuated opposite the fifth sacral segment. As viewed from the side, the bodies display a gradual increase in their antero- posterior width until the second lumbar vertebra is reached, below which, this 6a ■% < C?''-^ ^Aili Vertebral Coli'mx FROM THE Left Side. 90 OSTEOLOGY. diameter is slightly reduced. In the sacral region the reduction in this diameter is great in the first and second sacral segments, more gradual and less marked in the last three segments. The facets for the heads of the ribs in the upper thoracic region lie on the sides of the bodies ; those for the tenth, eleventh, and twelfth are placed ^sABtiP^' farther back on the pedicles. ^- . 1 „'^ , , , -1 1 mi Fig. 113.— The Hyoid Bone as seen this aspect irom the thyreo-hyoid membrane. Ihe from the Front. upper border, usually described with the anterior surface, is broad ; it is separated from the anterior aspect by a transverse ridge, behind which are the impressions for the attachment of the genio-hyoid muscles. Its hinder edge is thin and sharp ; to this, above, are attached the genio-giossi, whilst behind and below the thyreo-hyoid membrane is connected with it. The inferior border is well defined and narrow ; it serves for the attachment of the omo-hyoid, sterno-hyoid, thyreo-hyoid, and stylo-hyoid muscles. The great cornua are connected on either side with the lateral parts of the body. At first, union is effected by synchondroses, which, however, ultimately ossify. These cornua curve backwards as well as upwards, and terminate in more or less rounded and expanded extremities. Compressed laterally, they serve for the attachments laterally of the thyreo-hyoid and hyo-glossi muscles, and the middle 146 OSTEOLOGY. constrictor of the pharynx from below upwards, whilst medially they are con- nected with the lateral expansions of the thyreo-hyoid membrane, the free edges of which are somewhat thickened, and connect the extremities of the great cornua with the ends of the superior cornua of the thyreoid cartilage below. The lesser cornua, frequently cartilaginous in part, are about the size of grains of wheat. They rest upon the upper surface of the bone at the junctions of the great cornua with the body. In youth they are separated from, but in advanced life become ossified with, the rest of the bone, from which they are directed upwards, backwards, and a little outwards. Their summits are connected with the stylo- hyoid ligaments ; they also serve for the attachment of muscles. Connexions. — The hyoid is slung from the styloid processes of the temporal bones by the stylo-hyoid ligaments. Inferioiiy it is connected with the thyreoid cartilage of the larynx by the thyreo-hyoid ligaments and membrane. Posteriorly it is intimately associated with the epiglottis. Ossification. — In considering the development of the hyoid bone it is necessary to refer to the arrangement and disposition of the cartilaginous bars of the second and third visceral arches. That of the second visceral arch, the hyoid bar — or Reichert's cartilage, as it is sometimes called — is united above to the petrous part of the temporal, whilst ventrally it is joined to its fellow of the opposite side by an independent medial cartilage. Chondrifica- tion of the third visceral arch only occurs towards its ventral extremity, forming what is known as the thyreo-hyoid bar. This also unites with the medial cartilage above mentioned. In these cartilaginous processes ossific centres appear in certain definite situations. Towards the end of foetal life a single centre (by some authorities regarded as primarily double) appears in the medial cartilage, and forms the body of the bone (basihyal). About the same time ossification begins in the lower ends of the thyreo-hyoid bars, and from these the great cornua are developed (thyreo-hyals). During the first year the lower ends of the hyoid bars begin to ossify and form the lesser cornua (cerato-hyals). The cephalic ends of the same cartilages meanwhile ossify to form the styloid process (stylohyal ; see p. 120) on either side and one of the auditory ossicles called the stapes, whilst the intervening portions of cartilage undergo resorption and become converted into the fibrous tissue of the stylo-hyoid ligaments, which in the adult connect the lesser cornua with the styloid processes of the temporal bone. The great cornua fuse with the body in middle life ; the lesser cornua only at a more advanced period. Variations in the course of development lead to interesting anomalies of the hyoid apparatus. The lesser cornua may be unduly long or the stylo-hyoid ligament may be bony ; in this case the cartilage has not undergone resorption, but has passed on to the further stage of ossification, thus forming an epihyal element comparable to that in the dog. The ossified stylo-hyoid ligament, as felt through the pharyngeal wall, may be mistaken for a foreign body. (Farmer, G. W. S., Brit. Med. Journ. 1900, vol. i. p. 1405.) THE SKULL AS A WHOLE. The skull as a whole may be studied as seen from the front (norma frontalis), from the side (norma lateralis), from the back (norma occipitalis), from above (norma verticalis), and from below (norma basalis). Norma Frontalis. In front, the smooth convexity of the frontal bone limits this region above, whilst inferiorly, when the lower jaw is disarticulated, the teeth of the upper jaw form its lower boundary. The large openings of the orbits are seen on either side ; whilst placed medially and at a somewhat lower level is the anterior nasal aperture (apertura pyriformis) leading into the nasal fossae. The frontal region, convex from above downwards and from side to side, is limited laterally by two ridges, which are the anterior extremities of the temporal lines. Superiorly the fulness of the bone blends with the convexity of the vertex. Inferiorly the frontal bone forms on either side the arched superior border of the orbit (margo supraorbitalis). The space between these borders corresponds to the root of the nose, and here are seen the sutures which unite the frontal with the nasal bones in the middle line, and with the frontal process of the maxilla on NOEMA FRONTALIS OF THE SKULL. 147 either side, called the naso-frontal and fronto-maxillary sutures respectively. The orbital arch is thin and sharp laterally, but becomes thick and more rounded towards its medial side, wliere it forms the medial angular process and unites with the frontal process of the maxilla and the lacrimal bone on the medial wall of the orbit. This arched border is interrupted towards the medial side by a notch (incisura supraorbitalis), sometimes converted into a foramen, for the transmission of the supraorbital nerve and artery. In the middle line, just above the naso-frontal suture, there is often the remains of a median suture (sutura frontalis), which marks the fusion of the two halves from which the bone is primarily ossified. Here also a prominence, of variable extent — the glabella — is met with ; from this there passes out on either side above and over the orbital margin a projection called the superciliary ridge (arcus superciliaris). The orbital fossae, of more or less conical form, display a tendency to assume the shape of four-sided pyramids by the flattening of the superior, inferior, and lateral walls. The base, which is directed forwards and a little laterally, corresponds to the orbital aperture. The shape of this is liable to individual and racial variations, being nearly circular in the Mongoloid type, whilst it displays a more or less quadrangular form in Australoid skulls. The upper margin, as has been already stated, is formed by the frontal bone between the medial and lateral angular processes. The lateral, and about half the lower, margins are formed by the sharp curved edge between the facial and orbital surfaces of the malar bone. The medial border and the remainder of the lower margin are determined by the lateral surface of the frontal process of the maxilla, and the sharp edge separating the facial from the orbital surface of the same bone. Three sutures interrupt the continuity of the orbital margin — zygomatico-frontal laterally, the fronto-maxillary medially, both lying about the same level, and the zygomatico-maxillary inferiorly. The apex of the space is directed backwards and medially, so that the medial walls of the two orbits lie nearly parallel to each other, whilst the lateral walls are so disposed as to form almost a right angle with each other. The depth of the orbit measures, on an average, about two inches (5 cm.). At the apex there are two openings ; the larger, known as the sphenoidal fissure (fissura orbitalis superior), passes from the apex of the space laterally and a little upwards for the distance of three-quarters of an inch or so, between the roof and lateral wall of the orbit. The medial third of this fissure is broad and of circular form. Laterally it is consider- ably reduced in width. Through this the third, fourth, ophthalmic division of the fifth, and the sixth nerves enter the orbit, whilst the ophthalmic veins pass backwards through it. Above and medial to the medial end of the sphenoidal fissure there is a smaller circular opening, the optic foramen (foramen opticum), for the transmission of the optic nerve and ophthalmic artery. The roof of the orbit, which is very thin and brittle towards its centre, is formed in front by the orbital plate of the frontal bone (pars orbitalis) and behind by a small triangular piece of the lesser wing of the sphenoid, which surrounds the optic foramen and forms the upper border of the sphenoidal fissure. Laterally this surface is separated from the lateral wall by the sphenoidal fissure posteriorly, anteriorly by an irregular suture between the orbital part of the frontal and the upper margin of the orbital surface of the great wing of the sphenoid, lateral to which the zygomatic process of the frontal articulates with the zygo- matic bone. Medially the roof is marked off from the medial wall by a suture, more or less horizontal in direction, between the orbital plate of the frontal and the following bones in order from before backwards, viz. the frontal process of the maxilla, the lacrimal bone, and the os planum of the ethmoid. In the suture between the last-mentioned bone and the frontal there are two foramina, the anterior and posterior ethmoidal canals (foramen ethmoidale anterius et posterius) ; both transmit ethmoidal vessels — the anterior affording passage to the nasal nerve as well. The roof is concave from side to side, and to some extent also from before backwards. About midway between the fronto- maxillary suture and the supraorbital notch or foramen, but within the margin of the orbit, there is a small depression, occasionally replaced by a spine (fovea vel, spina trochlearis), for the attachment of the cartilaginous pulley 148 OSTEOLOGY. of tlie superior oblique muscle of the eyeball. Under cover of the zygomatic The Fio. 114. — Norma Fuoxtalis uf the Skull. nasal Vjones, os planum of the ethmoid, vomer, inferior turbinals, zygomatic, and parietal bones are coloured red. The sphenoid, lacrimal, perpendicular plate and middle turbinals of ethmoid, and the maxilla, are coloured l)lue. The maxilla; are coloured yellow. The frontal and temporal bones aud the orbital process of the palate bone (in the orbit on the left side of the figure) are left uncoloured. 9. 10. 11. 12. 13. Mental protuberance. Body of lower jaw. Ramus of lower jaw. Anterior nasal spine. Canine fossa. Infraorbital canal. Zygomatic canal. Orbital surface of maxilla. Temporal fossa. Os planum of ethmoid. Sphenoidal fissure. Lacrimal bone and groove. Optic foramen. 14. Orbital canals. 15. Temporal ridge. 16. Supraorbital notch. 17. Glabella. 18. P'lontal eminence. 19. Superciliary ridge. 20. Parietal bone. 21. Pronto-nasal suture. 22. Pterion. 23. Great wing of sphenoid. 24. Orbital surface of great wing of sphenoid. 25. Squamous partofthetemporal. 26. Left nasal bone. 27. Zygomatic bone. 28. S])heno-maxillary fissure. 29. Zygomatic arch. 30. Anterior nasal aperture, displaying nasal septum and inferior and middle turbinated bones. 31. Mastoid process. 32. Incisor fossa. 33. Angle of jaw. 34. Mental foramen. 35. Symphysis menti. process the roof is more deeply excavated, forming a shallow fossa for the lodg- NOEMA FEONTALIS OF THE SKULL. 149 ment of the lacrimal gland (fossa glandulae lacrimalis). In front, the roof separates the orbit from the frontal sinus, and along its medial border it is in relation with the ethmoidal air-cells. The relation to these air spaces is variable, depending on the development and size of the sinuses. The rest of the roof, which is very thin, forms by its upper surface the floor of the anterior cranial fossa, in which are lodged the frontal lobes of the cerebrum. The floor of the orbit is formed by the orbital plate of the maxilla, together with part of the orbital surface of the zygomatic bone, and a small triangular piece of bone, the orbital process of the palate, which is wedged in posteriorly. Laterally, for three-quarters of its length posteriorly, it is separated from the lateral wall, which is here formed by the great wing of the sphenoid, by a cleft called the spbeno - maxillary fissure (fissura orbitalis inferior). Through this there pass the superior maxillary division of the fifth nerve on its way to the infraorbital canal, the orbital or temporo-malar branch of the same nerve, the infraorbital vessels, a branch connecting the inferior ophthalmic vein with the pterygoid plexus, and some twigs from Meckel's (spheno-palatine) ganglion. By means of this fissure the orbit communicates with the spheno- maxillary (or pterygo- palatine) fossa behind, and the infra-temporal (or zygomatic) fossa to the lateral side, though in the recent condition the fissure is bridged over by the involuntary orbitalis muscle of Mliller. Medially the floor is limited from behind forwards by the suture between the following bones, viz. the orbital process of the palate below with the body of the sphenoid above and behind, and the os planum of the ethmoid above and in front — anterior to which the orbital plate of the maxilla below articulates with the os planum of the ethmoid and the lacrimal above and in front. At the anterior extremity of this line of sutures the medial edge of the orbital plate of the maxilla is notched and free between the point where it articulates :with the lacrimal posteriorly and the part from which its frontal process rises. Here it forms the lateral edge of a canal, down which the mem- branous nasal duct passes to the nose. The floor of the orbit is thin behind and at the sides, but thicker in front where it blends with the orbital margin. Passing in a sagittal direction through its substance is the infraorbital canal, the roof of which is usually deficient behind, where it becomes continuous with a broad, shallow groove, which leads forwards from the anterior margin of the spheno-maxillary fissure. This canal (canalis infraorbitalis) opens on the facial surface of the maxilla immediately below the orbital margin (foramen infraorbitale) and transmits the superior maxillary division of the fifth nerve, together with the infraorbital vessels. The floor forms a thin partition which separates the orbit from the antrum or sinus of the maxilla, which lies beneath it. Medially it completes the lower ethmoidal air-cells, and separates the orbit from the middle meatus of the nasal fossae. The lateral wall of the orbit, which is the strongest, is formed by the orbital surface of the great wing of the sphenoid and the upper part of the orbital surface of the zygomatic bone. Above it, behind, is the sphenoidal fissure (superior orbital fissure), whilst below, and extending much farther forward, is the spheno- maxillary fissure (inferior orbital fissure). The anterior margin of the lateral wall is stout and formed by the zygomatic bone, behind which, formed in part by the orbital process of the zygomatic bone and the zygomatic edge of the great wing of the sphenoid, it forms a fairly thick partition between the orbit in front and the temporal fossa behind. Crossing this surface from above downwards, close to the anterior extremity of the spheno-maxillary fissure, is the suture between the zygomatic bone and the great wing of the sphenoid (sutura spheno-zygomatica). This wall is pierced in front by one or two small canals (foramen zygomatico- orbitale), which traverse the zygomatic bone and allow the transmission of the temporal and zygomatic branches of the orbital portion of the superior maxillary division of the fifth nerve. The medial wall of the orbit is formed from before backwards by a small part of the frontal process of the maxilla, by' the lacrimal, and by the os planum or orbital plate of the ethmoid (lamina papyracea ossis ethmoidalis), posterior to which is a small part of the lateral aspect of the body of the sphenoid in front ot the 10 150 OSTEOLOGY. optic foramen. Above, the orbital plate of the frontal bone forms a continuous suture from before backwards with the bones just enumerated ; whilst below, the lacrimal and the os planum of the ethmoid articulate with the orbital plate of the maxilla; posteriorly the hinder extremity of the os planum and the fore-part of the body of the sphenoid articulate with the orbital process of the palate. The orbital surface of the lacrimal bone is divided into two by a vertical ridge — the lacrimal crest (crista lacrimalis posterior) — which forms in front the posterior half of a hollow, the lacrimal groove (sulcus lacrimalis), the anterior part of which is completed by the channelled posterior border of the frontal process of the maxilla. In the lacrimal groove or fossa (fossa sacci lacrimalis) is lodged the lacrimal sac, whilst passing from it and occupying the canal, of which the upper opening is at present seen, is the membranous nasal duct. The extremely thin wall of the lower part of the lacrimal fossa separates the orbit from the fore-part of the middle meatus of the nasal fossa. To the medial side of the upper and fore-part of the lacrimal bone, and separated from the orbit merely by the thickness of that bone, is the passage leading from the nose to the frontal sinus (infundibulum ethmoidale), whilst the part of the bone behind the lacrimal crest forms the thin partition between the orbit and the anterior ethmoidal cells. Behind, where the body of the sphenoid forms part of the medial wall of the orbit, the sphenoidal air sinus is in relation to the apej: of that space, though here the partition wall between the two cavities is much thicker. The skeleton of the face on its anterior surface is formed by the two maxillse, the frontal processes of which have been already seen to pass up to articulate with the mecUal angular processes of the frontal bone, thus forming the lower halves of the inner margins of the orbit. Joined to the upper jaws laterally are the zygomatic or malar bones, which are supported by their union with the temporal bones posteriorly through the medium of the zygomatic arches. The suture which separates the zygomatic from the maxilla (sutura zygomatico- maxillaris) commences above about the centre of the lower orbital margin and passes obliquely downward and laterally, its lower end lying in vertical line with the lateral orbital margin. The two maxillse are separated by the nasal fossae, which here open anteriorly. Above, the two nasal bones are wedged in between the frontal processes of the maxillee ; whilst below the nasal aperture, the maxillfe themselves are united in the middle line by the intermaxillary suture (sutura intermaxillaris). The nasal aperture (apertura pyriformis), which lies below and in part between the orbits, is of variable shape and size — usually pyriform, it tends to be long and narrow in Europeans, as contrasted with the shorter and wider form met with in the negroid races. Its edges are formed below and on either side by the free curved margin of the body and the frontal process of the maxilla ; and above, and partly at the sides, by the free border of the nasal bones. In the middle line, inferiorly, corresponding to the upper end of the intermaxillary suture there is an outstanding process — the anterior nasal spine (spina nasalis anterior) formed by the coalescence of spicules from Ijoth maxilhc ; arising from this, and passing backwards and upwards, is a thin bony partition — the osseous septum of the nose. Often deflected to one or other side, it divides the cavity of the nose (cavum nasi) into a right and left half. Projecting into these chambers from their lateral walls can be seen the medial surfaces and free borders of the middle (concha media) and inferior (concha inferior) turbinated bones, the spaces below and between which form the inferior and middle meatuses of the nose respectively. Below the orl)it, and to the lateral side of tlio nasal aperture, the anterior or facial surface of the body of the maxilla (corpus maxillae) is seen ; this is con- tinuous inferiorly -with the lateral surface of the alveolar process (processus alveo- laris), in which are embedded the roots of the upper teeth. A horizontal line drawn round the jaw on the level of a ])oint midway between the lower border of the nasal aperture and the alveolar edge corresponds to the plane of the hard palate. Below that the alveolar process separates the cavity of the mouth from the front of the face; whilst above, the large air space, the maxillary sinus (sinus maxillaris), or antrum of Highmore, lies within the body of the maxilla. NOEMA LATEKALIS OF THE SKULL. 151 The zygomatic or malar bone forms the lower half of the lateral and lateral half of the lower border of the orbit. Its lateral aspect corresponds to the point of greatest width of the face, the modelling of which depends on the flatness or projection of this bone. When the lower jaw (mandibula) is in position, and the teeth in both jaws are complete, the lower dental arch will be seen to be smaller in all its diameters than the upper, so that when the jaws are closed the upper teeth slightly overlap the lower both in front and at the sides. Exceptionally a departure from this arrange- ment is met with. Norma Lateralis. Viewing the lateral aspect of the skull, in the first instance, without the lower jaw, it is seen to be formed in part by the bones of the cranium, and in part by the bones of the face. A line drawn from the fronto-nasal suture to the tip of the mastoid process serves to define roughly the boundary between these portions of the skull. Of ovoid shape, the cranium is formed above by the frontal, parietal, and occipital bones from before backwards ; whilst below, included within these are the sphenoid and temporal bones. The sutures between these several bones are arranged as follows : Commencing at the zygomatic process of the frontal, the suture between that bone and the zygomatic bone is first seen ; tracing this backwards and a little upwards, the lower edge of the frontal next articulates with the upper margin of the great wing of the sphenoid for a distance varying from three-quarters of an inch to one inch. Here the posterior border of the frontal turns upwards and slightly back- wards, forming with the parietal the coronal suture (sutura coronalis). The lower border of the parietal bone, which is placed immediately behind the frontal, articulates anteriorly with the hinder part of the upper edge of the great wing of the sphenoid. The extent of this suture (sutura spheno-parietalis) is liable to very great indi- vidual variation — at times being broad, in other instances being pointed and narrow, whilst occasionally the parietal does not articulate with the sphenoid at all. Behind the spheno-parietal suture the parietal articulates with the squamous part of the temporal (sutura squamosa), the posterior extremity of which is about one inch behind the external auditory meatus. Here the suture alters its character and direction, and in place oF being scaly, becomes toothed and irregular, uniting for the space of an inch or so the mastoid or posterior inferior angle of the parietal with the mastoid process of the temporal bone. This suture (sutura parieto-mastoidea) is more or less horizontal in direction, and lies in line and on a level with the upper border of the zygomatic arch. At a point about two inches behind the external auditory meatus the posterior border of the parietal bone turns obliquely upwards and backwards, and forms with the tabular part of the occipital bone the strongly- denticulated lambdoid suture (sutura lambdoidea). Inferiorly this suture is con- tinued obliquely downwards between the occipital bone and the hinder border of the mastoid portion of the temporal, where it forms the occipito- mastoid suture (sutura occipito -mastoidea), much simpler and less serrated than the two previ- ously mentioned. These three sutures just described meet in tri-radiate fashion at a point called the asterion. Anteriorly the curve of the squamous suture is continued downward between the anterior edge of the squamous part of the temporal and the posterior border of the great wing of the sphenoid ; inferiorly it lies in plane with the middle of the zygomatic arch. The sutures around the summit of the great wing of the sphenoid are arranged like the letter H placed obliquely, the cross-piece of the H corresponding to the spheno-parietal suture. When this is short, and becomes a mere point of contact, the arrangement then resembles the letter X. This region is named the pterion. Curving over the lateral region of the calvaria in a longitudinal direction is the temporal crest (linea temporalis). This is often double. The lower line marks the limit of the attachment of the temporal muscle, whilst the upper ridge defines the attachment of the temporal fascia. Commencing in front at the lateral angular process of the frontal, the crest sweeps upwards and backwards across the lower part of that bone, and then crossing the coronal suture — at a point 152 OSTEOLOGY. called the stephanion — it passes on to tlie parietal, over which it curves in the direc- tion of its posterior inferior (mastoid) angle. Here it is continued on to the temporal bone, where it sweeps forward to form the supramastoid crest, which serves to separate the squamous from the mastoid portion of the temporal bone laterally. Carried forward, this ridge is seen to become continuous with the upper border of the Fig. 115. — Norma Lateralis of the Skull. The occipital, sphenoid, ethmoid, and maxillary bones are coloured blue. The parietal, zygomatic, ami nasal bones are coloured red. The temporal, frontal, and maxillary bones are left uucoloured. 11, Mental foramen. Body of the lower jaw. Maxilla. Ramus of lower jaw. Zygomatic arch. Styloid process. External auditory meatus. Mastoid process. Asterion. Superior curved line of occipital l)one. External occipital protuberance. 12. Lambdoid suture. 13. Occipital bone. 14. Lambda. 15. Obelion placed between the two parietal foramina. 16. Parietal bone. 17. Lower temporal line. 18. Upper temporal line. 19. Squamous part of temporal Vjone. 20. Bregma. 21. Coronal suture. 22. Stephanion. 23. Frontal bone. 24. Pterion. 25. Temporal fossa. 26. Great wing of sphenoid. 27. Zj'gomatic bone. 28. Zygomatic canal. 29. Lacrimal bone. 30. Nasal bone. 31. Infraorbital canal. 32. Anterior nasal aperture. zygomatic arch over the external auditory meatus. In front, the temporal ridge separates the temporal fossa from the region of the forehead ; above and behind, it bounds the temporal fossa which lies within its concavity, and serves to separate that hollow from the surface of the calvaria which is overlain by the scalp. Above the level of the temporal lines the surfaces of the frontal and parietal bones are smooth, the latter exhibiting an elevation of varying prominence and position, but usually situated about the centre of the bone, called the parietal eminence (tuber parietale). NOEMA LATERALIS OF THE SKULL. 153 A slight hollowing of the surface of the parietal behind and parallel to the coronal suture is not uncommon, and is referred to as the post -coronal depression. As seen in profile, the part of the calvaria behind and below the lambdoid suture is formed by the tabular part of the occipital bone. In line with the zygomatic arch this outline is interrupted by the external occipital protuberance or inion (protuber- antia occipitalis externa). The projection of this point is variable ; but its position can usually be easily determined in the Living. Passing forwards from it, and blending anteriorly with the posterior border of the mastoid process of the temporal bone, is a rough crest, the superior curved line (linea nuchse superior), a little above which there is often a much fainter line, the highest curved line (linea nuchas suprema) ; this aftbrds attachment to the epicranial aponeurosis. These two lines serve to separate the part of the cranium above, which is covered by scalp, from that below, which serves for the attachment of the fleshy muscles of the back of the neck, the latter surface (planum nuchale) being rough and irregular as contrasted with the smooth superior part (planum occipitale). The fulness of these two parts of the occipital bone varies much. There is frequently a pronounced bulging of the planum occipitale, and the position of the lambda can often be easily determined in the living ; similarly the planum nuchale may be either com- paratively flat or else full and rounded. These differences are of course associated with corresponding differences in the development of the cerebral and cerebellar lobes which are lodged in relation to the cerebral aspect of these parts of the bone. The further description of the planum nuchale is best deferred till the base of the skull (norma basalis) is studied. Temporal Fossa. — -Within the limits of the temporal lines the side of the cranium slopes forwards, inwards, and downwards, thus leaving a considerable interval between its lower part and the zygomatic arch. This space or hollow is called the temporal fossa (fossa temporalis) ; bounded above and behind by the temporal lines, its inferior limit is defined by the level of the zygomatic arch. Deepest opposite the angle formed by the frontal and temporal processes of the zygomatic or malar bone, the fossa becomes shallow towards its circumference. Its floor or medial wall, which is sUghtly concavo-convex from before backwards about mid-level, is formed above by the temporal surface (facies temporalis) of the frontal, behind by the anterior inferior angle (sphenoidal angle) of the parietal, as well as the lower portion of that bone, below the temporal line ; below and in front by the temporal surface of the great wing of the sphenoid, and behind and below by the squamous portion of the temporal bone. Inferiorly the floor is limited in front by the free inferior border of the great wing of the sphenoid, which forms the upper boundary of the spheno- maxillary (pterygo - palatine) fossa; behind that, by a rough ridge, the infra-temporal crest or pterygoid ridge (crista infratemporalis), which crosses the lateral surface of the great wing of the sphenoid, to become continuous posteriorly with a ridge on the lower surface of the squamous part of the temporal, from which the anterior root of the zygomatic process springs. Anteriorly the temporal fossa is separated from the orbit by the zygomatic process of the frontal above, and by the orbital process of the zygomatic and its junction with the lateral border of the great wing of the sphenoid between the orbital and temporal surfaces of that process. Laterally and in front, the fossa is overhung by the backward pro- jection of the frontal process of the zygomatic bone, and it is under cover of this, and within the angle formed by the frontal and orbital processes of the zygomatic bone, that we see the opening of the temporal canal, which pierces the orbital plate of the zygomatic bone and transmits the temporal branch of the orbital nerve — a filament of the superior maxillary division of the 5th nerve. The fore-part of the spheno- maxillary fissure (fissura orbitalis inferior) opens into the lower part of the temporal fossa, and thus establishes a communication between it and the orbit. If the floor of the fossa be carefully examined, some more or less distinct vascular grooves may be seen. One passing upwards over the posterior part of the squamous temporal, immediately in front of and above the external auditory meatus, is for the middle temporal artery ; two others, usually less distinct, pass up, one over the temporal surface of the great wing of the sphenoid, the other over the fore-part of the squamous part of the temporal ; these are for the anterior and posterior deep 10 & 154 OSTEOLOGY. temporal branches of the internal maxillary artery. Inferiorly the temporal fossa communicates with the infra-temporal (or zygomatic) fossa, beneath the zygomatic arch, the two being separated by an imaginary horizontal plane passing inwards at the level of that bony bridge. The fossa contains the temporal muscle with its vessels and nerves, together with the temporal branch of the orbital nerve and some fat ; all of which are enclosed by the fascia which stretches over the space from the upper temporal line above to the superior border of the zygomatic arch below. The extent and depth of the fossa depends on the size of the temporal muscle, the development of which is correlated with the size and weight of the lower jaw. Springing from the front and lower part of the squamous part of the temporal is the zygomatic process of that bone ; it has two roots, an anterior and a posterior, between and below which are placed the glenoid fossa (fossa mandibularis) in front, and the opening of the external auditory meatus behind. Of compressed triangular form, the process at first has its surfaces directed upwards and downwards, but curving laterally and forwards, it twists on itself, so that its narrowed surfaces are now turned laterally and medially, and its edges upwards and downwards ; passing forwards, it expands somewhat, and ends in an oblique serrated surface, which unites with the temporal process of the zygomatic bone completing the zygomatic arch. It is the upper edge of this bridge of bone which forms the posterior root. The lower border, turning medially, forms the anterior root, and serves to separate the temporal from the zygomatic surface of the squamous part of the temporal, blending in front with the infratemporal crest on the lateral surface of the great wing of the sphenoid. The under surface of this root is convex from before backwards, and is thrown into relief by the glenoid hollow, which passes up behind it. In this way a downward projection, which is called the eminentia articularis, is formed. The alar spine of the sphenoid (spina angularis) lies immediately to the medial side of the articular part of the glenoid fossa. Its size and projection vary. It is well to remember its relation to the condyle of the lower jaw when that bone is in position ; lying, as it does, to the medial side and a little in front of that pro- cess, it affords attachment to the so-called long internal lateral ligament (spheno- mandibular) of the tempore -maxillary articulation. As will be seen hereafter, the anterior extremity of the osseous Eustachian canal lies just to its medial side (p. 124). A noteworthy feature about the articular part of the glenoid fossa is the thinness of the bony plate which serves to separate it from the middle cranial fossa above. The vaginal process is a crest of bone which runs obhquely forwards from the front and medial side of the mastoid process, just below the external auditory meatus, to the alar spine of the sphenoid. Passing downwards and slightly forwards from the centre of this, and ensheathed by it in front and at the sides, is the pointed styloid process, the length of which is extremely variable. In the recess between the posterior root of the zygoma and the upper curved edge of the meatus there is usually a depression, though in some instances this may be replaced by a slight bulging of the bone. If from the posterior root of the zygoma a vertical line be let fall, tangential to the posterior edge of the meatus, a small triangular area is mapped off which has been named by Macewen the supra- meatal triangle. Surgically this is of importance, as it is the spot selected in which to trephine the bone to reach the mastoid antrum (see p. 118). In the suture between the posterior border of the mastoid part of the temporal and the squamous part of the occipital, there is usually a foramen (mastoid) for the transmission of an emissary vein from the lateral (transverse) sinus within the cranium to the cutaneous occipital vein of the scalp ; this opening, which may be double, varies greatly in size, and is usually placed on a level with the external auditory meatus. Infratemporal or Zygomatic Fossa. — The side of the cranium in front of the anterior root of the zygomatic yjrocess of tlie temporal bone is deeply hollowed, form- ing the infratemporal or zygomatic fossa (fossa infratemporalis) ; this in topographical anatomy corresponds to the pterygo-maxillary region. The student must bear in mind that, in examining this space, the ramus and coronoid process of the lower jaw form its outer wall ; but this bone for the present being withdrawn, enables us to get a better view of the boundaries of the space. In front its anterior wall NORMA LATERALIS OF THE SKULL. 155 is formed by the convex posterior or zygomatic surface (facies infratemporalis) of the maxilla, which rises behind the socket for the last molar tooth to form the tuberosity (tuber maxillare). Anteriorly, the zygomatic surface of the upper jaw is separated from its facial aspect by the rounded inferior margin of the malar or zygomatic process which supports the malar bone. This latter curves laterally and backwards, forming part of the upper and anterior wall of the fossa. On the medial surface of this wall will be seen the suture uniting the zygomatic and maxillary bones (sutura zygomatieo-maxillaris), which runs obliquely upwards and inwards to reach the lateral extremity of the spheno-maxillary fissure (inferior orbital fissure), the lower border of which forms the superior boundary of the zygomatic surface of the upper jaw. On this aspect of the bone are to be seen the openings of the posterior dental canals (foramina alveolaria) two or more in number, which transmit the nerves and vessels to the upper molar teeth. The medial wall of the zygomatic fossa is formed by the lateral surface of the external pterygoid plate (lamina lateralis processus pterygoidei), the width and shape of which varies greatly ; its posterior border is thin and sharp, and often furnished with spiny points, to one of which the pterygo-spinous ligament, which stretches from this border to the alar spine of the sphenoid, is attached. It occasionally happens that this ligament becomes ossified. Anteriorly the external pterygoid plate is separated from the maxilla above by an interval called the pterygo-maxillary fissure. Below this the bones are apparently fused, but a careful inspection of the skull, together with an examina- tion of the disarticulated bones, will enable the student to realise that, wedged in between the two bones at this point, is a part of one of the smaller bones of the face, the pyramidal process of the palate bone (processus pyramidalis ossis palatini). The lower border of the external pterygoid plate is usually curved and slightly everted. Superiorly, where the external pterygoid plate is generally narrower, it sweeps upwards to become continuous with the broad under surface of the great wing of the sphenoid ; this, which overhangs in part the zygomatic fossa superiorly, is limited above by the infratemporal crest which separates its zygomatic from its temporal surface. The zygomatic surface of the great wing of the sphenoid is limited in front and below by the edge which forms the upper boundary of the spheno-maxillary fissure, whilst behind it reaches as far back as the medial extremity of the G-laserian fissure, where it terminates in the alar spine. It is from this point that the suture (sutura spheno - squamosa) curves forward and upwards to reach the region of the pterion. The infratemporal or zygomatic surface of the great wing of the sphenoid, and the lateral surface of the external pterygoid plate, alike afford extensive attachments for the external pterygoid muscle, whilst the former is pierced by minute canals for the transmission of emissary veins. Occasionally a larger vascular foramen is present (foramen Vesalii), through which a vein runs from the cavernous sinus within the cranium to the pterygoid venous plexus situated in the pterygo-maxillary region. Immediately behind the root of the external pterygoid plate there is a large oval hole, the foramen ovale, and behind that, and in line with the alar spine, is the smaller foramen spinosum. These two foramina cannot usually be seen in a side view of the skull, and are better studied when the base is examined ; they are mentioned, however, because they transmit structures which here pass to and from the cranium, viz, the mandibular division of the fifth nerve, together with its motor root, and the small meningeal artery through the foramen ovale, and the middle meningeal artery and its companion veins through the foramen spinosum. A part of the squamous part of the temporal also forms a small portion of the roof of this fossa ; it consists of a triangular area immediately in front of the eminentia articularis, and between it and the anterior root of the zygomatic process of the temporal, which is here curving medially and forwards, to become continuous with the infratemporal crest. Medially this surface is continuous with the zygomatic surface of the great wing of the sphenoid, separated from it, however, by the hinder part of the spheno- squamosal suture. When the lower jaw is in position, the zygomatic or infratemporal fossa is concealed by the ramus of the mandible, the medial surface of which, in its upper half, forms the lateral wall of that space. Viewed from the outer side, the ramus of the mandible 156 OSTEOLOGY. displays considerable differences in different skulls. These are mainly due to varia- tions in its width and in the nature of the angle which it forms at its fusion with the body of the bone. A considerable interval separates the posterior border of the ramus from the front of the mastoid process. Within this space may be seen the free inferior edge of the tympanic plate (vaginal process), from which, just below the external auditory meatus, the styloid process of the temporal bone is observed passing downwards and slightly forwards. The width and height of the coronoid process vary much, oftentimes reaching the level of the top of the condyle. Its extremity, when the lower jaw is closed, lies just within the fore-part of the zygo- matic arch ; at other times it rises to a much higher level, so that its point may be seen above the level of the upper border of the zygomatic arch. The posterior edge of the coronoid process forms the anterior border of the sigmoid or mandibular notch, and limits in front the interval left between the lower border of the posterior lialf of the zygomatic arch and the upper hollowed edge of the ramus. On looking into this interval, the floor of the zygomatic fossa may be seen, formed anteriorly by the external pterygoid plate ; whilst posteriorly it is possible to pass a probe right across the base of the skull from one sigmoid notch to the other, the shaft of the probe lying immediately behind the pterygoid processes of the sphenoid, and cross- ing the foramina ovalia, through which the mandibular divisions of the fifth nerves pass. The ramus and coronoid process are so placed as to occupy a position inter- mediate between the zygomatic arch laterally and the external pterygoid plate medially; their medial surface, therefore, forms the lateral wall of the zygomatic fossa. On a level with the surface of the crowns of the teeth of the lower jaw, and situated about the middle of this aspect of the ramus, is the inferior dental foramen (foramen mandibulare), the superior opening of the inferior dental canal (canalis mandibulae), which traverses the body of the bone. Through this foramen there pass the inferior dental branch of the mandibular division of the fifth nerve, together with the inferior dental artery and its companion veins. As will now be seen, when the lower jaw is in position, the zygomatic fossa is closed in later- ally by the ramus of the mandible. In front there is an interval between the anterior border of the ramus and the zygomatic surface of the maxilla, through which pass the buccal branch of the fifth nerve and the communicating vein between the pterygoid plexus and the facial vein. Above, in the interval between the sigmoid edge and the lower border of the zygomatic arch, there pass from the fossa the vessels and nerves which supply the masseter muscle. Between the posterior border of the ramus and the styloid process there enter and leave the large vessels which are found within the space. Superiorly, under cover of the zygomatic arch, the zygomatic fossa communicates with the temporal fossa, whilst inferiorly it is continuous with the inframaxillary region. Medially, on the floor of the fossa there is an f-shaped fissure, the horizontal limb of which corresponds to the spheno-maxillary fissure (inferior orbital fissure), forming a channel of communication between the fossa and the orbit, through which passes the orbital branch of the maxillary division of the fifth nerve ; whilst the vertical cleft is the pterygo -maxillary fissure, which leads into a small fossa placed between the front of the root of the pterygoid process of the sphenoid and the back of the maxilla, called the spheno-maxillary or pterygo -palatine fossa. The following foramina open into the zygomatic fossa — the foramen ovale, foramen spinosum, posterior dental foramina, inferior dental foramen, minute foramina for the transmission of emissary veins ; of these one of large size is occasionally present, the foramen of Vesalius. Spheno-Maxillary or Pterygo-palatine Fossa. — This space, which corresponds to the angular interval between the pterygo -maxillary and spheno-maxillary fissures, and which lies between the maxilla in front and the root of the pterygoid process behind, is bounded medially by the vertical part of the palate bone, which separates it from the nasal cavity, with which, however, it communicates by means of the spheno-palatine foramen, which lies between the orbital and sphenoidal processes of the palate bone and the under surface of the body of the sphenoid. Opening into this fossa, above and behind, are the foramen NOEMA OCCIPITALIS OF THE SKULL. 157 rotundum, the Vidian canal and the pterygo-palatine (pharyngeal) canal from without inwards, whilst below is the superior orifice of the posterior palatine canal, together with openings of the accessory posterior palatine canals. Its roof is formed by the under surface of the body of the sphenoid and the orbital 13 24 23 22 Fig. 116. — Coronal Section through the Spheno-maxillart (Pterygo-palatine) Fossa of the Right Side. The sphenoid is coloured red. The maxilla, vomer, middle, and inferior tiirbinals are coloured blue. The palate bone is left uncoloured. L Anterior Wall. B. Posterior Wall. C. Diagrammatic representation of a horizontal section across the fossa. 1. Spheno-palatine foramen. 2. Apex of orbital cavity. 3. Spheiio-maxillary fissure. 4. Spheno-maxillary fi.ssure. 5. Pterygo-iiiaxillary fissure. 6. Dental foramina. 7. Part of pterygoid fossa. S, 9, 10. Posterior palatine and ac- cessory palatine (lesser pala- tine) canals. 11. Foramen rotundum. 12. Sphenoidal fissure. 13. Optic foramen. 14. Sphenoidal sinus. 15. Pterygo-palatine canal. 16. Vidian canal. 17. Spheno-palatine foramen. IS. Spheno - maxillary (pterygo - pala- tine) fossa. 19. Infra-orbital groove. 20. Spheno-maxillary fissure. 21. Pterygo-maxillary fissure. 22. Foramen rotundum. 23. Vidian canal. 24. Pterygo-palatine (pharyngeal) canal. plate of the palate bone. Anteriorly it lies in relation to the apex of the orbit, with which it communicates by means of the spheno-maxillary (inferior orbital) fissure ; whilst laterally, as already stated, it communicates with the zygomatic fossa through the pterygo-maxillary fissure. Norma Occipitalis. The view of the cranium as seen from behind includes the posterior halves of the two parietal bones above, the squamous part of the occipital bone below, and the mastoid portions of the temporal bones on either side inferiorly. The shape of this aspect of the skull varies much, but ordinarily the greatest width corresponds to the level of the parietal eminences. The sutures on this view of the calvaria display a tri-radiate arrangement, one limb of which is vertical, and corresponds to the posterior part of the interparietal or sagittal suture (sutura sagittalis). The other two limbs pass outwards and downwards in the direction of the mastoid processes, uniting the two parietal bones in front with the occipital bone behind ; these constitute the A-shaped lambdoid suture (sutura lambdoidea). The point of confluence of the sagittal and lambdoid sutures is called the lambda. This can generally be felt in the living, owing to the tendency of the tabular part of the occipital to project slightly immediately below this spot. About one inch and a quarter above the lambda the two small parietal foramina (foramina parietalia) are seen, through which pass the small emissary veins of Santorini, which connect the intracranial venous system with 158 OSTEOLOGY. the superficial veins of the scalp. These small holes lie about y\ of an inch apart on either side of the sagittal suture, which here, for the space of about an inch, displays a simplicity of outline in striking contrast with its serrated arrangement elsewhere. The term obelion is applied to a point on the sagittal suture in line with the two parietal foramina. The lambdoid suture is characterised by great irregularity of outline, and not unfrequently chains of separated ossicles are met with in it, the so-called Wormian bones (ossa suturarum). The tabular part of the occipital bone is divided into two parts by the superior curved line (linea nuchse superior), the central part of which forms the external occipital protuberance or inion (protuberantia occipitalis exterior). The part above, called the occipital surface (planum occipitale), comes within our present consideration ; the part below, the nuchal surface (planum nuchale), though seen in perspective, had best be considered when the base is examined. A little above the level of the superior curved line the occipital surface is crossed on either side by a faint lunated line, the highest curved line (linea nuchae suprema) to which are attached the occipitales muscles and the epicranial aponeurosis. The projection of the occipital surface varies much in individual skulls ; most frequently it overhangs the external occipital protuberance, forming a distinct boss ; exceptionally, however, the latter may be the most projecting part of the bone. The extremity of the superior curved line on either side corresponds to the position of the asterion (p. 151). Lateral to these points the outline of the skull is determined by the downward projection of the mastoid processes, the medial surfaces of which are deeply grooved for the attachment of the posterior belKes of the digastric muscles, thus causing these processes to appear more pointed when viewed from this aspect. Norma Verticalis. This is the view of the calvaria as seen from above. It is liable to great diversities of form. Thus its shape may vary from an elongated oval to an outline more nearly circular. These differences have been classified, and form important distinctions from a craniometrical standpoint (Appendix), the rounder varieties being termed the brachycephalic, whilst the elongated belong to the dolichoceplialie group. Another noteworthy point in this view is the fact that in some instances the zygomatic arches are seen, whilst in others they are concealed by the overhang and bulge of the sides of the fore-part of the cranium. The former condition is described as phoenozygous, the latter as cryptozygous, and each is more or less closely associated with the long or round varieties of head-form respectively. The sutures displayed have a T-shaped arrangement. Placed medially between the two parietal bones is the sagittal suture. This is fiinely denticulated, except in the region of the obelion, though, of course, this will not be apparent if obliteration of the suture has taken place through fusion of the two parietal bones. Posteriorly the sagittal suture unites with the lambdoid suture at the lambda, which marks in the adult the position of the posterior fontanelle of the foetus. Anteriorly it terminates by joining the transverse suture which separates the frontal bone anteriorly from the parietals behind ; this latter is called the coronal suture, and the point of junction between the sagittal and coronal sutures is known as the bregma, this corresponds in position to the anterior fontanelle of the foetus. The summit of the vault of- the calvaria corresponds to a variable point in the line of the sagittal suture, and is named the vertex. The coronal suture is less denticulated centrally than laterally. Occasionally there is a persistence of the suture (metopic) which unites the two halves of the frontal bone ; under these conditions the line of the sagittal suture is carried forward to the fronto-nasal suture, and a skull displaying this peculiarity is described as metopic. Behind the coronal suture may occasionally be seen the post-coronal depression (p. 153), and in some instances the vault of the calvaria forms a broad, slightly elevated crest along the line of the sagittal suture. On either side the temyjoral ridges can be seen curving over the lateral and superior aspects of the jjarietal bones. As the lower of these crosses the coronal suture in front it marks a spot known as the stephanion, useful as affording a fixed point from which to estimate the bi-stephanic diameter. The interval between the NOEMA BASALIS OF THE SKULL. 159 temporal ridges on either side will vary according to the form of the skull and the development of the temporal muscle. In this view of the calvaria a small part of the lambdoid suture on either side of the lambda is visible posteriorly. Norma Basalis. The base of the cranium — i.e. the skull without the mandible — includes a descrip- tion of the under surfaces of the skeleton of the face (cranium viscerale) and the cranium (cranium cerebrale). The former includes the hard palate formed by the maxillie and palate bones, the superior dental arch, and the bodies of the maxillae as seen from below ; whilst laterally, and united with the bodies of the maxillse, the zygomatic bones are displayed, curving backwards to form the anterior halves of the zygomatic arches. In the middle line, passing from the upper surface of the hard palate, is the osseous septum of the nose, here formed by the vomer, which is united above to the under surface of the body of the sphenoid. The under surface of the cranium is pierced by the foramen magnum for the transmission of the spinal cord and its membranes. In front of this a stout bar of bone extends forwards in the middle line, formed by the union of the body of the sphenoid in front with the basilar process of the occipital bone behind. In adult skulls all trace of the fusion of these two bones has disappeared ; when union is in- complete, it indicates that the skull is that of a person below the age of twenty-five. The sphenoid comprises that part of the calvaria which forms the roof and sides of the apertures which lie on either side of the nasal septum above the hard palate — the choanae or posterior nares. Laterally the under surfaces of the great wings of the sphenoid extend as far forward as the posterior border of the spheno- maxillary fissure ; whilst posteriorly they reach as far as the alar spine, lateral to which the spheno-squamosal suture, separating the great wing of the sphenoid from the squamous portion of the temporal, curves forwards and upwards, medial to the eminentia articularis, to reach the floor of the temporal fossa, along which its course has been already traced (p. 153). On a level with the front of the foramen magnum the jugular process of the occipital bone forms an irregular curved border, which sweeps outwards to terminate at a point just medial to the root of the styloid process. Here, in line with the spheno-squamosal suture, from which, how- ever, it is separated by a considerable interval, its extremity turns backwards, and may be traced at first medial to, and then turning upwards, behind the mastoid process of the temporal bone, separated from this latter by the occipito-mastoid suture. The bone behind the foramen magnum, which is included between the two occipito-mastoid sutures, comprises the nuchal surface of the squamous portion of the occipital bone, an area which is limited behind by the superior curved line which separates it from the occipital surface of the same bone. The remaining portions of the base of the calvaria, as at present exposed, are formed by the squamous and tympanic portions of the temporal bone together with the petro-mastoid part of the same bone, the latter of which is wedged in between the great wing of 'the sphenoid in front and the occipital bone behind. Stretching forwards from the squamous part of the temporal in front is seen the zygomatic process which, by its union with the zygomatic bone, completes the formation of the zygo- matic arch. Hard Palate. — Studying next the various parts in detail, the hard palate (palatum durum) may be first examined. Of horse-shoe shape as a rule, it presents many varieties of outline and size. Formed by the palatal processes (processus palatini) of the maxillse in front and the horizontal plates (partes horizon- tales) of the palate bones behind, its circumference in front and at the sides corre- sponds to the superior alveolar arch, in which are embedded the sixteen teeth of the upper jaw; posteriorly the edge of the hard palate is thin, ending medially in a pointed process, the posterior nasal spine (spina nasalis posterior), on either side of which the posterior free border is sharp and lunated. The vault of the palate, which is concave from side to side, and from before backwards, varies in depth according to the projection and development of the alveolar processes. When the teeth are shed and the alveoli are absorbed, the palate becomes shallow and flat. Eunning 160 OSTEOLOGY. Fig. 117. — Norma Basalts. The occipital, vomer, and maxillary bones, are coloured red. The temporal and palate bones, blue. The zygomatic bones, purple. The sphenoid and parietal bones, and the teeth, are left uncoloured. E.xternal occipital crest. 14. Superior curved line of the occipital bone. 15. Foramen magnum. 16. Occipital condyle. 17. Mastoid groove. 18. Mastoid process. 19. External auditory meatus. 20. Styloid process. 21. Glenoid fossa. 22. Foramen spinosum. 23. Alar spine of the sphenoid. Foramen ovale. 24. External pterygoid plate. 25. Hamular process of internal 26. pterygoid plate. 27. Nasal septum. 28. Posterior nasal spine. 29. Horizontal plate of palate Ijone. 30. Palatal process of maxilla. 31. Anterior palatine canal. 82. Intermaxillary suture. 33. Posterior palatine canal. 34. Zygomatic process of maxilla. 35. Spheno-maxillary or inferior orbital 36. fissure. 37. Zygomatic or infratemporal fossa. 38. Zygomatic arch. 39. Posterior opening of left nasal fossa. Pterygoid fossa. Scaphoid fossa. Foramen lacerum. Opening of osseous Eustachian canal. Carotid canal. Jugular fossa. Stylo-mastoid foramen. Jugular process of occipital bone. Grroo\'e for occipital artery. Mastoid foramen. Posterior condylic foramen. Inferior curved line of occipital bone. External occipital protuberance. NOEMA BASALIS OF THE SKULL. 161 throughout its entire length in the middle line is the middle palatine suture (sutura palatina mediana), which separates the palatal processes of the maxillge in front and the horizontal plates of the palate bones behind. A little behind the central incisor teeth, and in the line of this suture, is a little pit, the anterior palatine canal (foramen incisiviun). At the bottom of this may be seen the openings of some small canals, varying in number from one to four ; these are usually described as arranged in two pairs, the one pair placed side by side, the other lying medially in front and behind. The former are called the incisor foramina, or foramina of Stensen, and transmit the terminal twigs of the superior or descending palatine arteries which ascend to reach the nasal fossae. The latter, called the foramina of Scarpa, open, the anterior into the left, the posterior into the right nasal fossa, and afford passage for the fine filaments of the left and right naso- palatine nerves respectively. About half an inch (12 mm.) in front of the posterior nasal spine the middle palatine suture is crossed at right angles by the transverse palatine suture (sutura palatina transversa). This, which indicates the line of union of the palatal processes of the maxillte with the horizontal plates of the palate bones, passes transversely outwards on either side until it reaches the medial aspect of the base of the alveolar process, along which it turns backward, to disappear within the posterior palatine canal (foramen palatinum majus), the aperture of which lies just medial to the root of the wisdom molar. Through this there pass the superior or descending palatine artery and the large descending palatine nerve. Leading from this foramen is a groove which curves forward im- mediately to the medial side of the alveolar arch ; not unfrequently the medial edge of this groove forms a thin and sharp ridge on the surface of the palate. In this groove are lodged the aforementioned vessels and nerves. The surface of the palate in front of the transverse suture is rough, pitted for the palatine glands, and pierced by numerous small vascular foramina ; the part of the palate behind the suture, formed by the under surface of the horizontal plate of the palate bone, is much smoother. From this there rises, just posterior to the orifice of the posterior palatine canal, a thin sharp crest which curves medially immediately in front of the posterior free edge ; to this are attached some of the tendinous fibres of the tensor veli palatini muscle. Pterygoid Processes. — Buttressed against the hinder extremities of the alveolar arch are the pterygoid processes of the sphenoid. If carefully examined, these will be seen not to lie in actual contact with the maxillae, but to be separated from them by the triangular wedge-shaped pyramidal processes of the palate bones. It is these latter which are pierced by the posterior and lateral accessory palatine canals (foramina palatina minora) which lie just behind the posterior pala- tine canal, and through which pass the lesser palatine nerves. As here displayed, the pterygoid processes (processus pterygoidei) of the sphenoid lie on either side of the opening of the posterior nares ; each consists of two plates, an internal (lamina, medialis) and an external (lamina lateralis) ; the latter is the broader, and is directed backwards and slightly laterally. Its lateral surface has been already studied in connexion with the zygomatic fossa (p. 154). Medially it is separated from the inner pterygoid plate by the pterygoid fossa (fossa pterygoidea), wherein is lodged a considerable part of the internal pterygoid muscle. The floor of the fossa is formed in greater part by the coalescence of the two pterygoid plates ; but at the level of the hard palate the pyramidal process of the palate bone appears wedged in between the two plates, and so enters into the formation of the floor of the pterygoid fossa. The internal pterygoid plate separates the nasal from the pterygoid fossa ; to the hinder edge of the internal pterygoid plate are attached the pharyngeal aponeurosis, the superior constrictor of the pharynx, and the pharyngo- palatinus muscle. Above, the posterior border of this plate is channelled to form the small scaphoid fossa (fossa scaphoidea), which curves laterally over the summit of the pterygoid fossa, and furnishes a surface for the origin of the tensor veli palatini muscle. The sharp medial margin of this fossa, continuous below with the posterior border of the internal pterygoid plate, extends upwards, and on either side of the body of the sphenoid forms a blunt pointed process, the pterygoid tubercle, which extends backwards towards the apex of the petrous part of the temporal bone. 162 OSTEOLOGY. Just lateral to this, and concealed hj it, is the hinder extremity of the Vidian canal (eanalis pterygoideus), through which pass the Vidian vessels and nerve/ The medial surface of the internal pterygoid plate is directed towards the nasal fossae. Superiorly this surface curves medially to meet the under surface of the body of the sphenoid, forming on either side a lipped edge, the vaginal process (processus vaginalis), between which the alse of the vomer, which here forms the nasal septum, are wedged. Between the two a small interval, however, is occasionally left, which forms on either side the basi-pharyngeal canal. A little lateral to the line of union of the vaginal process with the vomer is the opening of the pterygo-palatine canal (eanalis pharyngeus). This lies between the under surface of the vaginal process and the sphenoidal process of the palate bone, which here articulates with the inferior surface of the body of the sphenoid. The pharyngeal branch of the spheno-palatine ganglion and the pterygo-palatine artery pass through this canal. Inferiorly the pterygoid processes project below the level of the hard palate. The inner plate ends in a slender recurved process, called the hamular process (hamulus pterygoideus), which turns backwards and laterally (this is frequently broken off in skulls which have been roughly handled). It reaches as low as the level of the alveolar margin, and lies just within and behind the posterior extremity of the alveolar process. It can readily be felt in the living by placing the finger against the soft palate behind and just within the gum around the root of the wisdom tooth. On the front of and below this process the tendon of the tensor veli palatini muscle glides in a groove. The posterior nares (choanae) lie within and between the pterygoid processes. Of a shape much resembling two Gothic windows, their bases or inferior boundaries are formed by the horizontal plates of the palate bone. Laterally they are bounded by the medial surfaces of -the internal pterygoid plates, whilst above, the lateral side of the arch is formed by the vaginal processes of the same plate ; medi- ally they are separated by the thin vertical posterior border of the vomer, whilst above the everted alee of the same bone form the medial sides of the arch. The plane of these apertures is not vertical but oblique, corresponding usually to a line drawn from the bregma above through the last molar tooth of the upper jaw below. Their size varies considerably, but the height is usually equal to twice the width. The region of the cranium which lies lateral to the maxilla and external pterygoid plate corresponds to the zygomatic or infratemporal fossa, which has been already described as seen from the side (norma lateralis, p. 154). Viewed from below, the zygomatic fossa is bounded in front by the posterior surface of the body of the maxilla and the medial surface of the zygomatic bone. The roof, which is traversed by the spheno-squamosal suture, is formed in front by the under surface of the great wing of the sphenoid, and behind by a small triangular surface of the under side of the squamous part of the temporal bone immediately in front of the eminentia articularis. Circumscril^ed laterally and behind by the anterior root of the zygoma, which curves forward to become continuous in front with the infra-temporal crest crossing the lateral surface of the great wing of the sphenoid, the roof of the fossa is separated from its anterior wall by the spheno -maxillary (inferior orbital) fissure, which is so inclined that with its fellow of the opposite side it forms an angle of 90°. Superiorly the zygomatic fossa communicates freely with the temporal fossa beneath the zygomatic arch, though the student must bear in mind the fact that when the mandible is in position the lateral limits of the space are very much reduced (p. 156). The under surface of the great wing of the sphenoid is here V-shaped. The angle corresponds to the spine, the lateral limb to the spheno-squamosal suture, whilst the medial limb corresponds to a narrow cleft, the fissura spheno-petrosa, which separates it from the petrous portion of the temporal bone to which it is united in the recent condition by a synchondrosis. Along the line of this latter fissure the edges of the adjacent bones (sphenoid and petrous part of the temporal) are bevelled so as to form a groove, which extends from the root of the internal pterygoid plate medially, to the medial side of the base of the alar spine laterally, where ' Artery and nerve of the eanalis pterygoideus (B.N. A.). NORMA BASALTS OF THE SKULL. 163 the groove ends by entering an osseous canal. In the groove (sulcus tubae auditivae) is lodfred the cartilaginous part of the Eustachian tube, whilst the osseous canal includes the bony part of the same tube, together with the tensor tympani muscle, which is lodged in a separate compartment immediately above it. The anterior extremity of the cartilaginous part of the Eustachian tube is supported by the posterior edge of the internal pterygoid plate, which is often notchetl for its recep- tion. Between the root of the external pterygoid plate and the alar spine there are two foramina which lie immediately in front of the sulcus tubte auditivse. Of these the larger and anterior is the foramen ovale, through which pass the motor root and mandibular division of the fifth nerve, together with the small meningeal artery. The smaller, which from its position immediately in front of the alar spine is called the foramen spinosum, transmits the middle meningeal artery and sympathetic plexus surrounding that vessel. The lesser superficial petrosal nerve here passes through the base of the skull to join the otic ganglion either through a small foramen (canalis innominatus) placed between the foramen ovale and the foramen spinosum, or through the foramen ovale or through the spheno-petrosal fissure. The position of the suture between the basi-occipital and basi-spheuoid corresponds to a Hne connecting the tips of the pterygoid tubercles at the root of the internal pterygoid plates. Occasionally in the centre of this line there is a small pit with a foramen leading from it. This probably represents the lower end of the cranio-pharyngeal canal. The under surface of the basi-occipital (pars basilaris) stretches between the body of the sphenoid in front and the anterior margin of the foramen magnum behind ; projecting from its centre is a slight elevation, the pharyngeal tubercle (tuberculiun pharyngeum), to which the pharyngeal aponeurosis, together with the central part of the anterior atlanto-occipital ligament, is attached. It should be noted, that when the atlas is in position the pharyngeal tubercle lies in line with the tubercle on the anterior arch of that bone. Curving laterally and backwards from the pharyngeal tubercle, on either side, is an irregular ridge (crista muscularis), in front and behind which are attached the longus capitis^ and rectus capitis anterior muscles. On either side of the basi-occipital, in front, there is an irregular opening of variable size ; this is placed between the root of the pterygoid process anteriorly, the apex of the petrous portion of the temporal bone laterally, and the lateral edge of the basi-occipital and basi-sphenoid medially. It is called the foramen lacerum. Opening into it in front, just lateral to the pterygoid tubercle, is the Vidian canal, whilst in correspondence with the apex of the petrous part of the temporal the large orifice of the carotid canal may be seen entering it behind and from the lateral side. In the recent condition the lower part of the foramen lacerum is occupied by fibro-cartilage, over the upper surface of which the internal carotid artery and great superficial petrosal nerve pass to reach their respective foramina, whilst a small meningeal branch of the ascending pharyngeal occasionally enters the cranium through it. Leading laterally from the foramen lacerum in the direction of the alar spine of the sphenoid is the spheno-petrosal fissure, wdiich lies at the bottom of the sulcus tubae auditivae, and disappears from view within the bony Eustachian canal. Passing backwards from the foramen lacerum there is a fissure between the lateral side of the basi-occipital and the posterior and medial border of the petrous part of the temporal bone. This, which is called the petro- occipital fissure (fissura petro-occipitalis), opens posteriorly into the jugular foramen. In the recent condition the fissure is filled up with cartilage. The under surface of the petrous bone included between these two fissures is rough and irregular, and affords attachments near its apex to two small muscles, the levator veli palatini and the tensor tympani. Immediately behind the alar spine the petrous part of the temporal is pierced by a circular hole, the inferior opening of the carotid canal (canalis caroticus). This passes upwards, and then turns medially and forwards towards the apex of the bone, where it may again be seen opening into the lateral and upper side of the foramen lacerum. Laterally the wall of the vertical part of this canal, which is usually very thin, separates it from the cavity of the tympanum, as may be seen ^ Longus capitis = rectus capitis anticus major. Rectus capitis anterior = rectus capitis anticus niiuor (old nomenclature). 164 OSTEOLOGY. by holding the skull up to the light and looking into the external auditory meatus. The carotid canal transmits the internal carotid artery, together with the sym- pathetic plexus around it. It is noteworthy that the two carotid canals lie in line with the anterior edges of the two external auditory meatuses. The jugular foramen is an opening of irregular shape and size placed be- tween the petrous part of the temporal in front and the jugular process of the occipital bone iDchind. The former is excavated into a hollow called the jugular fossa, which forms a roof to the upper and lateral part of the space, whilst the latter, by a curved edge, either rounded or sharp, constitutes its posterior border. There is often considerable difference in the size of the jugular foramina ; that on the right side (with the skull in its normal position) is usually the larger. The foramen is occasionally subdivided into two by spicules of bone which bridge across it. Lodged within the fossa is the sinus of the internal jugular vein, in front of which the inferior petrosal sinus passes down to join the internal jugular vein below the foramen. Effecting an exit between the two veins, in order from before backwards, are the glosso-pharyngeal, pneumogastric, and accessory nerves. Small meningeal branches from the ascending pharyngeal and occipital arteries also enter the foramen. The two jugular foramina lie in line with a line drawn through the centres of the two external auditory meatuses. Following the direction of a line connecting the alar spine of the sphenoid and the mastoid process of the temporal, and placed immediately lateral to the apertures of the carotid canal and jugular foramen, is the vaginal process of the tympanic plate of the temporal bone, the edge of which is sharp and thin, and serves to separate the under surface of the petrous part of the temporal from the non-articular part of the glenoid fossa. Springing from this crest immediately lateral to the jugular fossa, and in line with the middle of the external auditory meatus, is the styloid process (processus styloideus) of the temporal bone. Its relation to the jugular foramen is of great importance, as the internal jugular vein lies close to its medial side. Immediately behind the root of the styloid process, medial to and in line with the front of the mastoid process, is the stylo -mastoid foramen (foramen stylo- mastoideum), the lower aperture of the aquseductus Fallopii through which the facial nerve passes out and the stylo-mastoid branch of the posterior auricular artery passes in. The medial surface of the mastoid process is deeply grooved at its base for the origin of the posterior belly of the digastric muscle. Medial to this, and running along, just wide of the occipito-mastoid suture, is a shallow groove in which the occipital artery is lodged. Just medial to the stylo-mastoid foramen is the synchondrosis between the extremity of the jugular process (processus jugularis) of the occipital bone and the petrous part of the temporal. The former is a bar of bone which limits the jugular fossa posteriorly and abuts on the occipital condyles medially ; its under surface is convex from before backwards and affords attach- ment to the rectus capitis lateralis muscle. The occipital condyles are placed between the jugular processes and the foramen magnum. Limited in front by a rounded thickening which becomes confluent with the anterior border of the foramen magnum, they form by their medial sides the lateral boundaries of that aperture on its anterior half. Laterally they are continuous with the jugular processes, in front of which they overhang a fossa which is pierced behind by the anterior condylic foramen (canalis hypoglossi), through which passes the hypoglossal nerve, together with a small vein and occasionally a small meningeal branch derived from the ascending pharyngeal artery. The posterior condylic fossae are situated just behind the posterior extremities of the condyles. Not unfrequently their floor is pierced by the posterior condylic foramen (canalis condyloideus), through which the posterior condylic vein emerges. The base of the skull behind the jugular processes and condyles of the occipital bone is formed by the nuchal surface (planum nuchale) of the s(|uamous part of that bone. Posteriorly this surface is bounded by the superior curved line, in the centre of which is placed the projecting external occipital protuberance. Laterally the tabular plate is separated from the mastoid portion of the temporal bone by the occipito-mastoid suture, which curves backwards and laterally, from the extremity of the jugular process in front, around the base of the mastoid process behind. In NOEMA BASALTS OF THE SKULL. 165 front and in the middle line this plate of bone is pierced by the foramen magnum, the anterior half of which has been already seen to lie between the occipital condyles. Usually of oval form, though in some cases it tends to approach the circular, the plane of this opening is inclined downwards and slightly forwards. The extreme anterior edge of the foramen is sometimes called the basion, whilst the extreme posterior margin is termed the opistMon. The lower border of the medulla oblongata, where it becomes continuous with the spinal cord, is lodged within the foramen, together with the meninges which cover it, whilst the vertebral arteries and the spinal portions of the spinal accessory nerves pass upwards through it. The anterior and posterior spinal arteries, some small veins, and the roots of the first cervical nerves, also traverse it from above downwards. The student will, no doubt, experience considerable difficulty in bearing in mind the relative positions of the various foramina and processes which he has studied on the under surface of the base of the skull. If a line be drawn on either side from the anterior palatine canal in front, through the stylo- mastoid foramina jjosteriorly, it will be found to cut or pass near to the following ol)jects : — On the hard jjalate it will lie close to the posterior and accessory palatine canals. It will then pass between the hanuilar process and the external pterygoid plate overlying the foramen ovale, the foramen sjjinosum, the opening of the osseous Eustachian canal and the spine of the sjjlienoid ; behind this it will cut through the root of the styloid process and define laterally the limits of the jugular fossa. After passing through the stylo-mastoid foramen, if the line be prolonged backwards it will usually be found to pass over the mastoid foramen in the occipito-mastoid suture. Another line of much value is one drawn across the base of the skull from the centre of one external auditory meatus to the other. This will be found to pass through the root of the styloid process, the jugular foramen, the anterior condylic foramen ; it then crosses the front of the occipital condyles, and corresponds with the anterior edge of the foramen magnum. A line which may be found useful is one drawn from the stylo-mastoid foramen of one side to the posterior palatine canal of the opposite side. This will be seen to overlie, from behind forwards, the lateral part of the jugular foramen and the inferior opening of the carotid canal. The line indicates the direction of the carotid canal, and cuts the foramen lacerum anteriorly ; in front of this it usually corresponds to the position of the posterior aperture of the pterygo- palatine (pharyngeal) canal. Mandible and Atlas. — The examination of the base of the skull is incomplete unless the student examines it with the lower jaw and atlas in position. The relation of the ramus of the lower jaw to the zygomatic fossa has been already sufficiently studied (p. 156) ; one or two points, however, may be emphasised. The alar spine of the sphenoid lies just medial to the condyle of the jaw when that structure is in position in the articular part of the glenoid fossa, and it is noteworthy that immediately to the medial side of the alar spine is the commence- ment of the osseous Eustachian tube. The root of the styloid process occupies the centre of the interval between the mandibular ramus and the front of the mastoid process. Anteriorly the arcade formed by the body of the lower jaw adds greatly to the depth of the hard palate. In this space are lodged the tongue and the structures which form the floor of the mouth. The medial surface of each side of the body of the mandible is traversed by the mylo-hyoid line, which commences posteriorly just behind the root of the last molar tooth and runs downwards and forwards towards the symphysis in front. When the atlas is in articulation with the occipital bone it is well to recognise the relation of its transverse processes to the surrounding structures. The extremities of these processes lie in line with the ends of the jugular processes of the occipital bone, and thus come to be placed just medial to and immediately below and slightly in front of the tips of the mastoid processes. They can thus be easily felt in the living. Anteriorly they are separated by a short interval from the styloid processes, and the stylo-mastoid foramina lie immediately in front and sKghtly to the lateral side of their extremities. The student will note that there is no hole in the jugular process of the occipital bone corresponding to the arterial foramen in the transverse process of the atlas through which the vertebral artery passes. The course of this vessel over the upper surface of the posterior arch behind the superior articular processes of the atlas will be seen to coincide with the posterior condylic fossae and the margins of the foramen magnum immediately medial thereto, where a sUght grooving of the edge often indicates the course of the artery. 11 166 OSTEOLOGY. In front the anterior tubercle of the atlas falls in line with the pharyngeal tubercle on the under surface of the basi-occipital, and the student must not overlook the fact that the anterior surface of the cervical column does not coincide with the anterior margin of the foramen magnum, but lies nearly half an inch in front of that, in a coronal plane passing immediately in front of the external auditory meatus. Behind, the upper surface of the posterior arch of the atlas overlaps the hinder margin of the foramen magnum, and it is by the apposition of these two surfaces that extension is checked at the occipito-atlantal articulation. THE SKULL IN SECTION. By the removal of the skull-cap the cerebral aspect of the cranial cavity is exposed. The deep surface of the cranial vault is grooved medially for the superior longitudinal (sagittal) sinus, on either side of which are seen numerous depressions for the lodg- ment of Pacchionian bodies. On holding the bone up to the light, the floor of these little hollows is oftentimes seen to be very thin. A short distance in front of the lambda, and on either side of the sagittal suture, are the cerebral openings of the parietal foramina. The inner tables of the frontal and parietal bones are grooved for the meningeal arteries. The principal branch of the middle meningeal runs more or less parallel to and at a variable distance behind the line of the coronal suture. Along the bottom of these grooves small foramina may be seen for the passage of nutrient arteries to the bone, and the floor of the longitudinal sinus is likewise pierced by small apertures for the transmission of veins. The Upper Surface of the Base of the Skull. Cranial Fossae. — The upper surface of the base of the skull is divided into three fossae, of which the cerebrum occupies the anterior and middle, whilst in the posterior is lodged the cerebellum. The anterior fossa is defined posteriorly by the sharp, thin edge of the lesser wings of the sphenoid, which curve laterally and slightly upwards as well as back- wards to reach the region of the pterion laterally. The floor is formed from before backwards, in the middle line, by the upper surface of the ethmoid and the fore- part of the body of the sphenoid ; laterally it is constituted by the orbital plates of the frontal and the lesser wings of the sphenoid. On these the under surface of the frontal lobes of the cerebrum rests. In front the fossa is divided medially by the frontal crest, to whiG]|i the falx cerebri is attached. This is confluent below with the fore part of the crista galli, from which, however, it is separated by the foramen csecum, which usually transmits a smaU vein from the nose. On either side of the crista galli there are grooves which vary considerably in depth and width : therein are lodged the olfactory lobes. The floor and sides of the groove are pierced by numerous foramina ; of these the largest number transmit the olfactory nerves to the nasal fossse. In front an elongated slit, placed on either side of the crista, affords a passage to the nose for the internal ramus of the nasal nerve and a small branch of the anterior ethmoidal artery which accompanies it. To the lateral side of the olfactory groove and the cribriform plate, the anterior fossse communicate on either side by means of the two ethmoidal foramina with the cavities of the orbits. The anterior foramen transmits the internal ramus of the nasal nerve and the anterior ethmoidal artery ; the posterior affords passage to the posterior ethmoidal artery and the small spheno-ethmoidal nerve of Luschka. Lateral to the olfactory groove, the floor of the fossa, which here corresponds to the roof of the orbit, is very thin, as may be seen by holding the skull up to the light ; it is convex from side to side, and bears the impress of the convolutions of the under surface of the frontal lobes of the cerebrum which rest upon it. In front and at the side there are a number of vascular grooves for the branches of the anterior and middle meningeal arteries respectively. The middle fossa, which in form may be compared to the wings of a bird 41 1 Fig. 118. — Base of the Skull seen from Above. Tlie frontal and occipital bones are coloured red ; the ethmoid and temporal bones, blue ; the parietal, orange ; and the sphenoid is left uncoloured. 9. 10. 11. 12. 13. 14. 15. 16. 17. 18. 19. 20. 21. 22. 23, Frontal bone. Slit for nasal nerve. Anterior ethmoidal foramen. Posterior ethmoidal foramen. Optic foramen. Foramen for internal carotid artery formed by anterior and middle cliuoid process. Lesser wing of sphenoid. Anterior clinoid process, in this case united on its inner side to the middle clinoid processes. Posterior clinoid process. Foramen ovale. Groove for middle meningeal artery. Foramen spinosum. Hiatus Fallopii. Line of petro- squamosal suture. - Internal auditory meatus. Groove for superior petrosal sinus. Groove for sigmoid part of lateral sin\is. Jugular foramen. Anterior condylic foramen (canalis hypoglossi). Groove for lateral sinus. Internal occipital protuberance. Ridge for attachment of falx cerebri. Fossa for the lodgment of the occipital lobes of the brain. 24. Pudge for the attachment of the falx cerebelli. 25. Fossa for the lodgment of the left cerebellar hemisphere. 26. Foramen magnum. 27. Groove for the sigmoid sinus turning into the jugular foramen. . 28. Groove for the inferior petrosal sinus running along the line of suture between the petrous part of the temporal and the basi-occipital. 29. Depression for the Gasserian ganglion. 30. Middle cranial fossa for lodgment of the temporal lobe's of the brain. 31. Foramen lacerum. 32. Carotid groove. 33. Dorsum sellae of sphenoid. 34. Leads into foramen rotundum, 35. Pituitary fossa. 36. Olivary eminence of the sphenoid. 37. Anterior cranial fossa for lodgment of frontal lobes of the brain. 38. Cribriform plate of ethmoid. 39. Crista galli of ethmoid. 40. Foramen caecum. 41. Crest for attachment of falx cerebri. 11a 168 OSTEOLOGY. united by the body, is bounded in front by the curved thin posterior edge of the lesser wings of the sphenoid ; posteriorly, by the line of attachment of the tentorium cerebelli, extending from the posterior clinoid process along the superior border of the petrous portion of the temporal bone. The median part of the fossa, which is narrow, corresponds to the sella turcica and the olivary eminence of the sphenoid. It is limited anteriorly by a hne connecting the anterior margins of the two optic foramina, and is overhung behind by the dorsum sellse. In this area are lodged the structures which lie within the interpeduncular space on the base of the brain. The floor of the lateral parts of the fossa on each side is formed by the great wing of the sphenoid in front, the squamous part of the temporal bone to the lateral side, and the superior surface of the petrous part of the temporal behind. In the hoUows so formed the temporal lobes of the cerebrum are lodged. On either side of the olivary eminence are seen the optic foramina ; these pass into the orbital cavities and transmit the optic nerves and ophthalmic arteries. Immediately behind these openings the anterior and middle clinoid processes are sometimes united, so as to enclose a foramen. Through this the internal carotid artery passes upwards. Leading backwards from this, along the side of the body of the sphenoid, is the carotid groove, which turns downwards near the apex of the petrous part of the temporal, to become continuous with the carotid canal, which here opens on the posterior waU of an irregular aperture, placed between the side of the body of the sphenoid and the summit of the petrous part of the temporal, called the foramen lacerum. Through the medial angle of this opening the carotid artery accompanied by its plexus of veins and sympathetic nerves passes upwards. Eunning through the fibrous tissue, which in life blocks up this opening, the great superficial petrosal nerve coming from the hiatus Fallopii passes downwards and forwards to reach the posterior orifice of the Vidian canal (canalis pterygoideus), which is placed on the anterior and inferior border of the foramen lacerum. ' A small meningeal branch of the ascending pharyngeal artery also passes upwards through this foramen. In front and to the lateral side of the foramen lacerum, and separated from it by a narrow bar of bone, is the foramen ovale ; through this pass both roots of the mandibular nerve, the small meningeal artery, and some emissary veins. Some- what lateral and posterior to this is the foramen spinosum for the transmission of the middle meningeal vessels, together with a recurrent branch from the mandibular nerve (nervus spinosus). > Leading from the lateral extremity of the foramen lacerum there is a groove which passes laterally, backwards, and slightly upwards on the superior surface of the petrous part of the temporal to end in the hiatus Fallopii (a cleft opening into the aquseductus Fallopii), which gives passage to the great superficial petrosal branch_derived from the geniculate ganglion on the seventh nerve, together with the small petrosal branch of the middle meningeal artery. . Just lateral to the hiatus Fallopii there is another small foramen for the transmission of the lesser superficial petrosal nerve. Overhung by the posterior border of the lesser wing of the sphenoid is the sphenoidal fissure (fissura orbitalis superior), the cleft which separates the lesser from the great wings of the sphenoid, and which opens anteriorly into the hollow of the orbit ; through this pass the third, fourth, oph- thalmic division of the fifth, and sixth nerves, together with the ophthalmic veins as well as the sympathetic filament to the ciliary ganglion and the small orbital branch of tlie middle meningeal artery. Just below its medial extremity is the foramen rotundum for the passage of the maxillary nerve to the spheno-maxillary fossa. Behind this, and between it and the foramen ovale, the foramen Vesalii may occasionally be seen, through which a vein passes to reach the pterygoid plexus. The lateral parts of the middle fossa are moulded in conformity with the convolutions of the temporal lobes, but towards its medial part the splitting of the dura mater in the region of the cavernous sinus serves to separate the cranial base from the under surface of the cerebrum. As may be seen by transmitted light, the floor of the lateral parts of the fossa is thin as it overlies the temporal, zygomatic, and glenoid fossae. The grooves for the lodgment of the branches of the middle meningeal artery leading from the foramen spinosum are readily seen ; one, coursing backwards a little below the line of the squamoso-parietal suture, is specially well marked. Amongst other features may be noticed the depression for THE UPPER SURFACE OF THE BASE OF THE SKULL. 169 the lodgment of the Gasserian ganglion overlying the summit of the petrous temporal; behind and to the lateral side of the hiatus Fallopii, the arcuate eminence, indicating the position of the superior semicircular canal ; and immediately anterior and slightly to the lateral side of this the tegmen tympani, which roofs in the cavity of the tympanum, the thinness of which can readily be demonstrated if hght be allowed to fall through the external auditory meatus. The posterior fossa is larger and deeper than the others. In front it is limited by a line on either side leading backwards and laterally from each posterior clinoid process along the superior border of the petrous part of the temporal bone, where laterally and posteriorly it becomes confluent with the superior lip of the transverse groove for the lateral (transverse) sinus, ending posteriorly in the middle line at the internal occipital protuberance. Along the line thus indicated the process of dura mater called the tentorium xerebelli, which roofs in the posterior fossa, is attached. The floor of the fossa, in which the cerebellar lobes, the pons, and medulla are lodged, is formed by the petrous and mastoid portions of the temporal bone, with part of the body of the sphenoid and the basilar portion of the occipital bone wedged in between them. Above the mastoid part of the temporal a small part of the mastoid angle of the parietal enters into the constitution of the outer wall of the fossa. Behind and within these the lateral parts and lower portions of the squamous part of the occipital complete the floor. In the middle line the floor of the fossa is pierced by the foramen magnum, in which lies the lower part of the medulla, together with its membranes, and through which pass upwards the vertebral arteries and the accessory nerves. Iy On either side of the foramen magnum, and a little in front of a transverse line passing through its centre, is the opening of the anterior condylic foramen (canalis hypoglossi) for the passage of the hypo- glossal nerve, a small meningeal branch from the ascending pharyngeal artery and an emissary vein. Overhanging the opening of the anterior condylic foramen there is a thickened rounded bridge of bone, to the lateral side of which is placed the irregular opening of the jugular foramen. The size of this is apt to vary on the two sides, and the lumen is frequently subdivided by a spicule of bone which runs across it ; the posterior and lateral rounded part of the foramen is occupied by the lateral (transverse) sinus, which here joins the internal jugular vein. A meningeal branch from the ascending pharyngeal or occipital artery also enters the skull through this compartment. The fore and medial part of the foramen is con- fluent with the groove for the inferior petrosal sinus, which turns downwards in front of the spicule above referred to. The interval between the portions of the foramen occupied by the two veins allows the transmission of the glosso-pharyngeal, vagus, and accessory nerves in this order from before backwards. About a quarter of an inch above and to the lateral side of the fore part of the foramen jugulare the posterior surface of the petrous portion of the temporal bone is pierced by the internal auditory meatus, through which the facial and auditory nerves, together with the pars intermedia of Wrisberg (n. intermedins), and the auditory branch of the basilar artery, leave the cranial cavity. Behind the jugular foramen and close to the margin of the foramen magnum the opening of the posterior condylic foramen (canalis condyloideus), when present, may be seen. This gives passage to a vein which joins the vertebral vein inferiorly. The medial aperture of the mastoid foramen is noticed opening into the groove for the lateral sinus, a little below the level of the superior border of the petrous part of the temporal. Through it passes an emissary vein which joins the occipital vein laterally ; the mastoid branch of the occipital artery also enters the cranial cavity through this foramen. The posterior fossa is divided into two halves posteriorly by the internal occipital crest, to which the falx cerebelli is attached, the floors of the hollows on either side of which are often exceedingly thin and are for the lodgment of the lateral lobes of the cerebellum. The grooves for the following blood sinuses are usually distinct — the superior petrosal running along the superior border of the petrous part of the temporal, the inferior petrosal lying along the line of suture between the petrous part of the temporal and the basilar process of the occipital bone ; the occipital sinus grooving the internal occipital crest ; and the lateral sinus curving forwards and laterally from the internal occipital protuberance, across the cerebral surface 170 OSTEOLOGY. of the squamous part of the occipital, to reach the posterior inferior angle of the parietal bone, in front of which it turns downwards and medially to reach the jugular foramen, describing a sigmoid curve, and grooving deeply the medial surface of the mastoid and posterior aspect of the petrous portions of the temporal bone. Before it terminates at the jugular foramen it again reaches the occipital bone and channels the upper surface of the jugular process of that bone. Slight grooves for meningeal arteries are also seen — some pass upwards, whilst others turn downwards and are occupied by branches from the posterior offsets of the middle meningeal arteries. Medial Sagittal Section of the Skull. Such a section should be made a little to one or other side of the medial jjlane, so as to pass through the nasal fossae lateral to the septum ; one-half will then display the nasal septum in position, whilst in the other the outer wall of the nasal fossa of that side will be exposed. The form of the cranial cavity is, of course, subject to many variations dependent on individual and racial peculiarities. The following details are, however, worthy of note. The hinder border of the foramen magnum (opisthion), and consequently the floor of the posterior cranial fossa, occupies the same horizontal plane as the hard palate. The anterior border of the foramen magnum (basion) lies a little higher, so that the plane of the foramen is, in the higher races at least, oblique, and is directed downwards and slightly forwards. From the basion a line passing upwards and forwards to reach the suture between the sphenoid and ethmoid passes through the basi-cranial axis formed by the basi-occipital, the basi-sphenoid, and the j)resphenoid. The basi-cranial axis is wedge-shaped on section posteriorly, whilst anteriorly it is of considerable width, and has within it the large sphenoidal air sinus. Its upper surface leads upwards and forwards with a varying degree of obliquity from the basion to the overhanging edge of the dorsum sellse, in front of which the pituitary fossa, the floor of which is quite thin, is well seen in the section. From the olivary eminence the floor of the anterior fossa follows a more or less horizontal direction, corresponding pretty closely to the level of the axis of the orbital cavity. The roof of the orbit is seen to bulge upwards to a considerable extent into the floor of the anterior fossa ; whilst the floor of the middle fossa sinks to a level corresponding to that of the under surface of the basi-cranial axis, where it forms the roof of the posterior nares. The maximum length of the skull is measured from the glabella (a point between the superciliary ridges) to the occipital point posteriorly. It is noteworthy that the maximum occipital point does not necessarily correspond to the external occipital pro- tuberance (inion). The greatest vertical height usually corresponds to the distance from the basion to the bregma (point of union of the sagittal with the coronal suture), though to this rule there are many exceptions. On looking into the posterior fossa the anterior condylic and jugular foramina and the internal auditory meatus are seen in line, sloping from below upwards. The internal auditory meatus lies in a vertical plane, passing through the basion. The grooves for the middle meningeal artery and its branches are very obvious. The anterior groove curves forwards and laterally, and reaching the cerebral surface of the pterion, passes towards the vertex at a variable distance behind and more or less parallel to the coronal suture. From this grooves pass forwards across the suture to reach the frontal bone. Another groove curves upwards and backwards a little below the line of the parieto-squamosal suture. From this an upwardly-directed branch radiates on the central surface of the parietal bone, in the region of the parietal eminence, whilst a lower branch passes backwards some little distance above the lambdoid suture, and gives offsets which curve downwards and medially over the cerebral surface of the squamous portion of the occipital bone. Nasal Fossae. — In the section through the nasal fossa the structures which form its lateral wall can now be studied. These are — tbe nasal bone ; the frontal process of the maxilla ; the lacrimal bone ; the lateral mass of the ethmoid, comprising the superior and middle turbinated bones ; the vertical part of the palate bone ; the inferior turbinated bone ; and the medial surface of the internal pterygoid plate. The roof as seen in the section is formed by the nasal and frontal bones, the cribri- form plate of the ethmoid, the body of the sphenoid and the sphenoidal turbinals. THE NASAL FOSS^. 171 the sphenoidal process of the palate and the ala of the vomer. The floor, which is nearly horizontal from before backwards, is formed by the palatal processes of the maxiUa and palate bones. On sagittal section the nasal fossa appears some- 42 41 40 39 38 37 36 35 34 33 32 31 80 29 28 27 26 25 24 23 22 21 Fig. 119. — Medial Aspect of the Left Half of the Skull sagittallt divided. The frontal, ma.xillary, and sphenoid bones are coloured red ; the nasal and palate bones, blue ; and the occipital, yellow. The ethmoid and inferior turbinal, together with the left ala of the vomer, are left uncoloured. Posterior nasal sjjine. Hamular process of internal pterygoid plate. External pterygoid plate. Superior meatus of nose. Spheno-palatine foramen. Pterygo - spinous ligament almost completely ossified to enclose a foramen. Styloid process of temporal bone. Alar spine of sphenoid. Mastoid process. Basion (mid-point of anterior border of foramen magnum). Internal auditory meatus. Anterior condylic foramen (foramen hypoglossi). Leading into jugular foramen. Opisthion (mid-point of posterior border of foramen magnum). - Groove for sigmoid sinus. ' Opening of mastoid foramen. For lateral sinus and attachment of tentorium cerebelli. Fossa for lodgment of cerebellar hemisphere. Internal occipital protuberance, atal process of palate bone. what triangular in shape with the angles cut off; the base corresponds to the floor ; the anterior and posterior nares to the truncated anterior and posterior angles respectively ; the superior angle is cut off by the cribriform plate ; whilst the sides correspond to the frontal and nasal bones anteriorly, and the sphenoidal 1. Suture between parietal and temporal bones. 24. 2. Remains of the subarcuate fossa. 25. 3. Grooves for branches of the middle meningeal 26. artery. 27. 4. Dorsum sellse. 28. 5. Pitiiitary fossa. 29. 6. Anterior clinoid fossa-. 7. Optic foramen. 30. 8. Sphenoidal sinus. 31. 9. Nasal surface of superior turbinated bone. 32. 10. 11. Cribriform plate of ethmoid. Nasal surface of middle turbinated bone. 33. 12. Frontal sinus. 34. 13. Spine of frontal. 35. 14. Nasal bone. 36. 15. Frontal process of maxilla. 37. 16. Middle meatus of nose. 17. Directed towards opening of antrum. 38. 18. Nasal surface of inferior turbinated bone. 39, 19. Inferior meatus of nose. 40. 20. Anterior nasal spine. 21. Anterior palatine canal. 41. 22. Palatal process of maxilla. 42. 23. Palatal process of palate bone. 172 OSTEOLOGY. turbinals, sphenoidal process of the palate, and the ala of the vomer posteriorly. The cavity is therefore deep towards its middle, but gradually becomes shallower in front and behind where the openings of the nares are situated. The opening of the anterior naris, which is of half-heart shape, is larger than that of the posterior naris, and is directed forwards and downwards ; the opening of the posterior is of rhomboidal form, and slopes backwards and downwards. The inferior meatus is the channel which is overhung by the inferior turbinated bone, and its floor is formed by the side-to-side concavity of the upper surface of the hard palate. Opening into it above, under cover of the fore part of the inferior turbinated bone, is the canal for the nasal duct ; whilst its floor is pierced in front near the middle line by the anterior palatine canal. The middle meatus is the hollow between the middle and inferior turbinated bones ; it slopes from above downwards and back- wards, and is overhung by the free curved edge of the middle turbinal, beneath which there is a passage called the infundibulum, leading upwards and forwards to open superiorly into the frontal sinus, as well as into some of the anterior ethmoidal cells. Under cover of the centre of the middle turbinated bone and continuous with the infundibulum in front there is a curved groove, the hiatus semilunaris, into which open one or more orifices from the maxillary sinus. Above this groove there is a rounded eminence, the bulla ethmoidalis, overlying the middle ethmoidal cells which usually open on its surface. The superior meatus, about half the length of the middle meatus, is placed between the superior and middle turbinated bones in the back and upper part of the fossa ; it receives the openings of the posterior ethmoidal cells. Near its posterior extremity the spheno- palatine foramen pierces its outer wall, and brings it in relation with the spheno- maxillary fossa. The sphenoidal sinus opens on the roof of the nose, above the level of the superior turbinated bone, into a depression called the spheno- ethmoidal recess. Nasal Septum. — If the opposite half of the section in which the osseous nasal septum is retained be now studied, it will be seen to be formed by the crests of the maxillary and palate bones below, on which rests the vomer, the posterior border of which being free, forms the posterior edge of the nasal septum, which slopes obliquely upwards and backwards towards the under surface of the body of the sphenoid. Here the vomer articulates with the rostrum of the s^jhenoid. In front of this the vomer articulates with the perpendicular part of the ethmoid, between which anteriorly there is an angular recess into which the cartilaginous septum fits. Superiorly and anteriorly the osseous septum is completed by the articulation of the perpendicular part of the ethmoid with the nasal process of the frontal, together with the nasal crest formed by the union of the nasal bones ; whilst posteriorly and superiorly the perpendicular plate of the ethmoid articulates with the medial ethmoidal crest of the sphenoid. In most instances the osseous septum is not perfectly vertical, but is deflected towards one or other side. Air-sinuses in connexion with the Nasal Fossae. — Connected with the nasal fosste are a number of air-sinuses. These are found within the body of the sphenoid, the lateral mass of the ethmoid, the orbital process of the palate bone, the body of the maxilla, and the superciliary arch of the frontal bone. The sphenoidal sinus, of variable size, occupies the interior of the body of the sphenoid. In some cases it extends towards the roots of the pterygoid processes. In front it is formed in part by the absorption of the sphenoidal spongy bones, and is divided up into two cavities by a sagittally-placed partition, which, however, is frequently displaced to one or other side. It opens anteriorly into the roof of the nose in the region of the spheno-ethmoidal recess. The ethmoidal sinuses are placed between the lateral aspects of the upper part of the nasal fossse, and the cavities of the orbit, from which they are separated by thin and papery walls. These air-spaces are completed by the articulation of the ethmoid with the maxilla, lacrimal, frontal, sphenoid, and palate bones, and are divided into three groups — an anterior, middle, and posterior. The latter communicates with the superior meatus ; the anterior and middle open either independently or in conjunction with the infundibulum into tlie middle meatus. The sinus in the orbital process of the palate bone either communicates with CORONAL SECTIONS OF THE CEANIUM. 173 Frontal sinus Ciista galH of ethmoid Cribriform plate of ethmoid Sphenoidal sinus Pituitary fossa Dorsum sellse of sphenoid the sphenoidal sinus, or else assists in closing in some of the posterior ethmoidal cells. Its communication with the nasal fossa is through one or other of these spaces. The maxillary sinus or antrum of Higlunore lies to the lateral side of the nasal fossa3, occupying the body of the maxilla. Its walls, which are relatively thin, are directed upwards to the orbit, forwards to the face, backwards to the infra-temporal (or zygomatic) and ptery go-maxillary (or spheno-maxillary) fossa3,and medially to the nose. In the latter situa- tion the vertical plate of the palate bone, the uncinate process of the ethmoid, the maxillary process of the in- ferior turbinated bone, and a small part of the lacrimal bone assist in the formation of the thin osseous partition which separates it from the nasal fossa. The floor corre- sponds to the alveolar border of the jaw, and differs from the other walls in being stout and thick ; it is, however, deeply pitted inferiorly by the alveoli for the teeth. The antrum opens by a narrow orifice in the floor of the hiatus semilunaris into the middle meatus. Oc- casionally there are two openings. The frontal sinuses lie, one on either side, between the inner and outer tables of ^"'"""' p'^'='^""^ "^^■""''^" the frontal bone over the root of the nose, and extend laterally under the super- ciliary arches. The parti- tion which separates them is usually central, though it may be deflected to one or other side. They communicate with the nose through a passage called the infundibulum, which opens inferiorly into the fore part of the middle meatus, below the ethmoidal bulla and continuous with the hiatus semilunaris. The fact should not be overlooked that the air-spaces within the temporal bone, viz. the tympanic cavity and the mastoid air cells, are brought into com- munication with the naso-pharynx through the Eustachian tubes. Further details regarding the air-sinuses and the mode of their growth will be found under the description of the individual bones. Alar spine Vomer External pterygoid plate Hamular process Fig. 120. — The Nasal Septum as seen fkom the Left Side. The froutal, maxillary, aud sphenoid bones are coloured red ; the nasal, vomer, and basi-occipital blue ; the vertical plate of the ethmoid and the palatal process of the palate bone are left uncoloured. Coronal Sections. The relations of many parts of the cranium are best displayed in a series of coronal sections. By sawing off a thin slice from the front of the lower part of the frontal bone above, and carrying the section downwards through the medial wall of the orbit and the frontal process of the maxilla, into the anterior nares below, a number of important relations are revealed (see Fig. 121). In the frontal region the extent and arrange- ment of the frontal sinuses are displayed. The partition between the two sinuses, be it noted, is usually complete and central in position, though it may occasionally be perforated or oblique. The sinuses are hardly ever symmetrical, the right being usually the smaller of the two. (Logan Turner, Edin. Med. Jour. 1898.) The infundibulum on either side, leading from the frontal sinus above to the middle 174 OSTEOLOGY. meatus below, is seen with the middle turbinated bone medial to it, and the anterior ethmoidal cells to its lateral side above. If the section passes through the canal for the nasal duct the continuity of that channel leading from the orbit above to the inferior meatus of the nose below is clearly shown. Its medial wall above, by which it is separated fi'om the cavity of the nose, is formed by the thin lacrimal bone ; below, it passes under cover of the inferior turbinated bone to open into the fore part of the inferior meatus. It Fig. 121.- -Part of the Frontal, Nasal, and Maxillary Bones removed in order to DISPLAY THE RELATION OF THE VARIOUS CaVITIES EXPOSED. The frontal and maxillary bones, where cut, are coloured blue ; the ethmoid and the inferior turbinal red ; the ethmoid and vomer yellow. 1. Frontal sinus. 2. Septum of frontal sinus deflected towards the right. 3. Infundibulum leading from sinus to middle meatus. 4. Anterior ethmoidal air-sinuses. 5. Middle turl)inated bone. 6. Red line in upjier part of osseous canal for nasal duct, laid open throughout its entire length on the right side. 7. Cavity of antrum laid open. 8. Middle meatus of nose. 9. Inferior meatus of nose. 10. Inferior turbinated bone. 11. Nasal septum. 12. Canal for nasal duct laid open throughout its entire length. 13. Anterior nasal spine. is separated from the antrum laterally by a thin lamina of bone. The cavity of the antrum is seen to extend upwards and forwards so as to pass over the lateral side as well as slightly in front of the canal for the nasal duct. The lower margins of the middle turbinated bones lie pi'etty nearly on a level with the most dependent parts of the orbital margins, whilst the lower borders of the inferior turbinals are placed a little above the lower margin of the anterior nares on a level with the lowest point of the zygomatico-maxillary suture. Such a section will reveal any deflection of the nasal septum should it exist, and will also show that but a narrow cleft separates the upper part of the septum, on either side, from the medial surface of the superior turbinals. The next section (Fig. 122) passes through the fore part of the temporal fossa just COEONAL SECTIONS OF THE CKANIUM. 175 behind the zygomatic process of the frontal bone above ; inferiorly it passes through the alveolar process of the upper jaw in the interval between the first and second molar teeth. The cranial, orbital, nasal, and maxillary cavities are all ex- ' -' ^ posed, together with the roof of the mouth. The anterior cranial fossa is deepest in its centre, where its floor is formed by the cribriform plate of the ethmoid ; this corre- sponds to the level of the zygo- matico-frontal suture laterally. On either side the floor of the fossa bulges upwai'ds, owing to the arching of the roof of the orbit. Of the orbital walls, the latei'alisthethickestand stoutest; the superior, medial, and inferior walls, which separate the orbit from the cranial cavity, the eth- moidal cells, and the antrum, re- spectively, are all thin. Thecavity of the maxillary sinus lying to the lateral side of the nasal fossae is well seen. Its roof, which separates it from the orbital cav- ity, is thin and traversed by the infraorbital canal. Its medial wall, with which the inferior tur- binal articulates, is very slender, and forms the lateral walls of both the middle and inferior meatuses of the nose. Its lateral wall is stouter where it arches up to bracket the zygomatic or malar process. Its floor, which rests upon the upper surface of the alveolar border of the upper jaw, sinks below the level of the hard palate. The fangs of the teeth sometimes project into the floor of the cavity. The nasal fossae are narrow above, where they lie between the orbital cavities, from which they are separated by the cells within the lateral mass of the ethmoid. The roof which cor- responds to the cribriform plate is narrow, and lies between the septum medially and the lateral masses on either side. At the level of the orbital floor the nasal fosste expand later- ally, the middle meatus running longitudinally in the angle formed by the lateral mass of the ethmoid with the body of the maxilla, Fig. 122. — Cobonal Section passing inferiorly through THE Interval between the First and Second Molar Teeth. The frontal and maxillary bones, where cut, are coloured blue ; the ethmoid and inferior turbinals I'ed ; the vomer yellow. Groove for superior longi- 11. Orbital plate of maxilla. superior tudinal (sagittal) sinus. Crest for attachment of falx cerebri. 3. Crista galli of ethmoid. 4. Cribriform plate of ethmoid. 5. Perpendicular plate of eth- moid, assisting in the forma- tion of the nasal septum. 6. Lateral mass of ethmoid con- sisting of the ethmoidal cells. 7. Os planum of ethmoid. 8. Middle meatus of nose. 9. Middle turbinated bone. 0. Opening from middle meatus into antrum. 2. 12. Zygomatico-frontal suture. 1.3. Infraorbital groove. 14. Antrum or maxillary sinus. 15. Canal for the anterior dental nerve and vessels exposed. 16. Inferior turbinated bone. 17. Inferior meatus of nose. 18. Alveolar process of maxilla. 19. Groove for anterior palatine nerve and vessels. 20. Palatal process of maxilla. 21. Maxillary crest forming part of nasal septum. 22. Vomer forming part of nasal septam. overhung by the middle turbin- ated bone. This channel is seen to have the ethmoidal cells superior to it, the orbital cavity above and to the lateral side, the antrum laterally, whilst its floor is formed by the upper surface of the inferior turbinated bone. The inferior meatus, much more roomy, runs along under cover of the inferior 176 OSTEOLOGY. turbinated bone. Laterally it is related to the antrum, whilst its floor is formed by the concave superior surface of the hard palate. The hard palate is arched below, whilst its superior surface is concave upwards on either side of the median crest which supports the nasal septum. The sides of the arch below correspond to the medial surfaces of the alveolar processes and fall in line with the lateral walls of the nasal fossae superiorly. The summit of the arch lies a quarter of an inch above the level of the floor of the antrum. The next section (Fig. 123) passes through the spheno-maxillary (or ptery go- maxillary) and temporal fossae inferiorly, and cuts the cranial vault about half an inch in front of the bregma. The floor of the anterior cranial fossa is seen to be formed by the upper surface of the body and lesser wings of the sphenoid, and is almost horizontal. In the middle line the sphenoidal sinuses are exposed, separated by a thin bony partition, on either side of which the openings by which they communicate with the nasal fossae are seen. The section passes in front of the optic foramen, the groove of which may be seen on the under surface of the lesser sphenoidal wing close to the body, and lays open the sphenoidal fissure which here leads for- ward into the orbit, and which, inferiorly and laterally, is continuous with the cleft between the maxilla and the lower edge of the great wing of the sphenoid — the spheno - maxillary (or pterygo - maxillary) fissure. This also leads into the orbit. The nasal fossae, now much dimin- ished in height, are roofed in above by the under-surface of the body of the sphenoid and the aloe of the vomer, whilst the lateral walls are seen to be formed by the thin perpendicular plates of the palate bones, lateral to which the rounded posterior surface of the maxilla is directed backwards, here Fig. 123. — Coronal Section passing through the Spheno-Maxillary (or Pterygo- Maxillaby) Fossa. 1. Depression for Pacchion- ian Vjody. 2. Groove for superior longi- tndinal (sagittal) sinus. 3. Crista galli of etliiuoid. 4. Opening of sphenoidal sinus into superior meatus of nose through spheno - ethmoidal re- cess. 5. Sphenoidal (superior or- bital) fissure. 6. Part of middle fossa formed )>y cerebral surface of great wing of sphenoiil 9. Zygomatic process. 10. Zygomatic or malar pro- cess of maxilla. 11. Surface of maxilla which forms the anterior wall forming the anterior wall of the spheno- of the pterygo-maxii- maxillary (or ptery go-maxiUary) fossa — the space which lies between the fore part of the pterygoid process behind and the upper jaw anteriorly. As will lary fossa. Spheno-palatine foramen. Opening of posterior palatine canal. 14. Vertical part of palate be seen, the medial wall of this space is bone 15. Pterygoid fossa. 16. Superior meatus of nose. 17. Middle meatus of nose. 18. Inferior meatus of nose. Zygomatic crest of great 19. Inferior turbinate bone. wing of sphenoid. 20. Middle turl>inal bone. Spheno-maxillary (in- 21. Maxillary crest and vomer ferior orbital) fissure. fornung nasal septum. formed by the vertical plate of the palate, which is, however, deficient above im- mediately below the under surface of the body of the sphenoid. In the in- terval between the orbital process, which lies in front of the section, and the sphenoidal process, which lies l^ehind, this forms the spheno-palatine fora- men. Laterally the section has passed through the pterygo-maxillary fissure, which is continuous above with the spheno-maxillary fossa. Inferiorly the section passes through the line of fusion of the pterygoid processes with the pyramidal process of the palate CORONAL SECTIONS OF THE CRANIUM. 177 bone and the union of the latter with the maxilla. Just above this the opening of the posterior palatine canal, which leads from the pterygo-maxillary (spheno-maxillary) fossa to the under surface of the hard palate, is visible; whilst interiorly a small portion of the lower part of the pterygoid fossa is cut through. VV ithin tlie posterior nares the middle and inferior turbinate bones are seen ; the lower border of the former corresponds to the level of the upper border of the zygomatic arch, whilst the attached edge of the latter to the vertical plate of the palate lies in the same horizontal plane as the lower margins of that arch. Note also that the internal pterygoid plates lie considerably within the lines of the medial sur- faces of the alveolar border, and reach some little distance below the level of the hard palate. The next section (Fig. 124) passes through the glenoid fossa just behind the articular eminence ; superiorly, it cuts the vault half an inch behind the bregma. The middle cranial fossa is shown in section, the floor of which descends as low as the level of the under- surface of the body of the sphenoid, corresponding laterally to a hori- zontal plane passing through the upper edge of the posterior root of the zygomatic process of the temporal bone. The body of the sphenoid rises a finger's breadth above this in the middle line, the cavity within it is exposed, whilst on either side and below is seen the groove for the internal carotid artery, leading upwards from the medial part of the foramen lacerum, which is here divided. To the lateral side of the groove is seen the prominent edge of the lingula, immediately below which is the posterior aper- ture of the Vidian canal, the inferior edge of which is in part concealed by the pterygoid tubercle. Im- mediately lateral to the foramen lacerum the foramen ovale is seen separated from the surface of the section by a narrow bridge of bone. Here it is seen to overlie the root of the external pterygoid plate. The 8, section passes just in front of the foramen spinosum, and here is visible the stout suture between the great lo wing of the sphenoid and the 11 squamous part of the temporal bone. ^^ The glenoid fossa of the temporal jg bone is cut on either side, and in its 14 21 2b 25 24 Fig. 124. — Coronal Section of the Skull passing through THE Glenoid Fossa just behind the Articular Eminence. Great win Crista galli of ethmoid. Posterior cliuoid processes. Optic foraineu. Anterior clinoid process. Orbital plate of frontal. Lesser wing of sphenoid. Suture between squamous part of the temporal, and parietal bones. Sphenoidal (superior or- bital) fissure. Cerebral surface, great wing of sphenoid. Foramen rotundum. Squamous part of temporal. Posterior root of zygomatic process. Eminentia articularis. Glenoid fossa. 15. 16. 17. 18. 19. 20. 21. 22. 23. 24. 25. 26. 27. of siDhenoid iu front of spine. Foramen ovale. Lingula. Anterior margin of foramen lacerum and opening of Vidian canal. Postero - lateral margin of lateral pterygoid plate. Groove for carotid artery. Pterygoid fossa. Scaphoid fossa. Haniular process of medial pterygoid plate. Inferior turbinate bone. Inferior meatus of the nose. Nasal septum. Opening of sphenoidal sinus. Dorsum ephippii. deepest part is separated from the middle cranial fossa by but a thin lamina of bone. The thinness of the squamous part of the temporal and the manner in which it is sutured to the parietal is also well displayed. 178 OSTEOLOGY. The next figure (Fig. 125) displays the anterior surface of the section immediately behind that above described. In the centre, is seen the body of the sphenoid, and the hinder wall of the sinus is now exposed ; on either side the apex of the petrous part of the temporal abuts upon the sides of the body of the sphenoid, and the large orifice of the carotid canal is seen opening on to the hinder wall of the foramen lacerum, which is here divided. In the recess between the lateral wall of the carotid canal and the spine of the sphenoid is the groove leading into the osseous Eustachian canal, in front of which the base is pierced by the foramen spinosum. Lateral to the alar spine, the glenoid fossa is divided and its thin roof displayed. Crossing it transversely is seen theGlaserian fissure which divides the fossa, into an articular and non- articular part. The floor of the middle cranial fossa is here seen to be formed by the upward slope of the superior surface of the petrous part of the temporal, which is pierced by the hiatus- Fallopii, and the foramen for the lesser superficial peti'osal nerve. On the upper surface of the summit of the petrous part of the temporal the depression for the lodgment of the Gasserian ganglion is well seen on either side. The last section, the an- terior surface of which Fig. 126 is a representation, passes vertically through the base immediately in fi'ont of the root of the styloid process. In the middle line the basi-occipital is divided a little in front of the anterior extremities of the oc- cipital condyles, its upper surface- is concave from side to side and forms a wide groove for the medulla and pons. On either side there is a narrow interval between the lateral edge of the basi-occipital and the posterior- border of the petrous part of the temporal which in life is. occupied by dense fibrous tissue;, running along the upper surface of this suture is the inferior petrosal sinus. Laterally the section passes through the temporal bone, dividing the cavity of the tympanum and laying open the external auditory meatus. To the inner side of the tympanic wall the cocMea is exposed, whilst above and' lateral to it the aqueductus Fallopii is twice divided, tlie section passing posterior to the angle formed by its genu. Below the cochlea, and separated from it and the medial part of the floor of the tympanum, the carotid canal is in part exposed. Above the tympanum is the "attic" leading into the mastoid antrum, the whole being roofed in by the thin. Fig. 11 / / i\3 12 13 14 -^j 161718 19 20 21 22 23 125. — Anterior Surface of the Section of the Skull immediately behind the preceding section. 14. 15. 9. 10. 11. 12. 13. Impressio trigemini on apex of petrous Vjone. Squamo-parietal suture. Groove for posterior branch of middle meningeal artery. Eminence of superior semi- circular canal. Hiatus Fallopii. Posterior root of zygomatic process. Leads into external auditory meatus. Glenoid cavity. Tympanic plate. Mastoid process. Leading into stylo -mastoid foramen. Roof .of carotid canal. Alar spine of the sphenoid. Styloid process. Canal for Arnold's nerve -with opening of carotid canal just in front and above it. Position of osseous opening of Eustachian tube. Jugular foramen. Medial wall of open carotid canal. Anterior condylic foramen (canalis hypoglossi). Condyle of occipital bone. Petro-occipital suture. Posterior wall of sphenoidal sinus. Position of pharyngeal tubercle. Anterior margin of foramen magnum. 25. Occipital condyle. HOEIZONTAL SECTIONS OF THE CEANIUM. 179 tegmen tympani, which sepaiates it from the middle cranial fossa, medial end of the external auditory meatus, together with the groove for the attachment of the tympanic membrane is well seen, and the thickness of the upper wall of that passage is also noteworthy. The floor of the meatus, formed by the tympanic plate, which separ- ates it from the glenoid fossa, is much thinner, but in the region of the root of the styloid process there is a massing to- gether of dense bone. HORIZONTAL SECTION. Figure 127 represents a horizontal section passing- through the face a little below the level of the inferior orbital margin, cutting through the root of each pterygoid process posteriorly. The nasal fossae and the maxillary sinuses are thus exposed. The nasal fossa is divided slightly below the inferior edge of the middle turbinated bone, along the line of the middle meatus. The thin partition, which hei'e separates the nose from the antrum, is cut through, and the aperture into the antrum laid open. In front of this, the canal for the nasal duct is cut across, and its relations to the antrum in front and to the lateral side, and to the nose medially, are well displayed. The form of the maxillary sinus, as exposed, is triangular, the summit of the triangle being directed laterally to- wards the root of the zygomatic process, The obliquity of the Fig. 'J 10 11 12 13 14 126. — Vertical Section through the Skull immediately in front of the root of the styloid process. Inferior opening of carotid canal. Jugular foramen. Anterior coudylic foramen (canalis hypoglossi). Occipital condyle. Foramen magnum. Basi-occipital. Tabular part of occipital bone. 1. Cochlea. 10. 2. Entrance to the antrum (attic). 3. Sulcus tympanicus. 11. 4. Tympanic bone. 12. 5. Auricular fissure. 6. Part of glenoid cavity. 13. 7. Tympanic cavity (floor). 14. 8. Styloid process. 15. 9. Jugular fossa. 16. Its anterior wall, which is here stout, is pierced obliquely by the infra-orbital canal which at this point reaches the facial surface of the maxilla at the infra-orbital foramen. Its posterior wall, thin and convex backwards, is directed towards the zygomatic fossa laterally, and to the spheno-maxillary (or pterygo- maxillary) fossa medially, where it lies in front of the pterygoid processes- The latter fossa has been cut across and is seen to correspond to the interval between the back and upper surface of the maxilla, and the anterior aspect of the root of the pterygoid process. Laterally, it is seen to commnnicate with the zygomatic fossa by means of the pterygo- maxillary fissure which is here cut across ; medially, it opens into the nose by the spheno-palatine foramen, which is also divided. On one side the anterior orifice of the Vidian canal is seen opening on to the posterior wall of the fossa. On the other side, the canal has been laid open, by removing its lower wall, so as to expose its whole length as it leads backward to the anterior edge of the foramen lacerum. In the middle line, the nasal septum, here formed by the vomer and perpendicular of the ethmoid, is shown in section. A line passing through the pterygo-maxillary fissures cuts the zygomatic arch where the zygomatic process of the temporal articulates with the zygo- matic bone. 180 OSTEOLOGY. 9. 10. n. 12. 13. 14. 15. 16. 17. 31 30 29 28 Fig. 127. — Horizontal Section of the Skull a little below the level of the Inferior Orbital Margin. Nasal duct. Middle turbinal bone. Nasal septum. Middle meatus of nose. Nasal duct. Infra-orbital canal. Opening into antrum from the middle meatus of the nose. Roof of antrum. Spheno-maxillary (inferior orbital) fissure. Passing through pterygo-maxillary fissure into spheno-maxillary fossa and ending opposite opening of foramen rotundum. Infra- temporal crest of great wing of sphenoid. Zygomatic arch. Squamous part of temporal. Under surface of great wing of sphenoid. Cut pterygoid process. Eminentia articularis. Foramen ovale. 18. Glenoid fossa. 19. Foramen siiinosum. 20. Spine of sphenoid. 21. Petro-squamosal (glenoid) fissure. 22. Openiug of bony canal of Eustachian tube. 23. Carotid canal. 24. Upper opening of carotid canal (foramen lacerum). 25. Anterior opening of Vidian canal. 26. Roof of spheno-maxillary fossa just above spheno-palatine foramen. 27. Superior turbinal bone. 28. Sujjerior meatus of the nose. 29. Placed in position of siilieno - palatine foramen. Placed in the spheno - maxillary fossa near the upper f>art of the pterygo- maxillary fissure. Vidian canal laid open. 30 31 SEXUAL DIFFERENCES IN THE SKULL. Whilst it is a matter of difficulty, in all cases, to determine with certainty the sex of a skull, the following points of difference are usually fairly characteristic. The female skull is, as a rule, smaller than the male. In point of cranial capacity it averages about a tenth less than the male of corresponding race. Undue stress must not be laid on these facts, since the female in bulk and stature measures on an avei'age less than the male. It is lighter, smoother as regards the development of its muscular ridges, and possesses less prominent mastoid processes. In the frontal region, the superciliary ridges are less pro- nounced, and this imparts a thinness and sharpness to the upper orbital margin, which is fairly characteristic, and can best be appreciated by running the finger along that edge of bone. For the same reason, the forehead appears more vertical and the projections of the frontal eminences more outstanding, though it is stated that the frontal and occipital THE CLAVICLE. 181 regions are less capacious proportionately than in the male. The vertex in the female is said to be more flattened, and the height of the skull consequently somewhat reduced. In the male the edge of the tympanic plate is generally sharp, and divides to form the sheath of the styloid process, whilst in the female the corresponding box'der is described as being rounder and more tubercular. Whilst it is true that no one of these diflterences is sufficiently characteristic to enable us to pronounce with certainty on the matter of sex, it is the case that, taken together, they usually justify us in arriving at a conclusion which, as a rule, may be regarded as fairly accurate. In some instances, however, it is impossible to express any definite opinion. DIFFERENCES DUE TO AGE. At birth the face is proportionately small as compared with the cranivim, constituting about one-eighth of the bulk of the latter. In the adult the face equals at least half the cranium. About the age of puberty the development and expansion of some of the air- sinuses, more particularly the frontal sinus, lead to characteristic differences in form in both the head and face. The eruption of the teeth in early life and adolescence enables us to determine the age with fair accuracy. After the completion of the permanent dentition, the wear of the teeth may assist us in hazarding an approximate estimate. The condition of the sutures, too, may guide us, synostosis of the coronal and sagittal sutures not as a rule taking place till late in life. Complete obliteration of the synchondrosis between the occipital bone and sphenoid may be regarded as an indication of maturity. In old age the skull usually becomes lighter and the cranial bones thinner. The alveolar borders of the maxillse and mandibles become absorbed owing to the loss of the teeth. This gives rise to a flattening of the vault of the hard palate and an alteration in the form of the lower jaw% whereby the mandibular angle becomes more obtuse. THE BONES OF THE UPPER EXTREIYIITY. The Clavicle. The clavicle (clavicula), or collar bone, one of the elements in the formation of the shoulder girdle, consists of a curved shaft, the extremities of which are enlarged. The medial end, since it articulates with the sternum, is called the sternal end ; the lateral extremity, from its union with the acromion process of the scapula, is known as the acromial end. The sternal end (extremitas sternalis) is enlarged, and rests upon the meniscus Conoid tuberlle (Tuberositas cokacoidea)- FiG. 128 a. — The Right Clavicle seen from Above. of fibro-cartilage which is interposed between it and the clavicular facet on the upper and lateral angle of the manubrium sterni. It is also supported by a small part of the medial end of the cartilage of the first rib. Its articular surface, usually broader from above downwards than from side to side, displays an antero-posterior convexity, whilst tending to be shghtly concave in a vertical direction. The edge around the articular area which serves for the attachment of the capsule of the ster no-clavicular articulation is sharp and well defined, except below where it is rounded. The shaft exhibits a double curve, being bent forwards in the medial two- thirds of its extent, whilst in its lateral third it displays a backward curve. Of 12 182 OSTEOLOGY. rounded or prismatic form towards its sternal end, it becomes compressed and flattened at its acromial extremity. It may be described as possessing two surfaces, an upper and an under, separated by anterior and posterior borders, which are well defined towards the lateral extremity of the bone, but become wider and less well marked medially where they conform more to the cylindrical shape of the bone. The superior surface, which is smooth and subcutaneous throughout its whole length, is directed upwards and for- wards. The anterior border, which separates the upper from the under surface in front, is rough and tubercular towards its medial end for the attachment of the clavicular fibres of the pectoralis major, whilst laterally, where it becomes continuous with the anterior margin of the acromial end, it is better defined, and bears the imprint of the origin of the fibres of the deltoid muscle ; here, not uncommonly, a projecting spur of bone, called the deltoid tubercle, may be seen. The posterior border is broad medially. Fig. 128 b.- -The Upper Surface op the Right Clavicle WITH Muscle Attachments. Conoid tubercle -(Implssio coracoidea) Rhomboid impression (Impessio costalis) Fig. 129 «. — The Right Clavicle seen feom Below. where it is lipped superiorly to furnish an attachment for the clavicular fibres of the sterno-mastoid muscle ; behind and below this the sterno-hyoid and sterno-thyreoid muscles are attached to the bone. Laterally, the posterior border becomes more rounded, and is confluent with the posterior edge of the acromial end at a point where there is a marked outgrowth of bone from its under surface, the conoid tubercle (tuberositas coracoidea). Into the lateral third of this border are inserted the upper and anterior fibres of the trapezius trapezoid muscle. The inferior surface, inclined down- wards and backwards, is marked close to the sternal end by an ir- regular elongated im - pression (tuberositas cos- talis), often deeply pitted, for the attachment of the rhomboid ligament, which unites it to the cartilage of the first rib. Lateral to this the shaft is channelled by a groove which terminates close to the conoid tubercle ; into this groove the subclavius muscle is inserted. The acromial end of the bone is flattened and compressed from above down- wards, and expanded from before backwards ; its anterior edge is sharp and well defined, and gives attachment to the deltoid muscle, which also spreads over part of its upper surface. Its posterior margin is rougher and more tubercular, and provides a surface for the insertion of the trapezius. The area between these two muscular attachments is smooth and subcutaneous. The lateral edge of this forward-turned part of the bone is provided with an oval facet (facies articularis acromialis) for articulation with the acromion process of the scapula ; the margins Fig. 129 b.- Rhomboid ligament -The Under Surface of the Right Clavicle with the Attachments of the Muscles mapped out. THE SCAPULA. 183 around this articular area serve for the attachment of the capsule of the joint. The inferior surface of the acromial end of the bone is traversed obliquely from behind forwards and laterally by a rough ridge or line called the trapezoid or oblique ridge. The posterior extremity of this ridge, as it abuts on the posterior border of the bone, forms a prominent process, the conoid tubercle (tuberositas coracoidea) ; to each of these, respectively, are attached the trapezoid and conoid portions of the coraco-clavicular ligament. The morphology of the clavicle is of special interest. Its presence is associated with the freer use and greater range of movement of the fore-limb, such as are necessary for its employment for more specialised actions than those of mere progression. In conse- quence of these requirements, the limb, and with it the scapula, become further removed from the trunk, and so the support which the blade bone received through tlie union of its coracoid element with the sternum, as in birds and reptiles, and to some extent in the lowest mammals, is withdrawn. Some substitute, however, is necessary to meet the altered conditions, and in consequence a new element is introduced in the form of a clavicle. The origin of this bone appears to be intimately associated with the precoracoid element met with in amphibia or reptiles but whereas the precoracoid is always laid down in cartilage, which, however, not infrequently disappears, the clavicle develops in the membrane overlying the precoracoid cartilage. In the course of its development it may become intimately associated with the remains of that cartilage. Thus, it is probable that the interarticular fibro-cartilages at the sterno-clavicular and acromio-clavicular joints, as well as the sternal articular end of the clavicle, represent persistent portions of the primitive cartilage, whilst it is possible that the supra-sternal ossicles occasionally present may be also derived from it. In this way, in its most specialised form, a secondary support is established between the sternum and scapula, which serves as a movable fulcrum, and greatly enhances the range of movement of the shoulder girdle. Nutrient Foramina. — The foramina for the larger nutrient vessels, offsets of the supra- scapular artery,! of which there may be one or two directed outwards, are usually found about the middle of the posterior border, or it may be opening into the floor of the groove for the subclavius muscle. Ossification. — The clavicle in man is remarkable in commencing to ossify before any other bone in the body ; this nnniTTs cia oejrlt- qc tV.A fiftl". nv Sternal epiphysis Ossifies about Primary centre appears about occurs as eariy as tne nirn or ^oth year ; fuses about 25th year 5th or 6th week of fatal life sixth week of foetal life. The primitive centre from which the shaft and lateral extremity ai-e developed appears in mem- brane prior to the formation of any caililaginous matrix ; and it is not till a later Fig. 130. — Ossification of the Clavicle. stage that cartilage plays a part in the development of the bone by assisting in the growth of its extremities. A secondary centre or epiphysis appears at the sternal end about the age of twenty or later, and fusion rapidly occurring between it and the shaft, ossification is completed at the age of twenty-five or thereabouts. The Scapula. The scapula, shoulder blade or blade bone, is of triangular shape and flattened form. It has two surfaces, costal or ventral, and dorsal. From the latter there springs a triangular process called the spine, which ends laterally in the acromion ; whilst from its superior border there arises a beak-like projection called the coracoid process. The bone overlies the postero- lateral aspect of the thoracic framework, reacting from the second to the seventh rib. The body of the bone, which is thin and translucent, except along its margins and where the spine springs from it, has three borders and three angles. Of these borders the vertebral (margo vertebralis) is the longest ; it stretches from the medial angle above to the inferior angle below. Of curved or somewhat irregular outline, it affords a narrow surface for the insertion of the levator scapulae, rhom- boideus minor, and rhomboideus major muscles. The superior border (margo superior), which is thin and sharp, is the shortest of ^ Suprascapular artery = transverse artery of the scapula (B.N.A. ). 184 OSTEOLOGY. the three. It runs from the medial angle towards the root of the coracoid process, before reachini; which, however, it is interrupted by the scapular notch (supra- scapular), which Hes very close to the medial side of the base of that process. This notch, which is converted into a foramen by a ligament, or occasionally by a spicule of bone, transmits the suprascapular nerve, whilst the suprascapular artery ^ runs above it. Attached to the superior border, close to the notch, is the posterior belly of the omo-hyoid. The lateral or axillary border (margo axillaris), so called from its relation to the hollow of the armpit (axilla), is much stouter Clavicular facet Medial angle SUPBASPINOOS FOSSA Spine Vertebral bordep. INFRASPINOUS FOSSA Arterial foramen Head and glenoid fossa Neck Great scapular notch Groove for dorsal artery of scapula Axillary border Inferior angle Fig. 1-31 a. — The Right Scapula seen from Behind. than either of the others ; it extends from the lateral angle above to the inferior angle below. The upper inch or so of this border, which lies immediately below the glenoid articular surface, is rough and tubercular (tuberositas infraglenoidalis), and affords attachment to the long head of the triceps. Below this it is usually crossed by a groove which marks the position of the dorsal artery of the scapula.^ The medial (superior) angle (angulus medialis) is sharp and more or less rect- angular ; tlie inferior angle (angulus inferior) is blunter and more acute ; whilst the lateral angle (angulus lateralis) corresponds to that part of the bone which is some- times called the head, and which supports the glenoid surface and the coracoid process. The glenoid surface is a pyriform articular area, slightly concave from above down- wards and from side to side ; its border is but slightly raised above the general surface and affords attachment in the recent condition to the glenoid ligament, which helps to deepen the socket in which the head of the humerus rests. Below, the margin ' Suprascapular artery = transverse artery of the scapula (B.N. A.). * Dorsalis .scapulae artery = circumflex artery of the scapula (B.N. A.). THE SCAPULA. 185 LONO HEAD OF TRICEPS Groove for dor- sahs scapul.e ARTERY of the trlenoid fossa is confluent with the infraglenoid impression (tuberositas infra- glenoidaiis), whilst above it blends with a tubercle (tuberositas supraglenoidalis), to which the long head of the biceps muscle is attached. Springing from the upper part of the head, in line with the superior border, is the coracoid process (processus coracoideus). The base of this is limited laterally by the glenoid edge, whilst medially it is separated from the superior border by the scapular notch. Eising upwards for a short space, it bends on itself at nearly a right angle, and ends in a process which is directed laterally and slightly forwards, overhanging the glenoid fossa above and in front. Compressed from above down- wards, it has attached to its upper surface near its angle the conoid ligament, lateral to wdnch there is a rough area for the trape- zoid ligament. Attached to its dorsal border is the coraco- acromial ligament, whilst at its extremity and towards the front of its ventral border, is the com- bined origin of the biceps and coraco-brachialis, to- gether with the insertion of the pectoralis minor. The neck (coUum scapulse) is that somewhat con- stricted part of the bone which supports the head ; it corresponds in front and behind to a line drawn from the scapular notch to the infraglenoid tubercle. The body of the bone has two surfaces, a dorsal or posterior (facies dorsalis) and a ventral or costal (facies costalis). The former is divided into two fossse by an outstanding process of triangular form, called the spine (spina scapulae). The attached border of this crosses the back of the body .obliquely in a direction laterally and slightly upwards, extending from the vertebral border near the lower limit of its upper fourth towards the centre of the posterior glenoid edge, from which, however, it is separated by the great scapular notch, which here corresponds to the dorsal aspect of the neck. Within this notch the supra- scapular vessels^ and nerve pass to the infraspinous fossa. The surfaces of the spine, which are directed upwards and downwards, are concave, the upper entering into the formation of the supraspinous fossa, which hes above it, the lower forming the upper wall of the infraspinous fossa, which lies below it. The two fossa? are in communica- tion with each other round the free lateral concave border of the spine, where that curves over the great scapular notch. The dorsal free border of the spine is subcutaneous throughout its entire length. Its upper and lower edges are strongly lipped, and serve — the superior, for the attachment of the trapezius ; the inferior, for the origin of the deltoid. The intervening surface varies in width- broad and triangular where it becomes confluent with the vertebral border, it displays a smooth surface, over which the tendinous fibres of the trapezius play ; ' Dorsalis scapulfe artery = circumliex artery of the scapula (B.N. A.). Scapular slip of latissimus DORSI Fig. 131 ?>.— The Dorsum of the Right Scapula with the Attach- ments OF the Muscles mapped out. 186 OSTEOLOGY. Clavicular facet ' coracoid process narrowing rapidly, it forms a surface of vary- ing width which blends laterally with a flattened process, the two forming a compressed plate of bone which arches across the scapular notch above and behind, and then curves, upwards forwards, and laterally to overhang the glenoid fossa. The medial border of this pro- cess is continuous with the upper margin of the spine, and is gently curved. The lateral bor- der,more curved than the medial, with which it is united in front, is con- fluent with the inferior edge of the spine, with which it forms an abrupt bend, termed the acromial angle. The bone included between these two borders is called the acromion CORACO-BRACHIALIS AND SHORT HEAD OF BICEPS PeCTORALIS MINOR Ml DIAL ANGLE / Arterial foramen Subscapular fossa Axillary border Gmo-hyoid LOXO HEAD OF TRICEPS Fig. 132 6. — Ventual aspkct ok the Right Scapula, with the Attachments ok Mdscles mapped out. Inferior angle Fig. 132 «. — The Right Scapula seen from the Front. process. Of compressed form, it much resembles the acromial end of the clavicle, with which it articulates by means of a facet (fades articularis acromii) which is placed on its medial border near its anterior ex- tremity. The superior surface of the acromion, which is broad and expanded, is subcutaneous, and is directed upwards and dorsally, and in the normal position of the bone laterally as well. Its medial edge, where not in contact with the clavicle, has attached to it the fibres of the trapezius, whilst its lateral margin affords origin to the central part of the deltoid. At its anterior extremity it is connected with the coracoid THE SCAPULA. 187 process by means of the coraco-acromial ligament. Its under surface is smooth and overhangs the shoulder-joint. The supraspinous fossa, of much less extent than the infraspinous, is placed above the spine, the upper surface of which assists in forming its curved floor ; in it is lodged the supraspinatus muscle. The scapular notch opens into it above, whilst below and laterally it communicates with the infraspinous fossa by the great scapular notch, through which the suprascapular artery ^ and nerve pass to reach the infraspinous fossa. The infraspinous fossa, overhung by the spine above, is of triangular form. The axillary border of the bone limits it in front, whilst the vertebral margin bounds it behind ; the greater part of this surface aftbrds origin to the infraspinatus muscle, excepting a well-defined area which skirts the axillary border and inferior angle of the bone, and which affords an attachment to the fibres of origin, of the teres minor. This muscle extends along the dorsal surface of the axillary border in its upper two- thirds, reaching nearly as high as the glenoid edge ; whilst a crescentic surface, which occupies the lower third of the axillary border and curves backward round the dorsal aspect of the inferior angle, furnishes an origin for the teres major muscle. Here also, near the inferior angle, are occasionally attached some of the fibres of the latissimus dorsi mv;scle. The ventral aspect (facies costalis) of the body is hollow from above downwards and from side to side, the greatest depth being in correspondence with the spring of the spine from the dorsal surface. Its medial boundary, which is formed by the anterior lipped edge of the vertebral border, aftbrds attachment to the fibres of insertion of the serratus magnus (s. anterior) along the greater part of its extent. The area of insertion of this muscle is, however, considerably increased over the ventral aspects of the medial and inferior angles respectively. Eunning down from the head and neck above to the inferior angle below, there is a stout rounded ridge of bone, which imparts a fulness to the ventral aspect of the axillary border and increases the depth of the ventral hollow ; to this, as well as to the floor of the fossa, the sub- scapularis muscle is attached. The tendinous intersections of this muscle leave their imprint on this surface of the bone in a series of three or four rough lines which converge towards the neck. The scapula of man is characterised by the greater proportionate length of its base or vertebral border as compared with lower foi-ms. This proportion is expressed by what is termed the scapular index (Appendix D). The greater size of the acromion process is also a distinctive feature. The double ossification of the coracoid occurs only in mammals. It is probable that the centre for the upper and fore part of -the coracoid process represents the epicoracoid or precoracoid of lower forms, whilst the subcoracoid centre (metacoracoid) which assists in the formation of the glenoid fossa is the reduced and vestigial remains of the stout coracoid element met with in Ornithorhynchus, which articulates with the sternum. Nutrient Foramina. — Foramina for the jjassage of nutrient vessels are seen in different parts of tlie bone ; the most constant in position is one which opens into the infrasjjinous fossa, about an inch or so from the scajjular notch. Others are met with on the upper and under surfaces of the spine, on the ventral aspect near its deepest part, and also around the glenoid margin. Connexions. — The scapula is not directly connected with the trunk, but articulates with the latei-al end of the clavicle, in union with which it forms the shoulder girdle supporting the humerus on its glenoid surface. Placed on the uj^joer and back part of the thorax, it covers the ribs from the second to the seventh inclusive. Possessed of a wide range of movement, it alters its i^osition according to the attitude of the limb, rising or falling, being dra\\Ti inwards or outwards, or being rotated uj)on itself according as the arm is moved in various directions. These changes in ijosition can easily be determined by recognising the altered relations of the subcutaneous and l)ony prominences, more especially the former, which include the spine, the acromion process, and the lower half of the vertebral border. Ossification. — Ossification begins in the body of the cartilaginous scapula about the end of the second month of foetal life. At birth the head, neck, body, spine, and base of the coracoid process are well defined ; the vertebral border, inferior angle, glenoid fossa, acromion and coracoid processes, are still cartilaginous. The centre for the upper and fore part of the coracoid appears in the first year, and fusion along an oblique line leading ^ Suprascapular artery = transverse artery of the scapula (B.N. A.). 188 OSTEOLOGY. from the upper eds;c of the glenoid fossa to the conoid tubercle is complete about the fifteenth year. Aseparate centre (subcoracoid), which ultimately includes the upper part of the glenoid fossa and Appears about 1(5-17 yrs. ; I'uses about 20 yrs. Subcoracoid centre Primary centre appears about 2nd m. foetal life. Acromial centres appear 15-16 yrs. ; fuse about 25 yrs. Secondary centre for coracoid appears about end 1st yr. ; fuses about IS yrs. appears 10 yrs. ; fuses lb-17 yrs. Appears about 17 yrs. ; fuses about 20 yrs. . Appears about 16 or 17 yrs. ; fuses 18-20 JTS. /Appears 16-17 ■ yrs , fuses 20- 25 yis Appears 16-17 yrs. ; " fuses 20-25 yrs. Scapula at end of First Year. Scapiila about the Age of Puberty. Fig. 133. — Ossification of the Scapula. lateral part of the cora- coid process, makes its appearance about the tenth year, and fuses with the surrounding bone about sixteen or seventeen. Up till the age of puberty the ac- romion remains carti- laginous ; centres, two or more in number, then make their appearance, which coalesce and ulti- mately unite with the spine about the twenty- fifth year. Failure of union may, however, persist throughout life (see Appendix B — Varia- tions). Ossification com- mences in the cartilage in the inferior angle about puberty, and in- dependently and a little later, along the vertebral margin, fusion with the body occurring at from twenty to twenty-five years. Small scale-like epiphyses make their appearance on the upper surface and at the extremity of the coracoid, and are completed about the twentieth year. A thin epiphysial plate develops over the lower part of the glenoid fossa about sixteen or seventeen, fusion being complete about eighteen or tw^enty years of age. The Humerus. The humerus, or bone of the upper arm, articulates with the scapula above and with the bones of the forearm, the radius and ulna, below. Its upper end com- prises the head and greater and lesser tuberosities ; ^ its shaft, which is longer than any of the other bones of the upper extremity, is cylindrical above and flattened below. At the inferior extremity, which is expanded to form the epicondyles on either side, it supports the trochlear and capitular articular surfaces for the ulna and radius respectively. The superior extremity is the thickest and stoutest part of the bone. The head (caput humeri), which forms about one-third of a spheroid and is covered by articular cartilage, is directed upwards, medially, and slightly dorsally, and rests in the glenoid fossa of the scapula ; the convexity of its surface is most pronounced in its posterior half. Seijarating the head from the tuberosities laterally is a shallow groove, which fades away on the surface of the bone which supports the articular part inferiorly. This is named the anatomical neck (collum anatomicum) and serves for the attachment of the capsule of the shoulder joint. The articular edge of the groove opposite the lesser tuberosity is usually notched for the attachment of the superior gleno-humeral ligament. The greater tuberosity (tuberculum majus) abuts on the lateral side of the head and becomes continuous with the shaft below. Its upper surface forms a quadrant, which is subdivided into three more or less smooth areas of unequal size. Of these the highest and anterior is for the insertion of the supraspinatus muscle, the middle for the infraspinatus, wliilst the lowest and posterior serves for the insertion of the teres minor muscle. The lateral surface of this tuberosity, which bulges beyond the line of the shaft, is rough and pierced by ' I retain the Euglish word " tuljerosity " for tuberculum. ~ A. T. THE HUMEEUS. 189 Greater tubkrositv Bicipital groove Lesser Tl'BEROSITY numerous vascular foramina. Anteriorly the greater tuberosity is separated from the lesser tuberosity (tuberculum minus) by a well-defined furrow, called the bicipital groove (sulcus inter- ^ tubercularis). The transverse humeral ligament stretches across the groove between the two tuberosities, thus convertincr the groove into a canal in which the tendon of the long head of the biceps and the ascending articular branch of the anterior circumflex artery are lodged. The lesser tuberosity lies in front of the lateral half of the head ; SlTPRA-* SUBSCAPULARIS Deltoid emisesce — Arterial foramen Medial epicondylic RIDGE CORONOID fossa Medial epicoxdyle Lateral epicondyle Capitulum Fig. 1.34 a. — Anterior View of the Right Humerus. - Latissimus dorsi ■ Pectoralis major Teres major Deltoid Coraco-brachialis Brachio-radialis . Extensor carpi radialis longus Pronator teres and flexors Fig. 134 6. — The Anterior aspect op THE Humerus with Muscular At- tachments MAPPED OUT. it forms a pronounced elevation, which fades into the shaft below. The surface of^^ this tuberosity is faceted above and in front for the insertion of the subscapular 190 OSTEOLOGY. Head- Anatomicat. Greater tuberosity / s^ Surgical neck Arterial_ FORAMEN muscle, whilst laterally it forms the prominent medial lip of the bicipital groove. Below the head and tuberosities the shaft of the bone rapidly contracts, and is here named the surgical neck (coUum chirurgicum) owing to its liability to fracture at this spot. The shaft, or body (corpus humeri), is cylindrical in its upper half. On it the bicipital groove may be traced downwards and slightly inwards, along its anterior surface. The edges of the groove, which are termed its lips, are confluent above with the greater and lesser tuber- osities respectively. Here they are prominent, and form the crests of the greater and lesser tuberosities (cristse tuberculi majoris et minoris). Inferiorly the lips of the bicipital groove gradually fade away, the medial more rapidly than the lateral, which latter may usually be traced down to a rough elevation placed on the lateral side of the shaft about its middle, called the deltoid tuberosity. Into the lateral lip of the bicipital groove are inserted the fibres of the pectoralis major muscle ; hence it is sometimes described as the pectoral ridge. To the floor of the groove the latissimus dorsi is attached; whilst the teres major muscle is inserted into the medial lip. The deltoid eminence (tuberositas deltoidea), to which the powerful del- toid muscle is attached, is a rough, slightly elevated V-shaped surface, placed on the lateral side of the shaft about its middle. The anterior limb of the V is parallel to the axis of the shaft, and is continuous with the lateral lip of the bicipital groove above, whilst the posterior limb of the V winds obliquely round the lateral side of the bone towards the posterior surface, where it be- comes continuous with a slightly elevated and occasionally rough ridge which leads up the back of the bone towards the greater tuberosity superiorly ; from this latter ridge the lateral head of the triceps muscle arises. The medial anterior surface of the shaft about its middle inclines to form a rounded border, on which there is often a rough linear impression marking the insertion of the coraco-brachialis muscle. Below this the shaft becomes compressed and xpanded laterally, ending inferiorly on either side in the epicondyles. Its surfaces .Deltoid eminence musculo-spiral "groove Olecranon rossA -Lateral Ivl'ICONDYLE Medial epicondyle" Groove for - ulnar nerve Fig. 135 rt.- Thochlea -Posterior View ok the Right Humerus. THE HUMERUS. 191 Teres minor Infraspinatus Triceps (lateral head) Brachiai.is- I musculo-spiral groove' are now anterior and posterior, being separated from each other by two clearly defined borders, the epicondylic ridges. Of these, the medial, margo medialis, is the more curved and less prominent, and is continuous above with the surface to which the coraco-brachialis is attached, whilst inferiorly it ends by blending with the medial epicondyle. The lateral epicondylic ridge, margo lateralis, is straighter and more projecting ; its edge is usually distinctly lipped. Confluent with the lateral epicondyle inferiorly, it may be traced upwards to near the deltoid eminence, where it turns backwards more or less parallel to the posterior oblique border of that im- pression, to be lost on the posterior surface of the shaft. The interval between this bor- der and the deltoid eminence is thus con- verted into a shallow oblique furrow, which winds round the lateral surface of the bone just below its middle ; this constitutes the musculo-spiral groove (sulcus n. radialis) along which the musculo-spiral nerve,^ together with the superior profunda artery,- passes from the back to reach the front of the arm. To the epicondylic ridges are attached the inter- muscular septa, whilst the lateral in its upper two-thirds furnishes a surface for the origin of the brachio- radialis, and in its lower third for the extensor carpi radialis longus muscles. The anterior surface of the lower half of the shaft is of elongated triangular form, the base corresponding to the inferior extremity of the bone. Running down the centre of this is a broad, rounded, elevated ridge, most pronounced above, where it joins the deltoid eminence, and sloping on either side medial head of towards the epicondylic ridges ; it is into the lateral of these slopes that the musculo-spiral groove flows. Inferiorly the elevated surface spreads out, and becomes confluent with the epicondyles. The medial epicondyle (epi- condylus medialis) is the more prominent of the two, and furnishes a surface for the origin of the pronator teres, and the superficial flexor muscles of the forearm. The lateral epicondyle (epicondylus lateralis), stunted and but little projecting, serves for the attachment of the common tendon of origin of the extensor Fig. 135 b muscles. The brachialis muscle has an ex- tensive origin from the anterior surface of the lower half of the shaft, including between its upper slips the insertion of the deltoid. The posterior surface of the low^er half of the shaft is smooth and rounded from side to side ; somewhat flattened below, where the whole shaft tends to incline forwards, it becomes continuous on either side with the posterior surfaces of the epicondyles, the medial of which is grooved for the passage of the ulnar nerve, whilst the lateral supplies an origin for the anconasus muscle. The medial head of the triceps muscle has an extensive attachment from the posterior surface of the lower two-thirds of the shaft, medial to and below the musculo-spiral groove. />, Origin of extensors of forearm Anconeus Posterior aspect of the Right Humerus with Attachments of Muscles mapped out. 1 The musculo-spiral uerve = the radial nerve (B.N. A.), the groove for the radial nerve. - The superior profuuda artery = prof unda brachii (B.N. A. Heuce the musculo-spiral groove is known as 19: OSTEOLOGY. Lesser tuberosity Head iMEDIAL J EPI f CONDYLE '* Greater tuberosity Lateral epicondyle Fig. 136.— The Head of the Right Humerus seen from Above (witli the outline of the lower extremity in relation thereto shown in dotted line). Capitulum Olecranon fossa Groove for ulnar nerve Fig. 137. — The Lower Extremity of the Right Humerus seen from Below. The lower extremity of the humerus is furnished with two articular surfaces (the condyles proper), the lateral of which, called the capitulum, for articulation with the upper surface of the head of the radius, is a rounded eminence, placed on the anterior surface and lower border, but not extending up- wards on the posterior surface of the inferior end of the bone. Above it, in front, there is a shallow depression (fossa radialis), into which the margin of the head of the radius sinks when the elbowis strongly flexed. A shallow groove separates the capitulum medially from the trochlea, which is a grooved articular surface, with prominent edges winding spirally round the lower extremity of the shaft. The spiral curves from behind forwards and medially, and its axis is slightly oblique to the long axis of the shaft. The medial hp is the more salient of the two, and forms a sharp and well-defined margin to the articular area ; its cartilage -covered surface is slightly convex. The lateral lip, much less prominent, is rounded off into the articular groove which separates it from the capitulum, posterior to which, however, it is carried up as a more or less definite crest. It is by means of the trochlea that the humerus articulates with the semilunar notch of the ulna. On the anterior surface of the bone, immediately above the trochlea, is a depression — the coronoid fossa (fossa coronoidea) — into which the coronoid process of the ulna slips in flexion of the joint, whilst in a corresponding position on the back of the lower end of the shaft there is a hollow, called the olecranon fossa (fossa olecrani), just above the trochlea posteriorly. Into this the olecranon pro- cess sinks when the elbow is extended. The two fossae are separated by a thin translucent layer of bone which may be deficient, thus leading to the formation of a foramen between the two hollows in the macerated bone. The anterior part of the capsule of the elbow -joint is attached to the superior margins of the radial and coronoid fossee in front, whilst the posterior ligament is connected with the upper border and lateral edges of the olecranon fossa behind. The strong ulnar and radial collateral ligaments are attached superiorly to the medial and lateral epicondyles respectively. The pro- portionate length of the humerus to the body height is as 1 is to 4-93-5 -25. Nutrient foramina are usually to be seen, one at or near the surface for the insertion of the coraco-brachialis, the from the other usually close to the hinder border of the deltoid emin- ence ; both have a downward direction. Numerous vascular foramina are scattered along the line of the anatomical neck, the larger ones being situated near the upper end of the bicipital groove. The vascularity of the bone is here intimately associated with the activity of its growth in this situation. Lateral epicondylic ridge Lateral epicondyle Ext. lateral lioament (Radial Trochlea collateral) Fig. 138. — The Lower End op the Right Humerus seen Lateral Side. THE HUMERUS. 193 Connexions. — Tlie liumerus articulates witli the scai:>ula above, and radius and ulna below. Embedded as tlie humerus is in the substance of the upjjer arm, its shaft and head are surrounded on all sides. It is only at its lower part that it comes into direct relation with the surface, the medial epicondyle forming a characteristic projection on the medial side of the elbow ; whilst the lateral epicondyle, less prominent, and the lateral epicondylic ridge can best be recognised when the elbow is bent. Sexual differences. — Dwight (American Journ. of Anat. vol. iv. 1904) has shown that the head of tlic, humerus in the female is proportionately smaller than that of the male. Ossification. — At birth the shaft of the humerus is usually the only part of the bone ossified, if we except the occasional presence (22 per cent) of an ossific centre in the head. (H. R. Spencer, Journ. Anat. and Physiol, vol. xxv. p. 552.) The centre for the shaft makes its appearance early in the second month of intra-uterine life. Within the first six months after birth a centre usually appears for the head ; this is succeeded by At birtli. About 5 years. About 12 years. Fig. 139. — Ossification of the Humerus. About 16 years. 1. Appears early in 2iid month fcetal life. 2. For greater tuberosity, appears 2 to 3 years. 3. For head, appears within first 6 months. 4. For medial epicondyle, appears about 5 years. 5. For capitulum, appears 2 to 3 years. 6. Apyjears about 12 years. 7. Centres for head and greater tuberosity, coalesce about 5 years. S. Centre for lesser tuberosity fuses with other centres about 7 years. 9. Appears about 11 or 12 years. 10. Interior epiphysis fuses with shaft about 16 to 17 years. 11. Superior epiphysis fuses with shaft about 25 years. 12. Fuses with shaft about 17 to 18 years. one for the greater tuberosity during the second or third year. These soon coalesce ; and a third centre for the lesser tuberosity begins to appear about the end of the third year, or may be delayed till the fourth or iifth year. These three centres are all blended by the seventh year, and form an epiphysis, which ultimately unites with the shaft about the age of twenty-five. It may be noticed that the superior end of the diaphysis is conical and pointed in the centre, over which the epiphysis fits as a cap, an arrangement which thus tends to prevent its displacement before union has occurred. The first centre to appear in the lower extremity is that for the capitulum about the second or third year. This extends medially, and forms the lateral half of the trochlear surface, the centre for the medial half not making its appearance till the eleventh or twelfth year. Separate centres are developed in connexion with the epicondyles ; that for the lateral appears about the twelfth year, and, rapidly coalescing with the centres for the capitulum and trochlea, forms an epiphysis, which unites with the shaft about the sixteenth or seventeenth year. The centre for the medial epicondyle appears about the fifth year ; it forms a separate epiphysis, which unites with the shaft about eighteen or nineteen. These two epiphyses at the lower end of the bone are separated by a down-growth of the 194 OSTEOLOGY. shaft, which lies between the medial epicondyle and the trochlea, and forms part of the base and medial side of the latter process. The epicondylic process when present is developed from the diaphysis, and has been observed to be already well ossified by the third year. ("Proc. Anat. Soc." Journ. Anat. and Physiol. 1898.) Olecrajson process Tuberosity Greater sigmoid cavity (Incisura semilttnaris) The Ulna. Small sigmoid CAVITY (In- cisura RADIALIS) ~ Bicipital hollow Posterior border -Interosseous bordep. Of the two bones of the forearm, the ulna, which is placed medially, is the longer. It con- coRONoiD process sists of a large superior extremity supporting the olecranon and coronoid processes ; a shaft tapering from above downwards ; and a small rounded inferior end called the head. Superior Extremity. — The olecranon process (olecranon) lies in line with the shaft. Its dorsal surface, more or less triangular in form, is smooth and subcutaneous and covered by a bursa. ii V^B ^^^ superior aspect, which forms with the posterior I' 'f^B surface a nearly rectangular projection— the tip of the elbow — furnishes a surface for the in- sertion of the tendon of the triceps muscle, to- gether with a smooth area which is overlain by the same tendon, but separated from it by a bursal sac. To the anterior crescentic border of this process are attached the fibres of the posterior part of the capsule and portion of the ulnar col- lateral ligament of the elbow-joint. The ventral surface is articular, and enters into the formation of the greater sigmoid cavity (semilunar notch). The coronoid process (processus coronoideus) is a bracket-hke process, which juts forwards from the fore and upper part of the shaft, and is fused with the olecranon process superiorly. By its upper surface it enters into the formation of the semilunar notch (greater sigmoid cavity), whilst its anterior aspect, which is separated from its upper side by a sharp irregular margin, slopes downwards and backwards to become confluent with the anterior surface of the shaft. Of triangular shape, this area, which is rough and tubercular, terminates inferiorly in an oval elevated tubercle (tuberositas ulnse), into which the tendon of the brachialis muscle is inserted. Of the lateral margins of the coronoid process, the medial is usually the better defined. Above, where it joins the superior border, there is generally a salient tubercle, to which one of the heads of origin of the flexor digi- torum sublimis muscle is attached, whilst below this point the medial border furnishes origins for the pronator teres, and occasionally for the flexor poUicis longus muscles, from above downwards. The smooth medial surface of the coronoid process merges with the olecranon behind, and with the medial surface of the shaft below. The greater sigmoid cavity (incisura semilunaris), for articulation with the trochlea of the humerus, is a semicircular notch, the upper part of which is formed by the anterior surface of the olecranon, whilst below it is completed by the upper surface of the coronoid \^ ^Head '\ Articular sobface i OR RADIUS " — ^ -ji-.uOVF. FOB EXT. CARPI ULNABI8 Styloid pbocess Fig. 140.— The Right Ulna as viewed FROM THE Lateral Side. THE ULNA. 195 Olecranon process Greater sigmoid cavity (Incisura semilunaris)^ CoRONOiD process- Head Lesser SIGMOID cavity ( IXCI.SURA RADI- M.I.S) Tuberosity BK IPITAL HOLLOW Interosseous BORDER process. Constricted towards its deepest part by the notching of its lateral borders, the articular surface is occasionally crossed by a narrow impression which serves to define the olecranon process above from the coronoid below. The articular area is divided into a medial portion, slightly con- cave transversely, and a lateral part, transversely convex to a slight degree, by a longitudinal smooth ridge which extends from the most prominent part of the border of the olecranon above to the most outstanding point of the coronoid process below. The margins of the semilunar notch are sharp and well delined, and serve, with the exception of the area occupied by the radial notch (lesser sigmoid cavity), for the attachment of the capsule of the elbow-joint. The lesser sigmoid cavity or radial notch, placed on the radial side of the coronoid process, is an oblong articular surface for the reception of the head of the radius. It encroaches on the lower and lateral part of the semilunar notch, so as to narrow it considerably. Separated from it by a rectangular curved edge, it displays a surface which is plane from above downwards, and concave from before back- wards. Its anterior extremity is narrower and more pointed than its posterior, and becomes confluent with the anterior edse of the coronoid process, at which point the orbicular (annular) ligament, which retains the head of the radius in position, is at- tached in front. Its posterior border, wider and more out- standing, lies in hne, and is continuous with the interosseous margin of the shaft. Behind this border, the orbicular hga- ment is attached posteriorly. The shaft of the ulna (corpus ulnae), which is nearly straight, or but slightly curved, is stout and thick above, gradually taper- ing towards its lower extremity. It may be divided into two sur- faces, an anterior or flexor and a posterior or extensor, by tw^o well-defined borders, a lateral or interosseous (crista interossea), and a posterior (margo dorsalis), which latter is subcutaneous throughout its whole length. Interosseous BORDER" Fig. 141 «. — The PaoHx Radius and Ulxa seen FROM THE Front. 196 OSTEOLOGY. Flexor digitorcm sublimis Pronator teres Brachialis PlEXORPOLLICIS LONG0S Flexor digitordm sublimis The lateral, or interosseous border (crista interossea), is crisp and sharp in the upper three-fourths of the shaft, but becomes faint and ill-defined in the lower fourth. To this, with the exception onlj of the part which forms the posterior boundary of the hollow, in which the tuberosity of the radius is disposed when the two bones are articulated, is attached the interosseous membrane which connects the two bones of the forearm. The posterior border (margo dorsalis), of sinuous outline, curving laterally above, and slightly medially below, is continuous superiorly with the triangular subcutaneous area on the back of the olecranon, being formed by the confluence of the borders which bound that surface ; well marked above, it becomes faint and more rounded below, but may be traced downwards to the pos- terior surface of the base of the styloid process. To this border is attached an aponeurosis common to the flexor carpi ulnaris, extensor carpi ulnaris, and flexor digitorum profundus muscles. A note- worthy feature in connexion with this part of the shaft is the fact that it is subcutaneous, and can easily be felt beneath the skin throughout its whole length. The anterior or flexor surface corresponds to the front and medial side of the shaft. It is frequently described as consisting of two surfaces, an anterior and a medial, which are separated by a rounded anterior border (margo volaris), which extends from the tuberosity above towards the styloid process below. The prominence of this ridge varies in different bones, being well marked in bones of a pronounced type, but corresponding merely to the rounding of the surfaces in poorly- developed specimens. The flexor aspect of the bone affords an extensive origin to the flexor digitorum profundus muscle, which clothes its anterior and medial sides in its upper three-fourths, reaching as far back as the posterior border, and extending upwards as high as the medial side of the coronoid process. Immediately below the radial notch there is a hollow triangular area, limited behind by the upper part of the inter- osseous crest, and defined in front by an oblique Hne which extends downwards and backwards from the lateral margin of the coronoid process. In this hollow the tuberosity of the radius rests when the forearm is in the prone position, and to its floor are attached the fibres of origin of the supinator muscle. The lower fourth of the shaft is crossed by the fibres of the pronator quad- ratus muscle, which derives its origin from a more or less well-defined crest, which winds spirally downwards and backwards towards the front of the root of the styloid process, and is continuous above with the so-called anterior border. The posterior or extensor surface of the shaft lies posteriorly between the posterior border and the interosseous crest. At its upper part it is placed behind the semi- lunar and radial notches, extending on to the lateral side of the olecranon. Here an area corresponding to the upper third of the length of the bone is marked off inferiorly by an oblique ridge which leaves the interosseous crest about an inch or more Ijelow the hinder edge of the lesser sigmoid cavity. Into this somewhat triangular surface the fibres of the anconseus are inserted. Below this the posterior surface is subdivided by a faint longitudinal ridge, the bone between Fig. lilb. — Anterior aspect ok Bones OF THE Right Forearm with Mus- cular Attachments mapped out. THE ULNA. 197 which and the interosseous crest furnishes oi'igins for the abductor polUcis longus, extensor pollicis longus, and extensor iudicis proprius muscles, in order from above downwards. The surface of bone between the posterior border and the afore-men- tioned longitudinal line is smooth and overlain by the extensor carpi ulnaris muscle, which does not arise from it. The inferior extremity of the ulna presents a rounded head (capitulum ulnae), from which, on its medial and posterior aspect, there projects downwards a cylindrical pointed process called the styloid process (processus styloideus). To the extremity of this latter is attached the ulnar collateral ligament of the carpus, whilst in front it has connected with it the antero-medial portion of the capsule of the wrist-joint. The antero-lateral half of the circumference of the head is furnished with a smooth narrow convex articular surface, which fits into the ulnar notch (sigmoid cavity) of the radius. Its inferior surface, flat and semilunar in shape, and separated from the root of the styloid process by a well-marked groove, rests on the upper surface of the articular disc (triangular tibro-cartilage) of the wrist, the apex of which is attached to the groove just mentioned. The margins of the head in front and behind the radial articular surface have attached to them the anterior and posterior inferior radio-ulnar ligaments. The hinder and medial surface of the styloid process is channelled by a groove which separates it from the posterior surface of the head, and extends some little way up the posterior aspect of the lower end of the shaft. In this is lodged the tendon of the extensor carpi ulnaris muscle. The proportionate length of the ulna to the body height is as 1 is to 6-26-6-66. Nutrient Foramina. — A foramen, having an upward direction for the nutrient artery of the shaft, opens on the anterior surface of the bone from two to three inches below the tuberosity. Vascular canals of large size are seen above and behind the radial notch, just j^osterior to the notched lateral border of the semilunar notch. At the lower end of the bone similar openings are seen in the groove between the styloid process and the inferior articular surface of the head. Connexions. — The ulna articulates above with the trochlea of the humerus. On the lateral side it is in contact with the radius above and below, the superior radio-ulnar articulation being formed by the head of the radius and the radial notch of the ulna, the inferior radio-ulnar joint comprising the head of the ulna, which fits into the ulnar notch of the radius. Between these two joints the shafts of the bones are united by the interosseous membrane. The inferior surface of the head of the ulna does not articulate with the carpus, but rests on the upper surface of the interposed articular disc (triangular fibro-cartilage). The ulna is superficial throughout its entire extent. Superiorly the olecranon process can be readily recognised, particularly Fuses with shaft about 16 years when the elbow is bent, as in this position the \ olecranon is withdrawn from the olecranon ., Ai)pears about lO years fossa of the humerus in which it rests when the joint is extended. Below this the subcutaneous triangular area on the back of the olecranon can be easily determined, and from it the jjosterior border of the bone can readily be traced along the line of the " ulnar furrow " to the styloid process below. With the hand supine this latter process can be felt to the medial side and slightly behind the wrist. When the hand is pronated, the lower end •? of the radius rolls round the lower extremity ^ of the ulna, and the antero-lateral surface of | the head of the latter bone now forms a well- marked j^rojection on the back of the wrist in line Avith the cleft between the little and ring fingers. Ossification. — The ulna is ossified from one primary and two or more secondary centres. The centre for the shaft appears early in the second month of foetal life. At birth the shaft and a considerable part of the upper extremity, including the coronoid process, are ossified, as well as part of the lower extremity. The olecranon process and the inferior surface of the head and the styloid process are cartilaginous. About ten years of age a secondary centre appears in the cartilage at the upper end of the bone, and 13 Appears about years Fuses with shaft 20-23 years At Birth. About 12 years. About 16 years. Fig. 142. — The Ossification of the Ulxa. 198 OSTEOLOGY. Subcutaneous SURFACE Posterior border" ISTEROSSEOUS . B03EIDEB Post, oblique LINE forms an epiphysis which unites with the shaft about sixteen. In this connexion Fawcett (Proc. Anat. Soc. Great Britain and Ireland, 1904, p. xxvii.) has described the occurrence of two ossific centres in the olecranon. One, the more an- terior, the beak centre, enters into the formation of the uppermost end of the articu- lar surface of the semilunar notch, the other centre, not in any way forming it. A scale-like centre appears in the cartilage of the head about the sixth year, from which the under surface of that part of the bone is developed, and by the extension of which the styloid process is also ossified ; this epiphysis does not unite with the shaft till the twenti- eth or twenty-third year. In- dependent centres for the styloid process and for the extreme edge of the olecranon have also been described. The student may here be warned that the epiphysial line be- tween the shaft and superior or olecranon epiphysis does not correspond to the con- stricted part of the semilunar notch, but lies considerably above it. The Radius. The radius, or lateral bone of the forearm, is shorter than the ulna, with which it is united on the medial side. Superiorly it articulates with the hum- erus, and below supports the carpus. It consists of a head, a neck, a tuberosity, a shaft, and an expanded lower extremity. The shaft is narrow above, but in- creases in all its diameters below. Upper Extremity. — The head (capitulum) is disc-shaped and provided with a shallow concave sur- face (fovea capituli radii) superiorly for articulation with the capitulum of the humerus. The circumfer- ence of the head (circum- ferentiaarticularis) is smooth On the medial side it is Head Styloid proci Groove for ext.' Ext. dig. commnn. CARPI ui.NARis and ext.indicis propriuM Ext. poll, long. Ext. poll, brevis Ext. carpi rad. longiis Ext. carpi rad. brevi.s Styloid pkockss Fig. 143 a. — The Rk;ht Radius and Ulna seen from Behind. and is embraced by the orbicular (annular) ligament usually much broader, and displays an articular surface, plane from above down- THE EADIUS. 199 Supinator wards, which rolls within the radial notch of the ulna in the movements of pronation and supination. The character of the lateral half of the circumference differs from the medial, in being narrower, and rounded from above downwards. The neck (collum radii) is the constricted part of the shaft which supports the head, the overhang of the latter being greatest towards the lateral and posterior side. Below the neck, on the medial side, there is an outstanding oval prominence, the bicipital tuberosity (tuberositas radii). The posterior part of this is rough for the insertion of the biceps tendon, whilst the anterior half is smooth and covered hj a bursa which inter- venes between it and the tendon. The shaft (corpus radii), which has an outward curve and is narrow above and broad below, is wedge- shaped on section. The edge of the wedge forms the sharp medial interosseous margin of the bone (crista interossea), whilst its base corresponds to the thick and rounded lateral border over which the anterior or flexor surface becomes confluent with the posterior or extensor surface. The medial or interosseous crest, faint above where it lies in line with the posterior border of the tuber- osity, becomes sharp and prominent in the middle third of the bone. Below this it splits into two faint lines, which lead to either side of the ulnar notch on the lower end of the bone, thus includ- ing between them a narrow triangular area into which the deeper fibres of the pronator quadratus muscle are inserted. To this border, as well as to the pos- terior of the two divergent lines, the interosseous membrane is attached. The lateral border (oftentimes described as the lateral surface) is thick and rounded above, but becomes thinner and more prominent below, w^here it merges with the base of the styloid process. About its middle the anterior and posterior oblique lines become confluent with it, and here, placed between them, is a rough elongated impression which marks the insertion of the pronator teres muscle. Above this, and on the lateral surface of the neck, the supinator muscle is inserted, whilst inferiorly this border is over- lain by the tendons of the brachio- radialis and the extensor carpi radialis longus and brevis muscles. The anterior or flexor surface (fades volaris) is crossed obliquely by a line which runs from the tuber- osity above, downwards, and later- ally towards the middle of the lateral border of the shaft. This, often called the anterior oblique line, serves for the attachment of the radial head of origin of the flexor digitorum sublimis muscle. Above it, the front of the bone has the fibres of the supinator muscle inserted into it, whilst below and medial to it, extending as far down as the inferior limit of the middle third of the bone, is an extensive surface for the origin of the flexor pollicis longus muscle. In the lower fourth of the bone, where the shaft is broad and flat in front, there is a surface for the insertion of the pronator quadratus muscle, which also extends back to the inter- osseous ridge. The extensor or posterior surface (facies dorsalis) is also crossed by an oblique line, less distinct than the anterior. This serves to define the superior Extensor CARPI ULNARIS Extensor CARPI ULNARIb Radial extensors Abductor pollicis longus and extensor POLLICIS brevis Extensor digitorum communis and extensor INDICIS PROPRIUS Extensor pollicis longus Fig. 143 a. — Posterior aspect of Bones of Right Fore ARM WITH Attachments of Muscles mapped out. 200 OSTEOLOGY. limit of the origiu of the abductor pollicis longus muscle. Above this, the back of the neck and upper part of the shaft is overlain by the fibres of the supinator muscle which become attached to this surface of the bone in its lateral half. Below the posterior oblique line the posterior surface in the upper part of its medial half gives origin to the abductor pollicis longus and the extensor pollicis brevis muscles in that order from above downwards. The lower extremity, which tends to be turned slightly forward when viewed from below, has a somewhat triangular form. Its inferior carpal articular surface, concave from before backwards, and slightly so from side to side, is divided into tw^o facets by a slight antero-posterior ridge, best marked at its extremities where the anterior and posterior margins are notched; the lateral of these areas, of tri- angular shape, is for articulation with the navicular, whilst the medial, quadrilateral in form, is for the os lunatum. The anterior border, prominent and turned forward, is rough at its edge, where it serves for the attachment of the anterior part of the capsule of the wrist joint. The posterior border is rough, rounded, and tubercular, and is grooved by many tendons ; of these grooves the best marked is one which passes obhquely across its posterior surface. This is for the tendon of the extensor pollicis longus muscle. The lateral hp of this groove is often very prominent, and forms an outstanding tubercle. To the ulnar side of this oblique groove there is a broad shallow furrow in which the tendons of the extensor digitorum communis and extensor indicis proprius muscles are lodged, whilst to its radial side, and between it and the styloid process, there is another broad groove, subdivided by a faint ridge into two, for the passage of the tendons of the extensor carpi radialis brevis and the extensor carpi radialis longus in that order from within outwards. The styloid process (processus styloideus) lies to the lateral side of the inferior extremity ; broad at its base, it becomes narrow and pointed below where by its medial cartilage-covered sur- face it forms the summit of the inferior triangular articular area. The lateral surface of this process is crossed obliquely from above downwards and forwards by a shallow groove, the anterior lip of which is sharp and well marked, and serves to separate it from the anterior surface of the bone, whilst the posterior lip is often emphasised by a small tubercle above. The tendon of the brachio-radialis muscle is inserted into the upper part of either lip, and also spreads out on to the floor of the groove, whilst the tendons of the abductor pollicis longus and the extensor pollicis brevis muscles lie within the groove. To the tip of the styloid process is attached the radial collateral ligament of the wrist. On the medial side of the lower extremity is placed the ulnar notch (incisura ulnaris) for the reception of the head of the ulna. Concave from before backwards, and plane from above downwards, it forms by its inferior margin a rectangular edge which separates it from the inferior carpal surface. To this edge the base of the articular disc (triangular fibro- cartilage) is attached, a structure which serves to separate the inferior articular surface of the head of the ulna from the carpus. The anterior and posterior edges of the iilnar notch, more or less prominent, serve for the attachment of ligaments. The proportionate length of the radius to the body height is as 1 is to 6-70-7-11. Nutrient Foramina. — The openings of several small nutrient canals may be seen in the region of tlie neck. That for the shaft, which has an upward direction, is usually placed on the anterior surface of the bone, medial to the anterior oblique line, and from an inch and a half to two inches below the tuberosity. The posterior surface of the lower extremity of the bone is pierced by many small vascular foramina. Connexions. — The radius articulates with the capitulum of the humerus in the flexed position of the elbow, with the ulna to its medial side by the superior and inferior radio-ulnar joints, and with the navicular and lunate bones of the carj^us below. Above, the head of the bone can be felt in the intermuscular depression on the lateral side of the back of the elbow ; here the bone is only covered by the skin, superficial fascia, and the thin common tendinous origin of the extensor muscles, as well as the ligaments which support it. Its position can best be ascer- tained by pronating and supinating the bones of the forearm, when the head will be felt rotating beneath the finger. The lower end of the bone is overlain in front and behind by the flexor and extensor tendons, but its general form can be readily made out. The styloid process lying to the lateral side of the wrist in line with the extended thumb can easily be recognised ; note that it reaches a lower level than the corresponding process of the ulna. The lateral border of the lower third of the shaft can be distinctly felt, as here the bone is only overlain by tendons. Ossification. — The centre for the shaft makes its appearance early in the second THE EADIUS. 201 Fuses witli shaft lS-20 years Appears about / 2-3 years / Unites with sliaft 20-25 years At Birth. About 12 years. About 16 years. Fig. 144. — The Ossification of the Radius. epiphysis capping the summit of the tuberosity has been described ; this ap- pears about the fourteenth or fifteenth year, and rapidly fuses with that process. I. Metacarpal month of intrauterine Ufe. At birth the shaft is well formed ; its upper and lower extremities are capped with cartilage, and the tuberosity is beginning to appear. A secondary centre appears in the cartilage of the lower extremity about the second or third year ; this does not unite with the shaft until the twentieth or twenty-fifth year, somewhat earlier in the female. From this the carpal and ulnar articular surfaces are formed. The centre for the head appears from the fifth to the seventh year, and fuses with the neck about the age of eighteen or twenty. It forms the capitular articular sui-face and combines with the neck to form the area for articulation with the radial notch of the ulna. A scale-like Os HAMATUM Os TRIQDETRUM PisIFORM THE BONES OF THE HAND. Sesamoid bones The bones of the baud, twenty -seven in number, may be conveniently divided into three groups : — (1) The bones of the \7rist or carpus — eight in number. (2) The bones of the palm or metacarpus — five in number. (3) The bones of the fingers and thumb or phalanges — -fotir- teen in number. The Carpus. The carpal bones (ossa carpi) are arranged in two rows : the first, or proximal row, comprises from without inwards, the navicu- lar or scaphoid, os lunatum or semi-lunar, os triquetrum or cunei- form, and os pisiforme or pisiform ; the second or distal row includes the great multangular or trapezium, lesser multangular or trapezoid, OS capitatum or os magnum, and OS hamatum or unciform. Irregu- , — v. Metacarpal Fig. 145 «. -The Bones of the Right Wrist and Hand SEEN from the FRONT. 202 OSTEOLOGY. Os CAPITATUM Small multangular Naviculak Abductor pollicis bbevis \^L,i-} Large multangular ('^'^l ^' Opponens pollicis Abductor pollicis loncjus Flexor carpi radialis Os lunatum Os hamatum Os triquetrum I.EXOR CARPI ULNARIS Pisiform Abductor dioiti quinti i 1 \or digiti quinti I IJ \ 1-1 1 I?\OE CARPI ULNARIS )PP(JNENS DIGITI Adductor pollicis obliquus Adductor pollicis transversus Fig. 145^. — Palmar Aspect ob- Bones of the Right Carpus AND Metacarpus with Muscular Attachments mapped out. larly six-sided, each of these bones possesses non- articular palmar and dorsal surfaces. In addition, the marginal bones are non-articular along their ulnar and radial aspects according as they form the medial or lateral members of the series. Navicular or Scaphoid Bone. — This is the largest as well as the most lateral bone of the first row. Its palmar surface, rough for the attach- ment of ligaments, is irregularly triangu- lar. The inferior angle on the radial side forms a projec- tion called the tu^ber- osity; this can be felt at the base of the root of the thumb. Its superior surface is convex from side to side and before backwards for articula- tion with the radius. This area extends considerably over the posterior surface of the bone. Its inferior surface is convex from before backwards, and ex- tends on to the dorsal aspect of the bone, slightly convex from side to side ; it is divisible into two areas, the radial for articulation with the large multangular, the ulnar for the small multangular. The radial surface is narrow and rounded and forms a non-articular border, which extends from the radial articular surface above to the tuberosity below. The ulnar surface is hollowed out in front for articulation with the head of the capitate bone. Above this it displays a small semilunar- shaped facet for the os lunatum. The dorsal non - articular surface lies between the radial articular surface above and the surface for the large and small mult- angular bones below. It is obliquely grooved for the attachment of the posterior ligaments of the wrist. The navicu- lar articulates with five bones — the radius, tlie 08 lunatum, the capi- tate, the small mult- angular, and the large multangular. Os Lunatum or Semilunar Bone. — So called from its deeply excavated form, the os lunatum lies between the navicular on the radial side and the OS triquetrum on the ulnar. Its palmar surface, of rhombic form and consider- able size, is rough for the attachment of ligaments ; its supjerior surface, convex from side to side and from before backwards, articulates with the radius and in part with the under surface of the articular disc (triangular fibro- cartilage) of the wrist. Its inferior aspect, deeply hollowed from before backwards, is divided into two articular Os triquetrum Pisiform Os lunatum Os CAPITATUM Navicular Os hamatum Extensor carpi ULNARIS xtensor carpi radialis brevis Small multangular Large multangular Extensor carpi radialis longus Abductor pollicis longus Fig 145 c. — Dorsal Aspfx'T of Bones ok the Right Carpus and Metacarpus with Muscular Attachments mapi'ed out. THE CARPUS. 203 Os CAPITATl'M Os LU Os TRIQLETRl M Pisiform -T TANOULAR E MULTANGULAR I. Meta- .i:PAL areas, of which the radial is the larger ; this is for the head of the capitate bone ; the ulnar, narrow from side to side, articulates with the os hamatum. Its radial sur- face, crescentic in shape, serves for articulation with the navicular, and also for the attachment of the interosseous ligaments which connect it with that bone. Its idnar surface, of quadrilateral form, is cartilage-covered for articulation with the 08 triquetrum, and the edge which separates this from the superior surface has attached to it the interosseous ligament which unites these two bones. The rough dorsal non-articular surface is much smaller than the palmar; by this means the front and back of the bone can readily be de- termined. The semilunar ar- ticulates with five bones — the navicular, the radius, the os lunatum, the os hamatum, and the capitate bone. The Os Triquetrum or Cuneiform. — This bone may be recognised by the small oval or circular facet on its anterior surface for the pisiform. This is placed towards the lower part of the pcdmar surface, which is elsewhere rough for liga- ments. The bone is placed obliquely, so that its surfaces cannot be accurately described as inferior, superior, etc. ; but for convenience of description, the method already adopted is ad- hered to. The superior surface has a convex rhombic surface for articulation with the under surface of the triangular fibro- cartilage in adduction of the hand, though ordinarily it does not appear to be in contact with that structure. To the ulnar side of this it is rough for liga- ments. The inferior surface is elongated and concavo-convex from without inwards ; here the bone articulates with the os hamatum. The radial surface, broader in front than behind, articulates with the os lunatum. The ulnar surface, rounded and rough, is confluent above and behind with the superior and dorsal aspects of the bone. The dorsal surface, rounded and smooth laterally, is ridged and grooved medially for the attachment of ligaments. The cuneiform articulates with three bones, viz. the pisiform, the os hamatum, and the os lunatum. Pisiform bone (os pisiforme). — About vthe size and shape of a large pea, the pisiform bone rests on the anterior surface of the fore end of the os triquetrum, with which it articulates by an oval or circular facet on its dorsal aspect. The rounded mass of the rest of the bone is non-articular, and inclines downwards and radially so as to overhang the articular facet in front and laterally. The mass of the bone is usually separated from the articular surface by a small but distinct groove. Into the summit of the bone the tendon of the flexor carpi ulnaris muscle is Second PHALANX Third PHALANX Fig. llhd.- -The Bones of the Right Weist and Hand seen from behind. 204 OSTEOLOGY. Capitate inserted, and here also the anterior annular ligament is attached. The ulnar artery and nerve are in immediate relation with the radial side of the bone. Great Multangular or Tra- pezium. — The trapezium is the most lateral bone of the second row of the carpus. It may be readily recognised by the oval saddle- shaped facet on its inferior surface for articulation with the metacarpal bone of the thumb. From its palmar as;pect there rises a pro- minent ridge, within which is a groove along which the tendon of the flexor carpi radialis muscle passes. The ridge furnishes an attachment for the anterior an- dius nular ligament, as well as for some of the short muscles of the thumb. The superior surface has a half oval ■J ' p\ facet for the navicular, lateral to ^ , ^ ^ .. ^ -__ ^ ^ ^ !l^ which it is rough, and becomes Fig. 146. — The Right Navicular BonI".'^ ■ , . ■,, ?t. , • i ^^ ^, , ^ continuous with the non-articular JNOTE. — The bone is represented in the centre of the figure , . 7 , t • i, p ^ - radial aspect, which serves tor On Radius Os lunatuiu oca -The Right Navicular BonI".' Os hainatuin Capitate in the position which it occupies in the right hand viewed ■I'f^wi.u.v aspect, whlch SCrveS from the front. The views on either side, and above and the attachment of ligaments. below, represent respectively the corresponding surfaces of j^g ulnar surface there are twO , the bone turned towards the reader. ^^^^^^ . the upper is a half OVal, concave from above downwards, and very slightly convex from before backwards, and is for articulation with the small multangular. The lower, small and circular, and not always present, is for articulation with the radial side of the base of the second metacarpal bone. The dorsal surface, of irregular outline, is rough for the attach- ment of hgaments. The great multangular articulates with four bones, the navicular, small multangular, and the first and second metacarpal bones. Small Multangular or Trapezoid Bone. — With the exception of the pisiform, this is the smallest of the carpal bones. Its rough palmar sur- face is small and pentagonal in outline. By a small oblong surface on its superior aspect it articulates with the navicular. Inferiorly, by a somewhat saddle-shaped surface, it articu- lates with the base of the second metacarpal. Separated from this by a rough V-shaped im- note.— Tiie pression prolonged from its position palmar aspect, is the surface Radiui Radius Navicular FiQ. 147. — The Right Os Lunatum. hone is rei)re.sented in the centre of the fig are in the whicli it occupies in the right hand viewed from the front. The views on either side, and above and below, represent ^ , T 1 • T n , ■ 1 respectively the corresponding surfaces of the bone tui'ned to- On the rad%al side lor artlCUla- ^ards the reader. o tionwiththelargemultangular; "^C Th | ^ U h ■ i below, represent respectively the corresponding surfaces of ^ith the OS luuatum. Inferiorhj the bone turned towards the reader. there are tWO articular faCCtS separated by a ridge ; these are slightly concave from before backwards, and are for articulation, the radial with the fourth, and the ulnar with the fifth metacarpal bone. The dorsal surface, more or less triangular in shape, is rough for liga- ments. The unciform articulates with five bones — viz. the capitate, os lunatum, os triquetrum, and the fourth and fifth metacarpals. The Carpus as a Whole. When the carpal bones are articulated together they form a bony mass, the dorsal surface of which is convex from side to side. Anteriorly they present a grooved appearance, con - cave from side to side. This arrangement is furtlier empliasised by the forward projection, on the ulnar side, f'i«- 152.— The Right Capitate Bone. of the pisiform and hook of Note. — The bone is represented in the centre of the figure in the thp r.q hflmatiim ^^r\^\U^ position which it occupies in tlie riglit hand viewed from tlie tne OS namaium, wnUSt front. The views on either side, and above and below, represent radially the tuberosity of respectively the corresponding surfaces of the bone turned towards the navicular and the ridge *^'*^ reader. of the large multangular help to deepen the furrow by their elevation. To these Os luimatum THE METACAEPUS. 207 four points the anterior annular ligament of the wrist is attached, which stretches across from side to side, and thus converts the furrow into a canal through which the flexor tendons V. Metacarpal^..^--^' '^: ^JI^M ^^—-~ tV. Metacarpal paSS tO rcach the fiugCrS. %:■ Fig. Os lunatuii; Fig. 153.— The Eight Os Hama TIM. >^ '»'-'■ XoTE. — The bone is represented in the centre of the figure in the position which it occupies in the right hand viewed from the front. The views on either side, and above and below, represent respectively ijii-th [^ which the tarsus is shown the corresponding surfaces of the bone turned towards the reader. in 'part already ossified. 154. — Radiograph of the Hand at Birth. It will be noticed that whilst the primary centres for the metacarpus and phalanges are well ossified, the carpus is still entirely cartilaginous. Compare this with the tarsus at Ossification. — At birth the carpus is entirely cartilaginous. An exceptional case is figured by Lambertz, in which the centres for the os magnum and cuniform were already present. The same authority states that it is not uncommon to meet with these centres in the second month after birth. According to Debierre (Journ. cle VAnat. et de la Physiol, vol. xxii. 1886, p. 285), ossification takes place approximately as follows : — Capitate Bone or Os magnum . Os hamatum or Unciform Os Triquetrum or Cuneiform Os lunatum or Semilunar . Large multangular or Trapezium Navicular or Scaphoid Small multangular or Trapezoid Pisiform ..... 11 to 12 months. 12 to 14 months. 3 years. 5 to 6 years. 6 years. 6 years. 6 to 7 years. 10 to 12 vears. The same observer failed to note the appearance of a separate centre for the apophysis •of the OS hamatum, and records the occurrence of two centres for the pisiform. The lYIctacarpus. The metacarpal bones form the skeleton of the palm, articulating proximally with the carpus, whilst by their distal extremities or heads they support the bones of the fingers. Five in number, one for each digit, they lie side by side and slightly divergent from each other, being separated by intervals, termed interosseous spaces. Distinguished numerically from the radial to the ulnar side, they all display certain common characters ; each possesses a body or shaft, a base or carpal extremity, and a head or phalangeal end. The shafts, which are slightly curved towards the palmar aspect, are narrowest towards their middle. Their dorsal surface is marked by two divergent lines which pass forward from the back of the base to tubercles on either side of the 208 OSTEOLOGY. Head Shaft Base Fig. 155.— First Right Metacarpal Bone. head. The surface, included between the two lines is smooth and of elongated triangular form. On either side of these lines two broad shallow grooves wind spirally forward on to the palmar surface, where they are separated in front by a sharp ridge which is continuous with a somewhat triangular surface which corresponds to the palmar aspect of the base. The grooved surfaces on either side of the shaft furnish origins for the interossei muscles. Close to the palmar crest is the opening of the nutrient canal, which is directed towards the carpal extremity, except in the case of the first metacarpal bone. The head (capitulum) is provided with a surface for articulation with the proximal phalanx. This area curves farther over its palmar than its dorsal aspect. Convex from before backwards and from side to side, it is wider anteriorly than posteriorly ; notched on its palmar aspect, its edges form two prominent tubercles, which are sometimes grooved for the small sesamoid bones which may occasionally be found on the anterior surface of the joint. On either side of the head of the bone there is a deep pit, behind which is a prominent tubercle ; to these are attached the lateral Ugaments of the metacarpo-phalangeal joints. The bases (basis), all more or less wedge- shaped in form, articulate with the carpus ; they differ in size and shape according to their articulation. Of the five metacarpal bones, the first, viz., that of the thumb, is the shortest and stoutest, the second is the longest, whilst the third, fourth, and fifth display a gradual reduction in length. The four medial bones articulate by their bases with each other, and are united at their distal ex- tremities by ligaments. They are so arranged as to conform to the hollow of the palm, being concave from side to side anteriorly, and convex posteriorly. The first metacarpal differs from the others in being free at its distal extremity, whilst its jjroximal end possesses only a carpal articular facet. The first metacarpal bone is the shortest and stoutest of the series. Its shaft is compressed from before backwards. Its head, of large size, is but slightly convex from side to side, and is grooved in front for the sesamoid bones. The base is provided with a saddle-shaped surface for articulation with the large multangular, and has na lateral facets. Laterally there is a slight tubercle to which the abductor poUicis- Capitate bon Small niultangiilar Large multangulav Small multangular Fig. 156 a. — Second Right Metacarpal Bone. Note. — The bone is represented in the centre of the figure iu the position which it occupies in tlie right hand viewed from the front. The views on eitlier side, and below, represent respectively the corresponding surfaces of the bone turned towards tlie reader. THE METACAEPUS. 209 longus (extensor ossis metacarpi pollicis) muscle is attached. The caual for the nutrient artery is directed towards the head of the bone. The second metacarpal bone is recognised by its length and its broad and deeply -notched base for articulation with the small multangular. It has a small half-oval facet for the large mult- angular on the radial side of its base, whilst on its ulnar aspect it presents a narrow vertical strip for the capitate, in front of which there are two half-oval surfaces for the third metacarpal. To the dorsal aspect of the base is attached the tendon of the extensor carpi radialis longus muscle, whilst the flexor carpi radialis is inserted in front. The third metacarpal bone can usually be re- cognised by the pointed styloid process which springs from the back of its base, and is directed towards the radial side. styloid process Capitate bone Metacarpal Proximal Fig. 156 6. — Third Right ilEXACARPAL Bone. XoTE. — The bone is represented in the centre of the figure in the position which it occupies in the right hand viewed from the front. Tlie views on either side, and below, represent respectively the corre- sponding surfaces of the bone turned towards the reader. Capitate bone Os liamatmn V. Metacarpa III. -Metacarpal Capitate bone Os hamatum IV. Metacarpal Proxiiiial Fig. 156 c. — Focrth Right Metacarpal Boxe. Fig. 156 tf. — Fifth Right Metacarpal Bone. Note. — The bone in each figure is represented in the centre of the figure in the position which it occtipies in the right hand viewed from the front. The views on either side, and below, represent respectively the corre- sponding surfaces of the bone turned towards the reader. Superiorly there is a facet on the base for the capitate. To the radial side there are two half-oval facets for the second metacarpal. To the ulnar side there are usually two small oval or nearly circular facets for the fourth 210 OSTEOLOGY. metacarpal. The extensor carpi radialis brevis muscle is inserted into the back of the base. The fourth metacarpal bone maj be recognised by a method of exclusion. It is unlike either the first, second, or third, and differs from the fifth, which it resembles in size, by having articular surfaces on both sides of its base. Superiorly there is a quadrilateral surface on its base for articulation with the os hamatum. On its radial side there are usually two small oval facets for the third metacarpal. Of these facets the dorsal one not infrequently has a narrow surface for articula- tion with the capitate. On the ulnar side there is a narrow articular strip for the base of the fifth metacarpal. The fifth metacarpal bone can be recognised by its size and the fact that it has only one lateral articular facet on its base, namely, that on its radial side for the fourth metacarpal. The carpal articular surface is saddle-shaped, and there is a tubercle on the ulnar side of the base for the insertion of the extensor carpi ulnaris muscle. As has been ah-eady pointed out, tlie ojjenings of the arterial canals are usually seen on the pahnar surfaces of the metacarjsals, those of the four inner bones being directed upwards towards the base or carpal end, differing in this respect from that of the first metacarpal, which is directed downwards towards the head or phalangeal extremity. The opening of the latter canal usually lies to the ulnar side of the palmar aspect of the shaft. Ossification. — The metacarpal bones are developed from primary and secondary centres ; but there is a remarkable difference between the mode of growth of the first and the remaining four metacarpals, for whilst the shaft and head of the first metacarpal are developed from the primary ossific centre, and its base from a secondary epiphysis, in the case of the second, third, fourth, and fifth metacarpals, the shafts and bases are de- veloped from the primary centres, the heads in these instances being derived from the secondary epiphyses. In this respect, therefore, as will be seen hereafter, the metacarpal bone of the thumb resembles the phalanges in the manner of its growth, a circumstance which has given rise to considerable discussion as to whether the thumb is to be regarded as possessing three phalanges and no metacarpal, or one metacarpal and two phalanges. Broom {Anat. Anz. vol. 28), by a reference to reptilian forms offers an explanation in regard to the difference in the mode of ossification of the first metacarpal on the ground that the most movable joint is that between the first metacarpal and the carpus, whereas on the other digits the most movable joints are those between the metacarpals and phalanges. In consequence those ends of the bones which enter into the formation of the joints where movement is most free are the ends where the epiphyses will appear. This is in accord- ance with the law suggested in connexion with the fibula. The primary centres for the shafts and bases of the second, third, fourth, and fifth metacarpals appear in that order during the ninth or tenth week of intrauterine life, some little time after the terminal phalanges have begun to ossify, that for the shaft and head of the metacarpal bone of the thumb a little later. At birth the shafts of the bones are well formed. The secondary centres from which the heads of the second, third, fourth, and fifth metacarpals and the base of the first are developed, appear about the third year, and usually completely fuse with the shafts about the age of twenty. There may be an independent centre for the styloid process of the third metacarpal, and there is usually a scale-like epiphysis on the head of the first metacarpal which makes its appearance about eight or ten, and rapidly unites with the head. The occurrence of a basal epiphysis in the second metacarpal bone has been noticed. The Phalanges. The phalanges or finger bones (phalanges digitorum manus) are fourteen in number — three for each finger, and two for the thumb. Named numerically in order from the proximal toward the distal ends of the fingers, the first phalanx (phalanx prima), the longest and stoutest of the three, has a semi-cylindrical shaft which is curved slightly forwards. The palmar surface is flat, and bounded on either side by two sharp borders to which the sheath of the flexor tendons is attached. The dorsal surlace, convex from side to side, is overlain by the extensor tendons. The proximal end, considerably enlarged, has a simple oval concave surface, which rests on the head of its corresponding metacarpal bone. On either side of this the bone displays a tubercular form, and affords attachment to THE PHALANGES. 211 III. Phalanx, ungual or terminal II. Phalaiis the lateral ligaments of the metacarpo-phalangeal jomt, and also to the interossei muscles. The distal end is much smaller than the proximal ; the convex articular surface is divided into two condyles by a central groove running from before backward. The second phalanx (phalanx secunda) resembles the first in general form, but is of smaller size. It differs, however, in the form of its proximal articular surface, which is not a simple oval concavity, but is an oval area divided into two small, nearly circular con- cavities by a central ridge passing from before backwards ; these articulate with the condylic surfaces of the proximal phalanx. Into the margins of its palmar surface near the proximal end are inserted the split portions of the tendon of the flexor digitorum sublimis, whilst on the dorsal aspect of the proximal end the central slip of the extensor digitorum communis muscle is attached. The third, terminal or ungual phalanx (phalanx tertia), is the smallest of the three ; it is easily recognised by the spatula - shaped surface on its distal extremity which supports the nail The articular surface on its proximal end resembles that on the proximal end of the second phalanx, but is smaller. On the palmar aspect of this end of the bone there is a rough surface for the insertion of the tendon of the flexor digitorum profundus muscle. The dorsal surface of the same extremity has attached to it the terminal portions of the tendon of the extensor digitorum communis muscle. The phalanges of the thumb resemble in the arrangement of their parts the first and third phalanges of the fingers. Head -haft The arterial canals, usually two in number, placed on either i side of the palmar asjsect and nearer the distal than the proximal ^ ^ ^ '^°*' P^ end of the bone, are directed towards the finger-tiias. ^^^- ^^'- '^^^ Phalasges of THE Fingers (pahuar aspect). Ossification. — The phalanges are ossified from primary and secondary centres. From the former, which appear as early as the ninth week of %t » 1% i f df 4 H 5 15S. — Radiographs of Fcetal Hands. 1. About ten weeks. Here the ossifie nuclei of the terminal phalanges and the four inner metacarpal bones are seen. •2. A little later. The centre for the metacarpal for the thumb is now present, as also the centres for the first row of phalanges. The centres of the second row of phalanges have appeared in the case of the middle and ring fingers. 3. During tlie third month. All the primary centres for the metacarpal bones and phalanges are now developed. i. About the fourth to fifth month. .5. About the sixth to seventh month. foetal life, the shaft and distal extremities are developed ; whilst the latter, which begin to appear about the third year, form the proximal epiphyses which unite with the shafts 212 OSTEOLOGY. from eighteen to twenty. Dixey {Proc. Roy. Soc, xxx. and xxxi.) has pointed out that the primary centre in the ungual phah\nges commences to ossify in the distal part of the bone rather than towards the centre of the shaft. This observation has been confirmed by Lambertz, who further demonstrates the fact that ossification commences earlier in the distal phalanges than in any of the other bones of the hand. Of the other phalanges, those of the first row, beginning with that of the third finger, next ossify, subsequent to the appearance of ossific centres in the shafts of the metacarpal bones, whilst the second or intermediate row of the phalanges is the last to ossify about the end of the third month. Sewell has recorded a case in which the proximal phalanx had a distal as well as a proximal epiphysis. Sesamoid Bones. Two little oval nodules (ossa sesamoidea), which play in grooves on the palmar aspect of the articular surface of the head of the first metacarpal bone, are constantly met with in the tendons and ligaments of that metacarpo-phalangeal articulation. Similar nodules, though of smaller size, are sometimes formed in the corresponding joints of the other fingers, more particularly the index and little finger ; as Thilenius has pointed out (Morph. Arheiten, vol. v.), these are but the persistence of cartilaginous elements which have a phylogenetic interest. THE LOWER LIMB. THE PELVIC GIRDLE AND THE LOWER EXTREMITY. The pelvic girdle is formed by the articulation of the two innominate bones with the sacrum behind, and their union with each other in front, at the joint called the symphysis pubis. The Innominate or Hip Bone. The innominate or hip bone (os coxae) is the largest of the " flat " bones of thp skeleton. It consists of three parts — the ilium, the ischium, and the pubis — primarily distinct, but fused together in the process of growth to form one large irregular bone. The coalescence of these elements takes place in and around the acetabulum, a large circular articular hollow which is placed on the lateral side of the bone. The expanded wing-like part above this is the ilium ; the stout V-shaped portion below and behind it constitutes the ischium ; while the <;-shaped part to the medial side, and in front and below, forms the pubis. The two latter portions of the bone enclose between them a large aperture of irregular outline, called the obturator foramen (foramen obturatum), which is placed in front and below, and to the inner side of the acetabulum. The ilium, almost a quadrant in form, consists of an expanded plate of bone, having a curved superior border, the iliac crest (crista iliaca). Viewed from the side, this forms a curve corresponding to the circumference of the circle of which the bone is the quadrant ; viewed from above, however, it will be seen to display a double bend — convex anteriorly and laterally, and concave posteriorly and laterally. The iliac crest is stout and thick, and for descriptive purposes is divided into a lateral lip (labium externum), a medial lip (labium internum), and an intermediate surface (linea intermedia) which is broad behind, narrowest about its middle, and wider again in front. About 21 inches from the anterior extremity of the crest the lateral lip is usually markedly prominent and forms a projecting tubercle, which can readily be felt in the living. Attached to these surfaces and lips anteriorly are the muscles of the flank, whilst from them posteriorly the latissimus dorsi, quadratus lumborum, and sacro-spinalis muscles derive their origins. The crest ends in front in a pointed process, the anterior superior iliac spine (spina iliaca anterior superior). To this the lateral extremity of Poupart's inguinal ligament is attached, as well as the sartorius muscle, which also arises from the edge of bone immediately below it, whilst from the same process and from the THE INNOMINATE BONE. 213 anterior end of the lateral lip of the iliac crest the tensor fasciae lat» muscle takes origin. The anterior border of the ilium stretches from the anterior superior iliac spine to the margin of tlie acetabulum below. Above, it is thin ; but below, it forms a thick blunt process, the anterior inferior iliac spine (spina iliaca anterior in- ferior). From this the rectus femoris muscle arises, whilst the stout fibres of the Cre^jt nv THR ILIUM Middle gluteal line Posterior GLUTEAL line Posterior superior SPINE Posterior inferior spi.ne Cotyloid notch Groove for tendon of obturator Anterior superior spine Inferior gluteal line Anterior inferior sriNE Acetabulum pectineal eminence Lesser sciatic notch Ischial tuberosity Superior ramus of pubis I'UBic spine Crest of pubis Body of pubis us of pubis Fig. 159 rt. Inferior ramus of ischium -The Right Innominate Bone seen from the Lateral Side. ilio-femoral ligament of the hip-joint are attached to it immediately above the acetabular margin. Posteriorly, the crest terminates in the posterior superior iliac spine (spina iliaca posterior superior). Below this, the posterior border of the bone is sharp and irregularly notched terminating in a prominent angle, the posterior inferior iliac spine (spina iliaca posterior inferior), in front of which the edge of the bone becomes thick and rounded, and forms a wide notch which sweeps forwards and downwards to join the mass of bone behind the acetabulum, where it becomes fused with the ischium ; this is called the greater sciatic notch (incisura ischiadica major). 14 214 OSTEOLOGY. External obliqde QCADRATUS LUMBORUM Sartorids rNSOR FASCI.'E eflected head of rectus femoris Straight head of rfctds femoris The ilium has t^vo surfaces, medial and lateral. The lateral surface is divided into two parts, viz. a lower acetabular, aud an upper gluteal part. The lower forms a little less than the upper two-fifths of the acetabular hollow, and is separated from the larger gluteal surface above by the upper prominent margin of the articular cavity. The gluteal surface, broad and expanded, is concavo-convex from behind forward. It is traversed by three rough curved lines, well seen in strongly developed bones, but often faint and indistinct in feebly marked speci- mens. Of these the inferior curved line (linea glutsea inferior) curves backwards from a point immediately above the anterior inferior spine towards the great sciatic notch posteriorly ; the bone between this and the acetabular margin is marked by a rough shallow groove, from which the reflected head of the rectus fern oris muscle arises. The anterior or (middle) curved line (linea glutsea anterior) commences at the crest of the ilium, about one inch and a half behind the anterior superior iliac spine, and sweeps backwards and downwards towards the upper and posterior part of the great sciatic notch. The surface be- tween this line and the preceding furnishes an extensive origin for the glutseus minimus muscle. The posterior or (superior) curved line (linea glutsea posterior) leaves the iliac crest about two and a half inches in front of the posterior superior iliac spine, and bends down- wards and slightly for- wards in a direction anterior to the posterior inferior spine. The area between this and the middle curved line is for the origin of the glutfeus medius muscle, whilst the rough surface immediately above and behind it is for some of the fibres of origin of the gluteus maximus muscle. The medial surface of the ilium is divided into two areas which present very characteristic differences. The posterior or sacral part, which is rough, displays in front a somewhat smooth, auricular surface (facies auricularis) which is cartilage- coated in the recent condition, and articulates with the sacrum. Thi.s area is said to be proportionately smaller in the female, wliilst curving rmuid in front of its anterior margin there is often a groove, for the attachment of the filn-es of the anterior sacro-iliac ligaments, called the ^jre-auricular sulcus. According to Dcrry this groove is better marked in the female, and may be regarded as characteristic of that sex. Above and behind this there is an elevated irregular area, the tuberosity (tuberositas iliaca), which is here and there deeply pitted for the attachment of the strong posterior sacro-iliac ligaments. Above this the bone becomes confluent with the medial lip of the iliac crest, and here it affords an origin to the sacro-spinalis and multifidus muscles, and some of the fibres of the quadratus lumljorum. The anterior part of the medial aspect of the bone is smooth and extensive ; it Semimembranosus BICEP.S AND SEMITENDINOSUb Quadratus femoris Pyramidalis Rectus abdominis Adductor longus Gracilis Adductor brevis Adductor magnus Fio. 159 /a —Lateral Aspect of the Right Innominate Bone with the Attachments of the Muscles mapped out. THE INNOMINATE BONE. 215 is subdivided by an oblique ridge, called the ilio- pectineal line (linea arcuata), which passes forwards and downwards from the most prominent point of the auricular surface towards the medial side of the iUo- pectineal eminence which is placed just above and in front of the acetabulum, and marks the fusion of the Crest of the ilum IFJUM Anterior superior SPINE Anterior inferior SPINE Ilio-pectineal eminence Ilio-pectineal line Superior ramus OF PUBIS" Obturator groove Spine of pubis Crest f OF pubis Symphysis pubi Tuberosity FOR posterior sacro-iliac ligament Posterior superior SPINE Articular SURFACE Post. inf. spine Lesser sciatic notch ISCHIUM Ischial tuberosity Inferior ramus of pubis Ramus of ischium Fig. 160. — The Eight Innominate Bone (Medial Aspect). ilium with the pubis. Above this the bone forms the shallow iliac fossa (fossa iliaca), from the iloor of which the iliacus muscle arises, whilst leading from the fossa, below and in front, there is a shallow furrow, passing over the superior acetabular margin, between the anterior inferior iliac spine on the lateral side and the ilio-pectineal eminence medially, for the lodgment of the tendinous and fleshy part of the ilio-psoas muscle. If held up to the hght the. floor of the deepest part of the iKac fossa will be seen to be formed of but a thin layer of bone. A nutrient 216 OSTEOLOGY. foramen of large size is seen piercing the bone towards the hinder part of the fossa. Below and behind the ilio- pectineal line the medial surface of the ilium forms a small portion of the wall of the true pelvis ; the bone here is smooth, and rounded oti" posteriorly into the greater sciatic notch, where it becomes confluent with the medial aspect of the ischium. This part of the bone is proportionately longer in the female than in the male, and forms with the ischium a more open angle. Just anterior to the great sciatic notch there are usually the openings of one or two large vascular foramina. From this surface arise some of the posterior fibres of the obturator internus muscle. The ischium constitutes the lower and hinder part of the innominate bone. Superiorly its body (corpus) forms somewhat more than the inferior two-fifths of the acetabulum together with the bone supporting it behind and within. Below this, the superior ramus passes downwards and backwards as a stout three-sided piece of bone, from the inferior extremity of which a compressed bar of bone, called the inferior ramus, extends forwards at an acute angle. This latter unites in front and above with the descending ramus of the pubis, and encloses the aperture called the obturator foramen. Superiorly, and on the lateral aspect of the ischium, the acetabular surface is separated from the bone below by a sharp and prominent margin, which is, however, deficient in front, where it corresponds to the cotyloid notch, (incisura acetabuli) leading into the articular hollow ; the floor of this notch is entirely formed by the ischium. Below the prominent acetabular margin there is a well- marked groove in which the tendon of the obturator externus lies. Beneath this the antero-lateral surface of the superior and inferior rami furnish surfaces for the attachments of the obturator externus, quadratus femoris, and adductor magnus muscles. The postero-lateral surface of the ischium forms the convex surface on the back of the acetabulum. The medial border of this is sharp and well defined, and is confluent above with the border of the ilium, which sweeps round the great sciatic notch. From this border, on a level with the lower edge of the acetabulum, there springs a pointed process, the spine (spina ischiadica), to which is attached the lesser sacro-sciatic ligament (sacro-spinous ligament) and the superior gemellus muscle. Inferior to this, the postero-lateral surface narrows rapidly, its medial border just below the spine being hollowed out to form the lesser sciatic notch (incisura ischiadica minor). The lower part of this surface and the angle formed by the two rami are capped by an irregularly rough pyriform mass called the tuberosity ^ (tuber ischiadicum). This is divided by an oblique ridge into two areas, the upper and lateral for the tendon of origin of the semimembranosus muscle, the lower and medial for the conjoined heads of the biceps and semitendinosus muscles. Its prominent medial lip serves for the attachment of the great sacro-sciatic ligament (sacrotuber- ous ligament), whilst its lateral edge furnishes an origin for the quadratus femoris muscle; in front and below, the adductor magnus muscle is attached to it. The medial surface of the body and superior ramus of the ischium form in part the wall of the true pelvis. Smooth and slightly concave from before backwards, and nearly plane from above downwards, it is widest opposite the level of the ischial spine. Below this, its posterior edge is rounded and forms a groove leading to the lesser sciatic notch, along and over which the tendon of the obturator internus passes. To part of this surface the fibres of the obturator internus are attached, whilst the medial aspect of the spine supplies points of origin for the coccygeus and levator ani muscles, as well as furnishing an attachment to the " white line " of the pelvic fascia. The medial surface of the inferior ramus of the ischium is smooth, and so rounded that its inferior edge tends to be everted. To this, as well as to its margin, is attached the crus penis, together with the ischio-cavernosus, obturator internus, transversus perinei, and compressor urethrse (sphincter muscle of the membranous urethra) muscles. In the female, structures in correspondence with these are also found. The fore-part of the innominate bone is formed by the pubis ; it is by means of the union of this bone with its fellow of the opposite side that the pelvic girdle is completed in front. ^ I retain the word "tuberosity" here instead of tlie meaningless "tuber." — A. T. THE INNOMINATE BONE. 217 The pubis (os pubis) consists of two rami — a superior (ascending or horizontal) (ramus superior ossis pubis) and an inferior (or descending) (ramus inferior ossis pubis). The broad part of the bone formed by the fusion of these two rami is the body. The body of the pubis has two surfaces. Of these the posterior or postero-siiperior is smooth, and forms the fore-part of the wall of the true pelvis ; hereto are attached the levator ani muscle and puboprostatic ligaments, and on it rests tlie bladder. The anterior or antero-ivferior surface is rougher, and furnishes origins for the gracilis, adductor longus, adductor brevis, and some of the fibres of the obturator externus muscles. The medial border is provided with an elongated oval cartilage -covered surface by means of which it is united to its fellow of the opposite side, the joint being called the symphysis pubis (facies symphyseos). The upper border, thick and rounded, projects somewhat, so as to overhang the anterior surface. It is called the crest (pecten). Internally this forms with the medial border or symphysis the angle, whilst laterally it terminates in a pointed process, the spine (tuberculum pubicum). From the crest arise the rectus abdominis and pyramidalis muscles, and to the spine is attached the medial end of Poupart's Rectus femoris (straight head of origin) Rectus femokis (rfflncted head of origin) Attachment ok lO-FEMORAL BAND ADDUCTOR LONOUS (origin) Pyramidalis abdominis (origin) Rectus abdominis (origin) Gracilis (origin) Adductor erevis (origin) Semimembran osus (origin) Quadratus FEMORis (origin) Biceps and semitendinosus- (origin) Fig. 161. — Mdscle-Attachments to the Lateral Surface of the Pubis and Ischium. inguinal ligament. Passing upwards and laterally from the lateral side of the body towards the acetabulum, of which it forms about the anterior fifth, is the superior ramus (ramus superior). This has three surfaces : an antero-superior, an antero- inferior, and an internal or posterior. The antero-superior surface is triangular in form. Its apex corresponds to the pubic spine ; its anterior inferior border to the obturator crest (crista obturatoria), leading from the spine to the upper border of the cotyloid notch ; whilst its sharp postero-superior border trends upwards and laterally from the spine, and is continuous with the iliac portion of the ilio-pectineal line just medial to the iHo-pectineal eminence, forming as it passes along the superior ramus the pubic portion of that same line (pecten ossis pubis). On this line, just within the ilio-pectineal eminence, there is often a short, sharp crest which marks the insertion of the psoas parvus. The base of the triangle corresponds to the ilio-pectineal eminence above and the upper margin of the cotyloid notch below. Slightly hollow from side to side, and convex from before backwards, this surface provides an origin for, and is in part overlain by, the pectineus muscle. The posterior or ptosterior surface of the superior ramus is smooth, concave from side to side, and slightly rounded from above downwards ; by its sharp inferior curved border it completes the obturator foramen, as seen from behind. 218 OSTEOLOGY. The antero-inferior surface forms the roof of the broad obturator groove (sulcus obturatorius) wliich passes obliquely downwards aud forwards between the lower margin of the antero-superior surface in front and the inferior sharp border of the medial surface behind. The inferior or descending ramus of the pubis (ramus inferior) passes downwards and outwards from the lower part of the body. Flattened and compressed, it unites with the inferior ramus of the ischium, and thus encloses the obturator foramen, whilst in correspondence with its fellow of the opposite side it completes the formation of the pubic arch. Anteriorly it furnishes origins for the gracilis, adductor brevis, and adductor magnus mu.scles, as well as some of the fibres of the obturator externus muscle. Its inedial surface is smooth, whilst its lower border, rounded or more or less everted, has attached to it the fore-part of the crus penis and the subpubic ligament The acetabulum or cotyloid cavity is the nearly circular hollow in which the head of the thigh bone fits. As has been already stated, it is formed by the fusion of the ilium and ischium and pubis in the following proportions : the ilium a little less than two-fifths, the ischium somewhat more than two- fifths, the pubis con- stituting the remaining one-fifth. It is so placed as to be directed downwards, laterally, and forwards, and is surrounded by a prominent margin, to which the capsule and cotyloid ligament of the hip - joint are attached. Opposite the obturator foramen this margin is interrupted by the cotyloid notch (incisura acetabuli) ; immediately lateral to the ilio- pectineal eminence the margin is slightly hollowed, whilst occasionally there is a feeble notching of the border above and behind. These irregularities in the outline of the margin correspond to the lines of fusion of the ilium and pubis, and the ilium and ischium respectively. The floor of the acetabulum is furnished with a horseshoe-shaped articular surface, which lines the circumference of the hollow, except in front, where it is interrupted by the cotyloid notch. It is broad above ; narrower in front and below. Within this articular surface there is a more or less circular rough area (fossa acetabuli) continuous in front and below with the floor of the cotyloid notch. This, some- what depressed below the surface of the articular area, lodges a quantity of fat, and provides accommodation for the intra-articular ligament of the joint. As may be seen by holding the bone up to the light, the floor of this part of the acetabulum is not usually of great thickness. The major part of the non-articular area is formed by the ischium, which also forms the floor of the cotyloid notch. The obturator foramen (foramen obturatum) lies in front of, below, and medial to the acetabulum. The margins of this opening, which are formed in front and above by the pubis, and behind and below by the ischium, are sharp and thin, except above, where the under surface of the superior ramus of the pubis is channelled by the obturator groove. Below, and on either side of this groove, two tubercles can usually be seen. The one, situated on the edge of the ischium, just in front of the cotyloid notch, is named the posterior obturator tubercle (tuberculum obturatorium posterius) ; the other, placed on the lower border of the posterior surface of the superior ramus of the pubis, is called the anterior obturator tubercle (tuberculum obturatorium anterius). Between these two tubercles there passes a ligamentous band, which converts the groove into a canal along which the obturator vessels and nerve pass. Elsewhere in the fresh condition the obturator membrane stretches across the opening from margin to margin. The form of the foramen varies much, being oval in some specimens, in others more nearly triangular ; its relative width in the female is greater than in the male. Nutrient foramina ior tin- ilium are .seen on the floor of the iliac fossa, just in front of the sacrfj-auriciilar surface ; on the in;lvic aspect of the bone, close to th« greater sciatic notch ; and on the glvUeal surface laterally, near the centre ui' the luiddle curved line. For the ischium, on its pelvic surface, and also laterally on the groove l^elow the acetabulum. For the pubis, on the surface of the body, and deeply also from the acetabular fossa. Connexions. — The innominate bone articulates with the sacrum l)ehind, with the femur to the lateral side and below, and with its fellow of the opposite side medially and in front. Each of its three ])arts comes into direct relation with the surface. Above, the iliac crest assists in forming the iliac furrow, which serves to separate the region of the flank from that of the buttock. In front, the anterior .superior iliac spine forms a definite landmark : whilst behind, THE PELVIS. 219 Appears about later end of 2iid in. of foetal life Ajipears about 15 years ; fuses •22-25 the posterior superior iliac spines will Ije ibuiid to correspond witli dimples situated on either side of the middle line of tlic root of the l)ack. The symphysis, the crest, and spine of the pubis can all be distinguished in front, though overlain Ijy a considerable quantity of fat, whilst the position of the tuberosities of the ischia, Avhen" uncovered l)y the gi-eat gluta-al muscles in the flexed position of the thigh, can readily be ascertained. In the perineal region the outline of the pubic and ischial rami can easily be determined by digital e.xamination. Ossification commences in the ilium about the ninth week of intrauterine life ; about the fourth month a centre appears below the acetabulum for the ischium, the pubis being developed from a centre which appears in front of the acetabulum about the fifth or sixth month. At birth the form of the ilium is well defined ; the body and part of the tuberosity of the ischium are ossified, as well as the superior ramus and part of the body of the pubis. All three parts enter into the formation of the sides of the acetabulum, and by the third year have converged to form the bottom of that hollow, being separated from each other by a tri- radiate piece of cartilage, in which, about the twelfth year, independent ossific centres make their appearance, which may or may not become fused with the adjacent bones. In the latter case they unite to form an inde- pendent ossicle, the os acetabuli, which subse- quently fuses with and forms the acetabular part of the pubis. By the age Appea'rs about of sixteen the ossification t^, '"• °^ *'**"^ of the acetabulum is usu- ally completed, whilst the rami of the ischium and pubis commonly unite about the tenth year. Secondary centres, six in number, make their appearance about the age of puberty, and are found in the following situations : one for the anterior inferior iliac spine, one for the iliac crest and the anterior and posterior superior iliac spines, a scale -like epiphysis over the tuberosity of the ischium, a separate epiphysis for the spine of the ischium, (?) a point for the spine and another for the angle of the pubis. Fusion between these and the primary centres is usually complete between the twenty -second and twenty -fifth years. Le Damany states that the proportionate depth of the acetabular cavity at the sixth month of foetal life is greater than at birth. In the third year a rapid increase in its depth again takes place correlated with the assumption of the erect position. Parsons (Joiirn. Anat. and Physiol., vol. xxxvii. p. 315) regards the ischial epiphysis as the homologue of the hypo-ischium in reptiles, and suggests that the epiphysis over the angle of the pubis may represent the epipubic bone of marsupials. Appears about 15 years ; fuses 22- 25 years At Birth. About 12 or 13 years. Fig. 162. — Ossification of the Innominate Bone. Appears abdut IS years Appears about IS years ite about 10 years The Pelvis. The pelvis is formed by the union of the innominate bones with each other in front, and with the sacrum behind. In man the dwarfed caudal vertebrae (coccygeal) are curved forwards and so encroach upon the limits of the pelvic cavity inferiorly. The pelvis is divided into two parts by the ilio-pectineal lines, which curve forwards from the upper part of the lateral masses of the sacrum behind, to the roots of the spines of the pubis in front. The part above is called the false pelvis (pelvis major), and serves by the expanded iliac fossa3 to support the abdominal contents; the part below, the true pelvis (pelvis minor) contains the pelvic viscera, and in the female forms the bony canal through which, at full term, the foetus is expelled. 220 OSTEOLOGY. The true pelvis is bounded in front by the symphysis pubis in the middle Une, and by the body and rami of the pubis on either side, laterally by the smooth medial surfaces of the ischia and ischial rami, together with a small part of the ilium below the iliac portion of the ilio-pectineal line. Springing from the posterior margin of the ischium are the inturned ischial spines. Behind, the broad curved Fig. 163 a. — The Male Pelvis seen from the Front. anterior surface of the sacrum, and below it, the small and irregular coccyx, form its posterior wall. Between the sides of the sacrum behind, and the ischium and ilium in front and above, there is a wide interval, called the greater sciatic notch, which is, however, bridged across in the recent condition by the great and small sacro-sciatic ligaments (sacro-tuberous and sacro-spinous ligaments), which thus convert it into two foramina, the larger above the spine of the ischium— the greater Fig. 16:j//. — The Femalb Pelvis seen fuu.m the Front. sacro-sciatic foramen, the lower and smaller below the spine, called the lesser sacro-sciatic foramen. The inlet Tapertura pelvis superior) of the pelvis is bounded in front by the symphysis pubis, witli the body of the pubis on either side ; laterally by the ilio- pectineal lines ; and behind by the sacral prominence. The circumference of this THE PELVIS. 221 aperture is often called the brim of the pelvis ; in the male it is heart-shaped, in the female more oval. The antero-iwsterior or conjugate diavieter is measured from the sacro-vertebral angle to the symphysis pubis ; the oblique diameter from the sacro-iliac joint of one side to the ilio-pectineal eminence of the other ; whilst the transverse diameter is taken across the point of greatest width. The outlet (apertura pelvis inferior) is bounded anteriorly by the pubic arch (arcus pubis), formed in front and above by the bodies of the pubis, with the symphysis between them, and the inferior pubic rami below and on either side. These latter are continuous with the ischial rami which pass backwards and outwards to the ischial tuberosities, which are placed on either side of this aperture. In the middle line and behind, the tip of the coccyx projects forward, and in the recent condition the interval between this and the ischial tuberosities is bridged across by the great sacro-sciatic ligament (sacro-tuberous ligament), the inferior edge of which necessarily assists in determining the shape of the outlet. As the anterior wall of the cavity, formed by the symphysis puljis, measures from Ih to 2 inches, whilst the posterior wall, made up of the sacrum and coccyx, is from 5 to 6 inches in length, it follows that the planes of the inlet and outlet are not parallel, but placed at an angle to each other. The term axis of the pelvis is given to lines drawn at right angles to the centre of these planes. Thus, with the pelvis in its true position, when the figure is erect, the axis of the inlet corresponds to a line drawn downwards and backwards from the umbilicus towards the tip of the coccyx below, whilst the axis of the outlet is directed downwards and slightly backwards, or downwards and a little forwards, varying according to the length of the coccyx. Between these two planes the axis of the cavity, as it passes through planes of varying degrees of obliquity, describes a curve repeating pretty closely the curve of the sacrum and coccyx. Position of the Pelvis.^ — The position of the pelvis in the living when the figure is erect may be approximately represented by placing it so that the anterior superior iliac spines and the symphysis pubis lie in the same vertical plane. Under these conditions the plane of the inlet is oblique, and forms with a horizontal line an angle of from 50° to 60°. The position of the pelvis depends upon the length of the ilio-femoral ligaments of the hip-joint, being more oblique when these are short, as usually happens in women in whom the anterior superior iliac spines tend to lie in a plane sliglitly in advance of that occupied by the symphysis pubis. In cases where the ilio-femoral ligament is long, a greater amount of extension of the hip-joint is permitted, and this leads to a lessening of the obliquity of the pelvis. This condition, wliicli is more typical of men, results in the anterior superior iliac spines lying in a plane slightly posterior to the plane of the sym- physis, whilst the angle formed by the plane of the inlet and the horizontal is thereby reduced. Bearing in mind the oblique position of the pelvis, it will now be seen that the front of the sacrum is directed downwards more than forwards, and that the sacral pro- montory is raised as much as from 3^ to 4 inches above the upper border of the symphysis pubis, lying higher than the level of a line connecting the two anterior superior iliac spines. From the manner in which the sacrum articulates with the ilia, it will be noticed that the weight of the trunk is transmitted downwards through the thickest and strongest part of the bone (see Architecture, Appendix A) to the upper part of the acetabula, where these rest on the heads of the femora. Sexual Differences- — The female pelvis is lighter in its construction than that of the male ; its surfaces are smoother, and the indications of muscular attachments less marked. Its height is less and the splay of its walls not so pronounced as in the male, so that the female pelvis has been well described as a short segment of a long cone as contrasted with the male pelvis, which is a long segment of a short cone. The cavity of the true pelvis in the female is more roomy, and the ischial spines not so much inturned. The pubic arch is wide and rounded, and will usually admit a right-angled-set square being placed within, so that the summit touches the under surface of the symphysis pubis, whilst the sides lie in contact with the ischial rami. In the male the arch is narrow and angular, forming an angle of from 65° to 70°. The greater sciatic notch in the female is wide and shallow. The distance from the posterior edge of the body of the ischium to the posterior inferior iliac spine is longer, measuring on an average 50 mm. (2 inches) in the female, as contrasted with 40 mm. (1| inches) in the male. The angle formed by the ischial and iliac borders is more contracted and acute in the male as compared with the 222 OSTEOLOGY. female in whom it is wider and moi-e open. In the female the acetabukim is proportion- ately smaller than in the male. The inlet in the female is large and oval or reniform, as compared with the cribbed and heart-shaped aperture in the male. The sacro-vertebral angle is more pronounced in the female, and the obliquity of the inlet greater. The sacrum is shorter and wider. The posterior superior iliac spines lie wider apart ; the pubic crests are longer ; and the pubic spines are separated by a greater interval than in man. The outlet is larger ; the tubero- sities of the ischia are farther apart ; and the coccyx does not project forward so much. The curve of the sacrum is liable to very great individual variation. As a rule the curve is more uniform in the male, whilst in the female it tends to be flatter above and more accentuated below. There is a greater proportionate width between the acetabular hollows in the female than in the male. Of much importance from the standpoint of the obstetrician are the various diameters of the true pelvis. In regard to this it is worthy of note that the plane of " greatest pelvic expansion " extends from the union between the second and third sacral vertebrae behind, to the middle of the symphysis pubis in front, its lateral boundaries on either side corresponding with the mid-point of the medial surface of the acetabulum ; whilst the plane of "least pelvic diameter" lies somewhat lower, and is defined by lines passing through the sacro-coccygeal articulation, the ischial spines, and the lower third of the symphysis pubis (Norris). Subjoined is a table showing the principal average measurements in the two sexes : — False Pelvis (pelvis major) Males. Females. Maximum distance between the iliac crests Distance between the anterior superior iliac spines Distance t between the last lumbar spine and the front of the symphysis pubis ] 1| in., or 282 mm. 9^ in., or 240 mm. 7 in., or 176 mm. lOj in., or 273 mm. 9f in., or 250 mm. 7^ in., or 180 mm. True Pelvis (pelvis minor) Males. Females. \ 1 Inlet. Outlet. : Inlet. i Cavity. Outlet. Greatest. Least. Antero-posterior (conju- gate) diameter Oblique diameter . Transverse diameter 4 in., or 101 mm. 4| in., or 120 mm. .5 in., or 127 mm. j 3| in., or 4f in., or 95 mm. 110 mm. 3^ in., or 5 in., or "88 mm. ' 125 mm. 3| in., or l 5j in., or 88 mm. 1 135 mm. 5 in., or 127 mm. 4^ in., or 125 mm. 4§ in., or 110 mm. 4f in., or 110 mm. 4| in., or 115 mm. 4| in., or 115 mm. 4§ in., or 110 mm. Growth of the Pelvis.— From the close association of the pelvic girdle with the lower limb we find tliat its growtli takes place concurrently with the development of that member. At birth the lower limbs measure but a fourth of the entire l)ody lengtli ; consequently at that time the pelvis, as compared witli the liead and trunk, is relatively small. At this period of life the bladder in both .sexes is in greater part an abdominal organ, whilst in the female the uterus has not yet sunk into the true pelvic cavity, and the ovaries and Fallopian tubes rest hi the iliac fossa;. Tlie sacro-vertebral angle, though readily recognised, is as yet but faintly marked. Coincident with the remarkable gi'owth of the lower limlxs and the assumption of the erect position when the child begins to walk, striking changes take place in the foi-m and size of the pelvis. These consist in a greater expansion of the iliac bones necessarily associated with the growth of the muscles which control the movements of the hip, together with a marked increase in the sacro-vertebral angle due to the development of a forward lumbar curve ; at the same time, the weight of the trunk being thrown on the sacrum causes the elements of that bone to sink to a lower level between the innominate bones. The cavity of the true pelvis increases in size proportionally, and the viscera aforementioned now begin to sink down and have assumed a position within the pelvis by the fifth or sixth year. The extension of the thighs in the upright position necessarily brings about a more pronounced pelvic ol)liquity, whilst the stoutness and thickness of the ilium over the upper part of the acetabulum is much increased to withstand the pressure to which it is obviously subjected. Coincident with this is the gradual development THE FEMUE. 223 Head of the iliac portion of the ilio-pectineal line, which serves in the adult to separate sharply the false from the true pelvis. This part of the bone is reniarkaljly sti'ong, as has been shown (see Arcliitecture), and serves to transmit the body weight from the sacrum to the thigh bone. The sexual differences of the 2>elvis, so far as they refer to the general configviration of this part of the skeleton, are as pronounced at the third or fourtli month of fojtal life as they are in the adult (Fehling, Ztschr. f. Geburtsh. u. Gynaek. Bd. ix. and x. ; A. Thomson, Journ. Anaf. and Physiol, vol. xxxiii. p. 359). The rougher appearance of the male type is cor- related with the more powerful muscular development. The Femur The femur or thigh bone is remark- able for its length, being the longest Obturator internus %^ Piriformis Greatri trochantei Vastus medialis Ilio-psoas Fig. 164 /j. — Front Aspect of Ui'per Portion of THE Right Femur with Attachjients of Muscles mapped out. bone in the body. Superiorly the femora are separated by the width of the pelvis. Inferiorly they articulate with the tibiaj and patellae. In the military position of attention, with the knees close to- gether, the shafts of the thigh bones occupy an oblique position. For de- scriptive purposes the bone is divided into an upper extremity, comprising the head, neck, and two tro- chanters ; a shaft ; and a lower extremity, forming the expansions known as the condyles. The head (caput femoris) is the hemi- spherical articular sur- face which fits into the acetabular hollow. Its Pig. 164 a.— The Right Femur seen from the Front. pole IS directed upwards, medially, and slightly forwards. A little below the summit, and usually somewhat behind it, is a Lateral epicondyle Adductor tubercle Medial epicondyle Lateral condyle Patellar SURFACE Medial condyle 224 OSTEOLOG-Y. Head Fossa for lio. teres KOCIIANTERIC FOSSA Greater trochanter Tubercle of quadratns Intertrochan- teric RIDGE Gluteal ridge Arterial foramen hollow oval pit (fovea capitis femoris) for the attachment of the ligamentum teres. Piercing the floor of this depression are seen several foramina through which vessels pass to supply the head of the bone ; the superior epiphysis thus having a double blood supply, viz. from the neck below, and through the medium of the ligamentum teres above. The circumfer- ence of the head forms a lip with a wavy outline, more prominent above and behind than in front. The head is supported by a stout compressed bar of bone, the neck (collum femorig),which forms with the upper end of the shaft an angle of about 125 degrees, and is directed upwards, medially, and a little forwards. Its ver- tical width exceeds its antero-posterior thickness. Constricted about its middle, it expands medi- ally to support the head, whilst laterally, where it joins the shaft, its vertical diameter is much in- creased. Anteriorly it is clearly defined from the shaft by a rough ridge which commences above on a prominence, some- times called the tubercle of the femur, and passes obliquely downwards and medially. This constitutes tlie upper part of the spiral line (linea inter-tro- chanterica), and serves for the attachment of the ilio- femoral ligament of the hip-joint. Posteriorly where the neck unites with the shaft, there is a full rounded ridge passing from the trochanter major above to the trochanter minor below ; this is the posterior intertrochanteric line or ridge (crista inter- trochanterica). A little above the middle of this ridge there is usually a fulness which serves to indicate the upper limit of attachment of the quadratus femoris muscle, and is called the tubercle for the quadratus. Laterally the neck is embedded in the medial surface of the Medial epicondylic line Lateral epicondyijc line Popliteal surface Adductor tubercle Medial epicondyle Medial CONDVr I Surface for attachment of ijosterior crucial ligamunt I ■• im > mm,', i i, i i Fig. 165 «. — The Right FeiMur seen from Behind. ■Lateral epicondyle -Surface for attachment of ant. crucial ligament Lateral condyle THE FEMUE. 225 trochanter major, by which, at its upper and back part, it is to some extent overhung. Here is situated the trochanteric or digital fossa, into which the tendon of the obturator externus is inserted. Passing nearly horizontally across the back of the neck there is a faint groove leading into this de- pression ; in this the tendon of the obturator externus muscle lies. Interiorly the neck becomes confluent with the trochanter minor behind, and is continuous with the medial surface of the shaft in front. The neck is pierced by many vascular canals, most numerous at the upper and back part. Some are directed upwards towards the head, whilst others pass in the direction of the trochanter major. The trochanter major is a large quadrangular process which caps the upper and lateral part of the shaft, and overhangs the root of the neck above and behind. Its lateral surface, of rounded irregular form, slopes upwards and medially, and is separated from the lateral surface of the shaft below by a more or less horizontal ridge. Crossing it obliquely from the posterior superior to the anterior inferior angle is a rough line which serves for the insertion of the gluteeus medius muscle ; Head BTURATOR KXTERNUS Outurator inteenus Greater trochanter Gluteal ridqe --Arterial foramen LiNEA ASPERA Fig. 165 c.- -Posterior View of the Upper End of THE Right Femur. Fig. 165 6. — Posterior Aspect of the Upper Portion of the Right Femur WITH the Attachments of Muscles MAPPED OUT. above and below this the surface of the bone is smoother and is overlain by bursse. The anterior surface, somewhat oblong in shape, and inclined obliquely from below upwards and medi- ally, is elevated from the general aspect of the shaft below, from which it is separated in front by an oblique line leading upwards and medially to the tubercle at the upper end of the superior part of the spiral line. This surface serves for the insertion of the glutseus minimus. The superior border is curved and elevated ; into it are inserted the tendons of the obturator internus and gemelli muscles within and in front, and the piriformis muscle above and behind. The posterior border is thick and rounded, and forms the upper part of the posterior intertro- chanteric ridge. The angle formed by the superior and posterior borders is sharp and pointed, and forms the tip of the trochanter overhanging the trochanteric fossa, which lies immediately below and within its medial surface. The trochanter minor is an 226 OSTEOLOGY. elevated pyramidal process situated at the back of the medial and upper part of the shaft where that becomes continuous with the lower and posterior part of the neck. Continent above with the posterior intertrochanteric ridge, it gradually fades away into the back of the shaft below. The combined tendon of the ilio- psoas is inserted into this process and the bone immediately below it. The shaft (corpus femoris), which is characterised by its great length, is cylin- drical in form. As viewed from the front, it is straight or but slightly curved ; as seen in profile, it is bent forwards, the curve being most pronounced in its upper part. The shaft is tliinnest at some little distance above its middle ; below this it gradually increases in width to support the condyles interiorly ; its antero-posterior diameter, however, is not much increased below. Its surfaces are generally smooth and rounded, except behind, where, running longitudinally down the centre of its curved posterior aspect, there is a rough-lipped ridge, the linea aspera (linea aspera). Most salient towards the middle of the shaft, the linea aspera consists of a medial lip (labium mediale) and a lateral lip (labium laterals), with a narrow intervening rough surface. Above, about 2 to 2^ inches from the trochanter minor, the linea aspera is formed by the convergence of three lines. Of these the outer is a rough, somewhat elevated, ridge, which commences above, on the back of the shaft, lateral to and on a level with the trochanter minor, and becomes continuous below with the outer lip of the linea aspera. This serves for the bony insertion of the gluteus maximus, and is occasionally developed into an outstanding process called the trochanter tertius. Medially the medial lip of the linea aspera is confluent above with a line which winds round the shaft upwards and forwards in front of the trochanter minor to become continuous with the rough ridge which serves to define the neck from the shaft anteriorly (see p. 224). The whole constitutes what is known as the spiral line, and extends from the fore and upper part of the trochanter major above to the linea aspera below. Intermediate in position between the spiral line in front and medially, and the gluteal ridge laterally, there is a third line, the pectineal line (linea pectinea), which passes down from the trochanter minor and fades away inferiorly into the surface between the two lips of the linea aspera. Into this the pectineus muscle is inserted. About the junction of the middle with the lower third of the shaft the two lips of the linea aspera separate from one another, each passing in the direction of the condyle of the corresponding side. The lines so formed are called the medial and lateral epicondylic lines respectively, and enclose between them a smooth triangular area corresponding to the back of the lower third of the shaft ; this, called the popliteal surface ^ (planum popliteum), forms the floor of the upper part of the popliteal space. The continuity of the upper part of tlie medial epicondylic line is but faintly marked, being interrupted by a wide and faint groove along which the popliteal artery passes to enter the space of that name. Below, where the line ends on the upper and medial surface of the medial condyle, there is a little spur of bone called the adductor tubercle, to which the tendon of the adductor magnus is attached, and behind which the medial head of the gastrocnemius muscle takes origin. The linea aspera affords extensive linear attachments to many of the muscles of the thigh. The vastus medialis arises from the spiral line above and the medial lip of the linea aspera below. This muscle overlies but does not take origin from the medial surface of the sliaft. The adductor longus is inserted into the medial lija about the middle third of the length of the shaft. The adductor magnus is inserted into the intermediate part of the line, extending as high as the level of the trochanter minor, where it lies medial to tlie insertion of the glutaeus maximus. Below, its insertion passes on the medial epicondylic ridge, reaching as low as the adductor tubercle. The adductor brevis muscle is inserted into tlie linea aspera above, between the pec- tineus and adductor longus muscles medially and the adductor magnus laterally. Below the insertion of tlie glutfeus maximus the short head of the biceps arises from tlie lateral lij) as well as from the lateral epicondylic line ; in front these also serve for the origin of the vastus lateralis muscle. There is frequently a small tubercle which marks the lower attachment of the lateral intermuscular septum on the lateral condylic line, alwnit two inches above the condyle. Immediately above this there is often a groove for a large muscular artery which pierces the sei^tum at this point (Frazer). The canals for the nutrient arteries of the shaft, which have an upward direction, are usually two in number, and are placed on or near the linea aspera— the upper one about the level of the ' This ;ii)pe;us jireferable to "popliteal plain." — A. T. THE FEMUE. 227 Medial head of gas trocnemius Lateral head of oas- rROCNEMirS Posterior crchial anterior crucial LIflAMENX ligament junction of the middle and upper third of the bone, the lower some three or four inches below — usually on the medial side of the shaft, immediately in front of the medial lip of the linea aspera. The front and lateral aspects of the shaft are covered by, and furnish surfaces for, the origins of the vasti muscles. The lower extremity of the femur comprises the two condyles. These are two recurved processes of bone, each provided with an articular surface, and separated behind by a deep intercondylic notch. United in front, where their combined articular surfaces form an area on which the patella rests, the two condyles differ from each other in the following respects : If the shaft of the bone be held vertically, the medial condyle is seen to reach a lower le^el than the lateral ; but, as the femur lies obliquely in the thigh, the condyles are so placed that their inferior surfaces lie in the same horizontal plane. Viewed from below, the medial condyle is seen to be the narrower and shorter of the two. The lateral condyle is broader, and advances farther forward and higher up on the anterior surface of the shaft. The intercondylic notch (fossa inter- FiG. 166.— Posterior Aspect of Lower condyloidea) reaches forwards as far as a trans- PoKTioN OF THE RiGHT Fejiur WITH yersc liuc drawu through the centre of the lateral ATTACHMENTS OF MuscLEs MAPPED condyle. Its sides are formed by the medial and lateral surfaces of the lateral and medial condyles respectively, the latter being more deeply excavated, and displaying an oval surface near its lower and anterior part for the attachment of the posterior crucial hga- ment of the knee-joint. Placed high up, on the posterior part of the medial surface of the lateral condyle, there is a corresponding surface for the attachment of the anterior crucial ligament. The floor of the notch, which is pierced by numerous vascular canals, slopes upwards and backwards towards the popliteal surface on the back of the shaft, from which it is separated by a slight ridge (linea intercondyloidea) to which the posterior part of the capsule of the knee-joint is attached. The cutaneous aspect of each condyle (^i.e. the lateral surface of the lateral condyle and the medial surface of the medial condyle) presents an elevated rough surface, called the epicondyle, or tuberosity, the medial (epicondylus medialis) projecting more prominently from the line of the shaft ; capped above by the adductor tubercle, it affords attachment near its most prominent point to the fibres of the tibial collateral (internal lateral) ligament of the knee- joint. The lateral epicondyle (epicondylus lateralis), less pronounced and lying more in line with the lateral surface of the shaft, is channelled behind by a curved groove, the lower rounded lip of which serves to separate it from the in- ferior articular surface. This groove ends in front in a pit which is placed just below the most salient point of the tuberosity ; hereto is attached the tendon of the popliteus muscle, which overlies the lower lip of the groove in the extended position of the joint, but slips into and occupies the groove wdien the joint is flexed. Behind the most prominent part of the lateral epicondyle, and just above the pit for the attachment of the popliteus, the fibular collateral (external lateral) ligament of the knee-joint is attached, whilst superior to that there is a circum- scribed area for the origin of the tendinous part of the lateral head of the gastro- cne*tius muscle. Surface for the attachment of ext. lateral (fib- ular collateral) Groove for tendon of popliteus Fig. 167. — Lower End of the PvIGHt Femur (Lateral Side). 228 OSTEOLOGY. Trochlea or patellar surface Impression of lateral semi- lunar cartilage (meniscus) Lateral epicondyle POPLITEAI GROOVf. Lateral tibial surface Impression of medial semi- lunar cartilage (meniscus) Semilunar facet for medial edge of patella in extreme flexion Medial TIBIAL surface The articular surface on the lower extremity is divisible into three parts — that which corresponds to the inferior surface of the shaft and which is formed by the coalescence of the two condyles in front, and those which overlie the under and hinder aspects of each of those processes. The former is separated from the latter by two shallow oblique grooves which traverse the articular surface from before backwards, on either side, in the direction of the anterior part of the intercondylic notch. These furrows are the impressions in which fit the fore-parts of the medial and lateral semilunar cartilages of the knee-joint respectively, when the knee-joint is extended. The anterior articular area or trocMea (facies patellaris) is adapted for articulation with the patella. Convex from above downwards, it displays a broad and shallow central groove, bounded on either side by two slightly convex surfaces. Of the two sides, the lateral is the wider and more prominent, and rises on the front of the bone to a higher level than the medial, thus tending ta prevent lateral dislocation of the patella. The condylar or tibial surfaces are convex from side to side, and convex from before backwards. Sweeping round the under surface and posterior extremities of the condyles, they describe a spiral curve more open in front than behind. The medial condylar articular surface is narrower than the lateral^ and when viewed from below is also seen to de- scribe a curve around a vertical axis. Along the lateral edge of this, and in front, where it bounds the intercondylic fossa, is a semilunar articular area, best seen when the bone is coated with cartilage. This articulates with the medial edge of the patella in extreme flexion of the joint. The articular sur- face of the lateral con- dyle is inclined obliquely from before backwards and slightly laterally. The surfaces of the condyles above the articular area posteriorly are continuous superiorly with the popliteal surface of the shaft ; from these areas the heads of the gastrocnemius muscles arise. The bone from which the medial head of the muscle springs is often elevated in the form of a tubercle placed on the lower part of the popliteal surface of the shaft, just above the medial condyle. The proportionate length of the femur to the body height is as 1 is to 3-53-3*92. Arterial Foramina. — Numerous vascular canals are seen in the region of the neck, at the bottom of the trochanteric fossa, in the fossa for the ligamentum teres, on tlie posterior inter- troclianteric ridge, and on tlie lateral surface of the great trochanter. Tlie nutrient arteries for the shaft pierce the hone in an upward direction on or near the linea aspera. Both back and front of tlie lower end of the shaft display the openings of numerous vascular canals, and the floor of the intercondylic notch is also similarly pierced. Connexions. — The iemur articulates with the os innominatum above and the tibia and patella below. The lateral surface of the greater trochanter determines the point of greatest hip wddth in the male, being covered only by the skin and superficial fascia and the aponeurotic insertion of the glutteus maximus. In the erect position the tip of the trochanter corresponds to the level of the centre of the hip-joint. When the thigh is flexed the trochanter major sinks under cover of the antei'ior fibres of the glutieus maximus. In women the hip width is usually greatest at some little distance below the trochanter, due to the accumulation of fat in this region. The shaft of tlie Ijone is surrounded on all sides by muscles. Its forward curve, however, is account- able to some extent for the fulness of the front of the thigh. The exposed surfaces of the condyles determine to a large extent the form of the knee. In flexion the articular edges can easily be recognised on either side of and below the patella. Sexual Differences. — According to Dwight, the head of the femur in tlie female is propor- tionately HiiiHllcr than that of the male. Ossification. — The shaft begins to ossify early in the second month of foetal life, and at birth displays enlargements at both ends, which are capped with cartilage. If at birth the inferior cartilaginous end be sliced away, a small ossific nucleus for the inferior epiphysis will Fig. li Medial condyle Surface of attachment of posterior crucial ligament -Lower End of the Right Femur seen from Below. L\TLR\L CO.N'DYLE Intercondylic notch THE PATELLA. 229 cartilaginous at birth, prises the head, neck, Appears about early part of first year Fuses with sliaft about IS-l'.i years Appears about ■J-3 year usually be seen. This, as a rule, makes its appearance towards the latter end of the ninth month of fcetal life, and is of service from a medico-legal standpoint in determining the age of the foetus. According, to Hartman, it is absent in about 12 per cent of children at term, and may appear as early as the eighth month of foetal life in about 7 per cent. The superior extremity, entirely com- and trochanter major. A centre appears for the head during the early part of the fii'st year. It is worthy of note that this epiphysis has a double blood - supply — one through the neck, the other through the ligamentum teres. That for the tro- chanter major begins to ossify about the second or third year, whilst the neck is developed as an upward extension of the shaft, which is, however, not confined to the neck alone, but forms the lower circumference of the articular head, as may be seen in bones up to the age of twelve or sixteen ; after that, the separate epi- physis of the head begins to overlap it so as to cover it entirely when fusion is com- plete at the age of eighteen or twenty. The epiphysis of the greater trochanter unites with the shaft and neck about eighteen or nineteen, whilst the epiphysis for the ti'ochanter minor, which usually makes its appearance about the twelfth or thirteenth year, is usually completely fused with the shaft about the age of eighteen. The epiphysis for the lower end, although the first to ossify, is not completely united to the shaft until from about the twentieth to the twenty-second year. It is worthy of note that the line of fusion of the shaft and inferior epiphysis passes through the adductor tubercle, a point which can easily be determined in the living. The lower end is the so-called " growing end of the bone." Usually appears in tlie 9th mouth of foetal life Usually appears before birth At birth. Fuses with shaft about 20-22 years About 12 years. About 16 years. Fig. 169. — Ossification of the Femur. The Patella. The patella, the largest of the sesamoid bones, overlies the front of .the knee- joint in the tendon of the quadriceps extensor. Of compressed form and somewhat triangular shape, its lower angle projects downwards and forms a peak, called the apex (apex patellae), whilst its upper edge, or base (basis patellae), broad, thick, and sloping forwards and a little downwards, is divided into two areas by a transverse line or groove ; the anterior area so defined serves for the attachment of the common tendon of the quadriceps extensor muscle, whilst the posterior, of com- pressed triangular shape, is covered by synovial membrane. The medial and lateral borders, of curved outline, receive the insertions of the vastus medialis and laterahs muscles respectively, the attachment of the vastus medialis being more extensive than that of the vastus lateralis. The anterior surface of the bone, slightly convex in both diameters, has a fibrous appearance, due to its longitudinal striation, and is pierced here and there by the openings of vascular canals. The posterior or femoral articular surface is divided into two unequal parts (of which the lateral is the wider) by a vertical elevation which glides in the furrow^ of the trochlear surface of the femur, and in extreme flexion passes to occupy the intercondylic notch. The lateral of the two femoral surfaces is slightly concave in both its diameters ; the "" ^ 15 230 OSTEOLOGY. medial, though slightly concave from above downwards, is usually plane, or somewhat convex transversely. Occasionally, in the macerated bone, indications of a third vertical area are to be noted along the medial edge of the posterior aspect. This defines the part of latehal^articular FACET ^^^ artlcukr surface which rests on the lateral border of the medial condyle in extreme flexion. In the recent condition, when the femoral sur- face is coated with cartilage, a more com- plex arrangement of facets may be in some cases displayed (as in- dicated in rig. 170). Below the femoral articular area the deep surface of the apex is rough and irregular ; the greater part of this is covered by synovial membrane, the ligamentum patellse being attached to its summit and margins, reaching some little distance round the borders on to the anterior aspect of this part of the bone. Ossification. — The patella is laid down in cartilage about the third month of foetal hfe. At birth it is cartilaginous, and the tendon of the quadriceps is continuous with the ligamentum patellae over its anterior surface, and can easily be dissected off. About the third year an ossific centre appears in it and spreads more particularly over its deeper surface. Two centres, vertically disposed, have also been described. Ossification is usually completed by the age of puberty. Fig. 170, A. Anterior Surface. Surface for the ligamentum patellae -The Right Patella. B. Posterior Surface. Tuberosity Surf, for attachment of ant. extremity of Literal semilunar ilage (meniscus) The Tibia. The tibia is the medial bone of the leg. It is much stouter and stronger than its neighbour the fibula, with which it is united above and below. By its superior expanded extremity it supports the condyles ^^^'face for attachment of anterior extremity rf J , of medial semilunar cartilage (meniscus) of the femur, while Anterior crucial ligament inferiorly it shares in the formation of the anlde-joint,articula.ting with the upper surface and medial side of the talus or astragalus. The superior ex- tremity comprises the medial and lateral con- dyles (tuberosities), the «!-niTiP and tVip tiiliPrnQi+v '^'"'fiiceforattach. of post, extrem.of Spme, anu tne tUOerOSlty medial semilunar cartilage (meniscus) (tubercle). Each con- dyle is provided on its upper aspect with an articular surface (facies articularis superior), which supports the corresponding femoral condyle, as well as the interposed semilunar cartilage. Of these two condylic surfaces the medial is the larger ; of oval shape, its long axis is placed antero-posteriorly. Slightly concave from before backwards and from side to side, its circumference rises in the form of a sharp and well-defined edge. The lateral condylic surface is smaller and rounder. Slightly concave from side to side, and gently convex from before backwards, its circumference is well defined in front, but is rounded off behind, thus markedly increasing the convexity of its posterior Synovial curved SURFACE POPLIII M NOTCH Post, crucial ligament face for attach, of post, extremity of latpial semilunar tartilage (meniscus) Fig. 171. — The Upper Surface of the Superior Extremity of the Right Tibia. THE TIBIA. 231 part. Between the two condylic surfaces the bone is raised in the centre to form the spine (eminentia intercondyloidea), which consists of two lateral tubercles separated by an obliqu(^ groove, in the anterior part of which lies the anterior crucial ligament. The medial tubercle (tuberculum intercondyloideum mediale), the higher, is prolonged backwards and laterally by an oblique ridge to which part of the posterior corner of the lateral semilunar cartilage is attached. The lateral tubercle (tuberculum intercon- dyloideum laterale) is more pointed and not so elevated. In front and behind the spine the articular areas are separated by two irregular V- shaped surfaces, the intercondylic fossae. The anterior fossa (fossa in- tercondyloidea anterior), the larger and wider, furnishes areas for the attachment of the semilunar carti- lages on either side, and for the anterior crucial ligament immedi- ately in front of the spine. The floor of this space is pierced by many nutrient foramina. The posterior intercondylic fossa (fossa intercon- dyloidea posterior) is concave from side to side, and slopes down- wards and backwards. The lateral semilunar cartilage is attached near its apex to a surface which rises on to the back of the spine ; the medial semilunar cartilage is fixed to a groove which runs along its medial edge, and the posterior crucial Hgament derives an attach- ment from the smooth posterior rounded surface. The lateral condyle^ is the smaller of the two. It overhangs the shaft to a greater extent than the medial, though this is obscured in the living by its articulation with the fibula. The facet for the fibula, often small and indistinct, IS placed postero- laterally on the under surface of its most projecting part. Antero-laterally the imprint caused by the attachment of the ilio-tibial band is often quite dis- tinct. Curving downwards and forwards from the fibular facet Ilio-tibial band SriNK Posterior or ex- tensor SURFACE Anterior or flexor surface Subcutaneous SURFACE Lateral malleolo Subcutaneous MEDIAI SURFACE Medial malleolus Fig. 172 «. — The Right Tibia and Fibula as seen FROM THE Front. The anterior or flexor surface of the fibula is coloured blue. The posterior or exteusor surface of the fibula is coloured red. The lateral or peroneal surface of the fibula is left uncoloured. ^ I name "the tuberosities" of the tibia thus, according to international nomenclature, although I person- ally cannot regard the flat top of the tibia as such. — A. T. 232 OSTEOLOGY. Biceps External lateral ligament of knef (FiBULAP collateral) RTOEIUS Gracilis there is often a definite ridge for the attachment of the expansion of the biceps tendon ; below this the areas for the origins of the peronffius longus and extensor digitorum longus are often crisply defined. The circumference of the medial condyle is grooved postero-medially for the insertion of the tendon of the semi- membranosus. In front of the condyles, and about an inch below the level of the condylic sur- faces, tliere is an oval elevation called the tuberosity or tubercle of the tibia. The upper half of this is smooth and covered by a bursa, while the lower part is rough and serves for the attachment of the ligamentum patellae. Considered in its entirety, the upper extremity of the tibia is broader trans- versely than antero-posteriorly, and is inclined backwards so as to overhang the shaft posteriorly. The shaft (corpus tibiae) is irregularly three-sided, possessing a medial, a lateral, and a posterior surface, separated by an anterior crest, medial, and lateral or interosseous borders. It is narrowest about the junction of its middle and lower thirds, and expands above and below to support the extremities. Eunning down the front of the bone there is a gently-curved, prominent margin, the anterior crest, confluent above with the tuberosity, but fading away inferiorly on the anterior surface of the lower third of the bone, where it may be traced in the direction of the anterior border of the medial malleolus. This is the crest or shin (crista anterior), which is subcutaneous throughout its entire length. To the medial side of this is a smooth, slightly convex surface, which semitendinosus reaches as high as the medial tuberosity above, and in - feriorly becomes continuous with the medial surface of the medial malleolus. This is the medial or subcutaneous surface (facies medialis) of the shaft, Fig. Ii2b. — Front aspect of the Upper Portions of the Bones V,' V, ' A 1 "K V OF the Right Leg with Attachments op Muscles mapped out. wnicn IS COVerCQ oniy Dy SKin and superficial fascia, except in its upper fourth, where the tendons of the sartorius, gracilis, and semitendinosus muscles overlie it, as they pass towards their insertions. This surface is limited posteriorly by the medial border (margo medialis) which passes from the medial and under surface of the medial condyle above to the hinder border of the medial malleolus below. This border is rounded and indefinite above and below, being usually best marked about its middle third. To the lateral side of the tibial crest is the lateral surface of the bone (facies lateralis); it is limited behind by a straight vertical ridge, the crista interossea or lateral border, to which the interosseous membrane, which occupies the interval between the tibia and the fibula, is attached. This ridge commences above, near the middle of the lateral and under surface of the lateral condyle, and terminates below about two inches above the lower extremity by dividing into two lines, which separate and enclose between them the surface for articulation with the lower end of the fibula, and the area of attachment of the inferior interosseous ligament, which here unites the two bones. In its upper two-thirds the lateral surface provides an extensive origin for the tibialis anterior. Inferiorly, where the tibial crest is no longer well defined, the lateral surface turns forward on to the front of the shaft, and is limited inferiorly by the anterior margin of the inferior articular surface. Over this the tendon of the tibialis anterior, and the combined fleshy and tendinous parts of the extensor hallucis proprius and extensor digitorum communis muscles pass obliquely downwards. The posterior surface (facies posterior) of the shaft lies between the interosseous ridge laterally and the medial border on the medial side. Its contours are liable THE TIBIA. 233 to considerable variation according to the degree of lateral compression of the bone. It is usually full and rounded aljove, and Mat below. Superiorly it is crossed by the popliteal or oblique line (linea poplitea) which runs downwards and medially, from the fibular facet above, to the medial border on a level with the junction of the middle with the upper third of the shaft. To this line the deep transverse fascia is attached, whilst below it, as well as from the medial border of the bone interiorly, the soleus muscle takes origin. Into the bulk of the triangular area aljove it the popliteus muscle is inserted. Arising from the middle of the popliteal line there is a vertical ridge, which passes downwards and divides the posterior aspect of the shaft into two surfaces — a lateral for the tibial origin of the tibialis posterior muscle, and a medial for the flexor digitorum longus muscle. The inferior third of this surface of the shaft is free from muscular attachments, but is overlain by the tendons of the above muscles, together with that of the flexor hallucis longus. A large nutrient canal, having a downward direction, opens on the posterior surface of the shaft a little below the popliteal line and just lateral to the vertical ridge which springs from it. The inferior extremity of the tibia displays an expanded quadrangular form. It is furnished with a saddle-shaped articular surface on its under surface (facies articularis inferior), which is concave from before backwards and slightly convex from side to side. This rests upon the superior articular surface of the body of the talus or astragalus, and is bounded in front and behind by well-defined borders. The anterior border is the rounder and thicker, and is oftentimes channelled by a groove for the attachment of the anterior ligament of the joint ; further, it is occa- sionally provided with a pressure facet caused by the locking of the bone against the neck of the talus in extreme flexion. Laterally the edge of the articular area corresponds to the base of the triangle formed by the splitting of the interosseous ridge into two parts. Where these two lines join it, both in front and behind, tlie bone is elevated into the form of tubercles, in the hollow between which (incisura fibularis) the lower end of the fibula is lodged, being held in position by powerful ligaments. The cartilage-covered surface occasionally extends for some little distance above the base of the triangle. Medially there is a down - projecting process, called the medial malleolus, the medial aspect of which is subcutaneous and forms the projection of the inner ankle. Its lateral surface is furnished with a piriform facet (facies articularis malleolaris), confluent above with the cartilage -covered area on the inferior extremity of the shaft; this articulates with a corresponding area on the medial surface of the body of the talus. Inferiorly the malleolus is pointed in front, but notched behind for the attachment of the tibial collateral (internal lateral ligament) of the ankle. Eunning obliquely along the posterior surface of the malleolus there is a broad groove (sulcus malleolaris) in which the tendons of the tibialis posterior and flexor digitorum longus muscles are lodged ; whilst a little to the fibular side of this, and running downwards over the posterior surface of the lower extremity of the bone, there is another groove, often faintly marked, for the lodgment of the tendon of the flexor hallucis longus muscle. The proportionate length of the tibia to the body height is as 1 is to •4-32-4-80. Arterial Foramina. — Nutrient canals are seen piercing the upper extremity of the bone around its circumference and above the tuberosity. The floors of the intercondylic fossae are also similarly pierced, and there is usually a canal of large size opening on the summit of the inter- condyloid eminence. Two or three foramina of fair size are seen running upwards into the sub- stance of the bone a little below and to the medial side of the tuberosity, while the principal vessel for the shaft jmsses downwards into the bone on its jjosterior surface, about the level of the junction of the upper and middle thirds. The medial surface of the medial malleolus, as well as the anterior and joosterior borders of the inferior extremity, are likewise pitted by the orifices of small vascular channels. Connexions. — Superiorly the tibia supports the condyles of the femur, and is connected in front with the patella by means of the patellar ligament. Articulating laterally with the fibula above and below, it is united to that bone throughout nearly its entire length by the inter- osseous membrane. The crest and medial surface can be readily examined, as they are sub- cutaneous, except above where the medial surface is overlain by the thin tendinous aponeurosis of the muscles passing over the inner side of the knee. The form of the lower part of the knee in front is determined by the condyles on either side crossed centrally by the ligamentum patellae. 234 OSTEOLOGY. Interiorly the medial malleolus forms the j^rojection of the imier ankle, which is wider, not so low, less pointed, and placed in advance of the projection of the outer ankle. The front and back of the lower end of the bone are crossed by tendons, which mask to a certain extent its form. Ossification. — The shaft begins to ossify early in the second month of intrauterine life. At birth it is well formed, and Fuses -with shaft about 20-24 years May apjiear Appears indeijendeutly before birth about 11 years \ Appears about Ik years Fuses about ISth year At birth. About 12 years. About 16 years. Fig. 173. — Ossification of the Tibia. upper end is the so-called "growing end of the capped above and below by pieces of cartilage, in the upper of which the centre for the superior epiphysis has already usually made its ap- pearance. From this the condyles and tuberosity are developed, though sometimes an independent centre for the latter appears about the eleventh or twelfth years, rapidly joining with the already well - developed mass of the rest of the epiphysis. Complete fusion between the super- ior epiphysis and the shaft does not take place until the twentieth or the twenty-fourth year. The centre for the lower articular surface and the medial malleolus makes its appearance about the end of the second year, and union with the shaft is usually complete by the age of eighteen. Lambertz notes the occasional presence of an accessory nucleus in the malleolus. The bone." The Fibula. The fibula is a slender bone with two enlarged ends. It lies to the lateral side of the tibia, with which it is firmly united by ligaments, and nearly equals that bone in length. The first difficulty which the student has to overcome is to determine which is the upper and which the lower extremity of the bone. This can easily he done by recognising the fact that there is a deep pit on the medial aspect of the lower extremity immediately behind the triangular articular surface. Holding the bone vertically with the lower extremity downwards and so turned that the triangular articular area lies in front of the notch already spoken of, the subcutaneous non-articular aspect of the inferior extremity will point to the side to which the bone belongs. The superior extremity or head of the fibula (capitulum fibulae), of irregular rounded form, is bevelled on its medial surface so as to adapt it to the form of the under surface of the lateral condyle of the tibia. At the border, where this surface becomes confluent with the lateral aspect of the head, there is a pointed upstanding eminence called the styloid process (apex capituli fibulae) ; to this the short fibular collateral (external lateral) ligament is attached, as well as a piece of the tendon of the biceps, which is inserted into its fore-part. Immediately to the medial side of this, and occupying the summit of the medial sloping surface, there is an articular area (fades articularis capituli), of variable size and more or less triangular shape. This serves for articulation with the lateral condyle" of the tibia. The long fibular collateral (external lateral) ligament, together with the remainder of the tendon of the biceps muscle which surrounds it, is attached to the lateral and upper side of the head in front of the styloid process. In front and behind the head there are usually prominent tubercles. The anterior of these is associated with the origin of the peronteus longus muscle ; the posterior, whilst furnishing an origin for the upper fibres of the soleus, serves to deepen the groove, behind the superior tibio-fibular articulation, in which the tendon and fleshy part of the popliteus muscle play. The constricted portion of the shaft below the head THE FIBULA. 235 is often referred to as the neck ; around the Medial coni>vli LaTKKAL CONDYLIC Oblique line. Posterior or Ex- tensor SURFACE Posterior surface Groove for tendons of PERONiKUS LONOUS AND BREVIS Lateral malleolus Groove for- flexor halluois LONOUS Fig. 174 a. — The Right Tibia and Fibula seen from Behind. Posterior or extensor surface of the fibula is coloured red ; tlie lateral or peroneal surface is left uncoloured. lateral side of this the peroneal nerve winds. Tlie shaft of the fibula (cor- pus fibulae) presents many varieties of shape and form, being ridged and channelled in such a way as greatly to increase the difficulties of the student in recognising the various surfaces described. The most important point is first to determine the position of the interosseous ridge. Holding the bone in the position which it normally occupies in the leg, it will be noticed that the lateral surface of the lower extremity Semimembranosus SOLEUS :#; Tibialis posterior Flexor hallucis lonous Perox.-eus LOSGC'S and BREVIS Fig. 174 5. — Posterior aspect of the Bones of the Leg with Attach- ments OF Muscles mapped out. is limited in front and behind by two lines, which, converging above, enclose 236 OSTEOLOaY. Styloid process Facet for tibia . Interosseous crest— - Interosseous_ CREST RocoH surface FOR INTKR- OSSKOUS" ligament Facet for talus or astragalu.s- ■< M fj g •< O 0. Lateral malleolus Fio. 175.— Right Fibula as SEEN FROM THE MEDIAL SiDE. The anterior surface is coloured blue ; the posterior surface is coloured red. between them a triangular subcutaneous area which lies immediately above the outer ankle. From the summit of the triangle so formed a well-defined ridge may be traced up the front of the shaft to reach the anterior aspect of the head. This is the anterior crest, and must not be mistaken for the interosseous crest, which is now easy to find, for the next ridge which lies just medial to the anterior crest, or towards the tibial side on the anterior aspect of the bone, is the line to which the interosseous membrane is attached. As a rule these two lines are separated by a considerable interval in the lower half of the bone, but tend to run much closer together above ; indeed it is not uncommon to find that they coalesce to form a single crest. Let it therefore be clear that the interosseous line is that which lies just medial to the ridge which springs inferiorly from the malleolar subcutaneous triangular surface, notwith- standing the differences in width of the surface which separates the lines, or their occasional coalescence above. The position of the interosseous ridge enables us at once to separate the anterior or flexor aspect of the bone from its posterior or extensor surface, using these terms in relation to the movements of the anhle} In addition, there is the lateral or peroneal surface, which corresponds to the lateral side of the shaft. Start- ing then at the interosseous crest, and passing forwards round the lateral side of the shaft, the anterior or flexor surface is the first met with ; this is bounded laterally by the anterior crest, and, as has been said, may be either of considerable width or almost linear.^ From this arises the extensor digitorum communis, together with the peronseus tertius and the extensor hallucis proprius muscles, which, though extensors of the toes, are also important flexors of the ankle. The anterior crest serves for the attachment of the intermuscular septum, which separates the foregoing group of muscles from that which lies along the lateral side of the shaft, viz. the perongeus longus and brevis muscles. The surface from which these arise is limited behind by the posterior border, which is usually sharp and well defined below, where it is continuous with the bone immediately above the pit on the medial surface of the lower extremity, whilst it tends to be less distinct and more rounded above where it runs into the base of the styloid process. In its upper third or fourth this border is often rough and tubercular where it serves for the origin of the soleus. The lateral or peroneal surface 4s somewhat twisted, being directed rather forwards above, but tending to turn backwards below where it becomes continuous with the groove which courses along the back of the lateral malleolus and which lodges the tendons of the peronseus longus and ^ The use of these terms is not, strictly speaking, correct, and they are here used in a physiological and not in a morphological sense. The anterior surface of the leg is the true extensor surface, and is comparable with the posterior surface of the forearm, the change in position having been brought about developmentally by difference in the rotation of the limbs. Flexion of the ankle, so called, is in reality an extensor movement, and corresponds to extension at the wrist. (See Humphry, Journ. Anat. and Physiol., vol. xxviii. p. 15.) ^ This is not recognised as a surface but as a crest only (crista anterior) by the B.N.A. THE FIBULA. 237 brevis muscles. The remainder of the shaft, included between the posterior border behind and the interosseous ridge in front and medially, is the posterior or extensor surface, for here arise the several muscles wJwse action in j^ja?-^ is to extend the anide. This surface is cut up by a curved ridge often the most prominent and outstanding on the bone, and hence frequently mistaken by the student for the interosseous ridge ; it serves to define the area for the origin of the tibialis posterior, and arises below from the posterior border of the inter- osseous ridge at the junction of the middle and inferior thirds of the shaft, curves a little backwards, and passing upwards and obliquely forwards again joins the interosseous ridge once more in the region of the neck. This is oftentimes called the medial border (crista medialis) ; and the surface so mapped oft", the medial surface. The ridge itself serves for the attachment of the aponeurosis which covers the tibialis posterior muscle. The remainder of the posterior aspect of the shaft, which, above, is directed backwards, is so twisted that inferiorly it is directed medially. Prom this, in its upper part, the soleus muscle arises ; whilst lower down, the flexor hallucis longus muscle derives an extensive origin. Both of these muscles, together loith the tibialis posterior, act as extensors of the anide. On this aspect of the bone, at or near the middle of the shaft, and just behind the prominent tibial ridge, is the opening of the nutrient canal, which has a downward direction. The inferior extremity of the fibula, or lateral raalleolus, is of pyramidal form. Its medial surface is furnished with a triangular articular area (facies articularis malleoli), plane from before backwards, and slightly convex from above downwards, which articulates with a corresponding surface on the lateral side of the body of the talus or astragalus. Behind this there is a deep pit, to which the posterior fasciculus of the external lateral (posterior talo-fibular lig.) ligament is attached. Above the articular facet there is a rough triangular area on the posterior surface of the shaft, from tlie summit of which the interosseous ridge arises ; to this are attached the strong fibres of the inferior interosseous ligament which binds together the opposed surfaces of the tibia and fibula. The lateral surface of the inferior extremity forms the elevation of the lateral malleolus which determines the shape of the projection of the outer ankle. Bounded from side to side and from above downwards, it terminates below in a pointed process, which reaches a lower level than the corresponding process of the tibia, from which it also difters in being narrower and more pointed and being placed in a plane nearer the heel. Superiorly, this surface, which is subcutaneous, is continuous with the triangular subcutaneous area so clearly defined by the convergence above of the lines which unite to form the anterior border. The anterior border and tip of the lateral malleolus furnish attachments to the anterior and middle bands of the external lateral ligament of the ankle (anterior talo-fibular and calcaneo-fibular ligs.). The posterior surface of the lateral malleolus, broad above, where it is confluent with the lateral or peroneal surface, is reduced in width below by the presence of the pit which lies to its inner side. This aspect of the bone is grooved (sulcus malleolaris) by the tendons of the peronseus longus and brevis muscles, which curve round the posterior and lower-pointed aspect of the malleolus. The proportionate length of the fibula to the body height is as 1 is to 4-37-4-82. ^ Arterial Foramina. — Numerous minute vascular canals are seen piercing tlie lateral surface of the head, and one or two of larger size are seen on the medial surface immediately in front of the superior articular facet. The canal for the nutrient artery of the sliaft, which has a downward direction, is situated on the back of the bone about its middle. The lateral surface of the lateral malleolus displays the openings of many small canals, and one or two larger openings are to be noted at the bottom of the pit behind the inferior articular surface. Connexions. — The head and lateral malleolus, and jaart of the shaft immediately above the latter, are subcutaneous. The remainder of the shaft is covered on all sides by the muscles which surround it. Superiorly the bone plays no jiart in the formation of the knee-joint, but inferiorly it assists materially in strengthening the ankle-joint by its union with the tibia and its articulation with the talus. In position the bone is not jjarallel to the axis of the tibia, but oblique to it, its upper extremity lying posterior and lateral to a vertical line passing through the lateral malleolus. Ossification. — -The shaft begins to ossify about the middle of the second month of foetal life. At the end of the third month there is but little difference in size between it 238 OSTEOLOGY. and the tibia, and at birth the fibula is much larger in propoi'tion to the size of the tibia than in the adult. Its extremities are cartilaginous, the lower extremity not being as long as the medial malleolar cartilage of the ^^3.Tyea,^°"* ^^^'^h^ut 20--2Vy'ea?s tibia. It is in this, however, that an ossific centre '^"" " ' first appears about the end of the second year, which increases rapidly in size, and unites with the shaft about nineteen years. The centre for the superior epiphysis begins to ossify about the third or fourth year, and union with the shaft is not complete until a period somewhat later than that for the inferior epiphysis. The mode of ossification of the lower ex- tremity is an exception to the general rule that epi- physes which are the first to ossify are the last to unite with the shaft. This may possibly be accovmted for by the fact that the lower end is functionally more important than the rudimentary upper end, since in man alone, of all vertebrates, does the lateral malleolus reach beyond the level of the medial malleolus. Its early union with the shaft is doubtless required to ensure the stability of the ankle joint necessitated by the assumption of the erect position. Appears about 2ud year In its earlier stages of development it has been stated, on the authority of Leboucq, Gegenbaur, and others, that the fibula as well as the tibia is in contact with the femur. This is,' however, denied by Grimbaiim ("Proc. Anat. See," Journ. Anat. and Physiol, vol. xxvi. p. 22), who states that after the sixth week the fibula is not in contact with the femur, and that prior to that date it is impossible to differentiate the tissue which is to form femur from that wliich forms fibula. At birth. Fig. 176.- Fuses with shaft about 19 years About About 12 years. 16 years. -Ossification of Fibula. BONES OF THE FOOT. The bones of the foot, twenty -six in number, are arranged in three groups : the tarsal, seven in number ; the metatarsal, five in number ; the phalanges, fourteen in number. Comparing the foot with the hand, the student will be struck with the great proportionate size of the tarsus as compared with the carpus, and the reduction in size of the bones of the toes as compared with the fingers. The size of the metatarsal segment more nearly equals that of the metacarpus. The Tarsus. The tarsus (ossa tarsi) consists of seven bones — the talus or astragalus, cal- caneus, navicular or scaphoid, three cuneiforms, and the cuboid. Of irregular form and varying size, they may be described as roughly cubical, presenting for examina- tion dorsal and plantar surfaces, as well as anterior or distal, posterior or proximal, medial, and lateral aspects. The Astragalus. The talus or astragalus is the bone through which the body weight is trans- mitted from the leg above to the foot below. Superiorly the tibia rests upon it, whilst on either side it articulates with the medial and lateral malleolar processes of the tibia and fibula respectively ; interiorly it overlies the calcaneus, and anteriorly it articulates with the navicular. For descriptive purposes the bone is divisible into two parts — the body (corpus tali) blended in front with the neck (collum tali), which supports the head (caput tali). The upper surface of the body is provided with a saddle-shaped articular surface (trochlea tali), broader in front than behind, for articulation with the. under surface of the tibia. The medial edge of the trochlea is straight ; whilst the lateral border, which is sharp in front and more rounded behind, is curved medially pos- teriorly where it is bevelled to form a narrow, elongated, triangular facet, which is in contact with the transverse or inferior tibio-fibular ligament during flexion of THE ASTEAGALUS. 239 the ankle (Fawcett, Ed. Med. Journ., 1895). Over the lateral border the cartilage- covered surface is continvious laterally with an extensive area of the form of a quadrant. This is concave from above downwards, and articulates with the medial surface of the lateral malleolus. The inferior angle of this area is prominent and Surface of talus for articulation with flbula Surface of talus for articulation with tibia V. Metatarsal I. Metatarsal Sesamoid bone First PHALANX Third or terminal phalanx Fig. 177. — Bones of the Right Foot as seen from Above. somewhat everted, and sometimes referred to as the lateral process (processus lateralis tali). The medial aspect of the body has a comma-shaped facet, conflu- ent with the superior articular surface, over the medial edge of the trochlea ; this articulates with the lateral surface of the medial malleolus. Inferior to this facet the bone is rough and pitted by numerous small openings, and just below the tail 240 OSTEOLOGY. of the comma there is a circular impression for the attachment of the deep fibres of the internal lateral (deltoid) ligament (talo-tibial fibres). On the inferior surface of the body there is a deep concave facet, called the posterior calcanean facet (facies calcanea articularis posterior), which is of more or less oval or oblong form and Calcaneus SUSTEXTACULL'M TALI Surface of tains m blue rests on the plant i calcaneo-navicu i ligamei ]~ First cuneiform I. Metatarsal Sesamoid bote First phalanx " / Cuboid Second cuneiform Third cuneiform V. Metatarsal Third or terminal phalanx Fig. 178 «. — Bones of the Right Foot seen from Below. is placed obliquely from behind forwards and laterally; this rests upon a corre- sponding surface on the upper aspect of the calcaneus. In front of this, and crossing the bone from within outwards and forwards, is a deep furrow (sulcus tali), the floor of which is pierced by numerous large canals. It serves for the attach- ment of the strong interosseous ligament which unites the talus with the calcaneus, THE ASTEAGALUS. 241 and separates the facet already described from a smaller oval articular area having a slightly convex surface, which lies immediately in front of it. This is called the middle calcanean facet (fades articularis calcanea media), and articulates with the upper surface of the sustentaculum tali of the calcaneus. Posteriorly the body is provided with two tubercles, separated by a groove ; the lateral of these (processus posterior tali) is usually the larger, and is occasionally a separate ossicle (os trigonum). To it is attached the posterior fasciculus of the external lateral ligament (posterior talo-fibular lig.) of the ankle-joint. The groove, which winds Abductor digiti quiuti (origin) Quadratus plants (accessorius) (origin) |L!"ll Long and sliort plantar / ligaments |^ Tibialis posterior (part of insertion")' Perona>us brevis (insertion) Flexor digiti quinti brevis (origin) Adductor liallucis obliqiuis (origin)' Flexor digitorum brevis (origin) Abductor hallucis (origin) Attachments of plantar calcaneo- navicular ligament Flexor hallucis brevis (origin) Tibialis posterior (part of insertion) Peronteus longus (insertion) Tibialis anterior insertion) Fig. 178 i. — Muscle-Attachmexts to Left Tarsus axd Metatarsus (Plantar Aspect). obhquely from above downwards and medially over the posterior surface of the bone, lodges the tendon of the flexor hallucis longus muscle. The head (caput tali), of oval form, is directed forwards and medially. Its anterior surface is convex from side to side and from above downwards, and articu- lates with the navicular bone (facies articularis navicularis). Inferiorly this surface is confluent with the middle calcanean facet, but in well-marked specimens, or when the bones are articulated, it will be seen that a small area in front of, and lateral to, the middle calcanean facet rests upon an articular surface on the upper part of the fore portion of the calcaneus, and is called the anterior calcanean facet (facies articularis calcanea anterior). To the medial and under surface of the head there is a cartilage-covered surface which does not articulate with any bone, but rests on the upper surface of the plantar calcaneo-navicular ligament, and is supported on 242 OSTEOLOGY. the medial side by the tendon of the tibialis posterior muscle (Fawcett, Ed. Med. Journ., 1895, p. 987). Fig. 179 «. — The Right Talus. A. Upper Surface. B. Under Surface. 1. Groove fob flex, hallucis. long. 2. Median tubercle. 3. Trochlear surface for tibia. 4. Body. 5. For articulation with medial malleolus. 6. Head. 7. For articulation with navicular. 8. Xeck. 9. For articulation with lateral malleolus. 10. Surface against which the posterior talo-fibular liga- ment rests. 11. Lateral tubercle. 12. Lateral tubercle. 13. Posterior, middle, and anterior facets for calcaneus. 14. For ARTICULATION WITH NAVI- CULAR. 15. Surface resting on plantar calcaneo- navicular liga- MENT. 16. Interosseous groove. 17. Medial tubercle. IS. Groove for flexor hallucis LONOUS. The neck (coUum tali), best seen above, passes from the front of the body and inclines towards the medial side. It is confluent with the medial surface in C. Seen from the Lateral Side Seen from the Medial Side. Lateral tubercle. Groove for flexor hallucis i.ongus. Medial tubercle. Surface aoain.st which the posterior talo-fibular i.kia- ment rests. Trochlea for tibia. For articulation with lateral malleolus. Neck. 8. Head. For articulation with navicular. 10. Interosseous groove. 11. Anterior middle, and posterior facets for cal- caneus. 12. Body. 13. Surface resting on plantar CALCANEO - navicular LIGA- MENT. 14. For ARTICULATION WITH NAVI- CULAR. 15. Head. 16. Neck. 17. Trochlea for tibia. For articulation with medial malleolus. Body. Impression for deltoid liga- ment. Lateral tubercle. Groove for flexor hallucis long us. IjATERAL TUBERCLE. Interosseous groove. Posterior and middle facets FOR calcaneus. front of the medial malleolar facet, and laterally forms a wide groove, which becomes continuous inferiorly with the outer end of the interosseous groove. THE CALCANEUS. 243 The Calcaneus. The calcaneus is the largest of the tarsal bones. It supports the talus above and articulates with the cuboid in front. Inferiorly and behind, its posterior ex- tremity, or tuberosity (tuber calcanei), forms the heel on which so large a proportion of the body weight rests. The long axis of the bone inclines forwards and a little laterally. The upper surface of the calcaneus is divisible into two parts — a posterior non- articular part and an anterior articular portion. The length of the former varies according to the projection of the heel ; rounded from side to side, it is slightly con- cave from before backwards. In front of this there is a convex articular area of variable shape (fades articularis posterior), sometimes nearly circular, at other times oval and occasionally almost triangular. This is directed upwards and forwards, and articulates with the posterior calcanean facet on the under surface of the talus. Anterior to this facet the bone is deeply excavated, forming a fossa from Surface for attachment /■of short plantar ligament SUSTENTA- CDLtJM TALI Groove fok FLEXOR HALLUCIS LONQUS Surface for attachment of long plantar liga- ment Medial PROCESS TUBEROSITY A Fig. IS A. Seen from Above. -The Right Calcaneus. B B. Seen from Below. which a groove (sulcus calcanei) leads backwards and medially around the antero- medial border of the articular surface. When the calcaneus is placed in contact with the talus, this groove coincides with the sulcus on the under surface of the latter bone, and so forms a canal or tunnel (sinus tarsi) in which the strong interosseous ligament which vmites the two bones is lodged. To the front and medial side of this groove there is an elongated articular facet directed obliquely from behind forwards and laterally, and concave in the direction of its long axis. This is frequently divided into two smaller oval areas by an intermediate non- articular surface. Of these facets the hinder (fades articularis media) articulates with the middle calcanean facet on the under surface of the talus, whilst the anterior (facies articularis anterior) supports the under surface of the head of the talus (facies articularis calcanei anterior). The lateral side of the upper surface of the anterior extremity of the bone is rough, and to this is attached the origin of the short extensor muscle of the toes. The inferior surface of the bone is slightly concave from before backwards, and convex from side to side. The under aspect of the tuberosity is provided with two tubercles, a medial (processus medialis tuberis calcanei) and a lateral (processus lateralis tuberis calcanei), of which the former is the larger. From this the short flexor of the toes and the abductor hallucis muscle arise, whilst from both tubercles 244 OSTEOLOGY. Facets foe talus or astkagalus Sulcus calcanei PERU^EAL SPINE Lateral process c C. Seen from the Lateral Side. Facets for talus or astraoalur spring the fibres of origin of the abductor digiti quinti muscle. On the fore-part of the under surface there is an elevated elongated tubercle, which terminates some- what abruptly just behind the anterior border of this aspect of the bone, giving rise at times to a notch. From the former spring the fibres of the long plantar ligament, \Yhilst the latter serves for the attachment of the deeper fibres of the short plantar ligament. The two heads of origin of the quadratus plantse muscle arise from the bone on either side of the long plantar ligament. The medial surface of the calcaneus is crossed obliquely, from above downwards and forwards, by a broad groove of considerable depth ; along this pass many of the structures which enter the sole of the foot from the back of the leg. The groove is overhung in front and above by a pro- jecting bracket -like process, called the sustentaculum tali. The under surface of the sus- tentaculum is channelled by a groove, in which is lodged the tendon of the flexor hallucis longus muscle; whilst its medial border, to which is attached a part of the internal lateral (deltoid) ligament (tibio-cal- canean fibres) of the ankle, is overlain by the tendon of the flexor digitorum longus. To the anterior border of the sustentaculum is attached the plantar calcaneo-navicular liga- ment, and placed on its upper surface is the articular facet already alluded to (fades articu- laris media). Posteriorly the medial surface of the bone is limited inferiorly by the pro- jection of the medial tubercle, and above by the medial lipped edge of the tuberosity. The lateral surface, broad behind and narrower in front, is of flattened form. Springing from it, just below the outer end of the sinus tarsi, is the peroneal spine (processus troch- learis), often indistinctly marked. To this the fibres of the lateral annular ligament are attached ; whilst in grooves, above and below it, pass the tendons of the perontcus brevis and longus muscles respectively. To the upper and back part of this surface are attached the tiljres of the middle fasciculus of the external lateral ligament of the ankle. The anterior extremity, sometimes called the greater process, is furnished with a saddle-shaped surface on its anterior aspect for articulation with the cuboid. This facet is concave from above downwards, and slightly convex from side to side ; its edges are sharply defined, except medially, and serve for the attachment of ligaments. The posterior extremity, called the tuberosity (tulier calcanei), forms the projection of the heel. Of oval form and rounded surface, it rests upon the two tubercles inferiorly and is divisible into three areas. Of these the highest is smooth and crescentic, and is covered by a bursa ; the intermediate is also fairly smooth, SrSTENTACbLUM tali Groo\ e for flex. hallucis LONGUS Lateral process D D. Seen from the Medial Side. Fig. ISOh. — The RuiHT Calcaneus. AIedi \l PROcrss THE CUNEIFOEM BONES. 245 and is defined inferiorly by an irregular line, sometimes a definite ridge, the edges of which are striated. Into this surface the tendo calcaneus is inserted. The lowest surface is rough and striated, and is confluent below with the medial and lateral tubercles ; this is overlain by the dense layer of tissue which forms the pad of the heel. Second cuneiform Third cuneiform The Navicular Bone. The navicular or scaphoid bone, of compressed piriform shape, is placed on the medial side of the foot, between the head of the talus posteriorly and the three cuneiform bones anteriorly. The bone derives its name from the oval or boat-shaped hollow on its proximal surface, which rests upon the head of the talus. Its distal aspect is furnished with a semilunar articular area, which is sub- divided by two faint ridges into three wedge-shaped facets for articulation, from within outwards, with the first, second, and third cuneiform bones. The dorsal surface of the bone, convex from side to side, is rough for the attachment of the liga- ments on the dorsal aspect of the foot. On its plantar aspect the bone is irregularly con- cave ; projecting down- wards and backwards from its lateral side there is often a pro- minent spur of bone, the inferior navicular tubercle or plantar point (processus plantaris), to which is attached the plantar calcaneo - navicular ligament. The lateral surface is narrow from before backwards, and rounded from above downwards. In 70 per cent of cases (Manners Smith) it is provided with a facet which rests upon a corresponding area on the cuboid. Behind this in rare instances there is a facet for the calcaneus. The tibial surface of the bone projects beyond the general line of the medial border of the foot, so as to form a thick rounded tuberosity (tuberositas oss. navicularis), the position of which can be easily determined in the living. To the medial and under surface of this process an extensive portion of the tendon of the tibialis posterior muscle is inserted. Tuberosity For head of talus q A B Fig. 181. — The Right Navicular Bone. A. Seen from Behind. B. Seen from the Front. The Cuneiform Bones. The cuneiform bones, three in number, are placed between the navicular posteriorly and the bases of the first, second, and third metatarsal bones anteriorly, for which reason they are now named the first, second, and third cuneiforms, or, from their position, internal, middle, and external. More or less wedge- shaped, as their name implies, the first or internal is the largest, whilst the second or middle is the smallest of the group. Combined, they form a compact mass, the proximal surface of which, fairly regular in outline, rests on the anterior surface of the navicular ; whilst in front they form a base of support for the three inner metatarsals, the outline of which is irregular, owinir to the base of the second metatarsal bone being recessed between the first and thiid cuneiforms as it articulates with the distal extremity of the shorter second cuneiform. The first or internal cuneiform bone, the largest of the three, Lies on the medial border of the foot between the base of the metatarsal bone of the great toe in front, and the fore and medial part of the navicular behind. In form the bone is less characteristically wedge-shaped than those of its fellows of the same name, and differs from them in this respect, that whilst the second and third 16 2^:6 OSTEOLOGY. II. Metatarsal I. MeI \.T iRSAL III. Mfc-r\T4.RS\L cuneiforms are so disposed that the bases of their wedges are directed upwards towards the dorsum of the foot, the first cuneiform is so placed that its base is directed towards the plantar aspect ; further, the vertical diameter of the bone is not the same throughout, but is much increased at its anterior or distal end. The dorsal and medial surfaces are confluent, and form a convexity from above downwards, which is most pronounced inferiorly, where it is turned to become continuous with the plantar or inferior aspect, which is rough and irregular round the plantar side of the foot. On the fore-part of the medial aspect of the bone there is usually a distinct oval impression, which indicates the surface of insertion of a portion of the tendon of the tibialis anterior muscle. Elsewhere this surface is rough for ligamentous attachments. The lateral surface of the bone, quadrilateral in shape, is directed towards the second cunei- form; but as it exceeds it in length, it also comes in contact with the medial side of the base of the second metatarsal bone. Eunning along the posterior and upper edges of this area is an r-shaped articular surface, the fore and upper part of which is for the base of the second metatarsal bone, the remainder articulating with the medial side of the second cuneiform. The non-articular part of this aspect of the bone is rough for the attachment of the strong inter- osseous ligaments which biud it to impression , -l n • FOR TENDON the second cunei Fig. 182. — Anterior View of the three Cuneiform Bones of the Right Foot. II. Metatarsal Second cuneiform OF TIBIALIS' ANTERIOR Fig. 183.— The Right First Cuneiform (Medial Side). Fig. 184. — The Eight First Cuneiform (Lateral Side). II. First Metatarsal cuneiform form and second metatarsal bones respectively. The proximal end of the bone is provided with a piriform facet which fits on the medial articular area of the navicular. Here the wedge-shaped form of the bone is best displayed. Distally the vertical diameter of the bone is much increased, and the facet for the base of the metatarsal bone ol the great Third CUNEIFORM ^^^ -^ consequently much larger than that for the navicular. This metatarsal facet is usually of semilunar form, but not y_ \ m¥'^7mssm;'] infrequently is more reniform in shape, and may iu some cases display complete separation into two oval portions. The second or middle cuneiform is of a typical wedge shape, the base of II. Metatarsal ^^^ wcdgc being directed towards the Fig. 185 6.— The Right dorsum of the foot ; shorter than the Second Cuneiform f^^Y^Qy,^^ ^^ Hq^ between them, articulating (Lateral Side). ^.^^ ^^^ ^^^^ ^^ ^j^^ second metatarsal in front, and the middle facet on the anterior surface of the navicular behind. Its dorsal surface which corresponds to the base of the wedge, conforms to the roundness of the instep, and is slightly convex from side to side, affording attach- ments f.jr the dorsal ligaments. Its plantar aspect is narrow and rough, forming the edge of the wedge; with this the plantar ligaments are connected. The medial surface, quadrilateral in outline, is furnished with an T-shaped articular area along its Fig. 18.5 «.— The Right Sec(jnu Cuneiform (Medial Side). THE CUBOID BONE. 247 Second cuneiform Cdboid IV. Metatarsal posterior and superior borders in correspondence with the similar area on the lateral side of the first cuneiform. The rest of this aspect is rough for ligaments. The lateral side displays a facet arranged along its posterior border, and usually somewhat constricted in the middle; tliis is fur the third cuneiform. In front of this the bone is rough for the interosseous ligaments, which bind the two bones together. The proximal end is provided with a triangular facet slightly concave from above downwards ; this rests on the central articular surface on the anterior aspect of the navicular. In front the bone articulates by means of a wedge- shaped facet with the base of the metatarsal bone of the second toe. The third or external cuneiform, intermediate in size between the first and second, is also of a fairly typical wedge shape ; though its antero-posterior axis is not straight but bent, so that the distal end of the bone turns slightly medially. Its dorsal surface, which corresponds to the base of the wedge, is slightly convex from side to side, and provides attachments for the dorsal ligaments. Its inferior or plantar aspect forms a rough blunt edge, and serves for the attachment of the plantar ligaments. Its medial side, of quadrilateral form, displays two narrow articular strips, placed along its distal and proximal borders respectively, each somewhat constricted in the middle. The distal articulates with the lateral side of the base of the second metatarsal bone, the proximal with the lateral side of the second cuneiform. The rough non-articular surface, which separates the two elongated facets, serves for the attachment of ligaments. The lateral aspect of the bone is characterised by a large circular or oval facet, placed near its proximal border, for articulation with the cuboid ; in front of this the distal border is lipped above by a small semi-oval facet for articulation with the medial side of the base of the fourth metatarsal. The rest of the bone around and between these facets is rough for ligaments. Proximally the bone is furnished with a blunt, wedge-shaped facet for articulation with the corresponding area on the front of the navicular. Below this the surface is narrow and rough for the attach- ment of ligaments. The distal end of the bone articulates with the base of the third metatarsal by a surface of triangular shape. Fig. 186 a. — Right Third Cuneiform (Medial Side). Fig. 186 6.— Right Third Cuneiform (Lateral Side). The Cuboid Bone. The cuboid lies on the lateral side of the foot, about its middle, articulating with the calcaneus behind and the fourth and fifth metatarsal bones in front. Its dorsal surface, plane in an antero-posterior direction, is slightly rounded from side to side, and provides attachment for ligaments. Its plantar aspect is tra- versed obliquely from without medially and forwards by a thick and prominent ridge, the lateral extremity of which, at the point where it is confluent with the outer surface, forms a prominent tubercle (tuberositas oss. cuboidei), the anterior and lateral surface of which is smooth and facetted to allow of the play of a sesamoid bone which is frequently developed in the tendon of the peronaeus longus muscle. In front of this ridge there is a groove (sulcus peronsei) in which the tendon of the peronseus longus muscle is lodged as it passes across the under surface of the bone. Behind the ridge the bone is rough, and serves for the attachment of the short plantar ligament, the superficial fibres of which pass forwards and are attached to the summit of the ridge. The lateral aspect of the bone is short and rounded, and is formed by the confluence of the superior and in- ferior surfaces ; it is more or less notched by the peroneal groove which turns round its lower edge. The medial surface of the bone is the most extensive ; it is easily 248 OSTEOLOGY. recognisable on account ot the presence of a rounded or oval facet situated near its middle and close to its upper border. This is for articulation with the lateral side of the third cuneiform ; in front and behind this the surface is rough for ligaments. Not infrequently behind the facet for the third cuneiform there is a small articular Tuberosity Groove for peron/eus LONG OS A Fig. 187. — Thk Right Cuboid Bone. Lateral Side. B. Medial Side Navicular Third Cuneiform (occasional) surface for the navicular, as is the case normally in the gorilla, whilst behind and below, the projecting in- ferior angle is sometimes pro- vided with a facet on which the head of the talus rests (Sutton, " Proc. Anat. Soc," Jour. The distal surface is oval or conical in outline ; ..' Groove for Tuberosity per0n.eu8 longus Anat. and Physiol., vol. xxvi. p. 18) sloping obliquely from within laterally and backwards, it is divided about its middle by a slight vertical ridge into two parts, the medial of which articulates with the base of the fourth metatarsal bone, the lateral with that of the fifth. The proximal surface, also articular, has a semilunar outline, the convex margin of which corresponds to the dorsal roundness of the bone. The inferior lateral angle corre- sponds to the tubercle on the lateral border of the bone, whilst the inferior medial angle forms a pointed projection which is sometimes called the calcanean process. This surface articulates with the calcaneus by means of a saddle-shaped facet, which is convex from side to side, and concave from above downwards. The tarsus as a whole may be conveniently described as arranged in two ^^^^. Fig. 188. — Radiographs of the Fcetal Foot. 1. Aljout fifth luoutli. No ossification in the tarsus visible. 2. About sixth month. Appearance of a nucleus for the calcaneus. 3. About seventh month. Nucleus for calcaneus well developed. 4 and 5. About eighth month. Centres for talus and calcaneus now seen. 6. About birth. Centres for the talus and calcaneus are well developed, there is also a considerable centre for the cuboid, and the appearance of a centre for the third cuneiform is now displayed. columns ; the medial, corresponding to the medial border of the foot, comprising the talus, navicular, and tliree cuneiforms, and forming a base for the support of the three medial metatarsal bones and their phalanges. The lateral column, formed by the calcaneus and cuboid, supports the fourth and fifth metatarsal bones together with their phalanges. The superior surface of the anterior portion of the THE METATARSUS. 249 tarsus determines the side-to-side roundness of the instep, whilst its under surface forms arches in both a transverse and longitudinal direction, in which the softer tissues of the sole are lodged, and so protected from injury. Ossification. — Unlike the carpus, the tarsus is at birth partially ossified. At this period there is a well-marked osseous nucleus within the body and neck of the talus, and the calcaneus is extensively ossified. In the latter the deposition of earthy matter appears as early as the sixth mouth of foetal life, whilst in the talus the ossific centre makes its appearance in the later weeks of gestation. Shortly before or after birth the Fig. 189 «. — Radiograph of the Hand AT Birth. Fig. 189 6. — Radiograph of the Foot AT Birth. It will be noticed that whilst the primary centres for the metacarpus and phalanges are well ossified, the carpixs is still entirely cartilaginous. The centres of ossification for the calcaneus and talus are well developed, the nucleus for the cuboid is quite distinct, and in this instance the third cuneiform is already commencing to ossify. cuboid begins to ossify, succeeded early in the first year by the third cuneiform, followed in order by the second cuneiform, first cuneiform, and navicular. The ossific centre of the latter appears at the third year or somewhat later. An epiphysis, which forms a cap over the extremity of the tuberosit}^ of the calcaneus, appears from the seventh to the ninth year, and fusion is completed between the ages of sixteen and twenty. To emphasize the different conditions which obtain in the wrist and ankle, at, and for some time after birth, drawings of I'adiographs of both are given. The Metatarsus. The metatarsal bones, five in number, in their general configuration resemble the metacarpus. They are, however, slightly longer, their bases are proportionately larger, their shafts more slender and laterally compressed, and their heads propor- tionately smaller. They are named numerically the first, second, third, fourth, and fifth metatarsal bones, in order from the tibial to the fibular side. The first can be readily recognised on account of its stoutness ; it is also the shortest of the series. The second is the longest of the five, and the fifth can easily be dis- tinguished by the projecting tubercle at its base. 250 OSTEOLOGY. Grooves for sesamoid bones Shaft The first metatarsal or metatarsal bone of the great toe, the shortest of the series, is reuiarkable for its stoutness. Its proximal end or base, where the bone is provided with a reniform facet for articula- tion with the first cuneiform, is wider from the dorsal to the plantar aspect than from side to side. The concavity of the kidney -shaped arti- cular area is directed to the fibular side. As a rule the lateral aspects of the base are non-arti- cular, though occasionally on its outer side there is a "pressure" facet for the base of the second metatarsal bone. The inferior basal angle pro- jects backwards and laterally, and forms a pro- minent tubercle which is pitted for the insertion of the tendon of the peronteus longus muscle, whilst its tibial margin is lipped by a surface for the attachment of part of the tendon of the tibialis anterior. The shaft, short, thick, and pris- matic on section, tapers rapidly towards the head, the fore and under surfaces of which are articular. The former is convex from side to side, and from above downwards, and supports the proximal phalanx. It is confluent below with the inferior articular surface, which is divided by a median ridge into two shallow grooves, of which the tibial is the wider. In these grooves are lodged the two sesamoid bones which underlie the metatarso- phalangeal joint. On either side of the head, the bone is pitted for the strong lateral ligaments of the joint. The second metatarsal, the longest of the series, has a base of wedge-shaped Base TuBEROSiTV Tibialis anterior Fig. 190. — The First Metatarsal Bone of the Right Foot (Plantar Aspect). Shaft I. Metatarsal' (pressure facet) II. Metatarsal^ 11. METATARSAL First cuneiform Til. Metatarsal III. METATARSAL IV. Metatarsal IV. METATARSAL Third cuneiform 33R in. Metatarsal A. Medial sides V. Metatarsal B. Lateral sides Fig. 191. — View of the Bases and Shafts of the Second, Third, and Fourth Metatarsal Bones OP the Right Foot. form, the proximal aspect of which articulates with the second cuneiform. On its tibial aspect, near its superior edge, there is a small circular facet for the first THE PHALANGES. 251 Its proximal aspect cuneiform; below and in front of this there is sometimes a tubercle with a " pressure " facet on it, where the bone comes in contact with the base of the first metatarsal. On the fibular side of the base there is one, more usually two small facets, each divided into two parts, a proximal for articulation with the third cuneiform, and a distal for the base of the third metatarsal." The shafts of this and the three succeeding bones are slender and laterally compressed. The heads are small and narrow, and display a pronounced side-to-side and vertical convexity. The third metatarsal bone also possesses a base of wedge-shaped form, the proximal surface of which articulates with the third cuneiform. On its tibial side it is provided with one, more usually two, small facets, for articu- lation with the base of the second metatarsal. Laterally the base has a larger facet for articulation with the base of the fourth metatarsal, more or less conical in outline, and having its lower edge sharply defined by a narrow groove which underlies it. The fourth metatarsal has a base more cubical in shape, articulates with the cuboid, whilst medially an elongated oval facet, divided by a slight vertical ridge, provides sur- faces for articulation with the third metatarsal in front and the lateral side of the first cuneiform behind. On the lateral side there is a demi-oval facet, bearing a slightly saddle- shaped surface, for articulation with the tibial side of the base of the fifth metatarsal. The fifth metatarsal can be readily recognised by the peculiar shape of its base, from the lateral side of which there projects backwards and laterally a pro- minent tubercle (tuberositas oss. metacarpi quinti). To the hinder extremity of this is attached the tendon of the peroneeus brevis muscle. To its dorsal surface the tendon of the peronseus tertius is inserted, whilst its plantar surface provides an origin for the flexor digiti quinti brevis muscle. The tibial surface of the base is provided with a demi-oval, slightly concave facet, for the lateral side of the base of the fourth metatarsal, whilst proximally it articulates with the cuboid by means of a semicircular facet. Vascular Foramina. — The canals for the nutrient vessels open, as a rule, on the plantar aspects of the middle of the shafts. Those of the outer metatarsals are directed towards the bases of the bones, whilst that for the metatarsal of the great toe passes towards its head. Ossification. — In correspondence with the mode of ossification which obtains in the metacarpus, the primary centres for the metatarsus appear as early as the third month of foetal life. In the case of the second, third, fourth, and fifth, these centres furnish the bases and shafts of the bones, the heads being developed from secondary centres which appear from two to four years after birth, fusion with the shaft being usually completed about the eighteenth year. In striking contrast to this is the mode of ossification of the first metatarsal. From its primary centre the head and shaft is developed ; the secondary centre appears at its base about the second or third year, and fuses with the shaft about eighteen. In this respect, therefore, the metatarsal bone of the great toe resembles in its mode of development the phalanges. Mayet, however {Bull. Soc. Anat. Paris, 1895), describes the occurrence of two ossific centres in the proximal epiphysis. These fuse early, and he considers that the one represents the metatarsal element, whilst the other may be regarded as phalangeal in its origin. ClBoIi Peronaus brevis Fig. 192. — Fifth Right Metatarsal Bone (Dorsal Aspect). The Phalanges. The phalanges of the toes (phalanges digitorum pedis) differ from those of the fingers in the striking reduction of their size, and in the case of the bones of the first row, in the lateral compression of their shafts. Each toe is provided normally with three phalanges, except the great toe, which has only two. In 252 OSTEOLOGY III. Ungual' OR terminal' PHALANX 11. Phalanx their general configuration and in the arrangement of their articular facets they resemble the digital phalanges, though owing to the reduction in their size, the shafts, particularly those of the second row, are often so compressed longitudin- ally as to reduce the bone to a mere nodule. The proximal end of each of the bones of the first row is pro- portionately large, and is provided with a simple hollow in which the head of the metatarsal bone rests ; the distal ends are furnished with condyloid surfaces. The proximal extremities of the second row are each provided with two small concavities, separated by a slight ridge for articulation with the condyles of the first row. The joint between the second and third row displays the same arrangement — the third, terminal or ungual phalanx, being easily distinguished by the spatula-shaped surface at its extremity on which the bed of the nail is supported. The phalanges of the great toe, two in number, differ from the others in their size and length. Into the base of the first phalanx are inserted the short muscles of the great toe, whilst the second phalanx receives on its plantar aspect the insertion of the flexor hallucis longus muscle, the tendon of the extensor hallucis longus being inserted into the dorsal aspect. Ossification. — Each phalanx is developed from two centres — one primary for the shaft and distal extremity, the other for the epiphysis on the proximal end. The primary centres for the ungual phalanges are the first to appear, commencing to ossify from the eleventh to the twelfth week of fcetal life. The centre for the ungual phalanx of the great toe makes its appearance before that of its corresponding metatarsal bone. The primary centres for the phalanges of the first row appear from the fourteenth to the sixteenth week. The primary centres for the middle phalanges of the second and I. Phalanx Metatarsal Fig. 193.— The Phalanges OF THE Toes (Dorsal Aspect). I -m: Fig. 194. A. Aliout the end of the third month. The primary centres of all the metacarpus are shown as well as the centres for the phalanges of the great toe and the terminal phalanx of the third toe. B.^ A little later. Tlie centres for the terminal phalanges of the four inner toes are seen, as well as the centres for the first phalanges of the great and second toe. C. About the fourth mouth. The centres for all the terminal phalanges as well as those of the first row are well ossified. D. About the fifth month. In this the centre for the second phalanx of the second toe has already made its appearance. 1 ITiis specimen displays the occurrence of anomalou.s centres within llie tarsus the .significance of which is not apparent. The appearance is not due to any delect in tlie plate, but recurred in repeated radiographs. third toes begin to ossify about the sixth month, those for the fourth and fifth toes not till later — the shaft of the middle phalanx of the fourth toe being frequently cartilaginous at birth, the normal condition in the case of the fifth toe (Lambertz). The proximal epiphyses do not begin to ossify until about the fourth year, and are usually fused with the diaphyses about the age of sixteen or eighteen. Union between the shafts and epiphyses of the first row precedes that of the second and third rows. SESAMOID BONES. 253 Sesamoid Bones. As in the hand, small independent nodules of bone, called sesamoid bones, are met with in the ligaments and tendons of the foot. The most constant of these are found in connexion with the metatarso-phalangeal articulation of the great toe, where they lie in grooves on the under surface of the head of the metatarsal bone in connexion with the tendons of the short muscles of the great toe. Small osseous nodules occupying a corresponding position are occasionally met with in the other toes, and instances have been recorded of like ossicles occurring on the plantar aspect of the interphalangeal joint of the great toe. An osseous nodule is not infrequently met with in the tendon of the peronpeus longus as it turns round the lateral box'der of the foot to lie in the groove on the under surface of the cuboid. 17 APPENDIX TO THE SECTION ON OSTEOLOGY. A. Architecture of the Bones of the Skeleton. B. Variations in the Skeleton. C. Serial Homologies of the Vertebrae. D. Measurements and Indices employed in Physical Anthropology. E. Development of the Chondro-Cranium and Morphology of the Skull. F. Morphology of the Limbs. of Fhvti^cians & SurFGona, APPENDIX A. ARCHITECTURE OF THE BONES OF THE SKELETON. The Vertebrae. — The vertebra? are formed of spongy bone confined witliin a thin and dense envelope. In the bodies the arrangement of the cancellous tissue, wliich is traversed by venous channels, is such as to display a vertical striation with lamellaj arranged horizontally. The lateral, superior, and inferior walls are very tliin — that directed to the neural canal being usually thicker and denser than the others. In the pedicles and roots of the transvei"se pro- cesses the cancellous tissue is much more open. The outer envelope is much thicker where it bounds the neural ring, and where it forms the bottom of the superior and inferior intervertebral notches. In the laminae the spongy tissue is confined between two compact layers, of which that directed to the spinal canal is the thicker. In the spinous processes the upper edge is always the more compact. The Sternum consists of large-celled spongy bone, which is highly vascular, and is contained between two layers of thin compact tissue. The Ribs. — Each rib consists of a curved and compressed bar of bone, the interior of which consists of highly vascular cancellous tissue with an external envelope of compact bone. The inner table is much the stronger, attaining its maximum thickness opi^osite the angle — in front and behind which it becomes gradually reduced. The outer table, much thinner, is stoutest opposite the angle ; on the posterior surface of the tubercle and neck it forms but a thin layer. The compact layers forming the upper and lower borders are not so thick as those forming the inner and outer surfaces. The cancellous tissue, loose and open in the shaft, is most compact in the region of the head and towards the anterior extremity. The Frontal Bone. — The frontal bone is composed, like the other bones of the cranial vault, of two layers of compact tissue, enclosing between them a layer of spongy cancellous texture — the diploe. In certain definite situationSj owing to the absorption of this intermediate layer, the bone is hollow, forming the frontal air sinuses. The position and extent of these is to some extent indicated by the degree of projection of the suj)erciliary ridges, though this must not be taken as an absolutely reliable guide, for cases are recorded where the ridges were low and the sinuses large, and vice versa. Of much surgical importance, these air-spaces only attain their full development after the age of puberty, being of larger size in the male than in the female, a circumstance which accounts for the more vertical appearance of the forehead in woman as con- trasted ^v^th man. Usually two in number, they are placed one on either side of the middle line, and Jfeommunicate by means of the infundibulum with the nasal fossa of the same side. It is exceptional to find the sinuses of opposite sides in communication with each other, as they are generally separated by a complete partition which, however, is occasionally much deflected to one or other side. Logan Turner (" On the Illumination of the Air Sinuses of the Skull, with some Observations vij^on the Surgical Anatomy of the Frontal Sinus," Edin. Med. Jour.., May 1898) gives the average dimensions of these sinuses as follows : — Height, 31 mm., i.e. from the fronto- nasal aperture upwards ; breadth, 30 mm., i.e. from the sejjtum hoi-izontally outwards ; depth, 17 mm., from the anterior wall at the level of fronto-nasal suture backwards along tlie orbital roof. Exceptionally large sinuses are sometimes met with extending backwards over the orbit so as to form a double roof to that space. There is a specimen in the Oxford collection in which the sinus is so large, and extends so far back, that the optic nerve is transmitted through it in a bony tube. Another point of some practical importance is that the sinuses are hardly ever sym- metrical. It is rare to meet with cases of their complete absence, although sometimes the sinus on one or other side may be wanting. The lateral angular process, from the arrangement of its surfaces and tlie density of its structure, is particularly well adapted to resist the pressui-e to which it is subjected when the jaws are firmly closed. The Parietal Bone. — Thin towards its lower part, where it enters into the formation of the temporal fossa, it is thickest along the superior border and in the neighbourhood of the posterior superior angle. The Occipital Bone. — The squamous part displays thickenings in the position of the various ridge and crests, the stoutest part corresponding to the internal and external occipital protuberances, though it should be noted that the two protuberances do not necessarily coincide, the internal being, as a rule, placed at a higher level than the external If the bone be held up to the light ii OSTEOLOGY. it will be at once apparent that it is mucli thinner wliere it forms the floor of the inferior fossse than in the upper part. The basilar portion consists of a spongy core surrounded by a more compact outer envelope, thickest on its lower surface. In the condj'les the spongy tissue is arranged radially to their convex articular surfaces, the hypoglossal canal being surrounded by ]»articularly dense and compact bone, which assists in strengthening this naturally weak jaart of the Ijone. The Temporal Bone. — The temporal bone is remarkable for the hardness and density of its petrous part, wherein is lodged the osseous labyrinth Avhich contains the delicate organs associated with the senses of hearing and equilibration. The middle ear or tympanum is a cavity which contains the small auditory ossicles, and is separated from the external auditory meatus by the membrana tympani. In front it communicates with the pharynx by the Eustachian tube ; behind, it opens into the mastoid antrum and mastoid air-cells by the aditus ad antrum. Superiorhj, it is separated from the middle cranial fossa by a thin plate of bone called the tegmen tympani. Inferiorlij, its floor is formed in part by the roof of the jugular fossa and the carotid canal. Medially, it is related to the structures which form the inner ear, notably the cochlea and vestibule, in front of which it is separated by a thin plate of bone from the carotid canal. Owing to the disposition of the internal and external auditory canals the weakest part of the bone corresponds to a line connecting these two channels, the only parts intervening being the cochlea and tympanum. It is usually in this position that fracture of the bone occurs. Curving over the cavity of the tympanum is the aquseductus Fallopii, the thin walls of which are occasionally deficient. These details, together with an account of the tympanic ossicles, will be further dealt with in the section devoted to the Organs of Sense. The Sphenoid Bone. — In the adult the body of the bone is hollow and encloses the sphenoidal air-cells, usually two in number, separated by a septum. The arrangement and extent of these air- cells vary ; sometimes they are multilocular, at other times simple, while occasionally they extend backwards into the basi-occipital and outwards and downwards into the roots of the great wings and pterygoid processes. Cases are on record in which in the adult the body of the bone was not pneumatic. The Lacrimal Bone. — The bone consists of a thin papery translucent lamina, somewhat strengthened by the addition of the vertical crest. The Vomer. — The bone is composed of two compact layers fused below, but separated above by the groove for the lodgment of the rostrum of the sphenoid behind, and the septal cartilage in front. The lamellae are also separated from each other by a canal which runs horizontally from behind forwards in the substance of the bone, and which transmits the nutrient vessel of the bone. The Nasal Bone. — Formed of dense and compact bone ; the strength of the nasal bones is increased by their mode of union and the formation of a median crest posteriorly. The Maxillary Bone. — The disposition of the maxillary sinus within the body of the bone has been already referred to. In union with its fellow, the vaulted arrangement of the hard palate is well displayed, and the arched outline of the superior ah^eolar processes is obvious. It is in these latter processes around the sockets for the reception of the teeth that the cancellous tissue of the bone is seen ; elsewhere its walls are formed by thin and dense bone. The Zygomatic Bone. — In structure the bone is compact, with little cancellous tissue. Together with the zygomatic process of the temporal bone it forms the buttress which supports the maxilla and the lateral wall of the orbit. Additional strength is imj)arted to the bone by the angular mode of union of its orbital and facial parts. The Mandible. — The mandible is remarkable for the density and thickness of its medial and lateral walls. Where these coalesce below at the base of the body, the bone is particularly stout. Superiorly, where they form the walls of the alveoli, they gradually thin, being thicker, however, on the medial than the lateral side, except in the region of the last molar tooth, where the medial wall is the thinner. The cancellous substance is open-meshed below, finer and more condensed where it surrounds the alveoli. The mandibular canal is large and has no very definite wall ; it is prolonged beyond the mental foramen to reach the incisor teeth. From it numerous channels pass upwards to the sockets of the teeth, and it com- municates freely with the surrounding cancellous tissue. Above the canal the substance of the bone is broken up by the alveoli for the reception of the roots of the teeth. In the substance of the condyle the cancellous tissue is more compact, with a general striation vertical to the articular surface. The mental prominence is an essentially human characteristic; by some it is associated with the development of speech in man, others regard it as due to the reduction in the size of the teeth. The Clavicle. — The shaft consists of an outer layer of compact bone, thickest towards the centre, but gradually thinning towards the extremities, the investing envelope of which consists merely of a thin sliell. Within the shaft the cancellous tissue displays a longitudinal striation, which internally assumes a more cellular appearance. At the acromial end the general arrange- ment of tlie fil;res resembles the appearance of the sides of a Gothic arch. The curves of the bone imj)art an elasticity to it, which is of much service in reducing the effects of the shocks to which it is so frequently subjected. The Scapula. — For so light and thin a bone, the scapula possesses a remarkable rigidity. This is owing to tlie arrangement of its jmrts. Stout and thick where it supjjorts the glenoid surface ARCHITECTURE OF THE BONES OF THE SKELETON. iii and coracoid process, the rest of the bone is thin, except along the axillary border ; but strength is imparted to the body by the manner in which the s^jine is fused at right angles to its dorsal surface. The Humerus. — The shaft consists of a layer of compact bone surrounding a long medullary canal. The outer shell, thickest in the lower third of the bone, gradually thins until it reaches the superior epiphysial line, where it forms a layer no thicker than stout paper. Inferiorly the external shell is thicker and stouter than above, until it reaches the epicondyles, below which the articular surfaces are formed of a layer of compact spongy bone. The upj^er end of the medullary canal is surrounded by loose sjjongy tissue, the fibres of which arch inwards from the inner surface of the compact outer layer, whilst inferiorly the cancellous tissue which springs from the outer shell sweeps downwards in a radiating fashion on either side of the olecranon fossa towards the epicondyles. Above the olecranon fossa there is a number of laminee of dense bone which arch across from one side to the other, the con- vexity of the arches being directed downwards. The superior epijihysis, formed of spongy bone, is united to the shaft by a wavy line, concave laterally and convex medially, leading from the base of the greater tuberosity on the outer side to the inferior articular edge on the medial side. The mass above this includes the head and two tuberosities. The spongy tissue of the head is fine, and is arranged generally in lines radial to its surface ; that of the greater tuberosity is more open, and often displays large spaces towards its interior, which in old bones communi- cate freely with the medullary cavity of the shaft. The general direction of the fibres is parallel to the outer surface of the tuberosity. The lower articular end is formed of fine spongy tissue, more compact towards the surface, and arranged in lines more or less at right angles to its articular planes. In the adult the principal nutrient canal, viz. that which opens on the surface near the insertion of the coraco-brachialis, traverses the outer compact wall of the shaft obliquely downwards for a distance of two and a quarter inches before it opens into the medullary cavity. The Ulna. — The weakest parts of the bone are the constricted portion of the semilunar notch, and the shaft in its lower third, the bone being most liable to fracture at these points. On section the medullary cavity is seen to extend upwards as high as the base of the coronoid process ; inferiorly it reaches as low as the upper end of the lower fifth of the bone. The walls of the shaft, which are formed of dense bone, are much thicker posteriorly than anteriorly. Above they are continuous with the front of the coronoid process and the back of the olecranon, where they are composed of layers of looser texture, which, however, gradually become thinner as the points of these processes are reached. Inferiorly they gradually tajaer until the head and styloid process are reached, round which they form a thin shell, considerably thickened, however, in the region of the groove for the extensor carpi ulnaris muscle. The bulk of the upper extremity is formed of loose cellular bone, arranged in a series of arcades, stretching from the anterior to the posterior wall over the upper end of the medullary canal. Above the constricted part of the semilunar notch the bone displays a dift'erent structure ; here it is formed of spongy bone, of closer texture, arranged generally in lines radial to the articular surface. At the point of constriction of the semilunar notch the layer immediately subjacent is much denser and more compact. The lower fifth of the bone is formed of loose spongy bone, the fibres of which have a general longitudinal arrangement ; towards its extremity the meshes become smaller. The Radius. — The neck is the narrowest part of the bone ; here fracture may occur, though not commonly. The point at which the bone is usually broken is about one inch above the lower extremity. This is accounted for by the fact that the radius supports the hand at the radio-carpal articulation, and the shocks to which the latter is subjected, as in endeavouring to save oneself from falling, are naturally transmitted to the radius. On section, the medullary canal is seen to extend as high as the neck ; below, it reaches to the level of the inferior fifth of the bone. Its walls are thick as compared with the diameters of the bone, particularly along the interosseous border, thus imparting rigidity to the curve of the shaft ; these walls thin out above and below. Superiorly, the surface of the tuberosity is formed of a thin shell of bone, which, however, thickens again where it passes on to the neck. The upper extremity is formed of spongy bone arranged in the form of arcades, reaching below the level of the tuberosity medially, but not extending below the level of the neck laterally. Beneath the capitular articular surface there is a dense layer, thickest in the centre, and thinning towards the circumference ; this is overlain by a very thin layer of less compact bone. The inferior fifth of the shaft and lower extremity are formed of loose spongy bone arranged more or less longitudinally. Immediately subjacent to the carpal articular surface the tissue is more compact, and displays a striation parallel to the articular plane. The nutrient canal of the shaft pierces the anterior wall of the upper part of the medullary cavity obliquely from below upwards for the space of half an inch. The Carpus. — The bones are formed of fairly compact spongy tissue, surrounded by a thin shell of denser bone. They are very vascular, and their non-articular surfaces are pierced by many foramina. The Metacarpus. — Similar in arrangement to that of long bones generally, though it may be noted that the compact walls of the shaft are thicker in proportion to the length of the bone than in the other long bones of the upper extremity. The Phalanges. — Each j^halanx has a medullary cavity, the walls of the shaft being formed of dense comjaact bone, especially thick along the dorsal aspect. The extremities are made up of spongy bone within a thin dense shell. IV OSTEOLOGY. DlOirAI. KOSSA •^ Posterior siirface OF NECK Base of trochanter minor cut through Space containing loose cancellous tissue (scraped away) between the calcar and the base of the tro- chanter minor Great trochanter Interior of tro- chanter major ooutaining loose cancellous tissue scraped away Compact tissue with dense core forming the calcar lemorale The Innominate or Hip Bone. — As a flat bone the os iimominatum consists of spongy tissue between two comjjact external layers. These latter vary much in thickness, being exceptionally stout along the ilio-pectineal line and the floor of the iliac fossa immediately above it. The gluteal aspect of the ilium is also formed by a layer of considerable thickness. The si:)ongy tissue is loose and cellular in the tliick part of the ilium and in the body of the ischium ; absent where the floor of the iliac fossa is formed by the coalescence of the thin dense confining layers ; fine grained and more compact in the tuberosity of the ischium, the iliac crest, and the floor of the acetabulum, in which latter situation it is striated by fibres which are directed radially to the surface of that hollow, these again being crossed at right angles by others which are arranged circumferentially. This spongy tissue forms a more compact layer over the surface of the upjier and back portion of the acetabular articular area. The bottom of the floor of the acetab- ulum varies in thickness ; in most cases it is thin, and in exceptional instances the bone is here deficient. The same condition has been met with in the iliac Fig. 195. — Dissection showing the Calcar Femorale. A slice of bone has been removed from the pos- terior aspect of the upper part of the shaft of the femur, passing through the trochanter major superiorly and the trochanter minor inferiorly and to the medial side. The loose cancellous tissue has been scraped away, leaving the more compact tissue with the dense core forming the calcar femorale. By a similar dissection from the front the an- terior surface of the calcar may be exposed. amerior fossa, where absorption of the thin bony plate has taken jjlace. The Femur. — Tlie shaft has a medullary cavity which reaches as high as the root of the lesser trochanter. Inferiorly it extends to within 3^ inches of the lower articular surface. In the upper half the outer compact wall is very thick, but below the middle of the shaft it gradually thins until it reaches tlie condyles inferiorly, over which it passes as a thin, hardly definable external layer. Above, it is especially thick along the line of the linea aspera, and here the large nutrient caual may be seen passing obliquely upwards in the sub- stance of the dense bone for the space of two inches. In the up])er end of the shaft the osseous lamellae springing from the sides of the medullary cavity arch inwards towards the centre, intersecting each other in a manner comparable to the tracery of a Gothic window. The lower wall of the neck is thick below, near the trochanter minor, but thins rapidly before it reaches the head. From this aspect of the neck there spring a series of oblique lamellae which pass upwards and inwards, spreading in fan-shaped manner into the under surface of the head. These are intersected above by lamellai which arch inwards from the lateral side of the Posterior suri-aci- ^ OF ^ECh \ Calcar femoimlp Trochanter minor Fig. 196. —Section through Head and Neck of Femur to show Calcar Femorale. ARCHITECTUEE OF THE BONES OF THE SKELETON. v sliaft below tlie greater trochanter, as well as from the iiiuler surface of the thin but compact outer shell of the upper surface of the neck, the whole forming a bracket-like arrangement which assists materially in adding to the strength of the neck. Further support is affoi'ded by the addition of a vertical layer of more comjiact bone within the cancellous tissue of the neck. In- feriorly, as may be seen in Fig. 196, this is continuous with the dense jjosterior wall of the shaft below ; whilst superiorly it sweeps up beneath the lesser trochanter, from which it is separated by a quantity of loose cancellous tissiie, to fuse superiorly with the posterior dense wall of the neck above and medial to the posterior intertrochanteric line. It may be regarded as a con- tinuation upwards of the posterior wall of the shaft beneath the trochanteric epiphysis. When studied in section (see Fig. 197), the central dense core of this partition exhibits a spur-like appearance : hence the name calcar femorale a})2)lied to it. It is of surgical importance in cases of fracture of the neck of the femur (E. Thompson, Journ. Anat. and Physiol., vol. xlii. p. 60). From it, stout lamella; having a vertical direction arise. The sjaongy tissue of the head and greater trochanter is finely reticulated, that of the lower part of the neck and upper part of the shaft being more open in its texture. Passing vertically dowoiAvards through this tissue there is a vascular canal, the orifice of which oj)ens externally on the floor of the trochanteric fossa. The spongy tissue of the lower part of the shaft is more delicate and uniform in its arrangement, displaying a more or less parallel striation in a longitudinal direction. Subjacent to the articular surface the tissue is rendered more compact by the addition of lamellae disposed in curves in harmony with the external aspect of the bone. The Patella. — The bone consists of a thick dense layer anteriorly, which thins towards the edges on either side and below ; above, it corresponds to the area of insertion of the quadriceps. The femoral articular surface is composed of a layer of compact bone, thickest in correspondence with the vertical elevation. Sandwiched between these two layers is a varying thickness of spongy tissue of fairly close grain, the striation of which on cross section runs in parallel lines from back to front ; on vertical section the tissue appears to be arranged in lines passing radially from the deep surface of the femoral area to the more extensive anterior dense plate. The Tibia. — The shaft of the bone is remarkable for the thickness and density of the osseous tissue which underlies the crest. The posterior wall is stout, but the medial and lateral walls are thinner. The several walls are thickest oj^posite the middle of the shaft, and thin out above and below where the shaft unites with the epiphyses. The medullary canal, narrow and circular in the middle of the bone, increases in all its diameters above and below, and reaches to within 2^ to 3 inches of either extremity. Superiorly the arrangement of the lameUcB of the spongy tissue resembles a series of arches springing from the dense outer walls. These form a platform on which the superior epiphysis rests, the sjiongy tissue of which displays a more or less vertical striation. This is much more compact under the condylic surfaces, the superficial aspect of which is formed by a thin layer of dense bone. The spine and tuberosity are also formed of compact tissue, whilst the circumference of the tuberosities is covered by a thinner and less dense wall In the lower end of the shaft the spongy tissue, of a loose and cellular character, is arranged in vertical fibres, blending inferiorly with the closer tissue of the inferior epiphysis, the articular surface of which is covered by a thin but dense layer. In the adult bone the nutrient canal for the shaft is embedded in the dense posterior wall for the space of two inches. The Fibula. — A medullary canal runs throughout the length of the shaft, reaching as high as the neck above, and extending as low as a point about 2^ inches above the inferior extremity of the lateral malleolus. The lateral wall of the shaft is usually considerably thicker than the medial. The head is formed of loose cellular bone, enclosed within a very thin dense envelope. The spongy tissue of the lower extremity is more compact, and acquires considerable density on the surfaces underlying the articular area and the pit behind it. The canal for the nutrient artery of the shaft ojiens into the medullary cavity about an inch below its external aperture. The Bones of the Foot. — A longitudinal section through the articulated bones of the foot reveals the fact that the cancellous structure of each individual bone is determined by the stress to which it is habitually subjected. In this connexion it is necessary to refer to the arched arrangement of the bones of the foot, a subject which is also treated in the section which deals with the Joints. The summit of the arch is formed by the talus, on which rests the tibia. Subjected as the talus is to a crushing strain, it is obvious that this load must be distributed throughout the arch, of which the calcaneus is the j^osterior pillar, whilst the heads of the meta- tarsal bones constitute the anterior pillar. It is found, consequently, that the lamellse of the cancellous tissue of the talus are arranged in two directions, which intercross and terminate below the superior articular surface. Of these fibres, some sweej) backwards and downwards towards the posterior calcanean facet, bej'-ond which they are carried in the substance of the cal- caneus in a curved and wavy manner in the direction of the heel, where they terminate ; whilst others, curving downwards and forwards from the trochlea of the talus, pass through the neck to reach the articular surface of the head, through which in like manner they may be regarded as passing onwards through the several bones wliich constitute the anterior jjart of the arch, thus accounting for the longitudinal striation as displayed in the structure of the navi- cular, cuneiform, and metatarsal bones. In the calcaneus, in addition to the foregoing arrange- ment, another set of curving fibres sweep from back to front of the bone beneath the more com- pact tissue which forms its under shell. These are obviously of advantage to prevent the spread of the bone when subjected to the crushing strain. In the sustentaculum tali a bracket-like vi OSTEOLOGY. arrangement of fibres is evident, and tlie under surface of tlie neck of the talus is further strengthened by lamellae arranged vertically. In the separate bones the investing envelope is thin, though xinder the articular surfaces there is a greater density, due to the accession of lamellae lying parallel to the articular planes. The stoutest bony tissue in the talus is met with in the region of tlie under surface of the neck, whilst in the calcaneus the greatest density occurs along the floor of the sinus tarsi. The Metatarsus. — In structure and the arrangement of their lamellae the metatarsal bones agree witli the metacarjjus. The Phalanges. — In their general structure they resemble the bones of the fingers, APPENDIX B. VARIATIONS IN THE SKELETON. Cervical Vertebrae. — Szawlowski records the presence of an independent rib element in the transverse process of the fourth cervical vertebra. (Anat. Anz. Jena, vol. xx. p. 306.) Atlas. — The vertebrarterial foramen is often deficient in front. Imperfect ossification occasionally leads to the anterior and more frequently the posterior arches being incomplete. The superior articular surfaces are occasionally partially or com j)letely divided into anterior and posterior portions. In some instances the extremity of the transverse process has two tubercles. The trans- verse process may, in rare cases, articulate with a projecting process (paroccipital) from the under surface of the jugular process of the occipital bone (see p. ix). An upward extension from the median part of the anterior arch, due jDrobably to an ossification of the anterior occipito-atlantal ligament, may articulate with the anterior surface of the summit of the odontoid process of the axis. Allen has noticed the articulation of the suj^erior border of the posterior arch with the posterior border of the foramen magnum. Cases of partial or complete fusion of the atlas with the occipital bone are not uncommon (see p. ix). Axis. — In some instances the summit of the odontoid process articulates with a prominent tubercle on the anterior border of the foramen magnum (third occii^ital condyle, see p. viii). Bennett {Trans. Path. Soc. Dublin, vol. vii.) records a case in which the odontoid process was double, due to the persistence of the primitive condition in which it is develojDed from two centres. Occasionally the odontoid process fails to be united with the hodj of the axis, forming an OS odontoideum comparable to that met with in the crocodilia (Giacomini, Eomiti, and Turner). The vertebrarterial foramen is not infrequently incomplete, owing to the imperfect ossification of the posterior root of the transverse process. Elliot Smith has recorded a case in which there was fusion between the atlas and axis without any evidence of disease. Seventh Cervical Vertebra. — The vertebrarterial foramen may be absent on one or other side. Thoracic Vertebrae. — Barclay Smith (Joum. Anat. and Physiol. Lond. 1902, ]). 372) records five cases in which the superior articular processes of the twelfth thoracic A^ertebra disj)layed thoracic and lumliar characteristics on the opposite sides. Lumbar Vertebrae. — The mammillary and accessory processes are sometimes unduly de- veloped. The neural arch of the fifth lumbar vertebra is occasionally interrupted on either side by a synchondrosis which runs between the upper and lower articular processes. In macerated specimens the two parts of the bone are thus sejDarate and independent. The anterior includes the centrum, together witli the pedicles, transverse and superior articular processes ; the posterior comprises the inferior articular processes, the laminte, and the spine (Turner, Challenger Reports, vol. xvi.). Szawlowski and Dwight record instances of the occurrence of a foramen in the transverse process of the Vth lumliar vertebra {Anat. Anz. Jena, vol. xx.), and Ramsay Smith describes a case in which the right transverse process of the IVth lumbar vertebra of an Australian sprang from the side of the body in front of the j)edicle, being unconnected either with the pedicle or articular process. Sacrum. — The number of sacral segments may be increased to six or reduced to four (see p. vii). Transition forms are occasionally met with in which the first sacral segment disjalays on one side purely sacral characters, i.e. it articulates with the innominate bone, whilst on the opposite side it may present all the features of a lumbar vertebra. Through deficiency in the develoj)ment of the laminte, the neural canal may be exposed throughout its entire length, or to a greater extent than is normally the case (Paterson, Roy. Dublin Soc. Scientific Trans. voL V. Series II.). Szawlowski and Barclay Smith record the occurrence of a foramen in the lateral mass of the 1st sacral vertebra {Jonrn. of Anat. and Physiol., Lond. voL xxxvi. p. 372). Vertebral Column as a Whole. — Increase in the number of vertebral segments is usually due to ditfc.reiices in the numl;er of the coccygeal vertebra;; these may vary from four — which may Ije regarded as the normal number — to six. The number of jH'esacral or movable vertebrte is normally 24 (7 C, 12 D, and 5 L) ; in wliich case the 25th vertebra forms the fii-st sacral segment (vertebra fulcralis of Welcker). The number of presacral vertebrae may be increased by the intercalcation of a segment either in the thoracic or lumbar region without VAEIATIONS IN THE SKELETON. vii any alteration in the number of the sacral or coccygeal elements : thus we may have 7 C, 13 D, and 5 L, or 7 C, 12 D, and 6 L, or it may be reduced by the disappearance of a vertebral segment — thu.-r, 7 C, 12 D, and 4 L. Such an arrangement presupposes developmental errors either of excess or default in the segmentation of the column. On the other hand, the total number of vertebral segments remaining the same (24 or 25), we may have variations in the number of those assigned to different regions due to the addition of a vertebral segment to one, and its consequent subtraction from another region. Thus, in the 24 ^'resacral vertebrae, in cases of the occurrence of cervical ribs the formula is rearranged thus — 6 C, 13 D, and 5 L, or, in the case of a thirteenth rib being jj resent, the formula would be 7 C, 13 D, 4 L, as hajj^^ens normally in the gorilla and chimpanzee. Similarly, the number of the presacral vertebi'je (24) may be increased by the withdrawal of a segment from the sacral region — 7 C, 12 D, 6 L, and 4 S — or diminished by an increase in the number of the sacral vertebrge, as in the formula 7 C, 12 D, 4 L, and 6 S. In- crease in the number of sacral segments may be due to fusion with a lumbar vertebra, or by the addition of a coccygeal element : the latter is more frequently the case. This variability in the constitution of the sacrum is necessarily correlated with a shifting backwards and forwards of the pelvic girdle along the vertebral column. Rosenburg considers that the 26th, 27th, and 28th vertebrte are the jirimitive sacral segments, and that the sacral characters of the 25th vertebrae (the first sacral segment in the normal adult column) are only secondarily acquired. He thus supposes that during development there is a forward shifting of the sacrum and pelvic girdle, with a consequent reduction in the length of the presacral portion of the column. This view is opposed by Paterson (Eoy. Dublin Soc. Scientific Trans, vol. v. Ser. II.), who found that ossification took place in the alas of the 25th vertebra (first adult sacral segment) before it made its appear- ance in the alae of the 26th vertebra. He thus assumes that the alee of the 25th vertebra may be regarded as the main and j^rimary attachment with the ilium. His conclusions, based on a large number of observations, are at variance with Rosenburg's views, for, according to his opinion, liberation of the first sacral segment is more common than assimilation with the fifth lumbar vertebra, and assimilation of the first coccygeal vertebra with the sacrum is more common than liberation of the fifth sacral, thus leading to the inference that the sacrum tends to shift back- wards more often than forwards. Dwight (Anat. Anz. Jena, vol. xxviii. p. 33), after a study of this question, whilst admitting that some of these variations may be reversive, denies that there is any evidence that they are jjrogressive, and further states that after the occurrence of the original error in development, there is a tendency for the vertebral column to assume as nearly as possible its normal disposition and j^roportions. Sternum. — The sternum is liable to considerable individual variations affecting its length and direction. The majority of bones are asymmetrical, displaying irregularities in the levels of the clavicular facets. The higher costal facets may be closer together on one, usually the right side, than the other, whilst the pre-mesosternal joint is often oblique, sloping somewhat to the right. According to Birmingham, these are the result of the strain thrown on the shoulder by pressure either directly applied or through the pull of a weight carried in the hand. Sometimes the sternum articulates with eight rib cartilages. This may happen on one or both sides, but when unilateral, much more frequently on the right side — a condition by some associated with right-handedness. It is, however, more probably a persistence of the primitive condition of the cartilaginous sternum, in which each half is connected with the anterior extremities of the first eight costal arches. In some rare cases only six pairs of ribs articulate by means of their costal cartilages with the sternum. Recently Lickley has brought forward evidence to show that the seventh rib is undergoing regressive changes (Anat. Anz. vol. xxiv. p. 326). Occasionally the presternum supports the first three ribs ; in other words, the manubrium has absorbed the highest segment of the body. Keith has pointed out that this is the condition most commonly met with in the gibbon, and regards its occurrence in man as a reversion to the simian type. As far as is at present known, its occurrence seems more common in the lower races. Through errors of development the sternum may be fissured throughout, due to failure of fusion of the cartilaginous hemisterna. The two ossified halves are usually widely separated above, but imited together below by an arthrodial joint. The heart and pericardium are thus uncovered by the bone. Occasionally this condition is associated with ectopia cordis, under which circumstances life is rendered impossible. Through defects in ossification the mesosternum may be pierced by a hole, usually in its lower part, or through failure of fusion of the lateral centres one or more of the segments of the body may be divided longitudinally. Sometimes small ossicles are found in the ligaments of the sterno-clavicular articulation. These are the so-called episternal bones, the morphological significance of which, however, has not yet been satisfactorily determined. They are by some regarded as the homologues of the interclavicle or episternal bone of monotremata, whilst by others they are considered to represent persistent and detached portions of the pre-coracoids. Ribs. — The number of ribs may be increased or diminished. Increase may occur by the addition of a cervical rib due to the independent development of the costal element in the transverse process of the seventh cervical vertebra. This may happen on one or both sides. The range of development of these cervical ribs varies ; they may unite in front with the sternum, or they may be fused anteriorly with the cartilage of the first rib, or the cervical rib may be free. It may in some instances be represented mainly by a ligamentous band, or its vertebral and sternal ends may be alone developed, the intermediate part being fibrous. At times the vertebral end only may be formed, and may be fused with the first rib, thus leading to the formation of a bicipital rib such as occurs in many cetaceans. Increase in the number of ribs 17* viii OSTEOLOGY. may also be due to the ossification of the costal element which is normally present in the embryo in connexion with the first lumbar vertebra. (Rosenberg, Morph. Jahrb. i.) Reduction in the number of ribs is less common. The twelfth rib rarely aborts ; in some cases the first rib is rudimentary. Cases of congenital absence of some of the ribs have been recorded by Hiitchinson, Murray, and Ludeke. Fusion of adjacent ribs may occur. (Lane, Giiy's Hosp. Reports, 1883.) In this way, too, the occurrence of a bici25ital rib is explained. This anomaly occurs most usually in connexion with the first rib, which either fuses with a cervical rib above or with the second rib below. Variations in form may be in great jiart due to the occupation of the individual and the con- stricting influence of corsets. Independently of these influences, the fore part of the shaft is sometimes cleft so as to appear double ; at other times the cleft may be incomplete so as to form a perforation. Occasionally adjacent ribs are united towards their posterior part by processes liaving an intermediate ossicle between (Meckel), thus recalling the condition normally met with in birds ; more usually, however, the bony projections are not in contact. The number of true or vertebro-sternal ribs may be reduced to six, or increased to eight {vide ante, ji. vii). Costal Cartilages. — Occasionally a costal cartilage is unduly broad, and may be pierced by a foramen. The number of costal cartilages connected with the sternum may be reduced to six or increased to eight (see p. vii). In advanced life there is a tendency towards ossification in the layers underlying the perichondrium, more particularly in the case of the first rib cartilage, in which it may be regarded as a more or less normal occurrence. Frontal Bone, etc. — The variation most frequently met with is a persistence of the suture which unites the two halves of the bone in the infantile condition : skulls disj)laying this peculiarity are termed metopic. The researches of various observers — Broca, Ranke, Gruber, Manouvrier, Anoutchine, and Papillault {Rev. mens, de Vecole d'Anthropol. de Paris, annee 6, n. 3) — point to the more frequent occurrence of this metopic suture in the higher than in the lower races of man ; and Calmette asserts its greater frec|uence in the brachycei)halic than the dolichocephalic type. Separate ossicles (Wormian bones) may occur in the region of the anterior fontanelle. The fusion of these with one or other half of the frontal explains how the metopic suture is not always in line with the sagittal suture (Stieda, Anat. Anz. 1897, p. 227) ; they occasionally persist, however, and form by their coalescence a bregmatic bone (G. Zoja, Bull. Scientifico, xvii. p. 76, Pavia), Turner {Challenger Reports, part xxix.) records an instance of direct articulation of the frontal with the orbital plate of the maxilla in a Bush skull, and other examples of the same anomaly, which obtains normally in the skulls of the chimpanzee and gorilla, haA^e been observed {Jour. Anat. and Physiol. voL xxiv. p. 349). There is sometimes a small arterial groove just medial to the supraorbital notch or foramen, and occasionally the latter is double, the lateral aperture piercing the orbital margin wide of its middle jDoint. Schwalbe (1901) records the presence of small independent ossicles (supranasal bones) in the anterior part of the metopic suture. The same anatomist has also directed attention {Zeit. f. Morph. und Anthr. vol. iii. p. 93) to the existence of the metopic fontanelle, first described by Gerdy, and the occurrence of metopic ossicles (ossa interfrontalia) and canals. Parietal. — A number of cases have been recorded in which the parietal is divided into an upper and lower part by an antero-posterior suture parallel to the sagittal suture. Coraini (Atti. d. XL Gongr. Med. Internaz. Roma, 1894, vol. v.) records a case in which the parietal was in- completely divided into an anterior and posterior part by a vertical suture. A tripartite condition of the bone has also been observed (Frasetto). The parietal foramina vary greatly in size, and to some extent in position. They are sometimes absent on one or other side, or both. They correspond in position to the sagittal fontanelle. Sometimes the ossification of this fontanelle is incomplete and a small transverse fissure remains. The jmrietal foramen represents the patent lateral extremity of this fissiire after its edges have coalesced.. Occasionally in the region of the anterior fontanelle an ossicle of variable size may be met with. This is the so-called pre-interparietal bone. According to its fusion with adjacent bones it may disturb the direction of the sagittal suture. Occipital. — The torus occipitalis transversus is the term applied to an occasional eleva- tion of the bone which includes the external occipital j^rotuberance and extends laterally along the superior curved line. Occasionally an emissary vein pierces the bone opposite the occipital protuberance. In about 15 per cent of cases the anterior condylic canal is double. Much rarer three or even four foi-amina may be met with. The most striking of the many variations to which this bone is subject is the separation of the upper part of the squamous part of tlie occipital to form an independent bone — the interparietal bone, called also, from the frequency of its occurrence in Peruvian skulls, the os Incse. By a reference to the account of the ossi- fication of the bone (p. 112), the occurrence of this anomaly is explained developmentally. In T)lace of forming a single bone the interparietal is occasionally met with in two symmetrical halves, and instances have been recorded of its occurrence in three or even four pieces. In the latter cases the two anterior parts form the pre-interparietals. Not uncommonly the internal occipital crest is split and furrowed clo,se to the foramen magnum for tlie lodgment of the vermiform lobe of the cerebellum, and is hence called the vermiform fossa. Instances are recorded of the presence of a separate epiphysis between the basi-occipital and the sphenoid, the 03 basioticum (Albrecht) or the os pre-basi-occipital. An oval pit, the fovea bursse or pharyngeal fossa, is sometimes seen in front of the tuberculum pharyngeum. This marks the VARIATIONS IN THE SKELETON. ix site of the bursa i)liaryngea. Occasionally the basilar process is pierced l:)y a small venous canal. The articular surface of the condyles is sometimes divided into an anterior and posterior part. The so-called third occipital condyle is an outstanding process rising from the anterior border of the foramen magnum, the extremity of which articulates with the odontoid process of the axis. Guerri has recorded a case, in which in a foetal skull, there were two projecting tubercles in the position of the third occipital condyle, independent of the basi-occipital portions of the condyles {Anat. Anz. vol. xix. p. 42). This appears to confirm the view of Macalister that there are two different structures included under this name — one a medial ossification in the .sheath of the notochord, and the second, a lateral, usually paired process, caused by the deficiency of the medial part of the hypochordal element of the hindmost occij)ital vertebra, with thickenings of the lateral parts of the arch. Springing from the under surface of the extremity of the jugular process, a rough or smooth elevated surface, or else a projecting process, the extremity of which may articulate with the transverse process of the atlas, is sometimes met with. This is the paroccipital or paramastoid process. The size and shape of the foramen magnum varies much in different individuals and races, as also the disposition of its plane, Elliot Smith has called attention to the asymmetry of the cerebral fossa3, which is correlated with asj^mmetry of the caudal poles of the cerebral hemispheres. Numerous instances of fusion of the atlas with the occipital bone have been recorded. Many are, no doubt, pathological in their origin ; others are associated with errors in development. Interesting anomalies are those in which there is evidence of the intercalation of a new vertebral element between the atlas and occipital, constituting what is termed a pro-atlas. Temporal Bone. — The occurrence of a deficiency in the floor of the external auditory meatus is not uncommon in the adult. It is met with commonly in the child till about the age of five, and is due to incomplete ossification of the tympanic plate. The line of the petro-squamosal suture is occasionally grooved for the lodgment of a sinus (petro-squamosal) ; sometimes the posterior end of this is continuous with a canal which pierces the superior border of the bone and opens into the lateral sinus. Anteriorly the groove may pass into a canal which pierces the root of the zygoma and appears externally above the lateral extremity of the Glaserian fissure. These are the remains of channels through which the blood passed in the foetal condition (see ante). Kazzander has recorded a case in which the squamous jiart of the temporal was pneumatic, the sinus reaching as higli as the parietal and the squamoso - sphenoidal suture. Symington has described a case in which the squamous part was distinct and separate from the rest of the temporal bone in an adult ; whilst Hyrtl has observed the division of the squamous part of the temporal into two by a transverse suture. The zygomatic process has been observed separated from the rest of the bone by a suture close to its root (Adacni). P. P. Laidlaw {Journ. Anat. and Physiol, vol. xxxvii. p. 364) describes a temporal bone in which there was absence of the internal auditory meatus and of the stylo-mastoid foramen. The jugular fossa also was absent, and there was partial absence of the groove for the lateral sinus associated with the presence of a large mastoid foramen. An instance of a rudimentary condition of the carotid canal is also referred to in the same volume by G. H. K. Macalister. G. Caribbe {Anat. Anz. vol. xx. p. 81) notes the occurrence in idiots and imbeciles of a more pronounced form of j^ost-glenoid tubercle, and associates it with regressive changes in the develop- ment of the temporal bone. Sphenoid. — Through imperfect ossification the foramen sjDinosum and foramen ovale are sometimes incomplete posteriorly. Le Double {Bull, et to^t?). de la Soc. d'Anth. de Paris, 5"^ ser. vol. iii. p. 550) records a case in which the foramen rotundum and the sphenoidal fissure were united so as to form a single cleft. Through deficiency of its lateral wall, the optic foramen, in rare instances, communicates with the sphenoidal fissure. Duplication of the ojotic foramen is also recorded as a rare occurrence, the artery passing through one canal, the nerve through the other. Persistence of the cranio -pharyngeal canal is also occasionally met with. Owing to the ossification of fibrous bands which frequently connect the several bony points, anomalous foramina are frequently met with. Of such are the carotico-clinoid formed by the union of the anterior and middle clinoid processes, the pterygo-spinous foramen enclosed by the ossification of the ligament con- necting the alar spine with the external jDterygoid j^late, and the porus crotaphitico-buccina- torius similarly developed by the ossification of ligament immediately below and lateral to the inferior ajDerture of the foramen ovale. Ethmoid. — The size of the os planum is liable to considerable variations. In the lower races it tends to be narrower from above downwards than in the higher, in this respect resem- bling the condition met with in the anthrojjoids. The os planum may fail to articulate with the lacrimal owing to the union of the frontal with the orbital process of the maxilla in front of it. (Orbito-maxillary-frontal suture. A. Thomson, Journ. Anat. and Physiol. vol. xxiv. p. 349.) Division of the os planum by a vertical suture into an anterior and posterior part has been frequently recorded. The number of the turbinals may be increased from two to four, or may be reduced to one. (Eeport of Committee of Collect. Invest., Journ. Anat. and Physiol, vol. xxviii. p. 74.) Maxillae. — Not unfrec^uently there is a suture rumiing vertically through the bar of bone which separates the infraorbital foramen from the infraorbital margin. Through imperfections in ossification, the infraorbital canal may form an open groove along the floor of the orbit. Duckworth records four instances of a spinous process projecting inwards into the apertura 17* a X OSTEOLOGY. jivriformis from the lower jiart of the nasal notch. A case has been described (Fischel) hi which there was complete absence of the premaxillfe, together with the incisor teeth. A not uncommon anomaly is the occurrence of a rounded elongated ridge extending along the interj^alatal or intermaxillary sutures on the under surface of the hard j^alate. This is called the torvs 2^alatinus, and is of interest because its presence has given rise to the assumj^tion that it was due to a pathological growth. (See Stieda, Virchoiv's Festschrift, vol. i. p. 147.) Zygomatic Bone. — Cases of division of the zygomatic bone by a horizontal .suture have been recorded, as well as instances of its separation into two parts by a vertical suture. OMdng to the supposed more frequent occurrence of this divided condition in Asiatics the zygomatic has l)een named the os Japonicum. Barclay Smith (" Proc. Anat. Soc," Joiir. Anat. and Physiol, A^jril 1898, p. 40) describes a case in which the zygomatic bone was divided into two parts, an upper and lower, bj' a backward extension of the maxilla, which articiilated with the zygomatic process of the temporal, thus forming a temporo-maxillary arch. Varieties of a like kind have also been described by Gruber and others. Cases have been noted where, owing to deficiency in the develop- ment of the zygomatic, the continuity of the zygomatic arch lias been incomjjlete. Nasal Bones. — The size and configuration of the nasal bones vary greatly in different races, being, as a ride, large and prominent in the white races, and flat and reduced in size, as well as depressed, in the Mongolian and Negro stock. ComjDlete absence of the nasal bones has been recorded, and their division into two or more parts has also been noted. Obliteration of the internasal suture is unusual ; it is stated to occur more frequently in negroes, and is the recognised condition in adult apes. Duckworth has recorded a case {Journ. Anat. and Physiol, vol. xxxvi. jj. 257) of undue extension doMTiwards of the nasal bone, which may be perhaps accounted for on the supposition that the lower i^art is a jjersistent portion of the i)remaxilla. Lacrimal. — The lacrimal is occasionally absent. In some cases it is divided into two parts ; in others replaced by a number of smaller ossicles. In rare instances the hamular process may extend forwards to reach the orbital margin, and so bear a share in the formation of the face, as in lemurs (Gegenbauer). In other instances the hamulus is much reduced in size. Occasion- ally the lacrimal is separated from the os planum of the ethmoid by a down-growth from the frontal, which articulates with the orbital jjrocess of the maxilla, as is the normal disposition in the gorilla and chimpanzee. (Turner, Challenger Piejjorts, " Zoology," vol. x. Part IV. Plate I. ; and A. Thomson, Journ. Anat. and Physiol., London, vol. xxiv. p. 349.) Inferior Turbinal. — A case in which the inferior turbinals were aljsent has been recorded by Hyrtl. Vomer. — Owing to imperfect ossification there may be a deficiency in the bone, filled up during life by cartilage. The separation of the two lamellae along the anterior border varies considerably, and instances are recorded where they were separated by a considerable cavity within the substance of the bone. Instances of an extension forwards of the sphenoidal air sinus into and sej^arating the laminae of the bone have also been described. The spheno-vomerine canal is a minute opening behind the rostrum of the sphenoid, and between it and the alae of the vomer, by which the nutrient artery enters the bone. Palate Bones. — The occurrence of a torus palatinus may be noted (see Variations of Maxilla). Mandible. — Consideral:>le differences are met with in the height of the coronoid process : usually its summit reaches the same level as the condyle, or slightly above it ; occasionally, how- ever, it rises to a much higher level ; in other cases it is much reduced. These dift'erences naturally react on the form of the sigmoid notch. The projection of the mental protuberance is also liable to vary. Occasionally the mental foramen in double, and sometimes the mylo-hyoid groove is for a short distance converted into a canal. There is often a marked eversion of the angle of the mandible, which Dieulafe homologises with the angular apophysis met with in lemurs and carnivora. Clavicle. — The clavicles of women are more slender, less curved, and shorter than those of men. In the latter the bone is so inclined that its acromial end lies .slightly higher or on the same level with tlie sternal end. In women tiie bone usually slopes a little downward and laterally. The more pronounced curves of some bones are probably associated with a more powerful development of the pectoral and deltoid muscles, a circumstance which also affords an exjjlana- tion of the differences usually seen between the right and left bones, the habitual use of the right upper limlj reacting on the form of the bone of tliat side. The influence of muscular action, however, does not wliolly account for the production of the curves of the bone, since the bone has Ixjen shown to display its characteristic features in cases where there has been defective development or absence of the iipper limb (Reynault). Partial or comjjlete absence of the clavicle has Ijeen recorded. W. S. Taylor exhiljited an interesting case of tliis kind at the Clinical Society of London, October 25, 1901. Sometimes there is a small canal through the anterior border of the bone near its middle for the transmission of one of the supraclavicular nerves. Scapula. — The most common variation met with is a .separated acromion i)roce.ss. In these cases tliere has been failure in the ossific union between the spine and acromion, the junction between the two being effected by a layer of cartilage or by an articulation jjossessing a joint cavity. The condition is u.sually symmetrical on both sides, though instances are recorded where this arrangement is unilateral Very much rarer is the condition in which the coracoid VAEIATIONS IN THE SKELETON. xi process is sejjarable from the rest of the bone. The size and form of the scapular notch differs. In certain cases the superior border of the bone describes a unciform curve reaching the base of the coracoid without any indication of a notch. In some scapulaj, more particularly in those of very old people, the floor of the subscapiilar fossa is deficient owing to the absorption of the thin bone, the periosteal layers alone filling up the gap. At birth the vertical length of the bone is less in proportion to its width than in the adult. Humerus. — As has been stated in the description of the bone, the olecranon and coro- noid fossaj may communicate with each other in the macerated bone. The resulting supra- trochlear foramen is most commonly met with in the lower races of man, as well as in the anthropoid &i)es, and in some other mammals. The occurrence of a liook-like spine, called tlie epicondylic process, which projects in front of the medial epicondylic ridge, is not uncommon. Its extremity is connected with the medial epicondyle by means of a fibrous band, underneath which the median nerve, accompanied by the brachial artery, or one of its large branches, may pass, or in some instances, the nerve alone, or the artery unaccompanied by the nerve. This arrangement is the homologue in a rudimentary form of a canal present in many animals, notably in the carnivora and marsujiials. In addition to the broad musculo-spiral groove already described, and which is no doubt produced by the twisting or torsion of the shaft, there is occasionally a distinct narrow groove posterior to it, which marks precisely the course of the musculo-siiiral nerve as it turns round the lateral side of the shaft of the bone. Ulna. — Cases of partial or complete absence of the ulna through congenital defect have been recorded. Rosenm tiller has described a case in which the olecranon was separated from the ujDper end of the bone, resembling thus in some respects the patella. In powerfully developed bones there is a tendency to the formation of a sharp projecting crest corres^jonding to the inser- tion of the triceps. Radius. — Cases of congenital absence of the radius are recorded ; in these the thumb is not infrequently wanting as well. Carpus. — Increase in the number of the carpal elements is occasionally met with, and these have been ascribed to division of the navicular, os lunatum, os triquetrum, caj^itate, lesser multangular, and os hamatum. Of these the most interesting is the os centrale, first described by Rosenberg, and subsequently investigated by Henke, Leboucq, and others. This is met with almost invariably as an independent cartilaginous element during the earlier months of foetal life, and occasionally becomes developed into a distinct ossicle placed on the back of the carpus between the navicular and capitate bones and the small multangular. Its significance depends on the fact that it is an important component of the carpus in most mammals, and is met with normally in the orang and most monkeys. Ordinarily in man, as was pointed out by Leboucq, it becomes fused with the naviciilar, where its presence is often indicated by a small tubercle, a condition which obtains in the chimpanzee, the gorilla, and the gibbons. Dwight has described a case in which there was an OS subcapitulum in both hands. The ossicle lay between the base of the middle metacarpal bone and the capitate bone with the small multangular to its radial side {Anat. Anz. vol. xxiv.). Further addition to the number of the carpal elements may be due to the separation of the styloid process of the third metacarpal bone and its persistence as a separate ossicle. Reduction in the number of the carpus has been met with, but this is probably due to pathological causes. Morestin {Bull. Soc. Anat. de Paris, tome 71, p. 651), who has investigated the subject, finds that ankylosis occurs most frequently between the bases of the second and third metacarpal bones and the carpus, seldom or never between the carpus and the first meta- carpal, or between the pisiform and os triquetrum. Instances of complete fusion of the os lunatum and os triquetrum bones, without any apparent pathological change, have been recorded in Europeans, Negroes, and an Australian. Metacarpal Bones- — As previously stated above, the styloid apophysis of the third metacarpal bone ajapears as a separate ossicle in about 1"8 per cent of cases examined ("Fourth Annual Report of the Committee of Collect. Invest. Anat. Soc. Gt. Brit, and Ireland," Journ. Anat. and Physiol., vol. xxviii. p. 64). In place of being united to the third metacarj^al, the styloid apophysis may be fused with either the capitate bone or the small multangular, under which conditions the base of the third metacarpal bone is without this characteristic process. Phalanges. — Several instances have been recorded of cases in which there were three phalanges in the thumb. Bifurcation of the terminal phalanges has occasionally been met with, and examples of supjjression of a phalangeal segment or its absorption by another phalanx have also been de- scribed (Hasselwander, Zeits. F. Morph. u. Anthr., vol. vi. 1903). Innominate Bone, — Some of the anomalies met with in the innominate bone are due to ossifica- tion of the ligaments connected with it ; in other cases they depend on errors of development. Failure of union between the pubic and ischial rami has also been recorded. Cases have occurred where the obturator groove has been bridged across by bone, and one case is noted of absence of the cotyloid notch on the acetabular margin. In rare cases the os acetabuli (see Ossification) remains as a separate bone. Femur. — Absence of the pit on the head of the femur for the attachment of the liga- mentum teres has been recorded. This corresponds with the condition met with in the orang. Not infrequently there is an extension of the articular surface of the head on to the fore and upper aspect of the neck : this is a " pressure facet " caused by the contact of the iliac portion xii OSTEOLOGY. of the acetabular margin witli the neck of the bone, when the limb is maintained for long periods in the flexed jjosition, as in tailors, and also in those races who habitually squat (Lane, Journ. Anat. and Physiol., vol. xxii. p. 606). The occurrence of a trochanter tertius has been already referred to. Its presence is not confined to individuals of powerful j^hysique, but may occur in those of slender build, so far suggesting that it is not to be regarded merely as an indication of excessive muscular develop- ment. The observations of Dixon {Joihrn. Anat. and Physiol., vol. xxx. p. 502), who noted the occurrence of a sejsarate epiphysis in three cases in connexion with it, seem to point to its possessing some morjjhological significance. Occasionally the gluteal ridge may be replaced by a hollow, the fossa hypotrochanterica, or in some cases the two may co-exist. The angle of the neck is more open in the child than in the adult, and tends to be less when the femoral length is short and the pehdc width great — conditions which particularly appertain to the female. There is no evidence to show that after growth is completed any alteration takes place in the angle Avith advancing years (Humphry). The curvature of the shaft may undergo considerable variations, and the appearance of the posterior surface of the bone may be modified by an absence of the linea aspera, a condition resembling that seen in apes ; or by an unusual elevation of the bone which supj)orts the ridge {femur a inlastre), produced, as Manouvrier has suggested, by the excessive development of the muscles here attached. Under the term " platymerie," Manouvrier describes an an tero -posterior compression of the upper jjart of the shaft, frequently met with in the femora of prehistoric races. Patella. — Cases of congenital absence of the patella have been recorded. F. C. Kempson {Journ. Anat. and Physiol., vol. xxxvi.) has recently drawn attention to the condition described as emargination of the patella. In specimens displaying this appearance the margin of the bones is concave from a j)oint about half an inch to the oliter side of the middle line, to a jjoint half-way down the outer margin of the bone, here there is usually a pointed sj^ine directed uja wards and outwards. The condition ajspears to be associated with the insertion of the tendon of the vastus lateralis. G. Joachimstal {Archiv u. Atlas der nomalen und patholo- gischen Anatomie in typischen R'dntgenhildern, Bd. 8) figures a case in which on both sides the patella was double in an adult, the lower and much the smaller portion was embedded in the ligamentum patellae. Tibia. — The tibia is often unduly laterally compressed, leading to an increase in its antero-jjosterior diameter as compared with its transverse width. This condition is more commonly met with in the bones of j)rehistoric and savage races than in modern Europeans. Attention was first directed to this particular form by Busk, who named the condition platyknemia. The general appearance of such tibiae resembles that seen in the apes, and depends on an excejational development of the tibialis posterior muscle, though, as Manouvrier has pointed out, in apes this is associated with the direct action of the muscle on the foot, as in climbing, whereas in man, as a consequence of the bipedal mode of progression, the muscle is employed in an inverse sense, viz. by steadying the tibia on the foot, and thus providing a fixed base on which the femur can move. This explanation, however, is disputed by Derry {Journ. Anat. and, Phys., vol. xli. p. 123). Such jalatyknemic tibiae are occasionally met Avith in the more highly ciAdlised races, and are, according to Manouvrier, associated with habits of great activity among the inhabitants of rough and mountainous districts. Another interesting condition is one in which the upper extremity is more strongly recurved than is usuaL This retroversion of the head of the tibia was at one time supposed to rejDresent an intermediate condition in Avhich the knee could not be fully extended so as to bring the axis of the leg in line with the thigh ; but such oj^inion has now been upset by the researches of ManouAa'ier, Avho claims that it is the outcome of a habit not iincommon amongst peasants and countrymen, viz. that of Avalking habitually with the knees slightly bent. Habitual posture also leaves its impress on the form of the tibia, and in races in which the use of the chair is unknown, the extreme degree of flexion of the knee and ankle necessitated by the adoption of the squatting position as an attitude of habitual rest is associated Avith an increase in the convexity of the lateral condylic surface, and the aj^pearance, not infrequently, of a pressure facet on the anterior border of the lower extremity, Avhicli rests in that position on the neck of the talus. Cases of congenital absence of the tibia ha\'e been frequently described, amongst the most recent being those recorded Ijy Clutton, Joachimsthal, Bland-Sutton, and Waitz. Fibula. — The filjula may be ridged and grooved in a remarkable manner, as is the case in many bones of prehistoric races. This is probably associated with a greater or perhaps more active develoi>ment of tlie muscles attached to it. The superior articular facet varies much in size. Bennett {Dublin Journ. Med. Sc, Aug. 1891) records a case in Avhich it was doul^le, and also notes the occurrence of specimens in which it Avas absent and in which the head of the bone did not reach as high as the lateral condyle of the tibia. Many instances of partial or complete absence of the bone have been published. (Leffebre Contribution h I'dtude de I'absence cong6nitale du f&ron^, Lille, 1895.) Talus or Astragalus. — The anterior is sometimes separated from the middle calcanean facet by a non-articular furrow. The posterior lateral tubercle, often largely developed, is occasionally (2-6 per cent) a separate ossicle forming what is known as the os trigonum (Bardeleben) ; or it may be united to the body of the astragalus by a distinct synchondrosis. A SEKTAL HOMOLOGIES OF THE VERTEBE^. xiii smooth articular surface may occasionally be found on the medial side of the upper surface of the neck. This is a pressure facet dependent on the frequent use of the ankle-joint in a condition of extreme flexion, and is caused by the opi:)Osition of the bone against the anterior edge of the lower end of the tibia. The form of the bone at birth difi'ers from that of the adult in that the inward splay of the neck on the body is more pronounced, forming on an average an angle of 35° as compared with a mean of 12" in the adult ; moreover, the articular surfece for the medial malleolus extends forwards along the medial side of the neck, and to some extent overruns its upper surface. This is doubtless a consequence of the inverted position of the foot maintained by the foetus during intrauterine life. In these respects the foetal astragalus conforms to the anthro^^oid type. For a detailed study of the varieties of this bone, see R. B. S. Sewell {Journ. Anat. and Physiol., vol. xxxviii.) Calcaneus. — The peroneal tubercle is occasionally unduly prominent, constituting the sub- malleolar apophysis of Hyrtl, and cases are recorded of the calcaneus articulating with the navicular (Morestin, H., Bull, de la Soc. Anat. de Paris, 1894, ser. v. t. 8, n. 24, p. 798 ; and Petrini, Atti del XL Congr. Med. Internaz. Roma, 1894, vol. ii., "Anat." p. 71). Pfitzner {Moriiho- logische Arheiten, vol. vi. p. 245) also records the separation of the sustentaculum tali to form an OS sustentacixli. (See also P. P. Laidlaw, Journ. Anat. and Physiol., vol. xxxviii. p. 133.) Navicular or Scaphoid. — According to Manners Smith this bone displays more variety ol form than any other of the tarsal bones. He accounts for this both on morjihological and mechanical grounds. He regards the tubercle as probably of threefold origin, an apojjhj^sial, an epii^hysial, and a sesamoid element, the latter being the so-called sesamoid bone in the tendon of the tibialis posticus. Cases are recorded where the tubercle has formed an independent ossicle. Cuneiform Bones. — Numerous cases of division of the first cuneiform bone into dorsal and plantar parts liave been recorded ; the frequent division of its metatarsal articular facet is no doubt correlated with this anomalous condition. T. Dwiglit has described {Anat. Anz., vol. xx. IX 465) in two instances the occurrence of an Os Intercuueiforme. The ossicle so named lies on the dorsum of the foot at the proxiuial end of the line of articulation between the first and second cuneiform bones. Cuboid. — Blandin has recorded a case of division of the cuboid. Occasionally there is a facet on the lateral surface of the bone for articulation with the tuberosity of the Vth metatarsal (Manners Smith). Tarsus as a Whole. — Increase in the number of the tarsal elements may be due to the occurrence of division of either the first cuneiform or the cuboid bone, or to the occasional presence of an os trigonum. Cases of separation of the tuberosity of the navicular bone have been recorded, and instances of su23ernumerary ossicles between the first cuneiform and second metatarsal bone have been noted. Stieda mentions the occurrence of a small ossicle in connexion with the articular surface on the fore and upper jjart of the os calcis, and Pfitzner notes the occurrence of an os sustentacula For further information on the variations of the skeleton of the foot, see Pfitzner {Morphologische Arheiten, vol. vi. p. 245). The jjossibility of an injury having been the cause of the occurrence of some of these so-called supernumerary ossicles must not be overlooked. The use of the Rontgen rays has proved that accidents of this kind are much more frec[uent than was at first supposed. The reduction in the number of the tarsus is clue to the osseous union of adjacent bones. In many instances this is undoubtedly pathological, but cases have been noticed (Lebouccj) of fusion of the cartilaginous elements of the calcaneus and talus, and the calcaneus and navicular in foetuses of the third month. Metatarsal Bones. — Several instances of sej^aration of the tuberosity of the fifth metatarsal (os Vesaleanum) have been recorded, whilst numerous examples of an os intermetatarsum between the bases of the first and second metatarsal bones have been I'ecorded by Gruber and others. Tae tubercle on the base of the first metatarsal for the attachment of the peronnsus longus tendon is occasionally met with as a separate ossicle. An epijihysis over the spot where the tuberosity of the Y. metatarsal rests on the ground has been described (Kirchner, Archiv. Klin. Chir., B 80). Phalanges. — It is not uncommon to meet with fusion of the second and third phalanges, particularly in the fifth, less frequently in the fourth, and occasionally in the second and third toes. The union of the phalangeal elements has been observed in the foetus as well as the adult (Pfitzner). The proportionate length of the jjhalanges varies much ; in some cases the ungual jahalanges are of fair size, the bones of the second row being mere nodules, whilst in other instances the reduction in size of the terminal phalanges is most marked. APPENDIX a SERIAL ] HOMOLOGIES OF THE VERTEBRA. It is a self-evident fact that the vertebral column consists of a number of segments or verte- brte all possessing some characters in common. These vertebrse or segments undergo modifications according to the region they occupy and the functions they are called upon to serve, so that 17 *& XIV OSTEOLOGY. CERVICAL True traxsver I'ROCESS — Vertebrarterial FORAMEN Costal process Xeuro-central suture Transverse PROCESS True trans- verse PROCESS Costal process Rib LUMBAR Accessory process their correspondence and identity is thereby obscured. There is no difl&culty in recognising the homology of the bodies and neural arches throughout the column. According to some anatomists the neural arch is the more primitive element in the formation of a vertebra, whilst others hold that the centra are the foundation of the column. Be that as it may, we find that in the higher vertebrates, at least, the bodies are the parts which most persist. They are, however, subject to modifications dependent on their fusion with one another. This occurs in the cervical part of the column where the centrum of the first cervical or atlas vertebra has for functional reasons become fused with the body of the second or axis vertebra to form the odon- toid process of that segment. For similar reasons, and in association with the union of the girdle of the hind-limb with the column, the bodies of the vertebrae which correspond to the sacral segment become fused together to form a solid mass. In the terminal por- tion of the caudal region the centra ■R[B-/^ "V — \ V^ /-^ J-X^~\ Transverse alone represent the vertebral seg- process ments. As regards the neural arch, this in man Toecomes deficient in the lower sacral region, and absent altogether in the lower coccygeal segments. The spinous processes are absent in the case of the first cervical, lower sacral, and all the coccygeal vertebrae, and display characteristic differences in the cervical, thoracic, and lumbar regions, which have been already described. The articular processes (zygajjophyses) are secondary de- velopments, and display great diversity of form, determined by their functional requirements. It is noteworthy that, in the case of the upper two cervical vertebrae, they are so disposed as to lie in front of the foramina of exit of the upper two spinal nerves, and by this arrangement the weight of the head is transmitted to the solid column formed by the vertebral bodies, and not on to the series of neiiral arches. It is in regard to the homology of the transverse pro- cesses, so called, that most difficulty arises. In the thoracic region they can best be studied in their simplest form ; here the ribs — which Gegenbauer regards as a dift'erentiation from the inferior or luemal arches, in opposition to the view advanced by others that they are a secondary development from the fibrous intermuscular septa— articulate with the transverse processes and bodies of the thoracic vertebrae through the agency of the tuljercular (diapophyse.s) and capitular (parapophyses) processes respectively, the latter being placed, strictly speaking, on the neural arch behind the line of the neuro-central synchondrosis. An interval is thus left between the neck of the ril) and the front of the transverse process ; this forms an arterial passage which corresponds to the vertebrarterial canal in the transverse Costo-traxsverse fora- i MEN (vertebrarterial) ] Neuro-central suture Accessory tubercle Costal elejiext (lumbarial) OCCASIOXAL VERTE brarterial foramen Neuro-central suture Transverse process' Costal element (rib) SACRAL Costal element Occasional foramen (vertebrarterial) I N'euro-central suture Transverse processes Fig. 19/ Costal elements A B Diagram to illustrate the Homologous Parts of the VERTEBKiE. the neural arch and its processes, red ; the costal A, from above. B, from the side. The centra are coloured purple elements, lilue. MEASUEEMENTS AND INDICES. xv processes of the cervical vertebrie, the anterior Itar of which is homologous with the head and tubercle of the tlioracic rib, whilst the posterior part lies in series with the thoracic transverse process. These homologies are further enqjhasised by the fact that in the case of the seventh cervical vertebra the anterior limb of the so-called transverse process is developed from an independent ossific centre, which occasionally persists in an indejjendent form as a cervical rib. In the lumbar region the lateral or transverse process is serially homologous with the thoracic ribs, though here, owing to the coalescence of the contiguous parts, there is no arterial channel between the rib element and the true transverse process, which is represented by the accessory processes (anajjophyses), placed posteriorly at the root of the so-called transverse process of human anatomy. Support is given to this view by the presence of a distinct costal element in connexion with the transverse process of the first lumbar vertebra, which accounts for the occasional formation of a supernumerary rib in this region. The cases of foramina in the transverse processes of the lumbar vertebrae (see p. vi) are also noteworthy as supporting this view. In the sacrum the lateral mass of the bone is made up of combined transverse and costal elements, with only very exceptionally an intervening arterial channel (see p. vi). In the case of the upper three sacral segments the costal elements are largely developed, assist in sujjporting the ilia, and are called the true sacral vertebrae ; whilst the lower sacral segments, which are not in contact with the ilia, are referred to as the pseudo-sacral vertebrte. The anterior arch of the atlas vertebra is, according to Froriep, developed from a hypochordal strip of cartilage (hypochordal spange). APPENDIX D. MEASUREMENTS AND INDICES EMPLOYED IN PHYSICAL ANTHROPOLOGY. (1) Craniometry. The various grouj)s of mankind display in their physical attributes certain features which are more or less characteristic of the stock to which they belong. Craniology deals with these differences so far as they affect the skulL The method whereby these differences are recorded involves the accurate measurement of the skull in most of its details. Such procedure is included under the term craniometry. Here only the outlines of the subject are briefly referred to ; for such as desire fuller information on the subject, the works of Broca, Topinard, Flower, and Turner may be consulted. The races of man display great variations in regard to the size of the skull. Apart altogether from individual differences and the proportion of head-size to body -height, it may be generally assumed that the size of the skull in the more highly civilised races is much in excess of that displayed in lower types. The size of the head is intimately correlated with the develop- ment of the brain. By measuring the capacity of that part of the skull occupied by the encephalon, we are enabled to form some estimate of the size of the brain. The cranial capacity is determined by filling the cranial cavity with some suitable material and then taking the cubage of its contents. Various methods are employed, each of which has its advantage. The use of fluids, which of course would be the most accurate, is rendered impracticable, without special precautions, owing to the fact that the macerated skull is pierced by so many foramina. As a matter of practice, it is found that leaden shot, glass beads, or seeds of various sorts are the most serviceable. The results obtained display a considerable range of variation. For purposes of classification and comi^arison, skulls are grouped according to their cranial capacity into the following varieties : — Microcephalic skulls are those with a capacity below 1350 cc, and include such well-known races as Andamanese, Veddahs, Australians, Bushmen, Tasmanians, etc. Mesocephalic skulls range from 1350 cc. to 1450 cc, and embrace examples of the following vai'ieties : American Indians, Chinese, some African Negroes. Megacephalic skulls are those with a capacity over 1450 cc, and are most commonly met with in the more highly civilised races : Mixed Europeans, Japanese, etc. Apart from its size, the form of the cranium has been regarded as an important factor in the classification of skulls ; though whether these differences in shape have not been unduly em- phasised in the past is open to question. The relation of the breadth to the length of the skull is expressed by means of the cephalic index which records the proportion of the maximum breadth to the maximum length of the skull, assuming the latter equal 100, or — Max. breadth x 100 ~ , , . . , ,^ ^, y, =Cepnahc index. Max. length The results are classified into three groups : — 1. Dolichocephalic, with an index below 75 : Australians, Kaffirs, Zulus, Eskimo, Fijians. 2. Mesaticephalic, ranging from 75 to 80 : Europeans (mixed), Chinese, Polynesians (mixed). 3. Brachycephalic, with an index over 80 : Malays, Burmese, American Indians, Anda- XVI OSTEOLOGY. In order to provide for uniformity in tlie results of different observers, some system is neces- sary by which the A'arious 25oints from which the measurements are taken must correspond. Whilst there is much difference in the yalne of the measurements insisted on by individual anatomists, all agree in endeavouring to select such jwints on the skull as may be readily deter- mined, and which have a fairly fixed anatomical position. The more important of these " fixed points " are included in the subjoined table : — Bregma Stephanion Obelion Pterion Lambda Maximum occipital \ \ POINT \ \, ASTERIOK Supra-auricular POINT Nasion Dacryon Khinion Jugal point Akanthion Pbosthion (alveolar point) POQONION Nasion. — The middle of the naso-frontal suture. Grlabella. — A point midway between the two superciliary ridges. Ophryon. — The central point of the narrowest transverse diameter of the forehead, measured from one temporal line to the other. Inion. — The external occipital protuberance. Maximum Occipital Point. — The point on the squamous jjart of the occipital in the sagittal plane most distant from the glabella. OpistMon. — The middle of the posterior margin of the foramen magnum. Basion. — The middle of the anterior margin of the foramen magnum. Bregma. — The point of junction of the coronal and sagittal sutures. Ehinion. — The most i^rominent point at which the nasal bones touch one another. Alveolar Point or Prosthion. — The centre of the anterior margin of the upper alveolar margin. Subnasal Point. — The middle of the inferior border of the anterior nasal aperture at the centre of the nasal spine. Akanthion. — The most i)rominent jsoint on the nasal spine. Vertex. — The summit of the cranial vault. Obelion. — A j^oint over the sagittal suture, on a line with the parietal foramina. Lambda.. — The meeting-point of the sagittal and lambdoid sutures. Pterion. — The region of the antero-lateral fontanelle where the angles of the frontal, parietal, squamous part of tlie temporal, and alisphenoid lie in relation to one another. As a rule, the sutures are arranged like the letter H , the parietal and alisijhenoid separating the frontal from the squamous temi^oral. In other cases the form of the suture is like an X ; wliilst in a third variety the frontal and squamous part of the temporal articulate with eacli other, thus sej^arating the alisphenoid from the parietal. Asterion is the region of the jjostero-lateral fontanelle where the lambdoid, jjarieto-mastoid, and occipito-mastoid sutures meet. Stephanion.— Tlie point where the coronal suture crosses the temporal crest. Dacryon. — The point where the vertical lacrimo-maxillary suture meets tlie fronto-nasal suture at the inner angle of the orbit. Jugal Point. — Corresponds to tlie angle between the vertical border and the margin of the temporal process of the zygomatic bone. Supra-auricular Point.— A point immediately above the middle of the orifice of the external auditory meatus close to the edge of the posterior root of the zygoma. Gon-ion. — The outer side of the angle of the maxilla. Pogonion. — The most pi'ominent point of the chin as represented on the mandible. MEASUREMENTS AND INDICES. xvii The measurements of the length of the skull may be taken between a variety of points — the nasion, glabella, or ophryon in front, and the inion or maximum occipital point behind. Or the maximum length alone may be taken without reference to any fixed points. In all cases it is better to state larecisely where the measurement is taken. The maximum breadth of the head is very variable as regards its position ; it is advisal^le to note whether it occurs above or below the parieto-squamosal suture. The inter-relation of these measurements as expressed by the cephalic index has been already referred to. The width of the head may also be measured from one asterion to tlie other, biasterionic width, or by taking the bistephanic diameter. The height of the cranium is usually ascertained by measuring the distance from the basion to tlie bregma. The relation of the height to the length may be expressed by the height or vertical index, thus — Height X 100 ^ .. ... — ~ -, — = Vertical index. Length Skulls are classified in accordance with the relations of length and height as follows : — Tapeinocephalic index below 72. Chamaecephalic index up to 70. Metriocephalic index between 72 and 77. Orthocephalic index from 701 to 75. Akrocephalic index above 77 (Turner). Hypsicephalic index 75'1 and upwards (Kollmann, Ranke, and Virchow). The horizontal circumference of the cranium, which ranges from 450 mm. to 550 mm., is measured around a plane cutting the glabella or ophryon anteriorly, and the maximum occipital point posteriorly. The longitudinal arc is measured from the nasion in front to the opisthion behind ; if to this be added the basi-nasal length and the distance between the basion and the opisthion, we have a record of the vertico-medial circumference of the cranium. This may further be divided by measuring the lengths of the frontal, j)arietal, and occipital portions of the superior longitudinal arc. In this way the relative proportions of these bones may be expressed. The measureuients of the skeleton of the face are more complex, but, on the whole, of greater value than the measurements of the cranium. It is in the face that the characteristic features of race are best observed, and it is here that osseous structure most accurately records the form and proportions of the living. The form of the face varies, like that of the cranium, in the relative proportions of its length and breadth. Generally sj^eaking, a dolichocephalic cranium is associated with a long face, whilst the brachycephalic type of head is correlated with a rounder and shorter face. This rule, how- ever, is not universal, and there are many exceptions to it. The determination of the facial index varies according to whether the measurements are made with or without the mandible in position. In the former case the length is measured from the ojihryon or nasion above to the mental tubercle below, and compared with the maximum bizygomatic width. This is referred to as the total facial index, and is obtained by the formula — Ophryo-m^ntal l^igthxlOO^^^^^j ^^^.^^ .^^^^ Uizygomatic width More usually, however, owing to the loss of the lower jaw, the proportions of the face are expressed by the superior facial index. This is determined by comparing the ophryo-alveolar or naso-alveolar length with the bizygomatic width, thus — Ophryo-alveolar length x 100 „ . „.,.■, — £ — ^. -■ ?itt = Superior facial index. Jjizygomatic width The terms dolichofacial or leptoprosope and brachyfacial or chamceprosope have been employed to express the differences thus recorded. Uniformity in these measurements, however, is far from complete since many anthropologists compare the width with the length = 100. The proportion of the face-width to the width of the calvaria is roughly expressed by the use of the terms cryptozygous and phsenozygous as applied to the skull. In the former case the zygomatic arches are concealed, when the skull is viewed from above, by the overhanging and projection of the sides of the cranial box ; in the latter instance, owing to the narrowTiess of the calvaria, the zygomatic arches are clearly visible. The projection of the face, so characteristic of certain races (Negroes for example), may be estimated on the living by measuring the angle formed by two straight lines, the one passing from the middle of the external auditory meatus to the lower margin of the septum of the nose ; the other drawn from the most prominent part of the forehead above to touch the incisor teeth below. The angle formed by the intersection of these two lines is called the facial angle (Camper), and ranges from 62° to 85°. The smaller angle is characteristic of a muzzle-like projection of the lower part of the face. The larger angle is the concomitant of a more vertical profile. The degree of projection of the upper jaw in the macerated cranium is most commonly expressed by employing the gnathic or alveolar index of Flower. This records the relative proportions of the basi-alveolar and basi-nasal lengths, the latter being regarded as = 100, thus — Basi-alveolar length x 100 _ . , . . , ¥s -■ T-T-^ — 1 = Gnathic index. Easi-nasal length xviii OSTEOLOGY. The results are conveniently grouped into three classes : — Orthognathous, index below 98 : including mixed Europeans, ancient Egyptians, etc. Mesognathous, index from 98 to 103 : Chinese, Japanese, Eskimo, Polynesians (mixed). Prognathous, index above 103 : Tasmanians, Australians, Melanesians, various African Negroes. Unfortunately, however, little reliance can be placed on the results obtained by this method, since it takes no account of the proportion of the third or facial side of the gnathic triangle. For a further discussion of this matter see Thomson and Maclver, Races of the Thebaid (Oxford : Clarendon Press, 1905). Tlie form of the nasal aperture in the macerated skull is of much value from an ethnic standjioint, as it is so intimately associated with the shape of the nose in the living. The greatest width of the nasal aperture is compared with the nasal height (measured from thenasion to the lower border of the nasal aperture) and the nasal index is thus determined : — Nasal width x 100 „ , . , — ^r:,^ — ,-1 ^^r-. — = Nasal index. Nasal heiglit Skulls are — Leptorhine, with a nasal index below 48 : as in mixed Europeans, ancient Egyptians, American Indians, etc. Mesorhine, with an index ranging from 48 to 53 : as in Chinese, Japanese, Malays, etc. Platyrhine, with an index above 53 : as in Australians, Negroes, Kafl&rs, Zulus, etc. The form of the orbit varies considerably in different races, but is of much less value from the standpoint of classification. The orbital index expresses the proportion of the orbital height to the orbital width, and is obtained by the following formula : — Orbital height x 100 Orbital width = Orbital index. The orbital height is the distance between the ujaper and lower margins of the orbit at the middle ; whilst the orbital width is measured from a point where the ridge which forms the posterior boundary of the lacrimal groove meets the fron to - lacrimal suture (Flower), or from the dacryon (Broca) to the most distant point from these on the anterior edge of the outer border of the orbit. The form of the orbital aperture is referred to as — Megaseme, if the index be over 89 ; Mesoseme, if the index be between 89 and 84 ; Microseme, if the index be below 84. The variations met with in the form of the palate and dentary arcade may be expressed by the palato-maxillary index of Flower. The length is measured from the alveolar point to a line drawn across the hinder borders of the maxillary bones, whilst the width is taken between the outer borders of the alveolar arch immediately above the middle of the second molar tooth. To obtain the index, the following formula is employed : — Palato-maxillary width x 100 ^ , . .,, . , — V, 1 . 11 1 .1 = Palato-maxillary index. Palato-maxillary length For purposes of classification Turner has introduced the following terms : — Dolichuranic, index below 110. Mesuranic, index between 110 and 115. Brachyuranic, index above 115. As is elsewhere stated (p. 108), the size of the teeth has an important influence on the architecture of the skull. Considered from a racial standpoint, the relative size of the teeth to the length of the cranio-facial axis has been found by Flower to be a character of much value. The dental length is taken by measuring the distance between the anterior surface of the first jjre- molar and the posterior surface of tlie tliird molar of the upper jaw. To obtain the dental index the followiug formula is used : — Dental length x 100 Basi-nasal length = Dental index. Following the convenient method of division adopted with other indices, the dental indices may be divided into three series, called respectively — Microdont, index below 42 : including the so-called Caucasian or white races. Mesodont, index between 42 and 44 : including the Mongolian or yellow races. Megadont, index above 44 : comprising the black races, including the Australians. Many complicated instruments have been devised to take the various measuraments required, but for all practical purposes the calipers designed by Flower or the compas glissihe of Broca are sufficient. As an aid to calculating the indices, the tables published in the Osteological Catalogue of the Royal College of Surgeons of England, Part I., Man.; Index- Tahellen zuin Anthropometrischen Gebrauche, C. M. Furst, Jena, 1902 ; or the index calculator invented by Dr. Waterston will be found of much service in saving time. MEASUEEMENTS AND INDICES. xix (2) Indices and Measurements of other Parts of the Skeleton 111 addition to the indices employed to express the proportions of the cranial measurements, there are otliers similarly made use of to convey an idea of the proportions of different parts of the skeleton. Of these the following may be mentioned as those in most common use : — Scapula. — At birth the form of the human scapula more closely resembles the mammalian tyjje in tliat its breadth, measured from the glenoid margin to the vertebral border, is greater in comparison with its length than in the adult. This proportion is expressed as follows : — Breadth from glenoid margin to vertebral border x 100 „ i • •. T ?c-^ j ° w • r • ^ = Scapular index. Length irom medial to interior angle The index ranges from 87 in African pygmies, which therefore have proportionately broader scapidaj, to 61 in Eskimos. The average European index is about 65. Innominate Bone. — The relation of the breadth of this bone to its height is computed as follows : — Iliac breadth x 100 _ ■ j. ■ , T ,. — ^^^ — i — r-^i— = Innominate index. Ischio-iliac height Man as compared with the apes is distinguished by possessing proportionately broader and shorter innominate bones. The index in man ranges from 74 to 90. Pelvis. — The form of the human pelvis is characterised by an increased proi^ortionate width and a reduced proportionate height or length. The relation of these diameters is expressed by the formula : — Ischio-iliac height X 100 -r. i • i. j^j.-,. -,. ■ ^.J. ■ :, ^ 7— TT — j^i . ^ Tu ? — V ftt — T- T = Pelvic breadth-height index. Greatest breadth between the outer lips ot the iliac crests The average index for white races is 73. Pelvic Cavity. — The measurements usually taken are those of the brim. In man there is a proportionate increase in the transverse diameter as compared with lower forms : — Antero-posterior diameter (conjugate) from mid-point of sacral promontory to the posterior margin of pubic svmphvsis x 100 .r. i • , • ■ , ^ — ——^ ■ ^ 1 , f ^P — ^^-^. rr- = Pelvic or brim index. Greatest transverse width between ino-peetmeai lines Turner has classified tlie indices into three groups : — Dolichopellic, index above 95 : Australians, Bushmen, Kaflfirs. Mesatipellic, index between 90-95 : Xegroes, Tasmanians, New Caledonians. Platypellic, index below 90 : Europeans and Mongolians generally. Vertebral Column. — A characteristic feature of man's vertebral column is the pronounced lumbar curve associated with the erect posture in the living. Apart from the consideration of the interposition of the intervertebral discs between the segments, the bodies of the lumbar vertebrae influence and react on the curve by exhibiting differences in their anterior and pos- terior vertical diameters. Advantage has been taken of this to endeavour to reconstruct the lumbar curve from the dried and macerated bones, but it must be borne in mind that habitual posture or increased range of movements may yield results which are possibly misleading. Thus there is reason for believing that the squatting position, when habitually adopted, may give rise to a compression of the anterior parts of the bodies of the vertebrse which it might be assumed was associated with an absence of or flattening of the lumbar curve, which in fact did not exist during life. The quality of the ciu've is estimated from the macerated bones by an index which is com- puted as follows : — Sum of posterior vertical diameters of the bodies of five lumbar A'ertebrse x 100 _ p , , , . , Sum of anterior vertical diameters of the bodies of five lumbar vertebrae The results are classified as follows : — Kurtorachic, index below 98, displaying a forward convexity : includes Europeans generally, Chinese. Orthorachic, index between 98 and 102, column practically straight : includes examples of Eskimo and Maori. Koilorachic, index above 102, displaying a backward concavity : includes Australians, Xegroes, Bushmen, and Andamanese. Sacrum. — Man's sacrum is characterised by its great breadth in proportion to its length. These relations are expressed as follows : — Greatest breadth of base of sacrum x 100 Length from middle of promontory to middle of anterior inferior border of V. sacral vertebrae = Sacral index. XX OSTEOLOGY. The diverse forms are groiij^ed as follows : — Dolichohieric, index below 100, sacra longer than broad : includes Australians, Tasmanians, Buslimen, Hottentots, Kaffirs, and Andamanese. Platyhieric, index above 100, sacra broader tban long : includes Europeans, Negroes, Hindoos, Nortli and Soutli American Indians. Limb Bones. — The proportionate length of the limb bones to each other and to the body- height is of i:)ractical interest. It is a matter of common knowledge that the forearms of Negroes are ijroportionately longer than those of Europeans. Great differences, too, are met with in the absolute and proportionate length of the lower limbs, nor must the relation of these to body- height be overlooked. Aii enumeration of the more important of these indices, and the manner of their comjJutation, will suffice. The proportion of the length of the radius to the length of the humerus is expressed as follows : — Length of radius x 100 „ j- i. i • j -r ^ ^-, — n-T =Kaaio-huineral index. Length oi humerus Sub-divided into three groups : — Brachykerkic, index less than 75 : includes Europeans, Lapjjs, Eskimo. Mesatikerkic, index between 75-80 : Chinese, Australians, Polynesians, Negroes. Dolichokerkic, index above 80 : Andamanese, Negritoes and Fuegians, Bonindae in general The proportion of the length of the tibia to the femur is computed by the formula — Length of tibia from surface of condyle to articular surface for astragalus x 100 m-u • if i • j § -^^^^. f — -= — jr-c = Tibio-femoral index. Oblique length oi lemur Sub-divided into two groups : — Brachyknemic, index 82 and under : includes Europeans and Mongolians generally. Dolichoknemic, index 83 and over : includes Australians, Negroes, Negritoes, American- Indians. The proportion of the length of the upper limb to that of the lower limb is obtained thus :^ Lengths of humerus + radius x 100 ^ i. i. i - j ^ = ;n T^T-- = Intermembral index. Lengths oi lemur + tibia A comparison between the relative lengths of the upper segments of the limbs is obtained by the following formula : — Length of humerus x 100 ^t j? i • j — Of = — jn. = Humero-iemoral index. Length ot lemur Platymeria (see -p. xii.) — The amount of compression of the femur is estimated as follows : — Sagittal diameter of shaft immediately below lesser trochanter x 100 _ p. tvmpric index Transverse diameter of shaft immediately below trochanter minor Platyknemia (see p. xii.) — The degree of compression of the tibia is estimated by the formula— Tiansverse diameter of shaft at level of nutrient foramen X 100 t,, , , ■ • j„„ . T-- ?— ^i — ? 1 :, — T' ■■ T- = Platyknemic index. Antero-posterior diameter oi shait at level oi nutrient toramen The index ranges from 60 in a Maori tibia to 80 to 108 in modern French tibiaj. For further and more detailed information relating to the various measurements and indices employed by the jjhysical anthropologist, the reader is referred to Topinard's Elements d'Anthro- polofjie ; Sir W. Turner's Challenger Memoirs, Part 47, vol. xvi. ; and Duckworth's Morphology and Anthropology. APPENDIX E. DEVELOPMENT OF THE CHONDRO-CRANIUM AND MORPHOLOGY OF THE SKULL. As has been already stated (p. 24), the chorda dorsalis extends forwards to a point immediately beneath the anterior end of the mid-l)rain. In front of this the head takes a bend so that the large fore-ljrain overlaps tlie anterior extremity of tlie notochord. At this stage of deveh)pment the cerebral vesicles are enclosed in a memljranous covering derived from the mesenchyme surround- ing the notocliord ; this differentiated mesodermal layer is called tlie primordial membranous CJ-aniuni. From it the meninges which invest the lirain are derived. In lower vertebrates this memljranous capsule becomes converted into a thick-walled cartilaginous envelope, the j)rimordial cartilaginous cranium. In mammals, liowever, only tlie basal part of this capsule becomes chondrified, the roof and part of the sides remaining membranous. In considering the cliond- rification of the skull in mammals, it must be noted that jmrt only of the base is traversed by the MOKPHOLOGY OF THE SKULL. XXI notochord, viz. that portion wliicli extends from the foramen magnum to the doi-sum selLx' of the sphenoid. It is, therefore, conveniently divided into two parts— one posterior, surrounding the notochord, and hence called cliordal, and one in front, into which the notochord does not extend, and hence termed prechordal. These correspond respectively to the vertebral and evertebral regions of Gegenbauer. In the generalised type, a j^air of elongated cartilages called the para- chordal cartilages appear on either side of the chorda in the chordal region, similarly in the precliordal region two curved strips of cartilage named the prechordal cartilages, or the trabeculse cranii of Rathke, develop on either side of the crauio-pharyngoal canal. In the human embryo, however, this symmetrical arrangement has not hitherto been observed. Taking the i^lace of the parachordal cartilages is a mass of cartilage called the basi-cranial or occipital plate, which partly encloses tlie chorda, and extends as far forwards as the dorsum selhe ; from this by subsequent ossification are formed the basilar process of the occipital bone and the dorsum sellaj of the sphenoid. By backward extension from the occipital plate, on either side and around the foramen magnum, the cartilaginous exoccipitals and supraoccipitals are also formed. These, Froriep and others regard as the fused neural arches of four rudimentary verteljra?. In the prechoi-dal region in man the trabeculfe cranii are replaced by a median sheet of Crista Galli Pars ethmoidal i \ , Lamina cribrosa Orbito-sphenoid Sphenoidal fissure 7~^5* ^- ' >»^ Alisphenoid nj 5~ jg^ >, > Carotid canal — ~ Meatus auditoriu internus Subarcuate fossa Jugular foramen Canalis hypoglossi Foramen magnum \ \ Orbital portion of orbito-sphenoid Optic foramen ( ilivary process \ I r~T ^ella turcica y \- yA — Uorsum sells - ^' ' . I 'ars petrosa niperior semicircular canal / Pars mastoidea Supra-occipital Occipital fontanelle Fig. 199. — View of the Chondro-Craxidm of a Human Fcetus 5 cm. in length from Vertex to Coccyx (about the middle of the third month) ; the cartilage is coloured blue. The line to the right of the di-awing shows the actual size. cartilage, the ethmoidal plate, which is cleft posteriorly for the cranio - pharyngeal canal. Posteriorly this unites with the basi-cranial plate, thus enclosing the cranio-pharyngeal canal, the lumen of which is subsequently filled up to form the floor of the pituitary fossa in which rests the pituitary body. Owing to the presence of the nasal capsules, the forepart of the ethmoidal plate becomes differentiated into an ethmo -vomerine region, from the medial portion of which the nasal septum and its associated cartilages is derived, whilst from the lateral parts are developed the lateral masses of the ethmoid, the ethiuo-turbinals, the maxillo-turbinals, and the alar cartilages of the nose. Posteriorly the medial portion of the ethmoidal plate forms the presphenoid, whilst as lateral expansions appear the orbito-sphenoids and alisphenoids, both of which assist in com- pleting the orbital cavity for the lodgment of the eyeball. The membranous ear capsules which lie lateral to the parachordal cartilages become chondrified and form the cartilaginous ear capsules. These soon miite with the lateral aspects of the basilar plate, but are separated in front from the cartilaginous alisphenoid of the ethmoidal plate by a membranous interval, which is subsequently occupied by the squamosal, a bone of dermic origin. This disappearance of the cartilage under the squamosal was regarded by Parker as the diagnostic mark of the mammalian chondro-cranium. xxii OSTEOLOGY. The various foramina met with in the cranial base are formed either as clefts in the line of union of the several caitilaginous elements, or through inclusion by means of bridging processes derived from these same elements. From tlie veiitral surface of this cartilaginous platform — formed, as described, by the union of the trabeculje, parachordal cartilages, and cartilaginous ear capsules — is suspended the cartilaginous framework of the visceral arches, which play so important a part in the develop- ment of the face, an account of which is elsewhere given (p. 35). A consideration of the facts of comparative anatomy and embryology appears to justify the assumption that the mammalian skull is of twofold origin — that, in fact, it is composed of two envelopes, an outer and an inner, primarily distinct, but which in the process of evolution have become intimately fused together. The inner, called the primordial skull, is that which has just been described, and consists of the chondro-cranium and the branchial skeleton. The outer, which is of dermic origin, includes the bones of the cranial vault and face which are developed in membrane. This secondary skull, which first appears in higher fishes as ossified dermal plates overlying the primary skull, acquires a great importance in the mammalia, as owing to the expansion of the brain and the progressive reduction of the chondro-cranium, these dermal bones become engrafted on and incorporated Avith the ^^rimordial skull, and act as covering bones to the cavities of the cranium and face ; for it may be well to point out that these dermal or membrane bones are not necessarily external in position, as over the cranial vault, but also develop in the tissues underlying the mucous membrane of the cavities of the face. Advantage is taken of this difference in the mode of develojjment of the bones of the skull to classify them according to their origin into cartilage or primordial bones, and membrane or secondary bones. These differences in the growth of the bone must not be too much insisted on in determining the homologies of the bones of the skull, as it is now generally recognised that all bone is of membranous origin, and that whilst in some cases cartilage may become calcified, it never undergoes conversion into true bone, but is replaced by ossific deposit derived from a membranous source. In the subsequent growth of the skull, j)arts of the cartilaginous cranium persist as the septal and alar cartilages of the nose, whilst for a considerable period the basi- sphenoid and basi-occiioital are still united by cartilage. The cartilage also which blocks the foramen lacerum may be regarded as a remnant of the chondro-cranium. Fontanelles. — Till two years after birth there are membranous intervals between the edges and angles of the Ijones of the cranial vault. These are termed the fontanelles. Normally they are six in number, and correspond in the adiilt to the position of the bregma and lambda in the middle line and the pterion and asterion on either side. The anterior or bregmatic fontanelle is diamond-shaped, and corresponds to the converging angles of the parietals and two halves of the frontal l3one. The posterior fontanelle is triangular in form, and lies between the two parietals and the summit of the squamous part of the occipital. The antero-lateral fontanelle lies between the contiguous margins of the frontal, parietal, squamous part of the temporal, and great wing of the sj^henoid, whilst the postero-lateral fontanelle is situated between the adjacent borders of the jaarietal, occipital, and mastoid j)ortion of the temporal. The term occipital fontanelle is applied to a membranous interval which occurs in the foetal condition posterior to the foramen magnum, and between the lateral halves of the cartilaginous supra-occipital. Its persistence accounts for the occasional occurrence of an occipital meningocele.^ Whilst in many instances the primordial and secondary bones remain distinct in the fully- developed condition, they sometimes fuse to form complex bones, such as the temporal and .sphenoid (see pp. 119 and 126). Various theories have been advanced to account for the mode of formation of the skull. The earliest of these was called the vertebrate theory, which assumed that the cranium was built up of a series of modified vertebrae, the centra of which corresjDonded to the basi-cranial axis, whilst the neural arches were represented by the covering bones of the cranium. In view of the more recent researches regarding the composite origin of the skull above referred to, this theory was necessarily abandoned. It gave way to the suggestion of Gegenbauer that the primordial cranium has arisen by the fusion of several segments equivalent to vertebrae, the number of which he determined by noting the metameric arrangement of the cranial nerves, of which he concluded there were nine pairs, arranged much like s^jinal nerves, both as to their origin and distribution. The olfactory and ojjtic nerves, though frequently referred to as cranial nerves, are excluded, since from tlie nature of their development they are to be regarded as meta- morphosed parts of the brain itself. Gegenbauer therefore assumed that that portion of the cranial base which is traversed by the nine pairs of segmentally arranged cranial nerves must be formed Ijy the fusion of nine vertebral segments ; and as the region where the nerves escape corre.sponds to the part of the chondro-cranium traversed bj^ the notochord, he calls it the vertebral portion of the cranial base, in contradistinction to the trabecular or non-vertebral part which lies in front. This latter he regards as a new formation adapted to receive the greatly- developed brain and afl'ord protection to the organs of sight and smell. As has been pointed out by Hertwig, there is an essential difference between the development of the axial cartilaginous skeleton of the trunk and head. The former becomes segmented into distinct vertebrae alternating with intervertebral ligaments ; whilst the latter, in order to attain the rigidity necessary in this part of the skeleton, is never so divided. It follows from this that the original segmentation of the head is only expressed in three ways, viz. in the appearance of several ijrimitive segments (myotomes), in the arrangement of the cranial nerves, and in the * For further information regarding anomalous conditions of the fontanelles and tlie occurrence of Wormian or sutural ossicles, see F. Frassetto, Ann, des Sci. Nat. Zool. 8" ser. xviii. 1903. MOKPHOLOGY OF THE LIMBS. xxiii fundament of the visceral skeleton (visceral arclies). According to Froriep the mammalian occipital corresponds to the fusion of four vertebrte, and there is some reason for supposing that in some classes of vertebrates the occipital region of the primordial cranium is increased by fusion with the higher cervical segments. The form of skull characteristic of man is dependent on the large proportionate development of the cranial jaart, which contains the brain, and the reduction in size of the visceral part (face), which protects the organs of special sense. This leads to a decrease in the mass and projection of the jaws, as well as a reduction in the size of the teeth. Associated with the smaller mandible there is a feebler musculature, with a reduced area of attachment to the sides of the skull. In this wav the disappearance of the muscular crests and fosste, so characteristic of lower forms, is accounted for. At the same time the fact that the skull is poised on the summit of a vertical column, leads to important modifications in its structure. The disposition of parts is such that the occipito-vertebral articulation is so placed that the fore and hind parts of the head nearly balance each other, thus obviating the necessity for a powerful muscular and ligamentous mechanism to hold the head erect. Another noticeable feature in connexion with man's skeleton is the prolonged period during which growth may occur before maturity is reached ; this is associated with a more complete consolidation of the skull, since bones, which in lower forms remain throughout life distinct, are in man fused with each other, as exemplified in the case of the presphenoid and postsphenoid, the occipital and the interparietal, to mention one or two instances among many. It is noteworthy, however, that during ontogeny the morphological significance of these bones is clearly demonstrated by their independent ossification. The points of exit of the various cranial nerves remain remarkably constant, and in their primitive condition serve to suggest the segmental arrangement of the cartilaginous chondro- cranium already referred to. Owing to the very great modifications which the mammalian skull has undergone in the process of its evolution, it may be pointed out that the passage of the nerves through the dura mater — a derivative, the readers may be remiiided, of the primordial membranous cranium (see ante) — alone represents the primitive disposition of the nerves. Their subsequent escape through the bony base is a later and secondary development. In some cases the two, membranous or primary and the osseous or secondary foramina, correspond. In other instances the exit of the nerves through the dura mater does not coincide with the passage through the bone. Of interest in this connexion it may be pointed out that the foramina and canals which traverse the skull are either situated in the line of suture between adjacent bones or in the line of fusion of the constituent parts of which the bone pierced is made up. For example, the sphenoidal fissure is situated between the orbito and aKsphenoids ; the anterior condylic between the basi and exoccipitals ; the jugular between the petrous, basi, and exoccipital ; the optic between the orbito-sphenoid and the presphenoid ; the Vidian between the alisphenoid, internal pterygoid plate, and the lingula. APPENDIX F. MORPHOLOGY OF THE LIMBS. Development and Morphology of the Appendicular Skeleton. The paired limbs first appear in the human embryo about the third week as small buds on either side of the cephalic and caudal ends of the trunk. That these outgrowths are derived from a lar»e number of trunk segments is assumed on the ground that they are supjslied by a corre- sponding number of segmental nerves, and the circumstance that they are more particularly associated with the ventral offsets of these nerves would point to the conclusion that they belong rather to the ventral than the dorsal surface of the body. At first the surfaces of these limb buds are so disposed as to be directed ventrally and dorsally, the ventral aspect corresponding to the future flexor surface of the limb, the dorsal to the ex- tensor side. At the same time, the borders are directed headwards (pre-axial), and tailwards (post-axial). As the limbs grow, they soon display evidence of division into segments correspond- ing to the hand and foot, forearm and leg, upper arm and thigh. Coincident with this (about the second month) the cartilaginous framework of the limb is being differentiated. The disposition of these cartilages furnishes a clue to their homologies. In the fore limb the radius and thumb lie along the pre-axial borders, and correspond to the tibia and great toe, which are similarly dis- posed in the hind limb ; whilst the ulna and fifth finger are homologous with the fibula and fifth toe, which are in like manner arranged in relation to the posterior (post-axial) border of their respective limbs. Up to this time the limbs are directed obliquely ventralwards. During the third month a change in the position of the limbs takes place, associated with the assumption of the foetal position. Owing to the elongation of the limbs, they become necessarily bent at the elbow and knee, the upper arm inclining downward along the thoracic wall, whilst the thigh is directed upwards in contact with the abdominal parietes. At the same time a 17** XXIV OSTEOLOGY. Fig. 200. — Diagram to illcstrate the Homologies op THE Bones of the Limbs. The two limb buds of an embryo prior to Hexion and rotation. The anterior or pre-axial border is coloured red; the posterior or post-axial border, blue. B. After the assumption of the fcetal position. Flexion and rotation have now taken place. The red and blue lines indicate the altered position of the pre-axial and post-axial borders. C. The fully developed limbs with the flexor aspects directed towards the reader. The coloured lines indicate the effect of the torsion of the upper segment of the limb through quarters of a circle. rotation of each of these segments of the limb takes place in an inverse direction, so that the pre-axial border of the humerus is turned laterally, whilst the pre-axial border of the femur is turned medially. Assuming that these borders are homologous, it results from this, that the lateral condyle of the humerus correspouds to the medial condyle of the femur. This torsion of the limb is in part effected at the shoulder and hip joints, and to some extent also in the shafts of the bones. Some anatomists hold that this I'otation is not confined to the limb, but involves the dorsal part of the limb girdles. Others maintain that there is no evidence that such takes place. In the upper limb, owing to a certain amount of j^ronation, the pre-axial (radial) side of the forearm is now directed forwards and somewhat laterally, wliilst in the hind limb the pre-axial (tibial) side of the leg is turned backwards and laterally, the pi'e-axial borders of the hand with thumb, and foot with great toe being in corres^jondence. In consequence of these changes in the position of the limbs, amount- ing in all in the upper segments to a rotation through an angle of 90^, the extensor surface of tlie fore limb is directed backwards, whilst that of the hind limb is directed forwards. In order to homologise the ar- rangement of the bones in the extended limb, it is necessary to place them so that their flexor or extensor surfaces are similarly disposed. It will then be observed (see dia- gram) that the medial or tibial side of the leg and foot (primitively pre-axial) corre- sponds to the lateral or radial side of the forearm and hand (primitively pre-axial), whilst the fibula and lateral border *of the foot homologise with the ulnar or medial border of the forearm and hand (primitively post -axial), the result, as previously ex- plained, of the torsion or twisting in opposite directions through an angle of 90' of the upper segment of the limb. In accordance with this view, it will be evident that in the fore limb there is nothing homologous witli the patelhi, whilst in the hind limb there is no part to represent the olecranon. In the axial mesoderm of each member, differentiation into cartilaginous segments begins about the second month ; each of these cartilages becomes invested by a peri- chondria! layer which stretches from segment to segment, and ultimately forms the liga- ments surrounding the joints, which are subsequently developed between the seg- ments. Chondrification first begins in the basal part of the limb, and extends towards the digits. The homodynamy of the carpal and tarsal elements may be tabularly expressed, and compared with the more generalised types from wliich they are evolved. Type. Radiale (Tibiale) Intermedium Ulnare (Fibulare) Centrale Carpale (Tarsale), i. Hand. Foot. = Navicular (Ijody) = Talus. = Os lunatum = Absent, or Os trigonum (?) = 0s triquetrum = Calcaneus. = Absent, or fused with Navicular = Navicular, less its tuberosity. = Large multangular = First Cuneiform. MOEPHOLOGY OF THE LIMBS. xxv Type. Hand. Foot. Carpale (Tarsale), ii. = Small multangular = Second Cuneiform. Carpale (Tarsale), iii. = Capitate = Third Cuneiform. Carpale (Tarsale) iv. I =Osliamatum = Cuboid, plus the peroneal Carpale (iarsale), v. J sesamoid. The pisiform is omitted from the above table, since it is now generally regarded as being a vestige of an additional digit placed post-axial to the little j&nger (digitus post-minimus). Its homologue in the foot is by some considered as fused with the calcaneus. The tuberosity of the navicular, formed, as has been stated, of three elements, of Avhich the sesamoid bone in the tendon of the tibialis posterior may be one, is to be regarded as the homologue of the radial sesamoid in the hand, which probably fuses with the navicular to form its tuberosity. The l^eroneal sesamoid probably corresponds to the navicular process (sometimes an independent ossicle) of the os hamatum. Similarly, on the pre-axial border of the hand and foot, vestiges of a suppressed digit (prepollex and prehallux) may occasionally be met with. The frequent occur- rence of an increase in the number of digits seems to indicate that jjliylogenetically the number of digits was greater than at present, and included a prepollex or prehallux, and a digitus post- minimus. The correspondence of the metacarjjus with the metatarsus and tlie phalanges of the fingers with those of the toes is so obvious that it is sufficient merely to mention it. The differences in size, form, and disposition of the skeletal elements of the hand and foot is easily accounted for by a reference to the functions they subserve. In the hand strength is sacrificed to mobility, thus leading to a reduction in the size of the carpal elements, and a marked increase in the length of the digital jjhalanges. The freedom of movement of the thumb, and its opposability to the other digits, greatly enhances the value of the hand as a grasping organ. In the foot, where stability is the main requirement, the tarsus is of much greater jjroportionate size, whilst the phalanges are correspondingly reduced. Since the foot no longer serves as a grasping organ, the great toe is not free and opposable like the thumb. Limb Girdles. — The free limbs are linked to the axial skeleton by a chain of bones which constitute their girdles. The fundamental form of these limb girdles consists each of a pair of curved cartilages placed at right angles to the axis of the trunk on either side, and embedded within its musculature. Each cartilage has an articular surface laterally, about the middle, for the reception of the cartilage of the first segment of the free limb. In this way each pectoral and pelvic cartilage is divided into an ujjper or dorsal half and a lower or ventral half. The dorsal halves constitute the scajjula and ilium of the pectoral and pelvic girdles resi^ectively. With regard to the ventral halves there is more difficulty in establishing their homologies. The original condition is best displayed in the pelvic girdle ; here the ventral segment divides into two branches — one anterior, which represents the jjubis, the other posterior, which ultimately forms the ischium. Ventrally, the extremities of these cartilages unite to enclose the obturator foramen. In the pectoral girdle the disijosition of the ventral cartilages is not so clear, consisting primitively of an anterior branch or precoracoid, and a posterior jDortion or coracoid ; these, in higher forms, have undergone great modifications in adaptation to the requirements of the fore limbs. The posterior or coracoid element, the homologue of the ischial cartilage in the pelvic girdle, is but feebly represented in man by the coracoid process and the coraco-clavicular ligament. With regard to the homologue of the pubic element in the pectoral girdle, there is much difl'erence of opinion ; in reptiles and ami^hibia it corresponds most closely to the jjrecoracoid, but it is doubtful what represents it in mammals. According to Goette and Hoffman, the clavicle is a primordial bone, and not, as suggested by Gegenbaur, of secondary or dermic origin. If this be so, it corresponds to the ventral anterior segment of the pectoral girdle, and is therefore homo- logous with the ventral anterior (pubic) segment of the pelvic girdle. On the other hand, if Gegenbaur's view be accepted, the clavicle has no representative in the pelvic girdle. It must, however, be borne in mind that during its ossification it is intimately associated with cartilage, and that that cartilage may represent the precoracoid bar ; nor must too great stress be laid upon the fact that the clavicle begins to ossify before it is preformed in cartilage, since that may be merely a modification in its histogenetic development. According to another view (Sabatier), the subcoracoid centre (see Ossification of Scapula) is derived from the jjosterior ventral segment, and corresponds to the ischium, whilst the coracoid process is the remains of the anterior ventral segment (precoracoid), and is homodynamous with the pubis. In no part of the skeleton does function react so much on structure as in the arrangement of the constituent parts of the pectoral or pelvic girdles. In man, owing to the assumption of the erect position and the bipedal mode of progression, the jaelvic girdle acquires those characteristics which are essentially human, viz. its great relative breadth and the exp»ansion of its iliac portions, which serve as a support to the abdominal viscera, and also furnish an extensive origin for the powerful muscles which control the movements of the hip-joint. The stability of the pelvic girdle is insured by the nature of its union with the axial skeleton, as well as by the osseous fusion of its several parts, and their union in front at the symphysis pubis. Various attempts have been made to homologise the several parts of the ilium and scapula. All are open to objection ; that by Flower is perhaps the most generally accepted. Assuming that the primitive type is represented by a prismatic rod, of which the dorsal end represents •either the epiphysial border of the vertebral edge of the scapula or the iliac crest, whilst the ventral end corresponds to the glenoid or cotyloid articular areas respectively, the surfaces of the three-sided rod are disposed so that one is vertebral or internal, another pre-axial, and the XXVI OSTEOLOGY. third post-axial. These surfaces are separated by borders, of which one is lateral, separating the pre-axial and post-axial surfaces, whilst the antero- medial and postero- medial margins separate the pre-axial and post-axial surfaces respectively from the vertebral or medial aspect. It is a necessity of Flower's theory that this part of the girdle undergoes a rotation along with the rest of the limb. Thus in the fore limb the surfaces of the jjrimitive type are turned so that the vertebral surface looks forward, whilst in the case of the hind limb the vertebral surface is turned backward. A study of the accompanying diagram will enable the reader to realise how the ventral surface of the scapula is thus rendered homologous with the gluteal surface of the ilium, for by reference to the type, both these surfaces will be seen to correspond to the j^ost- axial areas of the primitive condition. In accordance with this view the surfaces and borders of the scapula are homologised by Flower, as shewn in the subjoined table : — Scapula. Supra-spinous fossa Infra-spinous fossa Subscapular fossa Surfaces Ideal. 1. Vertebral 2. Pre-axial 3. Post-axial Pelvis. Inner surface of ilium behind linea ar- cuata interna, including the articular surface for the sacrum and the portion of the bone above and below this Internal iliac fossa Gluteal surface of ilium Borders Axillary border, posterior on most animals (attachment of biceps muscle) Spine continued into acromion Superior border, anterior in most animals, with scapulo- coracoid notch 1. Lateral 2. Antero -medial 3. Postero-medial Anterior border (attachment of rectus muscle) Linea arcuata interna continued into pubis Posterior border with great sciatic notch 'Vertebral or internal surfaces Fig. 201.- -DlAGRAM TO ILLUSTRATE THE HOMOLOGOUS PaRTS OF THE SCAPULA AND ILIUM, ACCORDING TO FlOWER. A, ideal type ; three-sided rod. B, scapula rotated forward through quarter of a circle (90°), so that the primitive internal or vertebral surface is now directed anteriorly. C, ilium rotated backwards through quarter of a circle so that the primitive internal surface is now turned posteriorly. In the diagram the primitive internal or vertebral surface of each figure is coloured black, the pre-axial surfaces red, and the post-axial surfaces blue. Flower's views of this matter were strenuously opjDOsed by Humphry, who maintained that there is strong presumptive evidence against any rotation of the superior parts of the girdles, since it is difficult to suppose that the scapula and ilium can undergo a rotation which is not participated in by the coracoid and ischium. According to this anatomist the homologous parts of the two bones are as stated below : — Scapula. Pre-spinal ridge forming the floor of the pre- spinal fossa Spine and acromion Post-spinal part of scapula forming the floor of the post-spinal fossa Posterior angle Posterior border Medial or ventral surface Ilium. Linea ilio-pectinea Fore part of the blade and crest of the ilium, with its anterior spine or angle Hinder part of blade and crest of ilium Posterior spine or angle Posterior or sciatic border of ilium Inner or true pelvic surface of ilium, including the surface for the articulation of the sacrum MOKPHOLOGY OF THE LIMBS. XXVll Fig. 202. — Diagram to illustrate the Homologous Parts of the Scapula and Ilium, according to humphry. A, primitive rod-like ilium of kangaroo, prismatic on section. B, scapula. C, ilium. The corresponding surfaces are similarly coloured. The difficulty arising in this scheme of attempting to homologise the attachments of the triceps and rectus femoris, Humphry explains by pointing out that the former muscle also arises from the lateral surface of the scapula, whilst the rectus overruns the lateral surface of the ilium above the acetabulum, so that there is a correspondence in the origins of both these muscles from the lateral surface of their respective bones ; but in consequence of the rotation of the extensor surfaces of the limbs in opposite directions the triceps has been turned backwards on to the posterior border of the scapula, whilst the rectus has been turned forwards on to the anterior border of the ilium. Sufficient has been said to enable the reader to recognise that all attempts to determine in detail the homologies of these parts is beset with difficulty. It is wiser, therefore, in our present state of knowledge to be content with establishing a general correspondence, and so avoid the error of endeavouring to establish a closer homological relationship than actually . exists. In man, since the erection of the figure no longer necessitates the use of the fore limb as a means of support, the shoulder girdle has become modified along lines which enhance its mobility and determine its utility in association with a prehensile limb. Some of its parts remain independent (clavicle and scapula), and are united by diarthrodial joints, whilst others have become much reduced in size or suppressed (coracoid-precoracoid, see ante). The dorsal part of the girdle (scapula) is not directly united with the axial skeleton as is the ilium, but is only indirectly joined to it through the medium of the clavicle, which is linked in front with the presternum. The same underlying principles determine the diff"erences in mobility and strength between the shoulder, elbow, and wrist, and the hip, knee, and ankle joints of the fore and hind Umbs respectively, whilst the utility of the hand is further enhanced by the movements of pronation and supination which occur between the bones of the forearm. In the leg such movements are absent, as they would interfere with the stability of the limb. THE ARTICULATIONS OR JOINTS. ARTHROLOGY. By David Hepburn, M.D., F.R.S.E., Professor of Anatomy, University College, Cardiff. THE ARTICULATIONS OR JOINTS. ARTHROLOGY. By David Hepbuen. Arthrology is that branch of human anatomy which treats of the articulations or joints. An articulation or joint constitutes a mode of union or connexion subsisting between any two separate segments or parts of the skeleton, whether osseous or cartilaginous, and having for its primary object either the preservation of a more or less rigid continuity of the parts joined together, or else to permit of a variable degree of mobility, subject to the restraints of the uniting media. Classification of Joints. — In attempting to frame a classification of the numerous joints in the body, several considerations must be taken into account, viz. the manner and sequence of their appearance in the embryo ; the nature of the uniting media in the adult, and also the degree and kind of movement permitted in those joints where movement is possible. In this way we obtain two main subdivisions of joints : — (1) Those in which the uniting medium is coextensive with the opposed sur- faces of the bones entering into the articulation, and in which a direct union of these surfaces is thereby effected. (2) Those in which the uniting medium has undergone more or less of interrup- tion in its structural continuity, and in which a cavity of greater or less extent is thus formed in the interior of the joint. To the first group belong all the immovable joints, many of which are likewise of temporary duration ; to the second group belong all joints which possess as their outstanding features mobility and permanence. Iiitei'veiiiiig iiiPinbiaiie SYNARTHROSES. The general characteristics of this group are partly positive and partly nega tive. Thus there is uninterrupted union between the opposed surfaces of the bones joined together at the plane of the articulation, i.e. there is no trace of a joint cavity, and further, there is an entire absence of movement. Developmen tally, these joints result from the approxi- mation of ossific processes which have commenced from separate centres of ossification, and therefore the nature of the uniting medium varies according as the bones thus joined together have originally ossified in membrane or in cartilage. In the former case union is effected by an interposed fibrous membrane continuous with and corresponding to the periosteum. To such articulations the term suture (Fig. 203) is applied. In the latter case the uniting medium is a plate of hyaline cartilage. Such articulations are called synchondroses (Fig. 204). In all the synchondroses, and in many of the sutures, the uniting medium tends to disappear in the progress of Fici. 203. — Vkktical Skction THROUGH A SUTURE. 256 THE ARTICULATIONS OR JOINTS. ossification, and thus the plane of articulation becomes obliterated, so that direct structural continuity between the osseous segments takes place. The primary features common to all synarthroses are — (a) continuous and direct union of the opposing surfaces ; (&) no joint cavity ; (c) no movement. Suture. — This form of synarthrosis is only found in connexion with the bones of the skull. In a large number of cases the bones which articulate by suture present irregular interlocking margins, between which there is the interposed fibrous membrane to which refer- ence has already been made. When these interlocking margins present well-defined projections they are said to form true sutures — sutura vera ; on the other hand, when Fig. 204. — Section thkough the opposed surfaces present ill-defined projections, or THE OccipiTo-spHENoiD Syn- gyeu flat arcas, they are described as false sutures — cHONDRosib. sutura notha. In each of these subdivisions the particular characters of the articulating margins are utilised in framing additional descriptive terms. Thus true sutures may possess interlocking margins whose projections are tooth-like (sutura dentata), e.g. in the interparietal suture ; saw-like (sutura serrata), (Fig. 205) e.g. in the interfrontal suture ; ridge-like, or comparable to the parallel ridges on the welt of a boot (sutura limbosa). Similarly false sutures may articulate by margins which are scale- like (sutura squamosa), e.g. in the squamoso-parietal suture ; or by rough opposed surfaces (sutura harmonia), e.g. in the suture between the palate plates of the superior maxillary bones. There is one variety of synarthrosis which, in the adult, can scarcely be called a suture, although the differences are of minor importance, viz. schindylesis, which is an articulation between the edge of a plate- like bone, such as the rostrum of the sphenoid, and the cleft in another, such as the vomer. Synchondrosis. — Illustrations of this group can only be found ^^^- IH^^^^^^^^^ in the young growing individual, because as age advances and growth ceases, the process of ossification affects the hyaline cartilage which con- stitutes the uniting medium, and the plane of articulation disappears. Under this heading we may include the planes of junction between all epiphyses and the shafts or diaphyses to which they severally belong. The occipito- sphenoid (Fig. 204) and the petro-jugular articulations in the base of the skull provide other well-marked examples. MOVABLE JOINTS. The leading features of this group are capability of movement and permanence. In very few instances do such joints ever become obliterated under normal con- ditions. Determining their permanence, and regulating the amount of possible movement, there is always more or less of interruption in the continuity of the structures which bind the osseous elements together. That is, there is always some evidence of a joint cavity, although as a matter of course such interruption can never be so extensive as to entirely disassociate the articulating elements. There- fore in all movable joints a new class of structures is found, viz. the ligaments, by means of which continuity is maintained even when all the other uniting media have given i)lace to a joint cavity. The further subdivision of this group is founded upon the amount of movement permissible, and the extent to which the joint cavity takes the yjlace of the original continuous uniting medium. Thus we obtain the partly movable or ampMarthroses, and the freely movable or diarthroses. An amphiarthrosis (Fig. 208) presents the following characteristics : {a) partial movement ; (h) union by ligaments and by an interposed plate or disc of fibro-cartilage, in the interior of which there is, (c) an incomplete or partial joint cavity which may be lined by a rudimentary synovial membrane whose function it is to secrete a lubricating fluid, the synovia or joint-oil; {d) a plate of hyaline STKUCTUKE OF JOINTS. 257 , Articular cartilage .Joint capsule Synovial membrane cartilage coating each of the opposing surfaces of the bones concerned. All the joints belonging to this group occur in the mesial plane of the body. It includes the symphysis pubis, the joints between the bodies of the vertebrae, and the joint between the manubrium sterni and the gladiolus. A diarthrosis (Fig. 206) is the most elaborate as well as the most complete form of articulation. It is characterised by («) capability of movement which is more or less free in its range ; (6) a reduction of the uniting structures to a series of retaining liga- ments ; (c) a joint cavity which is only limited by the surrounding ligaments ; {d) the constant presence of synovial membrane ; (e) hyaline encrusting cartilage which clothes the opposed surfaces of the articulating bones. The majority of the joints in the adult belongs to this group. This series of joints has been subdivided into a number of minor sections, in order to emphasise the occurrence of certain well-marked structural features, or because of the particular nature of the move- ment by which they are characterised. Although in all diarthroses there is a certain amount of gliding movement between the opposed surfaces of the bones which enter into their formation, yet, when this gliding movement becomes their prominent feature, as in most of the joints of the carpus and tarsus, they are termed arthrodia. But bones may be articulated together so as to permit of movement in one, two, or more fixed axes of movement, or in modifications of these axes. Thus in uniaxial joints the axis of movement may lie in the longi- tudinal axis of the joint, in which case the rotatory form of joint results, as in the superior and inferior radio-ulnar articulations ; or it may correspond with the transverse axis of the articulation, as in the elbow-joint and knee-joint, when the ginglymus or hinge variety results. If movement takes place about two principal axes situated at right angles to each other, as in the radio-carpal joint, the terms biaxial or condyloid are applied. Movements occurring about three principal axes placed at right angles to each other, or in modifications of these positions, con- stitute multiaxial joints, in which the associated structural peculiarities provide the alternative terms of enarthrodial or ball-and-socket joints. Articular cartila.i^e Fig. 206 DiARTHRODIAL STRUCTURES WHICH ENTER INTO THE FORMATION OF JOINTS. The structures which enter into the formation of joints vary with the nature of the articulation. In every instance there are two or more skeletal elements, whether bones or cartilages, and in addition there are the uniting media, which are either simple or elaborate according to the provision made for rendering the joint more or less rigid or capable of movement. We have already seen that the uniting medium in synarthrodial joints is a remnant of the common matrix, whether fibro- vascular membrane or hyaline cartilage, in which ossification has extended from separate centres. Among the ampbiarthroses there is still extensive union between the opposing surfaces of the articulating bones, but the character of the uniting medium has advanced from the primitive embryonic tissue to fibrous and fibro- cartilaginous material, as well as hyaline cartilage. These, with very few exceptions, are permanent, non-ossifying substances, such as may be seen between the opposing, osseous surfaces of two vertebral bodies. The joint cavity, more or less rudimentary, is confined to the centre of the fibro-cartilaginous plate, and may result from the softening or imperfect cleavage of the central tissue. It may also present rudiments of a synovial membrane. In the diarthrodial group the extensive cavity has produced great interruption in the continuity of the uniting structures which originally existed between the bones forming such a joint. Ligaments have therefore additional importance in this group, for not only do they constitute the uniting media which bind the articulating bones together, but to a large extent they form the peripheral 18 258 THE AKTICULATIONS OE JOINTS. boundary of the joint cavity, although not etj[ually developed in all positions. Thus every diarthrodial joint possesses a fibrous or ligamentous envelope or capsule which is attached to the adjacent ends of the articulating bones. For special purposes, particular parts of the capsule may undergo enlargement and thickening, and so constitute strong ligamentous bands, although still forming con- tinuous constituents of the capsule. Within the capsule a series of intracapsular structures are present. Thus the capsule itself is always lined by a synovial membrane,^ which is continued from the inner surface of the capsule to the surface of the intracapsular portion of each articulating bone. The part of the bone included within the capsule consists of a " non-articular " portion covered by synovial membrane, and an " articular " portion covered by encrusting hyaline cartilage. The latter provides the surface which comes into apposition with the corresponding area of another bone. In its general disposition the synovial membrane may be likened to a cylindrical tube open at each end. This membrane is richly supplied by a close network of vessels and nerves. Certain diarthroses present additional intracapsular structures which may be distinguished as interarticular ligaments and interarticular fibro-cartilages. Interarticular ligaments extend between and are attached to non-articular areas of the intracapsular portions of the articulating bones. They usually occupy the long axis of the joint, and occasionally they widen sufficiently to form partitions v^hich divide the joint-cavity into two compartments, e.g. the costo-central, and certain of the chondro-sternal joints. Interarticular fibro-cartilages or menisci (Fig. 207) are more or less complete partitions situated between and separating opposing articular surfaces, and when complete they divide the joint cavity into two distinct compartments. By its periphery, a meniscus is rather to be associated with the joint capsule than with the articu- lating bones, although its attachments may extend to non-articular areas on the latter. Both interarticular ligaments and menisci have their free surfaces covered by syno\dal membrane. Adipose tissue forming pads of varying size is usually found in certain localities within the joint, between the synovial membrane and the surfaces which it covers. These pads are soft and pliable, and act as packing material, filling up gaps or intervals in the joint. During movement they ada^^t themselves to the changing conditions of the articulation. In addition to merely binding together two jNo THE Joint - Cavity into two Com- or more articulating bones, ligaments perform PAKTMENT.s. ^^^^ importaut functions in connexion with the different movements taking place at a joint. They do not appreciably lengthen under strains, and thus ligaments may act as inhibitory structures, and by becom- ing tense may restrain or check movement in certain directions. Synovial iiieuiljranes, in the form of closed sacs termed synovial bursse, are frequently found in other situations Ijesides the interior of joints. Such bursie are developed for the purpose of reducing the friction, (a) Ijetween the integument and certain prominent suljcutaneous bony i^ro- jections, as, for instance, the point of tlie elljow, or the front surface of the patella (subcutaneous synovial burste) ; Qj) between a tendon and some surface, bony or cartilaginou.s, over which it plays (subtendinous synovial burste) ; (c) between a tendon or a group of tendons and the walls of osteo-fascial tunnels, in which tliey play (thecal synovial bursa;). Subtendinous synovial bursse are often placed in the neighbourhood of joints, and in such cases it not infrequently Synovial membrane Fig. 207. — Diagram ok a Diarthrodial Joint WITH AN Interarticular Meniscus mvin- ' The terra " .synovial membrane " has been so long in use that one hesitates to discard it, even although the structure so described is not in many cases capable of being removed from the objects of which it forms a part. A more precise description in these cases would be "synovial surface." There is still considerable doubt whether the "synovial fluid " is a true secretion or merely a diluted friction product. THE DIFFERENT KINDS OF MOVEMENT AT JOINTS. 259 happens that there is a direct continuity between the bursa and the synovial niembi'ane which lines the cavity of the joint through an aperture in the joint capsule. THE DIFFERENT KINDS OF MOVEMENT AT JOINTS. Reference has already been made to the existence of fixed axes of movement as a basis for the classification of certain forms of diarthrodial joints. Hence it is evident that the movements which are possible at any particular joint depend to a large extent upon the shape of its articular surfaces as well as upon the nature of its various ligaments. Therefore the technical terms descriptive of movements either indicate the directions in which they occur, or else the character of the com- pleted movement. In the great majority of articulations between short bones, the amount of move- ment is so restricted, and the displacement of the opposing articular surfaces so slight, that the term gliding sufficiently expresses its character. A gliding movement of an extensive kind, for example that of the patella upon the femur, in which the movement largely resembles that of the tyre of a wheel revolving in contact with the ground so that different parts are successively adaj^ted to each other, is called co-aptation. Articulations between long bones, on the other hand, are usually associated with a much freer range of movement, with a corresponding variety in its character. Rotation is a movement about an axis which is longitudinal. Sometimes it is the only form of movement which a joint possesses ; at other times it is merely one of a series of movements capable of execution at the same joint. Flexion or bending is a movement in which the formation of an angle between two parts of the body is an essential feature. As it is possible to perform this movement in relation to two axes, viz. a transverse and an antero-posterior axis, it is necessary to introduce qualifying terms. Thus, when two anterior or ventral surfaces are approximated, as at the hip-, elbow-, or wrist-joints, the movement is called ventral, anterior, or palmar flexion ; but if posterior or dorsal surfaces be approximated by the process of bending, then the flexion becomes posterior or dorsi-flexion, as at the knee- or wrist- joints. Further, at the wrist-joint, the formation of an angle between the ulnar border of the hand and the corresponding aspect of the forearm, produces ulnar flexion, and similarly the bending of the hand towards the radial border of the forearm is radial flexion. Extension or straightening consists in obliterating the angle which resulted from flexion. In the case of certain joints, therefore, such as the elbow, wrist, and knee, the segments of the limb occupy a straight line as regards each other when extended. At the ankle-joint the natural attitude of the foot to the leg is flexion at a right angle. The diminution of this angle by approximating the dorsum of the foot towards the front of the leg constitutes flexion ; while any effort at placing the foot and leg in a straight line, i.e. obliteration of the angle, as in pointing the toes towards the ground and raising the heel, constitutes extension. Abduction is a term which either expresses movement of an entire limb, in a direction away from the mesial plane of the body, or of a digit, away from the plane of the middle finger in the hand, or the plane of the second toe in the case of the foot. Adduction is the reverse of abduction, and signifies movement towards the mesial plane of the body, or towards the planes indicated for the digits of the hand and foot. Circumduction is a movement peculiarly characteristic of multiaxial or ball- and-socket joints. It consists in combining such angular movements as flexion, extension, abduction, and adduction, so as to continue the one into the other, whereby the joint forms the apex of a cone of movement, and the free end of the limb travels through a circle which describes the base of this cone. THE DEVELOPMENT OF JOINTS. Just as the question of structure determines to a large extent the presence or absence of movement in joints, so in tracing their development it will be found that the 18 a 260 THE AETICULATIONS OE JOINTS. manner of their appearance forecasts their ultimate destination as immovable or mov- able articulations. All joints arise in mesodermic tissue which has undergone more or less differentiation. When this differentiation has produced a continuous membranous layer, in which ossific centres representing separate skeletal segments make their appearance, we get the primitive form of suture. The plane of the articulation merely indicates the limit of the ossific process extending from different directions. If, again, the differentiation of the mesoblast has resulted in the formation of a continuous cartilaginous layer, in which ossification commences at separate centres, the plane of the articulation is marked out by the unossified cartilage — in other words, the articulation is a synchondrosis. Ulti- mately this disappears through the extension of the process of ossification. To some extent sutures also disappear, although their complete obliteration is not usual even in aged people. Developmentally, therefore, synarthroses or immovable' joints do not present any special structural element, and, speaking generally, they have only a temporary existence. The development of all movable joints is in marked contrast to that of synar- throses. Not only are they permanent arrangements so far as concerns normal conditions, but they never arise merely as planes which indicate the temporary phase of an ossific process. From the outset they present distinct skeletal units, from which the special structures of the joint are derived. The primitive movable joint is first recognised as a mass of undifferentiated meso- dermic cells situated between two masses, which have differentiated into primitive cartilage. The cell-mass which constitutes the joint- unit presents the appearance of a thick cellular disc, the proximal and distal surfaces of which are in accurate apposition with the primitive cartilages, while its circumference is defined from the surrounding mesoderm by a somewhat closer aggregation of the cells of which the disc is composed. From this cellular disc or joint-unit all the structures characteristic of amphiarthrodial and diar- throdial joints are ultimately developed. Thus by the transformation of the circumferential cells into fibrous tissue the invest- ing ligaments are produced. Within the substance of the disc itself a transverse cleft, more or less well-defined and complete, makes its appearance. In this manner the disc is divided into proximal and distal segments, sepai-ated from each other by an interval which is the primitive joint cavity. This cleft, however, never extends so far as to inter- rupt the continuity of the circumferential part of the disc which develops into the fibrous tissue of the investing ligaments. From the proximal and distal segments of the articular disc the various structures, distinctive of movable joints, are developed. Thus, in amphiarthrodial joints the cellular articular disc or primitive joint-unit gives origin to the following structures : — From its circumference, investing ligaments ; from its interior, the fibro-cartilaginous plate or disc in which an imperfect joint cavity with corresponding imperfect synovial may be found. In the case of a diarthrodial joint the changes take place on a more extended scale. The joint cavity becomes a prominent feature, in relation to which the surrounding fibrous structures form an investing capsule, lined by a synovial membrane. When a single cleft arises, but does not extend completely across the longitudinal axis of the articular disc, the undivided portion develops into fibrous interarticular ligaments. On the other hand, when two transverse clefts are formed, that portion of the cellular disc which remains between them becomes transformed into a fibro-cartilaginous inter- articular disc or meniscus, which in its turn may either be complete or incomplete, and thus we may obtain two distinct synovial joint cavities belonging to one articulation. ^ In considering the development of the synovial membrane, and the surfaces on which it is found in the interior of a joint, it is necessary to keep clearly in mind that a synovial membrane is a special structure, whose function it is to produce a lubricating fluid or synovia, and that, therefore, its position is determined by the essential necessity of proximity to a direct blood-supply. In other words, this condition is provided by all parts of the interior of a joint cavity except the articular encrusting cartilage. Conse- quently synovial membrane is only absent from the free surface of articular cartilage, although it forms a thicker layer upon the inner surface of the joint capsule than upon the free surfaces of interarticular ligaments and menisci. ' From a serie.i of observations upon the development of diarthrodial joints, the writer considers that there is evidence to show that the "cellular articular disc " is directly responsible for tlie production of the epiphyses which adjoin the completed joint cavity, and that, among such ainjihiarthroses as exist between the bodies of vertebra', not only the intervertebral disc, but the proximal and distal epiphyses which ultimately unite with the vertebral bodies have a common origin in the joint-unit. LIGAMENTS OF THE VERTEBRAL COLUMN. 261 It is not necessary to suppose that the synovial membrane has disappeared from these articular cartilages as the result of friction, because, notwithstanding constant friction, such parts as the interior of capsular ligaments or the semilunar cartilages of the knee- joint have not been denuded of their synovial covering. MORPHOLOGY OF LIGAMENTS. From what has been said in connexion with the development of joints, it will be evident that ligaments are essentially products derived from the cellular articular disc. Nevertheless, in relation to the fully-formed joint, many structures are described as ligaments which do not take origin in the manner just indicated. Some of these ligamentous structures remain fairly distinct from the capsular ligaments wdth which they are immediately associated ; others become thoroughly incorporated with the capsular ligaments and cannot be separated therefrom, while yet others may be found situated within the capsule of a joint, and thus play the pai't of interarticular ligaments. Instances of each of these forms of adventitious ligaments may be readily given. For example, we may instance the expansion of the tendon of the semimembranosus muscle to the posterior ligament of the knee-joint, and the ofl'shoots from the tendon of the tibialis posticus muscle to the plantar aspects of various tarsal bones, as illustrations of structures which play an important part as ligaments, but are not indelibly incorporated with the joint capsule. Of structures which have become indelibly incorporated with the primitive capsule, we may instance the broad tendinous expansions of the quadriceps extensor muscle around the knee-joint. The internal lateral ligament of the same joint is regarded as a detached portion of the tendon belonging to that part of the adductor magnus muscle which takes origin from the ischium, while the external lateral ligament of the knee is considered by some to be the primi- tive femoral origin of the peroneus longus muscle. Another illustration of the same condition is found in the coraco-humeral ligament, which is regarded by some as representing a detached portion of the pectoralis minor muscle. Two illustrations may be given of structures plajang the part of ligaments within the capsule of a joint, although in the first instance they are not developed as ligaments. It is questionable if the ligamentum teres of the hip-joint is an interarticular ligament in the true sense of the term ; it has been regarded as the isolated and displaced tendon of the ambiens muscle found in biixls. In the shoulder-joint, many observers look upon the superior gleno-humeral ligament as representative of the ligamentum teres. Such structures a^ the stylohyoid ligament and the internal lateral ligament of the temporo- mandibular joint, although described as ligaments, are in reality skeletal parts which have not attained their complete ossific development. Again, certain portions of the deep or muscular fascia of the body which become specialised into restraining and supporting bands {e.g. the ilio-tibial band of the fascia lata ; the stylo-mandi- bular ligament ; the anterior and posterior annular ligaments of the wrist-joint ; the anterior, inner, and outer annular ligaments of the ankle-joint), although called ligaments, have no direct developmental association with articular ligaments. Lastly, the ligament of Poupart and the ligament of Gimbernat, being special develoi^ments in connexion with an expanded tendon or aponeurosis, are still further removed from associa- tion with an articulation. LIGAMENTS OF THE VERTEBRAL COLUMN AND SKULL. All vertebrae, with the exception of those which deviate from the common vertebral type, present two sets of articulations whose various parts are arranged upon a uniform pattern. Thus every pair of typical vertebrie presents an articula- tion between the centra, termed intercentral, and a pair of articulations between the neural arches, called interneural. With the latter there are associated various important accessory ligaments which bind together laminie, spinous processes, and transverse processes. Intercentral Articulations. — These are amphiarthrodial joints. Singly, they present only a slight degree of mobility, but when this amount of movement is added to that of the whole series, the range of movement of the spine becomes considerable. The articular surfaces are the flattened surfaces of adjacent vertebral bodies. They are bound together by the following structures : — Intervertebral Discs (tibro-cartilagines intervertebrales, Fig. 208). — Each disc accommodates itself to the space it occupies between the two vertebral bodies, to both of which it is firmly adherent. The discs, from different parts of the spinal column, vary in vertical thickness, being thinnest from the third to the seventh dorsal vertebra, and thickest in the lumbar region. In the cervical and lumbar regions each disc is thicker in front than behind, thereby assisting in the production of the 18 6 ' . 262 THE AETICULATIONS OK JOINTS. anterior convexity which characterises the spinal column in these two regions. In the dorsal region the discs are thinnest on their anterior aspects in correspondence with the anterior concavity of this section of the spine. Each disc consists of a circumferential portion (annulus fibrosus), formed for Vertebral body Intervertebral disc (/ Ligaiiientum flavum or subflavum Nucleus pulposus Spinous process Fig. 208. — Mesial Section through a Portion of the Lumbar Part of the Spine. the most part of oblique parallel fibres running from one vertebra to the other. Horizontal fibres are also found. The axial or central part of the disc is elastic, soft, and pulpy (nucleus pulposus).^ The upper and lower surfaces of the disc are closely adherent to the adjoining interior conimon ligament Anterior or superior costo- transverse ligament : slips of the ) Three stellate ligament Anterior or superior costo- transverse ligament Fig. 209. — Antekiok Common Ligament of the Vektebkal Column, and the Costo-vertebral .Joints as seen fr(jm the Front. epiphyseal plates of the vertel^ral bodies, and as ossification advances, the distinc- tion between epiphyseal plates and vertebral ])ody disappears. As a rule the transverse diameter of the disc corresponds to that of the verte- bral bodies which it joins together ; but in the cervical region, where the lower 1 This pulpy substance does not present a joint cavity, but in certain cases it is more or less divided by fissures which occupy a transverse horizontal direction. LIGAMENTS OF THE VERTEBEAL COLUMN. 263 margin of the superimposed vertebra is overlapped on each side by the one which bears it, the disc does not extend to the extreme lateral margin, and in this position a small diarthrosis may be seen at each lateral margin of the disc. The anterior common ligament (lig. longitudinale anterius, Fig. 209) consists of a wide stratum of longitudinal fibres which extends from the front of the axis vertebra to the front of the upper segment of the sacrum, and becomes gradually wider from above downwards. It lies in front of the intervertebral discs, to which it is firmly attached as it passes from one vertebra to the other. Its fibres vary in length. fSome are attached to contiguous margins of two adjoining vertebrae ; others pass in front of one vertebra to be attached to the next below, and yet others lind their lower attachment three or four vertebree below the one from which they started. None of the fibres are attached to the transverse depression on the front of a vertebral body. The posterior common ligament (lig. longitudinale posterius, Fig. 210) is found within the spinal canal upon the posterior aspect of the vertebral bodies. It con- sists of longitudinal fibres, and it extends from the back of the sacrum to the axis vertebra, superior to which it is continued to the skull as the posterior occipito-axial ligament. Opposite each interverte- bral disc it is attached to the entire width of the adjacent margins of the two vertebral bodies, its fibres being continued over the posterior surface of the disc. In the lumbar and dorsal regions the width of the ligament is considerably reduced opposite the back of each vertebral body, and thus it forms a series of dentate projections along both of its margins ; but in the cervical region the width of the ligament is more uniform. One or two large thin -walled veins escape from the l3ody of each vertebra under cover of this liga- ment. Interneural Articulations. — The neural arch of each typical verteljra carries two pairs of articular processes, by means of which it articu- lates with adjacent neural arches. The articu- lations between tliese processes are true diarthroses of the arthrodial variety. The distinctive characters of these articular sur- faces, as regards their shape and direction in the different groups of vertebrae, have been referred to in the section on osteology. All these articulations are provided with complete but very thin -walled cap- sules (capsulae articulares), which are thinnest and loosest in the cervical region, where also the movements are freest. Each capsule is lined by a synovial membrane. Associated with these interneural joints are certain ligaments which are accessory to the articulations, although they are quite distinct from the capsule. The laminae of adjoining vertebrae are bound together by the ligamenta subflava (ligamenta flava vel subflava. Fig. 211), which consist of yellow elastic fibres. The ligamenta subflava close the spinal canal in the intervals between the laminae. Each ligament is attached superiorly to the anterior aspect of one lamina at a short distance above its lower border, and inferiorly it is attached to the posterior aspect of the subjacent lamina. In the dorsal region, where the imbrication of adjoining laminae is a prominent feature, these ligaments are not so distinctly visible from behind as they are in the regions where imbrication of the laminae is not so marked. Laterally they extend as far as the articular capsules, while mesially the margins of the ligaments of opposite sides meet under cover of the root of the spinous process. Contiguous pairs of spinous processes are also attached to each other by inter- spinous ligaments (ligamenta interspinalia. Fig. 208). These are strongest in the Interverte- bral fibro- cartilaginous disc Fig. 210 — Posterior Common Ligament OF THE Vertebral Column. 264 THE AETICULATIONS OK JOINTS. Pedicle of ^'el■tebra i.Uvided lumbar, and weakest in the dorsal region. Each consists of layers of obliquely interlacing fibres which spring from near the tips of the two adjacent spines and radiate to their opposing margins. In the antero- posterior direction they extend from the base to the tip of the spinous process. The supraspinous liga- ments (ligg. supra- spinalia, Fig.208)consist of longitudinal bands of fibres of varying lengths. They extend from spine t o spine, being attached to their tips,and are situated superficial to, although in continuity with, the interspinous ligaments. In the cervical region this series of ligaments is extensively developed, where they project back- wards from the spinous processes between the muscles of the two sides „ „ ^ ^ of the neck in the form Fig. 211. — Ligamenta Subflava as seen from the Front after Re- n i . • . ■■• MOVAL OF the BODIES OF THE VeRTEBR^ BY SAWING THROUGH THE *^ ^^ ClaStlC partition Pedicles. called the ligamentum nuclise. The antero-posterior extent of the ligamentum nuchse increases as it approaches the occiput, where it is attached to the occipital crest from the external occipital protuberance to the posterior border of the foramen magnum. Its posterior margin is free, and extends from the external occipital protuberance to the spine of the vertebra prominens. Between the transverse processes there are intertransverse ligaments (ligg. inter- transversaria), which consist of vertical fibres extending from the postero-inferior aspect of one transverse process to the superior margin of that next below. These ligaments are generally absent from the cervical and upper dorsal regions. Sacro-coccygeal Joint. — The last piece of the sacrum is joined to the first piece of the coccyx by an intervertebral disc, and the junction is rendered more secure by the presence of certain strong ligaments. An anterior ligament (lig. sacro-coccygeum anterius), continuous with the anterior common ligament, is placed in front. A posterior ligament (lig. sacro-coccygeum posterius), which stretches downwards from the sharp border of the lower opening of the sacral canal, strengthens the joint behind. A lateral ligament (lig. sacro-coccygeum laterale) supports the joint on each side, whilst strong bands pass between the cornua of the two bones and constitute the interarticular ligaments. Inter-coccygeal Joints. — So long as they remain separate, the different pieces of the coccyx are joined by intervertebral discs and by anterior and posterior liga- ments. Movements of the Vertebral Column. — Although the amount of movement permissible between any two verteljraj is exti-emely limited, yet the total range of movement capable of being attained by the entire vertebral column is very considerable. Flexion may occur both forwards and backwards at the intercentral articulations, but more freely in the lumbar and cervical regions than in the dorsal region, where the limited amount of intervertebral disc and the imbrication of the laminai and spines restrict the movement. Back- ward flexion is most pronoiuiced in the cervical region, and forward flexion in the lumbar region. Between the articular surfaces of the interneural articulations a variety of movements are per- mitted, dependent upon the directions of these surfaces. Thus lateral flexion is permitted in AETICULATIOX OF ATLAS WITH AXIS. 265 the lumbar, but not in the cervical or dorsal regions. Again, in the lumbar region rotation •does not occur, owing to the shape of the articular processes, while it is possible in the dorsal region. In the cervical region the shape and position of the articular surfaces prevent the ■occurrence both of lateral flexion and of rotation as isolated movements, but a combination of these two movements may take place, whereby rotatory movement in an oblicpie median axis results. Finally, in the lumbar region, l>y coml)ining the four forms of flexion, viz. forward, backward, and lateral, a certain amount of circumduction is possible. Articulation of Atlas with Axis. Between these two vertebrae three diarthroses occur. Two of them are situated laterally in relation to the articular processes, and are called artlirodial diarthroses, because of the flattened nature of the articulating surfaces. The third articulation is mesial in, position. It is found between the smooth anterior surface of the odontoid process of the axis and the articular facet on the posterior aspect of the anterior arch of the atlas. This joint is a rotatory diarthrosis. Ligaments. — Each of the joints is furnished with a capsular ligament whereby Membrana tectoria Basi-occipital bone Anterior occipito-atloid ligament Liganientum apicis denti Transverse Inferior crus of Rudimentary intervertebral disc Superior crus of crucial ligament Synovial cavity Posterior occipito-atloid ligament -Occipital bon"e Posterior common ligament Posterior arch of atlas ?pine of axis Fic. 212. — Mesial Section through the Occipito-atloid and Atlo-axoid Joints. the joint cavity is circumscribed. In the case of the lateral articulations, each capsular ligament presents a distinct band, named the accessory ligament, which is situated within the neural canal (Fig. 213), and passes downwards and inwards from the lateral mass of the atlas to the superior aspect of the body of the axis. The following additional ligaments constitute the leading bonds of union : — The anterior atlo-axoid ligament (Fig. 212) is a membranous structure which is thin laterally, but strong mesially where it is thickened by a prolongation of the anterior common ligament. It extends from the anterior arch of the atlas to the front of the body of the axis. The posterior atlo-axoid ligament (Fig. 212) occupies the position which is elsewhere taken by the ligamenta subflava. It extends from the posterior arch of the atlas to the upper border of the neural arch of the axis. The transverse ligament of the atlas (lig. transversum atlantis, Figs. 212 and 213) is a strong band, placed transversely, which arches backwards behind the neck of the odontoid process of the axis. By its extremities it is attached to the tubercle on the inner aspect of each lateral mass of the atlas. A thin plate of fibro-cartilage is developed in its central part. Synovial membrane lines each of the three capsular ligaments, and in addition a synovial sac is developed between the odontoid process and the transverse Ligament. This is more extensive than the synovial cavity between the odontoid process and the atlas. 266 THE ARTICULATIONS OE JOmTS. Articulation of Spine with Cranium. There are two articulations between the atlas and the occiput. Each is a diarthrosis in which movement takes place in relation to two axes, viz. the transverse and the antero-posterior. The condyle of the occiput being biconvex, fits into the biconcave superior articular surface of the atlas, while the long axes of the two joints are directed horizontally forwards and inwards. Ligaments. — Each articulation is provided with a capsular ligament which is thin but complete. It is attached to the rough non-articular surfaces surrounding the articular areas on the atlas and occiput. The following supplementary ligaments are the chief structures which bind the atlas to the occiput : — The anterior occipito-atloid ligament (membrana atlanto-occipitalis anterior, Fig. 212) is a strong although thin membrane, attached inferiorly to the anterior arch of the atlas, and superiorly to the anterior half of the circumference of the foramen magnum. Laterally it is in continuity with the capsular ligaments, while in the mesial plane, where it extends from the anterior tubercle of the atlas to the basi-occiput, it presents a specially well-defined thickened band which might be regarded as a separate accessory ligament or as the beginning of the anterior common ligament of the vertebrae. The posterior occipito-atloid ligament (membrana atlanto-occipitalis posterior, Fig. 212) is another distinct but still thin membrane which is attached superiorly to the posterior half of the circumference of the foramen magnum, and inferiorly to the upper border of the posterior arch of the atlas. Laterally it also is continuous with the capsular ligaments. On each side of the mesial plane its inferior border is arched in relation to the vertebral groove, and is therefore to some extent free, in order to permit the passage of the posterior primary division of the first cervical nerve and the vertebral artery. IMot infrequently this arched border becomes ossified, thus converting the groove in the bone into a foramen. Synovial membrane lines each of the capsular ligaments. There is no direct articulation between the axis and the occiput, but union between them is effected by means of the following accessory ligaments : — The posterior occipito-axoid ligament (membrana tectoria, Fig. 213) is situated within the neural canal, and is usually regarded as the upward continuation of the posterior common ligament of the vertebral bodies. It extends from the posterior Membrana tectoria Cius superius Occipi Lateral ma.s.s of atla.s Atlanto-ax Ligaineiitum apicis dentis (middle odontoid) Ligainentum alare or check ligament Crus superius Ligameiitum cnicia- tum atlantis Accessorj' atlanto- axial ligament Crus inferius Membrana tectoria Fig. 213. — Dissection from behind of the Ligaments connecting the Occipital Bone, the Atlas, AND the Axis with each other. surface of the body of the axis to the basilar groove on the upper surface of the basi-occipital bone, spreading laterally on the circumference of the foramen magnum. Some of its deepest fibres are attached to the atlas immediately above the atlo-axoid articulation. TEMPOEO-MANDIBULAE JOINT. 267 Subjaceut to the preceding ligament there is the ligamentum cruciatum atlantis (Fig. 213), a structure which is very closely associated with the lig. transversum atlantis. It consists of a cms transversum, formed by the superficial fibres of the transverse ligament of the atlas ; a cms inferius, consisting of mesial longi- tudinal fibres which are attached below to the posterior surface of the body of the axis, and above to the crus transversum and a cms superius, also mesial and longitudinal, whose fibres extend from the crus transversum upwards to the posterior surface of the basi-occiput, immediately subjacent to the posterior occipito-axoid ligament. The check ligaments or lateral odontoid ligaments (ligamenta alaria. Fig. 213) are two very powerful, short, and somewhat rounded bands. They are attached mesially to the sides of the summit of the odontoid process, and laterally to the tubercle on the inner aspect of the condylar portions of the occipital bone, viz. the ex- occipital bones. The middle odontoid ligament (ligamentum apicis dentis, Fig. 213) consists of fibres running vertically upwards from the apex of the odontoid process to the mesial pan of the anterior margin of the foramen magnum. This ligament to some extent represents an intervertebral disc, in the centre of which remains of the notochord may be regarded as present. Even in advanced life a small lenticular mass of cartilage, completely sur- rounded by bone, persists in the plane of fusion between the odontoid process and the body of the axis. Movements at these Joints. — At the joints between occiirat and atlas the movements are very simple, and consist essentially of movements whereby the head is elevated and depressed upon the vertebral column (nodding movements). In addition a certain amount of oblique movement is jjossible, during which great stability is attained by resting the front and hinder parts of oi^ijosite condyles upon corresponding parts of the atlas. The head and the atlas rotate together upon the axis, the pivot of rotation being the odontoid process, and the amount of rotation is limited by the check ligaments. No rotation can occur between the occijjut and atlas, and .stability between atlas _ and axis is EMp.nal Hteiai ligament best attained after a slight amount (antenoi and postenoi paits) of rotation, similar to the oblique movement between occiput and atlas. TEMPORO-MANDIBULAR JOINT. This joint is an arthrodial diarthrosis. It occurs between the articular part of the glenoid fossa of the temporal bone and the condylar head of the mandible. These two articular surfaces are markedly dissimilar both in size and shape. In its general outline the articular surface of the head of the mandible is cylindrical, having its long axis directed from within outwards and forwards. On the other hand, the articular part of the glenoid fossa in front of the Grlaserian fissure is concavo-convex from behind forwards. Its articular surface includes the emiuentia articularis, the eminence at the base of the anterior root of the zygoma. The articular surfaces of the bones are clothed by hyaline encrusting cartilage, whilst the joint cavity is divided into an upper and lower part by a meniscus of fibro-cartilage. Ligaments. — The joint is invested by a capsular ligament which is quite com- Stjloul ijruci Stylo-mandibular ligament Fig. 214. — Temporo-Mandibular Joint. 268 THE ARTICULATIONS OE JOINTS. Z ^ Eminentia articularis Fig. 215. MANDIBLE -Section through the Temporo- mandibular Joint. plete, but is very thin on the inner side. The outer wall of the capsule — the external lateral ligament (lig. temporo-mandibulare. Fig. 214) — is divisible into anterior and posterior portions which are attached superiorly to the root tubercle ^ and lower border of the zygoma, and inferiorly to the outer side and posterior border of the neck of the mandible. The direction of its fibres is downwards and backwards. Within the capsule there is an inter- articular disc or meniscus of fibro-cartilage, the discus articularis (Fig. 205), which is moulded upon the condyle of the mandible below, and on the articular surface of the temporal bone above. It thus compensates for the incongruity between the articular surfaces of the two bones. The disc is attached circumferentially to the capsule. It is widest in the transverse direction, thicker behind than in front, and thinnest towards the centre, where it may be per- forated. Its anterior margin is intimately associated with the insertion of the external pterygoid muscle. A synovial membrane hnes each of the compartments into which the joint ca^dty is divided by the meniscus. As a rule these membranes are separate from each other, but they become continuous when the disc is perforated. The upper synovial membrane is larger and more loosely disposed than the lower. Situated on the mesial aspect of the joint, but at a short distance from it, and quite distinct from the capsule, there is an accessory band called the internal lateral ligament (lig. spheno-mandi- bulare. Fig. 216). Superiorly it is attached to the spinous process of the great wing of the sphenoid bone, and spheno-mandibuiar • o ■ 1 , ii 1 n ,T or internal laterak interiorly to the lower as well as the lisament hinder border or lingula of the inferior dental foramen. It is not an articular ligament in the true sense, for instead of being connected with the joint, it is developed in the tissue surrounding part of Meckel's cartilage. Portions of the following structures are found in the interval between the spheno- mandibuiar ligament and the ascending ramus of the mandible — viz. the external pterygoid muscle ; internal maxillaiy vessels ; inferior dental vessels and nerve ; middle meningeal vessels ; auriculo - tem - poral nerve ; a deep portion of the parotid gland. Movements of the Mandible. — The nature of the perform is determined partly by the character of the articular surfaces of the temporo-mandibular joint, and partly by the fact that, while the two joints always act simultaneously, they may also, to some extent, jaerform the same movement alternately. When movement takes place through the long or transverse horizontal axis of each joint, the mandible may be elevated, as in clenching the teeth, or it may be depressed, as in gaping. In the latter movement the condyle leaves the glenoid fossa, and, along with the meniscus, it moves forwards until they rest ui^on tlie articular eminence. Meantime the chin describes the arc of a circle, of which the centre or point of least movement corresponds to the position of the inferior dental foramen, and thus the structures which enter at that foramen are protected against stretching. Coincidently with the forward movement of the condyle, it glides in a revolving manner upon the inferior aspect of the meniscus. At any stage in the movement of depressing the chin the mandible may be protruded, so that the inferior incisor teeth are projected in front of the upper set, a movement which results from the condyles of the jaw being drawn forwards upon the articulai' eminences. A similar mandibular ligament Fig. 216. -Internal Lateral Ligament ok the Temporo-Maxillary Joint. movements which the lower jaw can THE JOINTS OF THE THOEAX. 269 relation of the condyle to the articular eminence occurs during the exaggerated depression of the mandible which results from yawning, in which jjosition tlie articulation is liable to be dislocated. When the two joints perform tlie same movement alternately, a certain amount of lateral motion results, from the fact that the long axis of each joint i)resents a sliglit oljliquity to the transverse axis of tlie skull, and consequently a grinding or oblique movement in the horizontal plane is produced. Excessive depression, wdtli the risk of dislocation, is resisted by the fibres of the external lateral ligament which Ijecomes tense. In all movements of the mandible the meniscus conforms closely to the position of the con- dyle, and they move forwards and backwards together, Itut at the same time the meniscus does not restrict tlie movements of the condyle. Thus while the meniscus, along with the condyle, is gliding upon the temporal aspect of the joint, the condyle itself revolves upon tlie inferior surface of the meniscus. Cranial Ligaments not directly associated with Articulations. The stylo -mandibular ligament (lig. stylo-mandibulare, Figs. 214 and 216) is a specialised portion of the deep cervical fascia which extends from the anterior aspect of the tip of the styloid process of the temporal bone to the posterior border of the angle of the mandible, between the insertions of the masseter and internal pterygoid muscles. The pterygo-spinous ligament (lig. pterygo-spinosum) is a membrane extending from the upper part of the posterior free margin of the external pterygoid plate, backwards and slightly outwards, to the spinous process of the sphenoid. An interval is left between its upper border and the floor of the skull for the outward passage of those branches of the inferior maxillary nerve which supply the external pterygoid, temporal, and masseter muscles. This ligament has a tendency to ossify either wholly or partially. The stylo-hyoid ligament (lig. stylo-hyoideum) may be regarded as the down- ward continuation of the styloid process of the temporal bone. Inferiorly it is attached to the lesser cornu of the hyoid bone. It is not infrequently ossified, in which case it constitutes the epihyal bone found in many animals. THE JOINTS OF THE THORAX. Costo-vertebral articulations (articulationes costo-vertebrales). The typical rib articulates with the vertebral column both by its head and by its tubercle. Thus, two sets of articulations, with their associated ligaments, exist between the ribs and the vertebree, but each set is constructed upon a common plan, with the exception of certain joints situated at the upper and lower ends of the series, where the ribs themselves deviate from the typical form. Costo-Central Joints. The articulations of the heads of the ribs with the centra or bodies of the vertebne (articulationes capitulorum, Fig. 209) are all diarthroses, which, from their somewhat hinge-like action, may be classed as ginglymoid. The head of every typical rib is wedge-shaped, and presents two articular facets, an upper and a lower, separated from each other by an antero-posterior ridge which abuts against an intervertebral disc, while the articular facets articu- late with similar surfaces on the contiguous margins of the two vertebrae adjoining the disc. These surfaces form a wedge-shaped depression or cup, the bottom of which is more elastic than the sides, and thus an arrangement is provided which tends to reduce the shock of blows upon the walls of the chest. Each of these articulations is provided with a capsular ligament which surrounds and encloses the joint, and is attached to contiguous non-articular margins on the head of the rib and the two vertebral bodies. On its anterior or ventral aspect the capsule presents three radiating fasciculi which collectively form the stellate or anterior costo-vertebral ligament (lig. capituli costas radiatum, Fig. 209). These fasciculi radiate from a centre on the front of the head of the rib, so that the middle fasciculus becomes attached to the intervertebral disc while 270 THE AETICULATIONS OK JOINTS. the upper and lower fasciculi proceed to the adjacent margins of the two vertebrae between which the disc is situated, and with which the rib articulates. To a slight extent these radiating fasciculi pass under cover of the lateral margin of the anterior common ligament of the vertebral bodies. In those joints in which the head of the rib does not articvilate with an intervertebral disc the central fasciculus of the stellate ligament is wanting, but the other two retain the same general arrangement. The interarticular ligament (lig. capituli costse interarticulare) consists of short transverse fibres within the capsule. These are attached, on the one hand, to the ridge which intervenes between the two facets on the head of the rib, and on the other to the lateral aspect of the intervertebral disc. This ligament is not a meniscus, but merely an interarticular ligament, of width sufficient to divide the joint cavity into an upper and a lower compartment. It is absent from those joints which do not articulate with an intervertebral disc, i.e. from those ribs which only articulate with the body of one vertebra. The interarticular ligament is supijosed to represent tlie outer end of a ligament which, under the name of the lig. conjugale costarum, connects the heads of the ribs of certain mammals across the posterior asj^ect of the intervertebral disc, and, in the human subject, until the seventh month of foetal life, connects the posterior aspect* of the necks of a pair of ribs with each other across the mesial plane. Synovial membrane lines each joint cavity, and therefore, in all cases where the joint is divided into two compartments, each one has its own synovial lining. Costo-Transverse Joints. The tubercle of each typical rib articulates with the transverse process of the lower of the two dorsal vertebrae with which the head of the rib is associated (articulatio costo-transversaria). Near the tip of the transverse process there is an articular facet, on its anterior aspect, for articulation with the corresponding facet on the mesial articular part of the rib tubercle. The joint so formed is an arthrodial diarthrosis. The joint cavity is surrounded by a comparatively feeble capsular ligament, which is attached immediately beyond the margins of the articular facets, and in which no special bands can be distinguished. A simple synovial membrane lines the capsular ligament in all cases where the latter is present. The following accessory ligaments, in connexion with this joint, strengthen and support the articulation : — The anterior or superior costo-transverse ligament (ligamentum costo-transver- sarium anterius, Fig. 209) consists of strong bands of fibres which are attached to the upper border of the neck of the rib, extending from the head outwards to the non-articular part of the tubercle. All these fibres may be traced upwards. Those situated nearest to the head of the rib proceed obliquely upwards and outwards, to be attached to the transverse process immediately above, but with extensions to the adjoining rib and its costo-transverse capsular ligament. Others proceed almost vertically upwards to the adjoining transverse process, while those which ascend from the upper surface of the tubercle pass obliquely upwards and inwards to reach the postero-inferior aspect of the adjoining transverse process. The posterior costo-transverse ligament (ligamentum costo-transversarium pos- terius) is a band of transverse fibres applied to the postero-external aspect of the capsule. By one end these fibres are attached to the tip of the transverse process behind its articular facet, and by the other to the external rough surface of the tubercle of the rib. The middle costo-transverse ligament (lig. colli costaj) consists of short fibres which stretch from the posterior aspect of the neck of the rib, backwards and in- wards, to the front of the transverse process, but, in addition, a proportion of the fibres passes to the posterior aspect of the inferior articular process of the upper of the two vertebrte with which the head of the rib articulates. COSTO-STERNAL JOINTS. 271 The following exceptions to the general plan of rib-articulation indicated above must be noted : — 1. There is no articulation between the eleventh and twelfth ribs and the transverse processes of the corresponding vertebrae. 2. The superior costo-transverse ligament is wanting from the first rib, and is either rudimentary or wanting in the case of the twelfth rib. 3. The middle costo-transverse ligament is rudimentary in the eleventh and twelfth ribs. The ligamentum lumbo-costale extends from the upper surface of the base of the transverse process of the first lumbar vertebra to the under surface of the neck of the twelfth rib, as well as to the under surface of the transverse process of the twelfth dorsal vertebra. Akticulations betW'Een the Ribs and their Cartilages. Each rib possesses an unossitied portion, termed its costal cartilage. As age advances, this cartilage may undergo a certain amount of superficial ossification, but it never becomes entirely transformed. The line of demarcation between bone and cartilage is clear and abrupt, and usually the bone forms an oval cup, in which the end of the cartilage is retained by means of the continuity which exists between the periosteum and the perichondrium. There is no articulation in the proper sense between the rib and its cartilage, although a synovial cavity has occasionally been found between the first rib and its cartilage. Interchondral Joints. These articulations are arthrodial diarthroses, and they are found between ad- joining margins of certain of the costal cartilages, viz. from the fifth to the eighth or ninth. The cartilages which thus articulate develop flattened, somewhat conical, prolongations of their substance, and thereby the intercostal spaces are interrupted where these flat articular facets abut against each other. Each joint is closed by a surrounding capsular ligament, the superficial and deep aspects of which are specially strengthened by external and internal interchondral ligaments. These bands extend obliquely between adjacent cartilages. A synovial membrane lines each joint capsule. Costo-sternal Joints. The upper seven pairs of costal cartilages, as a rule, extend to the lateral margins of the sternum (articulationes sternocostales). Of these, the first pair is implanted directly upon the manubrium sterni. The ossific process ends abruptly in connexion with the rib, and also ceases as suddenly in connexion with the sternum, and hence the cartilage does not normally present an articulation at either end. From the second to the seventh pairs of ribs inclusive, the costo-sternal joints are constructed upon the type of arthrodial diarthroses, although, in the case of the sixth and seventh cartilages, the joint cavity is always small, and is frequently obliterated. The sternal end of each of these costal cartilages presents a slight antero-pos- terior ridge which fits into a shallow V-shaped depression upon the lateral margin of the sternum. With the exception of the sixth cartilage, the others articulate opposite the lines of union between the primary segments of the sternum, whereas the sixth articulates upon the side of the lowest segment of the meso-sternum. Each joint is enclosed by a capsular ligament, composed of fibrous tissue, attached to the adjacent borders of the articulating elements. Specially strong fibres dis- tinguish the superficial and deep aspects of the capsule. The anterior costo-sternal ligament (lig. costo-sternalium radiatum, Eig. 217) is composed of strong fibres which radiate from the anterior surface of the costal cartilage, near its sternal end, to the front of the sternum. The ligaments of opposite sides interlace with each other, and so cover the front of the sternum with a felted membrane — the membrana sterni. 272 THE AETICULATIONS OE JOINTS. The posterior costo-sternal ligament — also a part of the capsule — has attach- ments similar to the foregoing, but the arrangement of its fibres is not so powerful. The ligamentum costo-xiphoidea passes from the i'rout of the upper part of the xiphoid cartilage, obliquely upwards and outwards to the front of the seventh, and sometimes to the Iront of the sixth costal cartilage. Within the capsules of these joints interarticular ligaments (ligg. sterno-costalia interarticularia, Fig. 217) may be found. Their disposition is somewhat uncertain, for . Costo-clavicular or jfM rhomboid ligament Anterior sterno-clavicular ligament Joint capsule Joint cavity Interarticular ligament Joint cav Anterior chondro-sternal or radiate ligament Fig. 217. — ST^R^o-CL\MCULVR A^D ( osto-sternal Joints. whereas, in the case of the second pair of cartilages, they invariably divide the joint cavity into two distinct compartments — an upper and a lower — such an arrange- ment is very uncertain in the other joints, and they occasionally, especially in the cases of the sixth and seventh cartilages, entirely obliterate the joint cavity. These ligaments extend horizontally between the ends of the costal cartilages and the side of the sternum. Synovial membrane is found wherever a joint cavity is developed, and therefore there may be one or two synovial membranes, according to the presence or absence of a proper interarticular ligament. When the joint cavity is obliterated by the fibrous structure which represents the interarticular ligament, a synovial membrane is also absent. Sternal Articulations. Primarily the sternum consists of an elongated plate of hyaline cartilage, which becomes subdivided into segments by the process of ossification. The four segments of which the gladiolus is originally composed unite with each other after the manner of typical synchondroses. Similarly the ensiform cartilage and the gladiolus ultimately become united. It is not usual to find the manul)rio-gladiolar joint obliterated by the ossification of the two bony segments. Even in advanced life it remains open, and the joint par- takes of the nature of an amphiarthrosis (Fig. 217), although a joint cavity is not found under any circumstances in the plate of fibro-cartilage which intervenes between the manubrium and the gladiolus. The membrana stemi, to which reference has already been made, assists in strengthening the union between the different segments of the sternum. Movements of the Ribs and Sternum. — Tliese movements may be considered either independently of, or as associated witli, respiration. In the former condition the ribs move in connexion with flexion and extension of the vertebral column, being more or less depressed and approximated in the former, and elevated or STERNO-CLAVICULAR JOINT. 273 pulled apart in the latter case. Considered iu connexion with respiration, it is necessary to observe that, to all intents and purposes, the vertebral column and the sternum are rigid structures. Next we must remember that the heads of all the ribs occupy fixed positions, and similarly the anterior ends of seven jjairs of cartilages are fixed to the lateral margins of the sternum. The ribs thus form arches, presenting a large amount of obliquity from behind forwards. There- fore, during ins])iration, when the rib is elevated, the arch becomes more horizontal, and the transverse diameter of the chest is increased. At the same time, the anterior ends of the sternal ribs tend to thrust the sternum forwards and upwards ; but the nature of the attachment of the first pair of ribs to the sternxim, as well as the attachment of the diaphragm to the ensiform cartilage, prevents this moveiuent from becoming excessive, and hence the sternum becomes a line of resistance to the forward thrust of the ribs. As a consequence, the ribs rotate upon themselves about an oblique axis which passes downwards, outwards, and backwards through the capitular joint and the neck of the rib anterior to the costo-transverse joint. In this way increase, both of the antero-posterior and transverse diameters of the thorax, is jjrovided for, although the amount of increase is not equally pronounced in all planes. Thus at the level of the first rib very little ever'sion is possible, because the axis of rotation is nearly transverse, and therefore any increase in the transverse or antero-posterior thoracic diameters at this level may be disregarded, although a certain amount of elevation of the manuljrium sterni and anterior end of the first rib is evident. Below the level of the sixth rib elevation and rotation of the rib during inspiration are usually said to be complicated by a certain amount of backward movement, due to the character of the costo-transverse joint, until, in the case of the last two ribs, which are destitute of costo- transverse joints, a movement backwards is almost entirely substituted for elevation. It is probable, however, that the movements of the asternal ribs exactly correspond to those of the sternal series, and that by the contraction of the costal digitations of the diajihx-agm the anterior ends of the asternal ribs are provided with fixed positions comparable to those supplied by the sternum to the ribs of the sternal series. We may therefore say that during insjoiration the ribs move upwards and outwards between, their fixed ends, while as a whole the rib rotates, and its anterior end is thrust slightly forwards. During exj^iration these movements are simply reversed. THE ARTICULATIONS OF THE SUPERIOR EXTREMITY. The bony arch formed by the clavicle and scapula articulates directly with the axial skeleton only at one point, viz. the sterno-clavicular joint. ARTICULATIONS OF THE CLAVICLE. The Sterno-clavicular Joint. The sterno-clavicular joint (articulatio sterno-cla\"icularis) is an example of an arthrodial diarthrosis. The articular surfaces concerned in its formation present the following appearances : — 1. The sternal end of the clavicle is somewhat triangular iu outline, having its most prominent angle directed downwards and backwards. The anterior and posterior sides of the triangle are slightly roughened for the attachment of Ugaments, while the base or inferior side is smooth and rounded, owing to the prolongation of the articular surface to the inferior aspect of the l^one. In the antero-posterior direction the articular surface tends to be concave, while vertically it is slightly convex. 2. An articular facet, situated on the superior lateral angle of the manubrium sterni, but in a plane slightly behind the supra-sternal notch, articulates with the clavicle. This facet is considerably smaller than the clavicular facet with which it articulates. 3. The superior surface of the first costal cartilage close to the sternum also participates to a small extent in the articulation. It should be noted that the articular surfaces of the clavicle and sternum are covered mainly by fibro-cartilage. A capsular ligament is well marked on all sides except inferiorly, where it is very thin. The anterior sterno-clavicular ligament (Fig. 217) forms part of the capsule, and consists of short fibres which extend obliquely downwards and inwards from the anterior aspect of the sternal end of the clavicle to the adjoining anterior surface of the sternum and the anterior border of the first costal cartilage. The posterior sterno-clavicular ligament also forms part of tlie capsule, and 19 274 THE ARTICULATIONS OE JOINTS. consists of similarly disposed, but not so strong, oblique fibres situated on the posterior aspect of the articulation. A flbro-cartilaginous meniscus (discus articularis, Fig. 217) divides the joint cavity into two compartments. It is nearly circular in shape, and adapts itself to the articular surfaces between which it lies. It is thickest at the circumference and thinnest at the centre, where it occasionally presents a perforation, thereby permitting the two synovial cavities to intercommunicate. By its cu'cumference it is in contact with, and adherent to, the surrounding capsule, but its upper margin is attached to the apex of the articular surface of the clavicle, while by its lower margin it is fixed to the sternal end of the first costal cartilage. Two accessory ligaments are associated with this joint, viz. the interclavicular and the rhomboid. The interclavicular ligament (Fig. 217) is a structure of considerable strength, forming a broad band of fibrous tissue which is attached to the superior rounded angle or apex of the sternal end of the clavicle as well as to the adjacent margins of the articular surface. Its fibres pass across the interclavicular notch to become attached to corresponding parts of the opposite clavicle, but in their course they dip down into the suprasternal notch, in which many of them are fixed to the sternum. In this way their presence neither bridges nor obliterates the notch between the two clavicles, and the hgament really becomes a superior sterno-clavicular Hgament for each joint. The rhomboid ligament (lig. costo-claviculare. Fig. 217) consists of short, strong fibres which are attached inferiorly to the upper surface of the first costal cartilage. They pass obhquely upwards and outwards to a rough impression situated on the lower aspect of the sternal end of the clavicle, and are distinct from the capsular Ligament. Occasionally a bursa is found in the interior of this ligament. As a rule there are two synovial membranes lining the two joint cavities (Fig. 217), separated from each other by the interarticular meniscus. Sometimes, however, the two membranes establish continuity through a perforation in the meniscus. The Acromio-clavicular or Scapulo-clavicular Joint. The acromio - clavicular joint (articulatio acromio - clavicularis) is another instance of an arthrodial diarthrosis. It is situated between the acromial end of the clavicle and the inner aspect of the acromion process of the scapula. Each articular surface is an oval, flattened facet, covered by fibro-cartilage. The ligaments which surround this small joint form a complete capsule (capsula articularis), of which the upper and lower parts are specially strong, and are therefore named the superior and inferior acromio-clavicular ligaments (Fig. 219). These consist of short fibres passing between the adjacent rough margins of the two bones in the positions indicated by their names. A meniscus (discus articularis), which is nearly always incomplete, and may occasionally be wanting, is usually found within the joint cavity, where it lies obliquely, with its upper margin farther from the mesial plane than its lower margin, and having its borders attached to the surrounding capsule. Frequently the meniscus is wedge-shaped, with its base directed upwards and its apex free. A synovial membrane is found forming either a single or a double sac, according to the condition of the meniscus. Complete division of the joint cavity, however, is rare. Ligamentum Coraco-claviculare.^ — Accessory to this articulation there is the strong coraco-clavicular ligament which binds the acromial end of the clavicle to the coracoid process of tlie scapula. It is readily divisible into two parts, viz. the conoid and trapezoid ligaments. The conoid ligament (Fig. 219) is situated internal to and sUghtly behind the trapezoid. It is narrow and pointed at its inferior end, by which it is attached to the upper aspect of the coracoid process, in close proximity to the suprascapular notch. Its upper end widens out in the manner expressed by its name, and is attached to the conoid tubercle of the clavicle. The trapezoid ligament (Fig. 219) is attached inferiorly to the u^jper surface of the posterior half of the coracoid process, external and anterior to the attachment of ACEOMIO-CLAVICULAE JOINT. 275 the conoid ligament. Superiorly it is attached to the trapezoid ridge on the under surface of the acromial end of the clavicle. Its outer and inner borders are free. Its anterior surface is principally directed upwards, and its posterior surface, to a similar extent, looks downwards. A synovial bursa usually occupies the re-entrant angle between these two ligaments. Movements at the Clavicular Joints. — The movements of the inner end of the clavicle at the sternoclavicular joint are limited m their range, owing to the tension of the ligaments. When the shoulder is raised or depressed the outer end of the clavicle moves uj^wards and downwards, whilst its sternal end glides upon the surface of the interarticular meniscus within the joint ; when, on the other hand, the shoulder is carried forwards or backwards, the inner end of the clavicle along with the interarticular meniscus moves upon the sternal facet. In addition to these movements of elevation, depression, forward movement and backward move- ment of the clavicle, there is also allowed at the sterno-clavicular joint a certain amoimt of circumduction of the clavicle. The part which is played by certain of the ligaments in restraining movement requires careful con.sideration. The rhomboid ligament checks excessive elevation of the shoulder, and restrains within certain limits Ijoth backward and forward movement of the clavicle. When the clavicle is depressed, as in cases where a heavy weight, such as a bucket of water, is carried in the hand, it receives support by resting upon the first rib, and the tendency for the inner end of the bone to start uja out of its sternal socket is obviated by the tension of the interarticular meniscus, the interclavicular ligament, and the anterior and posterior sterno - clavicular ligaments. The interarticular meniscus not only acts as a cushion which lessens the shock of blows received upon the shoulder, but it also acts as a most important bond of union, and prevents the inner end of the clavicle from being driven upwards upon the top of the sternum when force is applied to its outer end. The movements at the aero mio -clavicular joint are of such a kind as to allow the inferior angle, and to some extent the base of the scapula, to remain more or less closely applied to the chest-wall during the various movements of the shoulder. The strong connexion between the coracoid process and the acromial end of the clavicle, by means of the conoid and trapezoid ligaments, renders it necessary that the scapula should follow the clavicle in its various excursions. The presence of the acromio-claAncular joint, however, enables the scaj^ula to change its position somewhat with reference to the clavicle as the shoulder is moved. Thus, when the shoulder is raised and depressed, a marked difference takes place in the angle between the two bones ; again, when the shoulder is thrown forwards or backwards, these movements can be performed without altering in a material degree the direction of the glenoid cavity of the scapula, or in other words, the socket of the shoulder-joint. The conoid and trapezoid ligaments set a limit irpon the movements of the scapida at the acromio-clavicular joint. They both, but more particularly the trapezoid ligament, prevent the acromion process of the scapula from being carried inward below the outer end of the clavicle when blows fall upon the outer aspect of the shoulder. Ligaments of the Scapula. These ligaments are not directly connected with any articulation. The coraco- acromial ligament (lig. coraco-acromiale, Fig. 219) completes the arch between the coracoid and acromion processes of the scapula, and thus provides a secondary socket for the greater protection and security of the shoulder-joint. It is a flat triangular structure stretched tightly between its lines of attachment. By its base it is fixed to a varying amount of the postero-external border of the coracoid process, and by its narrower apical end to the tip of the acromion process, im- mediately external to the acromio-clavicular joint. Its surfaces look upwards and downwards, and its free borders outwards and inwards. It is thinnest in the centre, where it is sometimes perforated by a prolongation of the tendon of the pectoralis minor muscle. The suprascapular ligament (lig. trausversum scapulae superius) is a distinct but short flat band which bridges the notch of the same name. It may be continuous with the conoid ligament, and it is frequently ossified. As a rule the foramen completed by this ligament transmits the suprascapular nerve, while the corre- sponding vessels travel above the ligament to reach the supraspinous fossa. A small duplicate of this ligament may often be found bridging the foramen on its ventral aspect, subjacent to which small branches of the suprascapular artery return from the supraspinous to the subscapular fossa. The spino- glenoid ligament (lig. trans versum scapulae inferius) consists of another set of bridging fibres which are situated on the posterior aspect of the 276 THE ARTICULATIONS OE JOINTS. neck of the scapula. By one end they are attached to the external border of the scapular spine, and by the other to the adjacent part of the posterior aspect of the head of the scapula. The suprascapular nerve and vessels pass subjacent to this ligament. THE SHOULDER-JOINT. The shoulder-joint (articulatio humeri) is one of the largest as well as the most important of the joints of the upper hmb. It is an example of the enarthrodial, i.e. ball-and-socket variety of a diarthrosis, and, at the cost of a certain amount of security, it has obtained an extended range of movement. The bones which enter into its formation are the glenoid fossa of the scapula and the head of the humerus. The glenoid fossa is a shallow pyriform articular surface, having its narrow end directed upwards and slightly forwards. The upper half of the anterior margin of the fossa is characterised by a shallow notch which accommodates the narrow part of the subscapularis muscle as it runs outwards to its insertion. At the apex of the fossa there is a flat area for the attachment of the long tendon of the biceps flexor cubiti muscle. The head of the humerus is hemispherical and articular, while, external to its articular margin, there is a slight constriction (the anatomical or true neck of the humerus), which is most strongly marked in relation to the greater and lesser tuberosities of the humerus. Under ordinary conditions the two articular surfaces are maintained in apposition by muscular action, aided by atmospheric pressure, and thus, when the muscles are removed, the bones fall asunder to the full extent of the restraining ligaments. Only a small part of the humeral head is in contact with the glenoid fossa at any particular moment, because the former is much larger than the latter, but, by reason of the shallow character of this fossa, all parts of the two articular surfaces may successively be brought into contact with each other. In the position of rest, as the Hmb hangs parallel to the vertical axis of the trunk, the inferior aspect of the neck of the humerus is brought into close relation with the lower part of the glenoid fossa. The glenoid ligament (labrum glenoidale. Fig. 219) deepens the glenoid fossa, and thus extends the articular surface. It is situated within the joint capsule, and to some slight ex- Coraco-acromial ligament Acromion proces.s / /= Coracoid pioce-^b \ Curaco humeral li_, anient Communication between subscapular, bur.sa and joint cavity Capsule of joint Fig. 218. — Cap.sulk of thk Shouldek-Joint and Cokaco-acromiai, Lr(;AMHNT tent increases the security of the arti- culation. It con- sists of a strong hubscapuiaris ring of dcnsc fibrous tissue attached to the free margin of the glenoid fossa. Many of its fibres- are short, and pass obliquely from the inner to the outer aspect of the ridge, so that its attached base is broader than its free edge, and there fore in cross sec- tion it appears some- what triangular. The long tendon of the biceps, which considerable extent in- arises from the apex of the glenoid fossa, becomes to a corporateil with this linainent. The capsular ligament (capsula articularis. Fig. 218) presents the general shape which is characteristic of the corresponding ligament in other ball-and-socket joints, THE SHOULDEE-JOINT. 277 viz. a hollow cylinder. By its upper end the capsule is attached to the circum- ference of the glenoid fossa, external to the glenoid ligament, and also, to a consider- able extent, to the glenoid ligament itself. By its lower end it is attached to the neck of the humerus, and therefore beyond the articular area of the head. The capsule is strongest on its superior aspect, while inferiorly, where the neck of the bone is least defined, it extends downwards for a short distance upon the humeral shaft. Its fibres for the most part run longitudinally, but a certain number of them pursue a circular direction. A prolongation of the capsule, the transverse humeral ligament presenting both longitudinal and transverse fibres, bridges that part of the bicipital groove which is situated between the tuberosities of the humerus. At this point an interruption in the capsule, beneath the transverse humeral ligament, permits the long tendon of the biceps to escape from its interior. In addition to the opening just referred to, there is another very constant deficiency in the upper and anterior part of the capsule, where the narrowing tendon of the subscapularis muscle is brought into contact with a bursa formed by a protrusion of the syno^dal membrane. This defect in the capsule has its long axis in the direction of the longitudinal fibres. Occasionally there is a similar but smaller opening under cover of the tendon of the infraspinatus muscle. Through the two latter openings the joint cavity communicates with bursae situated between the capsule and the muscles re- ferred to. The tendons of the subscapularis, supraspinatus, and infraspinatus muscles fuse with, and so strengthen, the capsule as they approach their respective insertions. On the superior aspect of the articulation the capsule is augmented by an accessory structure, the ligamentum coraco-humerale (Fig. 218). By its inner end, which is situated immediately above the glenoid fossa, but subjacent to the coraco- acromial ligament, it is attached to the external border of the root of the coracoid process, while its outer end is attached to the humeral neck close to the great tuberosity. This ligament forms a flattened band, having its hinder and lower border fused with the capsule, but its anterior and upper margin presents a free edge, slightly raised above the level of the cap- sule. This struc- ture is believed to represent that portion of the pectoralis minor to which refer- ence has already been made in con- nexion with the coraco - acromial ligament (p. 275). The coraco- glenoid ligament is another accessory structure which is not always present. It springs from the coracoid process along with the former ligament, and extends to the upper and hinder margin of the head of the scapula. Gleno-humeral Ligaments (Fig. 219). — If the capsule be opened from behind, and the head of the humerus be removed, it will be seen that the longitudinal fibres of the anterior part of the capsule are specially developed in the form of thick flattened bands which extend from the anterior border of the glenoid fossa to the anterior aspect of the neck of the humerus. These gleno-humeral Coraco- "\ Conoid clavicular -Trapezoid ligament J Coraco-acroinial ligament Coracoid process ;;leno-humeral liaament Superior Bursal perforation in capsule Inferior gleno-liumeral li.arament Glenoid cavit\ Glenoid licament Fig. 219.- -Capsdlar Ligament of Shoulder-Joixt cut across and Humerus removed. 278 THE AETICULATIONS OE JOINTS. ligaments are three in numbei', and occu^)}' tlie following positions : the superior is placed above the aperture in the front of the capsule ; the middle and inferior on the antero-inferior aspect of the capsule, and heloiv the apertiire mentioned. The superior gleno-humeral ligament, which some believe to reiDi-esent the ligamentum teres of the hip-joint, springs, along with the middle gleno-humeral band, from the upper j^art of the anterior glenoid margin. The inferior band is the strongest of the three, and springs from the lower part of the anterior glenoid margin. Intra-capsular Structures. — 1. The glenoid ligament, already described. 2. The long tendon of the biceps passes outwards from its attachment to the apex of the glenoid fossa and the adjoining part of the glenoid ligament, above the head and neck of the humerus, to escape from the interior of the capsule by the opening between the tuberosities of the humerus, subjacent to the transverse humeral ligament. Synovial membrane (Fig. 220) lines the capsule of the joint, and extends from the margin of the glenoid fossa to the humeral attachments of the capsule, where it is reflected towards the margin of the articular cartilage. It is there- fore important to note that the inferior aspect of the humeral neck has the most extensive clothing of synovial membrane. Further, the synovial membrane envelops the intra-cap- sular part of the tendon of the biceps, and al- though this tubular sheath is prolonged upon the tendon into the upper part of the bi- cipital groove, yet the closed character of the synovial cavity is main- tained. Thus, while the tendon is within the capsule, it is not within continuous with those bursas the Head of scapula CaMt^ ofjomt Fig. 220. — Vertical Section through the Shouldee-Joint. the synovial cavity. The synovial membrane is which communicate with the joint cavity through openings in capsule. ligamentous Bursse (a) Communicating vjith the Joint Cavity. — Practically there is only one bursa which is constant in its position, viz. the subscapular, between the capsule and the tendon of the sub- scapularis muscle. It varies considerably in its dimensions, but its lining membrane is always continuous with that which lines the capsule (Figs. 21*7 and 218), and therefore it may be regarded merely as a prolongation of the articular sjTiovial membrane. Occasionally a similar but smaller bursa occurs between the capsule and the tendon of the infraspinatus uiuscle. (h) Not com/rmmicating with the Joint Cavity. — The sub-deltoid or sub-acromial bursa is situated between tlie muscles on the superior aspect of the shoulder-joint on the one hand and the deltoid muscle on the other. It is an extensive bursa, and is j^rolonged subjacent to the acromion process and the coraco-acromial ligament. It does not communicate with the shoulder- joint, but it gi'eatly facilitates the movements of the upper end of the humerus against the under surface of the coraco-acromial arch. Movements at the Shoulder-Joint. — A ball-and-socket joint permits of a great variety of movements, practically in all directions ; but if these movements be analysed, it will be seen that they resolve themselves into movements about three primary axes at right angles to each other, or about axes which are the possible combinations of tlie primary ones. Thiu3, about a transverse axis, the limb may move forwards (flexion) or backwards (extension). About an antero-posterior axis it may move outwards, i.e. away from the mesial plane of the trunk fabduction), or inwards, i.e. towards, and to some extent up to, the mesial plane (adduction;. About a vertical axis, the humerus may rotate upon its axis in an inward or out-ward direction to the extent of a quarter of a circle. THE ELBOW-JOINT. 279 Since these axes all pass through the shoulder-joiut, and since each may present varying degrees of obliquity, it follows that very elaborate comljiuations are possible until the movement of circumduction is evolved. In this movement the head of the humerus act-s as the apex of a cone of movement with the distal end of the humerus, describing the base of the cone. The range of the shoulder-joint movements is still further increased from the mobility of the scapula as a whole, and from its association with the movements of the cla\dcle already described. THE ELBOW-JOINT. lisameiit This articulation (articulatio cubiti) provides an instance of a diarthrosis capable of performing the movements of flexion and extension about a single axis placed transversely, i.e. a typical ginglymus diarthrosis or hinge-joint. The bones which enter into its formation are the humerus, ulna, and radius. The trochlea of the humerus articulates with the greater sigmoid cavity of the ulna (articulatio humero-ulnaris) ; the capitellum of the humerus articulates with the shallow depression or cup on the superior aspect of the head of the radius (articu- latio humero-radialis). The articular cartilage clothing the trochlea of the humerus terminates in a sinuous or concave margin both anteriorly and posteriorly, so that it does not line either the coronoid or the olecranon fossa. Internally, it merely rounds off the inner margin of the trochlea, but exter- nally it is continuous with the encrusting cartilage covering the capitellum, to the margin of which the cartilage extends in all directions, and thus it pre- sents a convex edge in relation to the supra-capi- tellar or radial fossa. The cartilage which lines the greater sigmoid ca"sdty of the ulna presents a trans- verse interruption, consider- ably wider on its inner as compared with its outer aspect. Thereby the coro- noid and olecranon seg- ments of the fossa are separated from each other. The cartilage which clothes the coronoid segment is continuous with that which clothes the lesser sigmoid cavity. The shallow cup- shaped depression on the head of the radius is covered by cartilage which rounds off the margin, and is pro- longed without interruption upon the vertical aspect of the head, descending to its lowest level on that part opposed to the lesser sigmoid ca-sdty. Ligaments. — Taken as a whole, the ligaments form a complete capsule (capsula articularis), which is not defective at any point, although it is not of equal thick- ness throughout, and certain bands of fibres stand out distinctly because of their greater strength. The anterior ligament (Fig. 221) consists of a layer whose fibres run in several Internal lateral igament don of insertion of biceps muscle Oblique (ulno-radial) licraiaent Fig. 221. — Axxekior View of Elbow-Joixt. 280 THE AETICULATIONS OE JOINTS. directions — obliquely, transversely, and vertically — and of these the vertical fibres are of most importance. It is attached above to the upper margins of the coronoid and supracapitellar fossse ; below, to the margins of the coronoid process and to the orbicular ligament of the superior radio-ulnar joint, but some loosely arranged fibres reach as far as the neck of the radius. The lateral portions of this ligament, which are situated in front of the capitellum and the inner margin of the trochlea respectively, are much thinner and weaker than the central part. Fibres of origin of the brachialis anticus muscle are attached to the front of this ligament. The posterior ligament is an extremely thin, almost redundant layer. Superiorly it is attached, in relation to the margin of the olecranon fossa, at a varying distance from the trochlear articular surface, and inferior ly to the summit and sides of the lip of the olecranon process. Externally some of its fibres pass from the posterior aspect of the capitellum to the posterior border of the lesser sigmoid cavity of the ulna. This ligament derives material support from, and participates in the movements of, the triceps extensor cubiti muscle, since they are closely adherent to each other in the region of the olecranon process. The internal lateral ligament (lig. collaterale ulnare. Figs. 221 and 222) is a fan- Interosseous membrane Radius Coronoid proce=& L Internal condyle ^Anterior part of internal lateral ligament Posterior part of T Mis internal lateral ligament Olecranon process Ulna Transverse part of internal lateral ligament Fig. 222. — Elbow- Joint (inner aspect). shaped structure of unequal thickness, but its margins, which are its strongest bands, are continuous with the adjoining parts of the anterior and posterior ligaments. By its upper end it is attached to the anterior, inferior, and posterior aspects of tlie internal condyle of the humerus. By its broad lower end it is attached to the inner margin of the greater sigmoid cavity, so that the anterior hand is associated principally with the inner margin of the coronoid process, and the posterior hand with the inner margin of the olecranon process, while the intermediate weaker portion sends its fibres downwards to join a transverse hand, sometimes very strong, which bridges the notch between the adjoining inner margins of the coronoid and olecranon processes. The external lateral ligament (lig. collaterale radiale, Fig. 221) is a strong flattened band attached superiorly to the lower and posterior aspects of the external condyle of the humerus. It completes the continuity of the capsule on the outer side, and blends inferiorly with the orbicular ligament, on the surface of which its fibres may be traced both to the anterior and posterior ends of the lesser sigmoid THE KADIO-ULNAE JOINTS. 281 Olecranon pad of fat Coronoid process Trochlea Olecranon process Fig. 223. Vertical Section through the Trochlear Part of Elbow-Joint. notch. Both of the lateral ligaments are intimately associated with the muscles which take origin from the inner and outer condyles of the humerus. Synovial Pads of Fat (Fig. 22.3).— Internal to the capsule, there are several pads of fat situated be- tween it and the sy- novial membrane. Small pads are so placed as to lie im- mediately in front of the coronoid antl supra-capitellar foss?e, but a larger one projects to- wards the olecra- non fossa. Synovial mem- brane (Fig. 223) lines the entire capsule and clothes the pads of fat above referred to, as well as those portions of bone enclosed within the capsule which are not covered by articular cartilage. By its disposition the elbow and the superior radio- ulnar joints possess a common joint cavity. It should be specially noted that the upper part of the neck of the radius is surrounded by this synovial membrane. Movements at the Elbow-Joint. — The movements of the radius and ubia upon the humerus have already been referred to as those characterising a uniaxial joint constructed on the plan of a hinge. In this case the axis of the joint is obliquely transverse, so that in the extended position the humerus and ulna form an obtuse angle open towards the radius, whereas in the flexed position the hand is carried inwards in the direction of the mouth. Extreme flexion is checked by the soft parts in front of the arm and of the fore-arm coming into contact, and extreme extension by the restraining effect of the ligaments and muscles. In each case the movement is checked before either coronoid or olecranon processes come into contact with the humerus. The anterior and posterior bands of the internal lateral ligament are important factors in these results. Lateral movement of the ulna is not a characteristic movement, although it may occur to a slight extent, owing to a want of complete adajitation between the trochlear surface of the humerus and the sigmoid caAdty of the ulna. This incongruence is noteworthy since the inner lip of the trochlea is prominent in front, and the outer lip is prominent behind. Consequently, this latter part is associated with a surface on the outer side of the olecranon which is only utilised in complete extension. The capitellum and the opposing surface ui^on the head of the radius are always in varying degrees of contact. The head of the radius jsarticipates in the movements of flexion and exten- sion, and is most closely and completely in contact with the humerus during the position of semi- flexion and semi-pronation. In complete extension a very considerable part of the capitellum is uncovered by the radius. THE RADIO-ULNAR JOINTS. These articulations, which are two in number, are situated at the proximal and distal ends of the radius and ulna. They provide an adaptation whereby the radius rotates around a longitudinal axis in the movements of pronation and supination, and hence this form of uniaxial diarthrosis is termed lateral ginglymus. Superior Radio-ulnar Joint (articuktio radio-ulnaris proximalis). — In this joint the articular surfaces which enter into its formation are the lesser sigmoid cavity of the ulna and the lateral aspect of the head of the radius. In each case the articular cartilage is continuous with an articular surface entering into the formation of the elbow-joint, consequently the joint cavity is continuous with that 282 THE ARTICULATIONS OE JOINTS. Olecranon process Lessei sia;mOKl caMty Transvei'se portion of internal lateral lisament llll Greater sigmoid peavity Orbicular ligament Coronoid process Fig. 224. — Orbicular Ligament of the Radius. of the elbow-joint, and therefore, in a sense, it lies within the cover of the capsule of the elbow-joint ; but its special feature is the — Orbicular ligament (hg. annulare radii, Figs. 221 and 224), which has formerly been mentioned as the inferior line of attachment of the external lateral ligament and the ligaments on the front and back of the elbow- joint. It is a strong,well-defined struc- ture, attached by its extremities to the anterior and posterior margins of the lesser sigmoid cavity, and thus it forms nearly four-fifths of an osseo-tendinous circle or ring. This circle is some- what wider at the upper than at the lower margin of the orbicular ligament, which, by encircling the upper part of the neck of the radius, tends to prevent displace- ment of the head of that bone in a downward direction. The lower margin of this ligament is not directly attached to the radius. The synovial membrane is continuous with that which lines the elbow-joint. It closes the joint cavity at the inferior unattached margin of the orbicular ligament, where it is somewhat loosely arranged in its reflexion from the ligament to the neck of the radius. Inferior Radio-ulnar Joint (articulatio radio-ulnaris distalis). — This joint is situated between the sigmoid cavity on the inner side of the lower end of the radius and the lateral aspect of the head of the ulna. In addition, it includes the inferior surface of the head of the ulna, which articulates with the superior surface of a triang'ular plate of fibro-cartilage, by means of which the joint is excluded from the radio-carpal articulation The triangular interarticular fibro-cartilage (discus articularis, Figs. 225 and 227), besides presenting articular surfaces to two separate joints, is an important ligament concerned in binding together the lower ends of the radius and ulna. It is attached by its apex to the de- pression at the outer side of the root of the styloid process of the ulna, and by its base to the sharp line of de- marcation between the sigmoid cavity and the carpal articular surface of the radius. The ligamentous cap- sule is very imperfect, and consists of scattered fibres, termed the anterior and posterior radio-ulnar ligaments (Fig. 226). These ligaments pass transversely between adjoining non-articular surfaces on the radius and ulna, and are of sufficient length to ]jermit of tiie movements of the radius in pronation and supination. The synovial membrane completes the closure of the joint cavity. It forms a loose bulging projection (recessus sacciformis), passing upwards between the lower ends of the shafts of the radius and ulna, and it also clothes the upper surface of the trkingular fibro-cartilage (Fig. 227). The cavity of this joint is quite distinct from that of the radio-carpal articulation, except when the triangular fibro-cartilage presents a perforation. Between the foregoing articulations there are two accessory ligaments, viz. the interosseous membrane and the oblique ligament, which connect together the shafts of the radius and ulna. Sui'face for scaphoid bone Groove for tendni ^ of extensor longus-^ ^ polliois Head of ulna Styloid process of ulna Ij — ■ I Apex of triangular tibro-cartilage Triangular fibro-cartilage Surface for semilunar bone Fig. 225. — Carpal Articular Surface of the Radius, and Triangular Fibro-cartilage of the Wrist. THE EADIO-CARPAL JOINT. 283 The interosseous membrane (Fig. 222) of the fore-arm (membrana interossea inter- brachii) is a strong filn'ous membrane which stretches across the interval between the radius and uhia, and is firmly attached to the interosseous border of each. Below it extends downwards to the lower limit of the space between the bones, whilst above it does not reach higher than a point about one inch below the tuberosity of the radius. A gap, called the hiatus interosseus, is thus left above its upper margin, and through this the posterior interosseous vessels pass backwards between the bones to reach the dorsal aspect of the fore-arm. This gap is bounded above by the oblique ligament. The fibres which compose the interosseous membrane run for the most part downwards and inwards from the radius to the ulna, although on its dorsal aspect several bands may be observed stretching in an opposite direc- tion. The interosseous membrane augments the surface available for the origin of the muscles of the fore-arm ; it braces the radius and ulna together ; and when shocks are communicated from the hand to the radius, owing to the direction of its fibres, the interosseous membrane transmits these, to some slight extent, to the ulna. The oblique ligament (Fig. 222) is a slender tendinous band of very varying strength which springs from the outer part of the coronoid process of the ulna, and stretches oljliquely downwards and outwards to the radius where it is attached immediately below the bicipital tuberosity. Movements of the Eadius on the Ulna. — The axis about wlucli the radius moves is a longitudinal one, having one end j^assing through the centre of the head of the radius and the other through the styloid process of the iilna and the line of the ring-finger. In this axis the head of the radius is so secured that it can only rotate upon the lesser sigmoid cavity of the ulna within the orbicular ligament, and consequently the radial head remains upon the same plane as the ulna ; but the lower end of the radius being merely restrained by the triangular fibro-cartilage, is able to describe nearly a half-circle, of which the apex of this ligament is the centre. In this movement the radius carries the hand from a position in which the palm is directed forwards, and in which the radius and ulna lie parallel to each other (supination), to one in which tliepalm is directed backwards, and the radius lies diagonally across the front of the ulna (pronation). The ulna is unable to rotate upon a long axis, but while the radius is travelling through the arc of a circle from without inwards in front of the ulna, it will usually be seen that the ulna ajJi^ears to move through the arc of a smaller circle in the reverse direction, viz. from within outwards. If the humerus be j)revented from moAdng at the shoulder-joint, a very large propor- tion, if not the entire amount, of this apparent movement of the ulna will disappear-. At the same time some observers maintain that it really occurs at the elbow -joint, associated with lateral movement during slight degrees of flexion and extension at that joint. THE RADIO-CARPAL JOINT. This joint (articulatio radiocarpea) is a bi-axial diarthrosis, frequently called a condyloid joint. The articular elements which enter into its formation are: on its proximal side, the inferior surface of the lower end of the radius, together with the inferior surface of the triangular fibro-cartilage ; on its distal side, the superior articular surfaces of the scaphoid, semilunar, and cuneiform bones. The articular surface of the radius is concave both in its antero-posterior and transverse diameters, in order to adapt itself to the opposing surfaces of the scaphoid and semilunar, which are convex in the two axes named. In the ordinary straight position of the hand the triangular fibro-cartilage is in contact with the semilunar bone, and the upper articular surface of the cuneiform bone is in contact with the capsule of the joint. When, however, the hand is bent towards the ulna, the cuneiform bone is carried outwards as well as the semilunar and scaphoid, and the triangular fibro-cartilage comes into contact with the cuneiform. The articular surface of the radius is subdivided by an antero- posterior, slightly elevated ridge, into an outer triangular facet which usually arti- culates with the scaphoid, and an inner quadrilateral facet for articulation with a portion of the semilunar bone. In the intervals between the scaphoid, semilunar, and cuneiform bones, the con- tinuity of the articular surfaces is usually maintained by the presence of interosseous ligaments which are situated upon the same level as the articular cartilage. Ligaments. — A capsular ligament completely surrounds the joint. It is some- what loosely arranged, and permits of subdivision into the following portions : — The external lateral ligament (Fig. 226) is a well-defined band which is attached 284 THE AETICULATIOXS OE JOINTS. Anterior radio- ulnar liframent Internal lateral ligament Pisiform bone bj one end to the tip of the styloid process of the radius, and by the other to a rough area at the base of the tubercle of the scaphoid bone, i.e. external to its radial articular surface. The internal lateral ligament (Fig. 226) is also a distinct rounded structure, having one end attached to the tip of the styloid process of the ulna, and the other to the rough non - articular border of the cuneiform bone, some of its fibres being prolonged to the pisiform bone. The anterior ligament (Fig. 226) is attached superiorly to the anterior margin of the lower end of the radius, as well as rubercie of .scaphoid sHghtly to the base of the styloid process of tlie Ridge oil T ri , trapezium uina. feomc transversc fibres may be seen, but riapezium the greater number pass obliquely downwards and inwards to the palmar non-articular surfaces of the scaphoid, semilunar, and cuneiform bones, while some of them may even be continued as far as the OS magnum. Those fibres from the ulna run obliquely out- wards. On its deeper aspect this ligament is the triangular fibro-cartilage of the Os magnum, with ligaments radiat- ing from it Unciform proves: Fig. 226. — Ligaments on Anterior Aspect of Radio-carpal, Carpal, and Carpo-metacarpal Joints. closely adherent to the anterior border of inferior radio-ulnar articulation. The posterior ligament extends from the posterior margin of the lower end of the radius, obliquely downwards and inwards, to the dorsal non - articular areas on the proximal row of the carpal bones. The slip to the latter assists in forming the fibrous sheath through which the tendon of the extensor carpi ulnaris muscle travels to its insertion. The principal bundle of fibres is connected with the cuneiform bone. The synovial membrane (Fig. 227) is simple, and is confined to the articulation, except in those cases in which the triangular fibro-cartilage is perforated, or in which one of the interosseous ligaments between the carpal bones of the first row is absent. Movements at the Radio-carpal Joint. — The radio-carpal joint affords an excellent example of a biaxial articulation, in which a long transverse axis of movement is situated more or less at right angles to a short axis placed in the antero-posteiior direction. The nature of the move- ments which are possible about these two axes is essentially the same in both cases, viz. flexion and extension._ The movements about the longer transverse axis are anterior or palmar flexion, extension, and its continuation into dorsi-flexion. About the shorter antero -posterior axis we get movements which re.sult from combined action by certain flexor and extensor muscles, whereby the radial or ulnar borders of the hand may be approximated towards the corresponding borders of the fore-arm. Lateral movement may also be possible to a slight extent. The range of move- ment in connexion with either of the principal axes is largely a matter of individual peculiarity, for, with the excej)tion of the lateral ligaments, there is no serious obstacle to the cultivation of greater mobility at the radio-carpal joint. CARPAL JOINTS. The articulations subsisting between the individual carpal bones (articulationes mtercarpeffi) are all diarthroses, and although the total amount of movement throughout the series is considerable, yet the extent of movement which is possible ARTICULATIONS OF THE CAEPUS. 285 between the two rows or between any two carpal bones is extremely limited. Yov this reason, as well as because of the nature of the movement, these articula- tions are called gliding joints (arthrodia). It is advisable to consider, j^rs^, the articulations between individual bones of the proximal row ; second, the articulations between the separate bones of the distal row ; third, the articulation of the proximal and distal rows with each other ; fourth, the pisiform articulation. The proximal row of carpal articulations (Fig. 226) comprises the joints between the scaphoid, semilunar, and cuneiform bones. On their adjacent lateral aspects these bones are partly articular and partly non-articular. Three sets of simple but strong, although short ligamentous bands bind these three carpal bones together, and form an investment for three sides of their inter- carpal joints. These are — (1) the anterior or palmar ligaments, two in number, which consist of transverse fibres passing between the adjacent rough palmar surfaces of the bones ; (2) the posterior or dorsal ligaments, also two in number, and composed of similar short transverse fibres passing between the adjacent dorsal surfaces ; (3) the interosseous ligaments (Fig. 227), again two in number, and transverse in direction, situated on a level with the superior articular surfaces, and extending from the palmar to the dorsal aspect of the bones, while attached to non-articular areas of the opposing surfaces. The radio-carpal joint is entirely shut off from the inter- carpal joints, and also from the joint between the two rows of carpal bones, except in rare cases, when an interosseous ligament is wanting;. The distal row of carpal articulations (Fig. 226) includes the joints between the trapezium, trapezoid, os magnum, and unciform bones. Articular facets occur on the opposing lateral faces of the individual bones. Associated with this row there are again simple bands of considerable strength, and presenting an arrangement similar to that seen in the proximal row. As in the former case, they invest the intercarpal articulations, except on the superior aspect, where they communicate with the transverse carpal joint, and on the inferior aspect, where they communicate with the carpo-metacarpal joint cavity. The anterior or palmar ligaments are three in number. They extend in a trans- verse direction between contiguous portions of the rough palmar surfaces of the bones. The posterior or dorsal ligaments, also three in number, are similarly dis- posed on the dorsal aspect. The interosseous ligaments (Fig. 227) are two or three in number. That which joins os magnum to unciform is the strongest ; that between the trapezoid and os magnum is situated towards the dorsal parts of their opposing surfaces ; the third, situated between contiguous non-articular surfaces of the trapezium and trapezoid, is always the feeblest, and is frequently absent. The transverse carpal articulation (Fig. 227) is situated between the proxunal and distal rows of the carpus. The bones of the proximal row present the following characters on iheir inferior or distal aspect. The outer part of the articular surface is deeply concave, both in the antero-posterior and in the transverse directions, but the inner part of the same surface is concavo-convex, more especially in the trans- verse direction. Superiorly, the articular surfaces of the distal row of carpal bones present an irregular outline. That part pertaining to the trapezium and trapezoid is concave in the antero-posterior and transverse directions, and lies at a considerably lower level than the portion belonging to the os magnum and unciform, which is, more- over, markedly convex in the antero-posterior and transverse directions, with the exception of the innermost part of the unciform, where it is concavo-convex in both of these directions. This articulation is invested by a complete short capsule (Fig. 226) which binds the two rows of the carpus together, and sends prolongations to the investing capsules of the proximal and distal articulations. The ligament as a whole is very strong, and individual bands are not readily defined, although certain special bands may be described. The palmar ligaments radiate from the os magnum to the scaphoid, cuneiform, and pisiform. The interval between the os magnum and semilunar is occupied by oblique fibres, some of which pass from scaphoid to cuneiform, while these are joined by others, prolonged obliquely downwards and inwards, from the 286 THE AETICULATIONS OK JOINTS. radial end of the anterior radio-carpal ligament. By these different bands the palmar aspect of the joint is completely closed. The dorsal ligaments are more feeble than the palmar. They form a thin, loosely- arranged stratum, in which the only noteworthy bands are one which joins the scaphoid to os magnum, and another which joins cuneiform to unciform. The external lateral ligament (lig. collaterale carpi radiale. Fig. 227) extends between contiguous rough areas on the radial aspects of the scaphoid and trapezium. By its margins it is continuous both with the palmar and dorsal ligaments. The internal lateral ligament (lig. collaterale carpi uluare. Fig. 227) is arranged Uke the former in regard to its margins, and by its ends it is attached to the con- tiguous rough ulnar surfaces of the cuneiform and unciform bones. Both of these lateral hgaments are directly continuous with the corresponding lateral ligaments of the radio-carpal joint. An interosseous ligament (Fig. 227) is occasionally found within the capsule, extending across the joint cavity between the os magnum and the scaphoid. The pisi-cuneiform articulation is an arthroidal diarthrosis. The mutual articular surfaces of the two bones are flattened and circular, and only permit of a small amount of gliding movement. The joint is provided with a thin but complete capsule of fibrous tissue, which is specially strengthened inferiorly by two strong bands, viz. pisi-unciform (lig. piso- hamatum) and pisi-metacarpal (lig. pisometacarpeum. Fig. 226). Both of these bands extend from the lower and inner aspect of the pisiform to adjoining parts of the hook of the unciform and base of the fifth metacarpal bone respectively. To a great extent these ligamentous bands may be regarded as extensions of the in- sertion of the tendon of the flexor carpi ulnaris muscle which is attached to the upper part of the pisiform bone. Looked at as ligaments, however, they are specially strong to prevent the displacement of the pisiform bone during contrac- tion of the muscle inserted into it. The synovial membranes (Fig. 227) of the carpal joints are two in number. Of these, one is restricted to I- ' fr- ,\ / , Recessus / / sacciformis / I -— of inferior radio-ulnar Joint Triangular 'fibro- cartilage Traijfzoi'l Trapezium —I the pisi-cuneiform articula- tion, and is correspondingly simple, although occasionally the joint cavity may com- municate with that of the radio-carpal joint. The other synovial mem- brane is associated with the transverse carpal joint which extends transversely be- tween the two rows of carpal bones, with prolongations into the vertical intervals between the adjoining bones of each row, i.e. the inter- carpal articulations. It is, therefore, an elaborate cavity, which may be still further extended, by the absence of interosseous ligaments, so as to reach the radio-carpal and carpo- metacarpal series of joints. The first condition is rare, but the second is not uncommon, and results from the absence of the inter- osseous ligament Ijetween trapezium and trapezoid, or of that between trapezoid and OS majmum. Fig. 227. — Coro.nal Section through the radio-carpal, carpal, carpo- metacarpal, anossible in the longitudinal axis of the digit. The very characteristic movement of opposition, in which the tijs of the thumb may be applied to the tips of all the fingers, results from a combination of flexion, adduction, and rotation, and Ijy combining all the movements possible at the various axes a considerable degree of circumduction may be produced, in spite of the fact that this is not a ball-and-socket joint.- (B) The articulationes carpo-metacarpese digitorum are the joints between the bases of the four inner metacarpal bones and the four bones of the distal row of the carpus. They are all arthrodial diarthroses, and the opposed articular surfaces present alternate elevations and depressions which form a series of interlocking joints. The joint cavities between the carpal bones of the distal row, and also the more extensive intermetacarpal joint cavities, open into this articulation. This series of joints is invested by a common capsule which is weakest on its radial side, but is otherwise well defined. Its fibres arrange themselves in small slips, which pass obliquely in different directions, and vary in number for each metacarpal bone. Thus the oblique palmar ligaments (ligamenta carpo-metacarpea volaria. Fig. 225) usually consist of one slip for each metacarpal bone, but there may be two slips, and the third metacarpal bone frequently has three, of which one lies obliquely in front of the tendon of the flexor carpi radialis muscle. The oblique dorsal ligaments (ligamenta carpo-metacarpea dorsalia) are similar short bands, of greater strength and clearer definition, by which the index meta- carpal is bound to the trapezium and trapezoid ; the middle metacarpal to the os magnum, and frequently to the trapezoid ; the ring metacarpal to the os magnum and unciform, and the metacarpal of the minimus to the unciform. Interosseous ligaments, one or sometimes two in number, occur within the capsule. They are usually situated in relation to one or both of the contiguous margins of the bases of the third and fourth metacarpal bones, from which they extend upwards to adjacent margins of the os magnum and unciform. Occasionally they are sufficiently developed to divide the joint cavity into radial and ulnar sections. 288 THE AETICULATIONS OR JOINTS. Accessory pal- mar ligament \ The synovial membrane (Fig. 227) is usually single and lines the capsule, but, as already explained, it has prolongations into the intermetacarpal and inter- carpal series of joints. In connexion with the latter, the frequent absence of the interosseous ligament between the trapezium and trapezoid permits the free communication of this joint-cavity with that of the transverse carpal joint. METACARPO-PHALANGEAL JOINTS. In the case of the pollex this joint is constructed on the plan of a gingiymus diarthrosis ; the four corresponding joints of the fingers are also diarthroses of a shghtly modified ball-and-socket variety. With the exception of the metacarpal bone of the pollox, each metacarpal bone has a somewhat spherical head articulating with a shallow oval cup upon the base of the first phalanx. It is important to note that the articular surface upon the head of each of these meta- carpal bones is wider on the palmar aspect and narrower on the dorsal aspect. The articulation in the thumb presents features similar to those of an inter-phalangeal joint. Each joint possesses an articular capsule (Eig. 228) which presents very different degrees of strength in different aspects of the articulation. Thus, on the dorsal aspect, it cannot be demonstrated as an independent ^ structure, but the necessity lor dorsal hgaments is to a I large extent obviated by the presence of the strong .1 flattened expansions of the extensor tendons. i The internal and external lateral ligaments (hgamenta I collateralia, Eig. 228) are strong cord-like bands which " pass from the tubercles and adjacent depressions on the sides of the heads of the metacarpal bones to the contiguous non-articular areas on the bases of the proximal phalanges. They are intimately connected on their anterior aspects with the palmar ligaments. ^ The palmar ligaments consist of thick plates of fibro- I cartilage loosely connected to the metacarpal bones, but 1'^ firmly adherent to the phalanges. They are placed £ between the lateral ligaments, to both of which they are I in each case connected. Each plate is grooved on the palmar surface for the long flexor tendons, whilst on its reverse or joint surface it supports and glides upon the head of the metacarpal bone during flexion and extension of the joint. In the case of the thumb this plate of Fig. 228.— Metacarpo-phalan- fibro-cartilage usually develops to sesamoid bones, and GEAL AjiD iNTERPHALANGEAL jj^ thc casc of thc luclex fiugcr ouB such sesamoid nodule '^"^'^"^■'^' is frequently found at the radial side of the plate. An important accessory ligament is found in connexion with the four inner metacarpo-phalangeal articulations, viz. : — The Transverse Metacarpal Ligament. — This structure binds together the distal extremities of the four inner metacarpal Ijones. The name is applied to three sets of transverse fibres of great strength which are situated in front of the three inner interosseous spaces. These fibres are continuous with the palmar metacarpo- phalangeal ligaments at their lateral margins. A synovial membrane lines the investing capsule of each joint. INTERPHALANGEAL JOINTS. Of these joints there are two for each finger and one for the thumb. They all correspond, in being gingiymus diarthroses in which the trochlear character of their articular surfaces is associated with one axis of movement directed transversely. In their general arrangement they correspond wdth each other, and to a large extent with the metacarpo-phalangeal series already described. Each is provided • ■ ' ,Cap.sule Lateral ligament LUMBO-SACEAL JOINTS. 289 with a definite capsule (Fig. 228), of which the palmar and cord-like lateral portions are well marked, while on the dorsal aspect the extensor tendons act as the chief support. The palmar ligaments are fibrous plates of considerable thickness, and are attached to the two lateral ligaments and to the intervening rough surface on the distal phalanges, while their proximal margins are not attached to bone. Each ligament has its lateral margins prolonged proximally to the adjacent sharply- defined lateral ridges on the phalangeal shafts. The lateral ligaments (Fig. 228) are strong, rounded, short bands, continuous with the preceding, and attached to adjacent non-articular lateral aspects of the phalanges. Each joint possesses a synovial membrane which lines its capsule, but its arrangement presents no special peculiarity. Movements of the Cakpal, Intermetacarpal, Metacarpo-phalangeal AND Interphalangeal Joints. The ainouut of movement wliicli is possible at individual joints of the intercarpal, inter- metacari^al, and carj^o-metacarpal series is extremely limited, both on account of the interlocking nature of the articular surfaces and the restraining character of the ligamentous bands. Taken as a whole, however, the movements of the carpus and metacarpus enable the hand to perform many varied and important functions. This is largely due to the greater mobility of those joints on the radial and ulnar borders of the hand, as well as to the general elasticity of the arches formed by the carpus and metacai'i^us. These conditions jjarticularly favour the movements of ojj position and prehension. In the opposite direction, i.e. when pressure is applied from the palmar aspect, the metacarpal and carpal arches tend to become flattened, but great elasticity is imparted by the tension of the various ligaments. The four inner metacarjjo-phalangeal joints are ball-and-socket joints, and movements of palmar-flexion and extension are freely performed about a transverse axis. In exceptional cases a certain amount of dorsi-flexion is possible. About an antero-jwsterior axis movements occur which are usually referred to the middle line of the hand, and hence called abduction and adduction, but in consequence of the difference in the width of the articular surface on the dorsal and palmar aspects of the heads of the four inner metacarpal bones it is only j^ossible to obtain abduction when the joints are extended, while in the flexed position the joints become locked and abduction is impossible. The movements of the index finger are less hampered than in the case of the others, but each of them can perform a modified kind of circumduction. The metacarjjo-phalangeal joint of the thumb and all the interphalangeal joints are uniaxial or hinge-joints acting about a transverse axis, which permits of palmar-flexion and extension being freely performed, but dorsi-flexion is, as a rule, entirely prevented by the j^almar and lateral ligaments. ARTICULATIONS AND LIGAMENTS OF THE PELVIS. Although we may consider the pelvis as a separate part of the skeleton, yet it is essential to remember that the bones which enter into its composition belong to the spinal column (sacrum, coccyx) and the lower limb (innominate bone). Accord- ingly, the articulations, with their corresponding ligaments, may be arranged as follows : — (a) Those by which the segments of the coccyx are joined together (already described, v. p. 264) ; (h) That by which the sacrum articulates with the coccyx (already de- scribed, V. p. 264) ; (c) Those by which the sacrum articulates with the last lumbar vertebra (Lumbo-sacral joints) ; (d) Those by which the innominate bones are attached to the spinal column (Sacro-iliac joints) ; {e) That by which the innominate bones are attached to each other (Sym- physis pubis). LUMBO-SACRAL JOINTS. The articulation of sacrum with the fifth lumbar vertebra is constructed precisely on the principle of the articulations between two typical vertebrae, and the usual ligaments associated with such joints are repeated. There is, however, an additional accessory ligament, termed the lateral lumbo-sacral ligament (Fig. 229). 20 290 THE AETICULATIONS OK JOINTS. This extends from the front of the inferior border of the transverse process of the last lumbar vertebra, downwards and slightly outwards, to the front of the lateral aspect of the ala of the sacrum, close to the sacro-iliac joint. Further, a variable membranous band extends between the lateral aspect of the lower part of the body of the last lumbar vertebra and tlie front of the ala of the sacrum. This band lies in front of the auterior primary division of the fifth lumbar nerve. SACRO-ILIAC JOINT. Each innominate bone articulates with the sacral section of the spinal column on each side through the intervention of a diarthrosis, termed the sacro-iliac joint (articulatio sacro-iliaca). This joint is formed between the contiguous auricular surfaces of the sacrum and ihum. Each of these surfaces is more or less completely clothed by hyaline articular cartilage. The joint cavity, which is little more than a capillary interval, may be crossed by fibrous bands. The joint cavity is surrounded l)y ligaments of varying thickness and strength. Posterior sacro-iliac ligament Sacrum [Great sacro-sciatic foramen Small sacro-sciatic foramen Great sacro- sciatic ligament Inter-pubic fibro-cartilage Fio. 229. — Coronal Section of Pelvis. which constitute its capsule. Thus the anterior part of the investing capsule is thin, and consists of short but strong fibres which pass between adjoining surfaces on the ala of the sacrum and the iliac fossa of the innominate bone ; they form the anterior sacro-iliac ligament (lig. sacro-iliacum aiiterius, Fig. 229). On the posterior aspect there are two ligtiments. The short posterior sacro-iliac ligament (lig. sacro- iliacum posterius breve, Fig. 230) consists of numerous strong fasciculi, which pass from the rough area on the inner aspect of the ilium, above and behind its auricular surface, downwards and inwards to the transverse tubercles and the depressions behind the first and second segments of the sacrum. This ligament is of great strength, and with its fellow it is respoMsit)le for suspending the sacrum and the weiti;lit of the su])C!rim])Osed trunk from the innominate bones. The long or oblique posterior sacro-iliac ligament (lig. sacro-iliacum posterius longum, Fig 230) is a superficial thickened portion of the preceding ligament. SYMPHYSIS PUBIS. 291 It consists of a definite band of fibres passing from tht*- postero-superior iliac spine to the transverse tubercles of the third and fourth segments of the sacrum. The synovial cavity of this joint is very imperfect and rudimentary. Several accessory ligaments are associated witli the articulati(in of the in- nominate bone to the sacral section of the spinal column. The ilio-lumbar ligament (lig. ilio-lumbale, Fig. 229), which is merely the ■lumbar liifaiiient Posterior sacro-iliac ligament Long or oblique posterior sacro-iliac ligament Reflected head of i ectus _ Great sacro-sciatic tVjianieu Small sacro-sciatic liL;ament Small sacro-sciatic foramen Great sacro-sciatic ligament ^-Obturator membrane Fig. 230. — Posterior View of the Pelvic Ligajients and of the Hip-Joint. thickened anterior lamina of the fascia lumborum, extends from the tip of the transverse process of the last lumbar vertebra, almost horizontally outwards, to the inner lip of the iliac crest at a point a short distance behind its highest level. A proportion of these fibres is attached to the inner rough surface of the ilium between the iliac crest and the auricular impression. To these the name of the lig. ilio-lumbale inferius is applied. The great or posterior sacro-sciatic ligament (lig. sacro-tuberosum, Fig. 230) is somewhat triangular in outline. It occupies the interval between the sacrum and the innominate bone, and is attached mesially to the posterior inferior spine of the ilium ; to the posterior aspect of the transverse tubercles and lateral margins of the third, fourth, and fifth segments of the sacrum, as well as to the side of the first segment of the coccyx. It passes downwards and outwards, becoming narrower as it approaches the ischium, near to which, however, it again expands, to be attached to the inner side of the ischial tuberosity, immediately below the groove for the tendon of the obturator internus muscle, i.e. the lesser sciatic notch. A continuation of the inner border of the ligament — the processus 292 THE ARTICULATIONS OR JOINTS. falciformis (Fig. 230) — runs upwards and forwards on the inner aspect of the ramus of the ischium. The great sacro-sciatic ligament is believed by many to represent the original or proximal end of the long or ischial head of the biceps flexor cruris muscle. The si^iall or anterior sacro-sciatic ligament (lig. sacro-spinosum, Figs. 229 and 230) is situated in front,' and in a measure under cover of the great sacro-sciatic ligament. Triangular in form, it is attached by its base to the last two segments of the sacrum and the first segment of the coccyx, and by its pointed apex to the tip and upper aspect of the ischial spine. This ligament is intimately associated with the coccygeus muscle, and by some it is regarded as being derived from it by fibrous transformation of the muscle fasciculi. By the great and small sacro-sciatic ligaments the two sciatic notches of the innominate bone are converted into foramina. Thus the small sacro-sciatic liga- ment completes the boundaries of the great sciatic foramen (foramen ischiadicum majus) ; while the great sacro-sciatic ligament, assisted by the small sacro-sciatic ligament, closes the small sciatic foramen (foramen ischiadicum minus). SYMPHYSIS PUBIS. The anterior wall of the osseous pelvis is completed by the articulation of the bodies of the two pubic bones constituting the symphysis pubis. This joint con- forms in its construction to the general plan of an amphiarthrosis. Thus it is mesial in position ; each, pubic bone is covered by a layer of hyaline cartilage, which closely adapts itself to the rough tuberculated surface of the pubic bone ; while between these two hyaline plates there is an interposed fibro-cartilage (lamina fibro-cartilaginea interpubica), in the interior of which there is usually a vertical antero-posterior cleft. This cavity, which is placed nearer the posterior than the anterior aspect of the joint, does not appear until between the seventh and tenth years, and as it is not lined by a synovial membrane, it is supposed to result from the breaking down of the interpubic lamina. The anterior pubic ligament (lig. pubioum anterius. Fig. 229) is a structure of considerable thickness and strength. Its superficial fibres, which are derived very largely from the tendons and aponeuroses of adjoining muscles, are oblique, and form an interlaced decussation. The deeper fibres are short, and extend trans- versely from one pubic bone to the other. The posterior pubic ligament (lig. pubicum posterius. Fig. 230) is very weak, and consists of scattered fibres which extend transversely between contiguous j)ubic surfaces posterior to the articulation. The superior pubic ligament (lig. pubicum superius, Fig. 229) is likewise weak, and consists of transverse fibres passing between the two pubic crests. The inferior or subpubic ligament (lig. pubicum inferius vel lig. arcuatum pubis. Fig. 230) occupies the arch of the pubis, and is of considerable jstrength. It gives roundness to the pubic arch and forms part of the pelvic outlet. It liks con- siderable vertical thickness immediately below the interpubic disc to which it is attached. Laterally it is attached to adjacent sides of the descending rami of the pubis. Its lower border is free, and separated from the triangular hgament of the perineum by a transverse oval interval through which the dorsal vein of the penis passes backwards to the interior of the pelvis. The Triangular Ligament of the Perineum. The triangular ligament of the perineum is a membranous structure which occupies the X"ihic arch jjelow and distinct from the subpubic ligament. It assists in completing the pelvic walls anteriorly in the same manner that the obturator membrane does laterally. Indeed, these two structures occupy the same mor- phological plane. The triangular ligament presents two surfaces — one superficial or perineal ; the other deep, or pelvic, and both of these surfaces are associated with muscles. Its lateral borders are attached to the sides of the pubio arch, while its base is somewhat ill-defined, by reason of its fusion with the fascia of Colles in the urethral region of the perineum. HIP-JOINT. 293 The apex of the triangular ligament is truncated, free, and well defined, constitut- ing the transverse perineal ligament, above which there is the interval for the dorsal vein of the penis. It is pierced hy a number of vessels and nerves, but the principal opening is situated mesially one inch below the pubic arch, and transmits the urethra. The Obturatoe Membrane. The obturator membrane (membrana obturatoria. Fig. 232) occupies the obturator or thyroid foramen. It is attached to the pelvic aspect of the circumference of this foramen. It consists of fibres irregularly arranged and of varying strength, so that sometimes it almost appears fenestrated. At the highest part of the foramen it is incomplete and forms a U-shaped border, between which and the bony circumference of the foramen, the obturator canal (canalis obtura- torius) is formed. In this position the membrane is continuous with the parietal pelvic fascia which clothes the inner side of the obturator internus muscle, above the upper free margin of the muscle. From the outer or crural aspect of the membrane some of its fibres are prolonged to the antero-inferior aspect of the capsule of the hip-joint. Mechanism and Movements of the Pelvis. — The liuman pelvis i^resents a meclianism the principal reqmrement of ^yhich is stability and not movement, for, through the pelvis, the weight of the trunk, superimposed upon the sacrum, is transmitted to the lower limbs. Moreover, its stability is largely concerned in the maintenance of the erect attitude. The movements of its various parts are therefore merely such as are consistent with stability, without producing absolute rigidity. The two innominate bones, being bound together by powerful ligaments at the pubic articula- tion, constitute an inverted arch, of which the convexity is directed downwards and forwards, while its piers are turned upwards and backwards, and considerably expanded in relation to the hinder parts of the ihac bones. Between the piers of this inverted arch the sacrum is situated. This bone is in no sense a key-stone to an arch, because, as may readily be seen in antero-posterior transverse section, the sacrum is wider in front than behind, and the superposed weight naturally tends to make the sacrum fall towards the pelvic cavity, and so fit less closely between the innominate bones. The sacrum is in reality an oblique platform, in contact with each innominate bone through its articular auricular surfaces, and in this position it is suspended by the posterior sacro-iliac ligaments, and kept securely in place by the " grip " due to the irregularity of the opposed surfaces of the two sacro-iliac articivlations. Since the weight of the trunk is trans- mitted to the anterior and upper end of this sacral platform, there is a natural tendency for the sacrum to revolve ujjon the transverse axis which j^asses through its sacro-iliac joints. If this wei'e permitted, the promontory of the sacrum would rotate do^vnwards and forwards towards the pelvic cavity, as really does occiu' in certain deformities. This revolution or tilting down- wards of the forepart of the sacrum is prevented by the action of the great and small sacro- sciatic ligaments, extending from the ischial tuberosity to the hinder and lower end of the suspended platform of the sacrum. Not only so, but these ligaments, acting on a rigid sacrum, tend to hold up the weight upon the sacral promontory. The various ligaments passing between the last lumbar vertebra and the sacrum and ilium retain the weight of the trunk in position upon the anterior end of the sacrum, and resist its tendency to slip forwards and downwards towards the pelvic cavity. The entire weight of the trunk and. pelvis is transmitted to the heads of the thigh bones in the most advantageous position, both for effectiveness and the strengthening of the inverted innominate arch, for it will be evident that the heads of the femora thrust inwards upon the convex side of the az'ch, very much at the place where the arches are weakest, viz. at the sj) ringing of the arch from its piers. The forces which tend to cause movement of the pelvic bones during parturition act from within the pelvis, and have for their object the increase of the various i^elvic diameters, in order that the foetal head may more readily be transmitted. For this purpose the wedge-like dorsal surface of the sacrum is driven backwards, and a certain amount of extra space may thereby be obtained. An important factor, however, in the increase of the pelvic capacity at this peiiod is found in the relaxation of its various ligaments. THE ARTICULATIONS OF THE LOAVER EXTREMITY. THE HIP-JOINT. The human body provides no more perfect example of an enarthrodial diarthrosis than the hip-joint (articulatio coxse). Combined with all that variety of movement which characterises a multi-axial joint, it nevertheless presents great stability, which has been obtained by simple arrangements, for restricting the range of its natural 294 THE AETICULATIONS OE JOINTS. Ischial spine movements. This stability is of paramount importance for the maintenance of the erect attitude, and the mechanical adaptations whereby this result is obtained are such that the erect attitude may be preserved without any great degree of sustained muscular effort. Articular Surfaces. — The head of the femur is globular in shape, and consider- ably exceeds a hemisphere. It is clothed by hyaline articular cartilage on those parts which come into direct contact with the acetabulum. There is frequently more or less of extension of the articular cartilage from the head to the adjoining anterior part of the neck, an extension which is accounted for by the close and constant apposition of this portion of the neck with the hinder aspect of the ilio - femoral ligament. The limit of the articular cartilage covering the head is indicated by a sinuous border. Further, there is an absence of articular cartilage from the pit or depression on the head of the femur. The acetabulum is a deep cup-shaped cavity which pre- sents an interruption or notch on its antero-inferior margin. The interior of the cup is lined by a ribbon -like band of articular cartilage which extends to the brim of the cavity, but does not cover the floor of the cup. This ar- ticular ribbon - shaped band is widest on its supero-posterior aspect, and narrowest at the anterior margin of the notch. The transverse ligament (lig. transversum acetabuli, Fig. 231) bridges the ace- tabular notch, and consists of strong transverse fibres which are attached to both of its margins, but more extensively to the postero-inferior. This ligament does not entirely fill the notch, but leaves an open interval between its lower border and the bottom of the notch through which vessels and nerves enter the cup. The acetabular aspect of this ligament constitutes an articular surface. The acetabulum is deepened by the cotyloid ligament (labrum glenoidale, Figs. 231 and 232), which consists of a strong ring of fibro-cartilaginous tissue attached to the entire rim of the cup. The attached surface of the ring is broader than its free edge, and, moreover, the latter is somewhat contracted, so that the ligament grasps the head of the femur which it encircles. Its fibres are partly oblique and partly circular in their direction. By the former it is firmly implanted on the rim of the acetabulum and the transverse ligament of the notch ; by the latter the depth of the cup is increased through the elevation of its edge, and its mouth slightly narrowed. By one surface this ligament is also articular. A capsule (capsula articularis. Figs. 230 and 232) completely invests the joint cavity. This is a fibrous membrane of great strength, although it is not of equal thickness throughout, being considerably thicker on the supero-anterior aspect than at any other part. Unlike the corresponding structure of the shoulder-joint, it does not permit of the withdrawal of the head of the femur from contact with the aceta- Vjular articular surfaces, except to a very limited extent. Its fibres are arranged Transverse acetabular ligament Retinacula Fig. 231. — Dissection of the Hip-Joint. Bottom of the acetabulum removed, and capsule of the joiut thrown outwards towards the trochanters. HIP-JOINT. 295 both in the circular and in the longitudinal direction, the former, known as the zona orbicularis, beiug best marked posteriorly, while the longitudinal fibres stand out more distinctly in front, where they constitute special ligaments. Looked at as a whole, the capsule has the following attachments : superiorly it surrounds the acetabulum, on the upper and hinder aspects of which it is attached directly to the innominate bone, while on the front and lower aspects it is attached to the non- articular surfaces of the cotyloid and transverse ligaments ; inferiorly it encircles the neck of the fenmr, where it is attached in front to the anterior inter- trochanteric line ; above, to the inner aspect of the root of the great trochanter ; below, to the lower part of the neck of the femur, in close proxindty to the small trochanter ; behind, to the line of junction of the outer and middle thirds of the neck of the femur. It is a matter of some importance to note that only part of the posterior surface of the neck of the femur is enclosed within the capsule. The femoral attachments of the capsule vary considerably in their strength, ^being particularly firm above and in front, but much weaker below and behind, where the orbicular fibres are well seen. Many fibres of the capsule are reflected from its deep aspect upwards upon the neck of the femur, where they form ridges, and to these the term rectinacula (Fig. 231) is applied. The longitudinal fibres of the capsule are arranged so as to form certain definite bands, viz : — (1) The ilio-femoral ligament (Kg. ilio-femorale, Fig. 232) consists of a triangular set of fibres attached above, by their apex, to the lower part of the anterior inferior iliac spine and the immediately adjoining part of the rim of the acetabulum, and below, by their base, to the anterior intertrochanteric line of the femur. This ligament is the thickest part of the capsule, but its sides are more pronounced than its centre, especially towards its base. Consequently the ilio-femoral band presents some resemblance to an inverted Y (A), and therefore it is very generally known as the Y-shaped ligament of Bigelow. The outer or upper limb of tlie ilio-femoral ligament maj" be somewhat extended by the inclusion of additional longitudinal fibres, and described as the ilio-trochanteric ligament (lig. ilio-trochantericum}. This band arises from the anterior part of the dorsum of the acetabulum, and extends to the femoral neck, close to the anterior end of the inner surface of the great trochanter. (2) The pubo-femoral or pubo-capsular ligament (lig. pubo-femorale v. pubo- capsulare. Fig. 232) is composed of some bands of fibres of no great strength, which extend from the outer end of the horizontal ramus of the pubis, the ilio- pectineal eminence, the obturator crest and the obturator membrane,- to lose them- selves for the most part in the capsule, although a certain proportion of them may be traced to the inferior aspect of the femoral neck, where they adjoin the lower attachment of the Y-shaped ligament. (3) The iscMo-capsular ligament (lig. ischio-capsulare. Fig. 230) consists of a broad band of short, fairly strong longitudinal fibres, which, by their upper ends, are attached to the ischium between the small sciatic notch and the obturator foramen, while their lower ends become merged in the zona orbicularis of the general capsule. Within the capsule, and quite distinct from it, there are the ligamentum teres and the Haversian gland. The inter articular ligament (lig. teres femoris. Fig. 231) is a strong, somewhat flattened band of fibrous tissue, attached by one end to the upper half of the pit or depression on the head of the femur. By its inner end it is attached to the lower edge of the articular surface of the transverse ligament, with extensions to the opposite borders of the acetabular notch, but chiefly to the hinder or ischial border. This ligament varies very greatly in its strength and development in different subjects, and in certain rare cases it is absent. The so-called Haversian gland occupies the bottom or non-articular area of the acetabulum. It consists of a mass of fat covered by synovial membrane. This pad of fat is continuous with the extra-capsular fat through the passage subjacent to the transverse ligament of the notch. A synovial membrane lines the capsule from which it is reflected to the neck of the femur along a line which corresponds to the femoral attachments of the 296 THE AETICULATIONS OE JOINTS. Anterior infei loi iliac spine Cotyloid ligament Head of femur capsule. Thus the synovial membrane clothes more of the femoral neck anteriorly than in any other position. Posteriorly, where the capsule is feebly attached to the neck of the femur, the synovial mem- brane may be seen from the outside of the capsule. The synovial membrane extends close up to the articular margin of the head of the femur, and on the upper and lower as- pects of the neck it in gathered into loose folds upon the re- tinacula. These folds or plications are best marked along the line of synovial re- flection, and do not reach as far as the femoral head. At its acetabular end the synovial membrane is prolonged from the inside of the capsule to the outer non- articular surface of the cotyloid and transverse liga- ments, upon which it is continued as a. lining for their acetabular or ^'ticular surfaces, and further, it provides a covering for the fat at the bo^m of the acetabular fossa, as well as a complete tubular investment for the ligamentum teres. Occasionally the synovial bursa, which is subjacent to the tendon of the ilio- psoas muscle, communicates with the interior of the hip-joint through an opening in the anterior wall of the capsule (Fig. 232), situated between the pubo-femoral ligament and the inner or lower limb of the iUo-femoral ligament. Movements at the Hip-Joint. — Tlie movements whicli occur at the liip-joint are those of a multiaxial joint. These are flexion, extension, abduction, adduction, rotation, and circumduction. The range of each of these movements is less extensive than in the case of the shoulder -joint, be- cause, at the hip, the freedom of movement is subordinated to that stability which is essential alike for the maintenance of the erect attitude and for locomotion. When standing at rest in the erect attitude the hip-joint occujiies the position of extension, and as the weight of the trunk is trans- mitted in a perpendicular which falls behind the centres of the hii^-joints, both the erect attitude and the extended position are maintained to a large extent mechanically, without sustained mus- cular action, by means of the tension of the ilio-femoral ligament. Moreover, the tension of this ligament is sustained by the pressure of the front of the head and neck of the femur against its synovial surface. In this association of parts it is important to note that the articular cartilage of tlie f(;moral head may l)e, and in certain races is, prolouged to the front of the femoral neck ; and further, that the constant friction does not destroy tlie synovial lining of the capsule. Again,.the same mechanism which preserves the erect attitude ])revents an excessive degree of extension or dorsiflexion. In movement forwards, i.e. ventral flexion, the front of the thigh is approximated to the anterior abdominal wall. The amount of this movement depends upon the position of the knee-joint, because when the latter is flexed the thigh may be brought into contact with the abdominal wall, whereas when the knee-joint is straightened {i.e. extended) the tension of the hamstring muscles greatly restricts the amount of flexion at the hip-joint. Abduction and adduction are likewise much more restricted than at the shoulder-joint. Abduc- tion is lirouglit to a close by the tension of the pubo-femoral band and the lower part of the capsule, and, in addition, the upper aspect of the neck of the femur locks against the margin of the acetabulum. Excessive adduction is prevented by the tension of the upper band of the ilio-femoral ligament and the upper part of the capsule. Rotation or movement in a longi- tudinal axis may be either inwards, i.e. towards the front, or outwards, i.e. toward the hack. Fig. 282. — Dissection of the Hip- Joint fkom the front. THE KNEE-JOINT. 297 In the former the movement is brought to a close by the tension of the ischio-capsular ligament and Ijack part of the capsule, aided by the muscles on the back of the joint ; in the latter — rotation outwards — the chief restraining factor is the outer or upper limb of the ilio-femoral ligament. The total amount of rotation is probably less than 60°. Circumduction is only slightly less free than at the shoulder, but it is complicated by the preservation of the balance upon one foot. The value and influence of the ligamentum teres are not easily estimated, because it may be absent without causing any known interference with the usefulness of the joint. In the erect attitude this ligament lies lax between the lower part of the femoral head and the acetabular fat. In the act of walking it is rendered tense at the moment when the pelvis is balanced on the summit of the supporting femur. Analysis of this position shows the femur to be adducted, with probably, in addition, a small amount of flexion {i.e. bending forwards) and internal rotation. Again, this ligament is said to be tense when the thigh is rotated outwards. The equivalent of this movement is doubtless found in the rotation of the jaelvis, which occurs in the act of walking at the moment of transition from the toe of the supporting foot to the heel of the advancing foot. The interest connected with this ligament is ^jerhaps morphological rather than physio- logical It is believed by some to represent the tendon of a muscle which in birds occuijies a position external to the joint capsule. THE KNEE-JOINT. The knee-joint (articulatio genu) is the largest articulation in the body, and its structure is of a very elaborate nature. The part it plays in maintaining the erect attitude materially influences its construction, and special arrangements are provided for the mechanical retention of the joint in the extended position, in view of the fact that the line of gravity falls in front of the centre of the articulation. Its principal axis of movement is in the transverse direction, consequently it Ijelongs to the ginglymus or hinge variety of the diarthroses. At the same time a sHght amount of rotation of the tibia in its long axis is permitted during extreme flexion ; but while this fact is of considerable importance in the study of certain accidents to which the joint is liable, as well as in the study of its comparative morphology, it is not sufficiently pronounced to interfere with its classification as a hinge-joint. Articular surfaces pertaining to the femur, tibia, and patella, enter into the formation of the knee-joint. The articular surface of the femur extends over a large part of both condyles, and may be divided into patellar and tibial portions by fain tly^- marked, almost transverse grooves, which pass across the articular surface immediately in front of the intercondylar notch. As a rule marginal indentations of the articular surface render the positions of these transverse grooves more distinct. The patellar portion (Fig. 233) is situated anteriorly, and is common to both condyles, although developed to a larger extent in association with the outer condyle, on which it ascends to a higher level than on the inner condyle. This surface is trochlear, and forms a vertical groove bordered by prominent lateral borders. The tibial portion of the articular surface of the femur is divided into two articular areas, in relation to the inferior aspects of the two condyles, by the wide non- articular intercondyloid notch. These two surfaces are for the most part parallel, but in front the internal tibial surface turns obliquely outwards as it passes into continuity with the patellar trochlea, while posteriorly, under certain circumstances, e.g. the squatting posture, the articular surface of the inner condyle may extend to the adjoiniug portion of the popliteal area of the bone. When the joint is in the position of extreme flexion, the patella is brought into direct contact with that part of the articular surface on the inner condyle which bounds the intercondyloid notch upon its inner and anterior aspects. This relation- ship is indicated by the presence of a distinct semilunar facet on the cartilage in that situation (Eig. 233). The articular surface of the femur may therefore be regarded as presenting femoro-patellar and femoro -tibial areas. The patella presents on its posterior aspect a transversely - elongated oval articular facet and an inferior rough, triangular, non-articular area. The articular facet is divided into two principal lateral portions by a prominent rounded vertical ridge. Of these the outer is the wider. A less pronounced and nearly vertical ridge marks off an additional facet called the internal perpendicular facet, close to the inner margin of the articular surface. Two faint transverse ridses cut off 298 THE AETICULATIONS OR JOINTS. narrow upper and lower facets from the general articular surface without encroach- ing on the narrow innermost vertical facet (Goodsir) (Fig. 233). The head of the tibia presents on its superior aspect two condylar articular surfaces, separated from each other by a non-articular antero-posterior area, which is wider in front and behind than in the middle, where it is elevated to form a bifid tibial spine. The external condylar facet is slightly concavo-convex from before backwards, and slightly concave transversely. This surface is almost circular, and extends to the free external border of the tibial head, where it is somewhat flattened. Posteriorly the articular surface is prolonged downwards on the tuberosity in relation to the position occupied by the tendon of the popliteus muscle. The P itellar surface of femur Impression of external semi- lunar cartilage External tibial surface of femur — External lateral ligament Cut tendon of biceps flexor cruris muscle Anterior superior tibio-fibular ligament External lateral ligament opening in interosseous membrane for anterior tibial vessels Semilunar facet for patella Internal tibial surface of femur Posterior crucial ligament Anterior crucial ligament Transverse ligament Internal semilunar ttbi'o- cartilage Internal lateral ligament Ligamentum patellee Inner perpendicular facet on patella Fig. 233. — Dissection of the Knee- Joint fkom the front : Patella thrown down. internal condylar facet is oval in outline, and distinctly concave both in its antero- posterior and transverse diameters. Ligaments. — Like all diarthroses, this joint is invested by an envelope or capsule (capsula articularis), which does not, however, entirely surround the joint cavity, for it is aljsent as a fibrous membrane above the joint cavity, subjacent to the tendon of the quadriceps extensor muscle. Its specially named bands are not of themselves sufficient to form a complete investment, and a capsular membrane, which largely consists of augmentations from the fascia lata and the t^endons of surrounding muscles, supplies the defective areas. Thus, anteriorly, on each side of the patella and the ligamentum patellar, expansions of the vasti tendons and fascia lata, constituting lateral patellar ligaments, are evident. On the outer side of the joint the external lateral ligament is hidden within a covering derived from the ilio-tibial band of the fascia lata. On the inner side expansions from the tendons of the sartorius and semi-membranosus muscles augment the capsule, which here becomes continuous with the internal lateral ligament. Posteriorly the capsule also receives augmentation from the tendon of the semi-membranosus muscle, but it is very thin subjacent to the origins of the gastrocnemius muscle, where it covers the hinder parts of the condyles. Not unfrequently the capsule presents an opening of communication between the interior of the joint cavity and a bursa which lies under cover of the inner head of the gastrocnemius muscle. THE KNEE-JOINT. 299 The anterior ligament (lig. ijatellis, Fig. 233), also called the ligamentum patellge, is a powerful flattened band, attached superiorly to the apex and adjoining margins of the patella, and interiorly to the rough anterior tuberosity at the upper end of the shaft of the tibia. This Hgament also serves as a tendon of insertion for the quadriceps extensor muscle, and a certain number of the filjres of the tendon may be observed to descend as a thin fibrous covering for the anterior surface of the"^ patella. The deep surface of the tendon is separated from the front of the head of the tibia by a synovial bursa, and above this it rests upon the infrapatellar pad of fat, which is placed between the tendon and the synovial membrane of the joint. The posterior ligament (Fig. 234) is a compound structure of unequal strength, Tendon of adductor luaguus muscle (cut) Inner head of gastrocuemms Posterior ligament or ligament of ■Winslo^\ Bursa beneath tendon of semi-membrau Popliteal surface of femur Plantaris muscle (cut) Tendon of semi-membiranosus muscle (cut) Posterior ligament (oblique slip) Internal lateral ligament- Outer head of gastro- cnemius muscle (cut) Long external lateral ligament Short external lateral ligament Popliteus muscle (cut) Biceps flexor "cruris muscle (cut) Head of iibula Popliteal surface of tibia Popliteal fa-,cia — ^■ Popliteus muscle (cut) Fig. 234. — The Kxee-Joixt. Posterior View. and those portions by which it establishes continuity with the lateral parts of the capsule are remarkably thin. It is attached superiorly to the popKteal surface of the femur, close to the intercondyloid notch, with lateral extensions to the non articular areas immediately above the posterior articular margins of the two con- dyles, where it is closely associated with the origins of the gastrocnemius muscle. Inferiorly it is attached to the rough non-articular posterior border of the head of the tibia, where, to its fibular side, it presents an opening of exit for the tendon of the popliteus muscle (Fig. 234). The tendon of insertion of the semi - membranosus muscle contributes an important expansion which augments the posterior ligament on its superficial aspect. This expansion — ligamentum posticnm Winslowii — passes obliquely upwards and outwards to lose itself in the general ligament, but it is most distinct in the region between the femoral condyles, where it may present upper and lower arcuate 300 THE AKTICULATIONS OE JOINTS. borders. A number of vessels and nerves perforate this ligament, and hence it presents a number of apertures. The internal lateral ligament (hg. coUaterale tibiale, Figs. 233 and 235) is a well- defined, strong, flat band which is applied to the inner side of the knee-joint, and is rather wider in the middle than at either end. It is frequently regarded as consisting of two portions — an anterior or long portion, and a posterior or short one. The two parts arise close together from the non-articular inner surface of the inner condyle, immediately below the adductor tubercle. The short or posterior portion descends shghtly backwards, to be attached to the postero-internal aspect of the inner part of the tibia above the groove for the semi-membranosus tendon. The long or anterior portion inclines somewhat forwards, and descending superficially to the tendon of the semi-membranosus, it is continued downwards, to be attached to the upper part of the inner surface of the shaft of the tibia below the level of the anterior tuberosity. On its superficial aspect the internal lateral ligament is augmented by prolonga- tions from the tendons of the semi-membranosus and sartorius muscles, but is separated by a bursa from the tendons of adductor-gracilis, semi-tendinosus, and sartorius. Its deep surface is adherent to the convex edge of the internal semilunar cartilacje, but lower down the inferior internal articular vessels intervene between the Kgament and the shaft of the tibia. The external lateral ligament (lig. collaterale fibulare,Figs. 233 and 235), sometimes called the ligamentum laterale externum longum, is a distinct rounded band which is under cover of the ordinary capsule, and yet well separated from the joint cavity by intervening objects. It is attached superiorly to a tubercle on the outer surface of the external condyle, immediately above the groove occupied by the tendon of the pophteus muscle, superficial to which the ligament descends. By its lower end it is attached to the outer side of the head of the fibula, in front of the styloid process. In its course vertically downwards it splits the tendon of insertion of the biceps flexor cruris (Fig. 233), the portions of which are fixed to the head of the fibula on either side of the hgament, and a bursa may intervene between the tendon and the ligament. The inferior external articular vessels pass forwards subjacent to this ligament and above the head of the fibula. Unlike the internal ligament, it is not attached to the corresponding semilunar cartilage. The ligamentum laterale externum breve seu posticum (Fig. 234) is an inconstant structure which is attached by its upper end immediately behind the j^receding, and subjacent to the outer head of the gastrocnemius muscle. It likewise descends superficial to the jjopliteal tendon, and is affixed inferiorly into the styloid process of the fibula. The intra-articular structures of the knee-joint are more important and more numerous than in any other joint of the body. The crucial ligaments (ligamenta cruciata genu) are two strong,rounded, tendinous bands, which extend from the non-articular area on the upper surface of the head of the tibia to the non-articular sides of the intercondyloid notch of the femur. These interarticular ligaments are distinguished from each other as the anterior or external and the posterior or internal. They cross each other like the limbs of an X, yet they remain distinct throughout, and each has its own partial synovial covering. They lie within the capsule of the joint, and extend between non- articular surfaces in relation to the longitudinal axis of the limb. The ligamentum cruciatum anterius (Figs. 233, 235, and 236) is attached inferiorly to the inner part of the rough, depressed area in front of and close to the spine of the tibia. It passes obliquely upwards, outwards, and backwards to the inner non-articular surface of the external condyle, where it finds attachment far back in the posterior part of the intercondyloid notch. This ligament is tense in the position of extension, and therefore it assists in maintaining the erect attitude. The ligamentum cruciatum posterius (Figs. 233, 235, and 236) is somewhat shorter than the preceding. It is attached inferiorly to the hinder part of the depressed surface behind the spine of the tibia and close to the popliteal notch. Its fibres pass obliquely upwards, forwards, and inwards, to be inserted into the outer non- articular surface of the inner condyle, far forwards towards the anterior margin of the intercondyloid notch. It is rendered tense in the position of flexion. THE KNEE-JOINT. 301 The semilunar interarticular fibro-cartilages are two in number — an inner and an outer — placed horizontally Ijetween the articular surfaces of the femur and til)ia. In general outHne they correspond to the circumferential portions of the tibial facets upon which they rest. Each has a thick, convex, fixed border in relation to the periphery of the joint, and a thin, concave, free border directed towards the interior of the joint. Neither of them is sufficiently large to cover the whole of the tibial articular surface upon which it rests. The upper and lower surfaces of each semilune are smooth and free, and each cartilage terminates in an anterior and a posterior fibrous horn or cornii. The internal semilunar fibre - cartilage (meniscus medialis. Figs. 235 and 236) Tendon of insertion of adductor niagnus' muscle (cut) Popliteal surface of fenuir Anterior crucial ligament Tendon of popliteus muscle (cut) Accessorj-attachment of external semilunar cartilage Internal semilunar cartilasre L\tt uial semilunar I ulilase Posterior crucial ligament Groove on tibia for tendon I if popliteus muscle Superior portion of cap- sule of superior tibio- fibular articulation External lateral ligament Mf knee-joint Posterior superior tibio- fibular ligament Tendon of semi-membranosus muscle (cut) Internal lateral ligament Head of fibula Popliteal surface of tibia --'^iH 1 Fig. 23.5. — The Knee-.Joint opened from Behixd by the Eemoval of the Posterior Ligament. forms very- nearly a semicircle. It is attached by its anterior horn to the non- articular surface on the head of the tibia, in front of the tibial attachment of the anterior crucial ligament, and by its posterior horn to the non-articular surface immediately in front of the tibial attachment of the posterior crucial ligament. The deep or hinder part of the internal lateral ligament is attached to its periphery. The external semilunar fibre -cartilage (meniscus lateralis, Figs. 235 and 236) is attached by its anterior horn to the non-articular surface of the tibia in front of the tibial spine, where it is placed to the outer side, and partly under cover of the tibial end of the anterior crucial ligament. By its posterior horn it is attached to the interval between the two tubercles which surmount the tibial spine, i.e. in front of the attachment of the posterior horn of the internal semilunar cartilage. This fibro- cartilage, with its two horns, therefore forms almost a complete circle. Posteriorly it is attached by its periphery to the posterior ligament, but on the outer side it 302 THE AETICULATIONS OE JOINTS. Transverse ligament Anterior cornu of internal semilunar cartila Anterior cornu of external semilunar cartilage Posterior cornu of internal semi- ■ -lunar cartilage Posterior crucial ligament Posterior cornu of exter- nal semilunar cartilage FabCiculu-5 from external semilunar cartilage to posterior crucial ligament b'lG. 236. — Upper End of Tibia with Semilunar Cartilages and Attached Portions op Crucial Ligaments. is separated from the external lateral ligament by the tendon of the popliteus muscle, and on this aspect its periphery is free. The two horns of the external semilune are eiuLraced by the two horns of the internal one, and, while the anterior crucial ligament has its tibial attachment almost between the anterior horns of the two semilunes, the tibial attachment of the posterior crucial ligament is situated behind the posterior horns of the two semilunes. Both semilunes possess certain accessory attachments. Thus the external semi- lune sends a large bundle of fibres from its convex posterior border to augment the posterioraspect of the posterior crucial liga- ment, by which these fibres are conducted to the femur. Again, the con- vex or periph- eral margins of each semilune possess certain attachments to the deep surface of the capsule on its inner and posterior as- pects, as has already been explained, but, in addition, they are attached to the non-articular circumference of the tibial head by short fibrous bands known as the ligamenta coronaria. Lastly, a rounded band which varies in strength, the transverse ligament (lig. transversum genu, Figs. 233 and 236), stretches between the anterior convex margins of the two semilunes, crossing the front part of the non-articular area on the tibial head in its course. The synovial membrane of the knee-joint is not only the largest, but the most /elaborately arranged of its kind in the body. It not only lines the capsule, but it forms a more or less extensive covering for the intracapsular ligaments and the free surface of the infra-patellar pad of fat. This pad acts as a wedge which fits into the interval between the patella, tibia, and femoral condyles, and the synovial membrane upon its surface forms a band or fold which extends from below the level of the patellar articular surface to the anterior part of the intercondyloid notch. This is in no sense a ligament, although it is named the ligamentum mucosum, or plica synovialis patellaris. At its femoral end it is narrow and attenu- ated, but at its patellar end it expands laterally to form wing-like fringes or mem- branes — the alar ligaments (plicae alares) — which are often distinguished from each other as the inner (yjlica aliformis medialis) and the ;. ^'^•r (plica aliformis lateralis). These folds are more or less loaded with fat. ^ Apart from these special foldings, the synovial membrane lines the deep surface of the common extensor tendon, and extends upwards for a variable distance above the patella. This extension of the joint cavity almost always communicates with a large bursa situated still higher on the front of the femur. Tracing the synovial membrane downwards, it will he found to cover both surfaces of the semilunar fibro- cartilages. The peripheral or convex margins of tliese cartilages are only covered by ;this membrane where they are unattached to the capsule. A prolongation invests the intracapsular portion of the tendon of. the popliteus muscle, and separates this tendon from the back part of the tibial head, besides intervening between the external semilune and the head of the tibia. From the back jjart of the joint cavity the synovial membrane extends forwards, THE KNEE-JOINT. 303 and provides a partial covering for the crucial ligaments between which a bursa may be found. This somewhat complicated arrangement of the synovial membrane may be readily comprehended if it be borne in mind that it really represents the fusion of three separate synovial cavities, which in some animals are permanently distinct. These are indicated in the two femoro-tibial and the single femoro-patellar parts of the articulation. The joint cavity may communicate with bursse situated in relation to the inner head of the gastrocnemius muscle and the tendon of the semi-membranosus muscle, besides the large supra-patellar bursa already described. Lastly, there may be intercommunication between this joint cavity and that of the superior tibio-fibular articulation. Movements at the Knee- Joint. — In studying the movements which may occur at the human knee-joint, it is necessary to bear in mind that the lower limb of man is primarily required for jjurposes of support and locomotion. The j^rincipal requirement of the former function is stability accompanied by rigidity, whereas in the latter function the special desideratum is regu- lated and controlled mobility. Thus, in the same joint, two entirely opposite conditions have to be provided. The stable conditions of support are chiefly concerned in the maintenance of the erect attitude, and the mechanism associated therewith does not call for the exertion of a large degree of sustained muscular effort. In standing erect the attitude of the limb is that of extension, which mainly concerns the femoro-tibial parts of the joint. In this position the force of gravity acts along a vertical line which falls in front of the transverse axis of the joint, and therefore any tendency to flexion, i.e. bending backwards, is mechanically counteracted by the ajaplication of a force which tends to produce bending forwards (so-called over-extension). This, however, is absolutely prohibited in normal states of the joint, by the tension of the posterior and lateral ligaments aided by the anterior crucial ligament. The value of this fact may be seen by observing the eftect produced by giving the joint a sudden push from behind, which causes an immediate reversal of the positions of the transverse and vertical axes, whereby the body weight at once produces flexion of the joint. The semilunar cartilages and the infra-patellar pad of fat also assist in maintaining extension, by reason of their close adaptation to, and packing round the condyles as these rest upon the tibia. The anterior margin of the intercondyloid fossa is also brought into contact with the front of the anterior crucial ligament. In the position of extension the patella is retained at a high level in relation to the trochlear sur- face of the femur, so that the lower articular facets of the patella are in contact with the trochlea. During locomotion the movements of the knee-joint are somewhat intricate, for both the femoro-tibial and the femoro-patellar sections of the joint are brought into action. The principal movement which results is flexion, with which there is associated, both at its beginning and ending, a certain amount of screw movement or rotation. Flexion and rotation occur at the femoro-tibial sections of the joint, whereas the movement at the femoro-patellar portion produces a regulating and controlling influence upon flexion. Taking these factors separately, we observe that each condyle adapts itself to a shallow cup formed by the head of the tibia and the corresponding semilunar cartilage, and as the two condyles move simultaneously and parallel to each other, there is more than the characteristic hinge-joint action, for each condyle glides and rolls in its cup " like a wheel restrained by a drag " (Goodsir) when the movement of bending occurs. Thus the difl'erent parts of the condyles are successively brought into relation with the transverse axis of the joint while it passes from extension to flexion and vice versa. From the fact that the internal condyle is longer than the external, it is believed that extension is completed by a movement of rotation whereby the joint becomes locked, and the anterior crucial, the posterior and the lateral ligaments, become tense. A similar rotation initiates the movement of flexion, and unlocks the joint by relaxing the liga- ments just mentioned. Since the tibia and foot are fi'-ed in the act of walking, it is the femur which rotates upon the tibia in passing from ex' i to flexion and vice versa ; and as relaxation of the ilio-femoral ligament is essential for this rotation, some observers are of opinion that the body weight falls behind the transverse axis of the knee-joint, as in the case of the hip-joint, and consequently that extension of the knee-joint is maintained by the ilio-femoral ligament, as it is not possible to bend the knee without first having bent the hip-joint. During flexion and extension the semilunar cartilages glide along with the condyles, so as to maintain their close adaptation and preserve their value as packing agents. When the movement of flexion is completed, the condyles are retained upon the tibia, and prevented from slipping off by the tension of the posterior crucial ligament. In this position a small degree of rotation of the tibia, both inwards and outwards, is also permissible. The regulating and controlling influence of the femoro-jjatellar portion of the articulation is brought into play during the movements of flexion and extension. In the latter position the inferior pair of patellar facets is in apposition with the up^ier part of the femoral trochlea. As flexion advances, the middle j^air of facets adapt themselves to a deeper area of the trochlea, into which the patellar keel fits. When flexion is still further advanced, tlie upper pair of patellar facets will be found fitting into that part of the trochlea adjoining the intercondyloid notch ; 304 THE AKTICULATIONS OK JOINTS. and tiually, Avlieu flexion is complete, tlie patella lies opposite tlie intercondyloid notch, wMle the forward thrust of the longer internal condyle brings its semilunar facet (Goodsir) into apposition -with the somewhat vertical facet at the inner border of the patella. The wedge-like influence of the patella is most marked, for it is only in the position of extension that it can be moved from side to side. The movements of the j^atella may be described as gliding and co-aptation, as it slips or rocks from one pair of facets to another in its progress along the trough of the femoral trochlea. THE TIBIO-FIBULAR JOINTS. The upper and lower ends of the fibula articulate with the tibia. Primarily, the fibula is required to form a strong lateral support for the ankle-joint, and therefore its articulations are so arranged as to provide a certain amount of elasticity without any sacrifice of the rigidity necessary for security. Hence the amount of movement is very small, but what there is enables these joints to be classified as arthrodial diarthroses. The superior tibio-fibular joint (articulatio tibio-fibularis) is formed, on the one hand, by a flat oval or circular facet which is situated upon the postero-external aspect of the outer tuberosity of the head of the tibia, and is directed downwards and backwards ; on the other, by a similar facet on the upper surface of the head of the fibula in front of the styloid process. A fibrous capsule (capsula articularis. Fig. 234) invests the joint, and it may be regarded as holding the articular surfaces in apposition, although certain special bands receive separate designations. Occasionally there is an opening in the capsule by which communication is established between the joint cavity and the knee-joint through the intermediation of the synovial prolongation, subjacent to the tendon of the popliteus muscle. The anterior superior tibio-fibular ligament (lig. capituli fibulae anterius, Fig. 233) is a strong flat band whose fibres extend from the anterior aspect of the fibular head, upwards and inwards, to the adjoining part of the tuberosity of the tibia. The posterior superior tibio-fibular ligament (lig. capituli fibulse anterius, Fig. 234) is a similar, but weaker band, passing upwards and inwards from the posterior aspect of the fibular head to the posterior aspect of the outer tuberosity of the tibia, w^here they are attached immediately below the opening in the capsule of the knee-joint, from which the tendon of the popliteus muscle escapes. Equally strong but much shorter bands are found on the superior and inferior aspects of the joint. The former is intimately associated with the tendon of the biceps flexor cruris muscle which strengthens the upper aspect of the joint, and here also is found the occasional opening by which it communicates with the knee- joint. . The synovial membrane is in certain cases continuous with that of the knee- joint in the manner already described. The interosseous membrane (membrana interossea cruris, Figs. 234 and 237) plays the part of an accessory ligament both for the upper and the lower tibio-fibular joint. It is attached to the interosseous borders on the shafts of the tibia and fibula, and binds them together. The general direction of its fibres is from the tibia downwards and outwards to the fibula, but many fibres pass in the opposite direction. The membrane may extend upwards until it comes into contact with the ligaments of the superior tibio-fibular joint, but there is always a vertical oval aperture in its upper part for the forward passage of the anterior tibial vessels. This aperture (Fig. 234), which is about one inch long, adjoins the shaft of the fibula at a point rather less than one inch below its head. Towards the lower end of the leg the distance between the tibia and the fibula rapidly diminishes, and consequently the width of the interosseous membrane is correspondingly reduced, 80 that it is tense throughout its entire length. In the lower part of the membrane there is a small opening for the passage of the anterior perforating vessels. There is no sharply-marked demarcation between the interosseous membrane and the interosseous ligament which connects the lower ends of the tibia and fibula — the one, indeed, may be said to run into the other. The inferior tibio-fibular joint (syndesmosis tibio-fibulare) is not on all occasions provided with articular cartilage, so that it may either be a separate articu- THE TIBIO-FIBULAK JOINTS. 305 lation, or it may merely present a series of ligaments which are accessory to the ankle- joint, because it is clear that, under any circumstances, the object aimed at in this articulation is to obtain additional security for the ankle-joint. The articular surface on the tibia, when present, constitutes a narrow articular strip on the outer side of the lower end of the bone, and the joint-cavity is practically an upward extension of the ankle-joint. The corresponding fibular facet is continuous with the ex- tensive articular area, by means of which the fibula articulates with the astragalus. By far the greater part of the opposing surfaces of tibia and fibula are, however, non-articular and rough. The supporting ligaments are of great strength. I-- Tibio-fibular interosseous membrane ^^ Lower end of shaft of fibula Lower end of shaft of tibia Groove ou internal malleolus for tendon of tibialis posticus tendon Trochlear surface of astragalus Internal lateral ligament Kbrous sheath for tendon of flexor longus hallucis Sustentaculum tal Flexor longus hallucis tendon (tut)— Posterior calcaneo-astragaloid ligament Posterior inferior tibio- fibular ligament Transverse inferior tibio- fibular ligament Facet ou astragalus for transverse inferior tibio- fibular ligament Posterior talo-fibular ligament (posterior fasciculus of external lateral ligament) Calcaneo-fibular ligament — (middle fasciculus of external "ateral ligament) Tuberosity of os calcis Fig. 2-37. — Axkle- Joint Dissected from Behind with Part of the Capsllar Ligament Removed. The anterior inferior tibio-fibular ligament (lig. malleoli lateralis anterius, Fig. 240) consists of strong fibres which pass ol»liqueiy downwards and outwards from the front of the lower end of the tibia to the front of the external malleolus. The posterior inferior tibio-fibular ligament (lig. malleoli laterahs posterius. Figs. 237 and 238) is equally strong, and passes in a similar direction between corre- sponding posterior surfaces. A transverse inferior tibio-fibular ligament (Figs. 237 and 238) stretches, in the direction indicated by its name, between the posterior inferior border of the tibia and the upper end of the pit on the inner and posterior aspect of the external malleolus. An interosseous ligament, powerful and somewhat extensive, connects the con- tiguous rough non-articular surfaces. Superiorly, as already mentioned, it is con- tinuous with the interosseous membrane. Anteriorly and posteriorly it comes into contact with the more superficial ligaments. Inferiorly it descends until it comes into intimate association with the joint-cavity. 21 306 THE AETICULATIONS OR JOINTS. A synovial membrane is found lining the small joint-cavity, but it is always a direct prolungatiuu Irom that which lines the ankle-joint. JOINTS OF THE FOOT. THE ANKLE-JOINT. The ankle-joint (articulatio talo-cruralis) is a giugl^uuus variety of a diarthrosis. The bones which enter into its formation are the lower ends of the til)ia and fibula, with the articular areas on the upper, lateral, and mesial surfaces of the astragalus. The tibia and tibula, aided by the transverse inferior tibio-fibular ligament, form a three-sided socket within which the astragalus is accommodated. The roof or higliest part of the socket, which is wider in front than behind, is formed chiefly by the quadrilateral articular surface which characterises the lower end of the tibia, but towards its postero-external margin the transverse inferior tibio-fibular liga- ment assists in its formation. Here also the tibial articular surface is continuous with the narrow articular facet already described as forming part of the inferior tibio-fibular joint. The inner wall of the socket is formed by the articular facet on the outer side of the internal malleolus, and there is no interruption of the articular cartilage between the roof and inner wall. The outer wall of the socket is quite separate from the foregoing parts, and consists of a large triangular facet upon the inner side of the external malleolus. This facet is situated immediately in front of the deep pit which characterises the posterior part of this surface of the fibula. A small lunated facet is frequently found upon the anterior surface of tlie lower end of the tibia, particularly among those races characterised by the adoption of the " sc|uatting '" posture. When this facet exists it is continuous Avith the anterior margin of the roof of the socket, and it articulates with a similar facet upon the upper surface of the neck of the astragalus in the extreme flexion of the ankle-joint wliicli "sqi^atting" entails. The articular surface upon the body of the astragalus adapts itself to the tibio- fibular socket, and presents articular facets corresponding to the roof and sides of the socket. Thus the superior surface of the astragalus possesses a quadrilateral articular area, wider in front than behind, distinctly convex in the antero-posterior direction, and slightly concave transversely. In addition, towards its postero- external margin, there is also a narrow antero-posterior facet corresponding to the transverse inferior tibio-fibular ligament. The articular cartilage of this upper surface is continued without interruption to the tibial and fibular sides of the bone, although the margins of the superior area are sharply defined from the lateral facets, the outer of which is triangular in outline, while the inner is pyriform, but in each case the surface is vertical. Ligaments. — The ligaments form a complete investment for the joint, i.e. a capsule in which the individual parts vary considerably in strength, and are de.scribed under separate names. Tlie anterior ligament is an extr>'inely thin membrane, containing very few longitudinal fibres. It extends from the lower border of the tibia to the upper border of the head of the astragalus, passing in front of a pad of fat which gament of fills uTj the hollow abovc the ankle-joint i f. ,1 . i neck 01 that bone. The posterior ligament is attached to contit^u- ous non- articular borders of the tibia and astragalus. Many of its fibres radiate inwards from the external malleolus. Tliis aspect of the joint is strengthened by the strong, well-defined, trans- verse ligament already described in connexion witli the inferior tibio-fibular joint. Anterior talc fibular ligament Articular facet on external malleolus Anterior inferior tibio-fibular lit;aineiit Internal lateral or eltoid Caleaneo- fibular ligament Posterior inferior tibio-fibular ligament Posterior talo-flbular ligament Fig. 2.38. — Articulau Scrkaces of Tibia and Fibula which are opposed to the astragalus. Internal malleolus Transverse inferior tibio-libular ligament Synovial pad of fat THE ANKLE-JOINT. 307 The external lateral Ugament (Figs. 237, 238, and 2-iOj is very powerful, and is divisible into three fasciculi, which are distinguished from each other by names descriptive of their chief points of attachment. The anterinr fasciculus (lig. talo-fibulare anterius) is the shortest. It extends from the anterior border of the external malleolus to the astragalus immediately in front of its external articular surface. The middle fascictdus (lig. calcaneo-fibulare) is a strong and rounded cord. It is attached by one end to the front of the tip of the external malleolus, and by the other to the outer side of the os calcis, immediately above the groove for the peroneal tendons. The posterior fasciculus (lig. talo-fibulare posterius) is the strongest. It runs transverselv between the lower part of the fibular or digital fossa on the inner aspect of the malleolus and the posterior surface of the astragalus, where it is attached Inner tarso- metatarsal joint (opened) Internal malleolus Internal lateral or deltoid ligament of the ankle Trochlear surface of astragalus Groove for tendon of tibialis l)0-,ticu» mn-iple on inferior ealcaneo-soaplioid ligament Groove and tunnel for the tendon of flexor longus hallucis muscle ^'Os calcis Long plantar ligauient , Tendon of tibialis posticus muscle (cut) Sustentaculum tali Fig. 239. — Axkle and Tarsal-.Joints from the Tibial Aspect. to the external tubercle and the adjoining rough surface. Sometimes this tubercle is detached from the astragalus, and represents a separate bone — the os trigonum. The internal lateral ligament (lig. deltoideum, Figs. 238 and 239) has the general shape of a delta, and is even stronger than the external ligament. It is attached above to a marked impression on the lower part of the internal malleolus, and below, in a continuous layer, to the scaphoid, astragalus, and os calcis. In it we may recog- nise the following special bands — (a) the lig. talo-tibicde anterius, which extends from the front of the inner malleolus to the neck of the astragalus; (b) the lig. talo-tibiale jyosterius, stretching between the back of the inner malleolus and the postero-internal rough surface of the astragalus ; (c) the lig. tibio-nariculare, which extends from the tip of the inner malleolus to the inner side of the scaphoid ; (d) the lig. calcaneo-tihiale, which extends between the tip of the inner malleolus and the inner side of the sustentaculum tali; (e) lig. talo-tibiale profundum, which consists of deeper fibres extending from the tip of the internal malleolus to the inner side of the astragalus. Synovial membrane lines the capsular ligament, and, as already described, the joint-ca%'ity communicates directly with the inferior tibio-fibular joint. Both at the front and back of the ankle-joint, as well as superiorly in the angle formed by the three bones, the synovial membrane covers pads of fat. 308 THE AETICULATIONS OR JOINTS. Movements at tlie Ankle-Joint. — In the erect attitude the foot is i^laced at right angles to the leg ; in other words, the normal position of the ankle-joint is flexion. Those movements which tend to diminish the angle so formed hj the dorsum of the foot and the front of the leg are called dorsiflexion, while those which tend to increase the angle, i.e. to straighten the foot upon the leg, are called extension. As a matter of fact neither dorsiflexion nor extension is ever completely carried out, and the range of movement of which the foot is capable is limited to about 90". These movejnents occur about an obliquely transverse axis, as is indicated by the natural outward pointing of the toes. The weight of the body falls slightly anterior to the ankle- joint, so that a certain amount of muscular action is necessitated in order to maintain the foot at right angles to the leg ; but additional stability is obtained from the obliquity above mentioned. When the foot is raised from the ground, muscular action tends naturally to produce a certain amount of extension. "When the foot is extended, as in standing on the toes, the hinder narrow part of the astragalus moves forwards into the wider part of the interval between the tibia and fibula, whereas in dorsiflexion, as in raising the fore part of the foot from the ground, the widest part of the astragalus is forced back between the tibia and fibula ; but notwithstanding the dif- ference between these two movements, the fibula remains in close contact with the astragalus by reason of the action of the transverse inferior tibio-fibular ligament and the posterior talo-fibular ligament, so that lateral movement is prevented. It is doubtful whether lateral movement at the ankle-joint can be obtained by any natural movement of the foot, although it is generally belieA^ed that in the position of partial extension a small amount of lateral movement may be produced by the application of external force. " This ajiparent play " of the ankle-joint during extension " is really due to oscillation of the small bones of the foot on each other, largely of the scaphoid on the astragalus, but also of the cuboid on the calcaneum. Excessive mobility of these latter is restrained by an important function of the posterior tubercle of the cuboid which locks into a notch in the os calcis" (Blake). INTERTAESAL JOINTS. These joints (articulationes intertarsese) are all diarthroses in which the gliding movement is characteristic, as in the carpus. With the view of obtaining a proper con- Fibula Posterior inferior L/,*\> tibio-fibular ligament' Articular surface of astragalus Posterior fasciculus of external lateral ligament of ankle Middle fasciculus of external lateral ligament of ankleN Posterior talo-t-alcaneal ligaiiienf Os calcis Tibia 'j \iiterior inferior tibio-fibular ligament Articular surface of astragalus Anterior fasciculus of external lateral ligament y^ of ankle / 1 '01 sal astragalo na\icular ligament Z \stragdlo na\icular joint Ext calcaneo navicular ligament Dorsal scapho-cuneiform ( . V^^i^r^l '■'i- scapho-cuboid ligaments I ' v* j^^ ~>^ Middle cuneiform External (■•uueiform Cnboiii rsal calcaneo-cuboid ligament Calcaneo-cnboid joint Tendon of peroneus longus Intel osseous tiilo-calcaneal ligament Talo-calcaiieal joint External talo-calcaneal ligament Fig. 240.— Ligaments on the Outer Aspect of the Ankle-Joint and on the Dorsum of the Tarsus. caption of the many beautiful mechanical principles involved in the construction of the foot, it is necessary to study these articulations with considerable attention to detail. Articulatio Talo-calcanea. — The astragalus and os calcis articulate with each other in the articulatio talo-calcanea or calcaneo-astragaloid joint. This joint is situated between the inferior facet on the body of the astragalus INTEKTAESAL JOINTS. 309 ^^eaphoi^l bone Inferior calcaneo- scaphoid ligament Internal calcane;- scaphoid ligameu: Tendon of tibialis posticus muscle (cut) Sustentaculum tali ; articular surface for astraealu Articular surface on scaphoid for head of astragalus Inner surface of external calcaneo-scaplioid ligament External calcaneo-scaphoid t Interosseous cal- caneo-astragaloid ligament Articular surface on OS calcis for liody of astragalus Os calcis and a corresponding facet on the upper aspect of the hinder part of the os calcis. On each bone the articulation is limited in front by a wide, deep groove which runs obliquely across each bone from within outwards and forwards. The supporting and investing ligaments form a capsule, consisting for the most part of short fibres, but the joint derives additional strength from the external and internal lateral ligaments of the ankle-joint. The capsule is subdivided into the following astragalo-calcaneal or talo-calcaneal bands : — The anterior talo-calcaneal ligament coDsists of a band of short fibres placed immediately in relation to the anterior end of the deep groove which bounds the articular facets. They are attached to the antero - external aspect of the neck of the astragalus, from which they extend downwards to the adjacent superior surface of the os calcis. The external talo-cal- caneal ligament (Fig. 240) is in continuity with the hinder border of the pre- ceding ligament, and it is placed parallel to, but on a deeper plane than, the middle fasciculus of the external lateral ligament of the ankle-joint. It con- sists of short fibres passmg between the adjacent rough outer margins of the two bones. The posterior talo-cal- caneal ligament (Fig. 240) closes the joint-cavity on its posterior aspect. It consists of fibres which radiate from the posterior aspect of the external tubercle of the astragalus to the upper surface of the os calcis, immediately behind the articular facet. The internal talo-calcaneal ligament Ues obliquely on the inner side of the joint, and consists of fibres which extend from the inner posterior tubercle of the astragalus to the hinder roughened border of the sustentaculum tali. Sonie of its fibres become continuous with the internal calcaneo-scaphoid Hgament. The interosseous talo-calcaneal ligament (Fig. 240) closes the antero-internal aspect of the joint. It is the strongest of the series of ligaments entering into the capsule. Compared with it the other bands are, comparatively speaking, insigni- ficant. Its attachments are to the bottom of each groove, so that it occupies the tarsal canal formed by these opposing grooves. A synovial membrane lines the capsule, and it is distinct from other tarsal synovial membranes. Articulatio Talo-calcaneo-navicularis. — This is one of the most important of the joints of the foot, not only because the astragalus is here situated in relation to the summit of the antero-posterior arch of the foot, but because the head of the astragalus is received into a composite socket made up of sustentaculum tali, scaphoid, and the inferior or internal calcaneo-scaphoid ligament. The articular surface on the head of the astragalus presents anteriorly a convex rounded facet for articulation with the scaphoid, inferioiiy a convex facet which rests upon the sustentaculum tali, and intermediate between these two there is a triangular facet which articulates with the inferior calcaneo-scaphoid ligament. All these facets are in continuity with each other, and are in front of the tarsal groove on the under surface of the astragalus. Occasionally a fourth narrow facet is Fig. 2-11. — The Composite Articular Socket for the Head of the astraualus. 310 THE AETICULATIONS OR JOINTS. found along the outer and hinder part of the articular surface of the head of the astragalus, whereby it articulates with superior or external calcaneo-scaphoid ligament. The scaphoid or navicular bone presents a shallow, cup-shaped, articular cavity towards the head of the astragalus. The articular surface of the sustentaculum tali is concave, and is usually marked off into two facets. Two ligaments play an important part in binding together the os calcis and the scaphoid, although these bones do not directly articulate ; and further, these ligaments provide additional articular surfaces for the head of the astragalus. These are the two following : — (a) The inferior or internal calcaneo-scaphoid ligament (Figs. 239 and 242) is an Tpiidon of insertion of peioneus longus muscle Base of metatarsal bone of hiUnx Plantar inter-metatarsal .- ligaments Plantar cuboid i idge Plantar cubo-cuneiform ligament Short plantar ligament -^jlifflWMf ! I Tendon of peroneus longus muscle —'-^^ Long plantar ligament Tendon of insertion of tibialis anticus muscle — Internal cuneiform bone Plantar scapho-cuneiform ligament iidon of tibialis posticus iscle < 1 3ove for tendon of tibialis i posticus muscle Inferior calcaneo-scaphoid ligament Inteinal lateral or deltoid i„ainent of ankle Internal malleolus Gino\e for tendon of flexor longus hrllucis muscle ( )s c ikis Fig. 242. — Plantar Aspect ok Taksal and Tahso-metatarsal Joints. extremely powerful fibro-cartilaginous tie-band. It extends between the anterior margin of the sustentaculum tali and the inferior surface of the scaphoid bone. Certain of its upper filjres radiate upwards on the inner surface of the scaphoid, and become continuous with the tibio-navicular portion of the deltoid ligament of the ankle- joint. The plantar aspect of this ligament is in contact with the tendon of the tibialis posticus muscle, through which the head of the talus receives great support. Superiorly it contributes an articular surface which forms a triangular portion of the iloor of the composite socket in which the head of the talus is received. (6) The superior or external calcaneo-scaphoid ligament (Fig. 241) lies deeply in the front part of the sinus tarsi, i.e. the interval l)etween the astragalus and os calcis. Its fibres are short, and extend from the dorsal surface of the front part of the os calcis, immediately to the outer side of the sustentacular facet, forwards to the outer side of the scaphoid bone. Frequently the ligament presents a surface INTEETARSAL JOINTS. 311 which articulates with the head of the astragalus, and in these cases it forms a part of the composite socket. The cavity of the talo-calcaneo-navicular joint is closed posteriorly by the interosseous talo-calcaneal ligament already described. On its inner and outer inferior aspects it is closed by the calcaneo-scaphoid ligaments. The superior and lateral aspects are covered by an astragalo-scaphoid membrane or ligament. This ligament is thin, and extends from the upper non-articular area on the head of the astragalus to the dorsal surface of the scaphoid bone. It may be subdivided into dorsal (superior), lateral (external), and medial (internal), astragalo-scaphoid ligaments (Fig. 239), which, with the calcaneo-scaphoid and interosseous talo-calcaneal Ligaments, complete the capsular investment of the joint. A distinct synovial membrane lines all parts of the capsule of the joint. Articulatio Calcaneo-cuboidea. — This is situated between the anterior concavo- convex surface of the os calcis and the posterior similar surface of the cuboid. The ligaments which invest this joint constitute a calcaneo-cuboid capsule, whose parts are arranged in relation to the four non-articular sides of the cuboid bone, and are especially strong upon the plantar aspect, in relation to their great import- ance in resisting strains. The internal calcaneo-cuboid ligament occupies part of the interval between the astragalus and os calcis — sinus tarsi. It is sometimes called the interosseous calcaneo-cuboid ligament, and, in conjunction with the superior or external calcaneo-scaphoid ligament, it forms a V-shaped structure, of which the single end is attached to the os calcis, and the double ends separate to reach contiguous areas on the scaphoid and cuboid respectively. The dorsal calcaneo-cuboid ligament (Fig. 240) is a broad portion of the capsule extending between the dorsal surfaces of the two bones. The external calcaneo-cuboid ligament is another but narrower part of the capsule which extends from the outer aspect of the os calcis to the outer side of the cuboid, immediately behind the facet on the tuberosity. The inferior calcaneo-cuboid ligaments are two in number — a superficial and a deep. The superficial series of fibres, the long plantar ligament (Fig. 242), is attached to the under surface of the os calcis in front of its tuberosities. It forms a long powerful structure which runs forwards to be fixed to the under surface of the cuboid ridge, but many- of its fibres pass superficial to the tendon of the peroneus longus, and extend to the bases of the third, fourth, and fifth metatarsal bones. The deep series of fibres, the short plantar ligament (Fig. 242), is distinctly separated from the former by a layer of areolar tissue. It forms a broad but short band of great strength, which is attached to the under surface of the front end of the os calcis, and extends to the under surface of the cuboid just behind the ridge. Both of these ligaments are of great importance in maintaining the longitudinal arch of the foot, and in this respect are only second to the inferior calcaneo-scaphoid ligaments. A synovial membrane lines the capsule. Transverse Tarsal Articulation. — This is a term sometimes applied to the astragalo-scaphoid and calcaneo-cuboid joints. These articulations do not com- municate with each other; and although there is an occasional direct articula- tion between the scaphoid and cuboid, it does not constitute an extension of the transverse tarsal joint, but is a prolongation from the series of scapho-cuneiform and cuneo-cuboid articulations. iS'evertheless there is always a set of ligaments which bind the scaphoid and cuboid bones together, and these may be regarded as accessory to the various transverse tarsal joints. The dorsal scapho-cuboid ligament (Fig. 240) consists of short oblique fibres which attach the contiguous dorsal surfaces of the cuboid and scaphoid bones. The plantar scapho-cuboid ligament is transverse in direction, and extends between adjacent plantar areas of the cuboid and scaphoid bones. The interosseous scapho-cuboid ligament intervenes between contiguous surfaces of the same bones. When there is an extension of the scapho-cuneiform joint back- wards between the scaphoid and cuboid, it is situated in front of the last-men- tioned ligament, and is called the articulatio scapho-cuboidea. Around this joint 312 THE AETICULATIONS OR JOINTS. the preceding Jigaments are grouped. Since, liowever, the joint is inconstant while the ligaments are always present, it is preferable to consider them as above indicated. Scapho-cuneiform Articulation (articulatio cimeo-navicularis). — This joint is situated between the scaphoid and the three cuneiform bones. The anterior surface of the scaphoid presents facets for each of the cuneiform bones, but its articular surface is not interrupted. These facets form a somewhat convex anterior surface which fits into the shallow articular concavity presented by the proximal ends of the three cuneiform bones. This joint may be extended by the occasioual scapho-cuboid articulation already referred to. The capsule is composed of short, strong bands which are distinctly visible on all sides except towards the cuboid bone, where the joint may communicate with the cuneo-cuboid and scapho-cuboid joints. Anteriorly the joint communi- cates with the intercuneiform articulations. The dorsal parts of the capsule are short longitudinal bands termed dorsal scapho-cuneiform ligaments (Figs. 239 and 240). These extend without interruption to the inner aspect of the joint. Inferiorly there are similar bands, known as plantar scapho-cuneiform ligaments, also longitudinal in direction, but intimately associated with offsets from the tendon of the tibialis posticus muscle. The synovial membrane which lines the capsule sends prolongations forwards on each side of the middle cuneiform bone, and in addition it often communicates with the cuneo-cuboid joint cavity, and it always communicates with the scapho- cuboid cavity when that joint exists. Intercuneiform Articulations. — These are two in number, and exist between adjacent contiguous surfaces of the three cuneiform bones. These surfaces are partly articular and partly non-articular. The small size of the middle cuneiform bone allows the internal cuneiform as well as the external cuneiform to project forwards beyond it on both sides, and therefore the articular surfaces turned towards the middle cuneiform are not entirely occupied by that bone. They form a recess towards the metatarsus, into which the base of the second metatarsal bone is thrust. Dorsal intercuneiform ligaments constitute fairly strong transverse bands which extend between adjacent dorsal surfaces and invest the joint cavities in this direction. The plantar or interosseous intercuneiform ligaments are two strong bands which pass from the rough non-articular areas on opposite sides of the middle cuneiform to the opposing surfaces of the inner and outer cuneiform bones. These ligaments shut in the joint cavities inferiorly, and also anteriorly in the case of the outer of the two joints. The synovial membrane is an extension of that which lines the scapho-cuneiform joint ; but while it is restricted to the outer of the two joints, in the case of the inner one it is prolonged still farther forward to the tarso-metatarsal series of joints. Cubo-cuneiform Articulation. — This occurs between the rounded or oval facets on the opposing surfaces of tlie cuboid and external cuneiform. The dorsal cubo-cuneiform ligament is a flat, somewhat transverse band which closes the joint on its superior aspect, and extends between the dorsal surfaces of the two bones. The plantar cubo-cuneiform ligament is difficult to determine. It is situated subjacent to the long plantar ligament, and extends between adjacent rough surfaces of the two bones. The interosseous cubo-cuneiform ligament is the strongest. It closes the joint cavity anteriorly, and is attached to the contiguous non-articular surfaces of the two bones. The synovial membrane is frequently distinct, but at other times the joint cavity communicates with those of the scapho-cuneiform and scapho-cuboid articulations. Synovial Membranes of the Intertarsal Joints. — Four and sometimes five distinct and separate synovial membranes may thus be enumerated in connexion with the tarsal articulations, viz. : (1) talo-calcaneal ; (2) talo-calcaneo-navicularis ; (3) calcaneo-cuboid ; (4) scapho-cuneiform and its extensions ; (5) occasionally cubo-cuneiform. TAESO-METATAKSAL JOINTS. 313 TARSO-METATARSAL JOINTS. The tarso-metatarsal joints are found between certain articular facets on the cuboid and three cuneiform bones on the one hand, and others on the bases of the five metatarsal bones. These articulations are associated with three distinct synovial cavities — namely, an inner, middle, and outer. (1) The inner tarso-metatarsal articulation occurs between the distal convex reniform surface of the internal cuneiform bone and the concavo-reniform surface on the proximal aspect of the base of the first metatarsal bone. Ligaments which form a capsule surround the articulation. In the capsule the dorsal and plantar tarso-metatarsal bands are its strongest parts, but it is not deficient either on the inner or on the outer aspects. A separate synovial membrane lines the capsule. (2) The middle tarso-metatarsal articulation is an elaborate joint. It involves the three cuneiform bones and the bases of the second, third, and part of the fourth metatarsal bones. The articulation presents the outline of an indented parapet both on its tarsal and its metatarsal aspects. Thus, on its tarsal side, the inner and the outer cunei- form bones project in front of the middle cuneiform, so that the latter only presents a distal surface to the articulation ; while the internal cuneiform presents a portion of its external surface, and the external cuneiform presents both its distal and portions of its outer and inner surfaces, since it projects in front of the cuboid bone. On its metatarsal side the base of the second metatarsal bone fits into the indentation between the outer and inner cuneiforms, to which it presents external and internal articular facets, but its proximal facet rests upon the distal facet of the middle cuneiform. The base of the third metatarsal bone rests its proximal facet upon the outer cuneiform. The fourth metatarsal base presents part of its internal facet to the external side of the outer cuneiform. In this way the indentations alternate on the two sides of the articulation, and an extremely powerful interlock- ing of parts is provided, which places any marked independent movement of these metatarsal bones entirely out of the question. The dorsal tarso-metatarsal ligaments are broad, flat bands which represent the most distinct part of an investing capsule. They pass from behind forwards, and while the second metatarsal bone receives three, i.e. one from each cuneiform, the third metatarsal only receives one — from the external cuneiform. The plantar tarso-metatarsal ligaments correspond with the foregoing in their general arrangement, but they are weaker. Tliat for the second metatarsal is the strongest. Oblique bands extend from the inner cuneiform bone to the second and third metatarsals. The interosseous cuneo -metatarsal ligaments are three in number. The inner connects the outer side of the internal cuneiform with the inner side of the base of the second metatarsal bone. The middle connects the inner side of the external cuneiform with the outer side of the base of the second metatarsal. The outer connects the adjacent outer sides of the external cuneiform and third metatarsal. The synovial membrane, which lines this articulation, sends a prolongation back- wards between the inner and middle cuneiform bones, where it opens into the scapho-cuneiform joint. It is likewise prolonged forwards upon both sides of each of the bases of the second and third metatarsal bones. (3) The external tarso-metatarsal articulation is found between the proximal surfaces of the bases of the fourth and fifth metatarsal bones and the distal surface of the cuboid. The investing capsule may be resolved into the following ligaments : — The dorsal tarso-metatarsal ligaments resemble those already described. The base of the fourth metatarsal receives one from the external cuneiform and one from the cuboid. The base of the fifth metatarsal receives one from the cuboid. The plantar tarso-metatarsal ligaments are the weakest bands of the series, and consist of scattered fibres passing from the cuboid to the bases of the two metatarsals. Some fibres, which are almost transverse, extend from the 22 314 THE ARTICULATIONS OR JOINTS. external cuneiform to the fifth metatarsal, and additional fibres reach the meta- tarsals in question from the long plantar ligament (calcaneo-cuboid). Occasionally the tarsal end of the external interosseous (cuneo-metatarsal) liga- ment is attached to the inner margin of the cuboid. The synovial membrane is restricted to this articulation, and merely sends a prolongation forwards between the opposing articulate aspects of the fourth and fifth metatarsal bases. INTERMETATARSAL JOINTS. The intermetatarsal articulations are found between adjacent lateral aspects of the bases of the four outer metatarsal bones. The articular facets are small, oval, or rounded surfaces which occupy only a limited portion of the flattened contiguous surfaces of the bones. Each joint is provided with a capsule, which, however, is not a complete investment, because the three joint cavities are in free communication on their proximal aspects with the tarso-metatarsal joint cavities— one with the outer and two with the middle. The definite fibres of each capsule are situated chiefly in the transverse direction. The dorsal ligaments are short bands which extend from one base to the other. The plantar and interosseous ligaments are similarly arranged, but the latter are the strongest and most important members of this series. The synovial membranes are extensions from those which line the outer and middle tarso-metatarsal joint cavities. Frequently a bursa is found between the bases of tbe first and second metatarsal bones. It produces an appearance of indistinct facetting upon these bones, and it may communicate with the inner tarso-metatarsal (cuneo-metatarsal) joint. The transverse metatarsal ligament lies upon, and is attached to, the non- articular plantar aspects of the heads of all the metatarsal bones. It differs from the corresponding ligament in the palm in the fact that it binds all the metatarsal bones together, whereas in the palm the thumb is left free. It is closely associated with the plantar fibrous plates of the metatarso-phalangeal joints, to the plantar surfaces of which it contributes prolongations termed ligamenta accessoria plantaria. METATARSO-PHALANGEAL JOINTS. Each of these joints is a modified ball-and-socket in which a shallow cup upon the bases of the first phalanges receives the somewhat globular head of a metatarsal bone. Each joint retains a modified capsule which invests the joint. Its only distinct bands are the ligamenta coUateralia. These are strong cord-like bands which are situated on the inner and outer sides of each joint, where they extend between adjacent rough surfaces. On the dorsal aspect ligaments distinct from the dorsal expansion of the ex- tensor tendons can hardly be said to exist. The plantar aspect of the capsule consists of a thick fibrous plate, which in the case of the great toe presents developed within it^vo large sesamoid bones. In the other toes this plate remains fibrous throughout, and is grooved on its plantar aspect for the accommodation of the long flexor tendons. It will thus be seen that the metatarso-phalangeal joints are constructed upon a plan very similar to that of the corresponding joints in the hand. A synovial membrane lines the capsule of each articulation. INTERPHALANGEAL JOINTS. Each toe possesses two interphalangeal joints except the great toe, which has only one. Not unfrequently in the little toe the distal joint is obliterated through ankylosis. All the joints of this series are uniaxial or hinge joints. The nature of the articular surfaces closely resembles the corresponding joints in the fingers. Each joint possesses a capsule which is either very thin or limited to synovial membrane on the dorsal aspect. The plantar surface of the capsule is strength- INTEKPHALANGEAL JOINTS. 315 ened by a fibroiis plate. The lateral ligaments (ligamenta collateralia) are well- defined bands similar to those already described in connexion with the metatarso- phalangeal joints. A ssmovial membrane lines each capsule in the series. Mechanism of the Foot. — The bones of the foot are arranged in the form of a longitudinal and a tran-svei.se arch. The longitudinal arch is built on a very remarkable plan. Posteriorly the mass of the os calcis constitutes a rigid and stable j^ier of support, while anteriorly, by increasing the number of component parts, the anterior pier acquires great flexibility and elasticity witliout sacrificing strength or stability. The summit of the arch is formed by the astragalus, which receives the weight of the body from the tibia, and the resilience of the arch is assured by the calcaneo-scaphoid and calcaneo-cuboid ligaments, together with the plantar fascia, which act as powerftil braces or tie bands, preventing undue separation of the piers of the arch, and consequent flattening of the foot. The weight of the body is distributed over all the five digits, owing to the arrangement of the bones of the foot in two parallel columns, an inner and an outer. The former, consisting of the astragalus, scaphoid, and the three cuneiforms, with the three inner metatarsal bones, distributes weight through the talo-scaphoid joint, while the latter {i.e. the outer column), comj^rising the calcaneum, cuboid, and the two outer metatarsal bones, acts in a similar manner through the talo-calcanean joint. The main line of immobility of this arch passes from the heel forwards through the middle toe, but its anterior section, which is slender, is supported on either side by two metatarsal bones, with their proximal tarsal associations, in all of which greater freedom of movement is found. The transverse arch is most marked at the level of tarso-metatarsal articulations. The intersection of these two arches at right angles to each other introduces an architectural feature of great importance in connexion with the support of heavy weights. These longitudinal and transverse arches of the foot are in effect " vaults " intereecting each other at right angles, and in relation to the area which is common to both " vaults " the body weight is superposed exactly as the dome of a cathedral is carried upon two intereecting vaults. Movements at the Joints of Tarsus, Metatarsus, and Phalanges. — Considered in detail, the amount of movement which takes jjlace between any two of these bones is extremely smali, and, so far as the tarsus and metatarsus are concerned, it is mostly of the nature of a gliding motion. At the metatarso-phalangeal and interphalangeal joints movement is much more free, and is of the nature of flexion (bending of the toes towards the sole of the foot, i.e. plantar flexion) and extension. The latter movement when continued so as to raise the toes from the ground, and bend or approximate them towards the front of the leg, is termed dorsiflexion. Coincident with dorsiflexion there is always associated a certain amount of spreading of the toes, which is called abduction, and similarly with prolonged flexion there follows a diminution or narrowing of the transverse diameter of the front part of the foot by drawing the toes together — a move- ment termed adduction. In the foot the movements of abduction and adduction take place in regard to a plane which bisects the foot antero-posteriorly through the second toe, for this toe carries the fii'st and second dorsal interosseous muscles. Notwithstanding the small amount of possible movement in connexion with individual tarsal and metatarsal joints, yet the sum total of these movements is considerable as regards the entire foot. In this way the movements of inversion and eversion of the foot result. By inversion we mean the raising of the inner border of the foot so that the sole looks inwards, while the toes are depre.ssed towards the ground, and the outer border of the foot remains down- wards. This takes place chiefly at the talo-calcanean joint, but the transverse tarsal joints also participate. Eversion is chiefly the opposite of inversion, and the return of the foot to the normal position of the erect attitude ; but under certain conditions it may be carried further, so that the outer border of the foot is raised from the ground, while the inner border is depressed. In both of these movements there is rotation between the astragalus and os calcis about an oblique axis which passes from the inner side of the neck of the astragalus to the outer and lower part of the os calcis. Of course all the movements of the foot are subordinated to its primary functions as an organ of support and progression. For these purposes its longitudinal and transverse arches are of extreme importance. The longitudinal arch resting on the os calcis behind and the heads of the metatarsal bones in front receives the weight of the body, as already explained, on the summit of the astragalus in the line of the third toe. Hence it is that the inner malleolus appears to be unduly prominent on the inner side of the ankle. The transverse arch buttresses the longitudinal one, and therefore, whether the body weight fall to the outer or the inner side of the longitudinal arch, it is supported by a mechanism at once stable, flexible, and elastic, or resilient, and capable of reducing to a minimum all jars that may be received by the fore-part of the foot. As the heel is raised in the act of walking, the weight is gradually transferred from the outer to the inner side of the foot, until the foot finally leaves the ground with a propulsive movement, which results from flexion of the phalanges of the great toe. In this connexion it is worthy of note that the longitudinal line of greatest strength is on the inner side of the longitudinal arch, i.e. in relation to the great toe. 22 a THE MUSCULAR SYSTEM. MYOLOGY. By A. M. Paterson/ M.D., Professor of Anatomy, University College, Liverpool. THE MUSCULAR SYSTEM. MYOLOGY. By A. M. Pateeson. The movements of the various parts and organs of the body are brought about by the agency of muscle-cells, which are characterised by a special histological structure and by the special function of contracting in length under the influence of a proper stimulus. There are three classes of muscle-cells : (1) the striated, and usually voluntary muscle-cells, out of which the skeletal muscular system is constructed ; (2) the non- striated, involuntary muscle-cells, occurring in the walls of vessels and hollow viscera, etc. ; and (3) the cardiac muscle-cells, striated but involuntary, of which the substance of the heart is composed. The following section deals solely with the skeletal muscles, the structure, arrangement, and mechanical action of which are based upon a common plan. The cells of which the skeletal muscles are composed are long, narrow, and characterised by a peculiar striation, which is different from the striation of the muscle-cells of the heart ; they also differ both in structure and function from the non-striated muscle-cells which occur in viscera and vessels. A typical skeletal muscle consists of a fleshy mass enveloped in a membranous aponeurosis or fascia, and provided at its extremities or borders with membranous or tendinous attachments to bone, cartilage, or fascia. Each muscle is made up of a number of fasciculi or bundles, arranged together in different muscles in different ways, so as to give rise to the particular form of the muscle in question. These fasciculi are clothed and connected together by a delicate connective tissue, the perimysiuin externum, continuous externally with the aponeurosis enclosing the muscle. Each muscular bundle or fasciculus is composed of a number of narrow, elon- gated muscle-cells or fibres, held together by a still more delicate connective tissue, the perimysium internum. This tissue is connected on the one hand with the sarco- lemma or cell-wall of the muscle-cell, and on the other hand with the coarser tissue of the perimysium externum enclosing the muscular bundles. By means of these connective tissue envelopes the muscle-cells, the essential agents of motor activity, are brought into firm and intimate relation with the osseous or other attachments of the muscle. Through the agency of sarcolemma, perimysium internum, perimysium externum, aponeurosis, and tendon, the muscle- cell when it contracts can produce a precise and definite effect upon the weight to be moved. Each muscle is supplied by one or more nerves, which, in their course through the muscle, separate into smaller and smaller branches, ultimately, by their terminal filaments (axons), forming special end-organs in relation to each muscle-cell. While a muscle may thus be looked upon as an organ endowed with particular properties, and executing a definite movement in response to a stimulus by the simultaneous contraction of its constituent cells, the various muscles may further be considered in groups, associated together by mode of development, nerve-supply, and co-ordination of action. For example, we speak of the hamstring muscles of 317 22 h 318 THE MUSCULAE SYSTEM. the thigh, the muscles of the back, and the prsevertebral muscles, — groups in which separate muscles are associated together by development, nerve-supply, and action. In their development the separate muscles arise from the subdivision of a larger stratum, as in the limbs, or from the fusion of segmental elements (myotomes), as in the case of the axial muscles. The peripheral nerves supplying skeletal muscles are distributed, through the plexuses or directly, so as to associate particular muscles morphologically and physiologically, and to secure a co-ordinated movement by the simultaneous contraction of several muscles. FASCIiE. Beneath the skin there are two (or in some regions three) layers of tissue which require consideration in relation to the muscular system : the superficial fascia (panniculus adiposus), the deep fascia (fascia lata), and, in animals, the panniculus carnosus (rudimentary in man, and represented chiefly by the platysma in the neck). Superficial Fascia. — The superficial fascia is a continuous sheet of areolar tissue which underlies the skin of the whole body. It is closely adherent to the cutis vera, and is sometimes termed panniculus adiposus, from the fact that, except beneath the skin of the eyelids, penis, and scrotum, it is usually more or less impregnated with fat. The cutaneous vessels and nerves ramify in this fascia ; and its deep surface, membranous in character, is in loose connexion with the subjacent deep fascia. It is in this layer that dropsical effusions chiefly occur. Deep Fascia. — Underneath the skin and superficial fascia is a fibrous membrane, bluish white in colour, devoid of fat, and in closest relation to skeleton, hgaments, and muscles. This is the deep fascia. It covers, invests, and in some cases forms the means of attachment of the various muscles. It has a special tendency to become attached to all subcutaneous bony prominences, and to be continuous with the connecting ligaments. It forms septal laminae, which separate groups of muscles and individual muscles ; enclose glands and viscera ; and form sheaths for vessels and nerves. Around joints it gives rise to bands which strengthen the capsule or limit the mobility of the joint, or, as in the case of annular ligaments, bind down the tendons passing over the joint. It not only ensheathes vessels and nerves, but is perforated by those which pass between super- ficial and deeper parts. The term aponeurosis is used in relation to muscles. It is synonymous with deep fascia, either as an investing fascia, or as a membranous layer which (e.g. vertebral aponeurosis) performs at one and the same time the purpose of a deep fascia and the expanded membranous attachment of a muscle. The panniculus carnosus is a thin muscular layer enveloping the trunk of animals with a hairy or furry coat. It is strongly developed in the hedgehog. In man it is represented mainly by the (rudimentary) platysma. It is placed between the superficial and the deep fascia. Bursae. — Where a tendon passes over a bony surface, or where the superficial fascia and skin cover a bony prominence, there is generally formed a synovial sac, or bursa, containing fluid, for the purpose of lubricating the surface over which the tendon or fascia glides. Allied to these are the synovial sheaths which envelop tendons beneath the annular ligaments in relation to the several joints. Description of Muscles. — In studying the muscular system it is necessary to note the following characters in reference to each individual muscle : (1) The shape of the muscle — flat, cylindrical, triangular, rhomboidal, etc. — ^and the character of its extremities — membranous, tendinous, or fleshy. (2) The attachments of the muscle. The origin is the more fixed or central attachment : the insertion is the more movable or peripheral attachment. (3) The relations of the surfaces and borders of the muscle to bones, joints, muscles, and other important structures. (4) Its vascular and nervous supply ; and (5) its action. It must be borne in mind that hardly any single muscle acts alone. Each muscle, as a rule, forms one FASCIA AND SUPEKFICIAL MUSCLES OF THE BACK. 319 of a group acting more or less in harmony with, and antagonised by, other and opposite groups. DESCRIPTION OF THE MUSCLES. The skeletal muscles may be divided into two series : axial and appendicular. The axial muscles comprise the muscles of the trunk, head, and face, including the panniculus carnosus (platysma). These muscles are more or less segmental in arrangement, grouped around the axial skeleton. The appendicular muscles, the muscles of the limbs, are grouped around the appendicular skeleton. They are not segmental in arrangement, they are morphologically separate from the axial muscles, and they are arranged in definite strata in relation to the bones of the limbs. APPENDICULAR MUSCLES. THE UPPER LIIVIB. FASOIiE AND SUPERFICIAL MUSCLES OF THE BACK. Fasciae. The superficial fascia of the back presents no peculiarity. It is usually of considerable thickness, and contains a quantity of fat. The deep fascia closely invests the muscles. It is attached in the middle line of the back to the ligamentum nuchee, supraspinous ligaments, and vertebral spines ; laterally it is attached to the spine of the scapula and the clavicle, and is continued over the deltoid region to the arm. In the neck it is attached above to the superior curved line of the occipital bone, and is continuous laterally with the deep cervical fascia. Below the level of the arm it is continuous, round the border of the latissimus dorsi muscle, with the fascia of the axilla and of the abdominal wall. In the back and loin it constitutes the vertebral aponeurosis (fascia lumbodorsalis) or aponeurosis of the latissimus dorsi. This layer conceals the sacro-spinalis (erector spin^e) muscle, forming the posterior layer of the lumbar fascia, and is attached medially to the vertebral spines, and laterally to the angles of the ribs, to the lumbar fascia, and to the iliac crest. The Superficial lYIuscIes of the Back. The muscles of the back are arranged in four series according to their attach- ments: (1) vertebro-scapularand vertebro-humeral; (2) vertebro-costal; (3)vertebro- cranial ; and (4) vertebral. The first of this series consists of the posterior muscles connecting the upper limb to the trunk, and comprises the first two layers of the muscles of the back — (1) trapezius and latissimus dorsi, and (2) levator scapulae and rhomboidei (major and minor). The deeper (axial) muscles of the back are dealt with later (p. 384). The trapezius is a large triangular muscle occupying the upper part of the back. It arises from the superior curved line of the occipital bone in its medial third, from the external occipital protuberance (Fig. 312, p. 400), from the ligamentum nuchse, from the spines of the seventh cervical and all the thoracic vertebrae, and the intervening supraspinous ligaments. The origin is by direct fleshy attachment, except in relation to the occipital bone, the lower part of the neck, and the lower thoracic vertebrae, in which places the origins are tendinous. From their origin the muscular fibres converge towards the bones of the shoulder, to be inserted continuously from before backwards as follows : (1) The occipital and upper cervical fibres — into the posterior surface of the clavicle in its lateral third (Figs. 243, p. 320, and 248, p. 325); (2) the lower cervical and upper thoracic fibres — into the medial border of the acromion process, and the upper 22 c 320 THE MUSCULAE SYSTEM. border of the spine of the scapula ; and (3) the lower thoracic fibres, by a triangular flat tendon, beneath which a bursa is placed — into a rough tuberosity at the base of the spine of the scapula (Fig. 245, p. 322). The fibres inserted into the clavicle, acromion, and the upper border of the spine of the scapula, spread over the adjacent subcutaneous surfaces of these bones for a variable distance. The occipital portion of the muscle may be in the form of a separate slip, or may be entirely absent. The trapezius is superficial in its whole extent. Its upper lateral border forms the posterior limit of the posterior triangle of the neck. The lower lateral border, passing over the upper edge of the latissimus dorsi and the vertebral border of the scapula, forms a boundary of the so-called triangle of auscultation, completed below by the latissimus dorsi, and laterally by the vertebral border of the scapula. This space is partly filled up by the rhomboideus major. The muscle overlaps the latissimus dorsi, and covers the levator scapulae, rhomboidei, and the deeper axial muscles of the back, along with the superficial cervical and posterior scapular^ arteries, the spinal accessory nerve, and muscular branches from the cervical plexus. The latissimus dorsi is a large triangular muscle occupying the lower part of the back. It has a triple origin. The greater part of the muscle arises — (1) from Pectoralis major (origin) Trapezius (insertion)- Fig. 243. — Muscle-Attachments to the Right Clavicle (Upper Surface). the vertebral aponeurosis (posterior layer of the lumbar fascia or aponeurosis of the latissimus dorsi). This is a thick membrane which conceals the erector spinas m the lower part of the back. Through it the latissimus dorsi gains attachment to the spines of the lower six thoracic vertebrae, the spines of the lumbar vertebrae, and the tendon of the sacro-spinalis, with which the aponeurosis blends below. It also arises laterally from the posterior part of the iliac crest. From this origin the muscle is directed upwards and laterally, its fibres converging to the lower angle of the scapula. In relation to its lateral and upper borders additional fibres arise. (2) Along the lateral border muscular slips arise from the lower three or four ribs, inter-digitating with the origins of the obliquus externus abdominis. (3) As the upper border of the muscle passes horizontally over the lower angle of the scapula, an additional fleshy slip usually takes origin from this part of the bone to join the muscle on its deep surface (Eig. 245, p. 322). Beyond the lower angle of the scapula the latissimus dorsi, greatly narrowed, curves spirally round the teres major muscle, and forms the prominence of the posterior axillary fold. It ends in a ribbon-like tendon, closely adherent at first to the teres major, which is inserted into the floor of the bicipital groove of the humerus (sulcus intertubercularis), extending for about three inches below the lower and lateral part of the lesser tuberosity (Fig. 253, p. 330). It is placed behind the axillary vessels and nerves, and in front of the insertion of the teres major, from which it is separated by a bursa. In the back the latissimus dorsi is superficial, except in its upper part, which is concealed by the trapezius. It covers the lumbar fascia, serratus posterior inferior, the ribs, and lower angle of the scapula, and at its borders two triangular spaces are formed ; at the upper border is the so-called triangle of auscultation ; at the outer border is the triangle of Petit (trigonum lumljale Petiti), a small space bounded by the iliac crest, the latissimus dorsi, and the obliquus externus abdominis. This is sometimes the site of a lumbar hernia. The levator scapulae is a strap-like muscle, arising by tendinous slips from ' Posterior scapular artery = descending ramus of the tra versus colli artery (B.N. A.). THE SUPEEFICIAL MUSCLES OE THE BACK. 321 the posterior tubercles of the transverse processes of the first three or four cervical vertebrte, between the attachments of the scalenus medius in front and the Posterior Triangle, STEBNO-CLEI DO-MASTOir SeMISPINALIS CAPl'llS (COMPLEXUS) Scapular aponeurosi Deltoid Teres.-' MAJOli. Lumbar Triangle of Petit- Serratus posterior inferior Latissimi'S dor&;i (reflected) Latissimus dorsi Obliqtjus internus abdominis Obliquus extebnus abdominis GlUT/EUS maximus, Fig. 244. — Superficial Muscles of the Back, and Vebtebro-scapular Muscles. splenius cervicis behind. It is directed downwards along the side of the neck, to be inserted into the vertebral border of the scapula in its upper fourth, from the superior angle to the spine (Fig. 245, p. 322). It is concealed in its upper third 322 THE MUSCULAE SYSTEM. Deltoid (origin) Triceps Braehii (origin of long head) Teres minor (origin) with gap for dorsal scapular artery by the sterno-mastoid muscle. In its middle third it occupies the floor of the posterior triangle. In its lower third it is again hidden from view by the trapezius. It conceals the splenius cervicis and ilio-costalis cervicis (cervicalis asceudens). The rhomboideus minor may be regarded as a separated slip of the rhom- boideus major, with which it is often continuous. It arises from the ligamentum nuchce and the spines of the seventh cervical and first thoracic vertebrae. Passing obliquely down- wards and laterally it is inserted into the vertebral border of the scapula be- low the levator scapulae muscle, and opposite to the base of the spine (Fig. 245, p. 322). The rhomboideus major arises from the spinous processes of the thoracic vertebrae from the second to the fifth inclusive, and from the corresponding supraspin- ous ligaments. Passing downwards and laterally it is inserted below the rhomboideus minor into the vertebral border of the scapula, between the spine and the lower angle (Fig. 245, p. 322). The muscle is only inserted directly into the scapula by means of its lower fibres. Its upper part is attached to a membranous band, which, connected for the most part by loose areolar tissue to the vertebral border of the scapula, is fixed to the bone at its extremities, above near the base of the spine, and below at the inferior angle. The rhomboid muscles are concealed for the most part by the trapezius. The lower part of the rhomboideus major is superficial in the triangle of auscultation. The muscles cover the serratus posterior superior and vertebral aponeurosis. Teres major (origin) Latissimus dorsi (origin) Fig. 245.- -Muscle-Attachments to the Right Scapula (Posterior Surface). THE FASCIvE AND MUSCLES OF THE PECTORAL REGION. FASCIA. The superficial fascia of the chest usually contains a quantity of fat, in which the mamma is embedded. The origin of the platysma muscle lies beneath its upper part. The deep fascia is attached above to the clavicle, and in the middle line to the sternum. Below it is continuous with the fascia of the abdominal wall. It gives origin to the platysma and invests the pectoralis major. At the lateral border of the great pectoral muscle it is thickened, and forms the floor of the axillary space (axillary fascia), continued posteriorly on to the posterior fold of the axilla and laterally into connexion with the deep fascia of the arm. FASCI.^: AND MUSCLES OF THE PECTOEAL EEGION. 123 Costo-Coracoid Membrane, — Beneath the pectorahs major a deeper stratum of fascia invests the pectoralis minor muscle. At the upper border of this muscle it forms the costo-coracoid membrane, which passes upwards to the lower border of the subclavius muscle, where it splits into two layers, attached in front of and behind that muscle to the borders of the under surface of the clavicle. The membrane traced medially along the subclavius muscle is attached to the first costal cartilage ; passing laterally along the upper border of the pectoralis minor it reaches the coracoid process. The part of the membrane extending directly between the first costal cartilage and the coracoid process is thickened and forms the costo-coracoid ligament. The costo-coracoid membrane is otherwise thin and of comparatively small importance. It is pierced by the cephalic vein, thoracic axis artery and vein, and branches of the external anterior thoracic nerve. By its deep surface it is connected to the sheath of the axillary vessels. At the lower border of the pectoralis minor there is a further extension of the deep fascia beneath the pectoralis major. It passes downwards to join the fascia forming the floor of the axilla, and is continued laterally into the fascia covering the biceps and coraco-brachialis muscles. MUSCLES OF THE PECTORAL REGION. The anterior muscles connecting the upper limb to the axial skeleton comprise the pectoralis major, pectoralis minor, subclavius, ser- stemo-cieido-mastoid (origin ratus anterior (s. magnus), and sterno-cleido-mastoid. The last is described in a later section (p. 420). The pectoralis major is a large fan-shaped muscle arising in three parts : (!) a pars clavicularis arising from the front of the clavicle in its medial half or two- thirds (Figs. 243, p. 320, and 248, p. 325) ; (2) a pars sterno-costalis, the largest part of the muscle, arising from the anterior surface of the pre-sternum and meso- sternum by tendinous fibres decussating with those of the opposite muscle (Fig. 247, p. 324), and more deeply from the cartilages of the first six ribs; (3) a pars abdominalis, a small and separate slip, arising from the aponeurosis of the obliquus externus muscle. The abdominal slip, at first separate, soon merges with the sterno-costal portion, but a distinct interval usually remains between the two first- named parts of the muscle. The fibres converge towards the upper part of the arm, and are inseparably blended at a point half an inch from their insertion into the humerus. The muscle is inserted into (1) the lateral border of the bicipital groove (sulcus intertubercularis) of the humerus, extending upwards to the greater tuberosity, and blending laterally with the insertion of the deltoid, medially with the insertion of the latissimus dorsi (Fig. 247, p. 324) ; (2) from the upper border of the insertion a membranous band extends upwards to the capsule of the shoulder-joint, enveloping at the same time the tendon of the biceps; and (3) from the lower border a band of fascia passes downwards to join the fascia of the arm. The arrangement of the fibres of the muscle at its insertion is peculiar. The muscle is twisted on itself, so that the lower (sterno-costal) fibres are directed upwards Fig. 246. — Muscle- Attach- and outwards behind the upper (clavicular) part of the '^'ents to the Front of muscle ; in consequence the clavicular part is attached to ™^ Sternum. the humerus lower down than the sterno-costal portion, and is inserted also into the fascia of the arm. The twisting of the fibres is specially found in the lower Rectus abdomini.s (insertion) 324 THE MUSCULAE SYSTEM. sterno-costal fibres of the muscle and the abdominal fibres. These curve upwards behind the upper sterno-costal fibres, and have the highest attachment to the shaft of the humerus, helping to form the fascial expansion which extends upwards over the biceps tendon to tlie capsule of the shoulder-joint. In this way a bilaminar tendon is produced united along its lower border ; consisting of a superficial lamina formed by the upper sterno-costal fibres, blending for the most part with the / H \. _.I)iGASTKic (anterior belly) Platysma/ Pectoralis major (pars sternalis) Pectoralis major (pars clavicularis) ''■. Stekko-cleido-mastoid Stepno-thyeeoid subclavius ,--'' ..■• Pectoralis major (sternal origin) Pectoralis MAJOR (pars aMominalis) Obliql-vs EXTERSf.S ABDOMINIS Sheath of rectu abdomini Rectus abdominis Fig. 247. — The Muscles of the Front of the Chest. tendon of the clavicular portion ; and a deep lamina, composed of the twisted lower sterno-costal and abdominal fibres. The disposition of the muscular fibres at their insertions is the reason for the application of the terms " 2:)ortio attollens" to the clavicular portion, and " portio deprimens" to the sterno-costal and abdominal por- tions of the muscle. Placed superficially, the pectoralis major forms the front wall and anterior fold of the axilla. Its upper border is separated from the edge of the deltoid muscle by an interval in which lie the cephalic vein and humeral artery. Its deep MUSCLES OF THE PECTOKAL EEGION. 325 surface is in relation with the ribs and intercostal muscles, the costo-coracoid membrane and the structures piercing it, the pectoralis minor, the axillary vessels, and the nerves of the brachial plexus. Stemalis muscle. — The sternalis is an occasional mnscle placed, when present, parallel to the sternum upon the stemo-costal origin of the ijectoralis major. It has attachments which are very variable both above and below, to the costal cartilages, sternum, rectus sheath, stemo- mastoid, and pectoralis major. Its nerve-supply is from one or both of the anterior thoracic nerves. In certain rare cases it has been said to be innervated by intercostal nerves. It is present in 4'4 cases out of 100, and it is slightly more frequent in the male than in the female. It has been regarded by different observers as (1) a vestige of the panniculus carnosus, (2) a homologue of the sterno-mastoid, or (3) a displaced slij) of the pectoralis major. Chondro-epitrochlearis, dorso-epitrochlearis, axillary arches, costo-coracoideus. — One or other of the above-named slips is occasionally present, crossing the floor of the axilla in the interval between the latissimus dorsi and the pectoralis major. They take origin from the costal cartilages, ribs, or borders of the pectoralis major {chondro-epitrochlearis, axillary arches, costo- coracoideus), or from the border of the latissimus dorsi {dorso-epitrochlearis, axillary arches, costo- coracoideus). Their insertion is variable. The chondro-epitrochlearis and clorso-epitrochlearis are inserted into the fascia of the arm, the medial intermuscular septum, or the mesial condyle of the humerus. The axillary arches are inserted into the border of the pectoralis major, the fascia of the arm, or the coraco-brachialis or biceps muscle. The costo-coracoideus, arising from the ribs or the ajjoneurosis of the obliquus externus, or detaching itself from the border of the pectoralis major or latissimus dorsi, is attached to the coracoid process, alone or along with one of the muscles attached to that bone. These variable slips of muscle are supplied by the internal anterior thoracic nerve, the lesser internal cutaneous nerve, or the intercosto- humeral. The pectoralis minor is a narrow, flat, triangular muscle. It arises under cover of the pectoralis major from (1) the surfaces and upper borders of the third, fourth, and fifth ribs near their anterior ends, and (2) from the fascia covering the third and fourth intercostal spaces between these ribs. It may have an additional origin from the second rib (Eig. 247, p. 324) ; and that from the fifth rib is often absent. Directed obliquely laterally and upwards, it is inserted by a short, flat tendon into the lateral half of the anterior border and upper surface of the coracoid process (Fig. 258, p. 326), and usually also into the conjoint origin of the biceps brachii and coraco-brachialis. It enters into the formation of the front wall of the axilla, and gives attachment along its upper border to the costo-coracoid membrane. It crosses the axillary vessels and the cords of the brachial plexus, and is pierced by branches of the anterior thoracic nerves. Either in j^art or wholly the pectoralis minor may pass over the coracoid process of the scapula, sejDarated from it by a bursa, to be inserted into the coraco-acromial ligament, or the acromion jJrocess ; or piercing the coraco-acromial ligament, it may be attached to the capsule of the shoulder-joint (coraco-humeral ligament). Pectoralis minimus. — This is a slender slip, rarely present, which extends between the first costal cartilage and the coracoid process. *r The subclavius muscle arises from the upper surface of the first costal cartilage in front of the costo - clavicular ligament, and from the upper surface of the Coraco-clavic- ular ligament (trapezoid) Pectoralis major (origin) Costo-clavic- ular ligament (rhomboid) Subclavius (insertion) Conoid ligament Fig. 248. — Mttscle-Attachmexts to the Right Clavicle (Under Surface). distal end of the first rib (Fig. 247, p. 324). It is inserted into a groove in the middle third of the under surface of the clavicle (Fig. 248, p. 325). The muscle is invested by the fascia which forms the costo-coracoid membrane, and is concealed by the clavicle and the clavicular origin of the pectoralis major. 326 THE MUSCULAE SYSTEM. Triceps biacl Fig. 249. — The Left Serratds Magnus (see- EATCS anterior) MUSCLE. partly superficial below the axil- lary space, on the side wall of the chest, where its slips of origin are seen inter-digitating with those of the obhquus externus abdom- inis. Higher up it forms the medial wall of the axilla, and is in con- tact with the pectoral muscles in front and the subscapularis be- hind. Its upper border appears in the floor of the posterior tri- angle, and over it the axillary artery and the cords of the brachial plexus pass in their course through the axilla. The lower border is oblique, and is in contact with the latissimus dorsi muscle. The muscle may extend higher than usual, so as to be continuous in the neck with the levator scapulae. Nerve-Supply. The nen'e-supply of the muscles connecthig the upper limb to tlie trunk is in the main derived from the cervical and brachial plexuses. The trapezius is innervated from two sources, by the spinal accessory- nerve 1 and by the cervical plexus (C. 3. and 4.). Tlie latissimus dorsi is innervated by the long sub- scapular nerve - from the brachial plexus (C. 6. 7. 8.). The levator scapulas receives two neives from the cervical plexus (C. 3. and 4.), and a branch from the posterior 1 Spinal accessory nSrve = accessory nerve (B.N. A.). 2 Long subscapular nerve = thoraco-dorsal nerve (B.N. A.). The sterno-clavicularis is a small separate slip, rarely present, extending beneath the pector- alis major from the up^^er part of the sternum to the clavicle. The serratus anterior (serratus mag- nus) is a large curved quadrilateral muscle occupying the side of the chest and medial wall of the axilla. It arises by fleshy slips from the lateral aspect of the upper eight and occasionally (as in the figure) from nine ribs. The first slip is a double one, arising from the first two ribs and the fascia cover- ing the intervening space (Fig. 249, p. 326). The insertion of the muscle is threefold. (1) The first portion of the muscle (from the first and second ribs) is directed back- wards to be inserted into the ventral aspect of the upper angle of the scapula. (2) The next three slips of the muscle (from the second, third, and fourth ribs) are inserted into the vertebral border of the scapula. (3) The last four slips (from the fifth, sixth, seventh, and eighth ribs) are directed ob- liquely upwards and backwards, to be in- serted on the ventral aspect of the lower angle of the scapula (Fig. 250, p. 326). The lateral surface of the muscle is Deltoid (origin) Biceps and coraeo-brachialis (origin) Pectoralis minor (insertion) Omohyoid (origin) Fig. 250. — Muscle-Attachments to the PacHT Scapula (Anterior Aspect). FASCIA AND MUSCLES OF THE SHOULDER 327 scapular nerve ^ from the brachial plexus (C. 5.), which supplies also the rliomljoid muscles. Each of the pectoral muscles is imiervated by both tlie external and internal anterior thoracic nerves from the brachial plexus (C. 5. 6. 7. and C. 8. T. 1.) (p. 626). The subclavius receives its nerve from the brachial plexus (C. 5. 6.). The serratus anterior is supplied by the posterior thoracic nerve '-^ from tlie brachial plexus (C. 5. 6. 7.). Actions. The muscles of this group (together with the sterno-cleido-mastoid and omohyoid muscles) act for the most part in the movements of the shoulder girdle at the sterno-clavicular and acromio- clavicular joints. At the former joint they produce the various movements of the clavicle on the sternum, and cause the shoulder to move in an arc the centre of which is the sterno-clavicular joint. At the acromio-clavicular articulation they produce a rotation of the scapula on the clavicle, and a consequent alteration in the direction of the glenoid fossa. At the same time the several muscles are agents in other equally important movements, when the shoulder girdle is fixed ; movements of the head and neck ; movements of the trunk and ribs ; and, in addition in the case of the pectoralis major and latissimus dorsi, important movements of the arm at the shoulder-joint. 1. Movements of the Shoulder Girdle. — The action of this group of muscles on the shoulder girdle (mainly corresponding to movements at the sterno-clavicular joint) may be expressed in the following table : — a. Movement in a Vertical Plane. , i- Movement in a Horizontal Plane. Elevation. Depression. Forwards. Backwards. Trapezius (upper fibres) Levator scapulee Rhomboidei Sterno-mastoid Omohyoid Trapezius (lower fibres) Subclavius Pectoralis minor Latissimus dorsi Pectoralis major (lower fibres) Serratus anterior Pectoralis major Pectoralis minor Traj^ezius Rhomboidei Latissimus dorsi c. Rotation — a combination of these muscles. 2. Movements of the scapula on the clavicle produce an alteration of the direction of the glenoid fossa of the scapula, and are accompanied by movements, inwards or outwards, forwards or backwards, of the inferior angle of the scapula. By the combined action of the muscles acting upon the shoulder girdle a rotatory movement of the scapula at the acromio-clavicular joint is effected, by which the relation of the glenoid fossa to the head of the humerus is preserved in movements of the arm. 3. In forced inspiration, the sterno-mastoid, trapezius, levator scapulae, rhomboidei, sub- clavius, omohyoid, serratus anterior, pectoral muscles, and latissimus dorsi, acting together, raise and fix the shoulder girdle ; while those of them which have costal attachments— subclavius, pectoral muscles, serratus anterior, and latissimus dorsi — simultaneously elevate the ribs and expand the thorax. 4. Lateral flexion and rotation of the spine in the neck is effected partly by the action of the trapezius, levator scapulae, and rhomboid muscles (with the shoulder fixed). The latissimus dorsi and pectoralis major act in climbing in a similar way, raising up the trunk towards the shoulder. 5. Action on the Upper Limb. — By reason of their insertion into the humerus the pectoralis major and latissimus dorsi muscles assist the movements of the upper limb. Acting together, the two muscles depress the shoulder, and draw the arm to the side of the body, at the same time rotating the humerus inwards. The two parts of the pectoralis major have slightly different actions on the humerus. The clavicular part of the muscle (portio attollens) draws the arm in- wards and upwards ; the sterno-costal part of the muscle (jjortio deprimens) draws it inwards and downwards. The latissimus dorsi acting alone, besides rotating the limb, draws it inwards and backwards, as in the act of swimming. FASCIAE AND MUSCLES OF THE SHOULDER. The deep fascia covering the scapular muscles presents no feature of special importance. Attached to the clavicle, acromion, and scapular spine, it is thin over the deltoid muscle. Below the deltoid it is thicker ; it encases and gives origin to the infraspinatus muscle, and is continuous with the fasciae of the axilla and the back. lYIuscIes. The muscles proper to the shoulder comprise the deltoid, supraspinatus, infra- spinatu.s, teres minor, teres major, and subscapularis. ^ Posterior .scapular nerve = dorsal nerve of the scapula (B.N. A.). - Posterior thoracic nerve = long thoracic or external respiratory nerve of Bell (B.N.A.). 328 THE MUSCULAR SYSTEM. The deltoid (m. deltoideus), a coarsely fasciculated, multipennate muscle, has an extensive origin from (1) the front of the clavicle in its lateral third (Figs. 243, p. 320, and 248, p. 325); (2) the lateral border of the acromion process; (3) the lower edge of the free border of Lkvator scapul.-e *^,^_gg^ the spme of the H^^^^T^k"-^'""''"'"'"''^'^ '"^°'' scapula (Figs. 245, 'fliSSift ^ p. 322, and 254, p. ^SBf -^^ *- 330) ; and (4) from .W^ .^^^^^^>»^ rhombo.b- the deep fascia Eus MAJOR covering the infra- spinatus muscle. Spine of .scapula ^'iSHBBfe. '•k. Its Origin embraces ^^^^^ the insertion of the /' ^^HHP, a trapezius. The spi.xATis —-J' ''''^/^^^^^B^KSB/tUSSB^Sm^^SM y tibres of the muscle ^ — ^>^^^^^^^^i^^^^^**5S«SI^H»''-f'|^ converge to the -|g lateral aspect of ^^^_^^^^_. e,,, 1° the shaft of the ' /mU^K^^ humerus, to be in- teres ;;>^^^^^^»bh^^~; ./^mJI^^P^^teres major serted into a well- "^'^^^^^^^^T^^^M^B^^ marked V-shaped J4_^J||^^^^'^"'^"^'"'^'^^P^'=e impression above ^ , ., , , the spiral groove Quadrilateral space ,„. j^^„ o^ \ (Fig. 253, p. 330). Triceps BRACHii The insertion is (Lateral head) partly United with the tendon of the H ' - '^g' ^1 M1MB |2 " 'A pectoralis major. hJS^^ , I BiailL¥-TBr-' T-cEPs (medial ^hc most anterior part of the . deltoid muscle is formed of parallel '.t\ H^BitW rWHI-MuscuIo-spiral nerve £!.>.„„„ j. i ^ Deltoid ' ' '. WHi'li WW iibres, uot Uncommonly separate Triceps brachii from the rcst of the musclc at their (longhead) ^^^-g-^^ f^,^^ ^^^ claviclc. ThcSC fibres may be continuous with the trapezius over the clavicle. The most posterior part arises by a fascial origin from the spine of the scapula and the fascia over the infraspinatus muscle. These por- tions are attached respectively to the front and back of the main Extensor CARPI tcndou of insertion. The inter- RADIALIS LONGUS T j_ r>l i,. mediate fibres are multi-pennate. Triceps brachii attached abovc and below to three (tendon of insertion) or four Septal tcudous, which ex- tend for a variable distance down- iRAmTLTBREvrs wards and upwards from the origin and insertion of the muscle. Olecranon process xhc deltoid is Superficial in its whole extent, and forms the pro- minence of the shoulder. Its an- terior border is separated from the pectoralis major by a narrow in- r 1(1. 251.- — LKFT SCAILLAI; .\lu.-,i I.Lb AND TlUCEPS. 4.^ 1 •„ 1 • I, L.\. ■!_ T terval, m which the cephalic vein and humeral artery are placed. The deep surface of the muscle, separated from the capsule of the shoiilder-joint by a large bursa, is related to (1) the coracoid process, associated with which are the coraco-acromial ligament, and the attachments of the pectoralis minor, the coraco-brachialis, and the short head of the biceps brachii ; (2) the capsule of the shoulder-joint covering the head of the humerus, associated with which are the long head of the biceps, and the attachments of the subscapularis. MUSCLES OF THE SHOULDEE 329 SeRRATI'S ASTERllpR (S. MAfiNUS) .StIBSCAPULARIS Slpkaspinatus I'KriORALIS MINOR Coracoid locess Triangular ■ipace See- rat u a AN- TERIOR (S. MA(iNUS) '. IjATISSIMUS DORSr Teres major CORACO-BRACHIALIb Biceps (short head) ' Teres major supraspinatus, infraspinatus, and teres minor ; and (3) the upper part of tlie lateral surface of the shaft of the humerus, associated with which are the posterior circumflex vessels and circumflex nerve.^ The supraspinatus arises by fleshy fibres froLu the supraspinous fossa (ex- cept near the neck of the bone) and from the deep fascia over it (Eig. 245, p. 322). It is directed outwards under the acro- mion process and coraco- acromial ligament to be inserted by a broad thick tendon into the uppermost facet on the greater tuber- osity of the humerus, and into the capsule of the shoulder-joint (Fig. 253, p. 330). The infraspinatus arises from the infraspin- ous fossa of the scapula (excepting near the neck of the bone and the flat surface along the axillary border) and from the thick fascia over it (Fig. 245, p. 322). The fibres of the muscle converge to the neck of the scapula ; and are inserted by tendon into themiddle facet on the greater tuberosity of the humerus, and into the capsule of the shoulder-joint (Fig. 253, p. 330). A bursa separates the muscle from the neck of the scapula, and in a minority of cases communicates with the synovial cavity of the shoulder- joint. The supraspinatus and the upper part of the infraspinatus muscles are concealed by the trapezius, acromion process, and deltoid. They cover theneckof thescapula, the suprascapular artery and nerve,- and the capsule of the shoulder -joint. The teres minor is a small muscle, arising by fleshy fibres from the upper two- thirds of the flat surface on the dorsal aspect of the axillary border of the scapula, and from fascial septa separating it from the infraspinatus and teres major muscles (Fig. 245, p. 322). Lying along- side the lateral border of the infraspinatus, it is inserted under cover of the deltoid by a thick flat tendon into the lowest of the three facets on the greater tuberosity of the humerus and into the capsule of the shoulder-joint, and by fleshy fibres into the posterior aspect of the surgical neck and shaft of the humerus below the tuberosity for about an inch (Fig. 253, p. 330). It is separated from the teres major by the long or scapular head of the triceps brachii, and by the posterior circumflex vessels and the cii-cumflex nerve. ^ ^ Circumflex nerve = axillarj' nerve (B.N. A.). ^ Suprascapular artery = transverse artery of the scapula (B.N. A.). Brachio-radialis Flexor carpi radialis Pronator teres Fig. 252. — Muscles of Posterior Wall of Left Axilla and Front of Arm. 330 THE MUSCULAE SYSTEM. Its origin is pierced by the dorsal scapular artery.^ The muscle is invested by the deep fascia enclosing the infraspinatus, and is sometimes inseparable from that muscle. The teres major is much larger than the preceding muscle. It arises by fleshy fibres from the lower third of the flat surface on the dorsum of the scapula along its axillary border (except for a small area at the lower angle), and from fascial septa, which separate it on the one side from the subscapularis, and on the other from the infraspinatus and teres minor (Fig. 245, p. 322). The muscle is directed along the axillary border of the scapula to the front of the shaft of the humerus, where it is inserted by a broad flat tendon into the medial border of the bicipital groove (sulcus inter tubercularis) medial to the latissimus dorsi muscle (Fig. 253, p. 330). Just before its insertion it is closely adherent to the tendon of the latissimus dorsi. The teres major lies below the subscapularis muscle on the posterior wall of the axilla. The latissimus dorsi muscle, sweeping round from the back, covers its axillary surface on its way to its insertion. The muscle forms the lower boundary Supraspinatus -(insertion) Subscapularis ["(insertion) Pectoralis major ■(insertion) Latissimus dorsi "(insertion) Teres major '(insertion) Deltoid'. (insertion) Coraco-brachialis 4 (insertion) ^/7 u ^' Brachialis . (origin) •^Iv o\\ _Bracliio-radialis "^ V ■(origin) 41 s U: Extensor carpi radialis longus -(origin) Common tendon for origin of pronator "teres and flexor muscles of forearm Common tendon for origin of extensoE muscles of forearm Fio. 253. — Muscle- Attachments to THE Front of the Right Humerus. Teres minor (origin) with gap for dorsal scap- ular artery Teres major (origin) Latissimus dorsi (origin) Fig. 254. — Muscle- Attachments to the Right Scapula (Posterior Surface). of a triangular space on the posterior wall of the axilla, of which the other boundaries are, above, the borders of the subscapularis and teres minor muscles, and laterally the surgical neck of the humerus. This space is subdivided by the long head of the triceps brachii, which passes behind the teres major muscle, into (a) a quadri- lateral space above, for the passage of the circumflex nerve- and posterior cir- ^ Dorsalis scapulae = circumflex artery of the scapula (B.N. A.). '^ Circumflex nerve = axillary nerve (B.N.A.). MUSCLES OF THE SHOULDER 331 ciimflex artery ; ^ and (b) a smaller triangular space below, for the dorsal scapular artery.- The subscapularis is a large triangular muscle occupying the venter of the scapula. It arises by tleshy fibres from the whole of the subscapular fossa and the groove along tlie axillary border, excepting the surfaces at the angles of the bone (Fig. 250, p. 326). Springing from several ridges in the fossa are septa projecting into the substance of the muscle, which increase the extent of its attachment. Con- verging to the head of the humerus, the muscular fibres are inserted by a broad, thick tendon into the lesser tuberosity of the humerus and into the capsule of the shoulder- joint, and by fleshy fibres into the surgical neck and the shaft of the humerus below the tuberosity for about an inch, under cover of the coraco-brachialis and short head of the biceps (Fig. 253, p. 330). This muscle forms the greater part of the posterior wall of the axilla. Its medial or anterior surface is in contact with the serratus anterior (s. magnus) and the axillary vessels and nerves. It is separated from the neck of the scapula by a bursa, which is in direct communication with the synovial cavity of the shoulder-joint. The subscapularis minor is an occasional muscle situated below the capsule of the shoulder- joint. It arises from the axillary border of the scapula below the subscapularis, and is inserted into the capsule of the joint or the upper part of the shaft of tlie humerus. Nerve-Supply. The muscles of this group are all supplied by the fifth and sixth cervical nerves, through nerves arising from posterior trunks of the brachial plexus. The deltoid and teres minor receive their nerve-supply from the circumflex nerve ^ (C. 5. 6.) ; the supraspinatus and infraspinatus from the suprascapular (C. 5. 6.) ; the teres major from the lower subscapular nerve (C. 5. 6.) ; and the subscapularis from the upper and lower subscapular nerves (C. 5. 6.). Actions. The principal action of this group of muscles is on the shoulder-joint. They have also secondary actions in relation to movements of the trunk and limbs. 1. Movements at the Shoulder -Joint. a. Abduction. Deltoid Supraspinatus Adduction. Teres major Teres minor Pectoralis major Latissimus dorsi Coraco-brachialis Biceps (short head) Triceps brachii (long head) Weight of limb b. Flexion (Forwards). Deltoid (anterior fibres) Subscapularis Pectoralis major Coraco-brachialis Biceps brachii Extension (Backwards). Deltoid (posterior fibres) Teres major Infraspinatus Latissimus dorsi Triceps brachii c. Rotation Outwards. Deltoid (posterior fibres) Infraspinatus Teres minor Rotation Inwards. Deltoid (anterior fibres) Teres major Pectoralis major Latissimus dorsi d. Circumduction— combination of previous muscles. The various movements at the slioulder-joint are greatly aided by the muscles acting on the shoulder girdle. In raising the arm above the head, for instance, the humerus is brought to the horizontal position by the deltoid and supraspinatus, and the movement is continued by the elevators of the shoulder girdle. Again, in forward and backward movements at the shoulder- joint, great assistance is derived from muscles acting directly on the shoulder girdle— pectoralis minor and serratus anterior ; trapezius and rhomboidei. 2. In relation to the trunk and limbs, the shoulder muscles, by fixing the humerus, have auxiliary power on the one hand in movements of the trunk, such as forced inspiration ; on the other hand, acting along with muscles fixing the elbow-joint, they stiften the limb so as to permit of the more refined movements of the wrist and fingers. ^ Posterior circumflex artery = posterior circumflex artery of the humerus (B.N.A. - Dorsal scapular artery = circumflex artery of the scapula (B.N. A.). 3 Circumflex nerve = axillary (B.N.A. ). 23 332 THE MUSCULAE SYSTEM. FASCIAE AND IVIUSCLES OF THE ARM. FASCIiE. The superficial fascia presents no features of importance. There is a bursa beneath it over the olecranon process, and occasionally another over the medial condyle of the humerus. The deep fascia forms a strong tubular investment for the muscles on the front and back of the humerus. It is continuous above with the deep fascia of the shoulder and axilla, and is further strengthened by fibres derived from the insertions of the pectoralis major, latissimus dorsi, and deltoid muscles. At the elbow it becomes continuous with the deep fascia of the forearm, and gains attachment to the condyles of the humerus and the olecranon process of the ulna ; it is strengthened also by important bands associated with the insertions of the biceps in front and the triceps behind, to which reference will be made in the account of these muscles. About the middle of the upper arm on the mesial side, the deep fascia is perforated for the passage of the basilic vein and the internal cutaneous nerve.^ The intermuscular septa are processes of the deep fascia attached to the epicondylic ridges of the humerus. The medial and stronger septum is placed between the brachiahs muscle in front and the medial head of the triceps behind, and gives origin to both. It extends upwards to the insertion of the coraco- brachialis (which is often continued into it), and the ulnar nerve and inferior profunda - vessels pass down over its inner edge. The lateral septum is thinner. It separates the brachialis muscle and brachio-radialis in front from the medial and lateral heads of the triceps behind, and gives origin to these muscles. It extends upwards to the insertion of the deltoid, and is pierced by the musculo- spiral nerve ^ and superior profunda vessels.^ MUSCLES OF THE ARM. The muscles of the arm comprise the biceps, coraco-brachialis, and brachialis on the front, and the triceps brachii on the back of the humerus. Except at its extremities, the biceps brachii is superficial, and forms a rounded fleshy mass on the front'of the arm. The coraco-brachialis is visible on its medial side in the upper half of the arm, particularly when the arm is raised. The brachialis is concealed by the biceps. The triceps brachii forms the thick mass of muscle covering the posterior surface of the humerus. The coraco-brachialis is a rudimentary muscle. It arises under cover of the deltoid from the tip of the coracoid processes by fleshy fibres in common with the short head of the biceps, and also frequently from the tendon of insertion of the pectoralis minor muscle. The fleshy belly is pierced by the musculo-cutaneous nerve, and ends in a flat tendon inserted into a faint linear impression about an inch in length on the middle of the medial border of the shaft of the humerus (Fig. 253, p. 330). It is often continued into the medial intermuscular septum. The coraco-bracliialis is the remains of a threefold muscle, of which only two elements are usually present in man, but of which in anomalous cases all the parts may be more or less fully developed. The passage of the musculo-cutaneous nerve through the muscle is an indication of its natural sejjaration into two parts, which represent the persistent middle and inferior elements. The commonest variety is one in which the more superficial (inferior) part of the muscle extends farther down the arm than usual, so as to be inserted into the medial intermuscular septum, or even into the medial condyle of the humerus. A third slip (coraco-brachialis superior or brevis, rotator humeri) may more rarely be present, forming a short muscle arising from the root of the coracoid process, and inserted into the medial side of the liumerus just below the capsule of the shoulder-joint. The biceps brachii arises by two tendinous heads. (1) The short head (caput breve) is attached in common with the coraco-brachialis to the tip of the coracoid process of the scapula (Fig. 250, ix 326). Concealed by the deltoid and tendinous at first, this head forms a separate fleshy belly, which is united to the long head by an investment of the deep fascia. (2) The long head (caput longum) 1 Internal cutaneous = medial uerve of the forearm (B.N. A). 2 Inferior profunda artery = superior ulnar collateral (B.N. A.). •* Musculo-spiral = radial nerve. ■* Superior profunda artery = profunda brachii (B.N. A.). MUSCLES OF THE AEM. 333 arises by a round tendon from the supra-glenoid impression at the root of the coracoid process and from the glenoid ligament on either side. Its tendon passes Insertion of pectok- . alis major coraco-brachialis Short head of ' BICEPS ' LOSO HEAD OF , BICEPS Musculo-cutaneons nerve" Musculo-spiral nerve" Brachio-radialis^ Extensor carpi RADIALIS LONOrS" Radial artery (cut) Abductor pollicis ONGUS (EXIENSOR OSSIS metacarpi pollicis) Radial artery (cut) Anterior annular ligament Insertion of .- PEG! oralis MINOR Axillary artery \ Musculo- f rjYstg:^^«^~^~~ cutaneous ner\e -TjA ^^»iv ■ \' ■ Median nerve ' (lateral head) Median nerve (medial head) Ulnar nerve ^ ^ ■ Triceps (medial head) Lacertus fibrosus or "bicipital fascia -Pronator teres "Deep fascia of forearm -Flexor carpi radialis -Palmaris longus -Flexor carpi ulnaris ;,FlEX0R Dir.ITORUM SUBLIMIS -Flexor pollicis longus -Pronator quadratus -Ulnar artery Fig. 255. — Superficial Muscles on the Front of the Right Arm and Forearm. Trapezius Latissimus do RSI Deep fascia of forearm Extensor carpi ulnaris Abductor pollicis longus (extensor ossis metacarpi pollicis) Extensor pollicis brevis Extensor digiti QUINTI PROPRIUS Tendons of Radial Extensoi OF carpus Posterior annular ligament Extensor pollicis longus Extensor indicis proprius Fig. 256. — The Muscles on the Back of the Left Arm, Forearm, and Hand. through the cavity of the shoulder-joint, and emerging from the capsule beneath the transverse ligament (invested by a prolongation of the synovial membrane), it occupies the bicipital groove of the humerus (sulcus inter tubercularis), covered by a )0-± THE MUSCULAE SYSTEM. fascial prolongation of the tendon of the pectoralis major. In the upper arm it forms a fleshy belly united to that derived from the short head by an envelope of deep fascia (inter tubular mucous sheath). The insertion of the muscle is likewise twofold. (1) The two bellies become connected with a strong te7idon, attached deeply in the hollow of the elbow to the rough posterior portion of the tuberosity of the radius (Figs. 264, p. 3^2, and 271, p. ^mf^-H V' Siipvaspinatiis "(insertion) _Subscapularis (insertion) Pectoralis major (insertion) Latissimus dorsi (insertion) Teres major "(insertion) Infraspinatus (insertion) Triceps : lateral head (origin) _Coraco-brachialis "(insertion) Deltoid (insertion) Brachio-radialis "(origin) Extensor carpi -radialis longus rigin) Common tendon for origin of , ])ronator teres and flexor muscles of forwujn Common tendon fer origin of extensor muscles oT forearm Fig. 2.57 a. — Muscle- Attachments to THE Front of the Right Humerus. A bursa separates the tendon from the anterior portion of the tuberosity. (2) From the medial and anterior part of the tendon, and partly in continuity with the fleshy fibres of the muscle, a strong membranous hand (the lacertus fibrosus or bicipital fascia) extends downwards and medially over the hollow of the elbow to join the deep fascia covering the origins of the flexor and pronator muscles of the fore- arm. Its upper part is thickened and can be felt subcutane - ouslyas a crescentic border. In the arm the biceps conceals the brachialis muscle and the musculo- cutaneous nerve. Its medial border is the guide to the position of the Common tendon brachial artery and for origm of "^ extensormuscies median uervc. of forearm Anconteus (origin) Triceps : medial head (origin) Fig. 257 6. — Muscle- Attachments to THE Back of the Right Humerus. The biceps is an extremely variable muscle. Its chief aii- omalies are due to an increase or diminution in the number of origins. A third head of origin is common (10 per cent), and usually arises from the humerus, between the insertions of the deltoid and coraco-brachialis. Two or even three additional heads may be present at the same time. The long head of the muscle may be absent, or may take origin from the bicipital groove. The muscle may have an additional insertion into the medial condyle of the humerus, or into the fascia of the forearm. The brachialis is a large muscle arising from the lower two-thirds of the front of the shaft of the humerus and from the intermuscular septum on each side (Figs. 257 a and 257 h, p. 334). Clasping the insertion of the deltoid above, it ends iDelow in a strong tendon inserted deep in the hollow of the elbow into the anterior ligament of the elbow-joint, the inferior surface of the coronoid process, and slightly MUSCLES OF THE AEM. 335 into the anterior surface of the shaft of the uhiu immediately below (Fig. 264, p. 342). The lateral part of the muscle arising from the lateral epicondylic ridge and lateral intermuscular septum forms a slip mure or less separate, which may be partially fused with the brachio-radialis muscle. The triceps brachii is the ouly muscle on the back of the arm. It arises by three heads : a lateral and a medial head, from the humerus, and a long or middle head from the scapula. (1) The long, middle or scapular head (caput longum) begins as a strong tendon attached to a rough triangular surface on the axillary border of the scapula just below the glenoid fossa (infraglenoidal tuberosity) (Figs. 245, p. 322, and 250, p. 326). This gives rise to a fleshy belly which, after passing between the teres major and teres minor muscles, occupies the middle of the back of the arm. (2) The lateral head is attached by fibres, partly tendinous and partly fleshy, to the curved lateral border of the humerus from the insertion of the teres minor above to the musculo-spiral groove below, and receives additional fibres from the back of the lateral intermuscular septum (Fig. 257 h, p. 334). Its fibres are directed downwards and medially over the musculo-spiral groove, concealing the musculo-spiral nerve, the superior profunda artery,^and the medial head of the muscle, to the tendon of insertion. (3) The medial head arises by fleshy fibres from an elongated triangular area on the back of the humerus, extending upwards to the level of the insertion of the teres major, and downwards nearly to the margin of the olecranon fossa (Fig. 257 h, p. 334). It also arises on each side from the intermuscular septum, — from the whole length of the medial septum, and from the part of the lateral septum which is below the passage of the musculo-spiral nerve.^ The three heads of origin are inserted by a common tendon, broad and membranous, into an impression occupying the posterior part of the upper end of the olecranon process of the ulna (Fig. 271, p. 349), and into the deep fascia of the forearm on either side of it. The long and lateral heads join the borders of the tendon of insertion, and the medial head is attached to its deep surface. A small thick-walled bursa separates the tendon of the triceps from the posterior ligament of the elbow- joint and the upper end of the olecranon process. The sub-anconseus is a small muscle occasionally present, which consists of scattered fibres arising from the lower end of the humerus beneath the triceps, and inserted into the posterior ligament of the elbow-joint. Nerve-Supply. The muscles of the arm are supjilied by two of the nerves of the brachial plexus. The musculo-cutaneous nerve (C. 5, 6) supplies the biceps and lu-achialis muscles, and conveys to the coraco-brachialis its nejve, derived from the seventh cervical nerve. The brachialis muscle usually receives an additional small nerve from the musculo-spiral (C. 5, 6).^ The trice jss is supplied by the musculo-spiral nerve, the fibres for the several heads being derived usually from the seventh and eighth cervical nerves. Actions. (1) The chief action of these muscles (exceiDting the coraco-brachialis) is on the elbow-joint, producing along with other muscles flexion and extension. The flexor muscles are much more powerful than the extensors. Table of Muscles acting on the Elbow-Joint. Flexors. Extensors. Bicejis brachii Brachialis Brachio-radialis Pronator teres Flexors of wrist and fingers Extensors of wrist (in pronation) Triceps brachii Ancouaius Extensors of wrist and fingers (in supination) (2) The coraco-brachialis muscle acts only on the shoulder-joint, assisting the biceps as an adductor and flexor of the humerus. (3) Subordinate and accessory movements are performed by all the muscles of this group except the In-achialis. The biceps supinates the forearm, flexes the elbow, and with the aid of the coraco-brachialis adducts and flexes the humerus at the shoulder-joint. The triceps through its scapular head adducts and extends the humeriis, besides extending the elbow-joint. ^ According to the B.N. A. nomenclature, the musculo-.spiral nerve is named the radial, the present radial nerve being known a.s the superficial ramus, the posterior interosseous as the deep ramus, thus the musculo- spiral groove is known as the "radial groove." 336 THE MUSCULAR SYSTEM. FASCIi^E AND MUSCLES OF THE FOREARIYI AND HAND. Flexor digitorum profundus Digital sheath LUMfcKICAL ^ICSCLES Fasciae. The superficial fascia in the forearm presents no exceptional features. On the dorsum of the hand it is loose and thin ; in the palm it is generally^ well furnished with fat, forming pads for the protection of the vessels and nerves. It is closely adherent to the palmar fascia and to the skin, especially along the lines of flexure. The palmaris brevis is a quadri- lateral subcutaneous muscle occupying the medialsideof the hand under the superficial fascia. It arises from the medial border of the thick central por- tion of the palmar fascia and from the front of the anterior annular ligament of the wrist, and is inserted into the skin of the medial border of the hand for a variable distance. It covers the ulnar artery and nerve, branches of which supply it. Its action is to wrinkle the skin of the medial border of the hand, and by raising up the skin and superficial fascia, to deepen the hollow of the hand. The deep fascia of the forearm and hand is continuous above with the deep fascia of the arm. In the upper part of the fore- arm it is strengthened by additional fibres around the elbow; in front by fibres from the lacertus fibrosus of the biceps, behind by the fascial insertions of the triceps, and laterally by fibres derived from the humeral condyles in relation to the common tendons of origin of the flexor and extensor muscles of the forearm which take in part their origin from it. It is attached to the posterior border of the ulna, and affords increased attachment to the flexor and extensor carpi ulnaris and the flexor digitorum profundus muscles. Above the wrist the fascia is pierced anteriorly by the tendon of the palmaris longus, and by the ulnar artery and nerve. At the wrist it gains attachment to the bones of the forearm and carpus, is greatly strengthened by addition of transverse fibres, and constitutes the annular ligaments (ligamenta carpi). The anterior annular ligament (transverse carpal ligament) is a band about an inch and a half in depth, continuous above and below with the deep fascia of the fore- arm and the yjalm of the hand. It is attached laterally to the navicular and large multangular; medially to the pisiform and os hamatum; and it forms a membranous Palmar fascia Thenar eminence Hypothenar eminence Palmaris brevis - Anterior annul ligament Abductor pollicis longus Flexor carpi radialis Palmaris longus Flexor pollicis longus — Flexor digitorum ., sublimis Flexor carpi ulnarh-. Fig. 258. — The Left Palmar Fascia. FASCIA AND MUSCLES OF THE ^OTIEAEM AND HAND. 33V Flexor caepi ulnaris Flexor dioitorum sublimis -Flexor carpi radialis Palmakis longus Pisiform bone Abductor pollicis longus Anterior annular ligament -Abductor digiti quinti Abductor pollicjs brevis Flexor dioiti quinti brevis _^Flexor pollicis BREVIS _. Adductor pollicis Flexor pollicis LONGUS arch binding down in the hollow of the carpus the flexor tendons of the fingers, and the median nerve. It is divided into hvo compartments, the larger accommodating the tendons of the flexors of the digits and the median nerve, the smaller (placed laterally) containing the tendon of the flexor carpi radialis. There are three synovial membranes in these compartments : one for the flexor carpi radialis tendon, and two others, which often communicate together, enveloping the tendon of the flexor pollicis longus and the flexor tendons of the fingers respectively. The surface of the ligament is crossed by the palmar branches iW^tv of the median and ulnar nerves ; by the tendon of the palmaris longus muscle, which is attached to its surface ; and by the ulnar artery and nerve, which are again bridged over and protected by a band of fibrous tissue passing from the pisiform bone and the superficial fascia to the surface of the ligament. To the lower border of the ligament are attached the palmar fascia in the centre, and the superficial muscles of the thumb and the muscles of the little finger on each side. The posterior an- nular ligament (dorsal carpal liga- ment) is placed at a higher level than the previ- ous ligament. It consists of an oblique band of fibres about an inch broad, con- tinuous above and below with the deep fascia of the forearm and hand. It is attached later- ally to the lateral Fig. 259.— Superficial Muscles and Tendons in the Palm of the Left Hand. side of the lower end of the radius, and medially to the lower end of the ulna (styloid process), the carpus, and the medial lateral ligament of the wrist.^ It is crossed by veins, by the radial nerve, and by the dorsal branch of the ulnar nerve. Six comimrtments are formed beneath it by the attachment of septal bands to the lower ends of the radius and ulna. Each compartment is provided with a synovial membrane, and they serve to transmit the extensor tendons of the wrist and fingers in the followmg order from without inwards : — (1) Abductor pollicis longus (extensor ossis metacarpi pollicis) and extensor pollicis brevis, (2) Extensores carpi radiales, longus and brevis, (3) Extensor pollicis longus, (4) Extensor digitorum communis and extensor indicis proprius, (5) Extensor digiti quinti proprius, (6) Extensor carpi ulnaris. The thin deep fascia of the dorsum of the hand is lost over the expansions ot 1 Ulnar collateral ligament (B.N. A.). LUMBRICAL MUSCLES Tendons of flexor digitorum ^v^sublimis Flexor digitorum sublimis - lexor digitorum profundus 338 THE MUSCULAE SYSTEM. the extensor tendons on the fingers. Between the metacarpal bones a strong layer of fascia covers and gives attachment to the interossei muscles. The palmar fascia (palmar aponeurosis) is of considerable importance. In the centre of the palm it forms a thick triangular membrane, the apex of which joins the lower edge of the anterior annular ligament, and more superficially receives the insertion of the tendon of the palmaris longus muscle. The fascia separates below into four slips, one for each finger, connected together by transverse fibres, and forming beneath the webs of the fingers the superficial transverse metacarpal ligament (fasciculi transversi). Beyond this each slip separates into two parts, to be con- nected to the sides of the metacarpo-phalangeal joints and the first phalanx of the inner four digits. In the cleft between the two halves of each slip the digital sheath is attached and extends downwards on to the finger. The lateral borders of this triangular central portion of the palmar fascia are continuous with thin layers of deep fascia, which cover and envelop the muscles of the thenar and hypothenar eminences. The inner border gives origin to the -palmaris hrevis muscle (p. 336). The digital sheaths (vaginae mucosae) are tubular envelopes extending along the anterior aspect of the digits and enclosing the flexor tendons. Each consists of a fibrous sheath attached to the lateral borders of the phalanges and inter-phalan- geal joints, and continuous above with the palmar fascia. Opposite each inter- phalangeal articulation the digital sheath is loose and thin ; opposite the first two phalanges (the first only in the case of the thumb) it becomes extremely thick, and gives rise to the ligamenta vaginalia, which serve to keep the tendons closely applied to the bones during flexion of the fingers. Within each digital sheath are the flexor tendons, enveloped in a synovial membrane which envelops the tendon, and lines the interior of the sheath. The synovial membranes of the digital sheaths extend a short distance upwards in the palm, and in some cases com- municate with the large synovial membranes lining the flexor tendons beneath the annular ligament. There may be a separate distinct synovial membrane for each digit ; but most commonly only the sheaths for the three middle digits have separate synovial membranes ; those for the flexor poUicis longus and the flexor tendons of the little finger usually communicate with the synovial mem- branes placed beneath the anterior annular (transverse carpal) ligament.^ THE MUSCLES ON THE FRONT AND MEDIAL ASPECT OF THE FOREARM. The muscles on the front and medial aspect of the forearm comprise the pronators and the flexors of the wrist and fingers. In the forearm they are arranged in three strata : (1) a superficial layer consisting of four muscles which radiate from the medial epicondyle of the humerus, from which they take origin by a common tendon, and named, from without inwards, pronator teres, flexor carpi radialis, palmaris longus, and flexor carpi ulnaris. These muscles conceal the muscle which by itself constitutes (2) the intermediate stratum, the flexor digitorum sublimis, which again conceals for the most part (3) the deep layer of muscles, including the flexor digitorum profundus covering the ulna, the flexor pollicis longus on the radius, and the pronator quadratus, which is more deeply placed than the previous muscles, and stretches across the forearm between the lower ends of the radius and ulna. I. Superficial IVluscIes. The pronator teres is the shortest muscle of this group. It has a double origin: (1) a superficial head, the main origin, partly fleshy, partly tendinous, from the lowest part of the medial epicondylic ridge of the humerus and from the medial intermuscular septum, from the medial epicondyle of the humerus, from the fascia over it, and from an intermuscular septum between it and the flexor carpi radialis (Fig. 257 a, p. 334) ; (2) a deep head, a slender tendinous slip from the medial side of the coronoid process of the ulna, whicli joins the superficial origin of the muscle on its deep surface (Tig. 264, p. 342). I'he median nerve separates the two heads from one another. The muscle is directed downwards and laterally to be inserted by tendon into an oval impression on the middle of the lateral surface of the shaft of the radius (Figs. 264, p. 342, and 265, p. ' Anterior annular ligament = transverse carpal (B.N. A.). MUSCLES ON FEONT AND MEDIAL ASPECT OF FOEEAEM. 339 Fig. 260. -Section across the Forearm in the Middle Third. 343). The fibres of the muscle are twisted on themselves, so that the highest humeral fibres form the lowest fibres of the tendon of insertion, and the lowest humeral fibres and those arising from the coronoid process are highest at the insertion. The muscle forms the medial boundary of the hollow of the elbow. It is superficially placed, except near its insertion, where it is covered by the brachio- radiaiis mviscle and by the radial vessels and nerve. The flexor carpi radialis muscle takes its origin from the common tendon from the medial epicondyle of the humerus, from the fascia over it, and from the inter- muscular septa on either side. Its fleshy belly gives place to a strong round tendon in the lower half of the forearm, which, at the wrist, enters the hand in a special compartment be- neath the anterior annular ligament, and after occupying the groove on the large mult- angular bone, is inserted into the upper ends of the second and third metacarpal bones on theiranteriorsurfaces (Fig.267, p. 345). Thechieftendonisthat to the second metacarpal bone. The flexor carpi radialis is superficial except near its insertion. Its tendon in the lower half of the forearm is an important guide to the radial vessels, which are placed to its radial side. After passing beneath the anterior annular ligament the tendon is concealed by the origins of the short muscles of the thumb, and is crossed from within outwards by the tendon of the flexor pollicis longus. Besides the synovial bursa enveloping the tendon beneath the ligament, another is found beneath the tendons at their insertion. The palmaris longus arises also from the common flexor tendon, from the medial epicondyle of the humerus, from the fascia over it, and from intermuscular septa on either side. It forms a short fusiform muscle, which ends in the middle of the forearm in a long flat tendon. This pierces the deep fascia above the wrist, and passing over the anterior annular ligament, is inserted (1) into the surface of the anterior annular ligament, and (2) into the apex of the thick central portion of the palmar fascia. A tendinous slip is frequently sent to the short muscles of the thumb and the fascia covering them. The palmaris longus is the smallest muscle of the forearm. In the lower third of the forearm its tendon is placed directly over the median nerve, alono; the radial border of the tendons of the flexor digitorum sublimis. The iDalmaris longus is the most variable muscle in the body, and is often absent (10 per cent). The flexor carpi ulnaris muscle has a double origin, from the humerus and from the ulna. (1) It arises from the common tendon attached to the medial condyle of the humerus, from the fascia over it, and from an intermuscular septum laterally. (2) By means of the deep fascia of the forearm it obtains an attachment to the medial border of the olecranon process and the posterior border of the ulna in its upper three-fifths. The fleshy fibres join a tendon which lies on the anterior border of the muscle and is inserted into the pisiform bone, and in the form of two ligamentous ^ Radial nerve = superficial ramus of radial nerve (B.N. A.). A, Pronator teres (insertion) ; B, Flexor carpi radialis ; C, Flexor DIGITORUM sublimis ; D, Palmaris longus ; E, Flexor carpi ulnaris ; F, Flexor digitorum profundus; G, Extensor carpi ulnaris; H, Extensor pollicis longus ; I, Extensor digitorum communis and extensor dioiti qdinti proprius ; J, Abductor pollicis longus ; K, Extensor carpi radialis brevis ; I;, Extensor carpi radialis longus ; M, Brachio-radialis. a, Radius ; b, Interosseous membrane ; c, Ulna. 1, Radial nerve ; 2, Radial artery ; 3, Anterior superficial ran^us of interosseous artery ; 4, Anterior interosseous nerve (underneath flexor pollicis longus) ; 5, Median nerv'e ; 6, Ulnar artery ; T, Ulnar nerve ; 8, Posterior interosseous artery ; 9, Posterior interosseous nerve. 340 THE MUSCULAR SYSTEM. bands (pisi-unciform and pisi-metacarpal) into the hook of the unciform bone, and the upper end of the fifth metacarpal bone (Fig. 267, p. 345). The muscle is superficially placed along the medial border of the forearm. It Biceps brachii Medial ixter- ML"SCrLAR SEPTUM Brachialis Medial condyle Lacertus FIBROSrs (bicipital fasci ■ SuPIXATOR MUSI I. (Supinator brevis) -j Pronator teres Flexor carpi radialis Palmaris LOKGUS Flexor carpi ULNARI.S Extensor CARPI.; radialis LONCrS Brachio- radialis Flexor digi- TORUM SUBLIMIS Flexor polligis. LONODS Brachio-radialis (tendon) -•■- Flexor carpi radialis (tendon) Palmaris longds (t<;ndon) Flexor carpi ulnaris (tendon) Pisiform bone Abdtjctor pollicis LONG us (extensor ossis metacarpi pollicis) Palmar fascia 'j Biceps brachi Brachialis Medial intermuscular septum Bicipital fascia (lacertus fibrosus) Biceps tendon Pronator teres (humeral origin) Pronator TEKESv^ (ulnar origm) '; Flexor carpi ._' radialis Supinator muscle Brachio-radialis •- Pronator teres (insertion) Flexor digitor' m sublimis (radial .. ongin) Flexor carpi ulnaris Flexor digitortjm sublimis -- Brachio-radialis tendon .. Flexor pollicis longus Pronator quadratus \A' Flexor digitorum profundus Pisiform bone Flexor carpi radialis Abductor pollicis longus (extensor ossi- metacarpi POLLICli) Fig. 261. — The Superficial Muscles ok THE Left Forearm. Fig. 262. — Deeper Muscles of the Left Forearm. conceals the flexor digitorum profundus muscle, the ulnar nerve (which enters the forearm between the two heads of origin of the muscle), and the ulnar artery. The tendon serves as a guide to the artery in the lower half of the forearm. MUSCLES ON FEONT AND MEDIAL ASPECT OF FOEEARM. 341 Ligament 2. Intermediate Layer. The flexor digitorum sublimis occupies a deeper plane than the four previous muscles. It has a threefold origin, from the humerus, radius, and ulna. (1) The chief or humeral head of origin is from the medial condyle of the humerus by the common tendon, from the internal lateral (ulnar collateral) ligament of the elbow, and from adjacent intermuscular septa. (2) The ulnar head of origin is by a slender fasciculus from the medial border of the coronoid process of the ulna, above and medial to the origin of the pronator teres (Fig. 264, p. 342). (3) The radial head of origin is from the oblique line and middle third of the anterior border of the radius by a thin fibro-muscular attachment (Fig. 264, p. 342). The muscle di^ddes in the lower third of the forearm into four parts, L'gainentum each provided with a separate tendon __ which goes beneath the transverse carpal ligament, passes through the palm of the hand, and enters the corresponding digital sheath of the finger. At the wrist the four tendons are arranged in pairs, those for the middle and ring fingers in front, and those for the fore and little fingers behind, and are sur- rounded by a synovial sheath, along with the tendons of the flexor digi- torum profundus, beneath the anterior annular ligament. In the palm of the hand the tendons separate, and conceal the deep flexor tendons and lumbrical muscles. Within the digital sheath each tendon is split into two parts by the tendon of the flexor digitorum profundus ; after surrounding that tendon the two parts are partially re-united on its deep surface, and are inserted, after partial decussation, in two portions into the sides of the second phalanx. The vincula tendinum form additional insertions of the muscle. They consist of delicate bands of connective tissue enveloped in syno%'ial membrane, and are known as the ligamenta longa and brevia. The ligamentum breve is a triangular band of fibres containing yellow elastic tissue (ligamentum sub- flavum), occupying the interval between the tendon and the digit for a short distance close to the insertion. It is attached to the front of the inter -phalangeal articulation and the head of the first phalanx. The ligamentum longum is a long narrow band extending from the back of the tendon to the upper part of the anterior surface of the first phalanx. Ligamentum breve Flexor digitorum sfblimis Expansion of extensor tendon Flexor digitorum profundus First luiibrical muscle First dorsal ixter- \\\ osseous muscle In Extensor indicis I h PROPRius tendon Extensor digitorum communis tendon Fig. 263. -The Tendoxs attached to the Index Finger. 3. Deep Layer. The flexor digitorum profundus is a large muscle arising from the ulna, the interosseous membrane, and the deep fascia of the forearm, under cover of the flexor digitorum sublimis and the flexor carpi ulnaris. Its ulnar origin is from the anterior and medial surfaces of the bone in its upper two-thirds,' extending up so as to include the medial side of the olecranon process, and to embrace the insertion of the brachialis muscle into the coronoid process. It arises laterally from the medial half of the interosseous membrane in its middle third (Figs. 264, p. 342, and 265, p. 343), and medially from the deep fascia of the forearm behind the origin of the flexor carpi ulnaris. 342 THE MUSCULAK SYSTEM. Brachialis muscle (insertion) Supinalor muscle (ulnar origin) (occasional origin) Biceps bracliii (insertion) Flexor digi- tonini sublimis (radial origin) Pronator teres (insertion) Flexor pollicis longus (origin) Flexor digitorum profundus (origin) The muscle forms a broad thick tendon which passes beneath the anterior annular ligament, covered by the tendons of the flexor digitorum sublimis, and enveloped in the same synovial sac, and divides in the palm into four tendons for insertion into the terminal phalanges of the fingers. The tendon associated with the forefinger is usually separate from the rest of the tendons in its whole length. Each tendon enters the digital sheath of the finger beneath the tendon of the flexor digitorum sublimis, which it pierces opposite the first phalanx, and is finally inserted into the base of the terminal phalanx. Like the tendons of •\ ■',- ra the flexor sublimis, those of the deep flexor are provided with vincula, viz. ligamenta brevia at- -Hmfs°(£™inf ■ tached to the capsule of the second (^iin"r^ori"?nr inter - phalangeal articulation, and Flexor poUicis longus ligamenta longa, which are in this case connected to the tendons of the subjacent flexor digitorum sub- limis. Lurabricales. — Eour small cy- lindrical muscles are associated with the tendons of the flexor digi- torum profundus in the palm of the hand. The two lateral muscles arise each by a single head from the radial sides of the tendons of the flexor digitorum profundus destined respectively for the fore and middle fingers. The two medial muscles arise, each by two heads, from the adjacent sides of the second and third, and third and fourth tendons. From these origins the muscles are directed downwards to the radial side of each of the metacarpo-phalangeal joints, to be inserted into the capsules of these articulations, the radial border of the first phalanx, and chiefly into the radial side of the extensor tendon on the dorsum of the phalanx. The lumbricales vary considerably in number, and may be increased to six or diminished to two. The flexor pollicis longus arises beneath the flexor digitorum sublimis by fleshy fibres from the volar or anterior surface of the shaft of the radius in its middle two- fourths, and from a corresponding portion of the interosseous mem- brane. It has an additional origin occasionally from the medial border of the coronoid process of the ulna (Fig. 264, p. 342). Its radial origin is limited above by the oblique line and the origin of the flexor digitorum sublimis, and below by the insertion of the pronator quadratus muscle. The muscle ends above the wrist in a tendon, which passes over the pronator quadratus into the hand beneath the transverse carpal ligament, enveloped in a special synovial sheath. In the palm the tendon is directed downwards along the ulnar side of the thenar eminence, between the flexor brevis and adductor muscles of the thumb, to be inserted into the base of the terminal phalanx of the thumb on its anterior surface. Pronator quadratus (origin) Pronator quad- ratus (insertion) Brachio-radia (insertion) IXJ Fig. 264. — Muscle-Attachments to the Right Radius AND Ulna (Anterior Aspects). SHOKT MUSCLES OF THE HAND. 343 The pronator quadratus is a quadrilateral fleshy muscle, occupying the lower fourth of the forearm. It is placed beneath the deep flexor tendons, and arises from the lower fourth of the anterior border and surface of the ulna (Fig. 2G4, p. 342), and is directed trans- versely outwards to be inserted into the lower fourth of the anterior surface of the radius, and into the narrow triangular area on its ulnar side in Iront of the attachment of the interosseous membrane (Fig. 264, p. 342). The pronator quadratus is sub- ject to considerable variations. It may even be absent ; or it may have an origin from radius or ulna, or from both bones, and an inser- tion into the carpus. Biceps brachii IjACiSBTDS FIBROSUS OR j^ Bicipital fascia • Brachialis muscle Pronator TERES Superficial FLEXOR (origin)' SHORT MUSCLES OF THE HAND. The short muscles belonging to the hand, in addition to the pal- maris brevis and the lumbrical muscles, already described, include the six muscles of the thumb constituting the thenar eminence, the three muscles of the little finger constituting the hypothenar eminence, and the interossei muscles, which are deeply placed between the metacarpal bones. Muscles of the Thumb. Biceps tendon BiClPITAI TL'BEROSI 1 -1 Supinator muscle. Brachio-kadialis. Pronator teres- The short muscles of the thumb are the abductor, opponens, and flexor brevis (with its deep portion, interosseus privius volaris), and the adductor muscle, subdivided into two parts, adductor obUquus, and adductor pollicis transversus. The abductor pollicis brevis (abductor pollicis) arises by fleshy fibres from the tubercle of the navicular, the ridge of the large multangular, the anterior surface of the transverse carpal ligament, and from tendinous slips derived from the insertions of the palmaris longus and abductor pollicis longus muscles (Fig. 266, p. 344). Strap-like in form, it is inserted by a short tendon into the radial side of the first phalanx of the thumb at its upper end, and into the capsule of the metacarpo-phalangeal joint. The opponens pollicis, partially concealed by the preceding muscle, arises by fleshy and tendinous fibres from the anterior surface of the anterior annular liga- Flexor digitorum profundus Flexor carpi ULNARIS"' Flexor digitorum profundus (foi' index finger) Flexor pollicis lonou Brachio-radialis Plexor digitorum sublimis Pronator quadratus Flexor digitorum sublimis Pisiform bone Flexor carpi radialis Abductor pollk i long I - Fig. 265. — The Drepest Muscles in the Front OP THE Left Foeeahm. su THE MUSCULAE SYSTEM. ment and from the ridge on the large multangular bone. Extending downwards and laterally it is inserted into the whole length of the lateral border and the radial half of the palmar surface of the first metacarpal bone (Fig. 267, p. 345). The flexor pollicis brevis consists of two parts, a. The superficial 'part of the muscle, partly concealed by the abductor pollicis, arises by fleshy and tendinous Abductor pollicis longus Extensor pollicis brevis Abductor pollicis brevis Opponens pollicis Flexok pollicis brevis (superficial part) ^.^^ iAdductor pollicis OBLIQirS ., _.f^~ Adductor pollicis trans- . ~-,, versus Abductor pollicis- (brevis) Pronator quadratus Flexor carpi ulnaris Pisiform bone Hook of oh hamatum Abductor dioiti quinti (cut) '^- Plexor digiti quinti brevis (cut) Third palmar interosseous muscle Fourth dorsal interosseous muscle Second palmar interosseous muscle Third dorsal interosseous muscle Flexor digiti "j quinti brevis I Attach- and Abductor j ments digiti quinti J is Tendons of third and fourth lumbkicals Flexor dioitoru.m sublimis tendon Tendon sheath Flexor digitorum profundus tendon Flexor digitorum profundus attachment Fir;. 266.— The Palmar Muscles (Right Side). fibres from the lower border of the anterior annular ligament, and sometimes from the ridge of the large multangular, and is inserted into the radial side of the base of the first phalanx of the thumb, a sesamoid bone being present in the tendon of insertion. h. The deep part of the muscle (interosseus primus volaris) arises from the ulnar side of the base of the first metacarpal bone, and is inserted into the ulnar side of the base of the first phalanx of the thumb along with the adductor pollicis obliquus. This little muscle is deeply situated in the first interosseous SHOET MUSCLES OF THE HAND. 345 space, in the interval between the adductor pollicis obliquus and the first dorsal interosseous muscle. It may be regarded as homologous with the palmar interossei muscles, with which it is in series, The adductor pollicis is separated into two parts by the radial artery. (1) The adductor pollicis obliquus lies deeply in the palm, covered by the tendons of the long tiexors of the thumb and fingers. It arises by fleshy fibres from the anterior surfaces of the large and small multangular and capitate bones, from the sheath of the tendon of the flexor carpi radialis, from the bases of the second, third, and fourth metacarpal bones, and from the palmar ligaments connecting these bones together (Fig. 267, p. 345). It is inserted by a tendon, in which a sesamoid bone is developed, into the ulnar side of the base of the first phalanx of the thumb. At its lateral border a slender slip separates from the rest of the muscle, and passing obliquely beneath the tendon of the flexor pollicis longus, is inserted into the radial Capitate bone or os magnum Navicular bone Abductor pollicis brevis (origin) Opponens pollicis (origin) Large multangular or trapezium! Abductor pollicis longus (insertion) Opponens pollicis (insertion) Flexor carpi radialis (insertion) Os Ir.natum or semilunar bone Os hamatum or unciform riuetrum or cuneiform bone , iiform bone Abductor digit! quinti (origin) Flexor carpi ulnaris (insertion) Flexor brevis digiti quinti (origin) Flexor carpi ulnaris (insertion) Adductor pollicis obliquus (origin) First dorsal interosseous muscle (one origin) First palmar interosseous muscle (origin) Second dorsal interosseou-, muscle (one origin) Opponens digiti quinti (origin and insertion) Third palmar mter- '^ osseous muscle (origin) Fourth dorsal interosseous muscle (one origin) Se( ond palmar interosseous muscle (origin) Adductor pollicis tians\ersu3 (ougm) Third doi^al interosseous muscle (one origin) Fig. 267. — Muscle-Attachments to the Palmar Aspect of the Carpus and Metacarpus. side of the base of the first phalanx along with the superficial part of the flexor pollicis brevis. (2) The adductor pollicis transversus, lying deeply in the palm beneath the flexor tendons, arises by fleshy fibres from the medial ridge on the palmar aspect of the shaft of the third metacarpal bone, in its distal two-thirds (Fig. 267, p. 345), and from the fascia covering the interosseous muscles in the second and third spaces. Triangular in form, it is directed laterally, over the interossei muscles of the first two spaces, to be inserted by tendon into the ulnar side of the base of the first phalanx of the thumb along with the adductor obliquus. lYIuscIes of the Little Finger. The short muscles of the little finger are the adductor, opponens. and flexor brevis digiti quinti. The abductor digiti quinti is most superficial. It arises from the pisiform 346 THE MUSCULAE SYSTEM. bone and from the tendon of the flexor carpi ulnaris and its ligamentous con- tinuations (Fig. 267, p. 345), and is inserted bj tendon into the ulnar- side of the base of the first phalanx of the little finger. The opponens digiti quinti arises beneath the preceding muscle by tendinous fibres from the anterior annular ligament and from the hook of the os hamatum, and is inserted into the ulnar margin and ulnar half of the palmar surface of the fifth metacarpal bone in its distal three-fourths (Fig. 267, p. 345). The flexor digiti quinti brevis may be absent or incorporated with either the opponens or abductor minimi digiti. It arises by tendinous fibres from the anterior annular ligament and from the hook of the OS hamatum (Fig. 267, p. 345), and is inserted along with the abductor into the ulnar side of the first phalanx of the little finger. The Interosseous IVIuscIes. The interosseous muscles of the hand occupy the spaces between the metacarpal bones. They are ar- ranged in two sets, palmar and dorsal. The palmar interossei (m. in- terossei volares) are three in num- ber, occupying the three inner inter- osseous spaces. Each arises by a single head ; the first from the ulnar side of the shaft of the second metacarpal bone ; the second, and third, from the radial sides of the shafts of the fourth and fifth meta- carpal bones respectively (Fig. 268, p. 346). Each ends in a tendon which is Extensor carpi radialis brevis (insertion) „ ^ .,,/ ^^ Extensor carpi radialis Extensor carpi ulnaris (insertion) J^j. ^j^y lon^us (insertion) First dorsal inter- osseous muscle (origin) Fourth dorsal interosseous muscle (origin) Fig. 268. — The Palmar Interosseous Muscles (Right Side). P^, first ; P^, second ; and P'^, third palmar interosseous muscles. Third dorsal inter- osseous muscle (origin) Second dorsal interosseous muscle (origin) Fig. 269. — Muscle-Attachments to the Dorsal Aspect ov the Right Metacarpus. directed downwards behind the deep transverse metacarpal ligament, to be inserted into the dorsal expansion of the extensor tendon, the capsule of the metacarpo- MUSCLES ON THE BACK OF THE FOEEAEM. 347 phalangeal articulation, and the side of the first phalanx of the finger ; the first is inserted into the ulnar side of the second finger ; the second and third into the radial sides of the fourth and fifth fingers. The deep part of the flexor poUicis brevis (iuterosseus primus volaris) is to be regarded as the homologous muscle of the first interosseous space. The dorsal interossei are four in number. Each arises by two heads from the sides of the metacarpal bones bounding each interosseous space (Figs. 269, p. 346, Abductor pollicis brevis : origin (cut) Insertion of flexor carpi radialis Insertion of opponens pollicis Interosseds primus volaris Abductor pollicis brevis : insertion (cut) -j,,- Adductor pollicis obliquus_ '-'-^ (insertion) Adductor pollicis transversus - (insertion) First dorsal interosseous muscle Second dorsal interosseous muscle Third dorsal interosseous muscle Fourth dorsal interosseous muscle Insertion of flexor carpi ulnaris Origins of palmar inter- osseous muscles Insertion of opponens digiti QUINT! Insertion of abductor digiti QUINTI Fig. 270. — Dorsal Interosseous Muscles of the Hand (seen from the Palmar Aspect). and 270, p. 347). Each forms a fleshy mass, ending in a membranous tendon, which, passing downwards behind the deep transverse metacarpal ligament, is inserted exactly like the palmar muscles into the dorsal aspect of each of the four fingers. The insertion of the first dorsal interosseous muscle is into the radial side of the index finger ; the second muscle is attached to the radial side of the middle finger ; the third muscle to the ulnar side of the same finger ; and the fourth muscle to the ulnar side of the ring finger. The interosseous muscles of the hand in some cases have a disposition similar to that of the corresponding muscles of the foot (p. 383). THE MUSCLES ON THE BACK OF THE FOREARM. The group of muscles occupying the radial side of the elbow and the back of the forearm and hand include the supinator muscles of the forearm and the extensors of the wrist and digits. They are divisible into a superficial and a deep layer. The superficial layer comprises seven muscles, which are in order, from without inwards, the brachio-radialis, the two radial extensors of the carpus, the extensor digitoruin communis and extensor digiti quinti proprius, the extensor carpi ulnaris, and the anconeus. The deep muscles are five in number : one, the supinator, extends between the upper parts of the ulna and radius ; the others are the special extensors of the thumb and forefinger, viz. the abductor pollicis longus, extensor pollicis longus and extensor pollicis brevis, and extensor indicis proprius. They cover the back of the bones of the forearm and the interosseous membrane, and are almost wholly concealed by the superficial muscles. Only the abductor pollicis longus and the extensor pollicis brevis become superficial in the lower part of the forearm, emerging between the radial extensors of the carpus and the extensor communis digitorum. 24 348 THE MUSCULAE SYSTEM. Superficial IVIuscIes. The brachio-radialis (supinator radii longus) arises by fleshy fibres from the anterior aspect of the upper two-thirds of the lateral supra-condylic ridge of the humerus, and from the front of the lateral intermuscular septum (Fig. 257 a, p. 334). Occupying the lateral side of the hollow of the elbow, the muscle descends along the radial border of the forearm, and ends about the middle in a narrow flat tendon which is inserted under cover of the tendons of the abductor pollicis longus and extensor pollicis brevis, by a transverse linear attachment, into the upper limit of the groove for the above-named muscles on the lateral side of the lower extremity of the radius. Some of its fibres gain an attachment to the ridge in front of the groove, and others spread over the surface of the groove for a variable distance (Figs. 264, p. 342, and 265, p. 343). The extensor carpi radialis longus arises by fleshy fibres from the anterior aspect of the lower third of the lateral supra-condylic ridge of the humerus, from the front of the lateral intermuscular septum, and from the common tendon of origin of succeeding muscles, which is attached to an impression on the antero- lateral surface of the lateral condyle (Figs. 257 a, and 257 &, p. 334). It ends in a tendon in the lower half of the forearm, which passes beneath the dorsal carpal ligament, to be inserted into the back of the base of the second metacarpal bone on its radial side (Fig. 269, p. 346). The extensor carpi radialis brevis arises from the common tendon, from the external lateral (radial collateral) ligament of the elbow, from the fascia over it, and from intermuscular septa on either side. It passes down the back of the forearm and under the posterior carpal ligament in close relation to the previous muscle, to be inserted by a tendon into the bases of the second and third metacarpal bones (Fig. 269, p. 346). A bursa is placed beneath the two radial extensor tendons close to their insertion. The extensor digitorum communis arises from the common tendon, from the lateral condyle, from the fascia over it, and from intermuscular septa on either side. Extending down the back of the forearm it ends above the wrist in four tendons, of which the outermost often has a separate fleshy belly. After passing beneath the posterior annular ligament in a compartment along with the extensor indicis proprius, the tendons separate on the back of the hand, where the three innermost tendons are joined together by two obliquely-placed bands. One passes downwards and later- ally, and connects together the third and second tendons ; the other is a broader and shorter band, which passes also downwards and laterally, and joins the fourth to the third tendon. In some cases a third band is present, which passes downwards and medially from the first to the second tendon ; and frequently the tendon for the little finger is joined to the tendon for the ring finger, and separates from it only a short distance above the lower end of the metacarpal bone. The tendons are inserted in the following manner : on the finger each tendon spreads out so as to form a membranous expansion over the knuckle and on the back of the first phalanx. The border of the tendon is indefinite over the meta- carpo-phalangeal articulation, of which it forms the posterior ligament. On the back of the first phalanx the tendon receives laterally the insertions of the inter- osseous and lumbrical muscles. At the lower end of the first phalanx it splits into iU- defined medial and lateral slips, proceeding over the back of the first inter-phalangeal articulation, of which they form the posterior ligament. The medial slip is inserted into the back of the base of the second phalanx, while the two lateral yjieces become united to form a membranous tendon on the back of the second X->halanx, which, after passing over the second inter-phalangeal articula- tion, is inserted into the base of the terminal phalanx. The extensor digiti quinti proprius has an origin similar to and closely connected with that of the preceding muscle, from the common tendon, the fascia over it, and from intermuscular septa. Passing down the back of the forearm as a narrow fleshy slip, between the extensor digitorum communis and the extensor carpi ulnaris, it ends in a tendon which occupies a groove between the radius and ulna in a special compartment of the posterior annular ligament MUSCLES ON THE BACK OF THE FOREAKM. 349 Tricei)s bracliii (insertion) Biceps bracliii (insertion Supinator muscle (insertion of the wrist. Ou the back of the hand the tendou, usually split into two parts, lies to the ulnar side of the tendons of the extensor digitorum communis, and is finally inserted into the expansion of the extensor tendon on the dorsum of the first plialanx of the little finger. The extensor carpi ulnaris has a double origin : (1) from the common tendon from the lateral condyle of the humerus, from the fascia over it, and from the intermuscular septa; and (2) through the medium of the deep fascia, from the dorsal margin of the ulna in its middle two-fourths. Lying in the forearm upon the dorsal surface of the ulna, it ends in a tendon which occupies a groove on the back of the ulna in a special compartment of the dorsal ligament of the wrist, and is inserted into the ulnar side of the base of the fifth metacarpal bone (Fig. 269, p. 346). The anconaeus is a small triangular muscle arising by a separate tendon from the lower part of the dorsal surface of the lateral condyle of the humerus (Fig. 267 h, p. 334), and from the posterior ligament of the elbow-joint. Spreading out over the dorsal surface of the elbow- joint and upper part of the ulna, it is inserted by fleshy fibres into a triangular surface on the lateral aspect of the olecranon process and dorsal surface of the ulna, as low down as the oblique line (Fig. 271, p. 349). It is also inserted into the fascia which covers it. The epitrocMeo-anconseus is an oc- casional small muscle arising from the dorsal surface of the medial condyle of the humerus, and inserted into the medial side of the olecranon process. It covers the ulnar nerve in its passage to the forearm. Deep IVIuscIes. The supinator muscle (supi- nator radii brevis) is the highest of the deeper muscles. It is almost wholly concealed by the superficial muscles, and has a complex origin, — (1) from the lateral condyle of the hu- merus ; (2) from the external lateral and orbicular (radial collateral and annular) ligaments of the elbow-joint ; (3) from the triangular surface on the shaft of the ulna just below the radial notch ; and (4) from the fascia over it. From this origin the muscle spreads laterally and downwards, enveloping the upper part of the radius, and is inserted into the palmar and lateral sur- faces of the bone, as far forwards as the tuberosity of the radius, as far upwards as the neck, and as far downwards as the oblique line and the insertion of the pronator teres. (Figs. 271, p. 349, and 273, p. 350.) The muscle is divisible into superficial and deep imrts with humeral and ulnar Abductor longus pollicis (origin) rronator teres (insertion) Extensor pollicis brevis (oiigin) Fig. 271.- J3rachio-radialis (insertion) Groove for tendons of ladial extensors of carpus (jroove for extensor pollicis longus Groove for extensor digitornm com- munis and extensor mdicis proprius -Muscle-Attachments to the Right Radius AND Ulna (Posterior Aspects). 350 THE MUSCULAR SYSTEM. origins, between which the dorsal part of the forearm. The abductor poUicis posterior interosseous nerve ^ passes in its course to the longns (extensor ossis metacarpi pollicis) arises by Triceps BRACK 1 1 TEKDON" Brachio- radialis Lateral _ epicondyle Deep fascia of the forearm Ancon.«us Extensor carpi radialis LONG us Dorsal border ^jj | of ulna Extensor carpi radialis BREVIS Extensor digitorum communis Extensor digiti quinti proprius Extensor carpi ULNARIS Flexor carpi ulnaris Abductor pollicis LONGUS Extensor indicis proprius Extensor pollicis brevis Extensor pollicis LONGUS Posterior ligament of the wrist Extensor carpi radialis longus extenhor carpi \ .... RADIALIS brevis/ Extensor carpi | ULNARIS / Triceps BRACHII TENDON Brachio- radialis Origin of superficial extensor MUSCLES Proximal radio- ulnar JOINT Anconeus Extensor carpi radialis longus Dorsal border of ulna Extensor carpi RADIALIS brevis Supinator muscle Abductor pollicis LONGUS (extensor OSSIS metacarpi pollicis' Dorsal border OF ULNA Fig. 272. — Suj-erficial Muscles on the Back of the Left Fokearm. Extensor pollicis LONGUS Extensor indicis proprius ----t— S- Bxtensor pollicis brevis.. Posterior ligament of the wrist' Extensor carpi ) RADIALIS LONGl'S f Extensor carhi \ radialis brevis / Extensor carpi | ULNARIS f Extensor digiti ^ quinti proprius / Extensor... pollicis longus Extensor INDICIS PROPRIUS T, Fig. 273. — Deep Muscles on the Back OF THE Left Forearm. fleshy fibres below the supinator muscle from the uppermost of the narrow impressions on the lateral half of the dorsal surface of the ulna ; from the middle third of the dorsal surface of the radius ; and from the intervening portion of the interosseous membrane (Fig. 271, p. 349). Becoming superficial in the lower part ' Posterior interosseous uerve = deep ramus of the radial nerve (B.N. A.). MUSCLES ON THE BACK OF THE FOEEAEM. 351 of the forearm along with the extensor poUicis brevis, between the extensors of the wrist and the common extensor of the fingers, its tendon passes with the latter muscle beneath the posterior ligament of the wrist, to be inserted into the radial side of the base of the first metacarpal bone (Fig. 269, p. 346). From the tendon close to its insertion a tendinous slip passes to the abductor poUicis brevis and the fascia over the thenar eminence, and another is frequently attached to the large mult- angular boue. The extensor poUicis brevis (extensor primi internodii poUicis), an essentially human muscle, is a specialised portion of the previous muscle. It arises from a rhomboid impression on the dorsal surface of the radius, and from the interosseous membrane, below the abductor pollicis longus (extensor ossis metacarpi polHcis) (Fig. 271, p. 349). It is closely adherent to that muscle, and accompanies it beneath the posterior ligament of the wrist and over the radial artery to the thumb. Its tendon is then continued along the dorsal surface of the first metacarpal bone, to be inserted into the dorsal surface of the base of the first phalanx of the thumb. Before reaching its insertion the tendon helps to form the capsule of the metacarpo- phalangeal joint. The extensor pollicis longus (extensor secundi internodii pollicis) arises from the lateral part of the dorsal surface of the ulna in its middle third, and from the interosseous membrane, below the abductor pollicis longus (Fig. 271, p. 349). Its tendon grooves the dorsal surface of the radius, and occupies a special compartment beneath the posterior ligament of the wrist. Extending obliquely across the dorsal surface of the hand, the tendon crosses the radial artery, and helps to form the capsule of the first metacarpo-phalangeal articulation, and is inserted into the dorsal surface of the base of the second phalanx of the thumb. At the wrist the tendons of the muscles of the thumb, the abductor pollicis longus (extensor ossis metacarpi pollicis) and extensor pollicis Ijrevis laterally, and the extensor pollicis longus medially, bound a hollow (the " anatomical snuff-box ") best seen in extension and abduction of the thumb, which corresponds to the position of the radial artery as it winds round the wrist to reach the palm of the hand. The extensor indicis proprius (extensor indicis) arises below the extensor pollicis longus from the lowest impression on the dorsal surface of the ulna, extending down from the middle of the shaft to within two inches of its lower end, and sometimes also from the interosseous membrane (Fig. 271, p. 349). Its tendon passes through a compartment of the posterior ligament of the wrist along with the tendons of the extensor digitorum communis. On the back of the hand the tendon lies on the ulnar side of the tendon of the common extensor destined for the forefinger, and is inserted into the forefinger, joining the membranous expansion of the tendon of the extensor digitorum communis on the dorsum of the first phalanx. Nerve-Supply. Four nerves are engaged in supplying the muscles of the forearm and hand, — the median and ulnar on the front, tlie musculo-spiral ^ and posterior interosseous- nerves on the back of the limb. Of the muscles on front of the forearm, the median nerve supplies the pronator teres, flexor carpi radialis, palmaris longus, flexor digitorum sublimis directly, the fibres being ultimately traceable to the sixth cervical nerve. By means of its anterior interosseous branch ^ (C. 7. 8. T. 1.) it also supplies the flexor pollicis longus, pronator quadratus, and the lateral half of the flexor digitorum profundus. The ulnar nerve (C. 8. T. 1) supplies the flexor carpi ulnaris and the medial half of the flexor digitorum profundus. The muscles in the palm of the hand are innervated by the median nerve (C. 6. 7.), and by the ulnar nerve (C. 8. T. 1). The median nerve suppUes the abductor, opponens, and flexor pollicis brevis (superficial head), and the first two lumbricals. The ulnar nerve supjjlies the jmlmaris brevis, and by its deep branch, the three muscles of the little finger, the two ulnar lumbrical muscles, all the interossei, the two adductors of the thumb, and the interosseus primus volaris. The muscles on the dorsal surface of the forearm are supplied by the musculo-spiral nerve and by its terminal muscular branch, the posterior interosseous nerve. The musculo-spiral nerve' supplies directly the brachio- radialis (C. 5. 6.), and the abductor pollicis longus (C. 6. 7.). The anconseus is supplied by a branch from the musculo-spiral nerve ' to the medial head of the triceps (C. 7. 8.). The posterior interosseous nerve - supplies the other muscles on the back of the forearm, — extensor carpi radialis brevis (C. 6. 7.), extensor digitorum 1 Musculo-spiral nerve = ratlial nerve (B.N. A.). - Posterior interosseous nerve = deep ramus of radial nerve (B.N. A.). ^ Anterior interosseous nerve = volar interosseous nerve of forearm (B.N. A.). 352 THE MUSCULAE SYSTEM. communis, extensor digiti quinti proprius, extensor carpi ulnaris (C. 6. 7. 8.), supinator, abductor pollicis longus (C. 6.), the two extensors of the thumb, and the extensor indicis proprius (C. 6. 7. 8.). Actions of the Muscles of the Forearm and Hand. These muscles are concerned in the movements of the elbow, wrist, and fingers. In the majority of cases the muscles act uj)on more than one joint. 1. Action on the Elbow- Joint. — It has been shown already that flexion and extension of the elbow are assisted by certain of these muscles. The flexor muscles are the pronator teres, and the flexor muscles of the wrist and fingers. In the position of pronation, the move- ment of flexion is aided by the brachio-radialis and extensor muscles of the wrist and fingers. The extensors are the supinator muscle and anconseus, and the extensor muscles of the wrist and fingers. 2. Pronation and supination of the hand are performed by special muscles, aided by muscles which act also upon other joints. The brachio-radialis assists in flexion and pronation on the one hand, and in extension and supination on the other hand. In the supine position it assists pronation, and in the prone position it assists supination, in each case bringing the hand into the position intermediate between pronation and supination. Pronation. Supination. Pronator teres Pronator quadratus Brachio-radialis Flexor carpi radialis Weight of the limb Supinator Biceps brachii B rachio -radialis Extensors of thumb and fingers Weight of the limb 3. Action on the Wrist-Joint. — The movements at the wrist-joint are flexion and extension, abduction and adduction. Flexion and adduction are much more extensive movements than extension and abduction, on account of the form of the wrist-joint. The following muscles pro- duce these movements : — Flexion. Extension. Adduction. Abduction. Flexor carpi radialis Palmaris longus Flexor carpi ulnaris Long flexors of thumb and fingers Extensors of the wrist Extensors of thumb and fingers Flexor carpi ulnaris Extensor carpi ulnaris Flexor carpi radialis Extensors of wrist Extensors of thumb 4. Movements of the Fingers. — Two separate series of movements occur in relation to the articulations of the fingers : flexion and extension (at the metacarpo -phalangeal and inter- phalangeal joints), and abduction and adduction (only at the metacarpo-phalangeal joints). The movements and the muscles concerned are given in the following tables : — Flexion. Extension. Flexor digitorum sublimis Flexor digitorum profundus Lumbricales '^ {acting on the metacarpo- Interossei / phalangeal articulations) Flexor digiti quinti brevis Extensor digitorum communis Extensor indicis proprius Extensor digiti quinti proj)rius Lumbricales \ {acting on the inter -pha- Interossei / langeal articulations) Abduction. Adduction. Lumbricales ^ Flexor brevis and 1 (from the inner side Opponens, digiti ' of the hand) quinti J C (from the middle 1 Dorsal interossei ^ line of the middle I finger) /-(to the middle line Palmar interossei] of tlie middle i finger) Flexion is more powerful and complete than extension of the fingers. The flexor digitorum profundus alone acts on the terminal phalanges ; the flexor sublimis and flexor profundus together flex the proximal inter-jjhalangeal joint ; and flexion of the metacarpo-phalangeal articulation is effected by the.se muscles, assisted by the intero.ssei, lumbricales, and flexor digiti quinti brevis. Extension of the phalanges is eft'ected Ijy the united action of the extensors of the digits, the interossei and lumbricales ; extension of the fingers at the metacar])o-phalaiigeal joints is produced solely by the long extensor muscles, tieparate extension of the index finger only \^ possible; the three inner fingers can only be flexed and extended together, on account of the connecting bands joining the extensor tendons together on the back of the hand. FASCIA AND MUSCLES OF THE THIGH AND BUTTOCK. 353 5. Movements of the Thumb. — The movements of wliich tlie thumb is capable are flexion and extension (occurring at the carpo-metacarpal, metacarpo-phalangeal, and inter-phalangeal joints) ; abduction and adduction, together with circumduction (occurring at the carpo-metacarpal joint). The muscles and their respective actions are given in the following table : — The characteristic features of the movements of the upper limb are their range and refinement. The hand, in addition to its intrinsic powers, can be moved through a wide range and in several planes by the muscles acting on the wrist and radio-ulnar joints ; this range is increased by the fore and aft movements at the elbow-joint, and the extensive movements of which the shoulder and clavicular joints are capable. The result is that the hand can be brought into a position to cover and guard any portion of the body. The precision and refinement of movement is made possible by the co- ordinate movements of the various muscles acting upon the several joints, so that actions can be performed (as raising the food to the mouth) in which all the articulations of the limb are brought into play ; while others (such as writing) are possible by movements at the joints of the wrist and fingers along with fixation of the elbow-joint. THE LOWER LIMB. FASCI>E AND IVIUSCLES OF THE THIGH AND BUTTOCK. FASCIA. The superficial fascia of the thigh and buttock is continuous above with the fascia of the abdomen and back, medially with that of the perineum, and below with that of the leg. It presents noticeable features in the buttock and groin. In the buttock the superficial fascia is of considerable thickness, and is usually loaded with fat, whereby it assists in forming the contour of the buttock and the fold of the nates. In the groin it is divisible into two layers : a superficial fatty layer, continuous with a similar layer on the front of the abdominal wall above, and over the perineum medially, and a deeper membranous layer, which is attached above to the medial half of Poupart's ligament (Lig. inguinale Pouparti), and to the deep fascia of the thigh just below the lateral half of that ligament. Medially it is attached to the pubic arch, and below the level of Scarpa's triangle (trigonum femorale) it blends inseparably with the superficial fatty layer. The separation of these two layers of the superficial fascia is occasioned by the presence between them of the femoral and inguinal lymphatic glands, the large saphenous vein and its tributaries, and some small arteries. The attachment of the deeper layer of the fascia to the pubic arch and Poupart's ligament cuts off the superficial tissues of the thigh from the perineum and the abdominal wall, and prevents the passage down the thigh of fluid collected in the perineum or beneath the fascia of the abdominal wall. The deep fascia or fascia lata forms a tubular investment for the muscles and vessels of the thigh and buttock. It is firmly attached above to the iliac crest, the 354 THE MUSCULAE SYSTEM. great sacro-sciatic (sacro-tuberous) ligament, the ischium, the pubic arch, the pubic symphysis and crest, and Poupart's ligament. In the lower part of the thigh it forms the intermuscular septa ; and in relation to the knee, it is continuous with the deep fascia of the leg, gains attachment to the patella, the condyles of the tibia and the head of the fibula, and forms the lateral ligaments of the patella. On the front of the thigh the deep fascia is thick and strong. It is pierced by numerous openings for vessels and nerves, the most important of which is the saphen- ous opening (fossa ovalis) for the passage of the saphenous vein. A femoral hernia passes through this opening to reach the groin and anterior abdominal wall. It is an Linea alba "^ ~ — ""~' Lig. fundiforme penis Intercrural fibres Dorsal vein of penis Obliquus Externus abdominis Anterior superior iliac spine External oblique aponeurosis Superficial circum- flex iliac artery Intercrural fibres ( Attachment of mem- ■ - branous layer of ( superficial fascia Poupart's inguinal ligament Superficial inferior epigastric artery Superior external pudendal artery Femoral lymphatic gland Large saphenous vein (internal) Fig. 274. — Superficial Anatomy of the Left Groin. oval opening of variable size situated just below the medial half of Poupart's ligament, and immediately in front of the femoral vessels. It is covered by the superficial fascia, and by a special layer of fascia, the cribriform fascia, a thin perforated lamina, attached to the margins of the opening. The lateral edge of the opening (margo falciforuiis) is formed by the margin of the iliac portion of the fascia lata, which is attached above to the iliac crest and Poupart's ligament ; the medial edge is formed by the puhic portion of the fascia lata (fascia pectinea), which is continued upwards behind the femoral sheath, over the adductor longus and pectineus muscles to the ilio-pectineal line and the capsule of the hip-joint. These two layers of the fascia lata are continuous at tlie lower concave margin of the saphenous opening, forming its inferior comu. As they pass upwards towards the pelvis they occupy different planes, the iliac portion being in front of the sheath of the femoral vessels, while the pectineal fascia is Vjehind it. The superior comu of the saphenous opening, placed in front of the sheath, is derived solely from the iHac portion of the fascia lata. FASCIA AND MUSCLES OF THE THIGH AND BUTTOCK. 355 It forms a strong triangular band of fascia known as the falciform ligament, attached above to the medial half of Poupart's ligament. It has an important share in directing the course of a femoral hernia upwards on to the abdominal wall. On the medial side of the thigh the fascia lata is thin where it covers the adductor muscles. At the knee it is associated with the tendons of the vasti muscles, and forms the lateral ligaments of the patella, attached to the borders of the patella and to the condyles of the tibia. On the lateral side of the thigh it forms the ilio-tibial band ( tractus ilio-tibialis) — a broad thick layer of fascia which is attached above to the iliac crest, and receives the insertions of the tensor fasciae lat*, and part of the glutajus maximus muscles ; it is attached below to the capsule Obliquus externts abdominis (reflected) Spermatic cord.. Intercolumnar fascia- Obliquus externus abdominis Obmquus INTERNDS abdominis .\nterior superior iliac spine Transversus abdominis Obliquus internus ABDOMINIS (reflected) Aponeurosis of obliquus externus (reflected) Abdominal inguinal ring Spermatic cord and infundibuliform fascia Fascia transversalis Conjoint tendon ■(Inguinal aponeurotic falx) Saphenous opening Large saphenous vein Fig. -The Dissection of the Left Inguinal Canal. of the knee-joint and the lateral condyle of the tibia. A strong band of fascia continued upwards from the iho-tibial band beneath the tensor fascise latae muscle joins the tendon of origin of the rectus femoris and the capsule of the hip-joint. On either side of the thigh above the knee an intermuscular septum is formed. The lateral intermuscular septum extends medially from the ilio-tibial band to the lateral epicondylic line and linea aspera of the femur, and gives attachment to the vastus lateralis (externus) and vastus iutermedius (crureus) in front, and the short head of the biceps behind. The medial intermuscular septum in the lower third of the thigh is associated with, and to a large extent represented by, the tendon of insertion of the adductor magnus muscle. It is also related to the fascia which envelops the adductor muscles, and forms the sheaths for the sartorius and gracihs muscles. In the middle third of the thigh the fascia under the sartorius is greatly thickened by transverse fibres and binds together the vastus medialis (internus) and adductor 356 THE MUSCULAK SYSTEM. longus and adductor magnus muscles. This layer of fascia roofs over the femoral vessels in their course through Hunter's canal (canalis adductorius Hunteri). The fascia lata of the buttock is thick in front where it covers and gives origin to the glutieus medius, thinner behind over the glutaius maximus, at the upper border of which it splits to enclose the muscle. It is thickened over the greater trochanter, where it forms the insertion of the greater part of the latter muscle. On the back of the thigh and over the popliteal space the fascia is strengthened by transverse fibres derived from the hamstring muscles. The popliteal fascia forming the roof of the popliteal space is specially thick, and is usually pierced by the small saphenous vein. Femoral Sheath. — This is a conical membranous investment, derived from the fascial lining of the abdominal cavity, the fascia transversalis in front and the fascia iliaca behind, prolonged along the femoral vessels in their passage behind Poupart's ligament into Scarpa's triangle. The sheath is about an inch and a half in length, and is divided into three compartments — a lateral space for the artery, an intermediate space for the vein, and a medial channel containing lymphatics and fat, and named the femoral canal. The wall of this channel is known as the femoral sheath. This canal is the passage through which a femoral hernia enters the thigh. Its upper limit is the femoral ring, bounded in front by Poupart's inguinal ligament, behind by the origin of the pectineus muscle from the pubis, medially by Gimbernat's ligament (lig. lacunare), and laterally by the femoral vein. In front of it the fascia transversalis forming the sheath is thickened to form the deep femoral arch. The part of Poupart's ligament in front of the ring is called the superficial femoral arch. The deep epigastric artery ^ separates the ring from the internal abdominal ring. The canal ordinarily contains fat which is continuous above with the extra- peritoneal tissue. The ring is filled by a plug of fat or a lymphatic gland, con- stituting the femoral septum (septum femorale Cloqueti). The femoral canal ends behind the saphenous opening, covered by the cribriform fascia, while the falciform ligament crosses over it and conceals its upper portion. The course of a femoral hernia is determined by this band. The hernia descends through the femoral ring, pushing the femoral septum before it ; after passing through the femoral canal, it is directed forwards through the saphenous opening. The anterior part of the hernia being pressed upon and retarded by the femoral arches and by the falciform ligament, the posterior part pushes onwards, hooks round the falciform ligament, and is directed upwards over Poupart's ligament. The coverings of a femoral hernia, in addition to peritoneum and extra-peritoneal tissue (femoral septum), are femoral sheath, cribriform fascia, superficial fascia, and skin. MUSCLES OF THE THIGH AND BUTTOCK. The muscles of the thigh and buttock are divisible into four main groups by their situation, action, and nerve-supply. On the front of the thigh are the quadriceps femoris, the sartorius, ilio-psoas, and pectineus muscles ; on the inner or medial side of the thigh are the adductor muscles; in the region of the buttock, the glutsei and rotators of the hip-joint ; and on the back of the thigh, the hamstring muscles. THE MUSCLES ON THE FRONT OF THE THIGH. The chief muscle on the front of the thigh is the quadriceps femoris, which occupies the space between the tensor fasciae latse and ilio - tibial band laterally, and the sartorius medially. The sartorius crosses the thigh obliquely ; it separates the quadriceps femoris from the adductor muscles ; it forms in the upper third of the thigh the lateral boundary of Scarpa's triangle, and in the middle third of the thigh, the roof of Hunter's canal. The ilio-psoas, passing into the thigh beneath Poupart's ligament, assists along with the pectineus and adductor muscles in forming the floor of Scarpa's triangle (trigonum femorale). The sartorius. a long strap-like muscle, arises from the superior anterior spine of the ilium and half of the notch below it (Fig. 276, p. 357). It passes down the thigh to the medial side of the knee, where it is inserted by aponeurotic fibres ^ Deep ejiigastric = inferior epigastric artery (B.N. A.). THE MUSCLES ON THE FEONT OE THE THIGH. 357 into the medial surface of the shaft of the tibia just below the medial condyle, and by its borders into fascial expansions which join the capsule of the knee-joint, the internal lateral (tibial collateral) ligament, and the fascia lata of the leg (Fig. 279, p. 359). The sartorius is superficial in its whole extent. Its upper third forms the lateral boundary of Scarpa's triangle ; its middle third forms the roof of Hunter's canal (canalis adductorius) ; and its lower third, in contact with the medial side of the knee,is separated from the tendon of the gracilis muscle by the large saphenous nerve and a branch of the anastomotica magna artery.^ A bursa lies be- neath the tendon at its insertion. The quadriceps femoris is composed of four muscles — the rectus femoris, vastus lateralis (externus), intermedins (crureus), and vastus medialis (internus). The rectusfemoris is superficial except at its origin, which is covered by the glutsei, sartorius, and tensor fascipe latse muscles. The vasti lie on either side of the rectus muscle, the vastus lateralis being partially concealed by the tensor fasciae lat?e and ilio-tibial band, the vastus medialis by the sartorius muscle. The vastus intermedins en- velops the femur, and is concealed by the other muscles. The rectus femoris has a double tendinous origin. (1) The straight head arises from the anterior inferior spine of the ilium (Fig. 282," p. 362); (2) the reflected head springs from a rough groove on the dorsum ilii just above the highest part of the acetabulum (Fig p. 362). A bursa lies beneath this of origin. The two heads, bound together and connected to the capsule of the hip- joint by a band of fascia derived from the under surface of the tensor fasciae latse (ilio- tibial band), give rise to a single tendon which extends for some distance on the front of the muscle, and from which the muscular fibres arise. The lauscular fibres springing from this tendon, and also from a median septal tendon, present a bipennate arrange- ment, and end below in a broad tendon which passes upwards for some distance along the posterior surface of the muscle, ^ Anastomotica magna artery = arteria genu suprema (B.N. A,). 282, head ri:N90R KASCI.*: Pectineijs Adductor LONGUSi Sartorius Uio-tibial band Gracilis Adductor MAGNUS Vastus lateralis (externus) Rectus femoris Vastus medialis (internus) Tendon of rectus femoris Ligamentum PATELLA Fig. 276. — The Muscles of the Front OF THE Right Thigh. This 358 THE MUSCULAK SYSTEM. Piriformis (insertion) tendon gradually narrows towards the knee, and spreading out again, is inserted into the upper border of the patella. It receives laterally parts of the insertions of the vasti muscles (lateral and medial), and on its deep surface is joined by the insertion of the vastus iutermedius (crureus). A bursa, which communicates with the synovial membrane of the knee-joint, lies beneath its tendon in front of the lower end of the shaft of the femur. The vastus lateralis has an origin, partly fleshy, partly membranous, from (1) the cap- sule of the hip-joint, (2) the tubercle of the femur, (3) a concave surface on the front of the shaft of the bone medial to the greater tro- chanter, (4) the lower border of the greater tro- chanter, (5) the lateral margin of the gluteal ridge of the femur and the tendon of the glutseus maximus, (6) the upper half of the linea aspera, and (7) the fascia lata and lateral intermuscular septum (Fig. 277, p. 358). It forms a thick, broad muscle directed downwards and forwards, and is inserted by a broad membranous tendon into (1) the lateral border of the tendon of the rectus femoris, (2) the upper and lateral border of the patella, and (3) the capsule of the knee- joint, and the external lateral (fibular col- lateral) ligament of the patella. A bursa intervenes between it and the membranous insertion of the glutseus maximus. The vastus medialis is larger than the vastus lateralis and has a more extensive origin, from (1) the lower two-thirds or more of the spiral (anterior intertrochanteric) Vastus lateralis (externus) (origin) Fig. 277.- TERIOR -Muscle-Attachments to the An- sueface of the upper part of THE Left Femur. Vastus mediai.is Saphenous nerve (Internal)^^ Femoral vessels. Sartorius Adductor lonous Adductor magnus Gracilis Rectus femoris Vastus lateralis Vastus intermedius (Crureus) Femur Biceps Femoris (short hear!) Semimembranosus BicEi'S Femoris (long head) Semitendinosus Sciatic nerve (Great) Fio. 278. — Transverse Section of the Thigh (Hunter's Canal). line, the linea aspera, and the upper two-thirds of the line leading from the linea aspera to the medial condyle of the femur ; (2) the membranous expansion of the fascia lata which lies beneath the sartorius and forms the roof of the adductor THE MUSCLES ON THE EEONT OF THE THIGH. 359 Semi-membranosus (insertion) amentum patellse (in&ertiou) Popliteus Attachment of internal lateral ligament of the knee (tibial collateral) Gracilis (insertion) Semi-tendinosus (insertion) canal of Hunter : and (3) the medial intermuscular septum and the tendon of the adductor magnus (Figs. 277, p. 358, and 281, p. 361). From its origin the muscle is directed downwards and laterally towards the knee ; it is inserted by a strong aponeurotic tendon into (1) the medial border of the rectus tendon ; (2) into the upper and medial border of the patella ; and (3) the capsule of the knee-joint and the internal lateral ligament of the patella. The muscle conceals the medial side of the shaft of the femur and the vastus inter- medialis, with which it is closely incorporated in its lower two-thirds. The vastus intermedius muscle (crureus) arises by fleshy fibres from (1) the upper two-thirds of the shaft of the femur on the anterior and lateral surfaces, (2) the lower half of the lateral lip of the linea aspera and the upper part of the line lead- ing therefrom to the lateral condyle, and (3) a corresponding portion of the lateral intermuscular septum (Fig. 277, p. 358). For the most part deeply placed, the muscle is directed downwards to an insertion into the deep surface of the tendons of the rectus and vasti muscles by means of jfibres which join a mem- branous expansion on its surface. It is closely adherent to the vastus lateralis muscle in the middle third of the thigh ; it is inseparable from the vastus medialis below the upper third. In the lower third of the thigh it con- ceals the articularis genu muscle (sub- crureus), a bursa, and the upward pro- longation of the synovial membrane of the knee-joint. The articularis genu (subcrur- eus) consists of a number of separate bundles of muscular fibres arising be- neath the vastus intermedius from the lower fourth of the front of the femur, and inserted into the synovial mem- brane of the knee-joint. The four elements composing the quadriceps femoris muscle have been traced in their convergence to the patella. Their ultimate insertion is into the tuberosity of the tibia (Fig. 279, p. 359), by means of the ligamentum patellae, and the vasti muscles are in addition connected with the lateral ligaments of the patella. The patella, indeed, is in one sense a sesamoid bone formed in the tendon of the muscle, the ligamentum patellse being the real tendon of insertion, and the lateral ligaments fascial expansions from its borders. The insertion of the muscle forms the front of the capsule of the knee-joint. The ilio-psoas muscle is a compound muscle, consisting of two elements, — psoas (major and minor), connecting the femur and pelvic girdle to the axial skeleton ; and another element, the iliacus, extending between the innominate bone and the femur. The muscles chiefly occupy the posterior wall of the abdomen and false (large) pelvis, their insertions only appearing in the thigh below Poupart's ligament, in the lateral part of Scarpa's triangle (trigonum femorale). The psoas magnus (m. psoas major) is a large piriform muscle, which has an extensive origin by fleshy fibres from the vertebral column in the lumbar region. It arises from (1) the intervertebral discs above each lumbar vertebra, and the adjacent margins of the vertebree — from the lower border of the 12th thoracic to the upper border of the 5th lumbar vertebra; (2) it arises also from four aponeurotic arches which pass over the sides of the bodies of the first four lumbar vertebrae ; and (3) it has an additional origin posteriorly from the transverse Fig. 279. — Muscle-Attachments to the medial side OF the upper part op the left Tibia. 360 THE MUSCULAR SYSTEM. processes of all the lumbar vertebrae. The fibres form a fusiform muscle directed downwards over the pelvic brim and beneath Poupart's ligament, ending in a tendon which is inserted into the apex of the lesser trochanter of the femur (Fig. 281, p. 361). A bursa, which may be continuous with the synovial cavity of the hip-joint, separates the tendon from the pubis and the capsule of the hip-joint. The psoas parvus (m. psoas minor) is often absent (40 per cent). It arises Opening of the vena cava CEsoplia_' Central tendon (middle part) Central tendon (right ijart) DiAPHKAGM, COSTAL FIBRES Internal arcuate ligament External arcuate ligament End of last rib- Last thoracic ner\e- Ant. layer of lumbar fascia. Lumbar fascia . Ilio-h}-pogastric_ Lumbar vessels and sympa- thetic communicating nerves" Ilio-lnguinal- QUADKATCS LUJIBORDJI - External cutaneous nerve - PSOA.S MAJOR j Iliaccs* Lumbo-sacral cord- Genito-crural nerve (genito-femoral) Anterior crural nerve (femoral) Obturator nerve Great sciatic nerve Diaphragm, right lateral cr0s Middle arcuate ligament ^ Aortic opening Central tendon (left part) Diaphragm, left lateral crus Last thoracic nerve End of last rib Lumbar nerve I. Ilio-hypogastric Lumbar nerve IL -Ilio-inguinal Quadratus lumborum Lumbar nerve IIL _^_^ Genito-crural nerve li V\ (genito-femoral) ' — ' — Lumbar nerve IV. Lumbo-sacral cord ^\ External cutaneous nerve '^ '^ Anterior crural (femoral) iierxe -1 — , - . ..— Obturator nerve Gieat sciatic nerve Obturator nerve Addoctor longus (origin) Adductor brevis (origin Gracilis (origin) I i Adductor magncs (origin) I I Pectineus (cut) I Superticial branch of obturator nerve I Deep branch of obturator nerve Obturator extf.bnus Fig. 280.— View of the PosTEnioK Abdominal Wall, to show the Muscles and the Nerves of THE Lumbo-Sacbal Plexus. from the intervertebral disc between the last thoracic and first lumbar vertebrae, and from the contiguous margins of these vertebrae. The muscle is closely apposed to the anterior surface of the psoas major. It forms a slender fleshy belly, and is inserted by a narrow tendon into the middle of the ilio-pectinoal Line and the ilio- pectineal eminence, its margins blending with the fascia covering the psoas major. Jjiaphragm Note. — Arcuate ligaments, internal and external = medial and lateral lumbocostal arches. Lateral and medial crura = lateral and intermedial crura. Middle arcuate ligament = medial crus. (B.N. A.) THE MUSCLES ON THE INNER SIDE OF THE THIGH. 361 Piriformis (insertion) Glutii-us medius (insertion) Obturator intemus and gemelli (insertion) Obturator externus (insertion) Qiiadratus femoris (insertion) llio-psoas (insertion) The iliacus muscle arises in the false (large) pelvis by fleshy fibres, mainly from a horseshoe-shaped origin around the margin of the iliac fossa ; it has additional origins also from the ala of the sacrum, the anterior sacro-iliac, lumbo-sacral, and ilio- lumbar ligaments, and outside the pelvis, from the upper part of the capsule of the hip- joint (ilio-femoral band). It is a fan-shaped muscle, its fibres pass- ing downwards over the hip-joint towards the lesser trochanter of the femur. Lying lateral to the psoas muscle, it passes through Scarpa's triangle, and is inserted by fleshy fibres (1) into the lateral side of the tendon of the psoas major; (2) into the concave anterior and upper surfaces of the lesser trochanter ; and (3) into the shaft of the femur below the lesser trochanter for about an inch (Fig. 281, p. 361) ; and (4) by its most lateral fibres into the capsule of the hip-joint. These fibres are often separate, forming the iliacus minor, or ilio-capsularis. The pectineus muscle arises by fleshy fibres from (1) the sharp anterior portion of the ilio- pectineal line of the pubis, and the triangular surface of the pubic bone in front of this (Fig. 282, p. 362), (2) the femoral surface of Gimbernat's ligament, and (3) the pubic portion of the fascia lata which covers it. Forming a broad muscular band, occupying the floor of Scarpa's triangle, medial to the ilio-psoas, it is inserted by a thin flat tendon about two inches in length into the upper half of the pectineal line, leading from the back of the lesser trochanter of the femur towards the linea aspera ; its lower attachment being placed in front of the insertion of the adductor brevis muscle (Fig. 282, p. 362). The muscle may be occasionally divided into medial and lateral parts, the former innervated by the obturator, the latter by the anterior crural nerve.^ Glutseus maxinius (insertion) Adductor magnus (insertion) Adductor brevis (insertion) Pectineus (insertion) Vastus medialis (origin) Fig. 281. — Muscle-Attachments to the Posterior Aspect OF the Upper Part of the Left Femur. THE MUSCLES ON THE MEDIAL SIDE OF THE THIGH. The muscles on the medial side of the thigh include the adductors of the femur, — the adductor longus, adductor brevis, and adductor magnus; the gracilis, and the obturator externus. The gracilis is superficially placed along the medial side of the thigh. The adductor muscles, occupying the space between the hip bone and the femur, are placed on different planes, the adductor longus being in the same plane as the pectineus and lying superficially in Scarpa's triangle ; the adductor brevis, on a deeper level, is in contact with the obturator externus, and along with it is largely concealed by the pectineus and adductor longus ; the adductor magnus, the largest and deepest of these muscles, is in contact with the other adductors and the sartorius anteriorly, while its posterior surface is in relation to the hamstring muscles on the back of the thigh. ^ Anterior crural nerve = femora! uerve (B.N. A). 562 THE MUSCULAE SYSTEM. The gracilis muscle is a long flat band placed on the medial side of the thigh and knee. It arises by a tendon from the lower half of the edge of the symphysis pubis, and for a similar distance along the border of the pubic arch (Fig. 282, p. 362). Its flattened belly passes down on the medial side of the thigh to the knee, to end in a tendon, placed between the sartorius and semitendinosus, which expands to be inserted into the medial side of the shaft of the tibia just below the medial condyle, behind the sartorius, and above and in front of the semitendinosus (Fig. 279, p. 359). It is separated from the sartorius tendon by a bursa, and beneatli its tendon is another bursa common to it and the semitendinosus. The adductor longus is a triangular muscle occupying Scarpa's triangle and the floor of Hunter's canal. It arises from the anterior surface of the body of - Rectus femoris (straight head of origin) .Rectus femoris (reflected head of origin) . Attachment of ilio-femoral band Pyramidalis abdominis (origin) \Rectus abdominis (origin) Gracilis (origin) Adductor brevis (origin) Senii-membranosus (origin) Quadratus femoris (origin) Biceps and semi-tendin- \ \ \ \ osus (origin) Fig. 282. — Mu.scle- Attachments to the outer surface of the Right Pubis and Ischium. the pubic bone in the angle between the crest and symphysis (Eig. 382, p. 362). Extending downwards and laterally, it is inserted into the middle two-fourths of the medial lip of the linea aspera in front of the adductor magnus. The adductor brevis is a large muscle which arises from an elongated oval surface on the front of the body and upper part of the inferior ramus of the pubic bone, surrounded by the other muscles of this group (Fig. 282, p. 362). Directed downwards and laterally, the muscle expands, to be inserted by a short aponeurotic tendon, behind the insertion of the pectineus, into the lower two-thirds of the line leading from the lesser trochanter of the femur to the linea aspera, and to the upper fourth of the linea aspera itself (Fig. 281, p. 361). The adductor magnus, the largest of the adductor group, is a roughly tri- angular muscle arising mainly by fleshy fibres by a curved origin from the lower part of the lateral border and a large portion of the adjoining inferior surface of the ischial tuberosity, from the edge of the inferior ramus of the ischium, and from the THE MUSCLES ON THE INNER SIDE OF THE THIGH. 363 anterior surface of the inferior ramus of the pubic bone, its most anterior fibres arising between the obturator externus and adductor brevis (Figs. 282, p. 362). Its upper fibres are directed horizontally and laterally from the pubic bone towards the upper part of the femur ; the lowest fibres are directed downwards from the ischial tuberosity to the medial condyle of the femur ; while the intermediate fibres radiate obliquely laterally and downwards. The muscle is inserted by tendinous fibres (1) into the space below the insertion of the quadratus femoris, above the linea aspera ; (2) into the whole length of the linea aspera ; (3) into the medial epicondylic line of the femur; (4) into the adductor tubercle on the medial condyle of the femur; and (5) into the medial intermuscular septum (Fio-. 281, p. 361). The part of the muscle attached to the space above the linea aspera is often separated from the rest as the adductor minimus. The attachment Obturator nerve Pubis Psoas major Branch to hip-jo Deep brai Superficial braiiLli Descending muscular branches Pectinel Ascending branch to obturatoi extern U-? Medial (internal) circumflex artery Adductor lonous Adductor brevis 'IRIFORMIS GlUT,«1'S MAXIMUS Pelvic fascia ObTURATOE 1NTERNC3 Cutaneous branch Obturator externus schium Ascending branch of medial (in- ternal) circumflex artery of femur Quadratus femoris Medial circumflex artery Descending muscular branches Adductor maonus Blanch to knee-joint Branch to femoral artery Gracilis Fig. 283.— Scheme of the Course and Distribution of the Plight Obturator Ner\t;. of the muscle to the supracondylic ridge is interrupted for the passage of the femoral vessels to the popliteal space. The attachment to the medial condyle is by means of a strong tendon which receives the fibres arising from the ischium (the part of the muscle associated with the hamstring group). This tendon is closely connected with the internal lateral (tibial collateral) Hgament of the knee-joint. The obturator externus is placed deeply under cover of the previous muscles. It is a fan-shaped muscle lying horizontally in the angle between the hip bone and the neck of the femur. It arises from the surfaces of the pubic bone and ischium, which form the inferior half of the margin of the obturator foramen, and from the corresponding portion of the superficial surface of the obturator membrane (Figs. 282, p. 362, and 283, p. 363). Its fibres converge towards the great trochanter, and end in a stout tendon which, after passing below and behind the hip-joint, is inserted into the trochanteric fossa of the greater trochanter of the femur (Figs. 281 p. 361, and 289, p. 367). Scarpa's triangle (trigonum femorale) is a large triangular space on the front of the thigh in its upper third, which contains the femoral vessels in the upper part 364 THE MUSCULAK SYSTEM. of their course and the anterior crural nerve.^ It is bounded above by Poupart's ligament, laterally by the sartorius, and medially by the medial border of the adductor longus muscle. Its floor is formed laterally by the ilio- psoas, and medially by the pectineus, adductor longus, and a small part of the adductor brevis. Hunter's canal (canalis adductorius) occupies the middle third of the medial side of the thigh, and contains the femoral vessels in the lower part of their course. It is bounded superficially by the sartorius, under which is a dense fascia derived from the fascia lata, binding together the vastus medialis, which forms the lateral wall of the canal, and the adductors, longus and magnus, which form the I medial wall or floor of the canal. ■* Besides the femoral vessels and their sheath, the canal contains the large saphenous nerve. Great sacro- sciatic liga- ment Gluteus MAxmus Obturator intern ds Biceps and semitendin- OSUS Semimem- branosus quadratus FEMORIS IA.DDUCTOR jVIAGNUS THE MUSCLES OF THE BUTTOCK. Gracilis This group includes the three gluteei muscles, the tensor fascise latae, piri- formis, obturator internus and gemelli. Biceps ^nd quadratus femoris. (short head) 'j'^-^g glutsBus maximus and tensor fasciae latse muscles are in the same plane, invested by envelopes of the fascia lata. The glutceus medius, partially covered by •Oong'head) the glutseus maximus, conceals the glutaeus minimus ; while the piriformis, obturator internus, gemelli, and quadratus femoris, intervene between the glutseus maximus and the back of the hip-joint. The glutseus maximus is a large quadrilateral muscle, with a crescentic origin, from (1) a portion of the area on the dorsum ilii above the superior curved line (Fig. 285, p. 365;; (2) the tendon of the sacrospinal muscle ; (3) the posterior surface of the sacrum and coccyx (Fig. 311, p. 390); and (4) the posterior surface of the great sacro- sciatic liga- ment. The fibres which form its upper and lateral border take origin directly from the fascia lata which envelops the muscle. The muscle forms a large fleshy mass, whose fibres are directed obHquely laterally over the buttock, invested by the fascia lata, and are inserted by short tendinous fibres, partly into the fascia lata over the great trochanter of the femur (joining the ilio-tibial band), and partly into the ^ Anterior crural nerve = femoral nerve (B.N. A.). Semimem- branosus Fig. 284.- -Deki' Muscles on the Back op THE RtcHT THICH. THE MUSCLES OF THE BUTTOCK. 365 gluteal ridge (Fig. 281, p. 361). The fascia lata receives the insertion of the whole of the superficial fibres of the muscle and the upper half of the deep fibres. The lower half of the deep portion of the muscle is inserted for the most part into the gluteal ridge ; but the lowest fibres of all are inserted into fascia lata, and are thereby connected with the lateral intermuscular septum and the origin of the short head of the biceps. The gliita3us maximus is the coarsest and heaviest muscle in the body. By its weight it helps to form the fold of the nates. It is superficial in its whole extent. The gluteus medius is visible at its upper border, covered by the fascia lata ; at its lower border the hamstring muscles and great sciatic nerve appear on their way down the thigh. Three bursse are beneath it : one (not always present) over the tuberosity of the ischium (tuber ischiadicum), a second over the lateral side of the greater tro- chanter, and a third over the vastus lateralis. The filjres of the glutseus maximus arising from the coccyx may form a separate muscle (agitator caudse). The tensor fasciae latae arises from the iliac crest and the dorsum ilii just Obliquus exteruus abdominis (iiisfrtiun) Glutii'US maximus (origin) Tensor fascise latse (origin) Savtorius (origin) Rectus femoris (reflected head of ou^in) Gemellus superior (origin) Gemellus inferior (origin). Semimembranosus (origin). Biceps and semitendinosus (origin) Adductor magnus (origin) Quadratus femoris (origin) Obturator externus (origin) Adductor magnus (origin) Fig. 285. — Muscle- Attachmexts to the Right Dorsum Ilii and Tubek Ischiadicum. lateral to the anterior superior spine, and from the fascia covering its lateral surface (Fig. 285, p. 365). Invested like the glutseus maximus by the fascia lata, it is inserted below the level of the great trochanter of the femur into the fascia, which forms the ilio-tibial band (p. 355). The muscle is placed along the anterior borders of the glutseus medius and glutseus minimus. The g-lutseus medius arises from (1) the dorsum ilii, between the iliac crest and superior (posterior) curved line above and the middle curved line below (Fig. 285, p. 365), and (2) the strong fascia lata covering its surface anteriorly. It is a fan-shaped muscle, its fibres converging to the greater trochanter, to be inserted by a strong, short tendon into the postero-superior angle of the greater trochanter, and into a well-marked diagonal line on its lateral surface (Figs. 277, p. 358, 281, p. 361). A bursa is placed beneath the tendon at its insertion. The glutseus minimus arises, under cover of the glutseus medius, by fleshy fibres from the dorsum ilii between the middle (anterior) and inferior curved lines (Fig. 285, p. 365). This muscle is fan-shaped and its fibres converge to the antero-superior 366 THE MUSCULAE SYSTEM. Piriformis (insertion) Glutrens medius I (insertion) angle of the greater trochanter, to be inserted into the anterior surface of the trochanter, and sometimes also into the front part of the upper border (Figs. 277, p. 358, and 289, p. 367). It is also inserted into the capsule of the hip-joint. A bursa is placed beneath the tendon in front of the greater trochanter. The piriformis is one of the few muscles connecting the lower limb to the axial skeleton. It arises (1) within the pelvis from the pedicles of the second, third, and fourth sacral vertebrae, and from the adjacent part of the bone lateral to the anterior sacral foramina. Passing out through the greater sacro-sciatic foramen, it receives an origin from (2) the upper margin of the greater sciatic notch of the ilium, and (3) the pelvic surface of the great sacro-sciatic (sacro- tuberous) ligament. In the buttock it forms a rounded tendon, which is inserted into a facet on the upper border and medial aspect of the greater trochanter of the femur (Figs. 286, p. 366, 288, p. 367, and 289, p. 367). The piriformis, at its origin, lines the pos- Obturator internus and gemelli (insertion) Obturator externus (insertion) Quadratus femoris (insertion) ^ Ilio-psoas (insertion) Glutseus maximus (insert!' Adductor magnus (insertion) Adductor brevis (insertion) _ Pectineus (insertion) Vastus medialis (internus) Fig. 286. — Muscle -Attachments to the Posterior Aspect of the Upper Part OF THE Left Femur. The lumbar triangle OF Petit Fascia lata Adductor maonus Semimembranosus Semitendinosus Ciroat sciatic nerve Biceps (long " ead) Fig. 287. — The Right Glutaius Maximus Muscle. terior wall of the pelvis. In the buttock it is covered by the glutseus maximus,^ and lies behind the cap- sule of the hip -joint, be- tween the glutseus medius and superior gemellus. The obturator inter- nus arises on the pelvic aspect of the hip bone, from (1) the whole of the margin of the obturator foramen (except the ob- turator notch); (2) the surface of the obturator membrane; (3) the whole of the pelvic surface of the hip bone behind and above the obturator foramen ; and (4) the parietal pelvic fascia covering it medi- ally. It is a fan -shaped muscle, and its fibres con- verging to the lesser sacro- sciatic foramen, give rise to several tendons united THE MUSCLES OF THE BUTTOCK. 367 Internal pudic nerve Nerve to obturator intern us Gracu ADDrCTOR MAG Hamstring mus' (bic Superior gluteal nerve Gldt^eus medics (cut) Inferior gluteal nerve Piriformis Obturator internos AND gemelli Obturator externus quadratus femoris Great sciatic )ier\'e (and subdivisions) Small sciatic nerve (posterior cutaneous of thigli) GUT.EUS MAXIMUS (insertion) Adductor magnus together, which hook round the margin of the foramen (a bursa intervening), and after passing over the back of the hip-joint, are inserted into a facet on the medial surface of the greater" trochanter of the femur above the trochanteric fossa (Figs. 288, p. 367, and 289, p. 367). In the pelvis the muscle oc- cupies the lateral wall, covered by the parietal (obturator) layer of pelvic fascia, which separates it from the pelvic cavity above and the ischio-rectal fossa below. In the buttock the tendon is embraced by the gemelli muscles which are attached to its upper and lower margins. The gemelli muscles form acces- sory portions of the obturator internus. The superior gemellus arises from the gluteal surface of the ischial (sciatic) spine(Fig. 285,p.36o). It is inserted into the upper margin and sup- erficial surface of the tendon of the obtur- ator internus muscle. The gemellus inferior arises from the upper part of the gluteal surface of the ischial tuberosity (Fig. 285, p. 365). It is inserted into the lower margin and __ superficial aspect of Obturator internus and gemelli (insertion) ^^^^^^^^^^^^ ^j_^g tcudon of the ob- turator internus. The quadratus femoris arises from the lateral margin of the ischial tuberosity (tuber ischiadicum) (Figs. 284, p. 364, and 285, p. 365), and is in- serted into the quad- rate tubercle and quadrate line of the femur (Fig. 286, p. 366). The muscle is concealed by the glutseus maximus and the hamstring muscles. Its deep surface is in contact with the obturator externus muscle and the lesser trochanter of the femur, a bursa intervening. The muscle is not infrequently fused with the adductor magnus. Fig. 288. — The Muscles and Nerves of the Eight Buttock. The jlutseus maximxis is reflected show the and the glutaeus medius is cut in part to arlutaiiis minimus. Glutfeus minimu (insert Piriformis (insertion) Fig Obtuiator e\tei nus (insertion) 289. — Muscle - Attachments to the Upper Aspect of the Greater Trochanter of the Left Femuk. 868 THE MUSCULAK SYSTEM. THE MUSCLES ON THE BACK OF THE THIGH. The Hamstring Muscles. The muscles comprised in this series include the biceps, semitendinosus, and semimembranosus. A part of the adductor magnus, already described, also belongs morphologically to this group. They occupy the buttock and back of the thigh, and diverge at the knee to bound the popliteal space. The origins of the muscles are concealed by the gluteus maximus. In the back of the thigh, enveloped by the fascia lata, they are placed behind the adductor magnus, the semitendinosus and semimembranosus medially, the biceps laterally. The two former muscles help to form the medial boundary of the popliteal space, of which the biceps is a lateral boundary. The biceps femoris has a double origin. (1) Its long head arises by means of a ^ Obliquus extenius abdominis (insertion) Tensor fascite lat.e Gluticus maximus (origin) Rectus femoris (reflected head of origin) Gemellus superior (origin) Gemellus inferior (origin) Semimembranosus (origin) Biceps and semitendinosus (origin) Quadratus femoris (origin) Obturator externus (origin) Adductor magnus (origin) Adductor magnus (origin)' Fig. 290. — Muscle- Attachments to the Right Dorsum Ilii and Tuber Ischiadicum. tendon, in common with the semitendinosus, from the lower and medial facet upon the tuberosity of the ischium (Figs. 284, p. 364, and 290, p. 368) and from the great sacro-sciatic (sacro-tuberous) ligament. This head, united for a distance of two or three inches with the semitendinosus, forms a separate fleshy mass, which extends to the lower third of the thigh, to end in a tendon joined by the short head of the muscle. (2) The short head arises separately from (1) the whole length of the lateral lip of the linea aspera and the upper two-thirds of the lateral epicondylic line of the femur, and (2) the lateral intermuscular septum. The upper limit of its origin is sometimes blended with the insertion of the lowest fibres of the glutseus maximus. The fibres of the short head, directed downwards, join the tendon of the long head, and the muscle is inserted (1) into the head of the fibula by a strong tendon, which is split into two parts by the long external lateral (fibular collateral) ligament of the knee-joint; (2) by a slip attached to the lateral condyle of the tibia ; and (3) along its posterior border by a fascial expansion which connects the tendon with the popliteal fascia. There is a bursa between the tendon and the external lateral (fibular collateral) ligament of the knee-joint. THE MUSCLES ON THE BACK OF THE THIGH. 369 Obtqrator internus andciemelli Obitjeator externus The short head may be absent : there may be an additional origin from the ischium or femur ; and the long head may send a slip to the gastrocnemius or teudo calcaneus (tensor fasciae suralis). The semitendinosus arises, in common with the long head of the biceps, from the lower and medial facet upon the ischial tuberosity (Fig. 290, p. 368). Separating from the common tendon two or three inches from its origin, the muscle forms a long, narrow band which becomes tendinous in the middle third of the thigh. Pass- ing over the medial side of the knee it spreads out and becomes membranous, and is inserted (1) into the medial side of the shaft of the tibia just below the medial condyle, below the gracilis and behind the sartorius (Fig. 292, p. 369), and (2) into the fascia lata of the leg. A bursa separates it Adductor magnus Semitendinosus Semimembranosus. Sartorius tendon Biceps tendon (along with peroneal nerve) Plantaris SemiinembraD- osus (insertion) Ligamentnm patellae (insertion) Popliteiis Attachment of in- ternal lateral ligament of the knee (tibial collateral) Gracilis (insertion) Gastro- cnemius Semitendinosus (insertion) Fig. 291. -The Muscles un the Back of the Right Thigh. FiQ. •A'd2. — Muscle- Attachments to the Medial Side of the Upper Part op the Right Tibia. from the sartorius in front, and another, common to it and the gracihs, lies beneath its insertion. The belly of the muscle is marked . by an oblique septal tendinous intersection about its middle. The semimembranosus arises by a tendon from the upper and lateral facet on the ischial tuberosity (Figs. 290, p. 368, and 291, p. 369). In the upper third of the thigh the tendon gives place to a rounded fleshy belly, which lies beneath 370 THE MUSGULAE SYSTEM. the ischial origin of the biceps and semitendinosus muscles. Becoming tendinous at the back of the knee, it is inserted into the horizontal groove on the back of the medial condyle of the tibia above the insertion of the popliteus (Figs. 299, p. 377, and 300, p. 377). A bursa lies beneath the tendon at its insertion. It has three additional memhranous insertions: (1) a fascial band extends downwards and medially to join the posterior border of the internal lateral (tibial collateral) ligament of the knee-joint ; (2) another fascial band extends downwards and laterally, forms the fascia covering the pophteus muscle {popliteus fascia), and is attached to the obUque line of the tibia; and (3) a third strong band extends upwards and laterally to the back of the lateral condyle of the femur, forming the posterior (oblique popliteal) ligament of the knee-joint. Nerve-Supply of the Muscles of the Thigh and Buttock. The nerves which supply these muscles have collectively a wide origin from the spinal cord, from the second lumbar to the third sacral nerve, through the trunks of the lumbar and sacral plexuses. The anterior crural nerve ^ (L. 2. 3. 4.) supplies the pectineus (L. 2. 3.), sartorius (L. 2. 3.), iliacus and psoas (L. 2. 3. 4.), and quadriceps muscles (L. 3. 4.). The obturator nerve (L. 2. 3. 4.) supiDlies the obturator externus (L. 3. 4.), adductor longus (L. 2. 3.), gracilis (L. 2. 3. 4.), adductor brevis, and adductor magnus (L. 3. 4.), — the last-named muscle being also supplied by the nerve to the hamstring muscles. The gluteeus maximus is supplied by the inferior gluteal nerve (L. 5. S. 1. 2.) ; while the superior gluteal nerve (L. 4. 5. S. 1.) supplies the glutajus medius, glutseus minimus, and tensor fasciae latae. The piriformis is supplied directly by branches from the first and second sacral nerves. Special branches from the sacral plexus supply (1) the obturator internus and superior gemellus (S. 1. 2. 3.), and (2) the quadratus femoris and inferior gemellus (L. 4. 5. S. 1.). A special nerve to the hamstring muscles from the sacral plexus (L. 4. 5. S. 1. 2. 3.) supplies the semitendinosus (L. 5. S. 1. 2.), semimembranosus (L. 4. 5. S. 1.), adductor magnus (L. 4. 5. S. 1), and the long head of the biceps (S. 1. 2. 3.). The short head of the biceps is supplied by the peroneal nerve ^ (L. 5. S. 1. 2.) by means of a branch, which may arise in common with the inferior gluteal nerve. Actions of the Muscles of the Thigh and Buttock. Most of the above muscles act on the pelvis and on the hip- and knee-joints. The psoas muscle in addition assists in tlie movements of the vertebral column (p. 392). 1. Movements at the Hip- Joint. — The movements of the thigh at the hip-joint are flexion and extension, adduction and abduction, internal and external rotation. The following table gives the muscles producing these movements : — a. Flexion and Extension. Sartorius Glutaeus maximus Iliacus „ medius Psoas „ minimus Rectus femoris Biceps femoris Pectineus Semitendinosus Adductor longus Semimembranosus Gracilis Adductor magnus Obturator externus b. Adduction and Abduction. Pectineus Tensor fascise latse Adductor longus Glutseus medius „ brevis „ minimus „ magnus Obturator externus Gracilis Piriformis "i Quadratus femoris Obturator internus Glutseus maximus Gemelli during (lower fibres) Sartorius Gluteus maximus flexion (upper fij^rcs) ^ Anterior crural nerve ^femcjig,] nerve (B.N. A.). ^ Peroneal nerve = common peroneal (B.N. A.). THE FASCIA AND MUSCLES OF THE LEG AND FOOT. 371 c. Internal Rotation and External Rotation. Tensor fasciae latse Obturator externiis Glutseus medius (anterior fibres) Glutteus maximus (lower fibres) „ minimus „ „ Quadratus femoris Glutseus medius "1 (jjosterior „ minimus j fibres) Pintbrmis | ^^^^. Obturator mternus - , °. Gemelli J extension Sartorius Ilio-psoas Pectineus Adductor longus „ brevis „ magnus Biceps femoris 2. Movements of the Pelvis on the Thigh. — It is to be noted that the several movements tabulated above refer to the movements of the femur at the hip-joint. The contraction of the same groups of muscles produces similar movements of the pelvis on the femur, exemplified in the various changes in the attitude of the i^elvis in relation to the thigh and the vertebral column, which occur in locomotion. 3. Movements at the Knee- Joint. — The movements at the knee-joint are mainly flexion and extension. Flexion is much more powerful than extension. There is also a limited amount of rotation of the tibia. The movements are produced by certain of the muscles described above, associated with certain of the muscles of the leg. a. Flexion ar id Extension. b. Rotation inwards and Rotation outwards. Sartorius Quadriceps femoris Sartorius Biceps femoris Gracilis Gracilis Semitendinosus Semitendinosus Semimembranosus Semimembranosus Biceps femoris Popliteus Gastrocnemius Plantaris Popliteus THE FASCIvC AND lYIUSCLES AND FOOT. FASCIiE. OF THE LEG The superficial fascia of the leg presents no special features except in the sole, where it is greatly thickened by pads of fat, particularly under the tuberosity of the calcaneum, and under the balls of the toes. The deep fascia has numerous important attachments about the knee. Posteriorly it forms the popliteal fascia, and is joined by expansions from the tendons of the sartorius, gracilis, semitendinosus, and biceps femoris muscles. In front of the knee it is attached fco the patella, the ligamentum patellae, and the tubercle of the tibia ; laterally it is connected to the condyles of the tibia and the head of the fibula, and forms the lateral patellar ligaments, broad fascial bands which pass obliquely from the sides of the patella to the condyles of the tibia, and are joined by fibres of the vasti muscles. Passing down the leg, the fascia blends over the medial surface of the tibia with the periosteum of the bone. It extends round the lateral side of the leg from the anterior to the medial border of the tibia, binding together and giving origin to the muscles, and gaining an attachment to the lower part of the shaft of the fibula. Two septa pass from its deep surface ; one septum (anterior peroneal septum), attached to the anterior crest of the fibula, encloses the musculo -cutaneous nerve,^ and separates the extensor from the peronsei muscles. The other septum (posterior peroneal septum) is attached to the lateral crest of the fibula, and separates the peronaei from the flexor muscles. From the last-named septum another extends across the back of the leg, forms a partition between the superficial and deep flexor muscles, and encloses the posterior ^ Musculo-cutaneous nerve — superficial peroneal nerve (B.N.A.). 372 THE MUSCULAR SYSTEM. Extensor halldcis lonct Anterior tibial nerve an dorsalis pedis aitei)~7~;^7pi Extensor DiGiTORUM LONOUb ^ <, 2c^i PeRON.EUS TERTIUi Fibula. Interosseous talo calcaneal ligament Calcaneus Peron.«us brevis Lateral annular ligament Peron^eus longus Abductor dioiti quinti Plantar aponeurosi Anterior annular ligament Tibialis anterior Tibia tiliial vessels and nerves.^ It gives rise to subordinate septa attached to the vertical line of the tibia and the medial crest or oblique line of the fibula, which separate the tibiaUs posterior from the flexors of the toes on either side. At the ankle the deep fascia is strengthened by additional transverse fibres, and gives rise to the three annular ligaments. The internal annular ligament (Lig. laciniatum) stretches between the medial malleolus and the tuberosity of the calcaneus. While it is continuous at its upper border with the general investment of the deep fascia, it is chiefly formed by the septal layer covering the deep muscles on the back of the leg. It sometimes gives insertion to the plantaris muscle. It is continuous below with the plantar fascia, and gives origin to the abductor hallucis muscle. It is pierced by the calcanean vessels and nerve. Along with the posterior tibial vessels and nerve, the tendons of the tibialis posterior, flexor digitorum longus, and flexor hallucis longus, pass beneath it, each enclosed in a separate synovial sheath. The lateral annular ligament, much smaller, is a thickened band of the deep fascia stretching between the lateral malleolus and the calcaneus. It binds down the tendons of the peronsei, which occupy a space beneath the ligament, lined by a single synovial membrane. The anterior annular ligament is in two parts. An upper band, (lig. transversum cruris) broad and unde- fined at its upper and lower borders, stretches across the front of the ankle between the two malleoli. This band binds down to the lower end of the tibia the tendons of the tibialis an- terior and extensor One synovial sheath is found beneath it, surrounding the Talus or Astragalus —Tibialis posterior Medial annular igament Flexor digitorum longus — ^Medial plantar artery Tjjrf-T-Medial plantar nerve ^'■^^^/'^Flexor hallucis longus Abductor hallucis Lateral plantar nerve Lateral plantar artery Plexor digitorum brevis Fig. 293.- Quadratus plant.e (accessorius) -Coronal Section through the Left Ankle-Joint, Talus, AND Calcaneus. muscles of the toes. tendon of the tibialis anterior. On the dorsum of the foot, where the general covering of deep fascia is much thinner, a special well-defined band stretches over the extensor tendons. This lower band of tlie anterior annular ligament (lig. cruciatum cruris) has an attachment laterally to the lateral border of the greater process of the calcaneus. It divides into two bands as it passes medially over the dorsum of the foot — an wpper part, wl)ich joins the upper ligament and is attached to the medial malleolus, and a loioer part, which passes across the dorsum of the foot, and joins the fascia of the sole at its medial border. Beneath this ligament are three special compartments with separate synovial sacs, one for the tibialis anterior tendon, a second for that of the extensor hallucis longus, and a third for the extensor digitorum longus and peroneeus tertius tendons. There are occasionally other additional bands of the deep fascia passing like the straps of a sandal across the dorsum of the foot. The plantar fascia or aponeurosis is of great importance. In the centre of the sole it forms a thick triangular band, attached posteriorly to the tuberosity of the calcaneus. It spreads out anteriorly and separates mio Jive slips, which are directed forwards to the bases of tlie toes. These slips as they separate are joined together by ^ Posterior tibial nerve = tibial nerve (B.N. A.). THE MUSCLES OF THE LEG AND FOOT. 373 ill-defined bands of transverse fibres, which constitute the superficial transverse meta- tarsal ligament (fasciculi transversi aponeurosis plantae). The slip for each toe joins the tissue of the web of the toe and is continuous with the digital sheath. It splits to form a band of fibres directed forwards on each side of the toe to be attached to the sides of the metatarso-phalangeal articulation and the base of the first phalanx. This central portion of the plantar aponeurosis assists in preserving the arch of the foot, by drawing the toes and the calcaneus together. On each side it is continuous with a much thinner layer which covers the lateral and medial muscles of the sole, and joins the fascia of the dorsum of the foot at each border. It also gives rise to intermuscular septa, which pass upwards on each side of the flexor digitorum brevis, enclosing that muscle in a separate sheath, and giving in- vestments on either side to the ab- ductor muscles of the great and little toes. At the lateral border of the foot the calcaneo - metatarsal ligament, a thickened band of the fascia, connects the tuberosity of the calcaneus with the base of the fifth metatarsal bone. The digital sheaths, though smaller, are the same in arrangement as those of the fingers (p. 341). Vaginal liga- ments are present in relation to the first and second phalanges. THE MUSCLES OF THE LEG AND FOOT. The muscles of the leg and foot are divisible into three series : (1) the extensor muscles on the front of the leg and dorsum of the foot ; (2) the peronsei on the lateral aspect of the leg; and (3) the flexor muscles on the back of the leg and in the sole of the foot. The IVIuscIcsonthc Front of the Leg and Dorsum of the Foot. The muscles on the front of the leg and dorsum of the foot include two groups : (1) on the front of the leg, the tibialis anterior, long extensors of the toes and peronaeus tertius ; and (2) on the dorsum of the foot, the extensor digitorum brevis. On the front of the leg the tibialis anterior and the extensor digitorum longus and peronasus tertius are superficially placed, and conceal the extensor hallucis longus muscle. On the dorsum of the foot the extensor digitorum brevis muscle lies beneath the tendons of the long extensor of the toes. The tibialis anterior arises from the lateral condyle and the upper two-thirds of the lateral surface of the shaft of the tibia, from the interosseous membrane, from Plantar aponeurosis Fig. 294. — The Left Plantar Fascia. 374 THE MUSCULAE SYSTEM. the fascia over it, and from an intermuscular septum laterally. The muscle ends in a strong tendon which passes over the dorsum of the foot, to be inserted into a facet on the medial surface of the first cuneiform and the medial side of the base of the first metatarsal bone (Fig. 295, p. 374). Its tendon occupies special compartments beneath both upper and lower parts of the anterior annular liga- ment, enclosed in a separate, single, synovial sac. Tlie tibio-fascialis anterior is a sei^arated i^ortion of the muscle occasionally present, inserted into the fascia on the dorsum of the foot. The extensor digitorum longus arises by fleshy fibres from the lateral side of the lateral condyle of the tibia, from the upper two-thirds or more of the anterior Abductor digiti quinti (oiigin) Quadratus plantfe (Accessorius) origu] Long and short plantar/ ligaments I Tibialis posterior (part of insertion) Peronseus brevis (insertion) Flexor digiti quinti brevis (origin) Adductor hallucis obliquus (origin) Flexoi digitorum brevis (origin) Abductoi hallucis (origin) Attachments of plantar calcaneo- navicular ligament Flexorhallucis brevis (origin) Tibialis posterior (part of insertion) Peronseus longus (insertion) Tibialis anterior (insertion) Fig. 295. — Muscle- Attachments to Left Tarsus and Metatarsus (Plantar Aspect). surface (crest) of the shaft of the fibula, from the fascia over it, and from inter- muscular septa on either side. It gives rise to a tendon which passes beneath the anterior annular ligament, and in front of the ankle subdivides into four tendons, inserted into the four outer toes, exactly in the same way as the corresponding tendons in the hand (see p. 341). They form membranous expansions on the dorsum of the first phalanx, joined by the tendons of the extensor digitorum brevis, lumbricales, and interossei, which separate into one central and two lateral slips, attached respectively to the middle and terminal phalanges. The tendon occupies a separate compartment along with the peronseus tertius beneath the lower part of the anterior annular ligament, invested by a special synovial membrane. THE MUSCLES ON THE OUTER SIDE OF THE LEG. 375 the anterior surface of the fibula SOLEUS. Extensor digitorum LONGUS Peron^eus LONGUS The peronaeus tertius is a separated portion of the extensor digitorum longus. It is an essentially liuman muscle. It arises (inseparably from the extensor digitorum longus) from the anterior surface (crest) of the fibula, and from the inter-muscular septum lateral to it. The tendon of the muscle is inserted into the dorsal aspect of the base of the fifth metatarsal bone. The extensor hallucis longus arises from in its middle three-fifths, medial to the origin of the extensor digitorum longus, and for a corresponding extent from the interosseous membrane. Its tendon passes over the dorsum of the foot, to be inserted into the base of the terminal phalanx of the great toe. The extensor primi internodii longus and ex- tensor ossis metatarsi hallucis are occasional separate slips of this muscle inserted into the proximal phalanx and the metatarsal bone. The extensor digitorum brevis arises on the dorsum of the foot from a special impression on the upper surface of the cal- caneus, and from the deep surface of the ligamentum cruciatum. It usually gives rise to four fleshy bellies, from which narrow tendons are directed for- wards and inwards, to be inserted into the four inner toes. The three lateral tendons join those of the loner extensor muscle to form the membranous expansions on the dorsum of the toes. The innermost tendon (extensor hallucis brevis) is inserted separately into the base of the first phalanx of the great toe. Peron.eus brevis The IVIuscIes on the Lateral Side of the Leg. These muscles comprise the perontei,^ longus and brevis. They are placed on the lateral side of the leg between the extensor digitorum longus in front, and the soleus and flexor hallucis longus behind, enclosed in a special compartment of the deep fascia. The peronaeus longus arises from the head and the upper two-thirds of the lateral surface of the shaft of the fibula, from inter-muscular septa on either side, and from the fascia over it. It forms a stout tendon, which, lying superficial to the peronieus brevis, hooks round the lateral malleolus beneath the lateral annular ligament, crosses the lateral side of the calcaneus, and passing through a groove on the cuboid bone, is directed across the sole of the foot to be inserted into the lateral sides of the first cuneiform and the base of the first metatarsal bones (Fig. 295, p. 374). As it enters the sole of the foot afilro- cartilage is formed in the tendon, which plays over a smooth tubercle on the cuboid bone, a bursa intervening. In its passage across the foot the tendon is enclosed in a sheath derived from the plantar calcaneo-cuboid ligaments and the tibialis posterior tendon. The peronaeus brevis arises by fleshy fibres from the lower two-thirds of the Lower portion of an- terior annular liga- ment (lig. cruciatum) Tendon or peron.eus TERTIUS Innermost slip of extensor digitorum BREVIS (extensor hallucis bkevis) Fig. 296. — Muscles of the Front of the Right Leg and Dorsum of the Right Foot. 376 THE MUSCULAE SYSTEM. lateral surface of the shaft of the fibula, and from an intermuscular septum along its anterior border. Its tendon grooves the back of the lateral malleolus and % ^ ^ m ^^® lateral side of the calcaneus, in- r K .« ilk vested by a synovial sheath common to it and the peronseus longus, and is inserted into the tubercle and dorsal surface of the base of the fifth meta- tarsal bone. jGus The perontBUS longus and brevis may be fused together, or additional sli^DS may be l^resent, as peronseus accessorius, peronseus digiti quinti, peronseo-calcaneus externus, and peronseo-cuboideus. Semimembranosus TEXDox (cut) ' Tibial nerve and popliteal vessels' Plantaris tendon (cut) Fig. 297. — The Insertions of the Tibialis Posterior and Peron^ieus Longus in the Sole of the Left Foot. The Muscles on the Back of the Leg. The muscles on the back of the leg are divisible into two groups, superficial and deep. The superficial group comprises the gastrocnemius and soleus (con- stituting together thetriceps surse)and the plantaris. The gastrocnemius forms the prominence of the calf of the leg, and is superficial except at its origin, where the two bellies forming the boundaries of the popliteal space are overlapped by the tendons of the hamstring muscles. The soleus muscle is partially concealed by the gastro- cnemius and plantaris, and becomes superficial in the lower part of the leg on each side of the common tendon (tendo Achillis or calcaneus) Tendo Achillis (Tendo" calcaneus) Medial annular ligamoiit- PERONiEUS LONGUS I>iileral annular meiit Fig. 298. — The Plight Soleus Muscle. The gastrocnemius arises by hvo heads, medial and lateral, by means of strong THE MUSCLES ON THE BACK OF THE LEG. 377 Tl Mkdial head of -uastrocnemius •Plantaris _Lateralheadof 1 "oastrocnemius -Semimem- BKAN0i3US i — POPLITEUS HiiLEUs (fibular "origin) _SoLEUs (tibial origin) yr I Tibialis "posterior rrR0N.«U8 LONGUS Poplitpus^ (inseitioii) Soleus (origin)" ' Tibialis ^ H_ posterior (origin) tendons which are prolonged over the surface of the muscle. The lateral head arises from an impression on the upper and posterior part of the lateral surface of the lateral condyle of the femur, and from the lower end of the lateral epicondylic line ; while the medial head arises from a prominent rough mark on the popliteal surface of the femur ahove the medial condyle behind the adductor tubercle. Each head has an ad- ditional origin from the rback of the capsule of the knee-joint. A bursa lies beneath each ten- don of origin. Each fleshy belly of the muscle is inserted separ- ately into a broad mem- branous tendon, pro- longed upwards on its deep surface for some distance. The medial head is the larger. The tendo Achillis (tendo calcaneus) is formed by the union of the two membranous insertions of the bellies of the gastrocnemius. Prolonged upwards be- neath the separate bellies, the tendon forms a broad mem- branous band connect- ing together the lower parts of the two bellies. Narrowing gradually, and becoming thicker in the lower half of the leg, the tendon is finally inserted into the posterior aspect of the calcaneus. A bursa lies beneath the tendon at its insertion. The tendo calcaneus also affords insertion to the soleus and (sometimes) the plantaris muscles. Theplantaris arises by fleshy fibres from the lateral epicondylic line of the femur for about an inch at its lower end, from the adjacent part of the popliteal surface of the femur, and from the posterior (oblique) ligament of the knee-joint. It forms a narrow fleshy slip which ends in a tendon extending down the back of the leg, to be inserted into the medial side of the tuberosity of the calcaneus, or the tendo calcaneus, or the medial annular ligament. The tendon of the muscle is capable Pli \ordigitorum ' 1 oNi. rs I I fxor hallucis LON'l.US /J _.Peron.eus beevis Medial annular "'ligameut ..Tendo calcaneus Lateral annular m Fig. 299. — The Deep Muscles on the Back of the Right Leg. Fig. 300. — Muscle - Attach- ments TO the Posterior Surface of the Right Tibia . 378 THE MUSCULAR SYSTEM. of considerable lateral extension. The plantaris lies between the lateral head of the gastrocnemius and the soleiis. In the lower half of the leg its tendon lies along the medial border of the tendo calcaneus. The muscle is not always present. The soleus has a triple origin from (1) the posterior surface of the head and the shaft of the fibula in its upper third ; (2) a fibrous arch (arcus tendineus m. solei) stretching over the popliteal vessels and tibial nerve between the tibia and fibula ; and (3) the oblique line and middle third of the medial border of the tibia (Fig. 300, p. 377). From this origin the upper muscular fibres are directed downwards to join a tendon placed on the super- ficial aspect of the muscle, which is inserted into the tendo- calcaneus ; the lower fibres are inserted directly into the tendo calcaneus to within one or two inches of the calcaneus. The deep muscles of the back of the leg comprise the popliteus, flexor digitorum longus, flexor hallucis -LuMBEicALs longus, and tibialis posterior. The popliteus muscle is deeply placed behind the knee-joint in the floor of the pophteal space, and is covered by the popliteal vessels and tibial nerve. The flexor digitorum longus lies behind the tibia, the flexor hallucis longus behind the fibula, and the tibialis posterior lying between them is related to the interosseous membrane and both bones of the leg. All these muscles are concealed by the superficial group, and are bound down to the bones of the leg by layers of the deep fascia. The popliteus arises by a stout tendon from a rough impression in front of a groove on the lateral aspect of the lateral condyle of the femur. The tendon passes between the lateral semilunar cartilage and the capsule of the knee-joint, and pierces the posterior (oblique) ligament, from which it takes an additional fleshy origin. A bursa is placed beneath the tendon, which usually communicates with the synovial cavity of the knee- joint. The muscle is inserted by fleshy fibres (1) into a triangular surface on the back of the tibia above the oblique line (Fig. 300, p. 377), and (2) into the fascia over it (the popliteus fascia, derived from the tendon of the semi-merabranosus muscle). The popliteus minor is a small occasional muscle attached to the popliteal space of the femur and the posterior ligament of the knee-joint. The flexor digitorum longus occupies both the back of the leg and the sole of Plexoe hallucis -BREVIS Flexor digitorum LO>rGUS Flexor digiti quinti brevis quadratus PLANTS (ACCESSORIUS) Abductor hallucis Abductor digiti QUINTI PERON/EUS -•LONGUS Flexor "digitorum LONGUS _ Flexor hallucis LONGUS _ Long plantar ""ligament Fig. -301. — The Muscles of tiik FiIcht Foot (sccoikI layer). THE MUSCLES IN THE SOLE OF THE FOOT. 379 the foot. Its origin is by fleshy fibres from the posterior surface of the shaft of the tibia in its middle three-fifths, below the oblique line, medial to the vertical line and the origin of the tibialis posterior, from the fascia over it, and from an inter- muscular septum on each side (Fig. 300, p. 377)- Its tendon, after crossing obliquely over the tendon of the tibialis posterior, passes beneath the medial annular ligament, invested in a special synovial sheath, and enters the sole of the foot. There it crosses superficially the tendon of the flexor hallucis longus, and finally divides into four subordinate tendons, which are inserted into the four outer toes in precisely the same manner as the flexor digitorum profundus is inserted in the hand (p. 341). Each tendon enters the digital sheath of the toe, perforates the tendon of the flexor digitorum brevis, and is inserted into the base of the terminal phalanx. Ligamenta accessoria (longa and brevia) are present as in the hand. The tendon of the flexor hallucis longus sends a fibrous band to the tendon of the fiexor digitorum longus as it crosses it in the sole of the foot, which usually passes to the tendons destined for the second and third toes. Associated with this muscle in the sole of the foot are the lumbricales and quadratus plantai muscles. The lumbricales are four small muscles arising in association with the tendons of the flexor digitorum longus in the sole. The first muscle arises by a single origin from the tibial side of the tendon of the flexor digitorum longus for the second toe ; the other three arise by two heads from the adjacent sides of all four tendons. Each muscle is inserted into the dorsal expansion of the extensor tendon, the metatarso-phalaugeal capsule, and the base of the first phalanx, precisely as in the case of the lumbrical muscles of the hand. Each muscle passes forwards on the tibial side of the corresponding toe, superficial to the transverse metatarsal ligament. The quadratus plantae (accessorius) arises by two heads : (1) the lateral tendinous head springs from the lateral border of the inferior surface of the calcaneus and from the lateral border of the long plantar ligament ; (2) the medial head, which is fleshy, arises from the concave medial surface of the calcaneus in its whole extent, and from the medial border of the long plantar ligament (Fig. 295, p. 37-1). The long plantar ligament separates the two origins. The two heads unite to form a flattened band, which is inserted into the upper aspect of the tendons of the flexor digitorum longus, and usually into those destined for the second, third, and fourth toes. In the sole of the foot the tendons of the flexor digitorum longus, along with the lumbricales and quadratus plantse, and the flexor hallucis longus muscles, constitute the second layer of muscles, lying between the abductors of the great and little toes and the flexor digitorum brevis superficially, and the flexor brevis and adductors of the great toe more deeply. The flexor hallucis longus arises on the back of the leg, between the tibialis posterior and the peronoei muscles, from the lower two-thirds of the posterior surface of the shaft of the fibula, from the fascia over it, and from intermuscular septa on either side. Its tendon passes beneath the medial annular ligament en- closed in a .special synovial sheath, and after grooving the back of the lower end of the tibia, the talus, and the under surface of the sustentaculum tali of the calcaneus, it is directed forwards in the sole of the foot, to be inserted into the base of the terminal phalanx of the great toe. In the foot it crosses over the deep aspect of the tendon of the flexor digitorum longus, and gives to it a strong fibrous slip, which is prolonged into the tendons for the second and third toes. The tibialis posterior muscle has a fourfold fleshy origin in the leg. It arises (1) from the upper four-fifths of the shaft of the fibula between the oblique line and the interosseous border (the medial surface) ; (2) from the lower part of the lateral condyle, and from the upper two-thirds of the shaft of the tibia below the oblique line and between the vertical line and the interosseous border (Fig. 300, p. 277) ; (3) from the interosseous membrane ; and (4) from the fascia over it and the septa on either side. The muscle gives rise to a strong tendon which passes beneath the medial annular ligament, invested by a special synovial sheath, and grooves the back of the medial malleolus, on its way to the medial border of the foot. After crossing over the inferior calcaneo- navicular ligament between the sustentaculum tah and the navicular bone, the tendon 26 380 THE MUSCULAE SYSTEM. spreads out and is inserted by three bands into (1) the tubercle of the navicular bone and the plantar surfaces of the first and second cuneiform bones, (2) the plantar aspects of the second, third, fourth, and sometimes the fifth metatarsal bones, the second and third cuneiform bones, and the groove on the cuboid, and (3) into the medial border of the sustentaculum tali of the calcaneus (Fig. 302, p. 380). The peronseo-calcaneus muscle, when present, arises from the fibula, and is inserted into the calcaneus. The Muscles in the Sole of the Foot. The muscles in the sole of the foot are divisible into four layers placed beneath the plantar fascia. The first layer includes the abductor hallucis, flexor digitorum brevis, and Abductor digiti quiiiti (origin) Quadratus'plant.*' (accessorius) (origin) Long and short plantar/ ligaments'! Tibialis posterior (part of insertion Peronteus brevis (insertion) Flexor brevis digiti quinti (origin) Adductor hallucis obliquus (origin) Flexor digitorum brevis (origin) Abductor hallucis (origin) Attachments of plantar calcaneo- navicular ligament Flexor hallucis brevis (origin) _\Tibialis posterior (part of insertion) Peronsus longus (insertion) Tibialis anterior (insertion) Fig. 302.— Muscle-Attachments to Left Tarsus and Metatak.sus (Plantar Aspect). abductor digiti quinti. The second layer consists of the lumbricales and quadratus plantte (accessorius), together with the tendons of the flexor hallucis longus and flexor digitorum longus. The third layer comprises the flexor hallucis brevis, adductor hallucis obliquus and transversus, and flexor brevis digiti quinti. The fourth layer consists of the interossei (plantar and dorsal), placed between the metatarsal bones : and the tendons of insertion of the tibialis posterior and peronseus longus. THE MUSCLES IN THE SOLE OF THE FOOT. 381 FIRST LAYER. The abductor hallucis has a double origin: (1) by a short tendon from the medial side of the medial process of the tuberosity of the calcaneus (Fig. 302, p. 380), and (2) by fleshy fibres from the medial annular ligament, the plantar aponeurosis which covers it, and the intermuscular septum between it and the flexor digi- torum brevis. Lying superficially along the medial border of the sole, its tendon is inserted, along with part of the flexor hallucis brevis, into the medial side of the posterior end of the first phalanx of the great toe. The flexor digitorum brevis has likewise a double origin : (1) from the fore-part of the medial process of the tuberosity of the calcaneus (Fig. 302, p. 380), and (2) from the thick central part of the plantar aponeurosis which covers it, and from the inter- muscular septa on either side. Passing forwards, it gives rise to four slender tendons, which are inserted into the second phalanges of the four outer toes, after hav- ing been perforated by the long flexor tendons, just as in the case of the tendons of the flexor digitorum sublimis of the hand (p. 341). The abductor digiti quinti has also a double origin : (1) by fleshy and tendinous fibres from the fore-part of both processes of the tuberosity of the calcaneus, partly concealed by the flexor digitorum brevis (Fig. 302, p. 380), and (2) by fleshy fibres from the lateral portion of the plantar aponeurosis and the calcaneo- metatarsal ligament, and from the intermuscular septum between it and the flexor digitorum brevis. Its tendon lies along the fifth metatarsal bone, and is inserted into the lateral side of the pos- terior end of the first phalanx of the little toe. The outermost fibres usually obtain an additional insertion into the lateral side of the plantar surface of the fifth metatarsal bone. Plantar aponeurosis Abductor digiti QUINTI QUADRATUS PLANT.-E (aocessorius) Flexor digitorum brevis Abductor hallucis Flexor digiti quinti brevis Flexor hallucis BREVIS Fourth lumbrioal Third lumbrical Second... LUMBRICAr, First-- lumbrical Flexor hallucis longus Fig. 303. — Superficial Muscles of the Right Foot. SECOND LAYER. The tendons of the long flexors of the toes, the lumbricales and quadratus plantae (accessorius) muscles, constituting the second layer of muscles, have already been described (p. 379). Lying beneath the abductor hallucis and the flexor digi- 382 THE MUSCULAE SYSTEM. torum brevis, thej occupy the hollow of the tarsus and the space between the first and fifth metatarsal bones ; their deep surfaces are in contact with the adductors of the o;reat toe and the interossei muscles. Long plantar ligament - Flexor hal- lucis lonous - Flexor digi- torum loxous "' quadratus — PLANTS / (accessorius) \ - (origins) Peron^us ,. LONGUS THIRD LAYER. The flexor hallucis brevis arises by tendinous fibres from (1) the medial part of the plantar surface of the cuboid bone (Pig. 302, p. 380), and (2) the tendon of the tibialis posterior. Directed for- wards over the first metatarsal bone, the muscle separates into two parts, between which is the tendon of the flexor hallucis longus. Each portion gives rise to a tendon which is inserted into the corre- sponding side of the base of the first phalanx of the great toe ; in each tendon, under the metatarso-phalangeal articula- tion, a sesamoid bone is developed. The medial tendon is united with the insertion of the abductor, the lateral tendon with the insertions of the adductor muscle of the great toe. The adductor hallucis^ consists of two parts. The oblicLue head (caput obliquum) of the muscle arises (1) from the sheath of the peronaeus longus, and (2) from the plantar surfaces of the posterior extremities of the second, third, and fourth metatarsal bones (Fig. 302, p. 380). Occupying the hollow of the foot, on a deeper plane than the long flexor tendons and lumbricales, and on the lateral side of the flexor hallucis brevis, it is directed ob- liquely medially and forwards, to be inserted on the lateral side of the base of the first phalanx of the great toe between and along with the flexor brevis and the transverse head of the adductor hallucis. The transverse head (caput transversum) arises from (1) the capsules of the lateral four meta- tarso-phalangeal articulations and (2) the transverse metatarsal Liga- ment. Directed transversely in- wards, under cover of the flexor tendons and lumbricales, the muscle is inserted, along with the oblicpe head, into the lateral side of the base of the first phalanx of the great toe. The flexor digiti quinti brevis arises from (1) the sheath of the peronseus longus and (2) the base of the fifth metatarsal bone (Fig. 302, p. 380). Partially concealed by the abductor digiti quinti, the muscle passes along the fifth 1 The ailchictor hallucis obliquus ami adductor hallucis transversus are now described as two heads of the same muscle (B.N. A.). Flexor digiti quinti brevis Flexor hal- lucis BREVIS Interosseous MUSCLES Adductor hallucis (oblique head) Adductor hallucis (transverse head) Fig, 304. — Deep Muscles of the Sole of the Foot. THE MUSCLES IN THE SOLE OF THE FOOT. 383 Fig. 305. — Interosseous Muscles of the Right Foot. metatarsal bone, to be inserted, in common with that muscle, into the lateral side of the base of the first phalanx of the little toe. FOURTH LAYER. The interossei muscles of the foot resemble those of the hand except in one respect. In the hand the line of action of the muscles is the middle line of the middle finger. In the foot the second toe is the digit round which the muscles are grouped, and their attachments and their actions differ accordingly. There are four dorsal and three plantar muscles, which occupy together the four interosseous spaces, and project into the hollow of the foot. The four dorsal muscles^ one in each interosseous space, arise by two heads each from the shafts ^, of the metatarsal dorsal. bones. Each gives 'os rise to a tendon, which, after passing dorsal to the transverse metatarsal ligament, is inserted on the dor- sum of the foot, into the side of the first phalanx, the meta- tarso-phalangeal cap- sule, and the dorsal expansion of the ex- tensor tendon. The Jirst and second muscles are inserted respectively into the tibial and fibular sides of the proximal end of the first phalanx of the second toe. The third and fourth muscles are inserted into the fibular sides of the third and fourth toes. The three plantar muscles occupy the three outer interosseous spaces. Each arises by a single head from the tibial side of the third, fourth, and fifth metatarsal bones respectively. Each ends in a tendon which passes dorsal to the transverse metatarsal ligament, and is inserted, in the same manner as the dorsal muscles, into the tibial sides of the third, fourth, and fifth toes. Nerve-Supply of the Muscles of the Leg and Foot. The nerves supplying the muscles of the leg and foot are branches of the peroneal or tibial nerves from the sacral plexus. The anterior tibial nerve ^ from the peroneal supplies the muscles on the front of the leg and dorsum of the foot (L. 4. 5. S. 1.), tibialis anterior, extensor digitorum longus, peronajus tertius, extensor hallucis longus, and extensor digitorum brevis. The musculo-cutaneous nerve,- also a branch of the peroneal nerve, supplies the peronseus longus and peronjeus brevis (L. 4. 5. S. 1.). The tibial nerve innervates directly the plantaris, popliteus (L. 4. 5. S. 1.), each head of the gastrocnemius, and the soleus (S. 1. 2.). The soleus receives on its deep surface an additional nerve from the tibial (L. 5. S. 1. 2.). This nerve supplies also the flexor digitorum longus and tibialis posterior (S. 1. 2.), and the flexor hallucis longus (L. 5. S. 1. 2.). The plantar nerves, terminal branches of the posterior tibial, innervate the small muscles of the sole of the foot. The internal plantar nerve ^ (L. 5. S. 1.) supplies the abductor hallucis, flexor digitorum brevis, flexor hallucis brevis, and first lumbrical muscle ; the external plantar nerve* (S. 1. 2.) supjjlies the other three lumbrical muscles, the quadratus plantse, adductor of the great toe, interossei, flexor brevis and abductor digiti quinti. Actions of the Muscles of the Leg and Foot. The muscles of the leg and foot act chiefly in the movements of the ankle-joint (assisted by movements of the inter-tarsal joints) ; of the metatarso-phalangeal joints (assisted, by movements of the tarso-metatarsal and inter-metatarsal joints) ; and of the inter-phalangeal joints. I. Tibio-Fibular Articulations. — The upper tibio-fibular articulation is only capable of 1 Anterior tibial nerve = deep peroneal nerve (B.N. A.). - Musculo-cutaneous nerve = superficial peroneal nerve (B.N. A.). •* Internal plantar nerve = medial plantar nerve (B.N. A.). ■* External plantar nerve = lateral plantar nerve (B.N.A.). 26 a 384 THE MUSCULAK SYSTEM. slight gliding movement, occasioned by the action of the biceps and popliteus and the muscles arising from the fibula. II. Movements at the Ankle-Joint. — The movements at the ankle-joint are movements of flexion and extension of the foot on the leg, along with inversion and eversion (only during extension). These movements are produced at the ankle, aided by movements in the inter-tarsal joints, and are occasioned by the following muscles : — a. Flexion. Extension. h. Inversion. Eversion. Tibialis anterior Gastrocnemius Tibialis anterior Peroneeus tertius Extensor digitorum longus Plantaris Peronseus longus Extensor hallucis longus SoleuR Tibialis posterior Peronseus brevis Peronseus tertius Tibialis posterior Peronseus longus Peronseus brevis Flexor digitorum longus Flexor hallucis longus III. Movements of the Toes. — A. At the Metatarso-Phalangeal Joints (assisted by move- ments at the tarso-metatarsal and inter-metatarsal joints). — These movements are flexion and extension, abduction and adduction (in a line corresponding to the axis of the second toe). a. Flexion. Extension. Flexor digitorum longus Quadratus plantse (accessorius) Lumbricales Flexor hallucis longus Flexor hallucis brevis Flexor digitorum brevis Flexor digiti quinti brevis Interossei Extensor digitorum longus Extensor digitorum brevis Extensor hallucis longus Extensor hallucis brevis h. Abduction. Adduction. {From and to the middle line of the second toe.) Abductor hallucis Dorsal interossei Abductor digiti quinti Adductor hallucis Plantar interossei B. At the inter-phalangeal joints the movements are Kmited to flexion and extension. Flexion. Extension. Flexor digitorum brevis {acting on the first joint) Flexor digitorum longus {acting on both joints) Flexor hallucis longus {acting on the hallux) Extensor digitorum longus a Extensor digitorum brevis Interossei Lumbricales Extensor hallucis longus {acting on both joints) Movements of the Lower Limb generally. The characteristic features of the lower limb are stability and strength, and its muscles and joints are both subservient to the functions of transmission of weight and of locomotion. In the standing position the centre of gravity of the trunk falls between the heads of the femora, and is located about the middle of the body of the last lumbar vertebra. It is transmitted from the sacrum through the posterior sacro-iliac ligaments to the hip bone, and through the bones of the lower limb to the arch of the foot, where the astragalus distributes it backwards through the calcaneus to the heel, and forwards through the tarsus and metatarsus to the balls of the toes. Locomotion. — The three chief means of progression are walking, running, and leajjing. In walking, the body and its centre of gravity are inclined forwards, the trunk oscillates from side to .side as it is supported alternately by each foot, the arms swing alternately with the corresponding leg, and one foot is always on the ground. The act of progression is performed by the leg, aided in two ways by gravity. The movements of the leg occur in the following way. At the beginning of a step, one leg, so to speak, " shoves ofl^" ; the heel is raised and the limb is extended By the action of the muscles flexing the hip and knee-joints, and extending the ankle-joint and toes, this limb is raised from the ground sufficiently to clear it, and passes forwards by the action of gravity, aided by the force given to the movement by the extensor muscles. After passing the AXIAL MUSCLES. 385 line of the centre of gravity the flexion of the joints ceases, the muscles relax, and the limb gradually returns to the ground. The other limb then passes through the same cycle, the weight of the body now resting on the limb which is in contact with the ground. As the foot reaches the groimd it, as it were, rolls over it ; the heel touches it first, then the sole, and lastly, as the foot leaves the ground again, only the toes. In running, the previous events are all exaggerated. The time of the event is diminished, while the force and distance are increased. Both feet are oflf the ground at one time ; the action of flexors and extensors alternately is much more powerful, so that on the one hand the knees are drawn upwards to a greater extent in the forward movement, and not the whole foot, but only the toes reach the ground in the extension of the limb. The attempt is made to bring the foot to the ground in front of the line of the centre of gravitj'-. At the same time the trunk is sloped forwards much more than in walking. In leaping, the actions of the limbs are still more exaggerated. The movements of flexion of the limb are still more marked, and the foot reaches the ground still farther in front of the line of the centre of gravity. Obliquus extersus abdominis \ Obliquus isternus \ abdominis Transversus abdominis Fascia transversali Peritoneum Colon AXIAL MUSCLES. THE FASCIit AND MUSCLES OF THE BACK. THE FASCIA OF THE BACK. The general fascial investments of the back have been described along with the superficial muscles associated with the shoulder -girdle (p. 319). The latissimus dorsi muscle has been described as arising in large part from the vertebral apo- neurosis. This is a strong fibrous lamina which conceals the sacro-spinalis muscle. In the loin it extends from the spines of the lumbar vertebrfe outwards to the interval between ,, 1 j_ -1 1 Rectus ABDOMINIS the last nb and the iliac crest, where it is con- cerned in forming the lumbar fascia (fascia lumbodor- salis). Below the loin the vertebral aponeurosis is at- tached to the iliac crest, and more medially blends with the subjacent tendinous origin of the sacro-spinalis ^'^''^^^"t^.^e^ (erector spinas). The fascia can be followed upwards over the sacro- spinalis in the region of the thorax, where it is attached laterally to the ribs and is continuous with the intercostal aponeuroses. In the lower part of the thorax it is replaced by the muscular slips of the serratus posterior inferior ; in the upper part of the thorax it passes beneath the serratus posterior superior and blends with the deep cervical fascia. The lumbar fascia (fascia lumbodorsalis) is a narrow ligamentous band which connects the last rib to the iliac crest between the muscles of the back on the one hand and those of the abdominal wall on the other. It is formed by the union of three fascial strata, called respectively the vertebral aponeurosis or posterior layer, just described ; the middle, and the anterior layers. The middle layer is a fascia which Kidney Lumbar fascia Latissimus dorsi quadratus lumborum Psoas fascia Second lumbar vertebra Psoas major Anterior layer of lumbar fascia MULTIFIDUS L Semispinalis dorsi Middle layer of lumbar fascia Ilio-costalis Vertebral aponeurosis LONGISSIMUS DORSI Fig. 306.- -Traxsverse Section through the Abdomen, opposite the Second Lumbar Vertebra. 386 THE MUSCULAE SYSTEM. stretches laterally from the ends of the transverse processes of the lumbar vertebrse, between the sacro-spinalis behind and the quadratns lumborum muscle in front. The anterior layer is attached to the lumbar vertebrse near the bases of their transverse processes. It covers the front of the quadratus lumborum muscle, and separates it from the psoas. The psoas fascia is continuous at the lateral border of the psoas muscle with the anterior layer of the lumbar fascia. At the lateral borders of the quadratus lumborum and sacro- spinalis muscles the three layers blend together to form the lumbar fascia, which in turn gives partial origin to the obliquus internus and transversus abdominis muscles. LONOISSIMUS CAPITIS (tRACHELO- mastoid) CAPITIS (COMPLEXUS) IlIO-COSTALI: DORSI (accessoeius) LONGISSIMUS DORSI Ilio-costaus lumborum THE MUSCLES OF THE BACK. The muscles of the back are ar- ranged in four series according to their attachments : (1) vertebro - scapular and vertebro -humeral, (2) vertebro- costal, (3) vertebro -cranial, and (4) vertebral. They are in irregular strata, the most superficial muscles having the most widely spread attach- ments. The first series of muscles of the back, connecting the axial skeleton to the upper limb, have already been described. They are arranged in two layers : (1) trapezius and latissimus dorsi superficially ; (2) levator scapulae, and rhomboidei, beneath the trapezius (p. 319). The remaining muscles are almost entirely axial, and may be divided into four groups : (1) serrati posteriores, superior and inferior, splenius capitis and splenius cervicis ; (2) sacro-spinalis (erector spinse) and semi-spinalis capitis (complexus) ; (3) transverse - spinales (semispinalis and multifidus) ; and (4) the small deep muscles (rotatores, inter- spinales, inter-transversarii, and sub- occipital muscles). They extend from the sacrum to the head, forming a cylindrical column in the loin, filling up the vertebral groove in the thorax, and giving rise to the muscular mass at the back of the neck. First Group. The serratus posterior superior has a membranous origin from the liga- mentum nuchse and the spines of the last cervical and upper three or four thoracic vertebrte. It is directed obliquely downwards and laterally, to be inserted by separate slips into the second, third, fourth, and fifth ribs. The muscle is concealed by the vertebro-scapular muscles, and crosses obliquely over the splenius, sacro- spinalis (erector spinas), and semispinalis capitis (complexus). It lies superficial to the vertebral aponeurosis. Fig. 307 — Schematic Repuesentation of the Parts OF THE Left Sacuo-Spinams (Ehector Spin^e) Muscle. THE MUSCLES OF THE BACK. 387 The serratus posterior inferior has a membranous origin through the medium of the vertebral aponeurosis from the last t^Yo thoracic and first two lumbar spinous processes. It forms four muscular bands which pass almost horizontally to an insertion into the last four ribs. The muscular slips overlap one another from below upwards. The muscle is on the same plane as the vertebral aponeurosis, and is concealed by the latissimus dorsi. The splenius muscle is a broad, flattened band which occupies the back of the neck and the upper part of the thoracic region. It arises from the ligamentum nucha? (from the level of the fourth cervical vertebra downwards) and from the spinous processes of the last cervical and higher (four to six) thoracic vertebrse. Its fibres extend upwards and laterally into the neck, separating in their course into an upper and a lower part. The upper part forms the splenius capitis, which is inserted into the mastoid process and the lateral part of the superior curved line of the occipital bone (Fig. 310, p. 390). The lower part forms the splenius cervicis, which is inserted into the posterior tubercles of the transverse processes of the upper three or four cervical vertebrae, behind the origin of the levator scapulee. The muscle is partially concealed by the trapezius and sterno-mastoid, and appears between them in the floor of the posterior triangle of the neck (splenius capitis). It is covered by the rhomboid muscles, levator scapulae, and serratus posterior 'superior. Second Group. The sacro-spinalis (erector spinae) possesses vertebral, vertebro-cranial, and vertebro-costal attachments. It consists of an elongated mass composed of separated slips extending from the sacrum to the skull. Simple at its oricrin, it becomes more and more complex as it is traced upwards towards the head. It arises (1) by Posterior tubercles of transverse processes Scalenus medius Levator scAPULiE Splenius cervicis Scalenus posterior Ilio-costalis cervicis LONGISSIMUS cervicis r LONOISSIMUS CAPITIS Articular.! Semispinalis capitis processes'! Semispinalis cervicis, L Multifidus ^C\LENUS (, anterior Anterior _ , tubercles of ^.ONG us capitis ^trausversB processes ONGUS COLLI Fig. 308. — Scheme of Muscular- Attachments to the Transverse Processes of the Cervical Vertebra. fleshy fibres from the iliac crest ; (2) from the posterior sacro-iliac ligament ; and (3) by tendinous fibres continuous with the former from the ihac crest, the back of the sacrum, and the spines of the upper sacral and all the lumbar vertebrae. Its fibres extend upwards through the loin, enclosed between the posterior and middle layers of the lumbar fascia, and separate into two columns — a lateral portion derived from the lateral fleshy origin, the ilio-costalis, and a medial portion com- prising the remaining larger part of the muscle, the longissimus. The ilio-costalis lumborum (ilio-costalis) is inserted by six slender shps into the lower six ribs. 388 THE MUSCULAR SYSTEM. Rectus capitis posterior mikor Rectus capitis posterior m \jor Obuquus capitis -^llprRlOK OBLIQUUS capitis INFERIOR-.^ Splenius CA.piris SpLENIUS ( FR% Klt)-- Sterno-cleido-m \stoid SbMISPIN \I lb clrvicis LONGISSIMUS cervicis (tran'sversalis colli) Semispinalis dorsi Levatores costarum QL'ADRATUS lumborum Mi'LTIFIDU LiGAMENTUM NUCH.E SeM I SPI NALIS ; CAPITIS^(COMPLEXUS) LONGISSIMUS CAPITIS (TRACHELO- JI \stoid) Splenius capitis'et cervicis LeVAIOR SCAPULA Ilio-costalis cervicis (cervicalis asc endens) LON&ISSIMUS CERVICIS (TRANSVERSALIS colli) Ilio-costalis dorsalis (accessorius) Spinalis dorsi LONGISSIMUS dorsi Ilio-costalis lumborum ■■•- Sacrospinalis (erector SPIN/E) Fig, 309. — The Deep Muscles of the Back. THE MUSCLES OE THE BACK. 389 Medial to the insertion of each of these slips is the origin of the ilio-costalis dorsi (accessorius), which, arising from the lower six ribs medial to the iUo-costalis lumborum, is inserted in Line with it by similar slips into the upper six ribs. The ilio-costalis cervicis (cervicalis ascendens) arises in the same way by six slips from the upper six ribs, medial to the insertions of the previous muscle. It forms a narrow band, which, extending into the neck, is inserted into the posterior tubercles of the transverse processes of the fourth, fifth, and sixth cervical vertebrae, behind the scalenus posterior. The ilio-costales- lumborum, dorsi, and cervicis form together a continuous muscular column, and constitute the most lateral group of the component elements of the sacro-spinalis or erector spinse. The longissimus is the largest element in the sacro-spinalis mviscle. The longissimus dorsi forms the middle column of the muscle. It is continued up into the neck as the longissimus cervicis (transversalis cervicis) and longissimus capitis (trachelo-mastoid). Mostly tendinous on the surface at its origin, it becomes fleshy in the upper part of the loin. It is thickest in the loin, and becomes thinner as it passes upwards in the back between the column formed by the iho-costalis and its upward continuations laterally, and the spinalis dorsi medially. It is inserted by two series of slips, medial and lateral, laterally into nearly all the ribs, and medially into the transverse processes of the thoracic and the accessory processes of the upper lumbar vertebrse. It is prolonged upwards into the neck by its associa- tion with the common origin of the longissimus cervicis (transversalis cervicis) and the longissimus capitis (trachelo-mastoid). The longissimus cervicis (transversalis cervicis) has an origin from the transverse processes of the upper six thoracic vertebree, medial to the insertions of the longissimus dorsi. Extending upwards into the neck, it is inserted into the posterior tubercles of the transverse processes of the second, third, fourth, fifth, and sixth cervical vertebrae. It is concealed in the neck by the ilio-costalis cer\'icis (cervicaHs ascendens) and splenius cervicis muscles. ^ The longissimus capitis (trachelo-mastoid) arises, partly by an origin common to it and the previous muscle, from the transverse processes of the upper six thoracic vertebriB, and partly by an additional origin from the articular processes of the lower four cervical vertebrae. Separating from the longissimus cervicis (trans- versalis cervicis), the muscle ascends through the neck as a narrow band which is inserted into the mastoid process beneath the splenius capitis muscle. In the neck the muscle is placed between the splenius capitis and semispinalis capitis (complexus). The spinalis dorsi forms the medial column of the sacro-spinalis. It occupies the thoracic region, and arises by tendinous fibres from the lower two thoracic and upper two lumbar spinous processes, and also directly from the tendon of the longissimus dorsi. It is a narrow muscle which, lying close to the thoracic spinous processes medial to the longissimus dorsi, is inserted into the upper (four to eight) thoracic spines. It is not prolonged into the neck. The semispinalis capitis (complexus) closely resembles in position and attachments the longissimus capitis (trachelo-mastoid). It takes origin from the transverse processes of the upper six thoracic and the articular processes of the lower four cervical vertebrae, medial to the longissimus cervicis and longissimus capitis. It has an additional origin also from the spinous process of the last cervical vertebra. It forms a broad muscular sheet which extends upwards in the neck, to be inserted into the medial impression between the superior and inferior curved lines of the occipital bone (Fig. 312, p. 391). The medial portion of the muscle is separate, and forms the biventer cervicis, consisting of two fleshy bellies with an intervening tendon, placed vertically in contact with the ligamentum nuchae. The muscle is covered mainly by the splenius and longissimus capitis muscles. It conceals the semispinalis cer\dcis and the muscles of the suboccipital triangle. Third Group. This group comprises the semispinals (dorsi and cervicis) and multifidus. They occupy the vertebral furrow under cover of the sacro-spinalis and semispinalis 390 THE MUSCULAE SYSTEM. Insertion of sterno MASTOID Splenius capitis. IjONOISSIMUS capiti (trachelo-mastoid) Semispinalis capitis (complexus). (thrown outwards) Least occipital nerve. Splenius capitis longissimus capitis (trachelo-mastoid)' Trapezius Semispinalis capitis (complex us Great occipital nerve Obliquus superior Rectus capitis posterior major Rectus capitis posterior minor Vertebral artery Suboccipital nerve Posterior arch of atlas Obliquus capitis inferior Posterior primary division of second cervical nerve Posterior primary division of third cervical nerve Deep cervical artery Posterior primary division of fourth cervical nerve Semispinalis cervicis Fig. 310. — The Suboccipital Triangle op the Left Side. capitis (complexus) muscles-. They are only incompletely separate from one another. Attachment of posterior sacro- iliac ligaments Glutseus maxiinus (origin) Fig. 311. — Muscle-Attachments to the Sacrum (Posterior Aspect). THE MUSCLES OF THE BACK. 391 The semispinales, dorsi and cervicis, form a superficial stratum, the multifidus being more deeply placed. The more superficial muscles have the longer fibres ; the fibres of the multifidus pass over fewer vertebra. Both muscles extend obliquely upwards from transverse to spinous processes. The semispinalis muscle extends from the loin to the axis vertel)ra. Its fibres are artificially separated into an inferior part, the semispinalis dorsi, and a superior part, the semispinalis cervicis. The semispinalis dorsi arises from the transverse processes of the lower six thoracic vertebrte. It is inserted into the spinous processes of the last two cervical and first four thoracic vertebne. The semispinalis cervicis arises from the transverse processes of the upper six thoracic, and the articular processes of the lower four cervical vertebrtTe. It is inserted into the spines of the cervical vertebrte from the second to the fifth. The multifidus differs from the previous muscle in extending from the sacrum to the axis, and in the shortness of its fasciculi, which pass over fewer vertebrae to reach their insertion. It arises from the sacrum, from the posterior sacro-iliac ligament (Fig. 311, p. 390), from the mammiUary processes of the lumbar vertebrae, from the transverse processes of the thoracic vertebrae, and from the articular processes of the lower four cervical vertebra. It is inserted into the spines of the vertebree up to and including the axis. Lying in contact with the vertebral lamina, the muscle is covered in the neck and back ])y the semispinalis, and in the loin by the sacro-spinalis muscle. Fourth Group. This group includes several sets of small muscles, which are vertebro-cranial or inter-vertebral in their attachments. The muscles bounding the suboccipital triangle are four in number — obliqui capitis, inferior and superior, and recti capitis posteriores, major and minor Semispinalis capitis (complexus) (insertion) Rectus capitis posterior minor (insertion) Rectus capitis posterior major (insertion) Trapezius (origin) Stenio-cleido-mastoid 'insertion) Splenius capitis (insertion) Obliquus capitis superior (insertion) Rectus capitis lateralis (insertion) Rectus capitis anterior (insertion (rectus capitis anterior minor) Longus capitis (rectus cai)itis anterior major) (insertion) ouperior constrictor of pharynx (insertion) Fig. 312.— Muscle- Attachments to the Occipital Bose (Parietal Surface). These muscles are concealed by the semispinalis capitis (complexus) and splenius capitis; they enclose a triangular space (the suboccipital triangle) in which the vertebral artery, the posterior primary division of the suboccipital nerve, and the posterior arch of the atlas are contained. The obliquus capitis inferior arises from the spine of the axis, and is inserted into the transverse process of the atlas. 392 THE MUSCULAE SYSTEM. The obliquus capitis superior arises from the transverse process of the atlas, and is inserted into the occipital bone beneath and lateral to the semispinalis capitis and above the inferior curved line (Fig- 312, p. 391). The rectus capitis posterior major arises from the spine of the axis, and is inserted into the occipital bone beneath the obliquus capitis superior and semi- spinalis capitis and below the inferior curved line (Fig. 312, p. 391). The rectus capitis posterior minor arises beneath the previous muscle from the spine of the atlas, and is inserted into the occipital bone below the inferior curved line medial to and beneath the rectus capitis posterior major (Fig. 312, p. 391). The rotatores are eleven pairs of small muscles occupying the vertebral groove in the thoracic region, beneath the transverso-spinales, of which they form the deepest fibres. Each consists of a small slip arising from the transverse process and inserted into the lamina of the vertebra directly above. The inter-spinales are bands of muscular fibres connecting together the spinous processes of the vertebrae. The inter-transversarii are slender slips extending between the transverse processes. They are double in the neck, the anterior divisions of the spinal nerves passing between them. In the loin the inter-transverse muscles are usually double, but they are often absent, or are replaced by membrane. The rectus capitis lateralis, extending from the transverse process of the atlas to the jugular process of the occipital bone (Fig. 312, p. 391), is homologous with the posterior of the two inter-transverse muscles. Nerve-Supply. With the exception of the vei'tebro- scapular and vertebro- humeral muscles (trapezius, latissimus dorsi, levator scapulae, rhomboidei, p. 327), the muscles of the back are all sup- plied hj the posterior primary divisions of the spinal nerves. In the upper part of the trunk the muscles are supplied mainly by the lateral branches ; in the lower part chiefly by the medial branches of the nerves. In tlie cervical and sacral regions a A^ariable plexiform arrange- ment of the nerves occurs (posterior cervical sjoA posterior sacral plexuses). Actions. The action of these muscles is extremely complex. Not only do they act on the spinal column, ribs, head, and jjelvis, in conjunction with other muscles, but some of them act also in relation to the movements of the limbs as well. In this section will be given an analysis of their movements in relation to the sjjinal column, head, and pelvis. The movements of the limbs and of the ribs (respiration) are dealt with in other sections. The chief muscles are engaged in pre- serving the erect position, and in the movements of the trunk they are assisted in large measure by muscles whose chief actions are referred to elsewhere. 1. Movements of the Spinal Column. — The movements of the vertebral column are flexion, extension, and lateral movement or rotation. These movements occur in all regions — neck, thorax, and loin ; flexion and extension and lateral movement are most limited in the region of the thorax ; while rotation is most limited in the region of the loin. a. Flexion and Extension. Longus colli Serrati jDOsteriores Longus cajjitis (rectus capitis anterior major) Splenius capitis Scaleni anteriores (together) SiDlenius cervicis Psoas major and minor Sacro-si^inalis (erector spinas) Levator ani Semispinalis dorsi Coccygeus Semispinalis cervicis Semis2)inalis cajjitis (complexus) Sphincter ani extemus Multifidus Rectus abdominis Interspinales Pyramidalis Obliquus externus abdominis Intercostal muscles Obliquus intemus „ Diaphragm Transversus „ Transversus thoracis (triangularis stemi) THE MUSCLES OF THE BACK. 393 b. Lateral Movement (Rotation). 1 Levator scapulae Loiigus capitis (rectus capitis anterior major) Serrati posteriores Scaleni, anterior, ruedius, posterior Splenius cervicis Psoas (major and minor) Sacro-spinalis (erector spin?e) Quadratus lumborum Semispinalis capitis (complexus) Obliquus externus abdominis Semispinalis (dorsi and cervicis) Obliquus internus „ Multitidus Transversus „ Eota tores Eectus „ Inter-transversarii Pyramidalis „ Longus colli 2. Movements of the Head. — The movements of the head are flexion and extension, at the occipito-atlantoid articulation ; lateral movement and rotation at the atlanto-axial joint. a. Flexion and Extension. Digastric Stylo -hyoid S ty lo -pharyngeus Mylo-hyoid Hyo-glossus Sterno-hyoid Sterno-thyreoid Omo-hyoid Recti capitis anteriores (major and minor) {the muscles of both sides acting together) Sterno-mastoid Splenius capitis Longissimus ca23itis (trachelo-mastoid) Semispinalis capitis (complexus) Obliquus capitis inferior Recti capitis posteriores (major and minor) b. Lateral Movement. c. Rotation. Sterno-mastoid Splenius capitis Longissimus capitis (trachelo-mastoid) Semispinalis capitis (complexus) Obliquus cajsitis superior Rectus capitis lateralis Sterno-mastoid Splenius capitis Longissimus capitis (trachelo-mastoid) Semispinalis capitis (complexus) Obliquus capitis inferior ,, „ superior Recti capitis posteriores (major and minor) Movements of the Pelvis. — The movements of the pelvis (as in locomotion) are partly caused by certain of the muscles of the back. Those muscles, which are attached to the spinal column or the ribs on the one hand, and to the innominate bone on the other, produce the movements (flexion, extension, and lateral movement) of the whole pelvis. In addition, the muscles jjassing between the innominate bone and femur, in certain positions of the lower limb, assist in these movements. a. Extension and Flexion. Latissimus dorsi Psoas major and minor Sacro-spinalis (erector spinse) Rectus abdominis Multifidus (acting on both sides) Pyramidalis abdominis Obliquus externus abdominis Obliquus internus „ Transversus abdominis (acting on both sides) Piriformis Glutaii Obturator (externus and internus) Sartorius Tensor fasciae latae Iliacus Rectus femoris Adductors (in the erect position) b. Lateral Movement. Flexors and extensors of one side only 1 Quadratus lumborum 394 THE MUSCULAE SYSTEM. THE FASCIi^ AND IVIUSCLES AND NECK. FASCIiE. OF THE HEAD The superficial fascia of the head and ueck possesses certain features of special interest. Over the scalp it is closely adherent to the skin and subjacent epicranial aponeurosis, and contains the superficial vessels and nerves. Beneath the skin of the eyelids it is loose and thin and contains no fat. Over the face and at the side of the ueck it is separated from the deep fascia by the facial muscles and the platy sma. Between the buccinator and the masseter it is continuous with a pad of fat {suctorial pad) occupying the interval between these muscles. The deep fascia of the head and neck pre- sents many remarkable characters. Over 'the scalp it is represented by the epi- cranial aponeurosis (galea aponeurotica), the tendon of the epicraneus or occi- pito - frontalis muscle. This is a tough mem- brane, tightly stretched over the calvarium, from which it is separated by loose areolar tissue. It is attached posteriorly, partly through the agency of the occipitalis muscle, to the superior curved line of the oc- cipital bone ; anteriorly it joins the frontalis muscle and the orbicu- laris oculi, and has no bony attachment ; laterally it is attached to the temporal ridge and the mastoid process. Below the temporal ridge it is continuous with the temporal fascia, a stout layer of fascia attached to the temporal ridge and zygomatic arch, which covers and gives origin to the temporal muscle. This fascia separates into two layers above the zygoma, to enclose a quantity of fat along with Ijranches of the temporal and orbital arteries. On the face the fascia is practically non-existent anteriorly in relation to the facial muscles. Posteriorly it forms the thin masseteric fascia, and is much thicker in relation to the parotid gland, for which it forms a capsule. In the neck the deep fascia invests the muscles, and forms aponeurotic coverings for the pharynx, trachea, oesophagus, glands, and large vessels. It encloses the Fig. 313. 45 44 ~-'43 -Transverse Section in the Cervical Region (between the iourth and fifth cervical vertebrae). 1. Crico-thyreoid mtiscle. 2. Inkekior constrictor muscle. 3. Pharynx. 4. Cricoid cartilage. 5. Vocal cord. 6. THYRE0-ARYT.«N01I1 MUSCLE. 7. Thyreoid cartilage. 8. Glottis. 9. Layers of deep cervical fascia. 10. Sterno-hyoid muscle. 11. Omohyoid muscle. 12. .Sterno-thyreoid muscle. 13. Cervical fascia. 14. Thyreoid body. . 15. CoiiiTiioii carotid artery. 16. Descendens hypoglossi nerve. 17. Sterno-mastoid muscle. 18. Internal .jngnlar .vein. 19. Pnenniogastric nerve. 20. Synipatlietic nerve. 21. Carotid sheath. 22. Phrenic nerve. 23. I.ONGUS COLLI MUSCLH. 24. LONOUS CAPITIS (RECTUS ANTERIOR major). 25. Scalenus antk.rior. 26. Vertebral vein. 27. Scalenus medius. 28. Posterior triangle. 29. Scalenus posterior. 30. Levator scapul.e. .Tl. Spinal accessory nerve. 3-J. Spt.enius ceevicis. 33. LONKISSIMUS CERVICIS ALIS CERVICIS). (transvers- 34. lonoissimus capitis mastoid). (trachelo- 35. Spinal nerve. 3(3. Vertebral artery. 37. Profunda cervieis vein. 38. Profunda cervieis artorj 39. MULTIFIDUS. 40. SEMISPINALIS CERVICIS. 41. Semispinalis capitis (c omplexus). 42. Splenius capitis. 43. Trapezius. 44. Ligamentuni nuclue. 4i. Spine of fourth cervical vertebra. 46. Lamina of fifth cervical \'ertebra. 47. Uura mater. CAPITIS 48. Spinal cord. 49. Transverse i)rocess. 50. Disc between fourth an( fifth cervical • vertebra-. THE MUSCLES OF THE HEAD. 395 sterno- mastoid muscle, and can be traced backwards over the posterior triangle to the trapezius and deeper muscles, which it surrounds ; it can be traced forwards over the anterior triangle to the middle line of the neck, where it forms a continuous membrane. Above the sternum the fascia, after enclosing the sterno- mastoid muscles, is attached in the form of two layers to the front and back of the episternal notch. The layer enclosing the infrahyoid muscles passes across the middle line of the neck in front of the trachea, and is attached above to the hyoid bone, below to the sternum, clavicle, and first rib. A third layer of fascia passes inwards in front of the trachea, enclosing the thyreoid body. Beneath the sterno- mastoid the fascia helps to form the carotid sheath, which is completed by septal processes stretching inwards across the neck in relation to the infrahyoid muscles, trachea, oesophagus, and pharynx, and the prsevertebral muscles. The trachea, oesophagus, and pharynx are likewise encapsuled in cervical fascia, a septal layer passing across the middle line of the neck between the trachea and oesophagus. Lastly, a strong prsevertebral fascia passes across the neck in front of the prevertebral muscles, and behind the oesophagus and pharynx. The cervical fascia is attached above to the bones of the skull : superficially to the superior curved line of the occipital bone, the mastoid process, the zygoma (over the parotid gland), and the lower border of the mandible ; more deeply to the styloid and vaginal processes of the temporal bone, the great wing of the sphenoid and the basilar process. This deeper attachment {prcevertehral fascia) is behind the parotid gland and pharynx, and is associated with the formation of three ligaments : stylo-mandibular ligament, internal lateral ligament of the lower jaw (spheno- mandibular), and pterygo-spinous ligament. The fascia is attached below, through its muscular connexions, to the sternum, first rib, clavicle, and scapula. By means of its connexion with the trachea and the common carotid artery it is carried down behind the first rib into the superior mediastinum, and so becomes continuous with the pericardium. By means of its connexion vv^ith the subclavian vessels and brachial nerves it is carried down to the axilla, as the subclavian sheath, which becomes connected with the costo-coracoid membrane. THE MUSCLES OF THE HEAD. The muscles of the head are divisible into three separate groups : the super- ficial muscles, muscles of the orbit, and muscles of mastication. Superficial IVIuscIes. The superficial muscles comprise a large group, including the muscles of the scalp and face, and the platysma in the neck. The platysma is a thin quadrilateral sheet extending from chest to face over the side of the neck, between the superficial and deep fasciae. It arises from the deep fascia of the pectoral region and the clavicle. It is directed upwards and forwards, and is partly inserted (by its intermediate fibres) into the lower border of the mandible, becoming connected with the quadratus labii inferioris (depressor labii inferioris) and triangularis (depressor anguli oris) muscles (Eig. 314, p. 396). The more anterior fibres pass across the middle line of the neck and decussate for a variable distance below the chin with those of the opposite side. The posterior fibres sweep over the angle of the jaw and become continuous with the risorius muscle. The platysma is the rudiment of the cervical portion of the panniculus carnosus of lower animals, in which it has a much more intimate connexion with the muscles of the face than is usually the case in man. The IVIuscIes of the Scalp. The muscles of the scalp comprise the occipito-frontalis (epicranius) muscle and the muscles of the external ear. The epicranius (occipito-frontalis) is a muscle with two bellies and an intervening tendon (the galea aponeurotica) which stretches uninterruptedly across the middle line of the cranium. The posterior belly (occipitalis) arises as a broad 27 396 THE MUSCULAE SYSTEM. flat band from the lateral two-thirds of the superior curved Hne of the occipital bone. The anterior belly (frontalis) has no bony attachments ; arising from the epicranial aponeurosis about the level of the coronal suture, it passes downwards to the supra-orbital arch, where it blends with the orbicularis oculi and corru gator supercilii muscles. It extends across the full width of the forehead, and blends in the middle line with the muscle of the opposite side. The epicranial aponeurosis or galea aponeurotica, extending between the two fleshy bellies, is a continuous membrane which glides over the calvarium, and has attachments laterally to the temporal ridge, and behind, between the posterior belhes, to the superior curved lines of the occipital bone. It has no osseous attach- Epicranial aponeurosis (Galea aponeurotica) Superior ACRICULAIl MUSCLE _ Anterior auricular MUSCLE Occipitalis -Orbicularis oculi M. PROCERUS (PVRAMIDALIS NASI) f — Caput angulare - Compressor naris "Caput angulare ]. Caput infraorbitale j ^^ Caput zygomaticum J Caninus (levator anguli oris) Zyoomaticds (major) Orbicularis oris Buccinator RiSORIUS - M. triangularis (depressor anguli oris) - m. qoadratus labii inferioris (depressor LABII INFERIORIS) Masseter I'l.A'l VSMA Fig. 314. — The Muscles of the Face and Scalp (Muscles of Expression). ment anteriorly. The epicraneus is usually rudimentary. By the contrac- tion of the fibres of the frontalis muscle the skin of the forehead is thrown into horizontal parallel folds. The extrinsic muscles of the ear are three in number : posterior, superior, and anterior (retrahens, attollens, and attrahens aurem). They are rudimentary and usually function less. The m. auricularis posterior (retrahens aurem) is a narrow fleshy slip which arises from tbe surface of the mastoid process and is inserted into the deep surface of the pinna. It bridges across the groove between the mastoid process and the pinna, and conceals the posterior auricular vessels and nerve. The m. auricularis superior (attollens aurem) is a small fan-shaped muscle which arises from the temporal fascia, and descends to be inserted into the top of the root of the pinna. The m. auricularis anterior (attrahens aurem) is a similar small muscle, placed J THE MUSCLES OF THE FACE. 397 in front of the attollens, and stretching obUquely between the temporal fascia and the top of the root of the pinna. The IVIuscIes of the Face. The facial muscles are divided into tliree groups, associated with the several apertures of the eye, nose, and mouth. 1. The muscles of the eyelids include four muscles : the levator palpebrte superioris (described with the orbital muscles (p. 399)), orbicularis oculi (palpe- brarum), tensor tarsi (tarsal part of the orbicularis oculi), and corrugator supercilii. The orbicularis oculi is a transversely oval sphincter muscle surrounding and occupying the eyelids. It is divisible into a 'peripheral 'portion (j)ars orhitalis) com- posed of coarse fibres, spreading on to the forehead, temple, and cheek, and a central portion (pars palpebralis), composed of finer fibres, situated beneath the skin of the eyelids. At the medial canthus of the eye the muscle (by its palpebral fibres) gains an attachment to the tarsal ligament and the borders of the naso- lacrimal groove. Its fibres enclose the lacrimal sac and the canaliculi. The posterior fibres, extending between the posterior edge of the naso-lacrimal groove and the tarsal ligaments behind the lacrimal sac, constitute the pars lacrimalis or tensor tarsi muscle. The fibres of the muscle which extend along the margins of the lids constitute a separate ciliary bundle. Laterally the orbicularis oculi has no bony attachment ; so that when it contracts and closes the eyelids, both lids at the same time tend to be drawn inwards towards the medial canthus of the eye. The corrugator supercilii arises from the nasal eminence, and passing horizon- tally outwards, blends with the upper fibres of the orbicularis oculi on its under surface. The contraction of this muscle throws the skin of the forehead into vertical folds, while at the same time drawing the medial half of the eyebrow upwards, it produces concentric curved folds on each side of the middle line of the forehead. 2. The muscles of the nose comprise five small muscles proper to the nose, and one common to the nose and upper lip : the m. procerus (or pyramidalis nasi), compressor naris, dilatores naris (anterior and posterior), depressor alee nasi, and angular head of the quadratus labii superioris (levator labii superioris alseque nasi). They are all small and feeble muscles. The m. procerus (pyramidalis nasi) arises from the epicranius muscle and the skin over the glabella ; it is inserted into a membrane stretching over the nose, which also gives attachment to the compressor naris. The m. nasalis (compressor naris) arises by a narrow origin from the maxilla, under cover of the quadratus (levator labii superioris alseque nasi). It passes forwards over the bridge of the nose, and ends in a membranous insertion common to it and the previous muscle. The dilatores naris are feeble muscular slips placed on the lateral surface of the margin of the nostril, one anteriorly, the other posteriorly. The depressor alse nasi is a small muscle arising from the upper part of the incisor fossa of the maxilla ; it divides into two parts as it passes upwards and medially, and is inserted into the ala and the septum of the nose (depressor septi). The levator labii superioris alaeque nasi now forms a portion (caput angxdare) of the quadrate muscle of the upper lip, and is a narrow band arising from the root of the frontal process of the maxilla. It descends alongside the nose, and is inserted, partly into the ala of the nose and partly into the orbicularis oris muscle. 3. The muscles of the mouth comprise a number of muscles, of which all but one, the orbicularis oris, are bilaterally placed. The muscles are : quadratus labii superioris, which includes the angular head or levator labii superioris alaeque nasi, the infra-orbital head or levator labii superioris, and the zygomatic head or zygomaticus minor, the canine muscle or levator anguli oris, zygomaticus (m. zygo- maticus major), risorius, orbicularis oris, triangularis or depressor anguh oris, m. quadratus labii inferioris or depressor labii inferioris, m. mentalis (levator menti), and buccinator. 398 THE MUSCULAR SYSTEM. The orbicularis oris is the sphincter muscle surrouuding the lips. It is con- tinuous with the other muscles converging to the mouth. It lies between the skin and mucous membrane of the mouth, and is limited above by the nose, below by the junction of the lower lip and chin. Its medial fibres are attached above to the septum of the nose {naso-lahial band) and to the incisor fossa (superior incisive bundle) ; below they are attached to the lower jaw on each side of the symphysis (inferior incisive bundle). These bundles radiate laterally to join the rest of the muscle, which is joined at its margin by the elevators and depressors of the lower lip and angle of the mouth, and by the buccinator muscle. The lower fibres of the muscle are continued laterally into the buccinator and canine (levator anguli oris) muscles ; its ^tp^jer fibres are continued into the buccinator and triangular (depressor anguli oris) muscles. The quadratus labii superioris comprises three muscles. (1) The caput angulare (levator labii superioris alaeque nasi) has already been described. (2) The caput infra- orbitale (levator labii superioris) arises from the maxilla just above the infra-orbital foramen. It passes almost vertically downwards to join the orbicularis oris and the skin of the upper lip between the attachments of the previous muscle (caput angulare) and the caninus (levator anguli oris). It conceals the infra-orbital vessels and nerve. (3) The caput zygomaticum (zygomaticus minor) arises from the zygomatic bone, and is often continuous with the most peripheral fibres of the orbicularis oculi. It is directed obliquely downwards and forwards over the caninus (levator anguli oris), to be inserted, along with the previous muscle (c. infra -orbitale), into the margin of the orbicularis oris. The caninus (levator anguli oris) arises from the canine fossa of the maxilla below the infra -orbital foramen and under cover of the foregoing muscle. It is directed laterally and downwards, to be inserted into the orbicularis oris and the skin at the angle of the mouth. The zygomaticus (zygomaticus major) is a narrow muscular band which arises from the zygomatic portion of the zygomatic arch. It passes to the angle of the mouth, to be inserted partly into the skin, partly into the orbicularis oris. The risorius is a thin flat muscle which forms in part a continuation of the platysma on the face, in part a separate muscle, with an origin from the masseteric fascia. It passes transversely forwards, to be inserted at the angle of the mouth into the orbicularis oris and skin. The triangularis (depressor anguli oris) arises from the oblique line of the lower jaw and is continuous with the platysma (Fig. 314, p. 396). It is triangular in form, its fibres converging to the angle of the mouth, where they are inserted into the orbicularis oris and the skin. Some of the fibres reach the upper lip through the orbicularis muscle. The quadratus labii inferioris (depressor labii inferioris) arises from the lateral surface of the lower jaw beneath and medial to the previous muscle (Fig. 314, p. 396). It is quadrilateral in form, and is directed upwards, to be inserted . into the orbicularis oris and the skin of the lower lip. Its lateral fibres are overlapped by the triangularis oris. Its medial fibres join with those of the opposite muscle. The mentalis ^levator menti) is a small muscle which arises from the incisor fossa of the mandible and is inserted into the skin of the chin. Tiie buccinator muscle forms the lateral wall of the mouth, and is in series posteriorly with the constrictor muscles of the pharynx. It arises (1) from the alveolar arches of the upper and lower jaws (Fig. 322, p. 404), and between these attachments, (2) from the pterygo- mandibular ligament. Its fibres are directed forwards to the angle of the mouth, where they blend with the corresponding (upper and lower) portions of the orbicularis oris muscle. The middle fibres of the muscle decussate at the angle of the mouth, so as to pass, the lower set to the upper lip, the upper set to the lower lip. The buccinator is covered on its deep surface by the mucous membrane of the mouth. Superficially it is concealed by FASCIA AND MtTSCLES OF THE ORBIT. 399 the muscles above mentioned, which converge to the angle of the mouth ; it is separated from the masseter by the suctorial pad of fat ; it is pierced by the duct of the parotid gland, and by branches of the long buccal nerve. Nerve-Supply. The facial and scalp muscles are all innervated by tlie facial nerve. The posterior auricular branch supj)lies the posterior auricular muscle and occipitalis ; tlie branches forming the pes anserinus supply the frontalis, superior and anterior auricular muscles, the several muscles associated with the apertures of the eye, nose, and mouth (including the buccinator), and the platysma. Actions. The almost infinite variety of facial expression is produced partly by the action of these muscles, partly by their inactivity, or by the action of antagonising muscles (antithesis). On the one hand joy, for example, is betrayed by the action of one set of muscles, while grief is accom- panied by the contraction of another (opposing) set. Determination or eagerness is accompanied by a fixed expression due to a combination of muscles acting together ; despair, on the other hand, is expressed by a relaxation of muscular action. For a philosophical account of the action of the facial muscles, the student should consult Darwin's Expression of the Emotions in Man and Animals, and Ducheune's MScanisme de la Physiologic humaine. The platysma retracts and depresses the angle of the mouth, and depresses the lower jaw. The epicranius, by its anterior bellj^, raises the eyebrows ; both bellies acting together tighten the skin of the scalp ; acting along with the orbicularis oculi, it shifts the scalp back- wards and forwards. The corrugator supercilii draws inwards the eyebrow and vertically wrinkles the skin of the forehead. The m. procerus (pyramidalis nasi) draws downwards the skin between the eyebrows, as in frowTiing. The upper eyelid is raised by the levator palpebrae superioris. The closure of the lids is effected by the orbicularis oculi, whose fibres also assist in the lowering of the ej'ebrows, in tlie protection of the eyeball, and, by j^ressure on the lacrimal gland, in the secretion of tears. The tarsal part, acting along with the orbicularis oculi, compresses the lacrimal sac and aids in the passage of its contents into the nasal duct. The muscles of the ear and nose have quite rudimentary actions. Of the muscles of the mouth, the orbicularis oris has a complex action, dejiending on the degree of contraction of its component parts. It causes compression and closure of the lips in various ways, tightening the lips OA'er the teeth, contracting them as in osculation, or causing pouting or protrusion of one or the other. The accessory muscles of the lips draw them upwards (zygomaticus, m. quadratus labii superioris), laterally (zygomaticus, risorius, platysma, triangularis, buccinator), and down- wards (triangularis, quadra tus labii infiTioris, platysma). The mental muscle elevates the skin of the chin and protrudes the lower lip. The buccinator retracts the angles of the mouth, flattens the cheeks, and brings them in contact with the teeth. Levator palpekr.e superioris Hkctus superior Obliquus Superior Rectus medialis The Fasciae and IVIuscIes of the Orbit. The eyeball, with its muscles, vessels, and nerves, is lodged in a mass of soft and yielding fat which entirely fills up the cavity of the orbit. Surrounding the posterior part of the eyeball is the fascia bulbi (capsule of Tenon), which constitutes a large lymph space or synovial bursa in relation to the posterior part of the eyeball. Anteriorly the capsule is in contact with the conjunctiva, and intervenes between the latter and the eyeball ; pos- teriorly it is pierced by and prolonged along the optic nerve. It is a smooth mem- brane connected to the globe of the eye by loose areolar tissue. It is pierced by the tendons of the ocular muscles, along which it sends prolonga- tions continuous with the muscular sheaths. ^ ,,- ^ ^^ ^ t ^ rp, p +1, K-+ Fig. 315. — Transverse \ ERTiCAL Section THROUGH THE Left Orbft Ine muscles or the orbit behind the Eyeball to show the Arrangement of Muscles. are seven in number : one, the levator palpebr^ superioris, belongs to the upper eyelid ; the other six are muscles of the eyeball. The levator palpebrae superioris lies immediately beneath the orbital peri- osteum and covers the superior rectus muscle. It has a narrow origin above that Rectus lateralis Obliquus inferior Rectus inkerior 400 THE MUSCULAE SYSTEM. Levator PALPEBRiE SUPERIORIS Fig. 3 1 6. — The Muscles op the Eight Orbit (from above). muscle from the margin of the optic foramen. It expands as it passes forwards, to end, in relation to the upper lid, in a membranous expansion which is inserted in a fourfold manner : (1) into the orbicularis oculi and skin of the upper lid, Orbicularis oculi (2) mainly into the Upper border of the superior tarsal plate, (3) into the con- junctiva, and (4) by its edges into the upper border of the margin of the orbital opening. The recti muscles are four in number — superior, inferior, medial, and lateral. They all arise from a membranous ring surrounding the optic foramen, which is separable into two parts — a swperior common tendon, giving origin to the superior and medial recti and the upper head of the lateral rectus; and an inferior common tendon, giving origin to the medial and inferior recti and th6 lower head of the lateral rectus. The two origins of the lateral rectus muscle are separated by the passage into the orbit of the oculo- motor, nasal, and abducent nerves. Forming flattened bands which lie in the fat of the orbit around the optic nerve and eyeball, the four muscles end in tendons which pierce the fascia bulbi (capsule of Tenon), and are inserted into the sclera about eight millimetres (three to four lines) behind the margin of the cornea. The superior and inferior recti are inserted in the vertical plane slightly medial to the axis of the eyeball ; the lateral and medial recti in the trans- verse plane of the eyeball ; and all are attached in front of the equator of the eyeball. The obliquus superior arises from the margin of the optic foramen between the rectus superior and rectus medialis. It passes for- wards as a narrow muscular band medial to the rectus superior, and at the anterior margin of the orbit forms a narrow tendon which passes through a special fibrous pulley (trochlea) attached to the roof of the orbit. Its direction is then altered, and passing laterally between the tendon of the superior rectus and the eyeball, it is inserted into the sclera between the superior and lateral recti, midway between the margin of the cornea and the entrance of the optic nerve. The obliquus inferior arises from the medial side of the floor of the orbit just behind its anterior margin, and lateral to the naso- lacrimal groove. It forms a slender rounded slip, which curls round the inferior rectus tendon, and passes between the lateral rectus and the eyeball, to be inserted into the sclera between the superior and lateral recti, and farther back than the superior oblique muscle. Obliquus superior Levator PALPEBRiE superioris (cut) Rlctus superior Rectus lateralis Oculo-motor nerve Nasal nerve Abducent nerve Rectus inferior Obliquus inferior Fio. 317. — The Muscles of the Left Orbit (from without). MUSCLES OF MASTICATION. 401 Miiller's muscle is a rudimentary bundle of non-striated muscular fibres bridging across the spheno-maxillary fissure and infra-orbital groove. It is supplied by fibres from the sympathetic, and may have a slight influence in the protrusion of the eyeball. Lacrimal nerve Nerves to rectus superior and levator palpebra? superioris from oculo-motor nervt Trochlear nerv Rectus laterali Abducent nervi Oculo-motor nerve (inferior, division) Ciliary ganglion' Nerve to rectus inferior, from oculo-motor nerve' Nerve to obllquus inferior, from oculo-motor nerve Lacrimal gland Frniit.ll VPvve Supra-orbital nerve Supra-trochlear nerve Levator palpebr* sliperioris ItECTUS SUPERIOR Obliquus superior Nasal nerve Infra-troclilear nerve Rectus medialis Nerve to rectus medialis from oculo-motor Oplitlialmic ai-tery Optic nerve Long ciliary nerves Rectus inferior Obliquus inferior FiQ. 318. — Schematic Representation of the Nerves which traverse the Cavity of the Right Orbit. Nerve-Supply. The muscles of the orbital cavity are supplied by the third, fourth, and sixth cranial nerves. The fourth nerve (trochlearis) supplies the obliquus superior ; the sixth (abducens) supplies the rectus lateralis; the third nerve (motor oculi) supplies the others — levator palpebrse superioris, recti, superior, inferior, and medialis, and obliquus inferior. Actions. The levator palpebrae superioris elevates the upper eyelid and antagonises the orbicularis oculi muscle. The six muscles inserted into the eyeball serve to move the longitudinal axis of the eyeball upwards, downwards, inwards, and outwards, besides causing a rotation of the eyeball on its o-mi axis. The following table expresses the action of individual muscles. It must be remembered that, while similar movements occur simultaneously in the two eyeballs, the horizontal movements may, by adduction of the muscles of both sides, cause convergence of the axes of the two eyeballs for the purposes of near vision. a. Adduction xnd Abduction. Rectus medialis Rectus superior Rectus inferior Rectus lateralis Obliquus superior \(correc. -Muscle-Attachmknts on the Medial Side of the Lower Jaw. MUSCLES OF MASTICATION. 403 Galpa aponeurotica -, Temporal fascia Temporal fascia (deep layer) EpICRANIUS Ml'SCLK Temporal muscle Aiiriculo-tem])oral nerve Superficial temporal artery " Masseter (deep fibres) Parotid gland (drawn backwards- and downwards Orbicularis oculi Caput zyoomaticus M. OF quadratus LABII SUPERIORIS Masseter (superficial fibres) Stenson's duct -^ Buccinator Triangularis (depressor anguli oris) Facial artery Fig. 320.— Muscles of Mastication (superficial view). Temporal muscle Buccinator Fig. 321. -The Right Temporal Muscle (the zygonia and the masseter muscle have been removed). 404 THE MUSCULAE SYSTEM. Nerve-Supply. Tlie inferior maxillary division of the fifth, nerve ^ supplies all the muscles of mastication except the bueeiuator, which is supplied by the facial nerve. The internal pterygoid muscle is supplied by the nerve before its division into anterior and posterior parts ; the other muscles are innervated by the anterior trunk. Temporal muscle (reflected) / I External pterygoid Internal pterygoid Pterygo-mandibiilar ligament Bdccinator Fig. 322. — The Pteeygoid Muscles of the Right Side. Actions. The above muscles, assisted by others in the neck, produce the various movements of the lower jaw, as follows : — a. Openin'g and Closure of the Jaw. Weight of the jaw Digastric Mylo-hyoid Genio-hyoid Genio-glossus Infra-hyoid muscles Masseter Temporal Internal pterygoid b. Protrusion and Retraction. External pterygoid Internal pterygoid Temporal {anterior fibres) Temporal {posterior fibres) c. Lateral Movement of the Jaw. ^ fntS/ P*^'^^°'^}(«/''^« ^de) THE MUSCLES OF THE NECK. In addition to those included among the muscles of the back (p. 386), the following series of muscles occur in the neck : (1) sterno-cleido-mastoid'; (2) the ^ The 3rd or inferior maxillary division of the 5th = the mandibular nerve of the B.N. A. classification. THE MUSCLES OF THE HYOID BONE. 405 muscles of the hyoid bone (supra-hyoid and infra-hyoid) ; (3) the muscles of the tongue (extrinsic and intrinsic) ; (4) the muscles of the pharynx and soft palate ; and (5) the praevertebral muscles. The sterno-cleido-mastoid muscle is the prominent muscle projecting on the side of the neck, and separating the anterior from the posterior triangle. It arises by two heads — (1) a narrow tendinous sternal head, from the anterior surface of the manubrium sterni (Fig. 246, p. 323), and (2) a broader clavicular origin, partly tendinous, partly fleshy, from the upper surface of the clavicle in its medial third Semispinalis capitis (complexus) (insertion) Rectus capitis posterior minor (insertion) Rectus capitis posterior major (insertion) Trapezius (origin) Sterno-cleido-mastoid (insertion) Splenius capitis (insertion) Obliquus capitis superior' (insertion) Rectus capitis lateralis (insertion) Rectus capitis anterior (insertion^ (rectus capitis anterior minor) Longus capitis (rectus capitis anterioi V minor) (insertion) Superior constrictor of pharynx (insertion) Fig. 323. — Muscle-Attachments to the Occipital Bone (Parietal Surface). (Fig. 325, p. 407). The muscle is inserted into the lateral surface of the mastoid process and into the superior curved line of the occipital bone (Fig. 312, p. 391). It conceals the cervical plexus and the (spinaJ) accessory nerve. The last-named nerve pierces the muscle. The sterno-cleido-mastoid muscle is properly divisible into three parts : (1) sterno-mastoid, placed superficially, and passing obliquely from tbe sternum to the mastoid process ; (2) cleido- mastoid, placed more deeply, and directed vertically upwards from the clavicle to the mastoid process ; and (3) cleido-occipitalis, passing obliquely upwards and backwards behind the cleido- mastoid to the superior curved line of the occipital bone. Nerve-Supply. The sterno-mastoid muscle is innervated by the (spinal) accessory nerve, joined by a branch from the cervical plexus (C. 2.). The action of the muscle is referred to below. The Muscles of the Hyoid Bone. The muscles attached to the hyoid bone are in three series: (1) infra-hyoid muscles, connecting the hyoid bone to the scapula, thorax, and thyreoid cartilage ; (2) supra-hyoid muscles, connecting it to the lower jaw, cranium, and tongue ; and (3) the middle constrictor muscle of the pharynx (p. 411). The infra-hyoid muscles comprise the omo-hyoid, sterno-hyoid, sterno-thyreoid, and thyreo-hyoid muscles. The omo-hyoid is a muscle with two beUies, anterior and posterior. The 406 THE MUSCULAE SYSTEM. posterior belly arises from the superior border of the scapula and the suprascapular ligament (Fig. 250, p. 326). It forms a narrow muscular band, which is directed obliquely forwards and upwards, to end in an intermediate tendon beneath the sterno-mastoid muscle. From this tendon the anterior belly proceeds upwards to be inserted into the lateral part of the lower border of the body of the hyoid bone. The posterior belly of the muscle separates the posterior triangle into occipital and subclavian parts; the anterior belly crosses the common carotid artery at the level of the cricoid cartilage, and in the anterior triangle forms the boundary between the muscular and carotid triangles. A process of the deep cervical fascia binds down the tendon and the posterior belly to the scapula and^^he first rib. The sterno-hyoid muscle arises from the posterior surface of the manubrium, from the back of the first costal cartilage, and from the clavicle (Fig. 243, p. 320). STYLO-GLOSSUb; Stylo-hyoid ligament Stylo pharyngeus Stylo-hyoid— Digastric (posterior- belly) Middle coNSTRiCTOEm. — ^~f«Y- -V- Hyo-glossus ■■*'~I-Genio-hyoid - Var ^aj^~ Sterno-thyreoid .Sterno-hyoid Fig. 324. — The Mcscles of the Tongue and Hyoid Bone (right side). It passes vertically upwards in the neck, medial to the omo-hyoid and in front of the sterno-thyreoid muscle, to be inserted into the medial part of the body of the hyoid bone. Except near its origin the muscle is superficially placed. The sterno-thyreoid muscle arises beneath the sterno-hyoid from the back of the manubrium and first costal cartilage. Broader than the preceding muscle, it passes upwards and slightly in a lateral direction in the neck in front of the trachea and thyreoid body, and beneath the omo-hyoid and sterno-hyoid muscles, to be inserted into the oblique line of the thyreoid cartilage. The muscle is marked by an obhque tendinous intersection in the middle of its length. The thyreo-hyoid muscle continues the line ot" the preceding muscle to the hyoid bone. Short and quadrilateral, it arises from the oblique line of the thyreoid cartilage, and passing over the thyreo-hyoid membrane beneath the omo-hyoid and sterno-hyoid, it is inserted into the body and great cornu of the hyoid bone. The levator glandulse thyreoideae is an occasional slip stretcliing between the hyoid bone and the isthmus or pyramid of tlie tliyreoid body. The supra-hyoid muscles comprise the digastric, stylo-hyoid, mylo-hyoid and THE MUSCLES OF THE HYOID BONE. 407 genio-hyoid muscles, and also two muscles, the genio-glossus and hyo-glossus, which will be described along with the extrinsic muscles of the tongue. The digastric muscle, as its name implies, possesses two bellies — anterior and posterior. The posterior belly arises under cover of the sterno-mastoid muscle from the digastric groove beneath the mastoid process. It is directed forwards and down- wards, in company with the stylo-hyoid muscle, to end in an intermediate tendon, which is connected by a pulley-like band of cervical fascia to the body of the hyoid bone. The anterior belly of the muscle is directed forwards and upwards over the mylo-hyoid muscle to the chin, and is inserted into an oval impression on the lower Sterso-cleido- MASTOID Semispinalis capitis (com plexus) Splenius capitis Scalenus ajjterior — Omo-hvoid Trapezius Mylo-hyoid Digastric Hyoglossus Stylo-hyoid JIlDDLE constrictor Thyreo-hyoid Inferior constrictor 0.M0-HY0ID Inferior constrictor Sterno-hyoid Sterno-thyreoid Fig. 325. — The Muscles of the Side of the Neck (anterior and posterior triangles). border of the mandible close to the symphysis (Fig. 319 h, p. 402). The muscle forms the lower boundary of the submaxillary division of the anterior triangle. The stylo-hyoid muscle arises from the lower border of the styloid process of the temporal bone. Crossing the anterior triangle obliquely along with the posterior belly of the digastric muscle, it is inserted into the body of the hyoid bone by two slips which enclose the tendon of the digastric muscle. The mylo-hyoid muscle forms with its fellow a diaphragm in the floor of the mouth. It arises from the lower three-fourths of the mylo-hyoid ridge of the lower jaw (Fig. 319 &, p. 402). It is directed downwards and medially, to be inserted into (1) the upper border of the body of the hyoid bone, and more anteriorly (along with the opposite muscle) into (2) a median raphe extending from the hyoid bone nearly to 408 THE MUSCULAE SYSTEM. External Ptery- goid (insertion) the chin. The muscle has in contact with its superficial or lateral surface the digastric muscle and the submaxillary gland. Its deep or medial surface is partially covered by the mucous membrane of the floor of the mouth, and is separated from the muscles of the tongue by the deep part of the submaxillary gland, the sublingual gland, Whar- ton's duct and the lingual and hypoglossal nerves. The genio - hyoid muscle, lying beneath the digastric and mylo- hyoid muscles, arises from the lower of the two mental spines on the back of the sym- physis of the lower jaw (Fig. 326, p. 408). It is directed downwards and backwards, along the lower border of the genio-glossus, to be inserted into the front of the body of the hyoid bone. The muscles of opposite sides are often fused together. Fig. 326. — Muscle-Attachments on the Medial Side of the Lower Jaw. -, ,. ,. Superior M. transyersus M. yerticalis longitudinal muscle Imguse linguae M. vertiealis linguae The Muscles of the Tongue. The muscular substance of the tongue consists of two symmetrical series of muscles placed on either side of a membranous raphe in the middle line. The series comprise (1) extrinsic muscles arising from the soft palate, styloid process, hyoid bone and lower jaw, and (2) intrinsic muscles proper to the tongue itself. Each set consists of four series of muscles. The extrinsic muscles are four in number : (1) genio - glossus, (2) hyo - glossus, (3) stylo - glossus, and (4) glosso-palatinus (palato- glossus). The genio-glossus muscle (genio-hyo-glossus) (Fig. 324, p. 406) is an ex- trinsic muscle of the tongue as well as a supra-hyoid muscle. It is a fan-shaped muscle arising by its apex from the upper of the two mental spines, behind the symphysis of the lower jaw (Fig. 326, p. 408). From this origin the muscular fibres diverge; the lowest fibres are directed down- wards and backwards, to be inserted into the body of the hyoid bone ; the highest fibres curve forwards, to be attached to the tip of the tongue ; the intermediate fibres are attached to the substance of the tongue in its whole length between the base and tip. The muscles of opposite sides are separated by the median raphe of .Septum M. transversus B lingUiB Inferior longitudinal muscle Fig. 327. — A, Transverse, and B, Longitudinal Vertical Sections through the Tongue (Krause). THE MUSCLES OF THE TONGUE. 409 the tongue. On the lateral aspect of each are the hyo-glossus and mylo-hyoid muscles. The hyo-glossus muscle is also an extrinsic muscle of the tongue as well as a supra-hyoid muscle. It arises from the body and great cornu of the hyoid bone, and is directed upwards and forwards, to be inserted into the side of the tongue, its fibres interlacing with the fibres of the stylo-glossus. The muscle is quadrilateral^ and lies between the genio-glossus and mylo-hyoid muscles, separated from the latter by the mucous membrane of the floor of the mouth, the sublingual and part of the submaxillary glands, the lingual and hypoglossal nerves, and Wharton's duct. The chondro-glossus is a small separated slip of the hyo-glossus, not always present. The stylo-glossus muscle arises from the upper border of the styloid process near its tip, and from the stylo-mandibular ligament. It sweeps forwards and medially, and is inserted into the side and under surface of the tongue, its fibres spreading out to decussate with those of the palato-glossus and hyo-glossus muscles beneath the parotid gland and the mucous membrane of the tongue. The glosso-palatinus (palato-glossus) is a thin sheet of muscular fibres arising from the under surface of the soft palate, where it is continuous with fibres of the opposite muscle. It passes downwards in the anterior pillar of the fauces, and spreads out, to be inserted into the sides of the tongue, blending with the stylo-glossus and the deep transverse fibres of the tongue. The muscle is placed directly beneath the mucous membrane of the soft palate and tongue. Intrinsic Muscles of the Tongue. — Besides receiving the fibres of insertion of the extrinsic muscles, the substance of the tongue is composed of four intrinsic muscles on either side, two in the sagittal plane, the superior and inferior longi- tudinal muscles ; two in the coronal plane, the transverse and vertical muscles. The superior longitudinal muscle extends from base to tip of the tongue. It is placed on its dorsum immediately under the mucous membrane, into which many of its fibres are inserted. The inferior longitudinal muscle is a cylindrical band of muscular fibres occupying the under part of the organ on each side, in the interval between the genio-glossus and the hyo-glossus muscles. Posteriorly some of its fibres extend to the hyoid bone. The transversus linguae (transverse fibres) arise from the median raphe, and radiate outwards to the dorsum and sides of the tongue, intermingling with the extrinsic muscles and the fibres of the vertical muscle. They occupy the substance of the tongue between the superior and inferior longitudinal muscles. The so-called verticalis linguae (vertical fibres) arise from the dorsal surface of the tongue, and sweep downwards and laterally to its sides, intermingled with the fibres of the previous muscle and the insertions of the extrinsic muscles. These two muscles form a very considerable part of the to.tal muscular substance of the organ. Nerve-Supply. Most of the muscles of the hyoid bone and tongue are supplied by the hypoglossal nerve, or through the hypoglossal, by cervical nerves with which it is connected. The hypoglossal nerve receives a communicating branch from the loop between the first and second cervical nerves, which thereby directly innervate the genio-hyoid and thyreo-hyoid muscles, and con- stitute the descendens hypoglossi. This nerve is joined by the descendens cervicis formed from the second and third cervical nerves, to form the ansa hypoglossi, from which branches go to the omo-hyoid, sterno-hyoid, and sterno-thyreoid muscles. The genio-glossus, hyo-glossus, stylo-glossus, and the intrinsic muscles of the tongue are supplied by the hypoglossal nerve. The glosso-palatinus receives its nerve-supjily from the spinal accessory nerve ^ through the pharyngeal plexus. The mylo-hyoid and anterior belly of the digastric are supplied by the mylo-hyoid branch of the inferior dental nerve.- The posterior belly of the digastric and the stylo-hyoid muscles are innervated by the facial nerve. Actions. These muscles have a complexity of action, owing to their numerous attachments to more or less movable points. The movements for which they are responsible in whole or part are (1) movements of the hyoid bone in mastication and deglutition, (2) movements of the thyreoid cartilage, (3) move- ments of the tongue, (4) movements of the head, (5) movements of the shoulder, and (6) respiration. (1) Movements of the Hyoid Bone. — The hyoid bone is elevated or depressed, and moved for- wards or backwards along with the lower jaw and tongue, in speech, mastication, and swallowing. ^ Spinal accessory = accessory nerve (B.N. A.). - Inferior dental nerve = inferior alveolar (B.N. A.). 410 THE MUSCULAE SYSTEM. a. Elevation and Depression. b. Protraction and Retraction. Digastric Thyreo-hyoid Genio-hyoid Stylo-iiyoid Stylo-hyoid Sterno-hyoid ] Genio-glossus Middle constrictor Mylo-hyoid Omo-hyoid Genio-liyoid Sterno-thyreoid ■ Genio-glossus 1 Hyo-glossus Muscles closing tlie 1 mouth (2) Movements of the Thyreoid Cartilage. during speech and deglutition. -The thyreoid cartilage is raised and lowered Elevation. Depression. Sterno-thyreoid Crico- thyreoid Depressors of hyoid bone Thyreo-hyoid Stylo-pharyngeus Pharyngo-palatinus (palato-pharyngeus) Elevators of hyoid bone Muscles closing mouth (3) Movements of the Tongue.— The chief movements of the tongue in speech and de- glutition are elevation and depression, protrusion and retraction, and lateral movements. Elevation and Depression. Stylo-glossus (base) Glosso-palatinus Muscles elevating hyoid bone Muscles closing mouth Genio-glossus Hyo-glossus Chondro-glossus Muscles depressing the hyoid bone h. Protrusion and Retraction. Genio-glossus {•posterior fibres) 1 Genio-glossus {anterior fibres) 1 Stylo-glossus c. Lateral Movements. - —The muscles of one side only. ] i (4) Movements of the Head. — The sterno-mastoid muscles, acting together, flex the head on the spinal column, assisted by the supra-hyoid and infra-hyoid muscles. The sterno-mastoid muscle of one side, acting alone, bends the head to the same side, and simultaneously rotates it to the opposite side, as seen in torticollis (wryneck). (5) Movements of the Shoulder Girdle. — The omo-hyoid and sterno-mastoid muscles have already been included among the elevators of the shoulder girdle. (6) Respiration. — The muscles in the front of the neck are auxiliary muscles in extraordinary or ditficidt inspiration. The masseter and temjDoral muscles fix the lower jaw ; the hyoid bone is raised and fixed by the supra-liyoid muscles ; and the sternum is raised by the sterno-mastoid and infra-hyoid muscles. The Muscles of the Pharynx. The muscular envelope of the pharynx is composed of two strata. The external or circular layer consists of the three fan-shaped constrictor muscles ; the internal or longitudinal layer consists of the fibres of the stylo-pharycgeus and pharyngo- palatinus (palato-pharyngeus) muscles. The superior constrictor muscle arises successively from the lower half of the posterior Ijorder of the medial plate of the pterygoid process (pterygo- pharyngeus), from the pterygo-mandibular ligament (bucco-pharyngeus), from the mylo-hyoid ridge of the lower jaw (mylo-pharyngeus) (Fig. o26, p. 408), and from the mucous membrane of the floor of the mouth (glosso-pharyngeus). The muscular fibres radiate backwards, and are inserted for the most part into a raphe extending down the posterior wall of the pharynx in the middle line. The highest fibres are attached to the pharyngeal spine of the occipital bone (Fig. 323, p. 405), and the lowest fibres are overlapped" by the middle constrictor. A crescentic interval occurs above the muscle, below the base THE MUSCLES OF THE PHAEYNX. 411 Fibrous aponeurosis of the pharynx Levator \ eli palatini MUSCLE (cut) Tensor \r^j palatini superiop constrictor Buccinator Pterygo-mandi- bular ligament St\lo pharyngeus Middle constrictor of the skull, in which the Eustachian tube and the levator and tensor palati muscles (levator and tensor veli palatini) appear. Its lower border is separated from the middle constrictor by the stylo-pharyngeus muscle. The middle constrictor muscle arises from the stylo -hyoid ligament and from both cornua of the hyoid bone (chondro-pharyngeus, cerato-pharyngeus). From its origin the muscular fibres radiate backwards, to be inserted into the medial raphe on the posterior aspect of the pharynx. The upper fibres overlap the lower part of the superior constrictor ; the lower fibres are concealed from view by the inferior constrictor muscle. In the interval between the middle and inferior constrictors are found the superior laryngeal artery and nerve. The inferior constrictor muscle arises from the oblique line of the thyreoid cartilage (thyreo-pharyngeus), and from the side of the cricoid cartilage (crico- pharyngeus). Its fibres radiate back- wards, to be inserted into the median raphe on the back of the pharynx, the upper fibres overlapping the lower part Eustachian tube- of the middle constrictor, the lower fibres blending with the muscular fibres of the oesophagus. Below the lower border of the muscle the inferior laryngeal artery and recurrent nerve enter into relation with the larynx. The deeper longitudinal stratum of muscles in the pharyngeal w^all is composed of the insertions of the stylo - pharyngeus and pharyngo - palatinus muscles. The stylo-pharyngeus arises from the root of the styloid process on its medial side, and passes downwards be- tween the externaland internal carotid arteries. It enters the wall of the pharynx in the interval between the superior and middle constrictor muscles. Spreading out beneath the middle constrictor muscle, it is inserted into the superior and posterior borders of the thyreoid cartilage and into the wall of the pharynx itself, becoming continuous posteriorly with thepalato- pharyngeus. In the neck the glosso- pharyngeal nerve winds round it on its way to the tongue. The pharyngo-palatinus (palato- pharyngeus) occupies the soft palate and the pharyngeal wall. In the sub- stance of the soft palate it consists of ttvo layers, a postero-superior layer, thin, and continuous across the middle line with the corresponding layer on the opposite side, and an antero-inferior layer, which is thicker, and is attached to the posterior border of the hard palate. The elevator of the palate and uvular muscles are enclosed between the two layers, which unite at the posterior edge of the palate, receiving at the same time additional fibres arising from the Eustachian tube (salpingo-pharyngeus). The muscle descends to the pharynx in the posterior pillar of the fauces. Its fibres spread out in the form of a thin sheet in the wall of the pharynx, in continuity anteriorly with the stylo-pharyngeus, and are inserted into the posterior border of the thyreoid cartilage, and behind that into the aponeurosis of the pharynx, reaching down as far as the lower border of the inferior constrictor. The muscle is placed beneath the middle and inferior constrictors in the pharyngeal'wall, and the fibres of the muscles of opposite sides decussate in the middle line in the lower part of the pharyngeal wall. 28 Inferior constrictor ■ — Fig. 328. -Posterior View of the Pharynx and Constrictor Mdscles. 412 THE MUSCULAE SYSTEM. The muscular fold is composed of five The IVIuscIes of the Soft Palate. The soft palate and uvula form a muscular fold, covered on each surface by mucous membrane, projecting backwards into the pharynx, and forming the posterior part of the floor of the nose and the roof of the mouth. pairs of muscles — the pharyngo- palatinus (palato-pharyngeus), m. uvulae (azygos uvulae), levator veli palatini, tensor veli palatini and glosso-palatinus (palato-giossus). The pharyngo-palatinus muscle has been already described (p. 411). The m. uvulae (azygos uvulae) consists of two narrow bundles enclosed, along with the inser- tion of the elevator muscle of the palate, be- tween the layers of the " pha- ryngo - palatinus. The slips arise from the posterior nasal spine and the aponeurosis of the soft palate, and unite as they pro- ceed backwards to end in the uvula. The levator veli palatini has a double origin : (1) from the under surface of the apex of the petrous por- tion of the tem- poral bone, and (2) from the lower part of the car- tilaginous Eus - tachian tube. It passes obliquely downwards and medially, across the upper border of the superior constrictor muscle, and enters the soft palate be- tween the two layers of the pharyugo-palatinus muscle. It is inserted into the aponeu- rosis of the soft palate, and some of its fibres become continuous with those of the opposite muscle. It is separated from the tensor veli palatini muscle by the Eustachian tube and the deeper layer of the pharyngo-palatinus muscle. The tensor veli palatini arises (1) from the scaphoid fossa and the alar spine of the sphenoid bone, and (2) from the lateral side of the cartilaginous Eustachian tube. It descends between the internal pterygoid muscle and the internal ptery- goid plate, and ends in a tendon which hooks round the pterygoid hamulus, and is inserted beneath the levator veli palatini into the posterior border of the hard palate, and into the aponeurosis of the soft palate. The glosso-palatinus ri)alato-glossus), occupying the under surface of the soft palate and the anterior pillar of the fauces, has already been described with the muscles of the tongue (jj. 409). Buccinator Mylo-hvoid Hyo-olossl's Digastric Stvlo-hyoid Omo-hyoid Steeno-hyoid Thyreo-hyoid Crico-thyreoid. Tensor veli palatini MIISCLE Eustacliian tube ■Levator veli palatini Pterygo-iiiandibular ligament ■Superior constrictor .Stylo-pharyngeus Stylo-glossds .Glosso-pliaryiigeal nerve Stylo-hyoid ligament Hypoglossal nerve Middle constrictor Digastric Superior laryngeal nerve ■Inferior constrictor External laryngeal 'nerve CEsophagus Interior laryngeal nerve Fig. .329.— Lateral View of the Wall ok the Pharynx. LATERAL AND PE^VERTEBEAL MUSCLES OF THE NECK. 413 Nerve-Supply. Most of the muscles of the pharynx and soft palate are innervated by the (spinal) accessory nerve, through the pharyngeal plexus. These muscles include the constrictors of the pharynx, glosso-palatinus and pharyngo-^ialatinus, levator veli palatini and uvular muscle. The tensor veli palatini is supplied by the trigeminal nerve through the otic ganglion ; the stylo- pharyngeus by the glosso-pharyngeal nerve. In addition to branches from the pharyngeal plexus, thf inferior constrictor ruceives tibres from the external ramus of the superior laryngeal nerve and from the recurrent or inferior laryngeal nerve. Actions. The muscles of the pharpix and soft palate are chiefly brought into action in the act of swallowing. This act is divided into a voluntary stage, in which the bolus lies m front of the pillars of the fauces, and an involuntary stage, during which the food passes from the mouth through the pharj-nx. The movements occurring during the passage of food through the mouth are as follows : the cheeks are compressed by the action of the buccinator muscles ; the tongue, hyoid bone, and thyreoid cartilage are successively raised upwards by the action of the muscles which close the mouth and elevate the hyoid bone. By these means the food is pushed back- wards between the pillars of the fauces. At the same time, by the contraction of the glosso-palatinus and pharyngo-palatinus, the pillars of the fauces are narrowed, while the muscles of the soft palate, contracting, tighten the soft palate, and by bringing it in contact with the posterior wall of the pharynx, shut off the upper (nasal) portion of the cavity. The elevation of the tongue, hyoid bone, and larynx simultaneously causes the elevation of the epiglottis and the aperture of the glottis, which is closed by the approxima- tion of the arytsenoid cartilages and the combined action of laryngeal muscles (aryta^noideus, thj-reo-arytsenoideus, and thyreo-epiglotticus). The food thus slips over the posterior surface of the epiglottis and the closed aperture of the glottis, and between the pillars of the fauces on either side, into the pharynx. It is now clasped by the constrictor muscles, which, by their contractions, force it do\vn into the oesophagus. The contraction of the constrictor muscles results in a flattening of the pharjnix and elevation of its anterior attachments. During the act of swallowing, it is generally thought that the Eustachian tube is opened by the contraction of the tensor veli palatini muscle which arises from it. It has been held, on the other hand, that the Eustachian tube is closed during swallowing by the compression of its waU by the contraction of the levator veli palatini. Serratus posterior superior (insertion) Deep Lateral and Praevertebral IVIuscIes of the Neck. Three series of muscles are comprised in this group : (1) vertebro-costal (scaleni, anterior, medius, and pos- terior), (2) vertebro- cranial (longus capitis and rectus capitis anterior, and lateralis), and (3) vertebral (longus colli). They clothe the front of the cervical portion of the vertebral column for the most part, and are in relation anteriorly with the pharynx and cesophagus, and the large vessels and nerves of the neck. The scalenus anterior arises from the anterior tubercles of the transverse processes of the third, fourth, fifth, and sixth cervical ver- tebrae, and descends behind the carotid sheath and sub- clavian vein, to be inserted into the scalene tubercle and ridge on the first rib (Fig. 33^0, p. 413). It is separated posteriorly from the scalenus medius by the cords of the brachial plexus, the subclavian artery, and the pleura. Serratus anterior (s. niagnus) (origin) Pectoralis minor (occasional origin) Fig. 330.— Muscle -Attachments to the Upper Surface of the FlKST ElB, AND THE LATERAL SURFACE OF THE SECOND RiB (Right Side). a, First rib ; B, Second rib. 414 THE MUSCULAE SYSTEM. Rectus capitis anterior lateralis Rectus capitis LOXCUS CAPITIS The scalenus medius arises from the posterior tubercles of the transverse processes of the cervical vertebrae, from the second to the sixth in- clusive. It descends in the ', posterior triangle behind the ^ subclavian artery and the Rectus capitis cords of the brachial plexus, to be inserted into the rough impression on the first rib behind the subclavian groove (Fig. 330, p. 413). The muscle is pierced by the posterior scapular and pos- terior thoracic nerves.^ . The scalenus posterior arises behind the scalenus medius from the posterior tubercles of the fourth, fifth, and sixth cervical transverse processes, and is inserted into an impression on the lateral side of the second rib. The longus capitis (rectus capitis anterior major) arises from the an- terior tubercles of the trans- verse processes of the third, fourth, fifth, and sixth cervi- cal vertebrae. It forms a flat triangular muscle, which is directed upwards alongside the longus colli muscle and behind the carotid sheath, to be inserted into an impression on the under surface of Longus colli Fig. 331. — The Pr.evertebRx\l Muscles of the Neck. Posterior tuberoles of transverse processes Scalenus medius Levator scapul.13 Splenius colli Scalenus posterior Ilio-costalis cervicis lonoissimus cervicis Scalenus anterior lonous capitis "(rectus CAPITIS ANTERIOR .MA.IOU) Longus colli Anterior tubercles of "transverse roccsses r LONOISSIMUS CAPITIS Articular I Semispinalis capitis processes"! Semispinalis cervicis V. Multifidus Fig, 332. — Scheme of Muscular Attachments to Ckhvical Vertebra.. the basilar process of the occipital bone, anterior and lateral to the pharyngeal spine (Fig. 333, p. 415). ^ Posterior scapular nerve = dorsal nerve of scapula (B.N. A.). Posterior thoracic nerve = long thoracic nerve (B.N. A.). THE MUSCLES OF THE THOKAX. 415 The rectus capitis anterior (rectus capitis anterior minor) arises under cover of the previous muscle from the anterior arch of the atlas, and is inserted into the basilar process between the previous muscle and the occipital condyle (Fig. 333,p.415). The longus colli is a flattened muscular band extending from the third thoracic vertebra to the atlas. It i|^ divisible into three portions — a vertical, a lower oblique, and an upper oblique portion. The vertical portion of the muscle arises from the bodies of the first three thoracic and the last three cervical vertebra} ; and passing vertically upwards, it is inserted into the bodies of the second, third, and fourth cervical vertebrae. The lower oblique portion arises from the bodies of the first three thoracic vertebrse, and is inserted into the anterior tubercles of the fifth and sixth cervical vertebrre. The upper oblique portion arises from the anterior tu})ercles of the transverse Semisiiinalis capitis (iiiserLioii) Rectus capitis posterior minor \,^-^ ^>^ Trapezius (origin) (insertion) \ Rectus capitis posterior major (insertion) Sterno-cleido-niastoid (insertion) Splenius capitis (insertion) Obliquus capitis supenoi (inseition) Rectus capitis lateralis (insertion) Rectus capitis anterior (insertion) Superior constrictor of jjharynx (insertion) Lonjjus capitis (in->eition) Fig. 333. — Muscle-Attachjie^'ts to the Occipital Bone (Inferior Surface). processes of the third, fourth, and fifth cervical vertebrte, and is directed upwards, to be inserted into the anterior tubercle of the atlas. The rectus capitis lateralis, in series with the posterior inter -transverse muscles in the neck, arises from the transverse process of the atlas, and is inserted into the under surface of tlie jugular process of the occipital bone. It is placed alongside the rectus capitis anterior, separated from it by the anterior primary division of the first cervical nerve. Nerve-Supply. The prteverteLral muscles are all suj^phed by anterior ijrimary divisions of the cervical spinal nerves : the rectus capitis anterior, and rectus capitis lateralis, by the looj) between the first two nerves ; the longus capitis (rectus capitis anterior major) by the first four ; the longus colli by the second, third, and fourth ; the scaleni by the loM'er four or five cervical nerves. Actions. The movements produced by these muscles are considered along with those of other muscles acting on the head, siDinal column, and thorax (pp. 392, 395). THE MUSCLES OF THE THORAX. Muscles of Respiration. The muscles which complete the boundaries of the thorax are the diaphragm and intercostal muscles (external and internal), along with three series of smaller muscles— the transversus thoracis (triangularis sterni), the levatores costarum, and the subcostal muscles. 416 THE MUSCULAR SYSTEM. The intercostal muscles are arranged in eleven pairs, which occupy the inter- costal spaces. Each external muscle arises from the sharp lower l)order of a rib, and is directed downward and forward, to be inserted into the lateral edge of the upper border of the rib below. It extends from the tubercle of the rib behind nearly to the costal cartilage in front. The anterior intercostal aponeurosis is continuous with it anteriorly, and extends forwards to the side of the sternum. Each internal muscle arises from the costal cartilage and the medial edge of the subcostal groove, and is directed downwards and backwards, to be inserted into the medial edge of the upper border of the rib and costal cartilage below. It extends External intekcostal MUSCLE Obliqdds externus. ABDOMINIS (reflected) Anterior intercostal membrane Internal inter- costal MUSCLE Rectus abdominis- (insertion) Sheath of the rectus abdominis Fig. 334. — The Muscles of the Right Thokacic Wall. from the side of the sternum in front to the angle of the rib behind, where it becomes continuous with the 'posterior intercostal aponeurosis extending to the tubercle of the rib. The superficial surface of the external muscle is covered by the muscles of the chest, axilla, abdomen, and back. The deep surface of the internal muscle is in contact with the pleura. The levatores costarum are in series with the external intercostal muscles. They are twelve small sH})S arising from the transverse processes of the seventh cervical and upper eleven thoracic vertebne. They spread out in a fan-like manner as they descend, to be inserted into the lateral surface of each of the ribs posterior to the angles. The subcostal muscles are slips of muscles found on the medial surface of the lower ribs near their angles. They are in series with the internal inter- costal muscles, but pass over the deep surface of several ribs. The transversus thoracis (triangularis sterni) occupies the posterior aspect THE MUSCLES OF THE THOEAX. 417 of the anterior thoracic wall, and is separated from the costal cartilages by the internal mammary vessels. It arises from the back of the ensiform cartilage and mesosternum as high as the level of the third costal cartilage. From this origin its fibres radiate laterally, the lower horizontally, the upper fibres obliquely upwards, to be inserted into the costal cartilages of all the sternal ribs except the first and seventh. The muscle is continuous below with the transversus abdominis. The diaphragm is the great membranous and muscular partition separating the cavities of the thorax and abdomen. It forms a thin lamella arching over the abdominal cavity, and clothed on this surface for the most part by peritoneum. It is related on its lower concave surface to the liver, stomach, and spleen, the kidneys and suprarenal capsules, and the duodenum and pancreas. Its upper convex surface projects into the thoracic cavity, rising higher on the right than on (Esophagus and its opening Foramen qnaJratuni (for inferior vena cava)^^ Middle arcuate liga-' ment (in front of aortic openin -_- - Ual arcuate ' '' hgament ^ — Lateral arcuate ligament QUADRATUS LUMBORUM MUSCLE Right cru3 of diaphragm Fig. 335. — The Diaphragm (fioni below). Psoas muscle diaphragm the left side, and is related to the pericardium and pleurae, and along its margin to the chest wall. The oesophagus and thoracic aorta are in contact with it posteriorly. It possesses a peripheral origin from the sternum, ribs, and vertebral column, and an insertion into a central tendon. It arises (1) anteriorly (pars stemalis) from the posterior surface of the ensiform cartilage by two slender fleshy slips, directed backwards ; (2) laterally (pars costalis), from the deep surface of the lower six costal cartilages on each side by fleshy bands which interdlgitate with those of the trans- versus abdominis ; (3) 'posteriorly (pars liimbalis), from the lumbar vertebrse, by the crura, and the arcuate ligaments (medial and lateral lumbo-costal arches). The crura are two elongated fibro-muscular bundles which arise on each side of the aorta from the front of the bodies of the lumbar vertebrae, on the right side from the first three, on the left side from the first two lumbar vertebrse. They are directed upwards and decussate across the middle line in front of the aorta, the fibres of the right cms passing in front of those of the left crus. The fibres then encircle the oesophagus, forming an elliptical opening for its passage, and finally join the central tendon, after a second decussation in front of the gullet. The arcuate ligaments (arcus lumbo-costales Halleri) are five in number. The middle arcuate ligament is a fibrous arch connecting together the crura of the diaphragm in front of the aorta, and giving origin to fibres (crus mediale) which join the crura as they decussate to encircle the gvillet. 418 THE MUSCULAR SYSTEM. The medial arcuate ligament (arcus lumbo-costalis medialis) is a thickening formed by the attachment of the psoas fascia to the body of the first lumbar vertebra medially and its transverse process laterally. Stretching across the upper end of the psoas muscle, the ligament gives origin to muscular fibres directed upwards on each side of the crura. The lateral arcuate ligament (arcus lumbo-costalis lateralis) is the thickened Opening for inferior vena cava (Ksophageal opening Central tendon (middle part) Central tendon (right pait) Diaphragm, costal fibhts Medial arcuate ligament Lateral arcuate ligament End of last rib Last thoracic ner\ e Tendon of transversus abdominis Transversus abdominis Ilio-hypogastric nerve — ^ — Lumbar vessels and sympa- ' thetic communicating nerves Uio-inguinal uer\e QUADRATCS LUilBORUM External cutaneous nen e Psoas major Iliacds Lumbo-sacral coid Genito-crural (genito 2 femoral) nerve Anterior crural (femoral) nerv r Obturator nerv c Great sciatic nerv < Diaphragm, right crus Aliddle arcuate ligament Aoitic opening Central tendon (left part) Diaphragm, left CRUS Last thoracic nerve End of last rib Lumbar nerve L ^ r-j'f ' ii' — Uio-hypogastric nerve -Lumbar nerve II. Iho inguinal nerve Quadratus lumborom Lumbar nerve III. Genito-crural (genito- fpnioral) nerve Lumbar nerve IV. Lumbo-sacral cord lj\tHinal cutaneous nerve inteiioi crural (femoral) nerve Obturator nerve Great sciatic nerve Fig. 336. I Adductor brevis (origin) Gracilis (origin) Adductor magnus (origin) I Pectineus (cut) Superficial branch of obturator nerve I Deep branch of obturator nerve Obturator e-xternum -View of the Postekioe Abdominal Wall, to show the Muscles and the Nerves of THE Lumbo-Sackal Plexus. upper border of the fascia over the quadratus lumborum muscle (anterior layer of the lumbar fascia), and is attached medially to the transverse process of the first lumbar vertebra, and laterally to the last rib. It gives origin to a broad band of muscular fibres, separated by an interval from the fibres arising from the medial arcuate ligament which sweep upwards to the central tendon. From this extensive origin the muscular fibres of the diaphragm converge to an insertion into a large trilobed central tendon (centrum tendineum"). Of its lobes the right one is the largest, the middle or anterior is intermediate in size, and the FASCIA AND MUSCLES OF ABDOMINAL WALL. 419 left is the smallest. It does not occupy the centre of the muscle, being placed nearer the front than the back. The fibres of the crura are consequently the longest ; those from the sternum are the shortest. The diaphragm is pierced by numerous structures. The superior epigastric artery enters the sheath of the rectus abdominis lietween its sternal and costal origins ; the musculo-phrenic artery passes between its attachments to the seventh and eighth ribs. The sympathetic cord and the splanchnic nerves pierce, or pass behind the diaphragm ; the last thoracic nerve passes beneath the lateral arcuate ligament ; and the aorta, the azygos vein, and thoracic duct pass between the crura, underneath the middle arcuate ligament {aortic opening or hiatus aorticus). The special foramina are two in number. T\\q foramen quadratum {foramen vence cavcc) in the right lobe of the central tendon transmits the iuferior vena cava, and small branches of the right phrenic nerve. The oesophageal opening {hiatus cesophageus) is in the muscular substance of the diaphragm, behind the central tendon, and is surrounded by a sphincter -like arrangement of the crural fibres. Besides the oesophagus, this opening transmits the two pneumogastric nerves. The diajihragiu is found as a complete septum between the thorax and abdomen only in mammals. It is occasionally deficient in the human subject, producing hernia of the diaphragm, either into the pericardial cavity through the central tendon, or into the thoracic cavity through the lateral portions of the muscle. A rare condition is congenital deficiency of a part of the lateral half of the muscle, generally placed posteriorly, and on the left side. This produces, by continuity of the pleural and peritoneal cavities behind the diaphragm, a congenital diaphragmatic hernia. Nerve-Supply. The intercostal muscles, levatores costarum, subcostal muscles, and transversus thoracis, are all supplied by the anterior primary divisions ^ of the thoracic (intercostal) nerves. The diaphragm receives its chief, if not its entire, motor supply from the phrenic nerves (C. 3. 4. 5.). It is in- nervated also by the diaphragmatic plexus of the sympathetic, and is sometimes said to receive fibres from the lower intercostal nerves. Actions. The act of respiration consists of two opposite movements — inspiration and expiration. 1. The movement of expiration is performed by (1) the elasticity of the lungs, (2) the weight of the chest walls, (3) the elevation of the diaphragm, (4) the action of muscles — transversus thoracis and muscles of the abdominal wall. It is sometimes stated that the interosseous fibres of the internal intercostal muscles are depressors of the ribs. 2. The movement of inspiration results in the enlargement of the thoracic cavity in aU its diameters. Its antero-posterior and transverse diameters are increased by the elevation and forward movement of the sternum, and by the elevation and eversion of the ribs, while its vertical diameter is increased by the descent of the diaphragm. The muscles of inspiration are divided into two series — ordinary and accessory. a. Ordinary Muscles. h. Extraordinary and Accessory Muscles. Diaphragm Intercostals Scaleui Serrati posteriores Levatores costarum Subcostales Quadra tus lumborum Pectorales Serratus anterior (magnus) Sterno-mastoid Latissimus dorsi Infra-hyoid muscles Extensors of the spine Of the ordinary muscles the diaphragm is the most important. Its action is twofold — centrifugal, elevating the ribs and increasing the transverse and antero-posterior diameters of the thorax, and centripetal, drawing downwards the central tendon and increasing the vertical diameter of the thorax. Of the two movements the former is the more important. There has been considerable diversity of opinion regarding the action of the intercostal muscles. It is generally agreed that the external muscles eleA-ate the ribs ; it is probable that the whole of each internal muscle acts in the same way, although it has been stated by difterent observer that the whole internal muscle is a depressor ; or that the interosseous part is a dej)ressor, the inter- chondral portion of the muscle an elevator of the ribs. FASCIAE AND lYIUSCLES OF THE ABDOIVIINAL WALL. The space between the base of the bony thorax and the pelvis is filled up by a series of muscular sheets, covered externally and internally by fascite. ^ Anterior primary divisions = anterior rami (B.X.A.). 420 THE MUSCULAE SYSTEM. FASCIiE. The fasciae of the abdominal wall q.xq— externally , the superficial and deep fasciae ; internalhj, the fascia transversalis, which is continuous with the diaphragmatic, lumbar, psoas, iliac, and pelvic fasciae, and is Hned within by the extraperitoneal tissue. The superficial fascia of the abdomen is liable to contain a large quantity of fat. In the groin it is separated into hvo layers : a superficial fatty layer con- tinuous over Poupart's inguinal ligament with the fascia of the front of the thigh (p. 353), and a deeper membranous layer attached to the medial half of Poupart's Linea alba" Lig. fundiforme penis" Subcutaneous \.-\ inguinal riii^""]»*~' Superior pill it -A Inferior pill u — Spermatic coi 1-*— Intercrural fibn ^ Dorsal vein of penis Dorsal arti'i \ - Dorsal iiei\ — - Obliquus Bxteenus abdominis Anterior superior iliac spine External oblique Liponeurosis •Superficial circum- flex iliac artery — Intercrural fibres ( Attachment of mem- — l branous layer of ( superficial fascia ■""Ir'oupart's inguinal ligament ...Superficial inferior epigastric artery Superior external pudendal artery .Femoral lymphatic gland Large saphenous vein (internal) Fig. -337 ff. — Supkhi-icial Anatomy of the Gkoin. ligament, and more laterally to the fascia lata of the thigh below Poupart's ligament. The two layers are separated by the lymphatic glands and the superficial vessels of the groin. Higher up in the abdominal wall the two layers blend together. Passing downwards over the spermatic cord, they unite to ibrm the fascfa and dartos muscle of the scrotum. The attachment of the fascia to the groin prevents the passage into the thigh of fluid extravasated in the abdominal wall. The deep fascia of the abdominal wall resembles similar fasciae in other situa- tions. It forms an investment for the obliquus externus muscle, and becomes thin and almost imperceptible in relation to the aponeurosis of tliat muscle. The fascial lining of the abdominal cavity (fascia transversalis) consists of a continuous layer of membrane which receives different names in dilTercnt parts of its extent. It covers the deep surface of the transversus muscle, and is continuous medially (through the lumbar fascia) with the fasciae of the quadratus lumborum THE MUSCLES OF' THE ABDOMINAL WALL. 421 and the psoas muscles. It is continuous above with the diaphragmatic fascia, and below the ihae crest and Poupart's ligament with the fascia iliaca. Along with the last-named fascia it forms the femoral sheath, enclosing the femoral vessels and the femoral canal in their passage to the thigh behind the medial part of Poupart's ligament (p. 356). It is pierced by the spermatic cord or round ligament of the uterus at the abdominal or deep inguinal ring (annulus inguinalis abdominalis), and its prolongation into the inguinal canal around the cord forms the infundibuliform fascia. It is lined internally by the peritoneum, from which it is separated by a layer of extraperitoneal tissue. The extraperitoneal tissue is usually loaded with fat ; it envelops the kidneys, ureters, suprarenal capsules, abdominal aorta and inferior vena cava and their branches, and forms sheaths for the vessels and ducts (ureter, vas deferens, etc.). It is continued upwards into the posterior mediastinum of the thorax through the aortic opening in the diaphragm, and below is in continuity with the extraperitoneal tissue in the pelvis. It not only completely invests the kidneys and suprarenal capsules, but it also becomes interpolated between the layers of peritoneum upholding and enveloping the intestines. This tissue is absent in relation to the diaphragm, on the under surface of which there is no fat. THE MUSCLES OF THE ABDOMINAL WALL. Themusclesof the abdominal wall are in threeseries — lateral, anterior, and posterior. Obliquus externds abdominis' (reflected) Spermatic cord- Intercolumuar fascia' Obliquus externus abdominis Obliquus internus abdominis Anterior superior 'iliac spine Transversus abdominis .Obliquus internus ABDOMINIS (reflected) Aponeurosis of obliquus 'externus (reflected) •Abdominal inguinal ring Spermatic cord and "infundibuliform fascia . Fascia transversalis Conjoint tendon •(Inguinal aponeurotic falx) ■ Saphenous opening Large saphenous vein Fig. 337ft. — The Dissection ("ve by the costal arch. Its lower fibres, Aponeurosis of obliquus externus (reflected) Linea alba Superficial inguinal ring Jriangolar fascia External or in- ferior pillar of ring Pubic fascia and suspensor\- liga- ment of penis Obliqucs exterkus abdominis Anterior superior iliac spine ^-^ Obliqx'us internus abdominis Aponeurosis of ■ -obliquus externus (reflected) Spermatic cord Inquinal canal Conjoint tendon Triangular fascia External pillar of superficial inguinal ring (Poupart's ligament) Spermatic cord (cut) Fig. 341a. — The Left Inguinal Canal. Stkuctcres seen on keflection of the Obliquus Externus. arching over the spermatic cord, assist in forming, laterally, the anterior wall of the inguinal canal ; medially, by means of the conjoint tendon, it helps to form the posterior wall of the canal. Its lowest fibres are continued into the cremaster muscle, which is prolonged along the spermatic cord through the inguinal canal. The cremaster muscle forms an investment for the testicle and spermatic cord beneath the intercoUimnar fascia. In the female it is more largely represented by fascia than muscular fibres, and constitutes the cremasteric fascia. It may be said to have an origin from the lower edge of the obliquus iuternus and the adjacent part of Poupart's ligament. Its fibres form loops over the spermatic cord and testicle, the highest fibres getting an insertion into the pubic spine. The transversus abdominis muscle arises (1) from the deep surface of the costal cartilages of the lower six ribs, interdigitating with the origins of the 426 THE MUSCULAE SYSTEM. diaphragm ; (2) from the himbar fascia ; (3) from the anterior half of the medial lip of the iliac crest ; and (4) from the lateral third of Poupart's ligament. The muscular fibres are directed for the most part horizontally forwards, and end in an aponeurosis which has a twofold insertion. (1) After forming (along with the aponeurosis of the obliquus internus) the posterior layer of the sheath of the rectus, the aponeurosis is attached to the ensiform cartilage and Knea alba. (2) The lower fibres of the muscle arising from Poupart's ligament are joined by the lower Obliquus exteknu abdomini (reflectt'il ) Spermatic cord-- Intercolumnar fascia" Obliquus externus abdominis ,Obi,iquus internus abdominis Anterior superior 'iliac sijine ^Transversus 'abdominis ,Obliquus internus abdominis (reflected) Aponeurosis of obliquus ■externus (reflected) ■•Abdominal inguinal ring Spermatic cord and "infundibuliform fascia . Fascia transversalis Conjoint tendon ■•(Inguinal aponeurotic falx) —Saphenous opening -Large saphenous vein Fig. 341 b. — The Dissection of the Inguinal Canal. part of the obliquus internus to form the larger part of the conjoint tendon (falx aponeurotica inguinalis), which passes in front of the lower part of the rectus muscle, to be inserted into the crest and spine of the pubis and the ilio-pectineal line. The transversus muscle is separated by the lower intercostal nerves from the obliquus internus muscle, and is lined on its deep surface by the fascia transversalis. Its lower border fprms a concave edge, separated from Poupart's ligament by a lunular interval in which the fascia transversalis appears, and through which^ the spermatic cord emerges at the abdominal inguinal ring, under cover of the obliquus internus muscle and the aponeurosis of the oblicpius externus. The anterior muscles of the abdominal wall include the pyramidalis and rectus abdominis, enveloped by the sheath of the rectus on either side of the linea alba. The pyramidalis abdominis is a small triangular muscle arising from the pubic crest in front of the rectus muscle (Fig. 342, p. 427). It is directed obHquely upwards, to be inserted for a variable distance into the linea alba. The muscle is often absent. j The rectus abdominis muscle is broad and strap-like, and arises, by a medial THE MUSCLES OF THE ABDOMINAL WALL. 427 and a lateral head, from the symphysis and crest of the pubis (Fig. 282, p. 362). Expanding as it passes upwards, the muscle is inserted from within outwards into the front of the ensiform cartilage (Fig. 342, p. 427), and into the front of the seventh, sixth, and fifth costal cartilages. On its anterior surface, but not extending through the entire substance of the muscle, are three or more transverse Aponeurosis of .obliquus exteruus abdominis (reflected) Rectts abdominis Anterior lamella of sheath of rectus rr— - Linea alba Obliqcxs ex- TERXrS ABCOMIXIS 'rOBUQrcs ix- TERSrS ABDOMIXIS Aponeurosis of obliquus extemus Pouparfs ligament ... Aponeurosis of ■ obliquus extemus (reflected) CrEJLASTER Ml'SCLE Spermatic cord Z OBLigrUS EXTERN l"8 ABDOMIXIS Rectus abdominis (cut) Posterior lamella of rectal sheatli Anterior lamella oi sheatli of rectus Aponeurosis of obliquus externus Obliquus internts abdominis Transvebsus abdominis Fold of Douglas Fascia transversalis Rectus abdominis (cut) Poupart's ligament Obliquus externus (aponeurosis reflected) Pvramidalis abdominis Suspensory ligament — uf penis Fig. .342. — Deep Dissectiox of the Abdumi.nal Wall. The Rectus Muscle and its Sheath. tendinous intersections (inscriptiones tendinese), adherent to the sheath of the muscle ; the lowest opposite the umbilicus, and the highest about the level of the ensiform cartilage. The medial border of the muscle lies alongside the linea alba ; its lateral border is convex, and corresponds to the linea semilunaris. The muscle is pierced by the terminal branches of the lower thoracic nerves. The sheath of the rectus muscle (vagina m. recti abdominis) is derived from the aponeuroses of the lateral muscles of the abdominal wall, which, after enclosing the muscle, give rise in the middle line to the linea alba. At the linea semilunaris, 29 428 THE MUSCULAE SYSTEM. the lateral border of the rectus muscle, the aponeurosis of the obliquus internus splits into anterior and posterior layers. The anterior layer, joined by the aponeurosis of the obliquus externus, passes in front of the rectus, and constitutes the anterior lamina of the sheath. The posterior layer, joined by the aponeurosis of the transversus muscle, passes behind the rectus, and constitutes the posterior lamina of its sheath. This arrangement obtains in the upper three-fourths of the abdominal wall. Below the level of the iliac crest the sheath of the muscle is deficient posteriorly, and a crescentic border, the semilunar fold of Douglas (linea semicircularis), marks the lower limit of the posterior lamina. In consequence, the rectus in the lower fourth of the abdominal wall rests directly upon the fascia trans- versalis. Close examination, however, usually reveals a thin layer behind the muscle in continuity with the fold of Douglas, and merging below with the fascia transversalis. In this region the rectus is covered anteriorly by the con- joint tendon (falx aponeurotica in- guinalis) of the obliquus internus and transversalis, and by the aponeurosis of the obliquus externus, which gradu- ally separates from the subjacent aponeurosis. The upper part of the rectus, lying on the chest wall, is only covered anteriorly by a single layer of aponeurosis derived from the obliquus externus, which in this situation is giving origin to the pectoralis major muscle. Inguinal Canal. — The spermatic cord in the male, and the round liga- ment in the female, in their passage through the lower part of the ab- dominal wall, pass through the inguinal canal, which is bounded by these ab- dominal muscles. The canal begins at the abdominal inguinal ring (anrmlus inguinalis ahdominalis), placed half an inch above Poupart's inguinal ligament, and midway between the anterior Fig. 343.- pubis. It ends at the superficial in- guinal ring (annulus inguinalis suhcu- taneus), placed above the spine and sheath ; /, Fascia transversalis ; g, Peritoneum Linea alba. 1, Deep (inferior) epigastric artery. -The Sheath of the Rectus Abdominis Muscle. (I.) In the thoracic wall; (II.) In the upper three- """ "TT^iii""! ^-nTnp ai^l thrsvmTihvql^ quarters of the abdominal wall ; (III.) In the lower SUpCllOr ^liiac SpiUC and tnc SympnySlS fourth of the abdominal wall. A, Rectus muscle ; B, Obliquus externus ; C, Dia- phragm ; D, Obliquus internus ; E, Transver- salis abdominis, a, Anterior layer of rectus sheath ; b, Fifth costal cartilage ; c, Sixth costal cartilage ; crest ot the publS. ihe anterior wall ot d, Xiphoid cartilage ; e, Posterior ^ayer of rectus ^^^q canal is formed by the aponeurosis of the obliquus externus, and in its lateral part by the muscular fibres of" the obliquus internus ; the posterior ivall of the canal is formed by the fascia transversalis, and in its medial part by the conjoint tendon (falx aponeurotica inguinalis) ; while the floor of the canal is formed by Poupart's ligament, and in its medial part by Gimbernat's ligament. The spermatic cord, piercing the transversalis fascia, enters the inguinal canal at the abdominal inguinal ring, and is there invested by its first envelope, the infundibuliform or internal spermatic fascia, a sheath of fascia derived from the margin of the ring and continuous witli the lascia transversalis. It then passes obliquely medially, downwards, and forwards, and escapes below the lower border of the obliquus internus muscle, from which it carries off a second investraent, partly fascial, partly muscular, — the cremaster muscle or cremasteric fascia. Continuing its course in front of the conjoint tendon, it emerges through the superficial inguinal ring, from the edges of which the intercolumnar fascia is derived, the third or external investment for the cord. THE MUSCLES OF THE ABDOMINAL WALL. 429 Hesselbach's triangle, bounded below by the line of Poupart's ligament, medially by the rectus abdominis muscle, and laterally by the deep epigastric artery ^ coursing upwards and medially beneath the fascia transversalis on the medial side of the abdominal inguinal ring, is the site of one form of inguinal hernia. The spermatic cord passes over the base of the triangle, covered over by the aponeurosis of the obliquus externus. Behind the cord, and forming the floor of Vena caval opening Oesophageal opening Central tendon (middle part) y Central ten ^ (left part) Central tendon (rii;ht part) Diaphragm, costal fibres Medial arcuate ligament Lateral arcuate ligament End of last rib Last thoracic nerve Tendon of transversus abdominis Transversus abdominis Ilio-hypogastric nerve Luni))ar vessels and sympa- thetic communicating nerves Ilio-inguinal nerve QUADRATUS LUMBOKUM External cutaneous nerve Psoas major Iliacus Lumbo-sacral cord Genito-crural (genito-femoral) nerve Anterior crural (femoral) nerve Obturator nerve Great sciatic nerve Diaphragm, right crus Middle arcuate ligament y Aortic opening tendon Diaphragm, lekt D-T^CRUS Last thoracic nerve End of last rib Lumbar nerve I. Ilio-hypogastric nerve Lumbar nerve II. Ilio-inguinal nerve QUADRATUS LUMBORUM Lumbar nerve III. Genito-cniral (genito- jFvT" femoral) nerve Lumbar nerve IV. Lumbo-sacral cord External cutaneous nerve Anterior crural (femoral) nerve Obturator nerve Great sciatic nerve (Jbturator nerve ADDrcTOR LONGUs (origin) \ Adductor brevis (origin) Gracilis (origin) I Adductor magnus (origin) Pectineus (cut) Superficial branch of obturator nerve I Deep branch of obturator nerve Obturator externus Fig. 344. — View op the Posterior Abdominal Wall, to show the Muscles and the Xerves of THE Lumbo-Sacral Plexus. the triangle, is the fascia transversalis partially covered in the medial portion of the triangle by the conjoint tendon of the obliquus internus and transversus muscles. Inguinal Hernia. — Eor an account of the anatomical relations of the inguinal canal to the various forms of inguinal hernia, see the section on " Applied Anatomy " (p. 1265). The posterior muscles of the abdominal wall and false (large) pelvis ^ Deep epigastric = inferior epigastric artery (B.N. A.). 430 THE MUSCULAR SYSTEM. include the psoas (major and minor) and iliacus, described already (p. 361), and the quadrat us lumborum. The quadratus lumborum lies on the posterior wall of the abdomen, lateral to the psoas, and extends between the iliac crest and the last rib. , It arises from the posterior part of the iliac crest, from the ilio-lumbar ligament, and from the transverse processes of the lower lumbar vertebrae. It is inserted above into the medial part of the lower border of the last rib and the transverse processes of the upper lumbar vertebrse. Its lateral border is directed obliquely upwards and medially. It is enclosed between the anterior and middle layers of the lumbar aponeurosis (p. 385), between the psoas muscle, in front, and the sacro-spinalis behind. Nerve-Supply. The nerve -svipi^ly of the majority of the foregoing muscles is derived from the anteriar primary divisions ^ of the lower six thoracic nerves. The pj-ramidalis muscle is imiervated by the last thoracic nerve. The cremaster muscle receives its supply from the genito-crural nerve,^ (L 1. 2.), whilst the quadratus lumborum is innervated by ihe first three or four lumbar nerves. The psoas and iliacus muscles are supplied, directly or through the anterior crural nerve,^ from the second, third, and fourth lumbar nerves. Actions. Many of the actions of the above muscles have already been given in previous sections. (1) Their chief action is to retract the abdominal walls, and, by compressing the contents of the abdomen, they are powerful agents in vomiting, defsecation, micturition, parturition, and laboured expiration. (2) They are also flexors of the spine and pelvis — the muscles of both sides acting together ; the spine and pelvis are laterally flexed, when one set of muscles acts alone. (3) The quadratus lumborum is a muscle of inspiration, an extensor of the spine, and a lateral flexor of the spine and pelvis. FASCIAE AND MUSCLES OF THE PERINEUIVI AND PELVIS. FASCIiE OF THE PERINEUM. The superficial fascia of the perineum possesses certain special features. It is continuous with the superficial fascia of the abdominal waU, thigh, and buttock, and is prolonged on to the penis and scrotum. In relation to the penis, it is devoid of fat and consists only of areolar tissue. In relation to the scrotum, it is intermino-led with involuntary muscular fibres, and constitutes the dartos muscle, which assists in suspending the testicles and corrugating the skin of the scrotum. This fascia also forms the septum of the scrotum, which, extending upwards, in- completely separates the two testicles and their coverings. In the female the superficial fascia, in which there is a considerable quantity of fat, takes a large share in the formation of the mons veneris and labia majora. The fascia over the ^josterior part of the 'perineum fiUs up the ischio-rectal fossse, in the form of two pads of adipose tissue, on either side of the rectum and anus. Over the tuberosities of the ischium the fat is intermingled with bands of fibrous tissue closely adherent to the subjacent deep fascia. The fascia in the anterior part of the perineum closely resembles the same fascia in the groin. It is divisible into a superficial fatty and a deeper membranous layer ; the former continuous with the same layer in the thigh, and with the fat of the ischio-rectal fossa posteriorly. The deeper membranous layer is attached laterally to the pubic arch, posteriorly to the base of the triangular ligament (dia- phragma urogenital), and in the middle hne to the root of the penis (bulb and corpus spongiosum) by a median raphe continuous farther forwards with the septum of the scrotum mentioned above. Anteriorly the fascia is continued over the sper- matic cords to the anterior abdominal wall. The importance of this fascia lies in relation to the extravasation of urine from a rupture of the urethra. By the fascial attachments the fluid is prevented from passing backwards into the ischio-rectal fossa, or laterally into the thigh. It is directed forwards into relation with the scrotum and penis, and along the spermatic cord to the anterior abdominal wall. 1 Anterior primary divisions = anterior rami (B.N. A.). '^ Genito-crural nerve =gemto-femoral nerve ,, 2 Anterior crural nerve = femoral nerve , , THE MUSCLES OF THE PEEINEUM. 431 The septum of the scrotum being incomplete, fluid extravasated on one side can pass across the middle line to the opposite half of the perineum and scrotum. The deep fascia of the perineum only exists in the form of the delicate aponeuroses of the muscles. THE MUSCLES OF THE PERINEUM. The perineal muscles are naturally separated into a superficial and a deep set by the triangular ligament (diaphragma urogenitale). Superficial to it are the sphincter ani externus, transversus perinei superficialis, bulbo-cavernosus, and ischio-cavernosus ; beneath the triangular ligament is the sphincter muscle of the membranous urethra (compressor urethrpe). Sphincter ani Externus. — This muscle is fusiform in outline, flattened, and obliquely placed around the anus and anal canal. It can be separated into three layers, — subcutaneous, superficial, and deep. (1) The most superficial lamina consists of subcutaneous fibres decussating behind and in front of the anus, but Perineal branch of small sciatic Anterior superticial perineal Posterior superticial perineal nerve GlutealV branches ol'_^ small sciatic nerve BULBO-CA \ ERNOSUS ISCHIO-CAVERNOSCS Transversus PERINEI Ischial tuberosity Levator ani Parietal pelvic fascia Inferior hemorrhoidal nei \ Levator ani Sphincter ani externus Anterior sacro-coccygeal nerve Fig. 345. — The Muscles and Nerves of the Male Perineum. Perforating cutaneous iier\ Perineal branch of fourth sacral utrvu without bony attachments. (2) The sphincter ani superficialis constitutes the main portion of the muscle. It is attached posteriorly to the coccyx, and in front of the anus reaches the central point of the perineum. (3) The deep fibres of the muscle form for the most part a complete sphincter for the anal canal. They are continuous with the fibres of the levator ani ; they encircle the anal canal, and blend anteriorly with the central point of the perineum and the transversus perinei muscle. The corrugator cutis ani consists of bundles of unstriped muscular fibres which radiate from the margin of the anal opening superficial to the external sphincter. The transversus perinei superficialis is not always present. It consists of a more or less feeble bundle of fibres, arising from the inferior or ascending ramus of the ischium and the fascia over it, and from the base of the triangular ligament (diaphragma urogenitale). It passes obliquely over the base of the triangular ligament to be inserted into the central point of the perineum. The bulbo-cavernosus (ejaculator urinse), tw the male, surrounds the bulb, corpus spongiosum, and root of the penis. It is sometimes separated into two parts — posterior (compressor bulbi), and anterior (compressor radicis penis). It arises from 432 THE MUSCULAR SYSTEM. the central point of the perineum, and from a median raphe on the under surface of the bulb and corpus spongiosum. The muscular fibres are directed laterally and forwards and have a triple insertion : from behind forwards, (1) into the under sur- face of the triangular ligament ; (2) into the dorsal aspect of the corpus spongiosum; and (3), after encircling the corpora cavernosa, into the fascia covering the dorsum of the penis. The ischio-bulbosus, not always present, arises from the ischium, and passes obliquely inwards and forwards over the bulbo-cavernosus, to be inserted into the raphe superficial to that muscle. It belongs to the same stratum as the transversus perinei superficialis and erector penis (ischio-cavernosus). The compressor hemispherium bulbi is frequently absent. It consists of a thin cap-like layer of muscular fibres surrounding the extremity of the bulb under cover of the bulbo-cavernosus. The bulbo-cavernosus (sphincter vaginse), in the female, is separated into lateral halves by the vaginal and urethral openings. It forms two thin lateral layers covering the vaginal bulbs, and arises behind the va- ginal orifice from the central point of the perineum. Anteriorly it is inserted into the root of the clitoris, some of its fibres em- bracing the corpora cavernosa so as to reach the dorsum of the clitoris. The ischio-cavern- osus (erector penis), in the male, covers the crus penis. It arises from the ischial tuber- osity and the greater sacro-sciatic ligament, and passing forwards, is inserted by a fascial attachment into the under surface of the crus penis, and into the lateral and dorsal aspects of the corpus cavernosum. Bulbo- cavernosus Transversus PERINEI SUPER- FICIALIS Levator ani \ Gluteus MAXIMUS SpH1>-CTER ANI EXTERNUS Fio. ■346. — The Muscles of the Female Perineum (after Peter Thompson). The erector clitoridis (ischio-cavernosus), in the female, has a similar disposi- tion, but is of much smaller size than in the male. The pubo-cavemosus is an occasional slip arising from the pubic ramus, and inserted into the dorsum of the penis. It corresponds to the levator penis of lower animals. The sphincter urethrse membranacese (compressor urethrae) constitutes the deej)er muscular stratum of the perineum. It is placed on the pelvic aspect of the triangular ligament. It arises from the lower part of the pubic ramus, and is directed medially, its fibres radiating so as to enclose the membranous urethra. It is inserted into a medial raphe, partly in front of the urethra, but for the most part behind it. The fibres most intimately related to the urethra form a muscular sheath for the canal, and have no bony attachments. The most posterior and most anterior fibres of the compressor urethrse exist sometimes as separate muscles, as the transversus perinei profundus, and the ischio-pubicus. FASCIA OF THE PELVIS. 433 The transversus perinei profundus consists of a bundle of fibres on either side, arising from tlie inferior ramus of the ischium just below the compressor urethrse. It is inserted into a medial raphe continuous with that of the compressor urethrse. The muscle, in fact, constitutes a separate bvuidle below and behind the compressor urethne. The ischio-pubicus is a term applied to a feeble bundle of fibres which, when present, lies above and in front of the compressor urethrte. It arises from the pubic ramus, and is inserted into a median raphe on the dorsum of the membranous urethra. This muscle is homologous with the compressor venae dorsalis penis of lower animals. The compressor urethrae in the female is smaller than in the male. Its insertion is modified by the relations of the urethra to the vagina. The anterior fibres are continuous with those of the opposite side above the urethra ; the Corpus cavernosuni (cut) Nerve to corpus cavernosum Nerve to dorsum of penis Sphincter urethr.e membranace.-b (compressor urethr.«) Nerve to bulb Triangular ligament (posterior layer) Internal pudic nerve Bulb of penis Triangular ligament —. — ^ (anterior layer) • " '^ Cms penis -5 — ^ — Lev ATOP. ANi Fig. 347. — The Triangular Ligament (diaphragma urogenitale) of the Perineum, and the Termination of the Pudic Nerve.' intermediate fibres pass between the urethra and vagina, and the posterior fibres are attached, along with the transversus perinei profundus (transversus vaginae), into the side of the vagina. Nerve-Supply. The pudic nerve i (S. 2. 3. 4.) supplies all the muscles in this group ; the external sphincter through the inferior hemorrhoidal, and the others through the perineal branch of the nerve. The external .sphincter is also supplied by the perineal branch of the fourth sacral nerve. Actions. The external sphincter closes the anal canal. The transversus perinei superficialis draws back and fixes the central point of the perineum, assisted by the external sphincter. The bulbo- cavernosus of the male constricts the bulb and corpus spongiosum, and so expresses the last drops of urine or semen. In the female it acts as a feeble sphincter of the vagina. The ischio- cavernosus and bulbo-cavernosus help in erection of the penis or clitoris. The sphincter of the membranous urethra constricts the membranous urethra, and in the female helps to flatten and fix the wall of the vagina. It also assists in causing erection of the penis or clitoris by compression of the veins in relation to it. THE FASCIiE OF THE PELVIS. The extra-peritoneal tissue in the pelvic cavity is of great importance. The internal iliac vessels and their branches, the visceral nerves and plexuses, the ureters, and vasa deferentia, take their course in this tissue beneath the peri- toneum. It forms in relation to the rectum a thick sheath, for the most part devoid of fat, which encloses the lower part of the rectum completely, down to its termination in the anal canal. It forms a kind of packing for the parts of the bladder uncovered by peritoneum, and is present under the organ in relation to the ^ Pudic nerve = pudendal nerve (B.N. A.). 434 THE MUSCULAE SYSTEM. symphysis pubis and pubo-prostatic ligaments. In the female it forms in addition the basis or matrix of the broad ligament, and also occurs as a layer devoid of fat, which loosely connects the front of the cervix uteri with the base of the bladder. PELVIC FASCIA. The cavity of the true (small) pelvis in the erect position resembles a basin tilted forward, with its margin formed by the inlet or brim of the pelvis, and with a cylindrical wall, and a concave floor, formed by bones, ligaments, and muscles. The deficiencies in the bony walls of the cavity are filled up laterally by the obturator membrane and the sacro-sciatic ligaments. Below and in front, behind the symphysis pubis, the triangular ligament (fascia diaphragmatis urogenitalis inferior) fills up the pubic arch, and separates the fore part of the pelvic cavity from the fore part of the perineum. Within this osseo-ligamentous chamber a series of muscles clothe its interior; the piriformis and coccygeus behind, the obturator internus on each side, and the compressor urethrte below and in front, on the pelvic surface of the triangular ligament. The pelvic fascia, continuous above with the fascial lining of the abdominal cavity, forms a continuous cylindrical investment for these muscles. On the pelvic surface of the pubis, where muscles are absent, it is merged with the periosteum. It gains an attachment to the spine of the ischium as that projects between the piriformis and obturator internus muscles. Perforations occur in relation to it for the transmission of the obturator nerve and the parietal branches of the internal iliac artery. Eeaching the outlet of the pelvis, it is attached to the posterior border or base of the triangular ligament, to the ischial ramus and tuberosity, and to the lower edge of the great sacro-sciatic ligament. Different names are applied to the fascia in relation to the several muscles which it covers. Posteriorly it constitutes the piriformis fascia : laterally it is the obturator fascia, while that part of the sheet of fascia which covers the pelvic surface of the com- pressor urethrEe is known as the deep layer of the triangular ligament (f. diaphragmatis urogenitalis superior) The disposition of the pelvic fascia is complicated by its relations to (1) the structures which constitute the pelvic floor, and (2) the genito-urinary passages and rectum. The pelvic floor, tense in its fore part and flexible behind, may be said to be formed behind the symphysis pubis by, successively, (1) the triangular ligaments and the sphincter muscle of the membranous urethra between them enclosing the urethra, and the vagina in the female ; (2) the perineal body ; (3) the levator ani and external sphincter of the anus on each side of the anal canal ; (4) the ano-coccygeal body, between the anal canal and the coccyx, containing the main insertions of the levatores ani and external sphincter. The levator ani muscle completes the concave floor of the pelvic cavity, sweeping downwards and backwards from its lateral wall, so as to form a muscular diaphragm, with an intra-pelvic and a perineal surface. Its upper concave pelvic surface occupies the lateral part of the pelvic floor. Its lower convex surface forms the oblique medial wall of the ischio-rectal fossa, the lateral wall of which is formed by the obturator fascia covering the pelvic surface of the obturator internus. In this wall is a fascial sheath (Alcock's canal), containing the internal pudic ^ vessels and nerve. The levator ani is covered on both surfaces by pelvic fascia. The anal fascia clothing its perineal surface is thin and unimportant. The fascia covering its intra-pelvic surface is thick and strong. At the origin of the muscle it is continuous with the general fascial lining of the pelvic cavity, and gives rise to a conspicuous thickening, the linea alba or white line (arcus tendinous), which stretches like a bow-string from the back of the symxjhysis pubis to the ischial spine. This band is related not so much to the origin of the levator ani muscle, which often extends higher up beneath the pelvic fascia, as to the attachments of the fascial investments of the genito-urinary passages, to be described below. There are sometimes additional thickenings of ^ Pudic vessels = pudendal (B.N. A.). FASCIA OF THE PELVIS. 435 the fascia, branching upwards from the white line towards the pelvic brim. At the insertion of the levator ani, the fascia clothing its pelvic surface is attached to the perineal body, the margin of the anal canal, and the ano-coccygeal body, over which it passes to be continuous, above the raphe of insertion of the levatores ani, with the layer of the opposite side. At the antero-inferior border of the muscle the fascise enclosing it become continuous with the deep layer of the triangular ligament (superior fascia of the urogenital diaphragm) : at its postero-superior border they join the fascia enclosing the coccygeus muscle. Within the pelvic basin, the walls and floor of which are thus continuously Ve.sicula scminalis Rfctal diaiiui-1 Recto- vesical layer of pelvic fascia Vas deferens Obturator foramen Suspensory ligament of prostate Lateral true ligament of bladder Wliite line Prostate Pubo-prostatic ligament Cavum Retzii Urethra Fig. 3 i8.— Relations of the Pelvic Fascia to the FvEctum and Prostate. invested by the pelvic fascia, are contained the rectum and bladder, and in the female the uterus, suspended and maintained in position by the peritoneum, extra-peritoneal tissue, and the pelvic vessels and nerves. They are essentially free to distend or collapse, and are not bound down by the pelvic fascia. The rectum in both sexes extends down to the floor of the pelvis, where the anal canal takes its origin, invested by the peritoneum and extra-peritoneal tissue, and occupying a special rectal channel ; this is lined by pelvic fascia, which gains an attachment to the floor of the pelvis at the margin of the anal canal. The arrangement of the fascia in relation to the genito-urinary passages is •436 THE MUSCULAE SYSTEM. essentially different. Just as from the perineal aspect the pelvic outlet is divisible into two different parts, — a posterior or dorsal part, comprising the ischio-rectal fosste for the passage of the anal canal, and characterised by looseness and dis- tensibility ; and an anterior or ventral part, — the urethral triangle for the genito- urinary passages, and characterised by firm fixation to the pubic bones ; so also from the abdominal aspect it is found that, while in the posterior part of the pelvis a rectal channel exists, in which the rectum is free to collapse and distend, in the ventral part of the basin the genito-urinary passages are firmly fixed by means of the pelvic fascia, which gives rise to a special suspensory ligament for the prostate gland and the prostatic urethra in the male, and for the urethra and vagina in the female. A crescentic fold of pelvic fascia arises in the neighbourhood of the ischial spine from the general fascia covering the pelvic wall. It has a posterior free Posterior (recto-vesical) layer Superior layer : lateral true ligament of the bladder Suspensory ligament of the prostate gland : Rectal channel White line Lateral true ligament Pubo-prostatic ligament Cavum Retzii Pubo-prostatic [ ligament! Sheath of the prostate gland' Deeji layer of, triangular ligament Superficial layer of. triangular ligament Compressor urethr.« muscle ] Anal canal Sheath of the prostate gland Fig. 349. — Relations op Pelvic Fascia to the Rectum and Prostate (Medial Section of the Pelvis). edge, through which the vas deferens, vesical vessels, and nerves pass. Sweeping across the middle line, this border is continuous with the fold of the opposite side, the two together constituting the anterior limit of the rectal channel. The fascial fold is composed of two layers, posterior and superior, between which is a large plexus of veins. They have separate attachments laterally to the general pelvic fascia. The posterior (recto-vesical) layer passes across the pelvis between the prostate gland and the rectum. Its lower edge is attached to the perineal body between the base of the triangular ligament and the beginning of the anal canal. It forms a sheath for the vesiculse seminales and vasa deferentia. This is rather in the form of a septum than a complete sheath ; it effectually separates the vesicuhe seminales and the bladder from the rectum, forming the front wall of the rectal channel, but it allows the vesiculse seminales to rest directly against the bladder. The superior layer extends forwards to the symphysis pubis. It has a lateral origin from the white Line (arcus tendineus) in its whole length, and sweeping over the prostate gland, it is inserted along its line of junction with the bladder, and constitutes the so-called lateral true lig-ament of the bladder (lig. pubo-prostaticum FASCIA OF THE PELVIS. 437 laterale). It contains numerous bundles of muscular fibres in its anterior part, and forms a sheath for the passage of the inferior vesical vein along the lateral surface of the prostate gland. In front the fascia stretches from the back of the symphysis pubis, the sub-pubic ligament, and the deep layer of the triangular ligament (superior fascia of the urogenital diaphragm) to the neck of the bladder Psoas mltscle Suspensory ligament of tlie vatcina ami iiretlira Obturator foramen White line Recto-vaginal layer. '\^ Lateral true ligament '\, of bladder.. "'-^^ \ . Urethro- vaginal layer "•,_ ^\-ii'- jO^ Anterior true liga- '■■._ "\ ^g ment of the bladder,^ ^jftSlH Cavum Retzii \^!^l^l R,-'^ '"'. '^ Clitori; Bulb of the vagina Pubo-urethral fascia (anterior true ligament of bladder) ; ; ,' ; j Urethral layer of pelvic fascia ; .' .' ; Urethra ! .' j Vagina • ! Bulb of the vagina ; BtTLBO-CAVERXOSUS Ischial spine Rectal channel • ■; • External sphiscter ani '• \ Levator axi \ Intermai, sphincter ani Anal canal Junction of rectum and anal canal Internal sphincter ani External sphincter ani Fig. 350. — Relations of the Pelvic Fascia to the Rectum, Urethra, and Vagina (Medial Sectiou). and the prostate gland, forming the anterior true ligament of the bladder, or pubo- prostatic ligament (lig. pubo-prostaticum mediale). It is continuous across the middle line with the ligament of the opposite side. In the middle line, where the two ligaments unite, a hollow occurs behind the symphysis pubis, known as the cavum Retzii. This ligament is composed of several layers separated by large veins (the prostatic plexus), which connect the inferior vesical vein with the dorsal vein of the penis and the internal iliac vein. The sheath of the prostate gland (fascia prostatae) is formed by (1) the deep layer of the triangular ligament on which it lies, (2) by the general pelvic fascia covering 438 THE MUSCULAE SYSTEM. the intra-pelvic surfaces of the levatores ani on each side, and (3) it is completed by the two special layers of pelvic fascia just described above and behind. By these means the prostate gland and prostatic urethra are given a lirm attachment to the fore part of the pelvic walls and floor. In the female an essentially similar arrangement of the pelvic fascia occurs in relation to the vagina and urethra. A crescentic fold of the fascia springs from the pelvic wall in the neighbourhood of the ischial spine, and sweeping medially to the lateral fornix of the vagina and in front of the rectum, separates into two layers, posterior and superior. Between the layers are numerous vessels, which, along with the visceral nerves, pierce its free edge. The posterior (recto-vaginal) layer passes medially behind the vagina, and gaining the middle line between the vagina and rectum, gives rise to the anterior wall of the rectal channel, and is attached below to the perineal body in the floor of the pelvis. The superior layer, taking origin from the white line, is attached medially to the neck of the bladder, and constitutes the lateral true ligament of the bladder. It is continuous in front with the anterior true ligament of the bladder, which, as in the male, is divisible into several layers separated by veins. An intermediate (urethro-vaginal) layer of the fascia passes between and separates the urethra and vagina. The urethra and vagina are by means of these layers of fascia firmly bound to the pelvic walls and floor, while the uterus and bladder are free to distend in the pelvic cavity. MUSCLES OF THE PELVIS. The pelvic diaphragm consists of several more or less rudimentary muscular slips, constituting the levator ani and coccygeus muscles, which serve to uphold the pelvic floor, and are related to the rectum and the prostate gland or vagina. The levator ani arises from (1) the lower part of the back of the body of the pubis, (2) the general pelvic fascia above or along the ivhite line (arcus tendineus), and (3) the pelvic surface of the spine of the ischium. Its fibres are directed downwards and backwards, to be inserted into (1) the central point of the perineum (perineal body), (2) the external sphincter around the origin of the anal canal, (3) the ano-coccygeal raphe behind the anus, and (4) into the sides of the lower sacral and the coccygeal vertebrse. The levator ani muscle fills up and completes the pelvic floor on each side of the middle line. Enclosed in a sheath derived from the general pelvic fascia along the white line, the muscle presents an upper concave surface in relation to the pelvic cavity, prostate gland, and rectum, and an inferior convex surface which appears in the perineum and forms the inner wall of the ischio-rectal fossa. The levator ani is divisible into four parts — pubo-rectalis, pubo-coccygeus, ilio- coccygeus, and ilio-sacralis. The pubo-rectalis (levator prostata)) is the part inserted into the central point of the perineum. The pubo-coccygeus is the part inserted into the anus and the ano-coccygeal raphe, and the ilio-coccygeus and ilio-sacralis are represented by the fibres attached to the sacrum and coccyx. The first two are best developed ; the last two series of fibres are the most rudimentary. These several parts of the muscle represent the remains of the flexor caudse of tailed animals. The coccygeus is a rudimentary muscle overlapping the posterior border of the levator ani. It arises from the ischial spine and the lesser sacro-sciatic ligament, and is inserted into the sides of the lower two sacral and upper two coccygeal vertebrae. The muscle is in contact by its anterior border with the levator ani. It is enclosed in pelvic fascia, assists in forming the pelvic floor, and is in contact laterally with the sacro-sciatic ligaments. Nerve-Supply. The levator ani is suppHed from two sources : by the perineal (nuisf'ular) branch of the internal pudic nerve,! ^^d^ on its pelvic surface, by special bi'anches froiii tla- third and fourth sacral nerves. The coccygeus is supphed on its pelvic surface by the third and fourth sacral nerves. 1 Internal pudic nerve = iiudendal nerve (B.N. A.). MOEPHOLOGY OF THE SKELETAL MUSCLES. 439 Actions. (1) The levator ani and coccygeus serve to uphold and slightly raise the pelvic floor. (2) They are likewise capable of producing slight flexion of the coccyx. (3) The anterior fibres of the levator ani, in the female, sweeping round the vagina, compress its walls laterally, and along with the sphincter vaginae, help to voluntarily diminish the lumen of the tube. (4) The same jsart of the muscle in the male elevates tlie prostate gland (levator prostatte). (5) The chief action of the levator ani is in defcecation. Along with the external sphincter it acts as a sjjhincter Sacro-sciatic ligament (cut) Sphincter ani externus Fig. 351. -The Fascial and Muscular Wall of the Pelvis after Removal of Part of the Left Innominate Bone. of the rectum, closing the anal canal. During defsecation the muscle draws uj^wards the anus over the faecal mass, and so assists in its expulsion. (6) In parturition, in the same way, the muscle, contracting below the descending foetal head, retards delivery. Contracting on the foetal head, it draws upwards the pelvic floor over the foetus, and so assists delivery. THE DEVELOPMENT AND MORPHOLOGY OF THE SKELETAL MUSCLES. It has already been shown, in the chapter on general embryology, that the meso- blast on either side of the embryonic medullary tube separates into three main parts — the myotome, nephrotome, and sclerotome or lateral plates (somatopleure and splanchno- pleure). 440 THE MUSCULAK SYSTEM. The myotomes ai-e probably directly or indirectly the source of the striated muscles of the whole body. Each consists at first of a quadrilateral bilaminar mass, resting against the medullary tube and notochord on either side. The cleft between its two layers represents the remains of the coelomic cavity. In the early stages of embryonic life the growth of the myotome is rapid. On its inner side masses of cells arise, which grow in- wards and surround the medullary tube and notochord to form the foimdation of the vertebral column. On its outer side cells appear to be given off which participate in the formation of the cutis vera. At the same time the dorsal and ventral borders of the myotome continue to extend, and present extremities (growing points) with an epithelial structure for a considerable period. On the dorsal side it overlies the medullary tube, and Fig. 352. — Scheme to Illustrate the Disposition of the Myotomes in the Embryo in Relation to THE Head, Trunk, and Limbs. A, B, C, First three ceithalic myotomes ; N, 1, 2, 3, 4, Last persisting cephalic myotomes ; C, T., L., S., Co., The myotomes of the cervical, thoracic, lumbar, sacral, aud caudal regions; I., IL, IIL, IV., V., VI., VTL, VIII., IX., X., XL, XII., refer to the cranial nerves aud the structures with which thej' may b© embryologically associated. gives rise to the muscles of the back ; while by its ventral extension, which traverses the somatopleuric mesoblast in the body wall, it produces the lateral and ventral muscles of the trunk. By an inward extension it probably gives rise also to the hypaxial muscles of the neck and loin. The cells of the inner layer of the myotome are responsible for the formation of the muscle fibres. The cells elongate in a direction parallel to the long axis of the embryo, and give rise, by fusion with the cells of neighbouring myotomes, to the columns and sheets of muscles of the back and trunk. For the most part {e.g. back and abdomen) the originally segmental character of the nuiscular elements is lost by the more or less complete fusion of adjacent myotomes. The intercostal muscles, however, are the direct derivatives of individual myotomes. Muscles of the Limbs. — In fishes and (doubtfully) reptiles there is evidence that the myotomes are concerned in the formation of the limb-muscles by their extension into the limb-bud in a manner similar to that described for the trunk. In birds and mammals, MOEPHOLOGY OF a:HE SKELETAL MUSCLES. 441 however, in which the limb -bud arises as an undifferentiated, unsegmented mass of mesoblastic tissue, partly from the mesoblast surrounding the notochord, and partly from the somatopleuric mesoblast, the myotomes stop short at the root of each limb, and do not penetrate into its substance. Instead, the muscular elements of the limb take origin independently as double dorsal and ventral strata of fusiform cells on the dorsal and ventral surfaces of the limb-bud. These strata are xmsegmented ; they are grouped around the skeletal elements of the limb, and they gradually become differentiated into the muscle masses and individual muscles of the limb. Muscles of the Head. — Notwithstanding the obscurity and complexity of this subject, it appears certain that at least tivo series of elementary structures are concerned in the formation of the muscles of the head and face — the cephalic myotomes and the muscular structure of the branchial arches. The number of myotomes originally existing in the region of the head is not known, although it is stated with some authority that nine is the complete number. The first three are described as persisting in the form of the ocular muscles, the last three in relation to the muscles of the tongue, while the three intervening myotomes disappear. The following table shows the possible fate of the cephalic myotomes : — First, Superior, medial and inferior recti, obliquus inferior, levator ijaljiebrse superioris. Second, Obliquus superior. TJiird, Eectus lateralis. Fourth, Fifth and Sixth, Absent. Seventh, ^ Eighth, \ Muscles of the tongue Ninth, Tenth (first cervical) Ninth, j Muscles connecting the ci-anium and shoulder girdle. The mesoblastic tissue of the branchial arches is probably concerned in the production of the following muscles of the face and neck : — First (mandibular) arch . . Muscles of mastication. iPlatysma and facial muscles. Muscles of the soft palate. Stapedius, stylo-hyoid, and digastric. Third (thyro-hyoid) arch . . (iJ^^erforSrSor. jj, ,, 7 rvii /i 1 • ;\ 7 f Middle and inferior constrictors. Fourth and Ftfth (branchial) arches ^Muscles of the larynx. THE NERVOUS SYSTEM. THE BEATN AND SPINAL CORD, WITH THEIR MENINGES. By D. J. Cunningham, M.D., F.E.S., Po^ofessor of Anatomy, University of Edinhurgh. THE NERVOUS SYSTEM. THE BRAIN AND SPINAL CORD, WITH THEIR MENINGES. By D. J. Cunningham. The nervous system connects the various parts of the body with each other and co-ordinates them into one harmonious whole. Its relatively great bulk and its extreme complexity constitute two of the most distinctive structural features of man. It consists of two parts, viz. the cerebrospinal nervous system and the sympathetic nervous system. The sympathetic nervous system is composed of a chain of serially disposed ganglia, bound to each other by intervening nervous cords, and placed one on either side of the vertebral column. In addition to these gangliated cords, the sympathetic system includes certain dense plexuses of nerves and numerous scattered ganglia. The whole is most intimately connected with the cerebrospinal nervous system, and both have apparently a common developmental origin. The separation of the nervous system into the two leading subdivisions of sympathetic and cerebro- spinal is therefore of a somewhat arbitrary kind. The cerebrospinal nervous system consists of the brain, which very nearly completely fills the cranial cavity, and the spinal cord or spinal marrow, which only partially fills the vertebral canal. These are continuous with each other, and together constitute the cerebrospinal axis. Attached to the brain and spinal cord are the numerous nerves which bring the various parts of the body into connexion with the central nervous axis. There are thirty-one pairs of symmetrically disposed spinal nerves attached to the sides of the spinal cord. Each of these nerves is connected to the side of the cord by a ventral or anterior and a dorsal or posterior root, and the dorsal root is distinguished by presenting a distinct oval swelling, termed a spinal ganglion, on that part of its course immediately internal to the place where the two roots unite to form the spinal nerve-trunk (Fig. 365, p. 453). The cranial nerves are twelve in number on each side, but one only (viz. the fifth or trigeminal) presents a double-rooted attachment similar to a spinal nerve Several, however, possess ganglia in every respect comparable with the ganglia on the dorsal roots of the spinal nerves. These are the fifth or trigeminal, the seventh or facial, the eighth or auditory, the ninth or glosso-pharyngeal, and the tenth or vagus cranial nerves. CEREBROSPINAL NEEVOUS SYSTEM. The brain and spinal cord are composed of two substances which present a different appearance to the eye, and which are distinguished by the terms wliite matter and gray martter. The difference in colour between these two substances depends not only upon the different elements which enter into their formation, but also upon the fact that the gray matter is the more vascular of the two. The white matter is chiefly composed of nerve-fibres, whilst the essential constituents of the gray matter are nerve-cells which give origin to nerve-fibres. An all per- vading matrix termed the neuroglia forms the bed in which the nerve-fibres and 443 444 THE NEKVOUS SYSTEM. nerve-cells lie, and is present both in the gray and the white matter. The elements, therefore, which constitute nervous tissue are nerve-cells, nerve-fibres, and neuroglia. Nerve-fibres. — Nerve-fibres arranged in bundles of greater or less bulk form the nerves which pervade every part of the body. They also constitute the greater part of the brain and spinal cord. Nerve-fibres are the conducting elements of the nervous system ; they serve to bring the nerve-cells into relation both with each other and with the various tissues of the body. There are different varieties of nerve-fibres, but in all the leading and essential constituent is a delicate thread-like band, termed the axis-cylinder. The difference between individual fibres depends upon the fact that in some cases the axis-cylinder becomes invested by one or two coats, whilst in other cases it remains naked. When the axis-cylinder is coated on the outside by a more or less thick sheath of a fatty substance termed myelin, it is said to be a myelinated or medullated fibre. When the coating of myelin is absent, the fibre is termed a non-myelinated or a non- medullated fibre. A second sheath — thin, delicate, and membranous, and placed externally — may also be present in both cases. It is termed the primitive sheath or the neurolemma. From a structural point of view, therefore, four different forms of nerve- fibre may be recognised : — Axis /cylinder Myelin ^_^^Primitive J^ sheath TVT J m i. J f !• Naked axis-cvhnders. JNon-meaullated < n \ ■ i- j -^.i • -u.- i, ^\. ( 2. Axis-cyhuders with primitive sheaths. j 3. Primitive sheath absent. Medullated \ 4. Primitive sheath present. Every nerve-fibre near its origin and as it approaches its termination is unprovided with sheaths of any kind, and is simply represented by a non -medullated naked axis - cylinder. The fibres of the olfactory nerves afford us an example of non-meduUated fibres furnished with a primitive sheath. Medullated fibres are present in greater quantity in the cerebro- spinal system than non-medullated fibres. Thus all the nerves attached to the brain and cord, with the exception of the olfactory and optic, are formed of medullated fibres provided with a primitive sheath ; whilst the entire mass of the white substance of the brain and cord, and also the optic nerves, are formed of medullated fibres devoid of a primitive sheath. It is important to note that the distinction between the medul- lated and non-medullated fibres is not one which exists throughout all stages of development. As will be presently pointed out, every fibre is a direct outgrowth from a cell, and in the first instance it is not provided with a medullary sheath. Indeed, it is not until about the fifth month of foetal life that those fibres which are to form the white substance of the cerebrospinal axis begin to acquire their coating of myelin. Further, this coating appears in the fibres of different strands or tracts at different periods, and a knowledge FROM A FaoG (after ^^ ^^^^ ^^^^ ^yg.^ enabled the anatomist to follow out the connexions' of the tracts of fibres which compose the white matter of the brain and cord. But it may be asked : How does a nerve-fibre arise and how does it end ? Every fibre is directly continuous by one extremity with a nerve-cell, whilst its opposite extremity breaks up into a number of ramifications, all of which end freely in relation to another nerve-cell, or in relation to certain tissues of the body, as, for example, to muscle-fibres or to the epithelial cells of the epidermis. The length of nerve-fibres, therefore, varies very greatly. Some fibres are short and merely bring two neighbouring nerve-cells into relation with each other : others travel long distances. Thus a fibre arising from one of the motor cells of the lower end of the spinal cord may, after leaving the cord, extend to the most outlying muscle in the sole of the foot before it reaches its destination. But even when a fibre does not leave the central axis a great length may be attained, and cells Fig. .353. Nerve-fibhe CEKEBKOSPINAL NEKVOUS SYSTEM. 445 situated in the motor area of the cortex of the cerebrum give origin to fibres which pass down to the lower end of the cord. Physiologists classify the fil^res whicli form the nerves into two sets, afferent and efferent. Afferent nerve-fibres conduct the impulse of impressions from the peripheral organs into the central nervous system ; and as a change of consciousness, or, in other words, a sensation is a frequent result, these fibres are often called sensory. Efferent nerve-fibres carry impulses out from the brain and cord to peri- pheral organs. The majority of these fibres go to muscles and are termed motor ; others, however, go to glands and are called secretory ; whilst some are inhibitory and serve to carry impulses which restrain or check movement or secretion. As previously stated, the spinal nerves are each attached to the cord by a ventral or anterior root, and a dorsal or posterior root; the fibres com- posing the former are efferent ; whilst the fibres of the posterior root are almost entirely afferent. Nerve - cells. — The nerve-cells con- stitute the active and all-essential elements of nerve- tissue. At the very start it is necessary to draw a broad distinction between the ganglionic cells, wliich are found in the spinal ganglia, and the cells which are so plentifully scattered through the gray matter of the brain and cord. They differ not only in their mode of origin and in their subsequent develop- ment, but also in the connexions of the nerve-fibres to which they give origin. Nerve-cells of the Brain and Cord. — The cells in the gray matter of the cerebrospinal axis are variable both in size and form. Some are relatively large, as, for example, certain of the pyramidal cells of the cerebral cortex and the motor cells in the gray matter of the cord, w^hich almost come within the range of unaided vision ; others are exceedingly minute, and require a high power of the microscope to bring them into view. The cell consists of a protoplasmic nucleated body, from which certain processes proceed. One process is termed the axis-cylinder process or axon ; and as a rule it is easily distinguished from the others, which are collectively called the protoplasmic processes of Deiters, or the dendrites. The axon presents a uniform diameter and a smooth and even outline. It gives off in its course fine collateral branches, but does not suffer thereby any marked diminution in its girth. The most important point to note in counexion with the axon, however, is the fact that it becomes continuous with the axis-cylinder of a nerve- fibre. The significance of this is obvious, and will become more striking Fic. 354. -Three Nerve-Cells from the Antekiur Horn ok Gray Matter of the Human Spixal Cord. 446 thp: nervous system. when the development of the nerve-cells is studied. The axon then is simply a nerve-fibre, and in certain circumstances it assumes, as already stated, one or two investing sheaths. The axon may run its entire course within the substance of the brain or cord either for a short or a long distance, or it may emerge from the brain or cord in one of the cranial or spinal nerves as the essential part of an efferent nerve -fibre, and run a variable distance before it finally reaches the peripheral structure in relation to which it ends. The axon and the collaterals which spring from it terminate either in small button-like swellings or knobs, or more frequently in terminal arborisations, the extremities of which are free and are furnished with ex- ceedingly small terminal varicosities. In those cases where the axon or its collaterals end within the brain or cord, some of the terminal arborisations interlace with the dendrites of nerve-cells, whilst others are twined around the bodies of other cells. In the latter case the interlacement may be so close and complete that it almost presents the appearance of an enclosing Fig. 355. — Two Multipolar Nebve- Cells, from a specimen prepared by the Golgi method. basket - work. In cases where the axon emerges from the cerebrospinal axis its terminal arborisation ends in relation to a muscle- fibre or some other tissue in the manner already re- ferred to. In all cases, however, it would appear that the terminal branches of the axon, no matter how complicated the connexion may seem, are free, and that the connexion is simply one of contact or contiguity, and not one of continuity. Held maintains that, although at first the terniinal arborisations of an axon are quite free, in the process of growth and development they exhibit a tendency to become fused with the dendrites and even the bodies of other nerve-cells. Fin. 356. — Nrrve-Cki.l from Cekebei lUiM (Cell ov Porkin.ie) SHOWING THE BRANCHING OK THE DkNDRITIC PROCESSES (from a lantern slide by Professor Symington). CEKEBROSPINAL NERVOUS SYSTEM. 447 The dendrites, or protoplasmic processes of the nerve-cell, are thicker than the axon, and present a rough - edged irregular contour. They divide into numerous branches, and these gradually, as they pass from the cell-body, become more and more attenuated until they finally end in free extremities. The branching of the dendritic processes sometimes attains a marvellous degree of complexity (Fig. 356), but except in exceptional circumstances, there is no anastomosis between the dendrites of neighbouring cells, or between the dendrites of the same cell. It would appear, therefore, tliat nothing in the shape of a network is formed by tliese processes. In the chapter upon Embryology it has been shown that in the early condition of the cerebrospinal axis the brain and cord consist simply of a tube (p. 21). The wall of this tube is formed of a single layer of tall colunniar neuro-epithelial cells, MID-DORSAL LAMINA MVELO- SPONIGIUM NEURO- BLAST RETIC- ULUM MID-VENTRAL LAMINA Fig. 357. — Transverse Section through the early Neural Tube, diagraiiimatically represented (Alfred H. Young). The left side of the section exhibits an earlier stage of development than the right side. Fig. 358. — The Developmental Stages exhibited by a pyra- midal Cell of the Brain (after Ramon y Cajal). a, Neuroblast with rudimentary axon, but no dendrites ; b and c, The dendrites beginning to sprout out ; d and e. Further develop- ment of the dendrites and ap- pearance of collateral branches on tlie axon. and in its deepest or most internal part large round cells make tlieir appearance in the intervals between the epithelial columns. These new cells are termed the germinal cells, and from them the nerve-cells are derived. They are present in considerable numbers, and towards the fourth week of embryonic life they form an almost continuous layer. Although these cells ultimately become nerve-cells they are absolutely without processes in their early state, and therefore at this period, although there is a nervous system, there are, as His remarks, no nerves. In course of time, and as the wall of the neural tube thickens, the germinal cells begin to migrate in an outward direction. They leave the deep part of the wall of the neural tube and proceed to take up the positions they occupy in the gray matter of the cord and brain of the adult. These migrating cells assume a pyriform shape, and are termed neuroblasts. The drawn-out portion or stalk of the pear- shaped neuroblast represents the early axon, and this continues to grow and increase in length until it ultimately attains the terminal relations characteristic of the adult. The study of embryology presents few more remarkable phenomena than the manner in which this axon grows out, and, in the efferent nerve-fibres, emerges 448 THE NEKVOUS SYSTEM. from the central axis, and yet pursues its allotted path with the most unerring exactitude and precision until it ultimately reaches the nerve-cell or the peripheral tissue element with which it becomes associated. The growing point of both it and its collaterals is slightly bulbous, and it is out of this that the terminal arborisation is formed. This conception in regard to the outgrowth of the axon in the case of the peripheral nerve-fibres has not been allowed to pass unchallenged, and it must be admitted that certain facts recently observed militate against it. Whatever opinion may be held in regard to the developmental origin of the axis- cylinder and medullary sheath of a peripheral nerve-fibre, there is every reason for the belief that the neurolemma is mesodermic in its origin, and is therefore formed from cells outside the ectodermic neural tube. There are some who think that the axis-cylinder is secreted in situ by a chain of these cells, whilst others consider that the mesoblastic cells of a nerve-fibre merely constitute a cellular tube through which the growing axon worms its way to its destination, and perhaps also supply the pabulum necessary for its growth. The dendritic processes of the nerve-cell appear at a later period than the axon. The surface of the neuroblast becomes rough and then somewhat spiny. By the growth and subdivision of these spiny projections the dendrites are formed. As His remarks, the nerve-cell is therefore the genetic centre from which all the parts of a nervous element proceed. It must now be clear that each nerve-cell is a unit which is separate and distinct from the nerve-cells which lie around it. Further, it is obvious that it is wrong to consider the nerve-cell as something apart from the nerve-fibre. The nerve-cell with its dendrites and axon, however wide-spreading these processes may be, constitutes an independent system to which the term neuron is applied, and the only relation which it has with other neurons or with peripheral tissues is one of contact. Ganglionic Nerve-Cells. — The ganglionic neurons found in the ganglia of the cranial nerves and in the ganglia on the dorsal roots of the spinal nerves have a different origin, and present many points of contrast with neurons in the gray matter of the brain and cord. As already indicated in the chapter on Embryology (p. 21) the ganglia in question are derived from the neural crest. The cells forming these ganglionic masses are somewhat oval in form, and from either extremity or pole a process grows out, and the neurons in this manner become bipolar. These processes are distinguished as central and peripheral, according to the direction which they take. The central processes grow inwards, and penetrate the wall of the neural tube. In the region of the spinal cord they form almost the whole of the fibres which enter into the composition of the dorsal roots of the spinal nerves. In the substance of the cerebrospinal axis they give off numerous collaterals, and after a course of varying extent they end, after the manner of an axon, in terminal arborisations, which enter into relationships of contact with certain nerve-cells in the cerebrospinal axis. The peripheral processes grow outwards along the path of the particular nerve with which they are associated, and they finally establish peripheral contact relations. Thus, to take one example : the majority of the fibres which go to the skin break up into fine terminal filaments, which end freely between the epithelial cells of the epidermis. The two processes of a ganglion cell, therefore, form the afferent fibres of the cerebrospinal nerves, and constitute the path along which the influence of peripheral impressions is conducted towards the brain and cord. The body of the cell is as it were interposed in the path of such impulses. But the original bipolar character of these cells, with very few exceptions (ganglia in connexion with the auditory nerve and the bipolar nerve-cells in the olfactory mucous membrane), gradually undergoes a change which ultimately leads to their transformation into unipolar cells. This is brought about by the tendency which the cell-body has to grow to one side, viz. the side towards the surface of the ganglion (v. Lenhossek). This unilateral growth leads to a gradual approxima- tion of the attached ends of the processes, and finally to a condition in which they appear to arise from the extremity of a short common stalk in a T-shaped manner CEEEBROSPIXAL NERVOUS SYSTEM. 449 .c« pAL ^!i SPINAL 'ganglion (Fig. 360). It is interesting to note that in certain fish the original bipolar condition of these cells is retained throughout life without change. Both the central and peripheral processes of these ganghonic cells become the axis- cylinders of nerve-fibres, which, acquiring a medullary sheath, belong therefore to the medullated variety. From this it might very naturally be thought that the ganglionic neuron, with its two axons and no typical dendrites, is a nervous unit very different from a neuron in the gray matter of the cerebrospinal axis. It is believed by some, however (van Gehuchten and Cajal), that the peripheral process, in spite of its enclosure within a medullary sheath, and though pre- senting all the characters of a true axon, is in reality a dendrite. If this be the case, the morphological difference between a dendrite and an axon disappears, and van Gehuchten's functional distinction alone remains character- istic, viz. that the axon is ceUulifugal and conducts impulses away from the cell, whilst the dendrites are celhdipetal and conduct im- pulses towards the cell. In the foregoing brief account of the elements which build up the nervous system, the neuron doctrine, as it has been enunciated by Waldeyer, has been followed. The observations of Ramon y Cajal and His form the foundation upon which this doctrine mainly rests, although it should not be forgotten that many other anatomists, amongst whom may be mentioned v. KoUiker, van Gehuchten, and v. Lenhossek, have by their investigations greatly strengthened the concep- tion. Two primary considerations may be considered to constitute its leading support : (1) the absolute independence of the early nerve-cell or neuroblast and its processes, as was first clearly shown by His ; (2) the fact that when nerve tissue is treated by the Golgi method or by the vital methylene blue method no continuity of any kind can lie observed between neighbouring cells, although the processes of the cells can apparently be traced to their ultimate divisions. Fiu-ther, it should be noted that the neuron doctrine receives strong support from pathological observa- tions, and that before it assumed concrete form ideas of a somewhat similar kind were present in the minds of pathologists. Still the neuron theory is not accepted by several leading Histologists. Apathy, Xissl, and Bethe at the present moment form a powei-ful combination against it. It is therefore necessary to indicate the views entertained by these observers. More than thirty years ago Max Schultze called attention to the fact that the axis - cylinder of a nerve-fibre is composed of exceedingly fine fibrils^ which, when traced to the cell from which the fibre takes origin, are there seen to enter the cell- body and spread out within it. By more delicate methods of research, Apathy and Bethe have been able to place this early observation of Schultze beyond the realm of doulit. Apathy, who worked chiefly at the invertebrate nervous system, not only traced the neuro-fibrilla3 through the cell-body but ' It may be mentioned that Eemak, the discoverer of the axis-cylinder in 1838, stated that it was finely striated in the longitudinal direction. Fig. 359. — Diagram of the Connexion estab- lished BY A Ganglionic and a Motor Necron (Ramou y Cajal). A. Fibre coining down from a pjTamiclal cell in the motor area of the cerebral cortex. B. Motor cell in gray matter of spinal cord. C. Muscle-fibres. D. Collateral branch from the pyramidal fibre. E. Cell in the medulla oblongata sending its axon upwards to the cerebral cortex. F. Cells in the spinal ganglion. G. Peripheral process of ganglionic cell ending in skin. I. Collateral branches of central process of gan- glionic cell. S.X. Spinal nerve. Fig. 360. — Three Stages in the Development of a Cell from a Spinal Ganglion. 450 THE NERVOUS SYSTEM. into all its processes, aud lie believes that he has been able to follow them beyond these into a delicate fibrillar interlacement which constitutes a bond of union between all the nerve-cells of the nervous sj'stem. Bethe's observations have been carried out in vertebrates. Two illustrations from his book are reproduced in Fig. 361. The cell represented in A is from the gray matter of the anterior horn of the human spinal cord, and the relation presented by the neuro-fibrils within the cell and to its various processes are very clearly depicted. The axon appears to receive a con- tribution of neuro-fibrilhe from all the dendritic processes ; this, according to Bethe, is character- istic of the great majority of nerve-cells. In the cells indicated by the letter B, Avhich are from the cerebral cortex of man, it will be noticed that tlie axons as they leave the cell become ex- ceedingly fine and delicate, and the neuro-fibrillte which compose them are so closely packed together that all trace of their individual existence disappears. When the medullary sheath is assumed by the fibi-e the neuro-fibrillae of the axis-cylinder again become apparent. !f .',1 ■'■, .\ V \ ■7^ Axon MM •^^<^ .;// Axons Fig. 361. — Neuve Cells as DEriCTEU by Bethe. A, A cell from the anterior horn of gray matter of the spinal cord of man. B, Two cells from the human cerebral cortex. In vertebrates Bethe has not been able to trace the neuro-fibrils into an all-pervading filjrillar network such as Apdthy has described as binding the various nerve elements together in the invertel)rates, but lie has followed them into the finest of the dendritic branchings, and he a,ssumes that the connecting network exists in the higher as well as in the lower members of the animal kingdom. This conception of the structure of the axon renders the giving off by the nerve-fibre ol collateral brandies and also its terminal splitting or arborisation, matters which can be the more easily understood. On the strength of the observations detailed above, Apathy, Bethe, and Nissl, all of whom are authorities who deserve the highest degree of attention, have assailed the neuron theory. Apdthy has advanced the liypothesis that the all-pervading filnillar interlacement, which streams continuously throughout the whole nervous system and is found not only in the cell and its proces.ses but also in the form of a connecting network outside the cells, is the essential part of the nervous system and not the so-called indejjcndent neurons of the neuron theory. It is aiso contended that axons or axis-cylinders may ari.se in two ways : (1) directly from the nervc- celLs ; (2) indirectly from the neuro-fibrillar network between the nerve-cells. In a striking address recentl^y delivered by Profes.sor Waldeyer to the Eoyal Society of Edin- CEREBROSPINAL NERVOUS SYSTEM. 451 burgh the essential iDoints of the neuron doctrine were vigorously maintained and several new preparations by Raniun y Cajal and Beilschowsky were demonstrated. In the latter the neuro- fibrillaj were seen to enter the cell-body, spread out and break up into a plexus within it, but none could be detected pursuing an uninterrupted course right through tlie cell and then passing out from it. As Edinger remarks, investigation in the immediate future will be largely concerned in the attempt to further elucidate the following questions : (1) Are the connexions between neurons merely those of contact? (2) Do the fibres which proceed from one cell fuse witli the constituent parts of another neuron ? (3) Do the neuro- fibril Ite form an inter-connecting network between the nerve-cells, and do axons or axis-cylinders arise from such a network ? It is questionable even if the last two of these queries are answered more or less in the affirmative whether it will be necessary to abandon the essential points in the neuron theory. Since the foregoing has been printed an instructive monograph on the subject has been published by Professor Gustaf Retzius ("Punktsubstanz ' Nervoses Grau' und Neuronenlehre," Biologische Unfersuchungen, Neue Folge, xii.). Neuroglia. — The neuroglia is the supporting tissue of the cerebrospinal axis. It may be considered to include two different forms of tissue, viz. the lining ependymal cells and the neuroglia proper. We place these under the one heading, seeing that in all probability they both have a common developmental origin. The ependymal cells are the columnar epithelial cells which line the central canal of the spinal cord and the ventricles of the brain. In the embryonic condi- tion a process from the deep extremity of each cell traverses the entire thickness of the neural wall and reaches the surface. It is not known whether this process exists in the adult. The neuroglia proper is present in both the white and the gray matter of the cerebrospinal axis. It constitutes an all- pervading basis substance, in which the various nerve elements are embedded in such a way that they are all bound together into a consistent mass and are yet all sever- ally isolated from each other. Neuroglia consists of cells and fine filaments. The fibrils are present in enormous numbers, and by their interlacements they constitute what appears to be a fine feltwork. At the points where the fibrils intercross may be seen the flattened glial cells. Whilst the neuroglia is for the most part intimately intermixed with the nerve elements, there are in both brain and cord certain localities where it is spread out in more or less pure layers. Thus upon the surface of the brain and of the spinal cord there is such a layer ; likewise beneath the epithelial lining of the central canal and of the cavities of the brain there is a thin stratum of neuroglia. The ependymal cells are derived from the original neuro- epithelial cells of the early neural tube, and in all probability the neuroglia proper has a similar origin. They both, therefore, are products of the ectoderm. Summary. — 1. The cerebrospinal nervous system is composed of two parts, viz. (a) a medullary part, consisting of the brain and spinal cord, with the efferent nerve- fibres which pass out from them: (&) the ganglionic part, with the afferent nerve-fibres. 2. Each of these parts has a different origin and is composed of neurons which possess characteristic features. 3. The ganglionic neurons are derived from the primitive cells of the neural crest, and have each one process which divides into two. Of these the central division enters the cerebrospinal axis and probably represents the axon, whilst the peripheral division, which becomes connected with a peripheral part, may pro- visionally be regarded as a dendrite. The central fibres from the ganglionic cells Fig. 362. — Section THiiouciH the Central Canal ok the Spinal Cord of a Human Embryo, showino Ependymal and Neur- oglial Cells (after v. Leuhossek). A, Ependymal cell. B, Neuroglial cell. 452 THE NEEVOUS SYSTEM. in the region of the cord form the dorsal or posterior roots of the spinal nerves. These roots have thus an origin outside the cord, and grow into its substance in the process of development in the same manner that the roots of a plant strike into the soil. 4. The cerebrospinal neurons are derived from the germinal cells in the wall of the early neural tube. Certain of these furnish efferent nerve-fibres, which issue from the cord in separate bundles termed the anterior or ventral roots of the spinal nerves. In the case of the cranial nerves, however, with the exception of the trigeminal and facial nerves, the efferent fibres are not thus separated from the afferent fibres at their attachment to the brain. 5. The brain and cord when studied by the naked eye are seen to be composed of white matter and gray matter. The white matter forms very nearly two-thirds of the entire cerebrospinal axis. It is composed of medullated nerve -fibres embedded in neuroglial tissue. The gray matter is composed of nerve-cells with their dendrites and axons. Some of the axons are in the form of naked axis cylinders, whilst others have a coating of medulla. Intimately intermixed with these parts is the neuroglia, which isolates them more or less completely from each other. SPINAL COED. The spinal cord is that part of the cerebrospinal axis which occupies the upper two-thirds of the spinal canal of the vertebral column. It is an elongated cylin- drical structure, slightly flattened in front and behind, which extends from the margin of the foramen magnum to the level of the lower border of the body of the first lumbar vertebra or to the upper border of the body of the second lumbar vertebra. Its average length in the male is 45 cm. and in the female 43 cm. ^Mesencephalon Cerebellum Fourtli ventricle Cervical swellin: of the cord Luuiliar swelling of the coi'd A considerable amount of variation within certain limits (viz. the mid-point of the body of the last dorsal vertebra and the upper border of the body of the third lumbar vertebra) is observed in different in- dividuals as to the precise level at which the spinal cord ends inferiorly, and in the female there would appear to be a tendency for the cord to reach a slightly lower point in the canal than in the male. Further, the relation presented by the spinal cord to the vertebral column differs in a marked degree in the foetus and infant at different periods of development. Up to the third month of intrauterine life the cord occupies the entire length of the spinal canal ; it ex- tends downwards to the lowest limit of the canal. But from this time on, as growth proceeds, the vertebral column lengthens at a more rapid rate than the cord. The spinal cord, therefore, has the appearance of shrinking in an upward direction within its canal, and at birth its lower end is usually found to be opposite the body of the third lumbar vertebra. The attitude assumed by the individual affects to a small degree the position of the lower end of the cord. Thus, when the trunk is bent well forwards, it is noticed that the terminal part of the cord rises slightly within its bony canal. At the margin of the foramen magnum the spinal cord becomes continuous with the medulla oblongata of the brain, whilst below, it tapers rapidly to a point and forms a conical extremity termed the conus medullaris. From the end of the conus medullaris a slender glistening thread is prolonged downwards within the spinal canal, and finally anchors the spinal cord to the back of the coccyx. This prolongation receives the name of the filum Fk;. 363. — Human F(etds in the 'rHiRD Month of Development, with the Brain and Spinal Cord exposed FROM behind. SPINAL COED. 453 fJoiuis iiieilullaris terminale. The diameter of the cord is very much shorter than that of the spinal canal within which it lies. A wide interval is left between its surface and the walls of its canal, and this excess of space is clearly a provision for allowing free movement of the vertebral column without producing any jar- ring contact between the delicate spinal cord and the surrounding bones. Three protective membranes are wrapped around the cord. From within outwards these are termed (1) the pia mater, (2) the arachnoid mater, and (3) the dura mater. The pia mater is a fibrous membrane which forms the im- mediate investment. It is closely applied to the cord, and from its deep surface numerous fine septa penetrate into the substance of the cord. The arachnoid mater is an exceedingly delicate transparent membrane which is loosely wrapped around the cord so as to leave a considerable interval, termed the subarachnoid space, between itself and the pia mater, in which there is always a varying amount of cerebro- spinal fluid. Outside the arachnoid mater, the dura mater forms a wide, dense, fibrous, tubular sheath, which extends downwards within the spinal canal for a considerable distance beyond the conical extremity of the cord. The spinal cord is suspended within its sheath or tJieca of dura mater by two lateral wing-like ligaments. Fig. 364.— The Conos Medullaris and the termed the ligamenta denticulata. outwards from the sides of the attached by a series of pointed FiLUM Terminale exposed within Spinal Canal. Postero-lateral iiroove ^ These extend cord and are or tooth-like processes to the inner surface of the theca of dura mater. Between the wall of the spinal canal and the dura mater there is a narrow interval, which is filled up by soft areolo- fatty tissue and numerous thin- walled veins arranged in a plexiform manner. Thirty-one pairs of spinal nerves arise Anterior nerve-root Posterior nerve-root First lumbar \ertebra Spinal ganglion Anterior primary division of nervn Posterior primary division of nerve Fig. 365. — The Roots of Origin of the Seventh Dorsal Nerve (semi -diagram- matic). Fig. 366.— Section through the Conus Medullaris and the Cauda Equina as they lie in the Spinal Canal. from the sides of the spinal cord. These are classified into eight cervical, twelve 33 a 454 THE NEKVOUS SYSTEM. dorsal, live lumbar, five sacral, and one coccygeal ; and according to the attach- ments of these groups of nerves the spinal cord is arbitrarily subdivided into cervical, dorsal, lumbar, and sacral regions. In employing these terms, therefore, for different districts of the cord, it must be understood that the regions are deter- mined by the nerve attachments, and not by any direct relationship between these parts of the cord and the sections of the vertebral column which bear the same names. Each spinal nerve is attached to the cord by a ventral and a dorsal root, and as these are traced to their central attachments they are seen to break up into a number of separate nerve fascicles or bundles, which spread out, in some cases very mdely from each other, as they approach the side of the cord (Fig. 365). Each pair of nerves is therefore attached to a portion of spinal cord of some length, and such a portion, with its pair of nerves, receives the name of a " segment of the spinal cord." It must be clearly understood, however, that, in so far as the surface of the cord is concerned, there is absolutely no means of marking off one segment from another, except by the nerve attachments. In the cervical and lumbar regions of the cord the nerve-roots are somewhat crowded together, so that little or no interval is left between the adjoining root fascicles of neighbouring nerves. In the dorsal region, however, distinct intervals may be observed, and the root fascicles ai'e more loosely arranged. From this, it will be evident that the cord segments in different parts of the cord are not of equal length. In the cervical region the segments measure about 12 mm. in length, in the dorsal region from 20 to 24 mm., and in the lumbar region about 10 mm. The number of fascicles which attach the different nerve -roots to the cord is very different in different nerves, and is not necessarily the same in the same nerve-root in different individuals. Owing to the great difference which exists between the length of the spinal cord and the length of the vertebral column, the farther we pass down the greater the distance becomes between the attachment of the various nerve-roots to the cord and the invertebral foramina through which the corresponding nerves leave the spinal canal. The lower nerve-roots, therefore, have to traverse the spinal canal for a considerable distance before they reach their apertures of emergence. It thus happens that the nerve-roots which spring from the lumbar and sacral regions of the cord attain a very great length and descend vertically in the lower part of the spinal canal in a bunch or leash, in the midst of which lie the conus medullaris and the filum terminale. This great bundle of nerve-roots receives the appropriate name of the cauda equina. Enlargements of the Cord. — Throughout the greater part of the dorsal region, the spinal cord presents a uniform girth and a very nearly circular outline when seen in transverse section. In the cervical and lumbar regions, however, it shows marked swellings. The cervical enlargement (intumescentia cervicalis) is the more evident of the two. It begins very gradually at the upper end of the cord, attains its greatest breadth (12 to 14 mm.) opposite the fifth or sixth cervical vertebra, and finally subsides opposite the second dorsal vertebra. To this portion of the cord are attached the great nerves which supply the upper limbs. The lumbar enlargement (intumescentia lumbalis) begins at the level of the tenth dorsal vertebra, and acquires its maximum transverse diameter (11 to 13 mm.) opposite the last dorsal verteljra. Below, it rapidly tapers away into the conus medullaris. To the lumbar enlargement are attached the great nerves of the lower limbs. These enlargemeuts of the cord are associated with the outgrowth of the limbs. In the earlier developmental stages of the spinal cord they are not present, and they only take form as the limbs become developed. In the lower mammalia their size corresponds with the degree of development of the limbs. Thus, in the long-armed orang and gibbon, the cervical swelling stands out with a remarkable degree of pi'ominence. It is, however, interesting to note that although in the cetacea there are no visible hind-limbs, there is nevertheless a well-marked lumbar enlargement of the cord. Fissures and Furrows of the Cord. — When cross-sections of the spinal cord are made, it is seen to be a bilateral structure which is partially subdivided into a right and left half by two median clefts — one upon the anterior and the other upon the posterior aspect. These clefts are termed the antero-median and the postero- median fissures, and they extend along the entire length of the cord. At the same SPmAL COED. 455 Postevo-mediaii_ tissui'e' Cervical swelling- Posterior i)ar.i-_ median fissure Postero-lateraL fissure -CVv -DVii time it must be noted that these two median clefts present many points of differ- ence. The antero-median fissure (fissura mediana anterior) is for the greater part of its length much shallower than the postero-median fissure. In the cervical and dorsal regions it only penetrates for a distance corresponding to somewhat less than a third of the antero-posterior diameter of the cord. Further, the antero- median cleft is much the wider and more apparent of the two, and the pia mater dips down into it and forms a fold or reduplication within it. The postero-median fissure (fissura mediana posterior) in the cervical and dorsal regions penetrates into the cord until it reaches a point somewhat beyond its centre. It is extremely narrow, and contains a single septum which is derived from ependymal and neuroglial elements, and is intimately connected with the adjacent sides of the two halves of the cord, between which it intervenes. The pia mater, which invests the surface of the cord, passes continuously over the postero-median fissure and sends no prolongation of any kind into it. In the lumbar region of the cord the postero-median fissure becomes shallower, whilst the antero-median fissure deepens, and ultimately in the lower part of the cord the two fissures present a very nearly equal depth. The two halves of the cord, which are marked off from each other by the median fissures, may show trifling differ- ences in the arrangement of the parts w^hich compose them ; but to all intents and purposes they are symmetrical. They are joined together by a more or less broad band or com- missure, which intervenes between the two median fissures. An inspection of the surface of each lateral half of the cord brings into view a longitudinal groove or furrow, at some little distance from the postero-median cleft, which extends along the whole length of the cord. Along the bottom of this groove the fascicles of the posterior nerve- roots enter the cord in accurate linear order. It is called the postero-lateral sulcus (sulcus lateralis posterior). There is no corresponding furrow on the forepart of each lateral half of the cord in connexion with the emergence of the fascicles of the anterior nerve-roots. These fascicles emerge irregularly over a broad strip of the surface of the cord, which corresponds in its width to the thickness of the subjacent extremity of the anterior horn of gray matter. The postero-lateral groove subdivides each lateral half of the cord into a small posterior column (funiculus posterior) and a much larger antero- lateral column, and it is customary to arbitrarily map off the latter into a lateral column (funiculus lateralis) and an anterior column (funiculus anterior) by a line corresponding to the emergence of the outermost fascicles of the anterior nerve-roots. In the cervical region a distinct longitudinal groove may be observed on the surface of the posterior column. It is placed rather nearer to the postero-median than to the postero-lateral furrow and as it is traced down into the dorsal region it gradually becomes indistinct and finally disappears. This is called the posterior paramedian groove, and it marks on the surface the position of a septum of pia mater which dips into the cord and subdivides the posterior column into an outer part, termed the funiculus cuneatus or the column of Burdach, and an inner portion, which receives the name of the funiculus gracilis or the column of Goll. 33 h -DVx Lumbar .swell! ns- U Fig. 367. — Diagram of the Spinal Cord as seen from behind. CVi shows tlie level of the 1st cervical vertebra ; CVv of the 5th cervical vertebra ; DVii of the 2nd dorsal vertebra ; DVx of the lOtli dorsal verte- bra : DVxii of the 12th dorsal vertebra ; LVii of the 2nd lumbar vertebra. 456 THE NEKVOUS SYSTEM. Column of Goll Posterior coin Column of Burdach Internal Structure of the Spinal Cord. The spinal cord is composed of a central core of gray matter thickly coated on the outside by white matter. At only one spot does the gray matter come close to the surface, viz. at the bottom of the postero-lateral groove. Gray Matter of the Cord. — The gray matter in the interior of the cord has the form of a fluted column, but it is customary to describe it as it appears in transverse sections through the cord. It then presents the appearance of the capital letter H. In each lateral half of the cord there is a semilunar or crescentic mass, shaped somewhat like a comma, the concavity of which is directed outwards and the convexity inwards. The two crescents of opposite sides are connected across the middle line by a transverse band, which receives the name of the gray commissure (commissura grisea). The postero- median fissure cuts through the cord until it reaches the gray commissure. The bottom of the antero-median fissure, however, is separated from it by an intervening strip of white matter, which is termed the anterior white commissure (commissura an- terior alba). la the gray commissure may be seen the central canal of the cord (canalis centralis), which tunnels the entire length of the cord and is just visible to the naked eye as a minute speck. The portion of the gray com- missure which lies behind the central canal is called the 'posterior gray commis- sure (commissura grisea posterior) ; whilst the portion in front receives the name of the anterior gray commissure (commissura grisea anterior). Each crescentic mass of gray matter presents certain well-defined parts. The projecting portions which extend behind and in front of the connecting transverse gray commissure are termed respectively the posterior and the anterior cornua of gray matter (column^e grisese). These stand out in marked contrast to each other. The anterior cornu (columna grisea anterior) is short, thick, and very blunt at its extremity. Further, its extremity falls consideraljly short of the surface of the cord and is separated from it by a tolerably thick coating of white matter. Through this the fascicles of the anterior nerve-roots, as they emerge from the gray matter of the anterior horn, pass on their way to the surface. The thickened end of the anterior cornu is called the caput cornu, whilst the part close to the gray commissure is termed the cervix or basis cornu. Throughout the greater part of the cord the posterior cornu (columna grisea posterior) is elongated and narrow, and is drawn out to a fine point, which almost reaches the bottom of the postero- lateral sulcus. This pointed extremity receives the name of the apex cornu ; the slightly swollen part which succeeds it is the caput cornu; whilst the slightly constricted part adjoining the gray commissure goes under the name of the cervix or basis cornu. The apex or tip of the posterior cornu differs considerably in appearance from the general mass of the gray matter. It is composed of a material which presents a lighter hue and has a somewhat translucent look. It is called the substantia gelatinosa Eolandi, and, when seen in transverse section, it exhibits a V-shaped out- lin« and fits on the caput cornu like a cap. A pointed and prominent triangular projection juts out from the external aspect of gray matter nearly opposite the gray commissure. This is the lateral horn (columna grisea lateralis), and it is best iiiarked in the upper dorsal region (Fig. Formatio reticulaiis Lateral colun Central can u Spinal accessory root Origin of spinal accessory ner\ e Anterior column Fig. 368. — Transverse Section through the Upper Part of the Cervical Region of the Cord of an Orang. (From a specimen prepared by the Weigert-Pal method, by which the white matter is rendered dark whilst the gray matter is bleached. ) INTEENAL STKUCTUKE OF THE SPINAL CORD. 457 369, B). Traced upwards it becomes absorbed in the greatly expanded anterior horn of the cervical swelling, but it reappears again in the upper part of the cord and is particularly noticeable in the second and third cervical segments ; followed in a downward direction it blends with the anterior horn in the lumbar swelling and contributes to the thickening ot that coruu. The gray matter is for the most part mapped oft" from the surrounding white matter with a considerable degree of sharpness ; but in the cervical region, on the outer aspect of the crescentic mass and in the angle between the anterior and posterior horns, fine bands of gray matter penetrate the white matter, and, joining with each other, form a network the meshes of which enclose small islands of white matter. This constitutes what is called the formatio or processus reticularis. Although best marked in the cervical region, traces of the same reticular formation may be detected in lower segments of the cord. Characters presented by the Gray Matter in Different Regions of the Cord. — The gray matter is not present in equal quantity nor does it exhibit the same form in all regions of the cord. Indeed, each cord segment presents its own special characters in both of these respects. It is not necessary, however, in the present instance to enter into this matter with any degree of minute detail. It will be sufiicient if we point out the broad distinctions which are evident in the different regions. It may be regarded as a general law that, wherever there is an increase m the size of the nerves attached to a particular part of the cord, a corresponding increase in the amount of gray matter will be observed. It follows from this that the regions where the gray matter bulks most largely are the lumbar and the cervical swellings. The great nerve-roots which go to form the nerves of the large limb-plexuses enter and pass out from those portions of the cord. In the dorsal region there is a reduction in the quantity of gray matter in correspondence with the smaller size of the dorsal nerves. In the dorsal region (Fig. 369, B) both horns of gray matter are narrow, although the distinction between the anterior horn and the still more attenuated posterior horn is sufficiently manifest. In this region the lateral horn of gray matter is likewise characteristic, and the substantia gelatinosa Eolandi in transverse section is pointed and spear-shaped. In the upper three segments of the cervical region the anterior horns of gray are not large and resemble the corresponding horns in the dorsal region. A lateral horn is also present. But in these segments (and more especially in the first and second) there is a marked attenuation of the neck of the posterior horn, and the posterior gray commissure is very broad. In the cervical sivelling of the cord the contrast between the two cornua is most striking ; the anterior horn is of great size and presents a very broad surface towards the anterior aspect of the cord, whilst the posterior horn remains narrow. This great increase in the bulk of the anterior horn is due to a marked addition of gray matter on the outer side of the horn, and seeing that this additional matter is traversed by a greater number of fibres, it stands out, in well-prepared specimens, more or less distinctly from the part of the horn which lies to the inner side, and which may be considered to represent the entire anterior horn in the dorsal and upper cervical segments. Within this lateral addition to the anterior horn are placed those collections of cells which constitute the nuclei of origin of the motor nerves of the muscles of the upper limb. The characteristic thickening of the anterior horn of gray matter is e^'ident, therefore, in those segments of the cord to which the nerves which enter the brachial plexus are attached, viz. the lower five cervical segments and the first dorsal segment. In the lumbar sicelling the anterior horns again broaden out, and for the same reason as in the case of the corresponding horns in the cervical swelling. The nuclear masses which contain the cells from which the motor fibres which supply the muscles of the lower limbs take origin are added to the outer aspect of the horns and give them a very characteristic appearance. In this region of the cord, however, the posterior horns are also broad and capped by substantia gelatinosa Rolandi, which in transverse section presents a semilunar outline. There is 458 THE NEEVOUS SYSTEM. consequently no difficulty in distinguishing from an inspection of the gray matter alone between transverse sections of the cord taken from the cervical and lumbar swellings of the cord. A. — Cervical region — at the level of the fifth cervical nerve (From a specimen prepared by Dr. A. Bruce.) 1. Postero-inedian fissure. 2. Paramedian septum. 3. Postero-lateral groove. 4. Posterior nerve-root. 5. Substantia gelatinosa Rolandi. 6. Root-Kljres entering gray matter. 11. Anterior nerve-root. 7. Formatio reticularis. 12. Antero-median fissure. S. Central canal. 0. Nuclei from which motor- fibres for muscles of upper limb arise. 10. Anterior commissure. B. — Through the mid-dorsal region. 1. Postero-median fissure. 2. Postero-lateral groove. 3. Posterior cornu. 4. Posterior vesicular column of cells. 5. Lateral cornu. 6. Central canal. ' 7. Anterior cornu. 8. Antero-median fissure. 1 S 1 / C. — Tlirough the luniT»ar region at the level of the fourth huiibar nerve. .\uclei of origin from which the motor- (ibres for mnscles of the lower limb arise. Anterior nerve-root. 9. Antero-)iiedian fissure. -Tlirough the sacral region at tlie level of the third sacral nerve. (From a sijecimen pre- pared by Dr. A. Bruce. ) 1. Postero-niedi.in fissure. 2. Posti'rior nerve-root. 3. Substantia gelatinosa Rolandi. 4. Postorioi' giay conunissure. 5. Anterior ciminiissiu-e. C. Antero-median fissure. 1. Po.sterior nerve-root. 2. Postero-median fissure. 3. Substantia gelatino.sa Rolandi. 4. Root- fibres entering gray )natter. ; f>. Central canal. 6. Anterior commissure. Fi(i. 369. — Section through each ok the Four IlECiiONS of the Cord. (From specimens prepared by the Weigert-Pal method, therefore the white matter is rendered dark in colour whilst the gray matter is bleached. ) In the lower part of tlie conus meduHaris the gray matter in each lateral half of the cord assumes the form of an oval mass joined to its iellow of the opposite side by a thick gray commissure. Here almost the entire bulk of the cord consists INTEENAL STEUCTURE OF THE SPINAL COED. 459 of gray matter, seeing that the white matter is reduced to such an extent that it forms only a thin coating on the outside. White Matter of the Spinal Cord. — In transverse sections of the cord the three cohmms into which the white matter is subdivided become very apparent. The posterior column is wedge-shaped, and lies between the postero-median fissure and the posterior horn of gray matter. The lateral column occupies the concavity of the gray crescent. Behind, it is bounded by the posterior horn of gray matter and the postero-lateral sulcus, whilst in front it extends as far as the outermost fasciculi of the anterior nerve-roots as they pass out from the anterior gray horn. The anterior column includes the white matter between the antero-median fissure and the anterior horn of gray matter, and also the white matter which separates the broad extremity of the anterior gray cornu from the surface of the cord. This latter portion of the anterior columu is traversed by the emerging fascicles of the anterior nerve-roots. In cross-sections of the cord the partition of pia mater, which dips in at the posterior paramedian groove and divides the posterior column into the column of Goll and the column of Burdach, is very strongly marked in the cervical regions, but as it is traced downwards into the dorsal region it becomes shorter and fainter, and finally disappears altogether at the level of the eighth dorsal nerve. Below this point there is no visible demarcation of the posterior column into two parts. The white matter is not present in equal quantity throughout the entire length of the cord. It increases steadily from below upwards, and this increase is most noticeable in the lateral and posterior columns. In the lower part of the conus medullaris the amount of gray matter is actually greater than that of the white matter : but verv soon this state of affairs is chanoed, and in the lumbar region the proportion of gray to white matter is approximately as 1:2-1; in the dorsal region as 1 : 5 ; and in the cervical region as 1 : 5'1. When it is remembered how the gray matter expands in the lumbar and cervical regions, and how greatly it becomes reduced- in the dorsal region, the significance of these figures will become more apparent. Central Canal (canahs centrahs). — As previously stated, the central canal is found in the gray commissure. It is a very minute tunnel, barely visible to the naked eye when seen in transverse section, and it traverses the entire length of the cord. Above, it passes into the medulla oblongata, and finally opens into the fourth ventricle of the brain ; below, it is continued for a variable distance into the filum terminale, and in this it ends bHndly. Only in the lumbar region does the central canal occupy the centre of the cord. Above this level, in the dorsal and cervical regions, it lies very much nearer the anterior than the posterior aspect of the cord ; whilst below the lumbar region, as it is traced down into the conus medullaris, it inclines backwards and approaches the posterior aspect of the cord. The calibre of the canal likewise varies somewhat in different parts of the cord. It is narrowest in the dorsal region ; and in the lower part of the conus medullaris it expands into a distinct fusiform dilatation (very nearly 1 mm. in transverse diameter), which is termed the ventriculus terminalis (Krause). The central canal is lined by a layer of ciliated columnar cells, the deep taper- ing ends of which are prolonged into slender processes, which penetrate into the substance of the cord. These cells constitute the lining ependymal cells of the canal. The cilia of the epithelial cells are very early lost, and it is not uncommon to find the canal blocked up by epithelial debris. The central canal is of interest because it represents in tlie adult the relatively wide -lumen of the early ectodermal neural tube from which the spinal cord is developed. Filum Terminale. — The delicate thread to which this name is applied is con- tinuous with the lower tapered end of the conus medullaris. It is easily distin- guished by its silvery and glistening appearance from the numerous long nerve-roots (cauda equina) amidst which it lies. It is about six inches long, and down to the level of the second sacral vertebra it is inclosed with the surrounding nerve-roots within the theca of dura mater. Piercing the tapered and closed end of the theca at this point, and receiving an investment from it, the filum terminale proceeds downwards in the sacral canal, and finally receives attachment to the periosteum on 460 THE NEEVOUS SYSTEM. the dorsal aspect of the coccyx (Fig. 364, p. 453). It is customary to speak of the filum as consisting of two parts, viz. the filum terminale internum and the filum terminale externum, or the part inside and the part outside the theca of dura mater. The filum terminale externum is simply a fibrous thread, strengthened by the prolongation it receives as it pierces the dura mater. The filum terminale intemiun is largely composed of pia mater ; but in its upper half it incloses the terminal part of the central canal, and around this a variable amount of the gray substance of the cord is prolonged downwards into the filum. When transverse sections are made through the upper part of the filum terminale internum some bundles of medul- lated nerve-fibres are observed chnging to its sides, and with these are associated some nerve-cells identical with those in the spinal ganglia. These represent rudi- mentary or aborted caudal nerves (Eauber). Summary of the Chief Chaeacters presented by the Coed in its Different Eegions. Cervical Region. Dorsal Region. Lumbar Region. Sacral Region. In transverse section, In transverse section, In transverse section. In transverse section, outline of cord trans- outline of cord more outline of cord more outline of cord, versely oval ; in the nearly circular ; but nearly circular than in nearly circular, but middle of the cervical still the transverse di- dorsal region. still somewhat com- svifelling the transverse ameter is greater than pressed from before diameter being nearly the antero - posterior backwards. one -third longer than diameter. the antero - posterior diameter. Postero - median cleft Postero - median cleft Postero - median cleft Postero - median and very deep, extending very deep, extending not nearly so deep as antero-median clefts beyond the centre of beyond centre of cord : in regions above : an- of equal depth. cord ; antero-median anteromedian cleft tero-median cleft, on cleft shallow. shallow. the other hand, much deeper. Gray matter greatly in- Gray matter greatly Gray matter greatly in- Both horns of gray creased in quantity in i-educed in quantity. creased in the lumbar matter very thick and the cervical swelling : Both horns slender. swelling. Both horns massive. Lateral horn anterior horn thick Lateral horn well very thick and massive. apparent. No form- and massive; posterior marked. Formatio Lateral horn absorbed atio reticularis. horn slender in com- reticularis scarcely ap- in anterior horn. For- parison. Lateral horn parent. matio reticularis ab- only evident above the sent. level of the fourth cer- vical nerve. Formatio reticnlaris strongly marked. White matter in great White matter less White matter small in White matter very quantity, and especi- in quantity than in quantity in relation to small in quantity in ally massed in the cervical region, but higher regions, and comparison with the lateral and posterior bulking largely in very small in amount gray matter. columns. comparison with the in relation to in- quantity of gray creased quantity of matter. gray matter. Posterior paramedian Posterior paramedian No posterior para- No posterior para- groove and septum groove absent ; but median groove or median groove and no well marked. the corresponding sep- tum can be traced as low down as the eighth dorsal nerve. septum. corresponding septum. Central canal consider- Central canal consider- Central canal in the Central canal in the ably nearer the anterior ably nearer the anterior centre of the cord. centre of the cord. surface than the pos- surface than the pos- terior surface of the terior surface of the cord. cord. COMPONENT PARTS OF GRAY MATTER OF SPINAL CORD. 461 Component Parts of the Geay Matter of the Spinal Cord. Neuroglia enters largely into the constitution of the gray matter of the cord. It forms a bed within which the nervous elements are distributed. These nervous elements consist of (1) nerve-cells and (2) nerve-fibres — both medullated and non- medullated. The nerve-cells lie in small spaces within the neuroglia, whilst the nerve-fibres traverse tine passages the waUs of which are formed of the same sub- stance. The neurogha is thus an all-pervading basis substance, which isolates more or less completely the nervous elements from each other, and at the same time binds them together into a consistent solid mass. In two situations the gray matter presents special characteristics which have earned for it the name of substantia gelatinosa, viz. the gray matter which constitutes the immediate sur- rounding of the central canal, and which is called the substantia gelatinosa centralis; and that which forms the apical part of the posterior horn of gray matter, and which receives the name of substantia gelatinosa Rolandi. In botli situations the substantia gelatinosa stains more deeply with carmine and presents a more translucent appearance ; in other respects the substantia centrahs and the substantia Rolandi are very different. The substantia gelatinosa centralis forms a thick ring around the central canal, which is traversed by the fine processes which proceed from the deep ends of the ependymal cells whicli line the canal. It is almost entirely composed of neuroglia. In transverse sections of the cord the substantia Rolandi, in the cervical and dorsal regions, presents the appearance of a V-shaped mass, embracing the extremity of the caput of the posterior horn of gray matter ; in the lumbar region this cap assumes a semilunar outline. In the substantia gelatinosa Rolandi the neuroglia is present in small quantity, and small nerve-cells are developed within it in considerable numbers. Nerve-Cells. — The nerve-cells are scattered plentifully throughout the gray matti'r, but perhaps not in such great numbers as might be expected when we note the enormous number of nerve-fibres with which they stand in relation. They are all, without exception, multipolar, and send off from their various aspects several branching protoplasmic processes or dendrites, and one axon, which becomes the axis-cylinder of a nerve- fibre. In size they vary considerably, and it is generally admitted that the bulk of a nerve-cell has a more or less definite relation to the length of the axis-cylinder which proceeds from it. When the nerve-cells are studied in a series of transverse sections of the cord, it will be noticed that a large proportion of them are grouped in clusters in certain districts of the gray matter ; and as these groups are seen in very much the same position in successive sections, it is clear that these cells are arranged in longitudinal columns of greater or less length. Thus we recognise (1) a ventral group or column of cells in the anterior horn of gray matter; (2) an intermedio-lateral group or column in the lateral horn of gray matter, where this exists ; and (3) a posterior vesicular column of cells (Clarke's column), forming a most conspicuous group in the mesial part of the cervix of the posterior horn in the dorsal region of the cord. Other cells besides those forming these columns are scattered somewhat irregu- larly throughout the gray matter of the posterior horn and the part of the gray crescent which Hes l)etween the two horns ; and although these also in some measure may be classified into groups, the arrangement thus effected is not of so definite a character as to justify us in dwelling upon it in the present instance. Ventral Cell- Column and the Origin of the Fibres of the Anterior Nerve- Roots. — The ventral cell-group occupies the anterior horn of gray matter, and in it are found the largest and most conspicuous cells in the spinal cord. It extends from one end of the cord to the other. These ventral nerve-cells have numerous wide-spreading dendritic processes, and it is to be noticed that certain of these dendrites do not confine their ramifications to the gray matter. Thus, some of the cells along the mesial border of the anterior horn of gray matter send dendrites across the mesial plane in the anterior commissure to end in the anterior gray horn of the opposite side ; whilst others, lying along the lateral or outer margin of 462 THE NERVOUS SYSTEM. the anterior horn of gray matter, send dendrites in amongst the nerve-fibres of the adjoining white matter. The axons or axis-cylinder processes of a large proportion of the ventral cells converge together ; and, becoming meduUated, form bundles which pass out from the gray matter, and through the white matter which separates the thick end of the anterior horn from the surface of the cord, to finally emerge as the fascicles of the anterior nerve-roots. These cells, then, are the sources from which the nerve- Postero-lateral furrow Posterior horn of gray matter Postero-median fissure Gray commissure Postero-lateral group of luotor cells Autero-mertian furrow Fig. 370. — Section through the Autero-mesial group of motor cells Autero-lateral group of motor cells Fifth Cervical Segment ok the Cord. on Plates in Dr. Bruce's Atlas.) (To a large extent founded fibres of the anterior nerve-roots proceed, and in consequence they are frequently spoken of as the " motor cells " of the cord. Whilst this is the arrangement of the axons of the great majority of the motor cells, it should be noted that a few cross the mesial plane in the anterior white commissure and emerge in the fascicles of origin of the opposite anterior nerve-root. The ventral cells are not scattered uniformly throughout the anterior horn of gray matter. They are aggregated more closely together in certain parts of the anterior horn, and thus form sub-groups or columns more or less perfectly marked off from each other. Thus one sub-group or column of ventral cells occupies the inner or mesial part of the anterior horn of gray matter throughout almost its whole length. In only two segments of the cord is it absent, viz. the fifth lumbar and the first sacral ; at this level in the cord alone is its continuity broken (Bruce). It is termed the ventro-mesial column or group of ventral cells. Behind this cell-column there is another which is classed with it to which '>the name of dorso-7)iesial cohtmn or group is given, but this column of cells is not con- tinuous throughout the entire length of the cord. It is present in the dorsal region of the cord where the motor nuclei for the muscles of the limbs are absent, and it is also seen in two or three of the segments of the cervical region and in the first lumbar segment (Bruce) ; elsewhere it is not represented. In the cervical and lumbar swellings of the cord, where the marked lateral outgrowth is added to the outer side of the anterior horn of gray matter, certain groups of lai'ge multipolar cells are visible. These are the nuclei of origin of the motor-fibres which supply the muscles of the limbs, and consequently they are not represented in the upper three cervical segments of the cord ; nor in any of the dorsal segments, with the exception of the first dorsal segment ; nor in the two lowest sacral segments. These lateral cells are arranged in several columns, which extend for varying distances in the superadded lateral parts of the anterior horn of gray matter. The two main columns are a ventro-lateral and a dor so-later at column ; in certain segments there is likewise a, pjost-dorso-lateral column, and in a number of segments in the lumbar and sacral regions a central column of cells (Bruce). COMPONENT PAETS OF GEAY MATTER OF SPINAL CORD. 463 I'ostt'io-inediai lissurt Posterior vesicular column (Clarke's column of cells) Gray commissure Aiitero-inedian farrow Antero-mesial grouj of motor cells Postero-mesial group of motor cells Fig. 371. — Section thhotjgh the Eighth Dorsal Segment of the Spinal Cord. (To a large ".xteiit founded on Plates in Dr. Bruce's Atlas.) There cannot be a doubt that the grouping of the motor cells in the anterior horn of gray matter of the cord stands in relation to the muscle groups to which their axis-cylinder processes are distributed ; but from what has been said it will '' irT7TT^'~r>-^ ,>„.*„ ,. , ^ II ; / I / ' 7^-^ I'ostero-latei-al furrow- be apparent that sharply defined cell -clusters associated with par- ticular muscles do not exist. Still, much can be learned re- garding the localisation of the motor nuclei in the anterior horn of gray matter of the cord from the study of the changes which occur in the cell-columns afteratrophiesof isolated muscles or groups of muscles, and after complete or partial amputations of limbs. It has been pointed out that the long muscles of the trunk (as, for example, the different parts of the erector spinae muscle) receive nerve - fibres from all the segments of the cord. Now, we have noted that there is only one cell-column, the ventro-mesial column, which pursues an almost uninterrupted course throughout the entire length of the cord. It may be assumed, therefore, that the nerve-fibres which go to these long trunk-muscles take origin in these mesial cells. Edinger states that in the anterior horn of gray matter the nuclei of origin of the nerves which supply the proximal muscles are medially placed ; that those for the distal muscles are in general situated laterally. If this be the case, the cells con- nected with the shoulder muscles would lie nearer the middle of the anterior horn of gray matter than those which are connected with the hand-muscles. In cases where the forearm and hand, or the leg and the foot, are amputated, it would appear that it is the postero-latei'al column of cells that shows changes in consequence of its separation from the muscles to which its fibres are dis- tributed. ^ lateral furrow Posterior lioni of matter Antero-median furrow Postero- lateral group of cells Central group of Cf Us Antero-lateral grouj) of cells Intermedio - lateral Cell- column. — The intermedio- LuMBAR Segment of the lateral cells form a long ^ ° slender column which ex- tends throughout theentire dorsal region of the cord in the lateral horn of gray matter. It is also prolonged downwards into the first and second lumbar segments, where it disappears. In Antero-niesial group of cells Fif Golgi remain within the gray matter, but the others emerge either for se of entering a peripheral nerve or for the purpose of entering a strand I the white matter of the cord. •rve-fibres thus derived are interwoven together in the gray ma,tter of the lense inextricable interlacement. Component Parts of the White Matter of the Coktx hite matter of the cord is composed of medullated nerve-fibres embedded ,dia. The fibres, for the most part, pursue a longitudinal course ; and ^ deep surface of the pia mater which the cord fibrous septa or partitions are along vertical planes between the fibres, so n an irregular and very imperfect fibrous c, of support. The neuroglia is disposed in :' varying thickness around the cord, sub- the pia mater, and is carried into the cord ve a coating to both sides of the various pial 'he neuroglia also is disposed around the :rve- fibres, so that each of these may be said a canal or tunnel of this substance. The •es are all medullated, but they are not vith primitive sheaths. It is the medullary of the nerve -fibres which gives to the tter its opaque, milky -white appearance, hin transverse section of the cord is stained e and examined under the microscope the tter presents the appearance of a series of plied circles, each with a dot in the centre. s the transversely divided axis -cylinder of ibre, and the dark ring which forms the 3nce of the circle represents the wall of the canal which is occupied by the fibre. Lillary substance is very faintly seen. It I filmy or cloudy appearance between the ler and the neuroglial ring. gement of the Nerve-fibres of the White n Strands or Tracts. — When the white a healthy adult cord is examined the fibres which compose it are iry considerably in point of size ; and although there are special places ^e fibres — or it may be small fibres — are present in greater numbers where, yet as a rule both great and small fibres are mixed up Absolutely no evidence can be obtained in such a cord, by any means sposal, of the fact that the longitudinally arranged fibres are grouped u more or less definite tracts or strands, the fibres of which run a definite 1 present definite connexions. Yet we know this to be the case, and the of these separate tracts has been proved both by physiological and by ;ical investigation. Fig. 374. — Transverse Section THKOaCiH THE WHITE MATTER OF THE Cord, as .seen tlirough the microscope. 466 THE NERVOUS SYSTEM. The physiological evidence depends on the fact that when a nerve-fibre is severed the part which is detached from the nerve-cell from which it is an offshoot degenerates, whilst the part which remains connected with the nerve-cell undergoes little or no change. This is called the law of " Wallerian " degeneration. Thus, if in a living animal one-half of the cord be cut across, and after a few weeks the animal be killed and the cord examined, it will be seen that there are degenerated tracts of fibres in the white matter, both above and below the plane of division ; but, still fui'ther, it will also be manifest that the tracts which are degenerated above the plane of division are not the same as those which are degenerated in the part of the cord which lies below this level The interpretation of this is obvious. The nerve -tracts which have degenerated above the plane of section are the offshoots of nerve-cells which lie in lower segments of the cord or in spinal ganglia below the plane of section. Severed from these nerve-cells, they undergo what is called ascending degeneration. The nerve-tracts, on the other hand, which have degenerated in the portion of the cord below the plane of division are the axons of cells which lie at a higher level than the j^lane of section, either in higher segments of the cord or in the brain itself. Cut off from the nerve-cells from which they proceed, they present an example of descending degeneration. The embryological evidence we owe to Flechsig, and it is no less satisfactory. It depends upon the fact that nerve-fibres in the earliest stages of their develoi^ment consist of naked axis- cylindei-s, and are not provided with medullary sheaths. Further, the nerve-fibres of different strands assume the medullary sheaths at difterent periods. By examining the foetal cord at different stages of its development, it is a comparatively easy matter to locate the different tracts of fibres by evidence of this kind. Speaking broadly, the tracts which myelinate first are those which bring the cord into relation with the jjeripheral parts (skin, muscles, etc.) ; then those fibres which Ijind the various segments of the cord together ; next, those which connect the cord with the cerebellum ; and, lastly, the tracts which connect the cord with the cerebrum. The nervous apparatus for the performance of automatic movements is fully provided, therefore, before this is put under the control and direction of the higher centres. It by no means follows that in all the higher animals corresj^onding strands myelinate at relatively corresponding periods. Take the case of a young animal which from the time of its birth is able to move about and perform voluntary movements of various kinds in a more or less perfect manner, and comj^are it with the helpless new-born human infant which is only capable of exhibiting automatic movements. In the former the pyramidal tracts, or motor tracts, which descend from the cerebrum into the cord, and which are the paths along which the mandates of the will travel, myelinate at an early period ; whilst in the human infant the corresponding fibres do not obtain their medullary sheaths until after birth. The study of the dates, therefore, at which the various strands of nerve-fibres myelinate not only gives the anatomist a means of locating their position in the white matter of the cord, but it also affords the physiologist most important information regarding their functions, and also the periods at which these functions are called into play. It is a matter of interest to note that influences which either accelerate or retard the periods at which nerve fibres are brought into functional activity have also an ett'ect in determining the dates at ■\\'hich these fibres assume their sheaths of mj^eliir. Thus, when a child is prematurely born the whole process of myelinisation is, as it were, hurried up ; and further, when in new born animals light Ls freely admitted to one eye whilst it is carefully excluded from the other, the filjres of the optic nerve of the former myelinate more rapidly than those of the opposite nerve. Posterior Column of the Cord and the Posterior Roots of the Spinal Nerves. — In the cervical and upper dorsal regions of the cord the posterior column is divided by the posterior paramedian septum into the tract of Burdach, which lies externally and next the posterior horn of gray matter, and the tract of Goll, which lies internally and next the postero-median septum. The tract of Burdacl i is compo.sed of nerve-fibres, which are for the most jjart larger than those entering into the formation of Goll's tract, and both tracts have a most intimate relation to the posterior nerve-roots ; indeed, they are both almost entirely composed o f fibres which enter the cord by these roots and then pursue a longitudinal course. • The nerve-fibres which form the posterior nerve-roots, on entering the cord along the postero-lateral groove, divide within the tract of Burdach into ascending and descending branches. These l>ranches diverge abruptly from each other ; and the former take an upward course, whilst the latter proceed dowuwards. The descending fibres are as a rule short, and soon end in the gray matter of the cord. These descending fibres occupy an area in the posterior column near to the place of entrance of the nerve-root. This area, when the spinal cord is divided, undergoes descending degeneration and then presents ; comma-shaped outline. The fibres in question are included xmder the name of the commfc tract of Schultze. The ascending fibres vary greatly in length, and at varying distances from the poin where the parent fibres enter the cord they end in the gray matter. A small contributior of ascending fibres, however, from each posterior nerve-root, extends upwards to the uppe end of the cord, to end in the medulla oblongata. As each posterior nerve-root enters, its fibres range themselves in the outer part COMPONENT PARTS OF WHITE MATTER OF SPINAL CORD. 467 the tract of Burdach close up against the posterior horn of gray matter. Tlie nerve- Tlie oval field of Flochsig CoiMiua tract of Scliultzo Fig. 375. — Diacjram to show the Arrangement of the Fibres of the Posterior Nerve -Roots in THE Posterior Columns of the Cord. Tlie oval field of Flechsig is present in the lumbar region and is composed of fibres which degenerate in a downward direction, and which are not derived from the posterior nerve-roots. In all probaliility they are connnissural fibres (from Edinger, modified). fibres of the nerve-root next above take the same position, and consequently those which entered from the nerve immediately below are displaced inwards, and come to lie in the tract of Burdach nearer to the mesial plane. This process goes on as each nerve-root enters, and the result is that the fibres of the lower nerves ai'e gradually pushed nearer and nearer to the postero-median septum in a successive series of lamellar tracts. Of course the greater proportion of the fibres, which are thus carried upwards from the posterior nerve-roots, sooner or later leave the posterior column and enter the gray matter, to end there in relation to some of its cells ; but, as we have said, every posterior nerve-root sends a few fibres up the whole length of that portion of the cord which lies above, and thus the posterior column gradually increases in bulk as it is traced upwards, and in the upper reaches of the cord a tract of Goll becomes evident. This tract of Goll is composed of the long ascending fibres of the posterior nerve-roots, which have entered the lower segments of the cord. To put the matter differently, the fibres of the sacral roots '•e displaced inwards by the entering lumbar fibres, while the fibres of the lumbar roots are in their turn pushed inwards by the entering dorsal fibres, and, lastly, the fibres of the cervical roots displace the dorsal fibres. The difference between the tract of Goll and the tract of Burdach simply consists in this, that the former is com- posed of the fibres of posterior nerve-roots which have entered the cord at a lower level than those which enter into the formation of the column of Burdach. The fibres of Goll's tract, taking them as a whole, must there- fore necessarily run a very much longer course. Our knowledge of the constitution of the posterior columns of the cord is largely derived from studying the course of degeneration in monkeys, in which the cord has been cut across — either partially or completely. It would appear, from the examination of the human cord Fig. 376.— Diagram to show the which has been injured or compressed, that the lamination Banner in which the Fibres op „ , „, • ,. 1 • ,. , • ^ THE Posterior Ner\t;- Roots enter or the fibres entering trom the sei'iesoi posterior nerve-roots ^^^ ascend in the Posterior is not nearly so complete as in the case of the monkey. Column of the Cord (from Edinger). 468 THE NERVOUS SYSTEM. Numerous collateral fibrils stream into the gray matter of the posterior horu both from the ascending and descending branches of the entering fibres of the posterior nerve- roots. These ai-e classified into long and short collaterals. The long collaterals extend forward into the anterior horn of gray matter and end in relation to the ventral nerve- cells. The short collaterals end in relation to the nerve-cells in the substantia Rolandi, and other nerve-cells of the posterior horn of gray matter. The majority of the fibres of the posterior nerve-root enter the cord on the inner side of the apex of the posterior horn of gi'ay matter. The manner in which these are related to the columns of Burdach and Goll has been noticed ; but a certain number of those fibres which lie most externally take a curved course forwards on the inner side of the posterior horn of gray matter and then pass into it. In the dorsal region these curved fibres end in connexion with the cells of Clarke's column (Fig. 369, p. 458). Tract of Lissauer. — This is a small tract of nerve-fibres of minute calibre which assume their medullary sheaths at a comparatively late period. It is placed at the surface of the cord close to the postero-lateral furrow. It is formed by some of the outer fibres of the posterior nerve-roots, which do not enter the tract of Burdach, and which pass upwards in the cord close to the substantia gelatinosa Rolandi, in which they ultimately end. It must now be evident that the fibres which enter the cord througli each posterior nerve-root have three main modes of distribution : (1) the majority take part in the forniation of the columns of Burdach and Goll ; (2) a few lie close to the posterior horn of gray matter and describe a series of graceful curves as they pass forwards prior to turning outwards into the gray matter, to end, in the dorsal region, in Clarke's A^esicular column ; (3) a third series form Lissauer's tract and end in connexion with the cells of the substantia gelatinosa Rolandi and other cells in the posterior and anterior horns of gray matter. The fil^res derived from the posterior nerve-roots which ascend in the posterior columns of the cord to the medulla oblongata of the brain constitute a direct sensory tract ; other fibres are described which give rise to a crossed sensory tract termed the spino-thalamic tract. These latter fibres arise as the axons of certain of the cells in the posterior horn in connexion Avith which fibres from the posterior nerve-roots have ended, and crossing to the opposite side of the cord through the anterior commissure they ascend in the anterolateral column to the brain, where they ultimately reach the optic thalamus. As the spino-thalamic tract ascends in the cord its fibres are not gathered into a compact strand, but are more or less loosely scattered in the lateral column. Association Fibres in the Posterior Column. — But the whole of the fibres of the posterior column are not derived from the posterior nerve-roots. A few fibres exist in this column which have a different origin. They are derived from certain of the cells of the gray matter of the coi'd, and entering the posterior column divide into ascending and descending branches which pass upwards and downwards in the column for a varying distance before they finally turn in to end in the gray matter at a higher and a lower level. These fibres, therefore, constitute links of connexion between different cord segments, and thus they are termed association or longitudinal commissural fibres. Our information regarding these fibres at present is somewhat defective ; but it is believed that the deepest part of the column, i.e. the part next the posterior gray commissure and termed the ventral field, and also the descending septo-marginal tract of Bruce, placed in apposition with the postero-median septum and in the adjoining jjart of the surface, belong mainly to this category. Lateral Column of the Cord. — -In the lateral column of the cord the well- e.stablished. tracts are : — 1. The direct cerebellar tract. 2. The tract of Gowers. 3. The crossed pyramidal tract. The remainder of the column goes under the name of the lateral basis-bundle. The direct cerebellar tract (fasciculus cerebello-spinalis) is a band-like strand which lies in relation to the surface of the cord immediately in front of the postero- lateral groove. It is an ascending tract, and is composed for the most part of coarse, large nerve-fibres, which are derived from the nerve-cells of the posterior vesicular column (Clarke's column) in the posterior horn of gray matter. It is, therefore, not found tliroughout the whole length of the cord. It first appears in the lower part of the dorsal region ; and as it ascends it gradually increases in size as it is joined by the axons of the cells of Clarke's column, which lie at higher levels. It finally enters the medulla oblongata, and through this proceeds to the cerebellum, in which it ends. COMPONENT PAETS OF WHITE MATTEK OF SPINAL COED. 469 Entering Lissaupr's tract It must not be forgotten that each posterior nerve-root in the doi-sal region of the cord gives a contribution of fibres to the posterior vesicular column of cells from which the fibres of the direct cerebellar tract arise (see p. 468). In this way a connexion is established between the posterior roots of the dorsal nerves and the cortex of the cerebellum. It is believed that the direct cerebellar tract is an important tactor in bringing about a proper co-ordination of muscular movements. Gowers's tract (fasciculus antero-lateralis superficialis) lies in front of the direct cerebellar tract, and, like it, next the surface of the lateral column. It is also an a.scending tract, and it likewise (in part at least) ultimately reaches the cerebellum, although after leaving the cord it takes a different route to gain its destination. In transverse sections of the cord it presents a comma-shaped appearance, the thick part abutting against the direct cere- bellar tract, and the narrower portion taper- ing forwards into the recjion of the emercjincj anterior nerve-roots. The tract of Gowers begins at a lower level in the cord than the direct cerebellar tract and it increases in vol- ume as it is traced up- wards. The fibres of this tract have probably their origin in the cells of the posterior horn of gray matter, but on this point there is at present no precise information. The crossed pyramidal tract (fasciculus cerebro- spinalis laterahs) is a large well-defined de- scending tract, which lies immediately in front of the posterior horn of gray matter and subjacent to the direct cerebellar tract, which shuts it out from the surface of the cord. Below the point where the direct cerebellar tract begins the crossed pyramidal tract becomes superficial, and in this position it can be traced as low as the fourth sacral nerve, at which level it ceases to exist as a distinct strand. The crossed pyramidal tract is composed of an admixture of both large and small fibres. These arise in the brain from the large pyramidal cells of the motor or Eolandic area of the cerebral cortex, and pass downwards through various subdivisions of the brain to gain the spinal cord. As they enter the cord they cross the mesial plane from one side to the other, and it thus happens that the crossed pyramidal tract in the right lateral column of the cord has its origin in the cortex of the left cerebral hemisphere, and vice versa. As the tract descends in the cord it gradually diminishes in size ; and this is due to the fact that, as it traverses each spinal segment, numerous fibrts leave it to enter the anterior horn of gray matter, and end in connexion with the ventral motor cells from which the fibres of the anterior nerve-roots arise. The entire strand is ultimately exhausted in this way. Numerous collateral fibrils spring from the pyramidal fibres, and, entering the gray matter, end in a similar manner, and in this way a single pyra- midal fibre may be connected with several spinal segments before it finally ends. The crossed pyramidal tract must be regarded as a great motor strand which brings the spinal motor apparatus under the control of the will. Schafer believes that many of the pyramidal fibres end in counexion with the cells of Clarke's column. In the rat, mouse, guiuea-pig, squirrel, sheep, kangaroo, etc., the pyramidal tract lies in the posterior column of the cord. Fn Emerging anterior root ;. 377. — Diagrammatic Representation of a Transverse Section THROUGH THE SpINAL CORD. Tlie nerve tracts in the white matter and the clusters of nerve-cells in the sn-av matter are shown. 470 THE NEEVOUS SYSTEM. The lateral basis-bundle (fasciculus lateralis proprius) represents the remainder of the lateral column. Our information regarding it is still imperfect ; but it would appear th it its fibres are largely derived from the cells situated in all parts of the gray matter, and also from the nerve-cells of the opposite side of the cord. After a course of very varying length in the basis-bundle, these fibres turn inwards and re-enter the gray matter. Such fibres may thus be regarded as inter- segmental association fibres binding two or more segments of the cord together. It may be mentioned that the association fibres which link together segments of the cord which are near to each other lie close to the gray matter, whilst those which connect the more distant segments are situated further out in the lateral basis-bundle. Anterior Column of the Cord. — One well-defined tract is situated in the anterior column. This is termed the direct pyramidal tract. The remainder of the column receives the name of the anterior basis-bundle. The direct pyramidal tract (fasciculus cerebro-spinalis anterior) is usually a nerve-strand of small size which lies next the antero-median fissure. As a rule, it cannot be traced lower than the middle of the dorsal region of the cord. It is a descending tract and must be associated with the crossed pyramidal tract of the opposite side, seeing that both of these strands arise from the motor area of the cortex of the same cerebral hemisphere. Erom this, it must be clear that the direct pyramidal tract does not cross the mesial plane as it enters the cord, but descends on the side of the cord corresponding to the cerebral hemisphere in which it arises. All the same its fibres do not end in the same side of the cord, but at every step along the path of the strand they make use of the anterior commissure and cross to the opposite side of the cord, to terminate in relation to the opposite ventral motor cells in the same manner as the crossed pyramidal fibres. From this crossing ot the pyramidal tracts, it results that the destruction of the fibres which compose them as they descend in one side of the brain must result in paralysis of the muscles supplied by the efferent nerves of the opposite side of the cord. In cases of old brain lesion it is sometimes possible to detect some degenerated fibres in the crossed pyramidal tract of the sound side of the spinal cord, and from this it is supposed that this tract contains a few uncrossed fibres. If this be the case, each side of the cord stands in connexion with the motor area of both cerebral hemispheres. It is well to note that the fibres of both pyramidal tracts are not medullated until the time of birth. They are the latest of all the cord-tracts to myelinate. The anterior basis-bundle (fasciculus anterior proprius), like the lateral basis- bundle, is composed largely of fibres which arise from the cells of the gray matter of the cord, and act the part of intersegmental association fibres. Summary of the Constitution of the White Matter of the Cord. — The white columns of the cord are formed of two kinds of nerve-fibres : — 1. Those which enter the cord from without. 2. Those which take their origin from the cells within the gray matter of the cord itself. Under the first categoiy we include (a) the greater part of the fibres of the posterior column (columns of Burdach and Goll), which arise from the cells of the spinal ganglia, and which enter the cord as the posterior nerve-roots ; and (h) the crossed and direct pyramidal tracts which come from the motor cells of the cerebral cortex. The fibres which arise within the gray matter of the cord may be classified thus: (a) Fibres which pass out from the cord as efferent nerves (anterior ntrve- roots) ; (b) fibres which form long tracts and pass up the cord to enter the brain (direct cerebellar tract and the tract of Gowers); (c) fibres which form short tracts, linking together different segments of the cord (intersegmental association fibres in each of the three columns of the cord). Anterior White Commissure. — The anterior commissure is composed of medullated nerve- Hbres passing from one side of the cord to the other and entering the anterior horn of gray matter, and also the anterior column of white matter. It is to be regarded more as a decussation than as a commissure, and its width, which DEVELOPMENT OF THE SPINAL CORD. 471 varies somewhat in diflerent regions, fluctuates in correspondence with tlie diameter of the cord. Amongst tlie fibres wliicli cross in the anterior commissure may be mentioned : (1) The fibres of the direct i^yramidal tract ; (2) collaterals from both the ventral and lateral columns ; (3) axons of many of the cells of the gray matter ; (4) the dendritic processes of some of the mesial ventral cells. Posterior Gray Commissure. — Although this is composed of gray matter with a large admixture of neuroglia, numerous transverse nerve-fibres pass through it, so as to bind the cells of one side of the cord to those of the other. MID-DORSAL LAMINA MVELO- SPONGIUM Development of the Spinal Cord. In the chapter upon General Embryology it has been pointed out (p. 21) that the brain and cord first take shape in the form of a tube of ectoderm, which receives the name of the neural tube. Three expansions, placed one behind the other at the cephalic end of the tube, represent the early brain ; whilst behind these primitive cerebi'al vesicles comes the elongated narrower part of the tube, which at this stage rejiresents the spinal cord. By a developmental process, which we now have to study, the walls of this portion of the neural canal give rise to the various elements which build up the substance of the cord, whilst a portion, if not the whole, of the primitive cavity is preserved as the central canal of the cord. The account which is here given of the development of the cord is taken almost entirely from the writings of Professor His. When first formed, the neural tube is compressed from side to side and presents an oval outline in transverse section (Fig. 16, p. 21). The two lateral walls are very thick, whilst the narrow dorsal and ventral portions of the wall are thin, and are termed the mid-dorsal and mid-ventral laminae (Fig. 378). The cavity of the tube in transverse section appears as a narrow slit. At this stage the wall of the neural tube is formed of a series of elongated neuro-epithelial columnar cells, closely applied to each other and extending throughout the whole thickness of the wall. The inner ends of these long columnar cells unite to form a delicate mem- brane termed the internal limiting membrane, which lines the lumen of the tube, whilst their outer ends present a similar relation to an ex- ternal limiting membrane, which invests the outer surface of the tube. The name of spongioblasts is given to these cells, and they soon develop in such a manner as to form the sustentacular framework of the growing cord. Between their inner parts, immediately subjacent to the internal limiting membrane, a series of clefts or open spaces are formed, in which appear large numbers of round cells called germinal cells. The precise origin of these germinal cells is not at present satisfactoril}' established ; but they rapidly in- crease in number, and in the human embryo of four weeks they are seen to form an almost continuous layer Vieneath the internal limiting mem- brane. It is well to note, however, that in the thin mid-dorsal and mid- ventral laminpe no germinal cells are formed. Here the wall remains purely spongioblastic. The peri- pheral portions of the spongioblasts likewise undergo a marked transformation. They give off branches or processes, and by the interlacement of these a sponge-like network with irregular meshes is formed in the outer portion of the wall of the neural tube. The mid-ventral lamina Fig. 378. — Schema of a Transverse Section through the Early Neural Tube (Young). The left side of the section shows an earlier stage than the right side. 472 THE NERVOUS SYSTEM. entire sustentacular framework into which the spongioblasts are developed is termed the myelosponge. The numerous germinal cells which are placed in the clefts between the inner columnar portion of the myelosponge are the progenitors of the nerve-cells. Many of them show karyokinetic stages, and by their division they give rise to the neuroblasts or young nerve-cells. A neuroblast presents a very characteristic pear-shaped appearance. From the body of the cell a tapering process grows out, and this represents the early axis- cylinder process or axon of the cell. But the crowds of neuroblasts which are thus formed do not remain in their early primitive position beneath the internal limiting membrane. They migrate outwards, and in the course of time they come to lie in the part of the myelosponge immediately adjoining the reticular mesh work, which is formed by the outer parts of the spongioblasts. Here their further outward migration is arrested. The reticular meshwork would almost appear to act as a sieve or a filter, which prevents their progress towards the periphery of the wall of the tube. It offers no impediment to the actively growing axons of the neuroblasts, however, which freely enter it and thread their way through it. At this stage the thick lateral wall of the neural tube presents three layers, viz. : — 1. An inner layer, formed by the columnar part of the myelosponge forsaken by the neuroblasts. This is termed the ependymal layer, and it ultimately resolves itself into the layer of columnar ciliated epithelial cells which lines the central canal of the cord. 2. An intermediate layer, in which the neuroblasts are present, and which is afterwards converted into the gray matter of the cord. This is called the mantle layer. 3. An outer layer, formed of the sponge-like meshwork of the outer parts of the original spongioblasts. Into this the axons of many of the neuroblasts are seen threading their way. This layer is ultimately transformed into the white matter of the cord, and at this stage it may be termed the peripheral reticular layer. Alar and Basal Laminae of the Lateral Wall of the Neural Tube.— From what has been said, it must be evident that the changes detailed above are confined to the thick lateral walls of the neural tube. In these alone do neuroblastic cells arise, whilst the thin mid-dorsal and mid-ventral laminae remain spongioblastic throughout. But whilst these changes are going on, the thick lateral wall begins to bulge outwards in -an angular fashion, so as to widen the central cavity of the tube and become itself, along the line where the cavity is widest, demarcated into two portions — a narrow dorsal strip termed the alar lamina, and a broader ventral strip called the basal lamina. The cavity AC. AH. AL. AMF. AR. Fig. 379.- Aiiterior column. BC. Anterior horn of gi'ay BL. matter. E. Alar lamina. GC. Antero-median fissure. LC. Anterior nerve-root. MDL. AMF AC AMF AC -Thrke Stages in the Development of the Spinal Cord (His). Column of Burdach. Basal lamina. Ependyma. Column of Goll. Lateral column. Mid-dorsal lamina. MVL. Mid-ventral lamina. PC. Early posterior column. PH. Posterior horn of gray matter. PMF. Postero-median fissure. PR. Posterior nerve-root. of the tube now appears on transverse section more or less lozenge-shaped, and it is at the lateral angles of the lozenge that this subdivision of the lateral wall becomes evident. This subdivision is a fundamental one, being present in the brain-part as well as the DEVELOPMENT OF THE SPINAL COED. 473 cord-part of the neural tube. By it the thick Uiteral wall is resolved into two longitudinal strips (the alar and basal laminte), which extend along the whole length of the tube, and which present definite and precise relations with the entering and emerging roots of the various cranial and spinal nerves. Confining our attention to the spinal cord, the posterior nerve-root is seen to enter the alar lamina, whilst the anterior nerve-root takes origin within and emerges from the basal lamina. Further Development of the Gray and White Matter of the Cord.— In the ventral part of the basal lamina the mantle layer thickens into a mass, which is readily recognised as the rudiment of the anterior horn of gray matter, and in this neuroblastic cells congregate in much larger numbers than elsewhere. Fui-ther, these neuroblastic cells begin to arrange themselves into groups, and the axis-cylinder processes of a large proportion of them converge and form bundles of fibres, which penetrate into the peri- pheral layer, and finally pierce the external limiting membrane, to emerge as the fascicles of the anterior nerve-roots. Behind the anterior horn the mantle layer still remains very thin, and the neuroblasts are few in number. There is, therefore, at this stage no appear- ance of the posterior horn of gray matter. Many of the axons of the neuroblasts which occupy this region are seen curving forwards, and, after traversing the anterior horn, they find their way across the middle line in the mid-ventral lamina. In this manner is laid down, at a very early stage, the rudiment of the anterior white commissure of the cord. The white matter of the anterior and lateral columns is gradually established by axons from various neuroblasts in different parts of the mantle layer, entering the peripheral reticular layer and taking a longitudinal course within it. The anterior horn is well coated with white matter, however, before the lateral column takes definite shape. The posterior columns of white matter are formed in a totally different manner, viz. by the introduction into the cord of nerve-fibres from without. The fibres of the posterior nerve-roots coming from the spinal ganglia strike the outer surface of the alar lamina of the lateral wall of the neural tube, and, piercing the external limiting membrane, take a longitudinal course in the peripheral reticular layer. On cross section these fibres first appear as an oval bundle, which lies in the outer part of the alar lamina (Fig. 379 pc). This bundle is the rudiment of Burdach's column, and at first it has a somewhat loose connexion with the cord ; but as the posterior horn of gray matter gradually takes shape, the bundle in question increases in volume, and, changing its position, comes to lie on the inner aspect of the posterior horn. The column of Goll gradually assimies form between the tract of Burdach and the postero-median septum. Later on the lateral and anterior columns are increased in bulk by the descent into them of the pyramidal tracts from the brain. The gray matter, in the first instance, is chiefly massed in the basal lamina ; but as the posterior columns of white matter begin to take shape it extends backward, and in the course of time the posterior horns are developed. The manner in which the dendritic processes of the neuroblasts are developed has been sufficiently described (p. -147). The ensheathment, also, of the axons by medulla has been referred to, and the fact that the different tracts of fibres receive their medullary sheaths at different periods mentioned. It is now only necessary to state that the oi'der of myeliuisation of the several tracts is as follows : — (1) Fibres of the anterior nerve-roots ; (2) tract of Burdach ; (3) fibres in the basis-bundles ; (4) tract of Goll ; (5) direct cere- bellar tract : (6) tract of Gowers ; (7) pyramidal tracts (Kahler). Development of the Median Fissures and of the Central Canal. — As the anterior horns of gray matter covered by the anterior columns of white matter increase in size, the anterior surface of the cord on either side of the mesial plane bulges forwards, and the antero-median fissure is produced as the natural result. The manner in which the postero-median fissure comes into existence is not fully understood, but the majority of embryologists believe that it is produced by the approxi- mation and fusion of the walls of the posterior part of the primitive cavity of the neural tube. The postero-median septum would thus appear to be formed of spongioblastic tissue. If the above view of the formation of the postero-median fissure be correct, it must be evident that the central canal of the cord does not represent the whole of the pi'imitive cavity of the early neural tube, but only the anterior portion of it. Among those observers who do not hold that the central canal and posterior fissure have this mode of origin the most prominent is Professor A. W. Eobinson, of Birmingham ; and he has brought forward evidence which seems to indicate that it is doubtful if the fusion of the walls of the posterior part of the canal, referred to above, takes place. Certainly the arrangement of the ependymal elements of the postero-median septum, as seen in the preparations of Cajal and V. Lenhossek, are extremely difficult to understand on the fusion theory. They run in the 474 THE NEEVOUS SYSTEM. aiitero-posterior direction, whereas, if fusion has taken place, most of them would present a transverse arrangement, and thus lie at right angles to the postero-median septu.m. THE BRAIN OR ENCEPHALON. The brain is the enlarged and greatly modified upper part of the cerebrospinal nervous axis. It is surrounded by the same membranes that envelop the spinal cord (viz. the dura mater, the arachnoid mater, and the pia mater), and it almost completely fills up the cavity of the cranium. So closely, indeed, is the skull capsule moulded upon the brain that the impress of the latter is almost everywhere evident upon the deep surface of the cranial wall. The relations, therefore, of cranium to brain are totally different from those presented by the vertebral canal Ojitic tract Olfactory bulb Corpora mammillaria TjOcus perforatus posticus Cms cerebri Olfactory tract Optic nerve Sixth nerve Hypoglossal nerv Locus perforatus anticus Optic tract Tuber cinereum Third nerve -Fourth nerve Fifth nerye Facial nerve Auditory nerve Pars intermedia Glosso-pharyngeal nerve Vagus nerve accessory nerve Spinal cord (cut) Hypoglossal nerve Fits. 380.— The Base of the Brain wrrn the Ckanial Nerves attached. ' to the spinal cord. As we have noted, the cord occupies only a part of its bony case ; and there is not only a wide and roomy space between the arachnoid mater and pia mater, but also an interval of some width l)etween the dura mater and the walls of the vertebral canal. General Appearance of the Brain. — When viewed from above the brain presents an ovoid figure, the broad end of which is directed backwards. Its greatest transverse diameter is usually found in the neighbourhood of that part which lies between the two parietal eminence-i of the cranium. The only parts which are visible when the brain is inspected I'rom this point of view are the two convoluted cerebral hemispheres. These present an extensive convex surface, which is closely applied to the deep aspect of the cranial vault, and Mre separated from each other by a deep median cleft, termed the great longitudinal fissure, which extends from the front to the back of the brain. THE BEAIN OK ENCEPHALON. 475 The iuferior aspect of the braiu is usually termed the " base. ' It presents an uneven and irregular surface, which is more or less accurately adapted to the inequalities on the tioor of the cranium. Upon this aspect of the brain some of its main subdivisions may be recognised. Thus behind is seen the short cylindrical portion, called the bulb or medulla oblongata, through which, at the foramen maguuni, the brain becomes continuous witli the spinal cord. The bulb lies on the ventral aspect of the cerebellum, and occupies the vallecula or hollow which intervenes between the two cerebellar hemispheres. The cerebellum is a mass of considerable size which is placed below the hinder portions of the two cerebral hemispheres. It is easily recognised on account of the closely-set, curved, and parallel fissures which traverse its surface and give it a foliated appearance. Above the medulla, and in close connexion with it, is a prominent white elevation called the pons Varolii. Im- mediately in front of the pons there is a deep hollow or recess. This is bounded behind by the pons Varolii, on either side by the projecting temporal lobe of the cerebral hemisphere, and in front by the orbital portions of the frontal lobes of the cerebral hemispheres. Passing out from either side of the fore-part of this recess is the deep Sylvian fissure which intervenes between the pointed and projecting extremity of the temporal lobe and the frontal lobe of the cerebrum, whilst in the middle line in front the great longitudinal fissure, which separates the frontal portions of the cerebral hemispheres, opeus into it. Within the limits of this deep hollow, in the base of the brain, two large rope- like strands, the crura cerebri, may be seen issuing from the upper aspect of the pons Varolii. Placed close together as they emerge from the pons, these crura diverge as they proceed upwards and forwards, and finally each disappears by plunging into the corresponding side of the cerebrum. Turning round the outer side of each crus, where it enters the cerebrum, a flattened band termed the optic tract may be observed. These bands converge in the fore-part of the holhtw, and are finally joined together by a short commissural portion, termed the optic chiasma. The optic nerve is continued forwards and outwards, on either side, from the chiasma and tract. The crura cerebri, the optic tracts, and the optic chiasma enclose a deep rhomboidal or lozenge-shaped interval on the base of the brain, which is termed the interpeduncular space. Within the limits of this area the following parts may be seen as we pass from behind forwards : (1) the locus perforatus posticus ; (2) the corpora mammillaria : (3) the tuber cinereum and the stalk of the pituitary body. At its posterior angle, immediately in front of the pons Varolii, the inter- peduncular space is very deep and is floored by a layer of gray matter, which is perforated by numerous small apertures. This is the locus perforatus posticus. Through the apertures which are dotted over its surface the small postero-mesial basal branches of the posterior cerebral artery enter the brain. The corpora mammillaria are two small white pea-like eminences placed side by side in front of the locus perforatus posticus. The tuber cinereum is a slightly raised field of gray matter, which occupies the interval between the anterior portions of the optic tracts in front of the corpora mammillaria. Springing from the fore-part of the tuber cinereum, immediately behind the optic chiasma, is the infundibulum, or the stalk which connects the pituitary body with the base of the brain. Outside the limits of the fore-part of the interpeduncular space there is on either side a small depressed triangular field of gray matter, which leads outwards into the Sylvian fissure. It is perforated by the antero-mesial and the antero- lateral groups of basal arteries, and receives the name of the locus perforatus anticus. General Connexions of the Several Parts of the Brain. — The medulla oblongata, the pons Varolii, and the cerebellum occupy the posterior cranial fossa, and they are separated from the cerebral hemispheres which lie above them by a partition of dura mater, termed the tentorium cerebelK. Further, they surround a cavity, a portion of the primitive cavity of the early neural tube, which is termed the fourth ventricle of the brain, and they all stand in intimate connexion with each other. The medulla is for the most part carried upwards into the pons 476 THE NEKVOUS SYSTEM. Varolii ; but at the same time two large strands from its dorsal aspect, termed the restiform bodies, are prolonged into the cerebellum, and constitute its inferior peduncles, or the chief bonds of union between the medulla and the cere- bellum. The pons Varolii has large numbers of transverse fibres enter- ing into its composition, and the great majority of these are gathered together on either side in the form of a large rope-like strand. This plunges into the corresponding hemi- sphere of the cerebellum, and con- stitutes its middle peduncle. The cerebrum, which forms the great mass of the brain, occupies the anterior and middle cranial fossae, and extends backwards into the oc- cipital region above the tentorium and the cerebellum. The greater part of the cerebrum is formed by the cerebral hemispheres, which are separated from each other in the mesial plane by the great longi- tudinal hssure. At the bottom of this fissure is the corpus callosum, a broad commissural band which connects the two hemispheres with each other. Each hemisphere is hollow, the cavity in its interior being termed the lateral ventricle of the brain. Between and below the cerebral hemispheres, and almost com- pletely concealed by them, is the inter-brain or diencephalon. The principal parts forming this portion of the brain are two large masses of gray matter, termed the optic thalami. Between these is the third ventricle of the brain — a deep narrow cavity occupying the mesial plane. The third ventricle communicates with the lateral ventricles by two small apertures, called the foramina of Monro. The cerebrum is connected with the parts in the posterior cranial fossa (pons Varolii, cerebellum, and bulb) by a narrow stalk called the mid-brain, or mesencephalon. The mid-brain is built up of the crura cerebri, passing from the pons Varolii to the cerebrum ; the corpora quadrigemina, forming its dorsal part ; and the superior cerebellar peduncles, proceeding from the cerebellum to the cerebrum. It is tunnelled by a narrow passage, the aqueduct of Sylvius, which extends between the fourth and third ventricles. Fig. 381.- Inferior cerebellar peduncle -Schema, showing the connexions of the several parts of the brain. Genekal Outline of the Development of the Brain. The brain is developed from the expanded anterior portion of the primitive neural tube. In the section deahng with the general principles of Embryology it has been pointed out that this part of the neural tube is marked off by two con- strictions into three primitive cerebral vesicles, which are termed respectively the hind-brain or rhombencephalon, the mid -brain or mesencephalon, and the fore- brain or prosencephalon. Hind-brain or Rhombencephalon. — The hind-brain is the largest of the three primary expansions of the neural tube : indeed, it may be said that in the earlier stages of brain development it is larger than both of the other primary subdivisions taken together. The portion immediately adjoining the mid-brain is constricted, and is termed the isthmus rhombencephali. This is a very small part, forming the extreme upper end of the vesicle, and i'rom its walls are developed the superior cerebellar peduncles and a thin lamina, which is stretched across the middle line between them, called the valve of Vieussens or the superior medullary velum. Immediately behind the isthmus the hind-brain expands suddenly, and then slowly and gradually tapers as it passes downwards towards the spinal cord part of the neural tube. Its junction with the latter is very early indicated by a sharp bend GENEEAL OUTLINE OF DEVELOPMENT OF THE BEAIN. 477 iu the tube, which is termed the cervical flexure. The large portion of hind-brain which extends from the isthmus to the cervical flexure is usually considered as being composed of two parts, viz. an upper portion, termed the metencephalon, and an inferior portion, called the myelencephalon. From the metencephalon are derived the cerebellum and pons Varolii. The cerebellum arises by a thickening of the dorsal wall of this portion of the vesicle, whilst the pons is formed by a thickening of the lateral and ventral walls. The ""•^AUC TL, ^^'2J:ifi. OPTIC VESICLE Fig. 382. — Two Stages in the Development of the Human Brain (after His). A. Brain of an embryo of the third week. B. Brain of an embryo of five weeks. myelencephalon gives origin to the bulb or medulla oblongata. This is chiefly formed by a thickening of the lateral walls of this part of the vesicle. These fall away from each other in an outward direction, and thus the ventral angle between them becomes greatly opened up. The growth which leads to the formation of the bulb appears, therefore, to take place chiefly on the ventral aspect of the vesicle. The dorsal wall remains thin and epithelial, and undergoes little or no development into nervous elements. The cavity of the original hind-brain is retained iu the adult brain as the fourth ventricle ; and from what has been said regarding the development of the different portions of the wall of the primitive hind-brain, it will be seen that in its lower or medullary part its dorsal wall or roof, to a large extent, remains epithelial. The parts of the adult brain which are derived from the rhombencephalon or hind -brain are those which lie below the ten- torium cerebelli in the posterior cranial fossa of the skull. Mesencephalon or Mid -brain. — The mid -brain takes a much more prominent part in the forma- tion of the early primitive brain than it does in the construction of the adult brain. It forms a very small part of the adult brain, and constitutes a stalk of connexion between the parts which are developed from the walls of the rhomben- cephalon and those which are developed from the walls of the prosencephalon or fore -brain. The entire wall of the mid-brain is transformed into nervous tissue. Thus, by the special development of the dorsal section of the wall, the corpora quadrigemina are formed. The lateral and ventral sections of the wall undergo a still inore marked degree of growth-thickening, and the result is the OPTIC VESICLE OPTIC VES OPTIC STALK A B Fig. 383. — Two Cross Sections through the Fore-Brain. Through the fore-brain of the early human embryo. B. Through the fore-brain and optic vesicles of a Lepidosteus embryo of eight days (after Balfour and Parker, modified). 478 THE NEEVOUS SYSTEM. F ORp __ formation of the two crura cerebri. The cavity of the inid-braiii is retained as the narrow passage termed the aqueduct of Sylvius, which connects the third ventricle of the brain with the fourth ventricle. Prosencephalon or Fore-brain. —In its early condition one of the leading peculiarities of the fore-brain is its great width. It extends outwards on either side for a considerable distance beyond the lateral walls of the mid- brain. These lateral expansions of the fore-brain are the optic vesicles, and at this stage they are in no way constricted off from the central part of the cavity (Fig. 383). Soon, however, the central portion of the fore-brain begins to expand upwards and forwards, whilst the terminal portions of the optic vesicles likewise undergo enlargement ; and the result is, that the originally single chamber shows subdivision into three parts, viz. a central portion or fore-brain proper, and two expanded optic vesicles, which are joined to the lower parts of the lateral aspects of the fore-brain proper by two short constricted tubular passages termed the optic stalks. The optic vesicle and the optic stalk become ulti- mately transformed into the retina of the eye-ball and the optic nerve. The changes which lead to this result are detailed in the section dealing with the anatomy of the organ of vision. The fore-brain under- goes a series of remarkable developmental changes, the most striking of which is the formation of the cere- bral hemispheres. The terminal or fore-portion of the fore-brain, in the first instance, expands in a for- ward and downward direc- tion, and from the upper and lateral aspects of the new portion of the vesicle thus formed the cerebral hemispheres bulge outwards in the form of two hollow pouches. The hinder original part of the fore- brain is termed the thal- mamencephalon or dien - cephalon, whilst the an- terior part with the cerebral hemispheres, which protrude out i'rom it, receives the name of telencephalon. The side walls of the diencephalon become thickened into the two large masses of gray matter termed tbe optic thalami ; the floor or ventral wall develops into those structures which occupy the interpeduncubir space in the base of the brain (viz. the posterior perforated spot, the corpora mammillaria, and the tuber cinereum) ; whilst the roof or dorsal wall remains thin and epithelial, and undergoes no nervous development. The hollow cerebral hemispheres soon outstrip all the other parts of the brain in their development. They expand not only in an upward and forward direction, Fk;. 384. — The Brain ok Brain as seen in profile Manimillary eminence A. Human Embryo in thk Fifth Wkkk (from His). B, Mesial section tlirougli the same brain. Tc. Tuljer cinereum ; Hp, Hypojiliysis (pituitary diverticulum from buccal cavity) ; Opt, Optic stalk ; TH, Optic tlialamus ; Tg, Tegmental part of mesencephalon ; Ps, Pars subthalamica ; Cs, Corpus striatum ; FM, Foramen of Monro ; L, Lamina terminalis ; RO, Recessus opticus ; Ri, Recessus infun- dibuli. GENEEAL OUTLINE OF DEVELOPMENT OF THE BEAIN. 479 but chiefly in a backward direction ; and by their excessive growth backwards they gradually come to overlie the diencephalon, the mesencephalon, and at last the parts derived from the rhombencephalon. It thus comes about that, when the adult brain is viewed from above nothing but the cerebral hemispheres are visible — all the other parts of the brain lie under cover of them. At first the cavity of each cerebral hemisphere is connected with the cavity of the front portion of the fore-brain by an exceedingly short but relatively wide passage. This is the early condition of the foramen of Monro. The fore-part of the fore -brain is now seen to be bounded in front between the two hollow cerebral hemisphere-pouches by a narrow thin strip, which represents the extreme anterior wall of the neural tube, and consequently it receives the name of lamina terminalis. The cavity of the fore-brain not only in its hinder diencephalic part, but also in its anterior telencephalic part (i.e. the part from which the cerebral hemispheres bud out), persists as the third ventricle of the brain, whilst the cavities of the primitive cerebral hemispheres are represented in the adult by the lateral ventricles of the brain. The foramina of Monro, relatively much reduced in size, are preserved as narrow throats of communication between the lateral ventricles and the third ventricle. The olfactory lobes are formed as hollow out- growths from the cerebral hemi- spheres. Flexures of the Brain-tube. — At a very early period, and while the changes detailed above are being carried on, the cerebral portion of the neural tube becomes sharply bent upon itself at certain points. The first flexure which occurs is the primary cephalic flexure. It occurs in the region of the mesencephalon, and involves the entire head. The fore-brain becomes bent in a ventral direction round the fore-end of the notochord and the fore-gut, until the long axis of the fore-brain forms an acute angle with the long axis of the hind-brain and the ventral wall of the one comes to lie nearly parallel with the corresponding wall of the other. Through this curvature the mid-brain is considerably modified in form, and for a time it comes to occupy the most prominent and foremost part of the embryonic head. The primary cephalic flexure is soon followed by the cervical flexure. This occurs at the junction of the hind-brain with the spinal cord. Here the entire head is bent in a ventral direction, and at the end of the fifth week the flexure is so pronounced that the cerebral and spinal cord portions of the neural tube meet each other at a right angle (Fig. 385). In the later stages of development the cervical flexure becomes obliterated by the elevation of the head and the straighten- ing of the neck of the embryo. The third bend takes place in the region of the future pons Varolii (meten- cephalon), and is consequently termed the pontine flexure. It differs from the other flexures in being confined to the brain tube and in not in any way involving the entire head. Further, the bend is much more marked in the thick ventral wall than in the thin dorsal wall of the tube. The neural tube is doubled forwards on itself and the pons Varolii becomes developed in connexion with the summit of the curvature. In the further growth of the brain the pontine flexure becomes almost completely obliterated. Fig. 385.- -Profile View of the Brain of Embryo of Ten Weeks (His). Human The various cranial nerves are indicated by numerals. A, Cerebral diverticulum of pituitarj^ body. B, Buccal diverticulum of pituitary body. 480 THE NEEVOUS SYSTEM. By reason of these curvatures the early brain assumes a sinuous, zigzag or S-shaped outline when viewed from the side, and the relationship of its various parts becomes materially altered. The essential factor at work in the production of the brain flexures is clearly the very unequal growth which takes place in different parts of the cerebral wall. Basal and Alar Laminae of His. — It has been pointed out that, in the development of the spinal cord, each of the thick lateral walls of the neural tube is marked off into a dorsal or alar and a ventral or basal lamina. This subdivision is also noticeable in the cerebral part of the neural tube, and the furrow on the inner aspect of the lateral wall, which indicates this subdivision, can be traced even in the adult brain throughout a considerable part of its length. In the spinal cord the motor cells are gathered in the basal lamina in more or less continuous columns. In the brain the corre- sponding cells from which the efferent fibres of the cranial nerves are given off are also placed within the basal lamina, but they are ar- ranged differently. They are collected together in dis- connec ted clusters termed the motor nuclei, and they do not extend higher up than the mid-brain. No motor nuclei In both Fig. 386. — Diagrams to illustrate the Alar and Basal Lamina cases the emljryonic brain is represented in mesial section (Hi: A, The different subdivisions of the brain are marked off from each other by dotted ocCUr in the forC- lines, and the dotted line running in the long axis of the neural tube indicates the l-,™„;,-, Tnrlppfi separation of the alar from the basal lamima of the lateral wall B. Mesial section through the brain of a human embryo at the end of the first month. Dotted lines mark off the different regions and also the alar and liasal laminaa from each other. H, Buccal part of pituitary body ; RL, Olfactory lobe ; C.Str, Corpus striatum the importance of the basal lamina' diminishes as we pass from the A, Entrance to optic stalk; 0, Optic recess; I', Infundibular recess; T, Tuber Inwpr to the higher cinereum ; M. Mammillary enuuence. , ,, ,., , * . parts of the brain. In the rhombic or hind-brain the greater part of the medulla oblongata and of the pons Varolii is formed from the basal laminje, whilst the cerebellum, with its superior and inferior cerebellar peduncles, is derived from the alar laminse. In the mid-brain the crura cerebri are the derivatives of the basal laminae, whilst the corpora quadrigemina are developed from the alar famime. In the fore-brain the subthalamic region and the optic vesicles are products of the growth of the basal laminae, whilst the optic thalami and cerebral hemispheres spring from the alar laminae. The fact that the cerebellum and the cerebral hemispheres owe their origin to the alar laminae is sufficient to show the predominant part wliich these laminae play in brain development, and the higher we ascend in the animal scale the more pronounced does this predominance become. The following table gives a summary of the various developmental processes which have been described in the foregoing pages : — MEDULLA OBLONGATA OE BULB. 481 Encejjlialon or Brain Rhombencephalon or Hind-brain (posterior cerebral vesicle) Myelencephalon Mesencephalon or Mid-brain (middle cerebral vesicle) Prosencephalon or Fore-brain (anterior cerebral vesicle) Metencephalon Isthmus rhonibencephali (narrow constricted part immediately adjoining the mesencephalon) Mesencephalon or Mid-brain Thalamencephalon or Diencephalon L Telencephalon ( Bulb or medulla oblongata -| Lower part of the fourth ven- ' tricle /'Cerel^elluiii J Pons Varolii I Ui)per part of the fourth veii- ^ tricle I.Superior cerebellar peduncles j Valve of Vieiissens j Corpora quadrigemina -, Crura cerebri I Aqueduct of Sylvius Optic thalami Suljthalamic tegmental regions Pituitary and pineal bodies Structures in interj^eduncular space Optic nerve and retina Hinder part of the third ven- tricle Cereljral hemispheres Olfactory lobes Lateral ventricles Foramina of Monro Anterior portion of the third ventricle THE PAETS OF THE ENCEPHALON DEEIVED EEOM THE HIND-BEAIN. MEDULLA OBLONGATA OR BULB. The medulla oblongata or bulb is the continuation upwards of the spinal cord. It is not more than one inch in length, and it may be regarded as beginning at the decussation of the pyramidal tracts, ^..=. .,.: " ^v_/^ — -optic nerve which takes place about the level of the foramen magnum. From this it proceeds upwards in a very nearly vertical direc- tion, and ends at the lower border of the pons Varolii. At first its girth is similar to that of the cord, but it rapidly expands as it approaches the pons, and conse- quently it presents a more or less conical form. Its ventral surface lies behind the grooved surface of the basilar portion of the occipital bone, whilst its dorsal sur- face is sunk into the vallecula of the cerebellum. The medulla oblongata is a bilateral structure, and this is indicated on the surface by a continuation upwards of the antero-median and postero-median fissures of the cord on the ventral and dorsal aspects of the medulla. 35 optic chiasina — Optic tract. Corpus geiiiculatuni externum Corpus geniculatuiii internum Locus perforatus posticus Middle peduncle of the cerebellum Restifonn body Olive Pyramid Anterior superficial arcuate fibres Decussation of pyramid fnfundibulum Tuber cinereinn Corpora mammillaria Oculo-motor nerve (III.) Trochlear nerve (IV.) winding round the cms cerebri Trigeminal nerve (V.) Abducent nerve (VI.) Facial nerve (VII.) Auditory nerve (VIII.) ^_ Vago-glossopharyngeal nerve (IX. and X.) Hypoglossal nerve (XII.) Spinal accessory nerve (XI.) First cervical nerve Fio. 387. -Front View of the Medulla, Pons, and Mesencephalon of FULL-TIME Human Fcetus. 482 THE NEEVOUS SYSTEM. The antero-median groove (fissura mediana anterior), as it passes from the cord on to the medulla, is interrupted at the level of the foramen magnum by several strands of fibres, which cross the mesial plane from one side to the other. This intercrossing is termed the decussation of the pyramids. Above this level the furrow is carried upwards to the lower border of the pons, but is often rendered very shallow by numerous superficial arcuate fibres which emerge upon the surface between its lips and then curve outwards to reach the hinder part of the medulla. At the lower margin of the pons Varolii it expands slightly and ends in a blind pit, which receives the name of the foramen caecum of Vicq d'Azyr. The postero-median fissure (fissura mediana posterior) is only carried up on the lower half of the medulla. As it ascends it rapidly becomes shallower, and, halfway up, the central canal of the cord opens on the dorsal surface of the medulla. At this point the lips of the postero-median fissure are thrust apart from each other and constitute the boundaries of a triangular field, which is thus opened up on the dorsal aspect of the medulla. This triangular field is the lower part of the fossa rhomboidalis, or the floor of the fourth ventricle of the brain. The lower half of the medulla, containing as it does the continuation of the central canal of the cord, is frequently termed the closed part of the medulla ; the upper half, above the opening of the canal, which by its dorsal surface forms the lower part of the floor of the fourth ventricle, is then called the open part of the medulla. Deferring for the present the examination of the medullary part of the floor of the fourth ventricle, the appearance presented by the surface of each side of the medulla, from the antero-median fissure in front to the postero-median fissure and the lateral limit of the floor of the fourth ventricle behind, may now engage our attention. In the spinal cord the corresponding surface area is divided into three districts or columns by the emerging motor roots and the entering sensory roots of the spinal nerves. Of these the latter enter along the bottom of the postero-lateral groove, whilst the motor fascicles are spread over a relatively broad surface area and have no groove in connexion with their emergence from the cord. In the case of the medulla corresponding rows of nerve - fascicles enter and emerge from the surface of each side. The efferent fascicles are the root -bundles of the hypoglossal nerve, and they carry up the line of the anterior nerve-roots of the cord. In one respect, however, they differ: they emerge • in linear order and along the bottom of a dis- tinct furrow, termed the antero - lateral furrow, which proceeds upwards on the surface of the medulla. The fascicles which carry up the line of the posterior nerve- roots on the surface of the medulla are the root-bundles of the spinal accessory, the vagus, and the glosso- pharyngeal nerves. These are attached along the bottom of a furrow which is the direct continuation upwards of the postero-lateral furrow of the cord, and therefore receives the name of the postero-lateral furrow of the medulla. The root-bundles Valve of Vieussenb. Superior peduncle of the cerebellum Middle peduncle of the cerebellum Striw acustictu Area acusticte Trigonum vagi Cuneate tubercle Funiculus gracilis Tsonia thalami Pineal body Superior quadri- geminal body- Inferior quadri- geminal body Crus cerebri Pontine part of floor of ventricle IV. Eminentia teres Fovea superior Restiform body Trigonum hypoglossi Rolandic tubercle Funiculus cuneatus Fig. 388. — Back View of the Medulla, Pons, and Mesencephalon of a full-time human fcetus. MEDULLA OBLONGATA OE BULB. 483 of these nerves differ, however, in so far that they are not all composed of afferent fibres springing from ganglionic cells placed without and entering the medulla. Certain of them are purely efferent (spinal accessory roots), whilst others likewise contain a considerable number of efferent fibres, and are therefore to be regarded as mixed roots. By the postero-lateral and the antero-lateral grooves, and also by the two rows of nerve fascicles attached along the bottom of these furrows, the surface of the medulla on each side is divided into three districts, viz. an anterior, a lateral, and a posterior, similar to the surface areas of the three columns on the side of the cord. Indeed, at first sight, they appear to be a direct continuation upwards of these three portions of the cord ; this is not the case, however, because the fibres of the three columns of the cord undergo a rearrangement as they proceed upwards into the medulla. Anterior Area of the Medulla — Pyramid (pyramis). — The district between the antero-median fissure and the antero-lateral furrow, along the bottom of which the root-fascicles of the hypoglossal nerve issue from the medulla, receives the name of the pyramid. An inspection of the surface is sufficient to show that the pyramid is composed of a compact strand of longitudinally directed nerve-fibres. Tapering below, it expands and assumes a prominent appearance as it is traced upwards, and, finally reaching the lower border of the pons Varolii, it becomes shghtly constricted and disappears from view by plunging into that portion of the brain. The two pyramids, separated from each other by the antero- median furrow, are the great motor strands of the medulla. Although the pyramid at first sight appears to be continuous with the anterior column of the cord, only a very small pro- portion of the fibres contained in the latter are derived from the pyramid. This at once becomes manifest when the lips of the antero-median fissure are thrust apart at the place of junction between the cord and the medulla. The pyramid is then seen to divide at this level into two parts, viz. a small portion composed of a variable number of the outermost fibres of the pyramid, termed the direct pyramidal tract, and a much larger portion situated next the antero-median fissure, called the crossed pyramidal tract. The direct pyramidal tract is continued down into the anterior column of the cord, and in this it takes up a mesial position next the antero-median fissure. The crossed pyra- midal tract is broken up into three or more coarse bundles, which sink backwards and at the same time cross the mesial plane, to take up a position in the posterior part of the opposite lateral column of the cord. The term decussation of the pyramids (decussatio pyramidum) is applied to the intercrossing of the corresponding bundles of the crossed pyramidal tracts of opposite sides. The direct pyramidal tract is, therefore, the only part of the pyramid which has a place in the anterior column of the cord. The much larger part of this column, termed the anterior basis-bundle, as it is traced up into the medulla is seen to be thrust aside by the decussating bundles of the crossed pyramidal tract. It thus comes to occupy a deep position in the substance of the medulla behind and to the outer side of the pyramid. Lateral Area of the Medulla. — This is the district on the surface of the medulla 35 a CROSSED PYR.TR. Fig. 389. — Diagram of the Decussation of THE Pyramids (modified from van Gehuchten). NH, Nucleus hypoglossi ; NV, Vago- glosso- pharyngeal nucleus ; FS, Fasciculus soli- tarius ; NA, Nucleus ambiguus. 484 THE NEEVOUS SYSTEM. which is iucluded between the two rows of nerve-roots, viz. the hypoglossal roots in front, and the root-bundles of the spinal accessory, the vagus, and the glosso- pharyngeal nerves behind. It presents a very different appearance in its upper and lower parts. In its lower portion it simply appears to be a continuation upwards of the lateral area of the cord ; in its upper part a striking oval prominence bulges out on the surface of the medulla, and receives the name of the olivary eminence. The lower part of this district, however, is very far from being an exact counter- part of the lateral column of the cord. The large crossed pyramidal tract is no longer present, seeing that it forms in the medulla the greater part of the pyramid of the opposite side. Another strand of fibres, viz. the direct cerebellar tract, prolonged upw^ards in the lateral column of the cord, gradually leaves this portion of the medulla. This tract lies on the surface, and is frequently visible to the naked eye as a white band, which inclines obliquely backwards into the posterior district of the medulla to join its upper part, or in other words the restiform body. The remainder of the fibres of the lateral column of the cord, comprising the lateral basis-bundle and the tract of Gowers, are continued upwards in the lateral area of the medulla, and at the lower border of the olive the majority of these fibres disappear from the surface by dipping into the substance of the medulla under cover of that projection. A small proportion of the fibres, how- ever, are retained on the surface and travel upwards towards the pons in the interval, which exists between the hinder border of the olive and the roots of the vagus and glosso-pharyngeal nerves. The olivary eminence (oliva) is a smooth oval projection which bulges out from the upper part of the lateral area of the medulla. Its long axis is vertical and is about half an inch long. It marks the position of the subjacent inferior olivary nucleus, a flexuous lamina of gray matter (nucleus olivaris inferior), which is only separated from the surface by a very thin layer of superficial white matter. Posterior Area of the Medulla. — In its lower half, this district is bounded behind by the postero-median fissure, and in ifcs upper half by the lateral margin of the medullary part of the floor of the fourth ventricle of the brain. In front it is separated from the lateral area by the row of root-fascicles belonging to the spinal accessory, vagus, and glosso- pharyngeal nerves. As in the lateral area, we recognise a lower portion and an upper portion, which appear continuous but in reahty are almost quite distinct from each other. The lower part of the posterior area corresponds more or less closely with the posterior column of the cord. In the cervical part of the cord the posterior column is divided by the paramedian septum of pia mater into an inner column of Goll and an outer column of Burdach. These are prolonged upwards into the medulla, and in the lower part of the posterior area they stand out distinctly, and are separated from each other by a continuation upwards from the cord of the paramedian groove. In the medulla the inner of these strands is called the funiculus gracilis, whilst the outer one is designated the funiculus cuneatus. Each of these strands, when it reaches the level of the lower part of the floor of the fourth ventricle, ends in a slightly expanded bulbous prominence. The swoUen extremity of the funiculus gracilis is called the clava. This is thrust aside from its neighbour of the opposite side by the opening up of the medulla to form the floor of the fourth ventricle, and the central canal of Optic tract Crus cerebri Corpus geniculatuin externum Pulvinar Corpus geniculatmu internum Superior bracliiuni Inferior brachiuni Inferior quadrigeminal body Lateral fillet Superior cerebellar peduncle nia pontis Middle i)eduncle of •erebellum / Kpstiforni body l^igula bounding lateral recess of ventricle IV. I )b\ai y eminence Aicuate fibres (anterior superficial) Clava, Cuneate tubercle Roland ic tuljercle Lateral district of medulla Anterior column of cord Fio. 390. — Lateral View of the Pons, and Me.sencephalon of a Human Fcetds. Medulla, full-time MEDULLA OBLONGATA OK BULB. 485 the cord opens on the surface in the angle between the two clavfe. Tlie bulbous end of the fasciculus cuneatns receives the name of the cuneate tubercle (tuberculuna cinereum), but it is only in the foetal or very young brain that it is well marked. The elongated promineQces formed on the surface of the medulla by these two strands and their enlarged extremities are, in a great measure, due to the presence of two elongated nuclei or collections of gray matter which make their appearance subjacent to the strands, and which gradually increase in bulk as they are traced upwards. These are termed respectively the gracile (nucleus funiculi gracilis) and cuneate (nucleus funiculi cuneati) nuclei, and it can be easily shown that as the gray matter increases in quantity the fibres of the two corresponding strands diminish in number by coming to an end in connexion with the cells of the subjacent nuclei. Indeed, it is doubtful if any of the fibres of the gracile and cuneate strands extend upwards beyond these nuclei. But a third longitudinal elevation is also apparent on the surface of the lower part of the posterior area of the medulla. This is placed on the outer side of the funiculus cuneatus — between it and the posterior row of nerve-roots — and it has no counterpart in the posterior column of the cord. It is called the funiculus of Rolando, because it is produced by the substantia gelatinosa Eolandi, which caps the posterior horn, coming close to the surface and forming a bulging in this situation. The funiculus of Eolando is wedge-shaped in outline. Extremely narrow below, it widens as it is traced upwards, and finally ends in an expanded extremity called the tubercle of Rolando (tuberculum Eolandi). A thin layer of white matter, com- posed of longitudinally arranged fibres, is spread over this district, and separates the substantia Eolandi from the surface. These fibres constitute the spinal root of the fifth or trigeminal nerve, which here assumes a superficial position as it descends in the medulla. The restiform body (corpus restiforme) forms the uj^per part of the posterior area of the medulla. It lies between the floor of the fourth ventricle and the roots of the vagus and glosso-pharyngeal nerves. It is a large and prominent rope -like strand, which inclines upwards and outwards, and then finally takes a turn backwards and enters the cerebellum. It forms the great link of connexion between the cerebellum on the one hand and the medulla and spinal cord on the other, and consequently it also receives the name of the inferior cerebellar peduncle. At the same time it must be understood that it is not formed by fibres which are prolonged into it from the funiculus cuneatus and funiculus gracilis of the medulla. It is true that a surface inspection of the medulla might very naturally lead the observer to this supposition, because there is no sharp line of demarcation marking it off from the tubercles of these strands. Such a conclusion, however, would be altogether erroneous, because it would appear that none of the fibres of the posterior columns of the cord are carried beyond the gracile and cuneate nuclei of the medulla. A study of the surface of the medulla yields some important information regarding the constitution of the restiform body. Thus the direct cerebellar tract from the lateral column of the cord can be traced into it, and large numbers of fibres which take a curved course on the surface of the medulla may likewise be followed into it. These are the superficial arcuate fibres. Numerous other fibres enter the restiform body on its deep aspect, but these will be studied at a later stage. Superficial Arcuate Fibres (fibrae arcuate externa). — These fibres enter into the constitution of the restiform body, and they may be regarded as con- sisting of two sets, viz. the anterior superficial arcuate fibres and the posterior superficial arcuate fibres, both of which present this feature in common that they run on the surface of the medulla. The anterior superficial arcuate fibres are more particularly seen in the neighbour- hood of the olivary eminence, round the lower border of which, and also over the surface of which, they may be observed coursing in the form of a number of coarse curved bundles. They vary greatly in number and in distinctness, and they are sometimes so numerous as to cover over almost entirely the eminence. An attentive examination will show that they come to the surface in the antero-median fissure between the pyramids, and also not unfrequently in the groove between the 35 h 486 THE NEEVOUS SYSTEM. pyramid and olive, or through the substance of the pyramid itself. The antero- median fissure in its upper part is often almost completely blocked up by these emerging fibres. The anterior superficial arcuate fibres reaching the surface of the medulla in this manner turn backwards, and the great majority enter the restiform body and form a considerable part of its outer portion. The posterior superficial arcuate fibres arise in the cuneate and gracile nuclei, and enter the restiform body of the same side. THE PONS VAROLII. The pons Varolii is a marked white prominence on the basal aspect of the brain which is interposed between the medulla and the crura cerebri, and which lies in front of the cerebellum. It is convex from side to side, as well as from above downwards, and transverse streaks on its surface show that, superficially at least, it is composed of bundles of nerve-fibres which course transversely over it. On either side these transverse fibres are collected together in the form of a large compact strand, which sinks in a backward and outward direction into the white matter of the corresponding hemisphere of the cerebellum. This strand is termed the middle peduncle of the cerebellum, and the term "pons," applied to the entire structure, expresses in an admirable way the arch-like manner in which this portion of the brain bridges across between the two cerebellar hemispheres. The ventral surface of tbe pons is in relation to the basilar process of the occipital bone and the dorsum sellse of the sphenoid bone. It presents a mesial groove (sulcus basilaris), which gradually widens as it is traced upwards, and in which the basilar artery lies. This mesial depression is produced by the prominence which is caused on either side by the passage of the pyramidal tract of fibres downwards through the pons. The trigeminal or fifth cranial nerve, with its large entering sensory root and its small emerging motor root, is attached to the side of the ventral aspect of the pons, nearer its upper than its lower border. It is usual to restrict the term " pons " to that portion of the structure which lies between the two trigeminal nerves, and to apply the designation of middle cerebellar peduncle to the part which extends beyond the nerve into the hemisphere of the cerebellum. The sixth or abducent nerve, tbe seventh or facial nerve, and the eighth or auditory- nerve are attached to the brain at the lower border of the pons. The sixth emerges at the outer border of the pyramid, the seventh immediately in front of the resti- form body, whilst the auditory nerve reaches the brain close to the facial nerve, on the ventral aspect of the restiform body. The whole of the medulla enters the lov-er aspect of the pons, and, with the exception of the restiform bodies, its constituent parts are, to a large extent, carried up within it. The crura cerebri emerge from its upper as2Ject. The dorsal surface of the pons looks backwards towards the cerebellum, and presents a triangular area covered with gray matter, which forms the upper part of the anterior wall or floor of the fourth ventricle. This area is directly continuous below with the medullary part of the floor of the fourth ventricle, and is bounded on either side by a band of white matter termed the superior peduncle of the cerebellum. Superior Cerebellar Peduncles (brachia conjunctiva). — These are hidden from view by the upper part of the cerebellum, under cover of which they he. They emerge from the lateral hemispheres of the cerebellum, and, as they proceed upwards on the dorsal aspect of the pons, they converge towards each other until, at the level of the inferior corpora quadrigemina, the inner margins of the two peduncles almost become contiguous (Fig. 388, p. 482). At first they form the lateral boundaries of the upper part of the fourth ventricle ; but, as they ascend and approach closer to each other, they gradually come to overhang that cavity and thus enter into the formation of its roof. They disappear from the surface by dipping under cover of the quadrigeminal bodies and entering the substance of the mesencephalon. Valve of Vieussens or the Superior Medullary Velum (velum medullare anterius). — Filling up the triangular interval between the two superior cere- THE PONS VAROLII. 487 bellar peduncles, and stretching across from the inner and free margin of the one to the corresponding margin of the other, is a thin layer of white matter which completes the roof or dorsal wall of the upper part of the fourth ventricle, and receives the name of the superior medullary velum. When traced downwards, it is seen to be carried with the superior peduncles into the white matter of the cere- bellum. Spread out on its dorsal surface is a small, thin, tongue-shaped prolongation of gray matter from tlie cortex of the cerebellum, which is termed tho lingula, whilst issuing from its substance close to the inferior quadrigeminal bodies are the two fourth or trochlear cranial nerves. Fourth Ventricle of the Brain (ventriculus quartus). — The fourth ventricle is somewhat rhomboidal in form. Below, it tapers to a point and becomes continuous with the central canal of the cord ; above, it narrows in a similar manner and is continued into the aqueduct of Sylvius, which tunnels the mesencephalon. The posterior wall is termed the roof and is concealed by the cerebellum. The anterior wall is called the floor and is formed by the dorsal surfaces of the medulla and pons. On either side a long, curved and narrow prolongation of the ventricular cavity is carried outwards from its widest part and curves round the upper part of the corresponding restiform body. This is termed the lateral recess. The roof of the cavity is very thin and intimately connected with the cerebellum. It is better, therefore, to defer its description until that part of the brain has been studied. Floor of the Fourth Ventricle (fossa rhomboidea).— In its lower part the floor of the fourth ventricle is formed by the dorsal surface of the open part of the Frenulum- -, Valve of Vieussens with lingula Eminentia tei-es Area acustica crossed by strife - acusticfe Fovea inferior - - Trigonuni liypoglossi Inferior quadrigeminal body Fourth nerve _ Superior cerebellar peduncle • Fovea superior Middle cerebellar -peduncle .Superior cere- bellar peduncle- L Inferior cere- bellar peduncle Stri;e acusticse '- - -Area acusticte Trigonum vagi Funiculus separans Area postrema Obex Clava Funiculus cuneatus Fifl. .391.— Floor of the Fourth Ventricle. Ou the right side the riglit half of the cerebellum has been removed by cutting through its three peduncles and dividing it in the mesial plane. On the left side the left half of the cerebellum is drawn over to the left so as to expose fully tlie floor of the ventricle. medulla, whilst in its upper part it is formed by the dorsal surface of the pons Varolii (Fig. 388, p. 482). The area thus constituted is lozenge-shaped, its widest part being opposite the upper ends of the restiform bodies or inferior peduncles of the cerebellum. A thick layer of gray matter, continuous with that which surrounds the central canal of the cord, is spread out like a carpet over the ventricular floor, and covering this is the usual ependymal layer, which lines all the ventricles of the brain. The area is circumscribed by definite lateral boundaries. 488 THE NEEVOUS SYSTEM. Thus, heloic it is bounded on either side by the clava, the cuneate tubercle, and the restiform body ; whilst alove the lateral limits are formed by the superior cerebellar peduncles. The floor of the fourth ventricle is divided into two lateral and symmetrical portions by a median groove. Its lower narrow pointed portion between the two clavfe receives the name of the calamus scriptorius, from its fancied resemblance to the point of a pen. Crossing each half of the floor, at its widest part, are several more or less conspicuous bundles of fibres termed the striae acusticae. They appear to emerge from the mesial groove and they are carried outwards over the floor of the ventricle in the region between its upper pontine and lower medullary portions. The strise acusticse exhibit a large amount of variation in different individuals both in their degree of prominence and also in the direction which they pursue. As a general rule they proceed towards the upper part of the restiform body, where they are connected with the cochlear nuclei. Except for this break on the surface, the medullary and pontine portions of the floor of the fourth ventricle are quite continuous with each other. On the lower medullary district of the ventricular floor a small triangular depression, placed immediately below the strise acusticae, catches the eye. This is termed the fovea inferior. It is shaped somewhat like an arrow-head. The apex or point looks towards the strise, whilst the lateral angles of the base are prolonged downwards in the form of diverging grooves (Eig. 391, p. 487). Of these, the inner groove runs towards the opening of the central canal at the calamus scriptorius, whilst the outer groove runs towards the lateral boundary of the floor. In this manner the portion of the floor which lies below the strise acusticae is mapped out into three triangular areas. The mesial subdivision is slightly elevated and is termed the trigonum hypoglossi, because subjacent to the inner part of this area is the nucleus of origin of the hypoglossal or twelfth cranial nerve. The intermediate area between the two diverging grooves which proceed from the base of the fovea inferior is the trigonum vagi (ala cinerea), so called because the nucleus of the vagus or tenth and the giosso-pharyngeal or ninth cranial nerves lies subjacent to it. The external area is the trigonum acustici. The base of this area is directed upwards and runs continuously into an eminence — the acustic area (area acustica) — over which the strise acusticse pass. Subjacent to this district of the floor of the ventricle lies the large terminal chief nucleus of the vestibular division of the auditory or eighth cranial nerve. A close inspection of tlie medullary part of the floor of tlie fourth, ventricle in the region of the calamus scriptorius will show that the base of the trigonum vagi is sejiarated from the inner margin of the clava by a narrow lanceolate strip of the ventricular floor, to which Retzius has given the name of area postrema. Beneath this area is some vascular tissue (Streeter), and mark- ing it off on its upper and inner aspect from the base of the trigonum vagi there is a translucent cord-like ridge caUed the funiculus separans. Wlien the floor of the A^entricle is examined under water with a magnifying glass, the trigonum hypoglossi is seen to consist of a narrow inner strij) which corresponds to the hypo- glos.sal nucleus, and a wider lateral part which has been shown to be the surface representation of another nucleus termed the nucleus intercalatus (Streeter). On the part of the floor of the ventricle which lies above the strias acusticse, and which corresponds to the dorsal surface of the pons, there is also a slight depression ' termed the fovea superior. Between it and the median groove is a marked pro- minence called the eminentia teres. Interiorly this elevation passes downwards and becomes continuous with the trigonum hypoglossi, whilst above it is carried upwards towards the opening of the aqueduct of Sylvius. In both directions it becomes gradually less prominent, but still it forms a distinct elongated elevation, which stretches along the whole length of the median groove. As already stated, the area acustica extends upwards into the pontine part of the ventricular floor and forms an elevated region in the outermost part of its widest portion, below and to the outer side of the fovea superior. Proceeding upwards from the fovea superior to the opening of the Sylvian aqueduct there is a shallow depression termed the locus caeruleus, seeing that it usually presents a faint slate-gray colour. When the ependyma is scraped away from the surface of this part of the floor, the colour is seen to be due to the substantia ferruginea, — a name applied to a linear group of INTERNAL STRUCTtlRE OF THE MEDULLA. 489 strongly pigmented cells, which lies in the lateral part of the gray matter covering this portion of the ventricular floor. When transverse sections are made through the upper part of the pons, the substantia ferruginea appears on tlie cut surface as a small black spot or dot. INTERNAL STRUCTURE OF THE MEDULLA. The internal structure of the medulla differs in a marked degree from that of the spinal cord ; indeed, in its upper part it presents very little in common with the latter. The various strands of the cord either come to an end within the medulla or undero-o changes in their relative position, whilst the gray matter is much modi- fied and new masses are added. Like the cord, however, the medulla consists of two nearly symmetrical right and left halves. When transverse sections are made throuo-h it at different levels each lateral half is seen to be partly marked off from the other in the lower closed part of the medulla by the anterior and posterior median fissures, whilst in the upper open part of the medulla the subdivision is rendered evident in transverse sections by the presence of a distinct median Funiculus gracilis Oraoile uucIrus Funiculus cuneatus ( uiuatf iiucltus Spinal root of trigeminal ner re Central gray matli i^ Central canal Anterior basis-bundle -^ ; * ^ Substantia gelatinosa Rolandi ios->icl pyramidal tract Detached head of anterior horn of gray matter Decussation of pyramids Pyramid Fig. 392. — Section through the Lower End of the Meddlla Oblongata of a Chimpanzee TO show the Decussation of the Pyramids. line, called the raphe, which occupies the mesial plane. The raphe is formed by the close intersection of fibres running in different directions and crossing from one side to the other. Each half of the medulla is composed of : (a) strands of white matter ; (6) gray matter ; and (c) the formatio reticularis. The white matter, as in the cord, is to a large extent disposed on the surface, and the gray matter in the interior ; but in the upper open part of the medulla the gray matter comes to the surface on the dorsal aspect, and is spread out over that area which forms the medullary part of the floor of the fourth ventricle. In the cord the white matter, in the shape of massive longitudinal strands of fibres, forms a thick coating round the central gray matter. In the medulla the only massive longitudinal strands which are seen on the surface are the gracile and cuneate strands (until they become absorbed by the subjacent nuclei), the inferior cerebellar peduncles or restiform bodies and the pyramidal tracts. Elsewhere the coating of white matter is thin, and in certain places is composed chiefly of the superficial arcuate fibres. New longitudinal strands, however, take shape within the medulla, and two of the most important are placed on either side of the median raphe. The gray matter of the cord, as it is continued upwards into the medulla, 490 THE NERVOUS SYSTEM. becomes greatly modified. A considerable part of it is broken up in the formatio reticularis, whilst the only portions which remain as compact masses in direct continuity with the gray matter of the cord are : (1) the thick layer which surrounds the central canal, and which, in the open part of the medulla, becomes spread out on the floor of the fourth ventricle ; and (2) the substantia gelatinosa Eolandi. New masses of gray matter, which are not represented in the cord, and which in some cases appear in isolated clumps, are also added. The chief of these are the gracile and cuueate nuclei, the inferior olivary nuclei, and the arcuate or pyramidal nuclei. The formatio reticularis is only feebly represented in the cord, but in the medulla it forms a very considerable part of its bulk. It is composed of gray matter coarsely broken up by fibres, which traverse it in different directions. In the following detailed account of the internal structure of the medulla, it must be understood that the appearances described are such as are seen when successive transverse sections through the bulb are examined. Decussation of the Pyramids and the Changes produced thereby. — As we pass under the microscope a series of successive transverse sections through the upper end of the cord and the lower end of the medulla, the most striking change which meets the eye is the decussation of the pyramids. The crossed pyramidal tract in the lateral column of the cord is seen to become looser in its formation ; then coarse strands leave it, pass right through the anterior horn of gray matter, and, crossing the mesial plane, take up their position in the other side of the medulla, close to the antero-median fissure. Strands from the right crossed pyramidal tract alternate with corresponding strands from the left side, and the interval between the bottom of the antero-median furrow and the gray matter surrounding the central canal becomes filled up with a great mass of intercrossing bundles of fibres. When the decussation is completed the pyramid is seen to be composed of a solid and compact bundle of fibres, well marked off from the surrounding structures, which lies at the side of the antero-median fissure of the medulla. As a rule the inner three-fourths of the pyramid is composed of fibres which, lower down in the opposite lateral column of the cord, form the crossed pyramidal tract, whilst the outer fourth of the pyramid proceeds downwards in the anterior column of the cord of the same side as the direct pyramidal tract. A considerable amount of variation, however, occurs in the proportion of fibres which is allotted to the formation of these two tracts of the cord. Sometimes the crossed pyramidal tract is much larger than usual, and then the direct pyramidal tract suffers a corresponding diminution in size. Cases indeed occur in which the entire pyramid enters into the decussation, and in these there is no direct pyramidal tract in the cord. Further, it is not uncommon to meet with variations of an opposite kind which lead to an increase of the direct pyramidal tract at the expense of the crossed tract. In the majority of cases the decussation appears to be symmetrical — the division of the pyramid at the lower end of the medulla being into parts of corresponding- size on the two sides ; in certain instances, however, the decussation is asymmetrical, and the corresponding yjyramidal tracts on opposite sides of the cord are then unequal in size. Seeing that the direct pyramidal tracts undergo a gradual decussation in the anterior commissure, as they descend in the cord, the final result is the same, no matter what . variations occur in the decussation at the lower part of the medulla. The variations indicated above receive an additional interest when viewed in the light of comparative anatomy. It would appear that only in man and the anthropoid apes is the decussation of the pyramids in the lower part of the medulla incomplete. According to Sherrington, a direct pyramidal tract in the cord of the anthropoid apes stands in con- nexion with the arm-centre in the cerebral cortex. If this be the case in man it must like- wise have other connexions as well, seeing that it is carried down the cord for a considerable distance beyond the level of the cord-segments which give motor fibres to the arm. In the lower apes a direct pyramidal tract does not seem to exist : the whole pyramid crosses over to the opposite side of the cord in the shape of the crossed pyramidal tract. As we have noted, the decussating pyramidal bundles pass through the anterior horn of gray matter of the cord, and cut it into two portions (Figs. 392 and 395). The basal part remains in position on the anterior and lateral aspect of the central canal, and forms part of the thick layer of gray matter which surrounds it. The INTERNAL STRUCTURE OF THE MEDULLA. 491 Decussatiou of pyramids Fig. 393. racilis Funiculus cnneatus Spinal root of tiftli nerve Substantia ^elatinosa Rolandi Direct cerebellar tract Detached head of anterior eornu _ Vnterior basis- bundle Antero-median furrow -Transverse Section through Lower End of the Medulla OF A full-time Fcetus, Treated by the Weigert-Pal method. The gray matter is bleached white, and the raedullated tracts of tibres are black. detached head of the anterior horn is set free ; and from the large multipolar cells which lie in its midst some of the tibres of the anterior root of the first cervical nerve, and also some of the root fibres of the spinal accessory nerve, take origin. On proceeding up into the medulla another effect of the decussation of the pyramids is seen in the submergence from the surface of the strand of fibres which, in the anterior column of the cord, lies to the outer side of the direct pyramidal tract, and which receives the name of the anterior basis-bundle. While the decus- sation is going on the anterior basis-bundle is thrust aside, and, sinking from the surface, it takes up its position as a flattened band -like strand on the outer side of the gradually increasing- pyramid' (Fig. 393). When the decussatiou is completed, this strand is seen to lie close to the median plane on the dorsal aspect of the pyramid, where it is separated from its fellow of the opposite side by the median raphe alone (Fig. 394). In the upper part of the medulla it approaches still nearer to the dorsal surface and appears to form the greater part of a strand, which is termed the posterior longitudinal bundle (Figs. 397 and 398). The detached head of the anterior horn of gray matter of the cord, as it is traced upwards, is observed to cling closely to its original relationship with the anterior basis-bundle. It is applied to the outer side of this strand, and, gradually becoming smaller, finally disappears at the level of the lower part of the inferior olivary nucleus. Cuneate and Gracile Strands, with their Nuclei. — As the funiculus gracilis and the funiculus cuneatus of the posterior column of the cord are traced up into the medulla they seem to increase in bulk, and in transverse sections they assume the form of massive wedge-shaped, strands, quite distinct from each other. When the decussation of the pyramids is fully established they change their shape. They increase in width and lose considerably in depth, and consequently the transverse diameter of the area which they occupy becomes greater. As a result of this, and also owing to the removal of the crossed pyramidal tract from the lateral region of the cord immediately in front, the posterior horn of gray matter is gradually rotated forwards and comes to lie transversely and in the same straight line with its fellow of the opposite side (Figs. 393 and 395). The substantia gelatinosa Rolandi, at the same time, becomes increased in quantity and presents a horseshoe- shaped outline in transverse section. It clasps within its concavity the somewhat reduced head of the posterior horn, and forms with it a conspicuous circular mass of gray matter which lies close to the surface, and produces upon it the bulging termed the funiculus and tubercle of Rolando. The basal portion of the posterior horn of gray matter remains upon the dorsal and lateral aspect of the central canal, and forms a portion of the central gray mass of the closed part of the medulla ; but very soon the neck of the horn, which at this level is greatly reduced owing to the absence of entering posterior nerve-roots, is invaded by bundles of fibres which traverse it in different directions and convert it into a formatio reticularis. By this means the rounded head of the posterior horn becomes cut off from the central gray matter, and from this point upwards it remains as an isolated gray column intimately associated with the spinal root of the trigeminal nerve. 492 THE NEEVOUS SYSTEM. The gracile and cuneate nuclei take shape before the decussation of the pyramids is fully completed (Fig. 395). The gracile nucleus appears in the form of a small irregular mass of gray matter in the interior of the funiculus gracihs, which Central canal Internal arcnate fibres Anterior basis- bnndle Decussation of fillet Inferior olivary nucleus Funiculus gracilis Gracile nucleus Funiculus cnneatus '"ff^^^^SSfc-,/ . Cuneate nucleus Accessory cuneate nucleus Spinal root of fifth nerve Substantia ■jf^*(^\- gelatinosa •^j Rolandi Formatio reticularis Anterior basis- bundle Mesial olivary nucleus Pyramid Arcuate nucleus covered superficially by anterior superficial arcuate fibres Fig. 394.— Section through the Closed Part of Human Medulla immediately above the Decussation of the Pyramids (Weigert-Pal Specimen). gradually infiltrates the entire strand. At first it is not directly connected with the gray matter which surrounds the central canal ; but as it is traced upwards it increases in bulk, absorbs more of the strand in which it lies, and such a con- nexion becomes established (Figs. 393 and 394). The cuneate nucleus, from the first, is a direct offshoot from that part of the base Gracile nucleus of thc postcrior hom of gray Cuneate nucifus ^^ matter which is preserved as a portion of the central gray mass. Cuneate nucleus In transvcrsc scctiou it is seen to Spinal root of fifth ^^^^^^ ^hc fuuiculuS . CUncatUS RoS'i*''' ^^^''*'"°''' "P°^ ^^^ ^®®P aspect, and it Direct cerebellar tract gradually grows backwards into its substance. It presents a very different appearance from the. gracile nucleus, because through- out its whole length the gray nucleus and the fibres of the strand are separated from each other by a sharp line of demarca- tion. A second and much smaller mass of gray matter appears in the funiculus cuneatus, super- ficial to the main nucleus, soon after the region of the decussation of the pyramids is left. This is termed the accessory or the external cuneate nucleus (Fig. 394). Gradually the fibres of the gracile and cuneate strands become absorbed in these nuclei. As the gray masses gain in size a corresponding diminution in the number of fibres composing the corresponding tracts is observed, until, at the level of the clava and cuneate tubercles, it is seen that these eminences are composed almost Crossed pyramidal tract Detached anterior horn of gray matter Decussation of jiyraniids Anterior basis-bundle Fig. 395. — Section through the lower part of the Medulla of the Orang. INTERNAL STRUCTURE OF THE MEDULLA. 493 entirely of the gray nuclei, covered by a thin skin of the few remaining fibres of the two strands involved. It would appear that no fibres belonging to the funiculus gracilis and funiculus cuneatus get beyond these nuclei. They all end in fine ' ' In the case of the funiculus terminal ramifications around the cells of the nuclei cuneatus the bundles 1 uiiiculu'5 ^lacili^ of fibres, pass from as they the sur- face into the sub- jacent gray nucleus, are very distinctly seen in transverse sections through the medulla. When the med- ulla oblongata opens up into the fourth ventricle the gracile and cuneate nuclei are pushed outwards by the expanding ventricular floor, and the gracile nucleus soon conies to an end : but the cuneate Funiculu'5 ( unpatii'5 (.ia( ilr iiucli us Cuneate nucleus Lowei eiiil of olnaij ennnence Mesial accessory oli\iiy nucleus Fascicles of hypoglossal nerve Fxu. 396. — Transverse Section through the Closed Part of a Fcetal Medulla, immediately above the Decussation of the Pyramids. Treated by Weigert-Pal method. nucleus extends upwards for a short distance farther, and only terminates when the restiform body begins to take definite shape on its outer aspect. Decussation of the Fillet (decussatio lemniscorum). — Immediately above the level of the decussation of the pyramids another decussation of fibres in the median plane, and upon the dorsal aspect of the pyramids, takes place in the substance of the medulla. This Gricile nucleus is termed the decus- sation of the fillet, or the sensory de- cussation, in contra- distinction to the term " motor decus- sation," which is sometimes applied to the decussation of the pyramids. The fibres which take part in this decussation are called deep arcuate fibres (fibraj arcuatse interme), and they are derived from the cells of the gracile and cuneate nuclei. From the deep aspects of these nuclei these fibres stream forwards and inwards towards the median raphe, form- ing a series of con- •centric curves in the substance of the medulla. They cross the mesial plane and decussate with the corresponding fibres of the opposite side, upon the dorsal •aspect of the pyramids. Having thus gained the opposite side of the medulla they Cuneate stiaud Cuneate nucleus Fasciculus sdlitarius Spinal root ot, trigeminal nerve Substantia gelatinosa Rolandi Deep arcuate fibres Hyposlossal nerve Anterior superficial (i_ arcuate fibres Inferior olivarj nucleus Mesial accessoi \ olivary nucleus Pyiannd anterior arcuate fibres Fl(i 397. — Transverse Section through the Human Medulla in the Lower Olivary Region. 494 THE NEEVOUS SYSTEM. immediately turn upwards and form a conspicuous strand of longitudinal fibres, which ascends close to the mesial plane and is separated from its fellow of the opposite side bj the median ra]3he alone. This strand is termed the fillet or lemniscus. As we proceed up the medulla the deep arcuate fibres which first come into sight appear as coarse bundles which curve forwards in a narrow group around the central gray matter (Figs. 394 and 396). Soon other fiuer bundles appear, which describe wider curves on the outer side of the coarser group until a very large part of each lateral half of the medulla is seen to be traversed by these arcuate fasciculi (Fig. 397). As they approach the mesial plane they come in contact with the remains of the anterior basis-bundle, which at this level, as already mentioned, lies upon the dorsal aspect of the pyramid, flattened up against the raphe. The deep arcuate fibres pierce the anterior basis-bundle obliquely, and in the interval between it and the corresponding strand of the opposite side they decussate in the middle line with the deep arcuate fibres of the opposite side. They then change their direction and turn upwards, and the fillet, as already stated, takes form and gradually increases in volume as it ascends. This great and important tract is thus laid down between the pyramid and the anterior basis-bundle ; and the consequence of this is that the latter tract is pushed still fai'ther backwards, and, when the fillet is fully established, it comes to lie immediately beneath the gray matter of the floor of the fomth ventricle (Fig. 398). It is important that we should realise at this stage the full significance of the decussation of the fillet and have a clear conception of the connexions of the fibres which take joart in it. The columns of Burdach and GoU, Avhich end in the cuneate and gracile nuclei, are derived from the posterior roots of the spinal nerves. The fillet fibres therefore carry on the continuity of the posterior columns of the cord, the gracile and cuneate nuclei, which are thrown across their path in the lower part of the medulla, merely constituting an internodal interruption. At this point the fillet strand is transferred to the opposite side of the medulla. But it will be remembered that a large proportion of the fibres of the entering posterior nerve-roots of the spinal nerves end in connexion with the cells of the posterior horn of gray matter of the cord. It must not be supposed that the path represented by these latter fibres comes to a termination thereby ; from these posterior horn cells other fibres arise which cross to the opposite side of the cord in the anterior white commissure and proceed up the cord to the lateral part of the medulla. These fibres con>stitute the spino-thalamic tract already referred to. The practical bearing of this is that owing to the crossing of the fillet and lower down of the spino-thalamic tract unilateral lesions of the medulla are apt to produce complete hemi-ansesthesia ; whilst unilateral lesions of the cord produce only partial hemi-anfesthesia. When the fillet is fully formed three longitudinal strands are observed travers- ing the medulla, close to the mesial plane. From before backwards these are : (1) the pyramid, (2) the fillet, and (3) the posterior longitudinal bundle. The pyramid forms a massive tract in front of and quite distinct from the fillet. The fillet and the posterior longitudinal bundle are, in the first instance, not marked off from each other. They appear as a broad flattened band applied to the raphe. One edge of this band is directed backwards and reaches the gray matter on the floor of the fourth ventricle, while the other edge looks forwards, and is in contact with the pyramid. In the upper part of the medulla the fillet and the posterior longitudinal fasciculus begin to draw asunder from each other. The intermediate longitudinal fibres become reduced in number and the two strands grow denser — the one on the dorsal aspect of pyramid, and the other ". immediately beneath the gray matter of the floor of the fourth ventricle (Fig. 398). The posterior longitudinal bundle (fasciculus longitudinalis medialis) is thus largely formed out of fibres, which in the cord constitute the anterior basis-bundle. These fibres are thrust back by the two decussations : the first decussation pushing them behind the pyramids, and the second decussation displacing them still farther backwards to a position behind the fillet. Olivary Nuclei. — The most conspicuous of the isolated clumps of gray matter in the medulla are the inferior olivary nucleus and the two accessory olivary nuclei. The inferior olivary nucleus (nucleus olivaris inferior) lies subjacent to the olivary eminence, and constitutes a very striking object in transverse sections through this region. It presents the appearance of a thick wavy or imdulating line of gray matter, folded on itself, so as to enclose a space filled with white matter. It is in reality a crumjjled lamina arranged in a purse-like manner, with an open INTERNAL STRUCTURE OF THE MEDULLA. 495 mouth or slit, which is called the hilum (hilum nuclei olivaris). directed towards the mesial plane. The hilum does not reach either extremity, so that in transverse Vago- , , glossopharyngeal R.st. form body j.^^t. Nucleus of the fasciculus solitdiiu-i Iji„'ula Vagus nucleus Tisficulus solitarius I)( sCLuding root of vestihulai- nerve (VIll.) i^ago-glossopharyngeal roots Posterior longitudinal fasficulus Sulistantia gelatinosa 7f Rulandi Ifjll^f Spinal root of fifth nerve Nucleus ainbiguus — j=_Csi'ebello-olivary fibres ^Dorsal accessory olivary nucleus \ntt rior superficial arcuate fibres 1 ill(t M si il accessory olivary nucleus Inferior olivary nucleus Pyramid Arcuate nucleus Anterior superficial arcuate fibres Fig. 398. — Transverse Section through the Middle of the Olivary Region of the Human Medulla OR Bulb. The floor of the fourth ventricle is seen, and it will be noticed that the restiforni body ou each side has now taken definite shape. sections through each end of the nucleus the gray lamina is seen in the form of a completely closed capsule. Into and out of the open mouth of the olivary capsule streams a dense crowd of fibres. These constitute what is called the olivary peduncle. The accessory olivary nuclei are two band-like laminae of gray matter, which are respectively placed on the dorsal and mesial aspects of the main nucleus. In trans- verse section each of these nuclei presents a rod - like appearance (Eig. 398). The mesial accessory oli- vary nucleus (nucleus olivaris accessorius mesialis) extends lower down in the medulla than the main nucleus, and it is much Fig. 399.— The Inferior Olivary Nucleus, as reconstructed and larger in its lower than its upper part. It begins immediately above the decussation of the pyramids, where it is seen lying on the outer side of the pyramidal tract and the anterior basis-bundle (Figs. 394 and 396). Higher up it lies across the movith of the main nucleus and on the outer side of the fillet. The dorsal accessory olivary nucleus (nucleus olivaris accessorius dorsalis) is placed close to the dorsal aspect of the main nucleus. The two accessory nuclei fuse together before they finally disappear. The gray matter forming the three inferior olivary nuclei consists of a close feltwork of neuroglia in which are interspersed numerous small round cells, each of which is provided with one axon and numerous dendrites. It is traversed by fibres, some of which -The Inferior Olivary Nucleus, as reconstructed and figured by Miss Florence R. Sabin. View of the dorso-lateral and lateral surfaces. 496 THE NEEVOUS SYSTEM. .GRACILENUCL. CUNEATENUCL. Fig. 400. — Diagram, Which shows in part the fibres which enter into the constitution of the restiform body. pass straight through the gray lamina, whilst others end in connexion with the cells. It is onh- in man and the higher apes that the infei'ior olivary nuclei are found strongly developed. In other mammals they are much smaller. The size of the olive appears to be correlated with that of the lateral hemisphere of the cerebellum and not in any way to be dependent on the development of the cerebral hemisphere. Thus in cetacea with a very extensive cerebral cortex the inferior olivary nuclei are small (Edinger). As the fibres of the fillet decussate and assume a longitudinal direction they RESTIFORM come to lie betv^een the olivary nuclei of opposite sides, and hence the term inter- olivary stratum (stratum interolivare lem- nisci) is frequently applied to them. Restiform Body (corpus restiforme). — The gracile and cuneate nuclei gradually give place to the restiform body in the upper part of the posterior district of the medulla. Fibres from various quarters converge to form this great strand. It first takes shape as a thin superficial layer of longitudinal fibres, which are gathered together on the outside of the cuneate nucleus ; but after that nucleus has come to an end, and as the upper part of the medulla is reached, the restiform body is seen to have grown into a massive strand, which presents a kidney-shaped or oval out- line on transverse section (Fig. 398), and which ultimately enters the white central core of the cerebellum as its inferior peduncle. The fibres which build up the restiform body are the following : (1) the direct cerebellar tract ; (2) the posterior superficial arcuate fibres ; (3) the anterior superficial arcuate fibres ; and (4) cerebello- olivary fibres. The direct cerebellar tract extends upwards from the lateral column of the cord. In the lateral district of the medulla it occupies a similar position ; but before the olivary eminence is reached it inclines backwards, crosses the postero- lateral furrow and passes ob- liquely upwards into the resti- form body. As its fibres diverge, backwards they pass over the tubercule of Eolando and cover up the spinal root of the tri- geminal nerve and the substantia Rolandi, thus shutting them ovit from the surface. The fibres of the direct cerebellar tract in the first instance enter into the outer or superficial part of the restiform body. Bruce has shown that the fibres of the direct cerebellar tract ultimately lie in the centre of the restiform body, forming as it were its central core, and that in the cerebellum they can be traced to the superior vermis. The posterior superficial arcuate fibres take origin from the gracile and cuneate nuclei, and enter the superficial part of the restiform body of the same side. The anterior superficial arcuate fibres proceed from the lower portions of the gracile and cuneate nuclei of the opposite side. After decussating in the middle line, it can easily be determined that all the deep arcuate fibres which arise from these nuclei do not enter the fillet. A large proportion of them gain the surface by sweeping round the inner aspect of the pyramid in the antero-mesial fissure. Many Funiculus gracilis Gracile nucleus Funiculus cuneatus Substantia gelatinosa Rolandi Spinal root of trigeminal nervp Direct cerebellar tract Crossed pyramidal tract Central canal Decussation of pyramids Detached anterior hoin of gray matter Fig. 401. — Section through the Junction between THE Cord and Medulla of the Orang. The direct cerebellar tract is well seen, especially on the right side. INTEKNAL STEUCTTJEE OF THE MEDULLA. 497 of them likewise gain the surface by piercing the pyramid or by passing out between it and the olive. These fibres constitute the anterior superficial arcuate group, and on the surface of the medulla they sweep backwards around it, forming a thin layer over the olivary eminence and ultimately reaching the restiform body. The anterior superficial arcuate fibres, as well as the direct cerebellar tract-fibres, cover over the trigeminal spinal root, which thus comes to take up a deeper posi- tion in the substance of the medulla (Figs. 397 and 398). Amongst the fibres which reach the surface of the medulla in this way Krilliker includes fibres from the striae acustic£e. If this be the case, these fibres connect the cochlear nucleus with the cerebellum, the path l^eing stripe acusticae, superficial arcuate fibres, and restiform body {vide p. 522). The fibres of the direct cerebellar tract, which come from the cells of the posterior vesicular column of the cord, and the superficial posterior arcuate fibres, wliicli are derived from the cells of the gracile and cuneate nuclei, do not cross the mesial plane, but enter the restiform body of the same side. The anterior superficial arcuate fibres arise from the cells of the cuneate and gracile nuclei, and cross the mesial plane so as to gain the restiform body of the opjjosite side. The cerebello-olivary fibres are only seen in the upper part of the medulla. They form the deep part of the restiform body and constitute its chief bulk. Streaming DESCENDING ROOTVlll. \ SPINAL \ JS?^?;"" ROOT v. XII. \ \>\ /^[hypoglossal] ' ARCUATE ^--i^_— ^ NUCLEUS Fig. 402. — Diagram of the Cerebello-Olivary Fibres. (This diagram has been constructed from the specimen figiu-ed on p. 495.) N.X., Vago-glossopharyngeal nucleus. N.XII., Hypoglossal nucleus. out from the hilum of the inferior olivary nucleus, they cross the mesial plane, and in the opposite side of the medulla they either pass through the inferior olivary nucleus of that side or sweep around it. Ultimately, on the dorsal aspect of the ohvary nucleus, they are gathered together in the form of a conspicuous group of arcuate fibres, which curve backwards to take up a position in the deep part of the restiform body. In passing back, they traverse the spinal root of the trigeminal nerve and break it up into several separate bundles. The cerebello-olivary fibres thus connect the inferior olivary nucleus of one side with the opposite side of the cerebellum. Although we have traced the cerebello-olivary tract in an upward direction from the olive to the cerebellum, and have thus inferred that it is composed of fibres which proceed from the cells of the inferior olivary nucleus of the oj^posite side, it is right to state that this view is not uni- versally accepted. There are some who regard these fibres as constituting an efferent tract from the cerebellum, or, in other words, as arising in the cerebellar cortex (probably as the axons of the cells of Purkinje), and descending in the inferior cerebellar peduncle to establish connexions with the cells of the inferior olivary nucleus of the opposite side. If this view be correct, the 36 498 THE NERVOUS SYSTEM. destination of tlie axons of the cells of tlie inferior olivary nucleus becomes a difficulty, but Kolliker considers that they enter the lateral column of the cord. Arcuate Nucleus (nucleus arcuatus). — Immediately above the decussation of the pyramids, a small fattened mass of gray matter, covered by superficial arcuate fibres, makes its appearance on the ventral or superficial aspect of the pyramid (Fig. 393). At a higher level, when the open part of the medulla is reached, this gray mass shifts its position and comes to lie upon the mesial aspect of the pyramid, and thus constitutes the immediate boundary of the antero- median fissure (Fig. 398). From its intimate connexion with the anterior superficial arcuate fibres, as they sweep out from the antero-median fissure, it receives the name of the arcuate nucleus. The nerve-cells which lie in its midst are smaller than those of the inferior olivary nucleus, and are fusiform in shape. It would appear that large numbers of the anterior superficial arcuate fibres end in this nucleus, whilst others take origin within it. Many of the anterior arcuate fibres, hoM^evei', sweej:! continuously over its surface and bind it down to the pyramid. At the upper end of the medulla the arcuate nucleus increases in size, and ultimately it becomes con- tinuous with the gray matter of the ventral part of the pons. Formatio Reticularis. — Behind the olive and the pyramid is the formatio reticularis. In the medulla it occupies a position which, to a large extent, corre- sponds with that of the lateral column in the spinal cord. In transverse section it appears as an extensive area, which is divided into a lateral and a mesial field by the root fascicles of the hypoglossal nerve as they traverse the substance of the medulla to reach the surface. In the lateral portion which lies behind the olive there is a considerable quantity of gray matter, continuous with that in the cord, present in the reticular formation ; it is, therefore, called the formatio reticularis grisea. In the mesial part which lies behind the pyramid the gray matter is extremely scanty, and the reticular matter here is termed the formatio reticularis alba. In the formatio grisea many of the cells which are scattered thickly amongst the intersecting bundles of fibres are to be regarded as association cells. They possess short axons, which serve to bind different levels of the medulla to each other, and therefore constitute association filsres. Probably the combined and harmonious activity exhibited by the nuclei of the vagus, facial and phrenic nerves in the process of respiration, is attained through the nuclear connexions established by these fibres (Edinger). Certain compact masses of gray matter are also seen in the formatio grisea. Of these may be mentioned (a) the dorsal accessory olivary nucleus, which has been already described, and (6) the nucleus lateralis. The nucleus lateralis is seen in the region between the olive and the substantia gelatinosa Rolandi. In the upper part of the medulla it gradually becomes diffuse and disappears. Except in the immediate vicinity of the raphe, the formatio alba may be said to be devoid of cells. The mesial accessory olive, however, forms an isolated compact mass of gray matter within its limits. The nerve fibres which traverse the formatio reticularis run both in a transverse and a longitudinal direction. The transverse fibres are the deep arcuate fibres. The longitudinal fibres are derived from different sources in the two fields. In the formatio grisea they represent to a large extent the fibres of the lateral column of the cord, after the removal of the direct cerebellar and the crossed pyramidal tracts. They consist, therefore, of the fibres of the tract of Gowers and of fibres correspond- ing to the lateral basis-bundle of the cord. In the formatio alba the longitudinal fibres are the tract of the fillet and the posterior longitudinal bundle, both of which have already been suriiciently described. Central Canal and the Gray Matter which surrounds it. — The central canal, as it proceeds u[)vvards through the closed part of the medulla, is gradually forced to assume a more dorsal position, owing to the accumulation of fibres on its ventral aspect. First the decussation of the pyramids, and then the decussation of the fillet, both of which take place in front of the canal, tend to push it backwards ; and the formation of the longitudinal strands in which these intercrossings result (viz. the pyramid and the fillet), together with the continuation upwards of the anterior basis -bundle, lead to a great increase in the amount of tissue which sejjarates it from the anterior surface of the medulla. In the closed part of the medulla it is surrounded by a thick layer of gray matter, which is continuous with INTEENAL STEUCTUEE OF THE MEDULLA. 499 the basal portions of the anterior and posterior horns of gray matter in the cord. This central gray matter is sharply defined on each side by the deep arcuate fibres which curve forwards and inwards around it. Finally, the central canal opens on the dorsal aspect of the medulla into the cavity of the fourth ventricle. The central mass of gray matter which surrounds the canal in the closed part of the medulla is now spread out in a thick layer on the floor of the fourth ventricle, and in such a manner that the portion which corresponds to the basal part of the anterior horn of the cord is situated close to the mesial plane, whilst the part which represents the Ijase of the posterior horn occupies a more lateral position. This is important, because the nucleus of origin of the motor hypoglossal nerve is placed in the mesial part of the floor, whilst the nuclei of termination of the afferent fibres of the vagus, glosso-pharyngeal, and auditory nerves lie in the lateral part of the floor. The gray matter of the ventricular floor is covered by epeudyma. Three Areas of Flechsig. — In transverse sections, througli the upper oimi jiart of the medulla, the root fibres of the hypoglossal and vagus nerves are seen traversing the sulistance of the medulla. The nucleus of origin of the hypoglossal is placed in the gray matter of the floor of the fourth ventricle close to the mesial plane ; the nucleus of the vagus is situated in the gray matter of the ventricular floor immediately to the outer side of the hyi^oglossal nucleus. From these nuclei the root-bundles of the two nerves diverge from each other as they are traced to the surface and subdivide the substance of the medulla, as seen in transverse section, into the three areas of Flechsig, viz. an anterior, a lateral, and a posterior. The anterior area, which is bounded internally by the median raphe and externally liy the hypoglossal roots, presents within its limits : (a) the formatio alba ; (b) the j^yramid ; (c) the fillet ; (d) the posterior longitudinal fasciculus ; (e) the mesial accessory olivary nucleus ; (/) the arcuate nucleus. Tlie lateral area lies between the root fibres of the hypoglossal and those of the vagus. It contains : (a) the inferior olivary nucleus ; (b) the doreal accessory olivary nucleus ; (c) the niicleus lateralis ; {d) the nucleus ambiguus, or the motor nucleus of the vagus and glosso-pliaryngeal nerves ; (c) the formatio reticularis grisea. The posterior area is situated behind the vagus roots, and within its limits are seen : (1) the restiform body ; (2) the upjjer part of the cuneate nucleus ; (3) to the inner side of this a crowd of transversely-cut bundles of fibres, loosely arranged and forming the descending root of the vestibular part of the auditory nerve ; (4) close to these, but placed more deejily, a round, com- pact, and very conspicuous bundle of transversely- cut fibres, viz. the fasciculus solitarius, or descending root of the vagus and glosso-pharyngeal nerves ; (5) the substantia gelatinosa liolandi, much reduced, with the large spinal root of the trigeminal nerve close to its outer side. INTERNAL STRUCTURE OF THE PONS VAROLII. When transverse sections are made through the pons, it is seen to be composed of a ventral part and a dorsal or tegmental part. The ventral part is much the larger of the two, and, broadly speaking, it corresponds to the pyramidal portions of the medulla and the pedal portions of the two crura cerebri, which lie above it and appear to issue from it. The dorsal tegmental part may be regarded as the con- tinuation upwards of the formatio reticularis grisea and the formatio reticularis alba. As these parts are traced upwards into the pons they become much modified, and new constituents are added. Ventral Part of the Pons (pars basilaris poutis). — This constitutes the chief bulk of the pons. It is composed of: (1) transverse fibres arranged in coarse bundles; (2) longitudinal fibres, gathered together in massive bundles; and (3) a large amount of gray matter, termed the nucleus pontis, which fills up the inter- stices between the intersecting bundles of fibres. The longitudinal fibres, to a large extent, consist of the same fibres which, lower down, are gathered together in the two solid pyramidal tracts of the medulla. When the pyramids are traced upwards they are seen to enter the pons in the form of two compact bundles. Soon, however, they become broken up into smaller bundles by the transverse fibres of the pons, and are spread out over a wider area. At the upper border of the pons they again come together and form two solid strands, each of which is carried into the central papt of the correspond- ing pedal portion of the crus cerebri. The transverse fibres at the lower border of the pons are placed on the super- ficial or ventral aspect of the pyramidal bundles. As we proceed upwards they increase in number, and many are seen breaking through the pyramids and even 500 THE NEEVOUS SYSTEM. passing across upon the dorsal aspect of the latter. Laterally these transverse fibres are collected together into one compact mass, which enters the white central core of the cerebellum and constitutes the middle cerebellar peduncle. At the mesial plane the transverse fibres of the two sides of the ventral portion of the pons intercross and form a coarse decussation. The gray matter (the nucleus pontis) forms a considerable part of the bulk of the ventral portion of the pons. It is packed into the intervals between the inter- secting transverse and longitudinal bundles. There is a close analogy between the pyramidal portions of the medulla and the ventral part of the pons. In the medulla fine arcuate fibres on their way to the surface pass through the pyramids. Other superficial arcuate fibres sweep over the surface of the pyramids. These present a strong resemblance to the transverse fibres of tbe pons. They likewise reach the cerebellum, although by a different route, viz. the inferior cerebellar peduncle. The nucleus pontis is also represented in the pyramidal part of the medulla by the arcuate Spinal root of fifth nerve Substantia gela- tinosa Rolandi Facial nerve Facial nucleus Sui^erior olive Central teg- mental tract' Fillet Middle jiedunclc of cerebellum \ rran!5ver.se fibres of pons Pyramidal bundles Transverse fibres of jjons Fig. 403. — Section through the Lowek Part of the Human Pons Varolii immediately above THE Medulla. nuclei, which are covered over by the superficial arcuate fibres, and even tend to penetrate, to a slight extent, into the pyramidal tracts. These arcuate nuclei, as already pointed out, are continuous with the nucleus pontis. Connexions of the Longitudinal and Transverse Fibres. — Our knowledge of the connexions of the longitudinal and transverse fibres of the ventral part of the pons is very far from being complete. When a transverse section through the uj)per part of the pons is compared with one close to its lower border, it becomes at once apparent that the numerous scattered bundles of longitudinal fibres which enter the ventral part of the pons from above, if brought together into one tract, would form a strand very much larger than the two pyramids which leave its lower aspect and enter the medulla. It is clear, there- fore, that many of the longitudinal fibres which pass into the pons from above do not pass INTERNAL STRUCTUEE OF THE PONS VAROLII. 501 out from it below into the medulla. What becomes of these fibres that are thus absorbed in the pons 1 It is known that the pj-ramidal bundles sutler a small loss by the fibres which they send to the nuclei of origin of the efferent nerves which arise within the pons (viz. the motor root of the fifth, the sixth, and seventh nerve nuclei) ; but this loss is, comparatively speaking, trifling. It is clear, therefore, that other longitudinal bundles enter the pons from above than those which form the pyramidal tracts. These bundles occupy a lateral and dorsal position in the ventral part of the pons, and may be termed the cortico-pontine fibres, seeing that they come from tlie cerebral cortex and end in fine ramifications around the cells of the nucleus pontis. The transverse fibres are of two kinds, viz. : (1) those which ai'ise in the cortex of the cerebellum ; and (2) those which take origin in the nucleus pontis. The former are the axons of certain of the cells of the cortex of the cere- bellum (cells of Purkinje). They come chiefly from the lateral hemi- sphere, but also to some extent from the median lobe of the cerebellum, and enter the pons by the middle peduncle. They end in fine rami- fications around the cells of the nucleus pontis, some on the same side as the peduncle through which they reach the pons, but the majority in the gray matter of the opposite side. The transverse fibres which arise in the pons take origin as axons of the cells of the nucleus pontis. Crossing the mesial plane, they enter the middle peduncle of the opposite side, and thus reach the cerebellar cortex, where they end in ramifica- tions round certain of the cortical cells. The middle peduncle thus contains both efferent and afferent cerebellar fibres, and no fibres pass continiiously through the pons from one middle peduncle into the other. In opposition to this view, Klimoft' and others hold that the middle peduncle is composed solely of centri- petal or afferent fibres, which pass from the nucleus pontis to the cere- bellum. Some of these fibres are crossed and others direct. Certain of the transverse fibres Fio. 404. — Diagram to show connexions of the Direct of the pons turn backwards and Cerebellar and the Olivo-Cerebellar Tracts. The enter the dorsal or tegmental part couuexions of the fibres of the middle pedunde of the cere- , ., 1 . ,1 • belluiu are likewise dia£;raiiimaticiulv shown (trom LdiDger, of the pons, but the precise con- modified) - ^ = nexions of these are doubtful. Corpus Trapezoides. — This name is applied to a group of transverse fibres which traverse the lower part of the pons (Fig. 405). They are quite distinct from those which have been just described as entering the middle peduncle of the cerebellum, and they lie in the boundary between the dorsal and ventral parts of the pons, but encroaching considerably into the ground of the former. They arise from the cells of the terminal nucleus of the cochlear division of the auditory nerve, and constitute a tract which establishes certain central connexions for that nerve. They will be more fully described when w^e treat of the cerebral connexions of the auditory nerve. Dorsal or Tegmental Part of the Pons (pars dorsalis pontis). — On the dorsal surface of the tegmental part of the pons there is spread a thick layer of gray Iiifevior olivary nucleus Posterior nerve root Posterior vesicular column of cells 502 THE NERVOUS SYSTEM. matter, covered by ependyma, which forms the floor of the upper or pontine part of the fourth ventricle. Beneath this the mesial raphe of the medulla is continued up into tlie pons, so as to divide its tegmental part into two symmetrical halves. In the lower 'part of the pons, immediately beyond the medulla, the restiform body is placed on the outer side of the tegmental part (Fig. 403). In transverse sections through the pons it appears as a large, massive oval strand of fibres which gradually inchnes backwards into the cerebellum, and thus leaves the pons. Between the restiform body and the median raphe the tegmental part of the pons is composed of forma tio reticularis, continuous with the same material in the medulla. Thus arcuate or transverse fibres, curving in towards the raphe, and also longitudinal fibres, are seen breaking through a mass of gray matter which occupies the interstices of the intersecting fibres. To the naked eye the formatio reticularis presents a uniform gray appearance, but its constituent parts are revealed by low powers of the microscope in properly-stained and prepared specimens. Embedded in this formatio reticularis are various clumps of compact gray matter and certain definite strands of fibres. These we shall describe as we pass from the restiform body inwards towards the median raphe. (1) Spinal root of the trigeminal nerve and the substantia gelatinosa Rolandi.- — Close to the inner side of the restiform body, but separated from it by the vesti- bular root of the auditory nerve as it proceeds backwards through the pons, is seen a large crescentic group of coarse transversely-divided bundles of fibres. This is the spinal root of the fifth nerve, and applied to its inner concave side is a small mass of gray matter, which is the direct continuation upwards of the substantia gelatinosa Eolandi. (2) The nucleus of the facial or seventh nerve comes next. It is sunk deeply in the tegmental part of the pons and lies close to the transverse fibres of the corpus trapezoides. It is a conspicuous, obliquely placed, ovoid clump of gray matter. From its outer and dorsal aspect the root-fibres of the facial nerve stream backwards and inwards towards the gray matter on the floor of the fourth ventricle. Passing forwards between this nucleus and the substantia Eolandi a solid nerve-bundle may be observed. This is the facial nerve, traversing the pons towards its place of emergence from the brain. (3) Immediately internal to the facial nucleus, but placed more deeply in the tegmental part of the pons, is the superior olivary nucleus (nucleus olivaris superior). It lies in a bay formed for it by the transverse fibres of the corpus trapezoides. These fibres curve round its ventral aspect, and many of them may be observed pene- trating into its svibstance. In man it is a very small mass of gray matter, and presents little resemblance to the inferior olivary nucleus, except in the size and shape of its constituent cells. In sections through the part of the pons where it attains its greatest size, it appears in the form of two, or it may be three, small isolated masses of gray matter. It is intimately connected with the trapezial fibres, many of which end in it, whilst others take origin within it. Upon the inner and dorsal aspect of tlie superior olive there is a dense grouj) of longitudinal fibres. These constitute the central tegmental tract; but as precise information in regard to its connexions is still to a large extent wanting, it is not necessary to do more than indicate its position. (4) The posterior longitudinal bundle and the fillet come next. As they proceed upwards through the tegmental part of the pons, these longitudinal tracts occupy the same relative position as in the medulla. They are placed close to the median raphe ; but they have drawn further apart from each other, and their fibres are more distinctly concentrated into separate strands, with an interval of some little width between them. The posterior longitudinal bundle lies immediately under cover of the gray matter of the floor of the iburth ventricle. The fillet is placed close' to the trapezial fibres, many of which traverse it as they pass towards the mesial plane. (5) The nucleus of the sixth nerve also forms a conspicuous object in sections through the lower part of the pons. It is a round mass of gray matter, which is situated close to the outer side of the posterior longitudinal bundle, and immediately INTERNAL STRUCTURE OF THE PONS VAROLII. 503 under cover of the gray matter of the floor of the fourth ventricle. From its inner side numerous root-bundles of the sixth nerve pass out and proceed forwards beween the fillet and the superior olivary nucleus. They occupy in the pons, therefore, a position similar to that occupied by the hypoglossal root-fibres in the medulla. Up to the present only the lower part of the tegmental portion of the jjons has been described, i.e. the portion immediately adjoining the medulla. As we proceed upwards and gain a point above the level of the trajtezial fihrcs, many of the structures which have attracted attention lower down gradually disappear from the formatio reticularis. The posterior longitudinal bundle, the fillet, and the spinal root of the fifth nerve, however, are still carried upwards. Further, the Superior cprebollar piidniicle- Mesenoephalic root of tlif fifth ncr\( Motor nucleus of the lifth nene Motor root of the fifth nerve Superior medullary velum or valve of Vieussens Corpus trai)ezoi(les Sensory nucleus of the fifth nerve Superior olive -.^^ Sensory root of ' fifth nerve ^~ Middle peduncle of cerebellum Transverse fibres of i)ons Pyramidal binidle.s Fig. 405. -Transverse Section throuoh the Pons Varolii at the Level of the Nuclei ok THE Trigeminal Nerve (Oraiig). floor of the fourth ventricle becomes narrower, and other objects appear in the tegemental substance. The superior cerebellar peduncle (brachium conjunctivum) is a very con- spicuous object, in sections, through the middle and upper parts of the pons. In transverse section it presents a semilunar outhne, and as it emerges from the cerebellum it lies immediately on the outer side of the fourth ventricle, towards which its concave aspect is turned (Fig. 405). Its dorsal border is joined with the corresponding peduncle of tlie opposite by the thin lamina of white matter, termed the superior medullary velum, whilst its ventral border is sunk to a small extent in the dorsal part of the pons. As it is traced upwards it sinks deeper and deeper into the pons until it becomes completely submerged, with the exception of the posterior border to which the superior velum is attached. It now lies on the outer side of the tegmental or reticular substance of the pons, and this position it maintains until the mesencephalon is reached (Fig. 406). About half-wccij uf the pons the nuclei of the trigeminal or fifth cranial nerve mark a very important stage in its tegmental portion. Tliese nuclei are two in 604 THE NEEVOUS SYSTEM. number on each side, viz. a large oval terminal nvicleus for certain of the sensory fibres of the nerve and a nucleus of origin equally conspicuous for certain of the motor fibres (Fig. 405). The sensory nucleus lies close to the outer surface of the pons, deeply sunk in its tegmental part, and in the interval between the submerged anterior border of the superior cerebellar peduncle and the ventral part of the pons. The motor nucleus is placed on the inner side of the sensory nucleus, but somewhat nearer the dorsal surface of the pons. At this level the spinal root of the fifth nerve disappears by joining the fibres of the sensory portion. The sensory and motor roots of the fifth nerve traverse the ventral part of the pons on their way to and from the region of the nuclei. Above the level of the nuclei of the trigeminal nerve a new tract of fibres comes into view. This is the mesencephalic root of the fifth nerve, as it descends to join the emerging fibres of the motor part of the fifth nerve. It is a small bundle of nerve fibres, semilunar in cross section, which hes close to the inner side Upper end of Ventricle IV Mesencephalic root of the fifth neive Posterior longitudinal bundle Forinatio reticularis Nucleus of lateral fillet - Vah e of Vieussens Gray matter on floor of Ventricle IV. Superior cerebellar peduncle Lateral fillet Commencing decussa- tion of superior cerebellar peduncles Mesial fillet Transverse fibres of pons Pyramidal bundle Fig. 406.— Section theodgh the Upper Part of the Pons Varolii of the Orang, above the Level of the Trigeminal Nuclei. of the superior cerebellar peduncle and on the outer and deep aspect of the gray matter on the floor of the fourth ventricle (Figs. 406 and 407). On a slightly deeper plane than the mesencephalic root of the fifth nerve, between it and the posterior longitudinal bundle, and in close relation to the gray matter of the floor of the ventricle, is the collection of pigmented cells which con- stitutes the substantia ferruginea. The posterior longitudinal bundle, as it is traced upwards through the tegmental part of the pons, maintains the same position throughout, and as it ascends it becomes more clearly mapped out as a definite and distinct tract. It lies close to the mesial raphe, and immediately subjacent to the gray matter of the floor of the fourth ventricle. The fillet as it ascends through the tegmental part of the pons undergoes striking changes in shape. In the lower portion of the pons its fibres, which in the medulla are spread out along the side of the median raphe, are collected together in the form of a loose bundle, which occupies a wide field, somewhat triangular in shape, on either side of the median raphe and immediately behind the ventral portion of the pons. As it proceeds up, the fibres spread out laterally until a compact ribbon-like layer is formed in the interval between the tegmental and ventral portions of the pons. This constitutes what is termed the mesial fillet (Figs. 406 and 407). Above the level of the trigeminal nuclei another flattened layer of fibres comes THE CEEEBELLUM. 505 into view to the outer side of the mesial fillet. To this the name of lateral fillet is given. These fibres spread outwards and backwards, and finally take vip a position on the outer surface of the superior cerebellar peduncle. In the angle between the mesial and lateral fillets a little knot of compact gray matter, termed the lateral Upper end of ventricle IV, Tioohleai nene Mesencephalic root ot lifth nerve^ ^^ Gowerb tract Posterior longi tudinal bundle Superior cere- bellar peduncle Infeiior quadri- f^pnnnal body Decussation ot ti'ochlear iH I ves Upper end of ventiicle IV. Supeiior cere- bi llai ])eduncle I' jsterior Icingi- tudinil bundle T iteial fillet Fig. 407.— Two Sections through the Tegmentum of the Pons at its Upper Part, clo.se to THE MeSENCEPHALOX. A is at a slightly lower level than B. fillet nucleus, comes into view (Fig. 406). This appears to be in more or less direct continuity with the superior olivary nucleus. Many of the fibres of the lateral fillet take origin in this nucleus. Bruce has called attention to the continuity between the superior olive and the lateral fillet nucleus in man, and the writer can confirm his statement in so far as the orang brain is concerned. THE CEREBELLUM. The cerebellum lies behind the pons Varolii and the medulla oblongata, and below the hinder portions of the cerebral hemispheres. From the latter it is Central lobule Mesencephalon Autenor crescentio lobule Posterior cres- centio lobule Postero- superior lobule Folium cacuniinis Postero-inferior lobule Tuber valvulie Posteiiur nuLch Fig. 408. — Upper Surface of the Cerebellum. separated by an intervening partition of dura mater, termed the tentorium cerebelli. It is distinguished by the numerous parallel and more or less curved sulci, which traverse its surface and give it a foliated or laminated appearance. It is composed of a cortex of gray matter (substantia corticalis) spread over its surface, with white matter in the interior, forming a central core (corpus medullare). 50G THE NERVOUS SYSTEM. The cerebellum is subdivided somewhat arbitrarily into a median portion termed the vermis, and two much larger lateral portions, called the lateral hemi- spheres (hemispha^ria cerebelli). The demarcation jjetween these main subdivisions of the organ is not very evident from every point of view. In front, and also behind, there is a marked deficiency or notch. The posterior notch (incisura cere- belli posterior) is smaller and narrower than the anterior notch. It is bounded laterally by the lateral hemispheres, whilst its bottom is formed by the median lobe or vermis. It is occupied by a fold of dura mater, called the falx cerebelli. The anterior notch (incisura cerebelli anterior) is wide, and, when viewed from above, it is seen to be occupied by the inferior quadrigeminal bodies and by the superior peduncles of the cerebellum. As in the case of the hinder notch, its sides are formed by the lateral hemispheres and the bottom by the vermis. On the superior surface of the cerebellum there is little distinction to be noted between the median lobe and the upper surface of each lateral hemisphere. On this aspect the median lobe receives the name of superior vermis, and it forms a high median elevation, from which the surface slopes gradually downwards on each side to the margin of the hemisphere. The superior vermis is highest in front, immediately behind the anterior notch, and from this it shows a somewhat sharp descent towards the posterior notch. This elevation of the superior worm is frequently called the monticulus cerebelli. The folia on the surface of the superior vermis are thicker and fewer in number than those on the upper surface of the lateral hemisphere. It is this which gives it the worm-like appearance from which it derives its name. On the inferior surface of the cerebellum the distinction between the three main constituent parts of the organ is much better marked (Fig. 409). On this aspect the lateral hemispheres are full, prominent, and convex, and occupy the cerebellar fossa3 in the floor of the cranium. They are separated by a deep mesial hollow, which is continued forwards from the posterior notch. This hollow is termed the vallecula cerebelli, and in its fore-part is lodged the medulla oblongata. When the medulla is raised and the lateral hemispheres are pulled apart, so as to expose the bottom of the vallecula, it will be seen that this is formed by the vermis inferior, or inferior aspect of the median lobe, and, further, that the latter is separated on each side from the corresponding lateral hemisphere by a distinct furrow, termed the sulcus valleculas. Sulci Cerebelli. — Certain of the fissures which traverse the surface of the cerebellum are deeper and longer than the others, and they map out districts which are termed lobes. One of the most conspicuous of these clefts is the great horizontal fissure. The great horizontal fissure (sulcus liorizontalis cerebelli) of the cerebellum begins in front and passes continuously round the circumference of the organ, cutting deeply into its outer and posterior margins. In front, its lips diverge to enclose the three cerebellar peduncles as they pass into the interior of the cerebellum. The great horizontal fissure divides the organ into an upper and a lower part, which may be studied separately. The prominence which is accorded to the great horizontal fissure in descriptive anatomj' is not justified by its develo^jmental histor}^ and morphological status. It is very late in making its appearance in the fcetal cerebellum, and not infrecpiently the part of the fissure on the one side fails to establish a continjiity across the vermis with the part of the fissure on the other side of the organ. Lobes on the Upper Surface of the Cerebellum. — When examined from before backwards, the superior vermis presents the following sulidivisions : (1) the lingula; (2) the central lobule (lo})ulus centralis); (3) tlie culmen monticuli; (4) the clivus monticuli ; (5) the folium cacuminis (folium vermis). With the exception of tlie lingula, each of these is continuous on either side, witli a corresponding district on tiie upper surface of the hemisphere, thereby forming a cerebellar lobe. Thus the central lobule is prolonged outwards on either side in the form of a small, flattened, wing-like expansion called the ala ; the culmen constitutes the median connecting piece between the two anterior crescentic lobules of the liemjs])heres ; the cHvus stands in the same relation to the two posterior crescentic lobules ; and THE CEREBELLUM. 507 the folium cacuminis is the connecting band between the postero- superior lobules of the hemispheres. It should be noted that this subdivision of tlie uiijjer surface of the cerebellum is to some extent conventional, and in certain 2:)articulars receives little suppoi't from morphological data. The lingula can only be seen when the part ol" the cerebellum which forms the bottom of the anterior notch is pushed backwards. It consists of four or five small fiat folia continuous with the gray matter of the vermis superior, which are pro- longed forwards on the upper surface of the superior medullary velum in the interval between the two superior cere1)ellar peduncles. Lobus Centralis with its Alae. — The loljulus centralis lies at the bottom of the anterior cerebellar notch, and is only seen to a very small extent on the upper surface of the organ. It is a little median mass which laterally is prolonged out- wards for a short distance round the anterior notch in the form of two expansions, termed the alse. Lobus Culminis. — The culnien monticuli constitutes the highest part or summit of the monticulus of the vermis superior. It is bounded behind by a deep and strongly marked fissure called the fissura prima (Elliot Smith), and is prolonged outwards on either side into the lateral hemisphere as the anterior crescentic lobule. This is the most anterior subdivision on the upper surface of the hemisphere. The two anterior crescentic lobules, with the culmen monticuli, form the lobus culminis cerebelli. Lobus Clivi. — The clivus monticuli lies behind the culmen, from which it is separated by the fissura prima, and it forms the sloping part or descent of the monticulus of the vermis superior. On each side it is continuous with the posterior crescentic lobule of the lateral hemisphere, and the three parts are included under the one name of lobus clivi. The two crescentic lobules on the upper surface of the liemisjihere are sometimes classed together and described as the lobulus quadrangularis. They are separated from each other by a lateral extension on the upper surface of the hemisphere of the fissura prima, whilst the posterior crescentic lobule is bounded behind by a curved sulcus termed by Elliot Smith the fissura postlunata. The union of the two postlunate furrows across the vermis separates the clivus from the folium cacuminis, but in many cases this junction fails to take place. Lobus Cacuminis. — The folium cacuminis forms the most posterior part of the vermis superior, and when the right and left portions of the great horizontal fissure are continuous across the vermis it bounds that fissure superiorly at the posterior notch. It is a single folium, subject to considerable variation in the degree of its development, and its surface may be smooth or beset with rudimentary secondary folia. It is the median connecting link between the two postero-superior lobules of the hemispheres, the three parts forming the lobus cacuminis. As the folium cacuminis is traced outwards into the postero-superior lobule, it is found to expand greatly, and as a result of this the postero-superior lobule on each side forms an extensive foliated district bounding the great horizontal fissure above. Lobes on the Under Surface of the Cerebellum. — The connexion between the several parts of the inferior vermis and the corresponding districts on the under surface of the two hemispheres is not so distinct as in the case of the vermis superior and the lobules on the upper surface of the hemispheres. A groove, the sulcus valleculas, intervenes between the vermis inferior and the hemisphere on each side. From behind forwards the following subdivisions of the vermis inferior may be recognised : (1) the tuber valvulse (tuber vermis) ; (2) the pyramid (pyramis) ; (3) the uvula ; (4) the nodule (nodulus). On the under surface of the hemis]3here there are four main lobules nuipped out by intervening fissures. From behind forwards these are: (1) the postero-inferior lobule, a large subdivision which bounds the o-reat horizontal fissure on its under aspect ; (2) the biventral lobule (lobulus biventer) which lies in front of the postero- inferior lobule, and is partially divided into two parts by a curved fissure which traverses its surface ; (3) the tonsil or amygdala (tonsilla), a small rounded lobule which bounds the fore-part of the vallecula, and is lodged in a deep concavity on 508 THE NERVOUS SYSTEM. the inner aspect of the biventral lobule ; (4) the flocculus, a minute lobule situated on the middle peduncle of the cerebellum in front of, and partially overlapped by, the anterior border of the l^iventral lobule. These lobules, with the corresponding portions of the vermis inferior, constitute the lobes on the under surface of the cerebellum. Still, it should be noted that, just as in the case of the upper surface of the organ, this subdivision is to some extent artificial, and is not in every particular provided with a sound morphological basis. Lobus Tuberis. — The tuber valvule, which forms tlie most posterior part of the vermis inferior, is composed of several transversely arranged folia which, on either side, run directly into the postero-inferior lobule. The three parts of the lobus tuberis are thus linked together. The postero-inferior lobule, which is wider towards the vallecula than it is further out, is traversed by two or it may be three curved fissures. The most anterior of these cuts off a narrow, curved strip of cerebellar surface, which presents a more or less uniform width throughout its whole length. This is the so-called lobulus gracilis. Lobus Pyramidis. — The pyramid is connected with the biventral lobule on each side by an elevated ridge which crosses the sulcus valleculse. The term lobus pyramidis is applied to the three lobules, which are thus associated with each other. The pyramid is separated from the tuber valvulse by a deep furrow which has been termed by Elliot Smith the suprapyramidal fissure. It is in a measure continuous with the curved fissure, whicli on the under surface of the hemisphere intervenes between the biventral lobule and the lobulus gracilis or fore part of' the postero-inferior lobule. The name applied to the latter fissure by Elliot Smith is fissura parapyramidalis. Lobus Uvulae. — The uvula is a triangular elevation of the vermis inferior. It lies between the two tonsils, and is connected with each of these by a low-lying Cpntral lobule Superior inedullary velum Superior peduncle of c£ j' ^ 11 im Middle peduncle of cerebellum Ventricle IV Nodule Flocculus Tonsil Postero-inferior lobule^ 1 jstero inferior lobule Lobulus gracilis/ Bi\ I Pyj-anud Tubei \al\ulte Fig. 409. — Lower Surface of the Cerebellum. The tonsil on the right side has been removed so as to display more fully the inferior medullary velum and the furrowed band. band-like ridge of gray matter scored by a few shallow furrows, and in consequence termed the furrowed band. The two tonsils and the uvula form the lobus uvulae. Ji«tw(;eii tlie pyi'amid and the uvula there is a deep cleft which may be termed the infra- pyramidal fissure (tlie fissura secunda of Elliot Smith). This is more or less directly connected with the retrotonsillar fissure which curves round the tonsil. Tlic large size of the tonsil is characteristic of the Ijraiii of man and the anthropoid apes. Lobus Noduli. — The lobus noduli comprises the nodule and the flocculus of each side, with a delicate connecting lamina of white matter termed the inferior medullary velum. THE CEREBELLUM. 509 Tlie cleft l)et\veen the nodule and the uvula is termed the postnodular fissure (Elliot Smith) ; that between the flocculus and the l)i ventral lolnile is called tlie floccular fissure. The flocculus will usually be ol>served to be partially divided into two pieces. The smaller hinder portion, which, as a rule, is completely overlapped by the overhanging edge of tlie biventral lolnile, is the paraflocculus. This assumes very large proportions in certain of the lower mammals. Arrangement of the Gray and White Matter of the Cerebellum.— The white matter of the cereLellum forms a solid compact mass in the interior, and over this is spread a con- tinuous and uui- <^"''"«"" '"on«cuii form layer of gray matter. In each lateral hemi- sphere the white central core is more bulky than in the median lobe or worm, in which the central white matter is reduced to a re- latively thin bridge thrown across between the two lateral hemispheres. The white matter in the interior of the median lobe or worm is termed the corpus trapezoides. When sagittal sections are made through the cerebellum, the gray matter on the surface stands out clearly Further, from all parts of the surface of Inferior olivary nucleus Fici. 410. -Sagittal Section through the Left Lateral Hemisphere OF the Cerebellum, Showing tlie " arbor vits" and the corpus dentatum. from the white matter in the interior. TH'uia semicircularis- Pulvinar" Inferior quadrigeminal body Middle cerebellar peduncle Inferior cerebellar peduncle Ay^ Third ventricle -1 Titnia tlialanii --Trigonuni liabenuke . - Pineal body —Superior quadrigeminal body --Inferior braeliiuni Fourth nerve Valve of Vieus.sens Superior cerebellar peduncle -.Corpus dentatum Fig. 411.— From a dissection by Dr. Edward B. Janiieson in the Anatoniical Department of the University of Edinburgh. The corpus dentatum is displayed from above ard the superior cerebellar peduncle has been traced from it to the mesencephalon. the central core stout stems of white matter are seen projecting into the lobes of the cerebellum. From the sides of these white stems secondary branches proceed 510 THE NEKVOUS SYSTEM. at various angles, and from these again tertiary branches are given off. Over the various lamellas of white matter thus formed the gray cortex is spread, and the fissures on the surface show a corresponding arrangement, dividing up the organ into lobes, lobules, and folia. When the cerebellum is divided at right angles to the general direction of its fissures and folia, a highly arborescent appearance is thus presented by the cut surface. To this the term arbor vitse cerebelli is applied. Corpus Dentatum and other Gray Nuclei in the White Matter of the Cerebellum. — Eml ledded in the midst of the mass of white matter which forms the central core of each lateral hemisphere there is an isolated nucleus of gray matter, which presents a strong resemblance to the inferior olivary nucleus of the medulla. It is called the corpus dentatum (nucleus dentatus), and it consists of a corrugated or plicated lamina of gray matter, which is folded on itself so as to enclose, in a flask-like manner, a portion of the central white matter (Figs. 410 and 411). This gray capsule is not completely closed. It presents an open mouth, termed the hilum, whicli is directed inwards and upwards, and out of this stream the great majority of the fibres of the superior cerebellar peduncle. Three small additional masses of gray matter are also present on either side of the mesial plane in the central white matter of the cerebellum. These are termed the nucleus emboli- formis, the nucleus globosus, and the nucleus fastigii. The nucleus emboliformis or embolus is a small lamina of gray matter which lies immediately internal to the hilum of the corpus dentatum, being thus related to it somewhat in the same manner that the mesial accessory olivary nucleus is related to the main inferior olivary nucleus. The nucleus globosus lies internal to the embolus and on a somewhat deeper horizontal plane. The nucleus fastigii or roof nucleus is placed in the white substance of the worm (corpus trapezoides) close to the mesial plane and its fellow of the opposite side. It is, therefore, situated on the mesial aspect of the nucleus globosus. Although isolated from the gray matter of the surface, these small nuclei and the corpus dentatum are connected at certain points with each other. The corpus dentatum and the embolus present a structure very similar to that of the inferior olivary nucleus. In the • nucleus gloljosus and the nucleus fastigii the cells are somewhat larger in size. Cerebellar Peduncles. — These are three in number on each side, viz. the middle, the inferior, and the superior (Fig. 391, p. 487). The fibres of which they are composed all enter or emerge from the white medullary centre of the cerebellum. The middle peduncle is much the largest of the three, and has already been described on pp. 486 and 501. It is formed by the transverse fibres of the pons, and it enters the cerebellar hemisphere on the outer aspect of the other two peduncles. The lips of the anterior part of the great horizontal fissure are separated widely from each other to give it admission (Fig. 409). Within the cereljellar hemisphere its fibres are distributed in two great bundles. Of these, one, composed of the upper transverse fibres of the pons, radiates out in the lower part of the hemisphere ; whilst the other, consisting of the lower transverse fibres of the pons, spreads out in the upper part of the hemisphere. The inferior peduncle is simply the restiform body of the medulla. After leaving the medulla it ascends for a short distance on the dorsal surface of the pons and then turns sharply backwards, to enter the cerebellum between the other two peduncles. The superior peduncle, as it issues from the cerebellum, lies close to the inner side of the middle peduncle (Fig. 409). Its further course upwards on the dorsum. of the pons to the inferior quadrigeminal body lias been previously described (pp. 486 and 503). Connexions established by the Peduncular Fibres.— The fibres of the middle peduncle are both afferent and efferent. The connexions which they establish in the pons are described on p. 501. The efferent fibres arise from cells in the gray cortex of the lateral hemisphere (also probably to some small extent in the cortex of the vermis), and end in connexion with the cells of the nucleus pontis, and likewise in the tegmental part of the pons. The afferent fibres, arising in the pons, end in the gray cortex of the lateral hemisphere of the cerebellum, and perhaps also in the cortex of the worm. The inferior peduncle is also composed of afferent and efferent fibres (see p. 496) ; only the more important connexions which these establish in the cerebellum can be touched on here. The principal afferent strand is the direct cerebellar tract. The fibres of this strand end in the cortex of the superior worm on both sides of the mesial plane, but chiefly on the opposite side. The cerehello-olivary fibres are also probably afferent. It THE CEREBELLAIl PEDUNCLES. 511 appears that thoy end iu connexion with cells in the cortex of both the worm and hemi- sphere, and also cells in the nucleus deutatus. The numerous arcudte fibres, which enter the inferior peduncle establish connexions with cells in the cortex of the lateral hemisphere and of the worm. The superior peduncle is an eflferent tract. The majority of its fibres come from the cells of the nucleus dentatus, whilst a small proportion appear to come from the cere- bellar cortex. According to Risien Russell, the fibres which form the dorsal edge of the band come from the opposite side of the cerebellum and cross the mesial plane to join the peduncle. Our knowledge of the connexions of the peduncles of the cerebellum has been greatly extended by Ferrier and Aldren Turner ; and the account which is given above, and also at p. 501, is lai'gely derived from their memoir on this subject. Commissural and Association Fibres. — In addition to those fibres of the white medullary centre which belong to the system of peduncles, there are others which have exclusively cerebellar connexions. Thus the vai'ious folia are bound together by numerous association fibres, which pass from one folium into anotlier around the bottom of the inter- vening fissure. Tracts of transversely-directed commissural fibres cross the mesial plane in the white centre of the vermis, connecting corresponding parts of opposite sides. These, in some measure, are analogous to the corpug callosum of the cerebrum. The roof nuclei are also closely bound by connecting fibres with the cortex. Medullary Vela. — The medullary vela are closely associated with the cerebellar peduncles. They consist of two thin laminte of white matter, which are projected out from the white central core of the cerebellum. The superior medullary velum is described on p. 486. Laterally, it is continuous with the dorsal edges of the superior cerebellar peduncles ; whilst, interiorly, it is prolonged downwards and backwards under the lingula and the central lobule of the superior worm, to become continuous with the central white matter or corpus trapezoides of the worm. The inferior medullary velum is more complicated in its connexions. It presents much the same relations to the nodule of the inferior vermiform process that the superior velum presents to the lingula of the superior vermiform process. It is a wide thin lamina of white matter — so thin that it is translucent — which is pro- longed out from the white centre of the cerebellum above the nodule. From the nodule it stretches outwards to the flocculus on each side, thereby bringing these three small portions of the cerebellum into association with each other (Fig. 409). Where it issues from the white matter of the cerebellum it is in contact with the superior medullary velum, but, as the two laminte are traced forwards, they diverge from each other. The superior velum is carried upwards between the two superior cerebellar peduncles, whilst the inferior medullary velum is curved forwards and then downwards round the nodule, and ends at a variable point in a free, slightly thickened, crescentic edge. The cavity of the fourth ventricle is carried backwards into the cerebellum between the two vela, which thus form a peaked and tent-like root for it. Relation of the Tract of Gowers to the Superior Medullary Velum. — The ascending tract of Gowers has been noticed in connexion with the latei'al column of the cord (p. 469). The fibres which compose it are carried upwards through the foi-matio reticvdaris grisea of the medulla and the corresponding part of the tegmental portion of the pons. In this part of its course the fibres are scattered and do not form a compact strand. Reaching the upper end of the pons the tract turns backwards, enters the superior medullary velum, and proceeds downwards in it into the cerebellum. Roof of the Fourth Ventricle. — In its upper part the roof of the fourth ventricle is formed by the superior medullary velum as it stretches across between the two superior cerebellar peduncles, and also, to some extent, by the approximation of these peduncles themselves as they approach the mesencephalon. In its lower part the roof of the ventricle is exceedingly thin and is not all formed of nervous matter. The inferior medullary velum enters into its formation, and, where this fails, the epithelial lining of the cavity, supported by pia mater, is carried downwards towards the lower boundaries of the floor of the ventricle. At the lowest part of the calamus scriptorius, and also along each lateral boundary of 512 THE NEEVOUS SYSTEM. the floor, a thin lamina of white matter is carried for a short distance over the epithelial roof. The small semilunar lamina which stretches across between the lower parts of the two clavfe at the calamus scriptorius and overhangs the opening Fornix Foramen of Jlonro ^ Septum lucidum , X, Genu of corpus callosum / Declive Anterior commissure Corpus mammillare' Lamina cinerea ' Optic nerve Tuber valvnlse Pyramid Pituitary b Tuber cinereum Tliird nerve ■ Uvula Central lobule Fig. 412.- Pons Valve of Vieussens Ventricle IV. \ , Module Medulla choroid plexus in ventricle IV. -Mesial Section through the Corpus Callosum, the Mesencephalon, the Pons, Medulla, AND Cerebellum. ShoT\-ing the third and fourth ventricles joined liy the aqueduct of Sylvius. of the central canal is termed the obex (Fig. 391, p. 487). The lamina in connexion with the lateral boundary of the ventricular floor is more extensive, and is called the ligula (Figs. 388 and 390). It begins on the clava and passes upwards over the cuneate tubercle to the restiform body. On the outer surface of the restiform body it turns outwards so as to bound the lateral recess of the ventricle below, and in some cases it may be seen to become continuous around the extremity of the lateral recess with the inferior medullary velum. A short distance above the calamus scriptorius there is, in the mesial plane, an opening in the epithelial and pial roof of the ventricle, by which the cavity of the ventricle communicates with the subarachnoid space. This opening is termed the foramen of Majendie. There is also an aperture of a similar nature in the epithelial and pial roof at the extremity of each lateral recess. Two choroid plexuses, or highly vascular infoldings of the pia mater, invaginate the lower part of the roof of the fourth ventricle. These are placed one on either side of the mesial plane, and, although they appear to lie within the cavity, they are in reality excluded from it by the epithelial lining of the ventricle, which covers over and is adapted to every sinuosity on their surface. Two lateral offshoots from these longitudinal choroid plexuses proceed outwards, and protrude in a similar manner into the lateral recesses. Minute Structure of a Cerebellar Folium. A cerebellar folium is composed of a central core of white matter, covered by a layer of gray matter. The gray cortex is arranged in two very evident layers, viz. a superficial molecular layer and a subjacent rust-coloured granular layer. Between these strata a single layer of large cells, termed the cells of Purkinje, are disposed in the form of a very nearly continuous sheet. The cells of Purkinje constitute the most characteristic, and probably the most essential, constituents of the cerebellar cortex. The cells of Purkinje are most numerous on the summit of the folium. At the bottom of the sulci which intervene between the folia they become fewer in number, and, therefore, looser in their arrangement. Each consists of a large flask-shaped or pyriform MINUTE STEUCTUEE OF A CEEEBELLAE FOLIUM. 5U cell body, the narrow end of which projects into the molecular layer, whilst the thicker, deeper end rests on the granular layer. From the latter arises a single axon, which passes into the granular layer and presents the peculiarity of almost immediately assuming its medullary sheath. From this axon a few collateral branches soon arise, which, taking a recurrent coui^se, enter the niolecular layer, to end in connexion with certain of the adjoining cells of Purkinje. They would seem to have the function of binding together adjacent cells, and thus enabling them to carry on their operations in harmony with each other. The dendritic processes spring from the narrow end of the cell either in the form of one or perhaps two stout stalks. These ascend into the molecular layer, branch- ing and rebranching until an aborescent arrangement of extraordinary richness and extent results. The den- dritic branches extend throughout the entire thickness of the molecular layer, and the branching takes place in one plane only, viz. in a plane which is trans- verse to the long axis of the folium. Consequently, it is only when transvei*se sections are made through a folium that the full dendritic effect is obtained ; in sections made parallel to the long axis of the folium the cells are seen in profile, and are observed to occupy qmte a narrow area (Fig. 414). The bi'anching of the dendrites of a cell of Purkinje may, therefore, be compared to that which takes place in the case of a fniit-tree which is trained against a Fig. 41.3.- Cerebellar Folium Transverse Section through (after Kolliker). Treated by the Golgi method. P. Axon of cell of Piukinje. F. Moss fibres. K and K^. Fibres from white core of folium ending in molecular layer in connexion with the dendrites of the cells of Purkinje. M. Small cell of the molecular layer. GR. Granule cell. GR^. Axons of granule cells in molecular layer cut transversely. Ml. Basket-cells. Basket-work around the cells of Purkinje. Neuroglial cell. Axon of an association cell. ZK. GL. wall. In the molecular layer x. the cells are not particularly numei-ous, and of these the most characteristic are the basket -cells which lie in the deeper part of the layer. In addition to numerous dendrites the basket-cell gives off an axon which runs transversely, as regards the long axis of the folium, between the planes of adjacent dendritic arborisations of the cells of Purkinje. At first very fine these axons gradually become coarse and thick, and at intervals they give oft" collaterals which run towards the bodies of the cells of Purkinje. Reaching these, they break up into an enormous number of fine terminal branches, which enclose the cells of Purkinje, as well as the short non-medullated portions of their axons, in a close basket-work of fine filaments. The granular layer is, for the most part, composed of large numbers of small granule-like bodies closely packed together. Each of these possesses a somewhat large nucleus, with a very small amount of surrounding protoplasm. From the cell body three or four, or perhaps five, dendrites and one axon proceed. The dendrites are short and radiate out from different aspects of the cell body. They end in tufts of claw-like twigs, which either embrace or are otherwise in contact with neighbouring granule cells. The whole multitude of granule cells, therefore, are brought into intimate connexion with each other. The axon passes into the molecular layer, in which it ends at a varying 37 514 THE NEEVOUS SYSTEM. distance from the surface by dividing into two branches. These diverge so sharply from each other that they almost form a right angle with the parent stem, and they run parallel to the long axis of the folium, threading their way between the branches of the various dendritic planes of the cells of Purkinje and entering into contact association with them. When the great number of granule cells is borne in mind, and the fact that each sends an axon into the molecular layer, the important part which these fibres, with their longitudinal branches, take in building up the molecular layer will be understood. They are found pervading its entire thickness — from the surface down to the bodies of the cells of Purkinje. Near the cells of Purkinje a few scattered cells are seen in the granular layer of a different kind. These are much larger than the ordinary granule cells, and are probably of the nature of association cells. They are stellate in form, and have numerous long branching dendrites and an axon which divides up in the granular layer to a singular extent. The white centre of the folium becomes thinner as it approaches the summit. This is due to the fibres which compose it gradually entering the gray matter on the surface. These fibres are of three kinds, viz. : (1) axons of the cells of Purkinje; (2) fibres which apparently end in the granular layer ; and (3) fibres which end in the molecular layer. The axons of the cells of Purkinje are medullated fibres which, entering the white centre of the folimn, form a not inconsiderable part of it. The fibres which end in the granular layer are called moss-fibres. This name is applied to them because, in the granular layer, they present at certain points moss-like thickenings, from which short rough twigs proceed. The fibres which proceed into the molecular layer give off" few or perhaps no branches as they traverse the granular layer. In the deeper part of the molecular layer they break up into varicose branches, which twine around the primary and secondary stems of the Purkinje dendrites. Entering into the constitution of the molecular layer are the following elements : (1) dendrites of the cells of Purkinje; (2) basket-cells and somewhat smaller cells nearer the surface ; (3) axons of the granule cells, with their longitudinally arx'anged branches ; (4) the terminations of certain fibres from the white core of the folium, which end in contact with the Purkinje dendrites. In the granular layer are found: (1) granule cells; (2) larger stellate association cells; (3) axons of the cells of Purkinje; (4) moss-fibres ; (5) fibres traversing this layer, to end in the molecular layer. Fig. 414. — Section through the Molecular AND Granular Layers in the Long Axis OF a Cerebellar Folium (after Kolliker). Treated by the Golgi method. P. Cell of Purkuije. GR. Granule cells. N. Axon of a granule cell. N^. Axons of granule cells iu molecular layer. THE DEEP CONNEXIONS OF THE CRANIAL NERVES ATTACHED TO THE MEDULLA AND PONS. There are twelve pairs of cranial nerves, of which the lower eight are attached to the medulla and pons Varolii. From above downwards these are named the fifth or trigeminal, the sixth or abducent, the seventh or facial, the eighth or auditory, the ninth or glossopharyngeal, the tenth or vagus, the eleventh or spinal accessory, and the twelfth or hypoglossal. The liypoglossal, the spinal accessory, the greater part of the facial, the abducent, and the motor root of tlie trigeminal are efferent nerves; the aiiditory, the pars intermedia of the facial, and the sensory root of the trigeminal are purely afferent nerves ; whilst the vagus and the glosso- pharyngeal are composed of both efferent and afferent fibres. In all cases afferent fibres arise from ganglionic cells placed outside the brain and penetrate the brain- stem, to end iu connexion with the cells of certain nuclei of termination. Efferent THE DEEP CONNEXIONS OF THE CKANIAL NERVES. 515 fibres, on the other hand, take origin within the brain as the axons of cells which are grouped together in certain places in the form of nuclei of origin. Nuclei of Origin, or Motor Nuclei. — In the spinal cord the nuclei of origin are represented by elongated columns of cells which run more or less continuously in the anterior horn of gray matter of successive cord-segments, and from these the series of efferent anterior nerve-roots take origin. In the medulla and pons the nuclei of origin, or, in other words, the motor nuclei of the individual nerves become, for the most part, discontinuous, and are represented by certain isolated clumps of compact gray matter, in which are placed the clusters of cells from which the fibres of the efferent nerves arise. The nucleus ambiguus, however, which consists of a column of cells from which root fibres of the medullary part of the spinal accessory, of the vagus, and possibly also of the glossopharyngeal are derived, is an exception to this rule. At the decussation of the pyramids, the anterior horn of gray matter of the cord is broken up by the intercrossing bundles into a detached head and a basal part which remains in relation with the ventro-lateral aspect of the central canal. Certain of the efferent or motor nuclei of the medulla and pons lie in the line of the basal portion of the ventral horn of gray matter of the spinal cord, and thus close to the mesial plane. These are termed mesial nuclei of origin, and are met with at different levels in the brain-stem. This group comprises the hypoglossal nucleus, the dorsal motor nucleus of the vago-glossopharyngeal nerve, the abducent nucleus (and, in the mesencephalon, the trochlear nuclevis and the oculo-motor nucleus). Other motor nuclei of origin are present in the form of isolated clumps or columns of gray matter, which lie at different levels in the medulla and pons in the line of the detached head of the anterior horn of gray matter. They are the nucleus ambiguus of the spinal accessory, the vagus and glossopharyngeal, the facial nucleus, and the nucleus of the motor root of the trigeminal nerve. From their position in the tegmental substance of the medulla and pons they constitute a group to which the name of lateral motor nuclei is applied. The different nuclei of origin of the efferent fibres which belong to the various cranial nerves, both mesial and lateral, are connected with the motor area of the cerebral cortex by fibres from the pyramidal tract, which enter the nuclei and end in connexion with their cells. Nuclei of Termination. — In the brain the nuclei of termination are likewise discontinuous, and are represented by more or less isolated clusters or columns of cells. Unlike the motor nuclei, however, these nuclei show no regular or definite position within the medulla and pons. Some are found in the gray matter which surrounds the central canal, and in its continuation upwards as the gray matter in the floor of the fourth ventricle ; others are placed in the tegmental substance ; whilst two actually lie on the surface of the brain- stem, viz. the lateral and ventral nuclei of the cochlear or outer division of the auditory nerve. The axons of the cells of the nuclei of termination enter the reticular formation of the tegmental substance as arcuate fibres, and, crossing the mesial plane, are carried upwards in the tegmental substance of the opposite side to establish direct connexions with the optic thalamus and indirect connexions with the cerebral cortex. Hypoglossal Nerve (nervus hypoglossus). — ^The nucleus of origin of the hypo- glossal nerve, the motor nerve of the tongue, lies in the substance of the medulla oblongata. It is composed of several groups of large multipolar cells, which closely resemble the cells in the ventral horn of gray matter in the spinal cord, and is pervaded by an intricate network of fine fibrils. In form it is elongated and rod-like, and in length it is somewhere about 18 mm. It extends from a point immediately above the decussation of the pyramids up to the level of the stride acusticse. The lower portion of the nucleus is thus placed in the closed part of the medulla (Fig. 397, p. 493), whilst its upper part is situated in the open part of the medulla (Fig 402, p. 497). The former lies in that part of the central gray matter which is continuous with the basal part of the ventral horn of gray matter of the cord. It is thus placed on the ventral and lateral aspect of the central canal, close to the mesial plane and the corresponding nucleus of the opposite side. The upper part of the nucleus occupies a position in the gray matter on the floor of 516 THE NERVOUS SYSTEM. the fourth ventricle, subjacent to the inner part of the surface area, which has been described under the name of the trigonum hypoglossi. Within the nucleus the axons of the cells arrange themselves in converging bundles of fine fibres, which come together and leave the ventral aspect of the nucleus as the fasciculi of the nerve. The nerve bundles thus formed traverse the entire antero-posterior thickness of the medulla between the formatio reticularis grisea and the formatio reticularis alba, and emerge on the surface in linear order at the bottom of the furrow between the olivary eminence and the pyramid. In the substance of the medulla the root- bundles of the hypoglossal pass between the main inferior olivary nucleus and the mesial accessory olivary nucleus, and many of them on their way to the surface pierce the ventral lamina of the main olivary nucleus. No decussation between the nerves of opposite sides takes place in the medulla, but commissural fibres pass between the two nuclei (Kolliker). Further, numerous fibres from the opposite pyramidal tract enter the nucleus and end in connexion with its cells. The nucleus is thus brought into connexion with the motor area of the opposite side of the cerebral cortex. Spinal Accessory Nerve (nervus accessorius). — The spinal accessory is likewise a motor nerve, and it is generally described as consisting of a spinal and a medullary or accessory part. Column of GoU Column of Burdach POST.ROO ANTROG, Fig. 415. — Diagram of the Spinal Origin of the Spinal Accessory Nerve (after Bruce). Entering — posterior nerve root Substantia gelatinosa Rolandi Emerging ■ — fascicle of spinal accessory nerve Fibres of origin — of spinal accessory Emerging — anterior nerve root Fig. 416. — Section through the Upper Part of the Cervical Region of the Cord (Orang), Showing the origin of the spinal part of the spinal accessory nerve. The spinal part of the nerve emerges by a series of roots which issue from the surface of the lateral column of the upper part of the cord as low down as the fifth cervical nerve. These take origin in a column of cells situated in the anterior horn of gray matter of the cord close to its lateral margin, and immediately behind the nerve-cells which give rise to the fibres of the anterior roots of the upper five cervical nerves. The cells of the accessory nucleus are large, multipolar, and in every respect similar to the motor cells of the spinal nerves. The axons from these cells leave the dorsal aspect of the nucleus in converging groups to form the root- bundles of the nerve. These, in the first place, proceed straight backwards in the anterior horn of gray matter. Reaching the bay between the two horns of gray matter, they turn sharply outwards into the white matter and traverse the lateral column to gain their points of exit from the cord. At the decussation of the pyramids, root-bundles, which join the spinal accessory nerve, are seen to proceed from the detached head of the anterior horn of gray matter. The medullary part of the spinal accessory nerve has its nucleus of origin in the medulla ; and its root-bundles, as they proceed outwards from this, can be distin- THE DEEP CONNEXIONS OF THE CEANIAL NEEVES. 517 guished by the tact that they pursue a course on the ventral side of the spinal root of the trigeminal nerve, whereas the vagus roots, with which they are apt to be confused, pass through or lie on the dorsal aspect of the trigeminal root (Kolliker). The nucleus of origin of the medullary part of the accessory nerve is formed by the same column of cells which constitutes the nucleus ambiguus, and which, at a higher level, gives motor fibres to the vagus and glossopharyngeal nerves. The part of the spinal accessory nerve which takes origin in the spinal cord supplies the stemo -mastoid and tiapeziiis muscles. The medullary or accessor}- portion joins the vagiis, and through the external and recurrent lar^Tigeal nerves it supplies the muscles of the larj-nx. The portion of the nucleus ambiguus from which it arises has tlius been termed the laryngeal nucleus (Edinger). Collaterals and fibres of the opposite pyramidal tract end in connexion with the cells of origin of the accessory nerve, and thus bring its nucleus into connexion with the motor area of the cerebral cortex. Fibres also from the posterior roots of the spinal nerves (afferent or sensory fibres) end in the nucleus. Va^s and Glossopharyngeal Nerves (nervus vagus, nervus glossopharyu- geus). — These nerves present similar connexions with the brain, and they may therefore be studied together. The greater part of both nerves is composed of afferent fibres, which arise outside the brain-stem from ganglionic cells placed in relation to the nerve-trunks. Both nerves likewise possess motor or efferent fibres, which spring from two special nuclei of origin situated within the medulla and termed respectively the dorsal motor nucleus and the nucleus ambiguus. The afferent ganglionic fibres of the vagus and glossopharyngeal enter the brain by a series of roots which penetrate the medulla along the outer or ventral side of the restiform body. Within the medulla they separate into two sets, viz. a series of bundles (chiefly composed of vagus fibres), which end in the dorsal nucleus of termination of the vagus and glossopharyngeal nerves, and another series of bundles (chiefly composed of glossopharyngeal fibres), which join a conspicuous longitudinal tract of fibres called the fasciculus solitarius. The dorsal nucleus (Figs. 398, p. 495, and 402, p. 497) of the vagus and glosso- pharyngeal nerves is mixed, and contains both motor cells which give origin to efferent fibres and cells around which afterent fibres of the vagus, and possibly also of the glossopharyngeal nerve, break up into terminal arborisations. It very nearly equals in length the nucleus of the hypoglossal nerve, with which it is closely related. Above, it reaches as high as the strife acusticse, whilst below its lower end falls sUghtly short of that of the hypoglossal nucleus. In specimens stained by the "Weigert-Pal method the two nuclei offer a marked contrast. The hypoglossal nucleus presents a dark hue, owing to the enormous numbers of fine fibres which twine in and out amidst its cells ; the vago-glossopharyngeal dorsal nucleus is pale from the scarcity of such fibres within it. In the closed part of the medulla the dorsal vago-glossopharyngeal nucleus lies in the central gray matter immediately behind the hypoglossal nucleus, and upon the lateral aspect of the central canal ; in the open part of the medulla it lies in the gray matter of the floor of the fourth ventricle, immediately to the outer side of the hypoglossal nucleus and subjacent to the surface area termed the trigonum vagi. The ceUs in the portion of the dorsal nucleus which acts as a nucleus of termination are spindle-shaped in form and similar to those found in the posterior horn of gray matter in the cord. In connexion with these cells, the greater number of the afferent fibres of the vagus nerve, and a small proportion of the afterent fibres of the glossopharyngeal nerve end in fine terminal arborisations. A small part of the upper portion of the nucleus may be said to belong to the glosso-pharyngeal nerve aud the remainder of the nucleus to the vagus nerve. The cells which constitute the dorsal motor or efferent nucleus as seen in trans- verse section appear in a more or less compact cluster, which lies immediately to the outer side of the hypoglossal nucleus. These cells, although very conspicuous, are not so large as those in the hypoglossal nucleus, nor as those in the anterior horn of gray matter of the cord ; nor do they stain so deeply. The fasciculus soUtarius (Figs. 397, p. 493 ; 398, p. 495 ; and 402, p. 497) is a round bundle of longitudinal fibres which forms a very conspicuous object in trans- verse sections through the meduUa. It begins at the upper limit of the medulla, 37 « 518 THE NEEVOUS SYSTEM. and can be traced downwards through its whole length. Its precise point of termination is not known, but it is believed that it is carried for some distance downwards into the upper part of the cord, viz. to the level of the fourth cervical nerve, according to Kolhker. The relations of the fasciculus solitarius are not the same in all parts of its course. It lies immediately to the outer side of the dorsal vago-glossopharyngeal nucleus; but whereas in the upper part of the medulla it is situated somewhat on the ventral side of that nucleus, in the lower closed part of the medulla it is placed on its dorsal aspect. Throughout its entire length it is intimately associ- ated with a column of gelatinous gray substance which constitutes the nucleus of ter- mination in which its fibres end. When traced from above downwards, the solitary tract is observed to be- come gradually smaller from the loss of fibres which it thus sustains. The great bulk of the solitary tract is formed of fibres derived from the gl s s op hary n geal nerve ; only a few of the afferent fibres of the vagus enter it. As the fibres of the two nerves join the tract they im- mediately turn downwards, and at different levels come to an end in the associated gelatinous gray nucleus. As the root- bundles of the vagus and the glosso- phai'yngeal nerves traverse the substance of the medulla in a backward and inward direction to reach the fasciculus solitarius and the dorsal nucleus of termination, they pass through the spinal root of the trigeminal nerve and the substantia gelatinosa liolandi associated with it. The term ascending root is sometimes applied to the fasciculus sohtarius ; but as this conveys an altogether false conception of its character it should be discarded. The axons of the nucleus of termination and of the nucleus of the fascicidus solitarius form central connexions with other parts of the brain, but these have not as yet been completely elucidated. The dorsal efferent nucleus gives off fibres which join the afferent fibres of the vago-glossopharyngeal rootlets as they traverse the medulla, and mixing with them they X->ass along the same path to emerge from the medulla. The nucleus ambiguus (Figs. 398, p. 495, and 402, p. 497) also gives origin to Fig. 417. — Diagram, showing the brain connexions of the vagus, glosso- pharyngeal, auditory, facial, abducent, and trigeminal nerves. THE DEEP CONNEXIONS OF THE CKANIAL NERVES. 519 motor or efferent fibres which join the vagus and glossopharyngeal nerves. The cells which compose it are large, multipolar, and similar in every respect to the large cells in the ventral horn of gray matter of the spinal cord. These cells are arranged in a slender column which is best developed in the upper open part of the medulla. Here the nucleus can easily be detected in transverse sections as a small area of compact gray matter which lies in the formatio reticularis grisea, midway between the dorsal accessory olive and the substantia gelatinosa Eolaudi. It there- fore lies more deeply in the substance of the medulla than the mixed dorsal vago- glossopharyngeal nucleus. Kolliker states that it can be traced downwards as low as the level of the decussation of the fillet, and upwards as high as the place of entrance of the cochlear root of the auditory nerve. From its dorsal aspect the axons of the cells proceed, and in the first instance they pass backwards towards the floor of the lourth ventricle ; then, bending suddenly outwards and forwards, they join the afferent roots of the vagus and possibly also of the glossopharyngeal nerves, and emerge from the brain in company with these. Upon anatomical grounds it might be questioned whether the ghjssopharyngeal nerve contains any efferent fibres. It gives off, it is true, one motor branch, viz. to the stylo-pharjTigeus muscle, but there are paths by means of which these fibres might enter the nerve other than by coming directly from the motor nuclei, which have been described in connexion with the vago- glossopharyngeal nerve-roots. There is, further, some ground for the belief that all the fibres of the glossoi^liaryngeal pass into the fasciculus solitarius. In a very instructive case descril^ed by Alexander Bruce in which the glossopharyngeal was destroyed in the jugular foramen by the pressure of a tumour, no degenerated fibres could be traced beyond the fasciculus solitarius. Auditory Nerve (nervus acusticus). — -This is a large nerve which joins the brain at the lower border of the pons Varolii and on the ventral aspect of the restiform body. It is an afferent nerve, and its fibres spring from bipolar ganglionic cells either within or in the immediate neighbourhood of the labyrinth or internal ear (see section dealing with the organs of sense). Eeaching the brain the auditory nerve divides into two parts, viz. the nervus cochlearis and the nervus vestibularis, which present totally ditlerent connexions and apparently exercise absolutely distinct functions. In their further course these two divisions de\'iate from each other so as to embrace the restiform body — the vestibular part entering the pons on the inner or mesial aspect of the restiform body, whilst the cochlear part sweeps round its outer surface. Special nuclei of termination require to be studied in connexion with each part of the nerve. The cochlear nerve is composed of finer fibres than the vestibular nerve, and these acquire their medullary sheaths at a later period. It is the true nerve of hearing, and its fibres end in a ganglion which lies in intimate relation to the restiform body, and which may be described as consisting of two parts. Of these one, called the tuberculum acusticum or the lateral cochlear nucleus, is a pyriform mass which is placed on the outer aspect of the restiform body — between it and the flocculus of the cerebellum. The second part, termed the ventral cochlear nucleus, does not extend so low down as the tuberculum acusticum. It is a wedge- shaped nuclear mass which is placed on the ventral aspect of the restiform body in the interval between the cochlear and vestibular divisions of the auditory nerve, after they have separated from each other. The fibres of the cochlear nerve enter these two ganglia and end around the cells in terminal arborisations, which are finer, closer, and more intricate than those met with in any other nerve nucleus in the brain. The vestibular nerve enters the brain at a slightly higher level than the cochlear nerve and on the mesial aspect of the ventral cochlear nucleus. It forces its way backwards through the pons between the restiform body, which lies on its outer side, and the spinal root of the fifth nerve, which is placed on its inner side. Its fibres come to an end in three nuclei of termination, which are situated in the dorsal part of the pons and medulla, viz. (1) the principal nucleus or dorsal nucleus; (2) the nucleus of the descending root ; and (3) the nucleus of Deiters. The principal nucleus (Figs. 403, p. 500, and 418, p. o'lO) is a large diffuse nuclear mass, which lies in the floor of the fourth ventricle subjacent to the surface 37 h 520 THE NERVOUS SYSTEM. CORPORA QUADRIGEMINA district known as the area acustica (Fig. 391, p. 487). It is situated, therefore, in both the pons and the medulla to the outer side of the fovea superior and the fovea inferior. In transverse section it is prismatic in outline, and crossing the surface of its upper or pontine part immediately under the ependyma of the ventricle are the strife acusticse. When the nervus vesti- bularis, as it traverses the brain, reaches the inner aspect of the dorsal portion of the restiform body, a very large proportion of its fibres turn vertically downwards in separate bundles and form the de- scending root of the vesti- bular nerve (Figs. 398, p. 495; 402, p. 497; 403, p. 500; 418, p. 520). This proceeds through the lower part of the pons into the medulla, in which it may be traced as far as the level of the decussa- tion of the fillet. As- sociated with the descend- ing root there is a column of gray matter, with nerve- cells strewn sparsely throughout it. This is the nucleus of the de- scending root, and the fibres end in fine arborisa- tions around these nerve- cells. The fibres of the vestibular nerve likewise end in the nucleus of Deiters. This aucleus is composed of a number of large and conspicuous multipolar nerve-cells, which are scattered amidst the bundles of the upper part of the descending root of the vestibular nerve. As it is traced upwards into the pons the nucleus gradually inclines backwards, and finally it occupies a place in the lateral wall of the fourth ventricle. It attains its greatest development at the level of the emerging part of the facial nerve, and this upper part is sometimes termed the nucleus of Becliterew. Fig. 418. — Central CoNNfiXiONs of the Cochlear and Vestibular Divisions op the Auditory Nerve. (Diagram founded on drawings by Edinger and Ferrier and Turner.) Central Connexions of the Cochlear Nerve.— The cochlear nerve is brought into connexion with the inferior quadrigeniinal body, and the corpus geniculatum internum of the opposite side by the fibres of the corpus trapezoides and the lateral fillet. But this connexion is not direct ; the chain is composed of several separate links or neurons superimposed one over the other. The fibres of the cochlear nerve end in the ventral cochlear nucleus and in the tuber- culum acusticum. From the cells of these nuclei two tracts arise, viz. a ventral tract, composed of the fibres of the corpus trapezoides, and a dorsal tract, which is represented by the stria; aciisticte. The corpus trapezoides (Figs. 418 and 419) is formed of the axons of the cells of the ventral cochlear nucleus, as well as certain of the axons of the cells of tuberculum acusticum. In the midst of the corpus trapezoides are lodged large cells which are known as the nucleus trapezoideus, and these give off axons which join the strand with which they are associated. Further, the superior olive forms an important internode in the path of the corpus trapezoides. Many of the fibres of the corpus trapezoides end in this THE DEEP CONNEXIONS OF THE CEANIAL NERVES. 521 internode, whilst othei's are added to the tract from the cells of that nuclear mass. So constituted, the trapezial fibres cross the mesial plane and decussate with the correspond- ing fibres of the opposite side. Reaching the opposite superior olivary nucleus a further interchange of fibres takes place, and almost inmiediately after this the strand turns upwards and becomes the lateral fillet (Figs. 405, p. .503 ; 406, p. 504). But still another nucleus is interposed in its path, viz. the nucleus of the lateral fillet. Here some fibres are dropped, whilst from the nuclear cells others are acquired, and the lateral fillet then proceeds onwards without further interruption until it reaches the inferior quadrigeminal body and the corpus geniculatum internum, in which its fibres end. It is probable, however, that some likewise extend into the superior quadrigeminal body. But the latei-al fillet also includes the fibres of the striae acusticse of the opposite side. These fibres arise from the cells of the tuberculum acusticum, and arrange them- selves in the conspicuous bundles which sweep round the dorsal aspect of the resti- form body and proceed inwards across the floor of the fourth ventricle, immediately beneath the ependyma (Fig. 391, p. 487). Reaching the middle line they dip forwards into the substance of the medulla, and, crossing the mesial plane, thev join the lateral fillet. It is well to remember that the connexion between the terminal cochlear nuclei and the inferior quadrigeminal body is not altogether with that of the opposite side, as the foregoing description and the diagram (Fig. 418) might lead one to infer. A few fibres pass directly to the inferior quadrigeminal body of the same side, but none to the corre- sponding corpus geniculatum internum : the connexion with the latter is entirely crossed (Ferrier and Turner). From the corpus geniculatum internum there proceeds a tract to the gray cortex of the superior convolution of the temporal lobe. The whole nervous apparatus is thus linked on to the cerebral cortex, and the succession of neurons which build up the entire chain are therefore : ( 1 ) the bipolar cells of the ganglion spirale ; (2) the neurons of the terminal cochlear nviclei ; (3) the neurons of the superior olive and the nucleus of the lateral fillet ; (4) the neurons of the corpus geniculatum internum. It must be bpme in mind that all the axons of the cells of the superior olive do not join the trapezoid strand. Many leave its dorsal aspect and pass backwards in a group called the pedicle of the superior olive, to end in the nucleus of the sixth nerve, and, through the posterior longitudinal bundle, in the nuclei of the fourth and third nerves. In this way the organ of hearing is brought into connexion with the nuclei, which preside over the movements of the eyeballs (Figs. 403, p. 500, and 420, p. 523). Central Connexions of the Vestibular Nerve. — Although the central con- nexions of the vestibular nerve have been closely studied by many observers, they are still very far from being fully understood. The principal nucleus and the nucleus of Deiters both stand in intimate relation with the superior vermis of the cerebellum ; and in consideration of the fact that the vestibular nerve is the nerve of equilibration, this is an important and significant circumstance. The strand which establishes this con- nexion has been termed by Edinger "the direct sensory cerebellar tract," and in all probability it is an efferent tract from the cerebellum. Its fibres arise to a large extent in the cerebellar roof nuclei of the opposite side, and, crossing the mesial plane, they sweep forwards around the outer side of the superior cerebellar peduncle as it emerges from the cerebellum to end in the nucleus of Deiters, the chief vestibular nucleus, and very possibly also in the terminal sensory nuclei of certain other cranial nerves, such as the trigeminal, vagus, and glossopharyngeal. Until the precise nature of the nucleus of Deiters is discovei'ed, the exact character of the central connexions of the vestibular nerve will remain more or less obscure. It cannot be regarded as a nucleus specially given over to the vestibular nerve. Composed of large cells scattered amidst the bundles of the upper part of the descending root of the vestibular nerve, it only becomes a compact nucleus above the level of that nerve, viz. at the point where the restiform body turns backwai-ds into the cerebellum, or, in other woi-ds, at the level of the emerging facial nerve and the lower end of the abducent nucleus. Here, in the outer part of the floor of the fourth ventricle, its cells are gathered together in a crowded mass. Deiters himself considered that this nucleus should be regarded as an internode between the cerebellum and the spinal cord, and Ferrier and Turner have brought forward strong evidence in support of this view. Klimoff attaches a very high importance to the direct " sensory " tract of Edinger. From his description it would appear that he regai-ds it as the only cerebellar efferent tract which takes a downward direction. He believes, further, that the axons of the cells of Deiters form the anterior marginal tract of Lowenthal (tractus vestibulo-spinalis of Monakow), which oz 2v> THE NEEVOUS SYSTEM. descends in the antero-lateral column of the cord as far as the lumbar region. It is supposed that the fibres of this tract end in the cord in arborescent terminations around the motor cells in the ventral horn of gray matter. From what has been said it must be apparent that the nucleus of Deiters plays a most important part in connexion with the maintenance of the equilibrium of the body and the co-ordination of its muscular movements. Thus it constitutes an internode in the path of those fibres which connect the cortex and roof nuclei of the cerebellum with the motor apparatus of the spinal cord ; it receives fibres through the vestibular nerve from the labyrinth of the ear ; and it sends fibres into the posterior longitudinal bundle, through which it in all probability exercises some iniiuence over the nuclei of the ocular nerves. Opinion is also divided as to the composition and nature of the so-called descending root of the vestibular nerve. After division of the eighth nerve, Ferrier and Turner were unable to detect any degeneration in this root, and they therefore are inclined to call in question its direct continuity with the nerve. They consider that in all probability it forms an internuncial connexion between the nucleus of Deiters and the cuneate nucleus, in which Bruce has seen its lower end to terminate. Fig. 419. — Section thkough the Pons Varolii of the Orang, Showing the nucleus and intrapontine course of the facial nerve. The left side of the drawing is taken from a section at a slightlv lower level than the section from which the right side is taken. 1. Ascending part of facial nerve. 2. Posterior longitudinal bundle. 3. Descending root of eighth nerve. 4. Radicular fibres of facial nerve. 5. Restiforin body. C. Facial nucleus. 7. .Spinal root of fifth nerve. 8. Ve.stibular nerve. 9. Superior olive. 10. Fillet. 11. Pyramidal tract. 12. Transver.se fibres of pons. B 1. Ascending part of facial nerve. 2. Emergent portion of facial nerve. 3. Restiform body. 4. Nucleus of sixth nerve. 5. Sixth Nerve. 6. Emergent part of facial nerve. 7. Peduncle of superior olive. 8. Superior olive. 9. Corpus trapezoides. 10. Facial nerve. 11. Sixth nerve. 12. Pyramidal tract. 13. Transverse fibres of pons. Facial Nerve (nervus i'acialis) (Figs. 419 and 420). — The facial nerve is com- posed of two distinct parts, viz. a large efferent or motor portion, the facial nerve proper, and a small efferent sensory portion termed the pars intermedia of Wrisberg. The facial nerve emerges from the brain at the lower border of the pons, immediately in front and to the inner side of the auditory nerve, whilst the pars intermedia sinks into the upper part of the medulla between the facial and auditory nerves. The three nerves, therefore, lie in intimate relation with each other, where they are attached to the surface of the brain, and they pass in company into the internal auditory meatus. THE DEEP CONNEXIONS OF THE CRANIAL NERVES. 523 The nucleus of origin of the facial nerve is an oval mass of gray matter, about five mm. in length, and containing numerous groups of large multipolar cells. It is sunk deeply in the dorsal or tegmental part of the lower portion of the pons Varolii, and is placed close to the inner side of the spinal root of the fifth nerve. When transverse sections are made through the brain-stem, the facial nucleus is encountered the moment the boundary line between the medulla and pons is passed, and the region immediately above the inferior olivary nucleus is reached. At first it lies so deeply in the tegmentum of the pons that it actually rests upon the dorsal aspect of the corpus trapezoides ; but a little farther up the superior olive comes into view, and insinuates itself between the facial nucleus and the trapezial fibres. The upper part of the nucleus is in this way tilted somewhat backwards, and thus comes to lie on the dorsal and outer aspect of the superior olive. The facial nucleus is situated close to the place where the nerve emerges from the brain, but the nerve does not at once pass to this point of exit. It pursues a long and devious path within the pons before it finally reaches the surface. This intrapontine part of the nerve may be divided into three parts, viz. : (1) a radicular part, (2) an ascending portion, and (3) an emergent part. The radicular part of the facial nerve (Fig. 420) is composed of a large number of fine loosely-arranged bundles of fibres, which issue from the outer and dorsal aspect of the nucleus and proceed backwards and slightly inwards through the pons. Reaching the floor of the fourth ventricle they curve inwards, and the bundles which lie highest up sweep over the outer and dorsal aspect of the lower part of the nucleus of the sixth nerve. Close to the mesial plane they turn sharply upwards and are collected into a single solid nerve-bundle, which consti- tutes the ascending part of the facial nerve (Figs. 419 and 420). This proceeds vertically upwards immediately beneath the ependyma of the ventricular floor, on the dorsal aspect of the posterior longitudinal bundle, and along the inner side of the sixth or abducent nucleus for a distance of about five milli- metres. Suddenly the nerve bends outwards at a right angle, and curves a second time over the dorsal aspect of the sixth or abducent nucleus. The nerve now passes straight to the place of exit from the brain, and this part of the intrapontine trunk may be termed the emergent portion (Figs. 419 and 420). The facial nerve thus forms a curved loop over the dorsal aspect of the abducent nucleus. The emergent part of the nerve takes an oblique course through the pons to reach the surface. It inclines outwards and downwards as it proceeds towards the ventral aspect of the pons, and on its way it passes between its own nucleus and the spinal root of the fifth nerve. Fig. 420.- -DlAGRAM OF THE INTRAPONTINE CoURSE PURS0ED BY THE Facial Nerve. Entering tlie facial nucleus, and ending in fine terminal arborisations around its cells, are many fibres from the opposite pyramidal tract ; fibres from the sj^inal root of the fifth nerve ; fibres from the corpus trapezoides, etc. The nucleus is thus brought into connexion with the motor area of the cerebral cortex, with the trigeminal nerve or sensory nerve of the face, and with the auditory nerve, etc. 524 THE NEEVOUS SYSTEM. The fibres of the pars intermedia of Wrisberg arise from the cells of the geni- culate ganglion of the facial nerve. These, like the cells of a spinal ganglion, are unipolar, the single process in each case dividing into a peripheral and a central branch. The group of peripheral fibres represent the chorda tympani branch of the facial nerve, whilst the central fibres form the pars intermedia. The latter penetrate the brain, and, passing either through or on the dorsal side of the spinal root of the fifth nerve, they finally reach the upper part of the column of gray matter in connexion with the fasciculus solitarius, and in this they end. The pars intermedia presents, therefore, the same terminal connexions within the brain as the glossopharyngeal nerve. Efferent secretory fibres are also described as being present in the pars intermedia. These are said to spring from cells wliich constitute a salivary nucleus placed in the pons on the dorsal aspect of the facial nucleus. Abducent or Sixth Nerve (nervus abducens) (Eigs. 419 and 420).- — This is a small motor nerve which emerges from the brain at the lower border of the pons on the outer side of the pyramid of the medulla. It is the nerve of supply to the external rectus muscle of the eyeball. Its nucleus of origin is a small spherical mass of gray matter, containing large multipolar cells, which lies in the dorsal part of the tegmental portion of the pons, close to the mesial plane and immediately subjacent to the gray matter of the floor of the fourth ventricle. Its position can be easily indicated on the ventricular floor, seeing that it is placed subjacent to the emenentia teres and immediately above the level of the striae acusticas. Its peculiar and intimate relation to the intrapontine portion of the facial nerve has already been indicated. It lies on the ventral aspect of, and within the concavity formed by, the two limbs of the loop of that nerve. The axons of the multipolar cells of this nucleus emerge from the inner aspect of the nucleus in the form of several bundles, which proceed through the whole antero-posterior thickness of the pons towards the place of exit. As they pass forwards they incline downwards and slightly outwards. In the tegmental part of the pons they proceed forwards on the inner side of the superior olive, whilst in the ventral part of the pons they keep for the most part to the outer side of the pyramidal bundles, although several of the nerve fasciculi pierce these on their way to the surface. It would appear probable that certain of the axons of the cells of the abducent nucleus enter the posterior longitudinal fasciculus and proceed upwards in it to join the third or oculo- motor nerve of the oj^posite side. Further mention of these will be made later on. Fibres and collaterals from the pyramidal tract of the opposite side enter the nucleus, and, ending around the cells, bring the nucleus into connexion with the motor area of the cerebral cortex. The pedicle of the superior olive ends partly within the nucleus of the abducent nerve (p. 621). Trigeminal or Fifth Nerve (nervus trigeminus). — The trigeminal nerve strikes its roots deeply into the brain and establishes a connexion with it which extends from the upper part of the mesencephalon above to the level of the second cervical nerve below. No other cranial nerve presents so extensive a connexion (Fig. 417, p. 518). It is composed of two roots — a large afferent or sensory root and a small efferent or motor root. Both roots appear close together on the surface of the pons, rather nearer its upper border than its lower border, and in the same line as the facial and auditory nerves. The sensory root of the fifth nerve is composed of fibres which arise outside the brain from the cells of the G-asserian ganglion. They end within the brain in two nuclei of termination. One of these is situated in the pons and is termed the sensory nucleus of the trigeminal nerve, and tlie other is a long column of gray matter which is directly continuous below with the substantia gelatinosa Eolandi of the spinal cord. The sensory nucleus (Fig. 421) is an oval mass of gray matter which is placed half-way up the pons in the outer part of its tegmental portion. It lies close to the outer surface of the pons and immediately subjacent to the ventral submerged margin of the superior cerebellar peduncle. It is directly continuous with the substantia gelatinosa Eolandi, and may be regarded as being merely the enlarged upper end of that column of gray matter. THE DEEP CONNEXIONS OP THE CEANIAL NEKVES. 525 The fibres of the sensory root of the fifth nerve, on reaching the sensory nucleus, divide in a manner similar to the fibres of the entering posterior roots of the spinal nerves into a system of ascending and descending branches (Fig. 417, p. 518). The ascending fibres are short, and almost immediately enter the sensory nucleus and end within it ; the descending fibres turn sharply downwards and form the spinal root (tractus spinalis : the ascending root of many text-books). This root descends on the outer side of the column of gray matter formed by the substantia gelatinosa Eolandi, which constitutes its terminal nucleus. Fibres constantly leave it to enter the nucleus, so that tlie lower it gets the smaller does the spinal root become until, in the upper part of the spinal cord, about the level of the first or second spinal nerve, it disappears altogether. Superior cerebellar peduncle Mesencephalic root of the fifth nerve Alotor nucleus of the fifth nerve >[otor root of tlie fifth nerve-— Sensory nucleus of the fifth nerve Superior olive - Sensory root of ^^ fifth nerve^ ^ ~ _ Middle peduncle of cerebellum Superior medullary velum or valve of Vieussens Floor of s-entricle IV'. Posterior longitudinal fasciculus Format io reticularis Fig. 421. -Section through the Pons Varolii of the Orang, at the Le\t;l of the Nuclei OF the Trigeminal Nerve. The large spinal root of the fifth nerve is a conspicuous object in sections through the pons and medulla. In the former it traverses the tegmental part, first, between the emei-gent part of the facial nerve and the vestibular nerve ; and then lower down, between the restiform body and the nucleus of the facial nerve (Fig. 419, A, p. 522). In cross sections it presents a well-defined semilunar or curved pyriform outline. In the upper part of the medulla it lies on the ventral aspect of the restiform body, and therefore nearer to the surface (Fig. 398, p. 495). Here it is traversed and broken up into separate bundles by the cerebello-olivary fibres and the roots of the glossopharyngeal and vagus nerves. Finally, it comes to the surface and its fibres are spread over the area on the side of the medulla known as the tubercle and funiculus of Rolando (Fig. 394, p. 492). The small motor part of the trigeminal nerve is chiefly distributed to the muscles of mastication, and derives its fibres from two sources, viz. from the motor nucleus and from the mesencephalic root of the trigeminal nerve. The motor nucleus (Fig. 421) lies in the lateral part of the tegmental portion of the pons, close to the inner side of the sensory terminal nucleus, but somewhat 526 THE NEEVOUS SYSTEM. nearer to the floor of the fourth ventricle. It is not placed iu the exact line of the facial nucleus, as it is situated somewhat nearer the dorsal aspect of the pons ; but, nevertheless, it may be considered as being equivalent in this region to the detached head of the anterior horn of graj matter in the lower part of the medulla. The cells of this nucleus are large and multipolar, and their axons run together to form the greater portion of the motor root of the fifth nerve. The mesencephalic root takes origin in the mesencephalon from a column of large loosely-arranged cells which are placed in the extreme lateral part of the gray matter which surrounds the Sylvian aqueduct. As the lower end of this column of cells reaches the pontine part of the floor of the fourth ventricle it becomes continuous with the dark cells of the locus coeruleus. The mesencephalic root as it is traced downwards gradually gains strength by the addition of new fibres, and it assumes a crescentic form in transverse section (Figs. 430, p. 535 ; 432, p. 537 ; 407, p. 505 ; 406, p. 504). In the lower part of the mesencephalon it lies on the inner side of the superior cerebellar peduncle ; and the fourth nerve, on its way to the surface, runs downwards in its concavity and on its mesial aspect. In the upper part of the pons, it continues its course downwards on the outer and deep aspect of the gray matter which forms the floor of the fourth ventricle, and here it stands in relation to the cells of the locus coeruleus. Finally, reaching the level of the nuclei of the trigeminal nerve, the fibres of the mesencephalic root turn forwards and join the motor part of the trigeminal nerve (Fig. 421). S. Eamon y Cajal lias shown tliat an intimate relationship is established between the mesencephalic nucleus and the principal motor nucleus of the trigeminal nerve. Large numbers of collaterals from the fibres of the mesencephalic root enter the latter nucleus and break up into close networks around its cells. It has been suggested that through this connexion a weak impulse proceeding from the higher nucleus may be transformed within the lower or princijDal nucleus into a powerful excitation. (1) It is not known to what parts the fibres of the mesencephalic root go. KoUiker suggests that they sujjply the tensor veli palatini and the tensor tympani ; perhaps, also, they may be dis- tributed to the mylo-hyoid and the anterior belly of the digastric. (2) Fibres from the ojjposite pyramidal tract go to the motor nucleus and bring it into connexion with the motor area of the cerebral cortex. (3) By degeneration methods the root of the fifth nerve has been traced down to the level of the second cervical nerve (Ferrier and Turner). (4) The axons of the terminal nuclei emerge as arcuate fibres, and, proceeding through the raphe, assume a longitudinal course in the tegmentum of the opposite side, and thus establish connexions with parts higher up (tractus quinto-thalamicus). (5) Some of the axons of the cells of the terminal nucleus enter the motor nucleus, and thus establish a simple reflex apparatus. The Development of the Parts derived from the Ehombencephalon. A general sketch of the development of the me'dulla, pons, and cerebellum has already been given (p. 476). It is only necessary, therefore, in this section to call attention to some of the more important details connected with the pi'ocess. Medulla. — In the embryo the cervical flexure indicates in a sharp and definite manner the point of junction between the cord and the brain (Fig. 382, p. 477). In the early condition of the rhombencephalon the calamus scriptorius extends downwards to this level, so that, in the first instance, there is no part of the medulla which corresponds to the closed portion present in the adult. The lower closed part of the medulla makes its appearance at a later period, and is termed by His the intercalated portion (Schaltstlick). In our study of the development of that part of the neural tube which forms the spinal cord we have recognised two thick lateral walls connected in front and behind by narrow mid-ventral and mid-dorsal laminse. The same parts are seen in the developing medulla. Owing, however, to the expansion of the cavity in this portion of the tube the mid-dorsal lamina is stretched out into an extensive and thin epithelial membrane which forms the dorsal wall or roof of the ventricle in this section of the early brain. The thick lateral walls have also fallen away from each other, and are joined in front by the narrow mid-ventral lamina. On section, therefore, the medullary part of the neural tube presents a triangular figure — the base, which is directed backwards, being formed by the thin epithelial expansion derived from the mid-dorsal lamina, the apex by the narrow mid- ventral lamina, and the sides by the thick lateral walls of the tube. Further, each lateral wall consists of an alar or dorsal and a basal or ventral lamina. Tliis subdivision is more clearly indicated than in the cord, and on the inner surface of the lateral wall a strongly- marked longitudinal furrow marks the line of junction of the two laminae. The histo- DEVELOPMENT OF THE MEDULLA. 527 «f;*«/s/- logical development of these several parts of the wall of the medullary portion of the neural tube proceeds in a manner very similar to that already detailed in the case of the cord. No neuroblasts are formed in the mid-ventral and mid-dorsal laminse ; the entire neuroblastic formation is confined to the basal and alar lamina;. Within the basal lamina, likewise, are collected the neuroblasts which form the nuclei of origin of the effei-ent nerves ; whilst within the alar lamina are developed the neuroblasts which constitute the nuclei of termination for the fibres of the afferent nerves. As development pi'oceeds, the two laminae of the lateral wall fall outwards to a still greater extent, so that they come to lie very nearly in the same horizontal plane. In this manner their originally mesial or ventricular surfaces come to form the floor of the fourth ventricle. Even in the adult the groove, which sepai-ates the basal and alar laminae so clearly from each other in the early con- dition, is more or less distinctly perceptible on the ventricular floor. It is represented by the fovea inferior and by the fovea superior. Between these depressions and the mesial groove on the floor of the fully -developed fourth ventricle there is an elongated eleva- tion, which, in its lower part, forms the tri- gonum hypoglossi, above this the emenentia teres, whilst higher up it is continued towards the commencement of the Sylvian aqueduct. This clearly-marked and bulging mesial strip of the ventricular floor corresponds to the basal lamina, whilst the part of the floor which lies to the outer side of it and the two foveas is derived from the alar lamina. The latter, therefore, includes the trigonum vagi, the area acustica, and the locus coeruleus. The further development of the medulla takes place on the ventral aspect of the two laminae by the deposition of new parts on those which are already formed. An oval bundle of longitudinal fibres makes its ap- pearance on the outer surface of the alar lamina, at the point where this joins the basal lamina. This is the early fasciculus solitarius. It is composed of afferent fibres from the glossopharyngeal and vagus nerves. These, on I'eaching the surface of the medulla, turn downwards upon it. At first the con- nexion of the fasciculus solitarius with the medulla is very loose, and it may be regarded as being the equivalent in this part of the neural tube of the oval bundle of longitudinal fibres which, in the early cord, constitutes the first stage of the column of Burdach. Throughout the further stages of development the fasciculus solitarius in- dicates in a sufliciently clear manner the point of jvinction between the alar and basal laminae. Very soon it becomes covered over by parts developed on its ventral aspect, and it ultimately comes to lie deeply in the substance of the medulla. This change in the position of the fasciculus solitarius with reference to the surface is asso- ciated with a striking developmental process which leads to certain remarkable results, and which is termed the formation of the rhombic lip of His (Fig. 422, B and C). Before the alar lamina falls outwards, while it still stands erect and its inner surface faces the corresponding surface of the opposite lamina, its dorsal edge is folded outwards and becomes fused with the outer surface of the remaining portion of the alar lamina. This HOMBIC LIP HYPOGLOSSAL Fig. 422. — Three Stages in the De\t;lopment of THE Medulla Oblongata (from His — slightly modified). 528 THE NERVOUS SYSTEM. is the rhombic lip, and, when the fusion is complete, a multitude of neuroblasts take form within it and migrate in a forward and inwards direction into the ventral parts of the alar and basal laminae. The mid-ventral lamina — which consists of spongioblastic cells alone, and which forms a narrow partition between the two basal laminae — is reached on either side by the axons of many of these migrating cells. Whilst acting as an impassable barrier to the neuroblasts, this spongioblastic septum gives free passage from one side to the other to their axons, and a decussation of arcuate fibres in the mesial plane results. In this way the raphe of the medulla is formed. The process is very similar to that which takes place in the course of the formation of the anterior coinmissure of the cord, of which the raphe may be regarded as the equivalent in the medulla. The development of the inferior olivary nucleus and of its two accessory parts is like- wise closely connected with the migration of the neuroblasts from the region of the rhombic lip. Many of these cells collect together so as to form a nuclear lamella, which afterwai'ds assumes its characteristic crumpled form. As the neuroblasts of the rhombic lip stream inwards they pass both on the dorsal and the ventral aspects of the fasciculus solitarius, which thus comes to be covered over and separated from the surface. The spinal root of the trigeminal nerve, like the fasciculus solitarius, is also, in the first instance, throughout its entire course on the surface of the medulla, and its change of position in the greater part of its course within the pons and medulla is due to the subsequent development of those parts which cover it over. The importance of the rhombic lip in the development of the medulla will be better appreciated if we enumerate the parts which spring from it : (1) the inferior olivary nuclei; (2) the cuneate nucleus ; (3) the substantia gelatinosa Rolandi ; (4) the arcuate nucleus ; (5) the internal arcuate fibres ; (6) the olivary system of fibres ; (7) the restiform body. From this it is evident that the formation of the rhombic lip constitutes an extremely important step in the development of the human brain. Recent investigation, however, makes it clear that in most of the lower mammals the rhombic lip does not attain any- thing like the degree of prominence which it presents in the early brain of man. The pyramidal tracts which come down from the cerebral cortex are late in making their appearance in the medulla. The formatio reticularis precedes them in development. They appear in the fourth month of fcetal life, and as they are developed the antero- median furrow between them takes form on the ventral aspect of the medulla. His has pointed out that the earliest formed part of the medulla is the floor of the fourth ventricle, and that the other parts, speaking generally, are added in succession as we pass towards the surface. " The oldest layer of the medulla is the floor of the fourth ventricle with its nuclei. It is followed, in the first instance, by the reticular formation, and afterwards by the layer containing the olivary and other nuclei. Last of all come the pyramids and the outer (superficial) arcuate fibres " (His). Pons Varolii. — The information which we possess at the present moment regarding the development of the pons Varolii is somewhat deficient ; but there is little doubt that the course pursued is, in general, very similar to that which has been described for the medulla. It has been seen to be composed of parts which are in a great measure equivalent to those met with in the medulla, the formatio reticularis of the latter passing into the tegmental substance in the former, while the pyramids and arcuate nuclei and anterior superficial arcuate fibres of the medulla are represented by the large venti'al part of the pons. Further, as His points out, similar relations between the chronological and local succession of layers may be recognised. Thus the primitive position of the motor nucleus of the trigeminal nerve, and also of its spinal root, is a superficial one, and it is only by a later process of develoj^ment that the nucleus pontis and the thick layer of transverse and longitudinal fibres are formed. From the phylogenctic point of view the tegmentum is the oldest part of the pons. The study of the compai^ative anatomy of the brain makes it evident that the large ventral part is comparatively a recent acquisition. As the cerebral cortex extends with the increasing evolution of the cerebral hemispheres (pallium), the ventral part of the pons is seen to keep pace with it in its development. This should easily be understood from what has been said in regard to its structure and connexions. It is composed of the nucleus pontis, the transverse fibres, and the pyramidal and cortico-pontine fibres, all of which stand in direct relation to the cerebral cortex. One of the striking features of the brain of a microcephalic idiot, where the cerebral cortex is greatly rediiced, is the corresponding marked diminution in the size of the ventral part of the pons. Cerebellum. — The roof of the fourth ventricle is formed for the most part by the thin epitholi^d layer already described as being formed Vjy the expanded mid-dorsal lamina. DEVELOPMENT OF THE CEREBELLUM. 529 This does not stretch, however, over its entire extent. As we approach the upper part of the ventricle, it is seen to become continuous in the region of tlio isthmus with a thicker lamella. This lamella is bounded above by the intercrossing of the two trochlear nerves, which marks on the dorsal aspect of the neural tube the place of junction between the rhombencephalon and the mesencephalon ; hdow, it is limited by a forwardly-directed semilunar fold of '^^tL the thin epithelial ventricular roof, which takes place into the ventricular cavity at the level of the pontine flex- ure of the brain. The fold so con- stituted is termed the plica choroidea, seeing that meso- derm is introduced between its two layers, and this ul- timately gives rise to the choroid plexus of the fourth ventricle (Fig. 425, A) MONTICULUS wr B C Drawings to illustrate thk Development of the Cerebellum (from Kuithan). Transverse section through the forepart of the cerebelluni of a sheep eiiiliryo. Transverse section through the hinder part of the cereliellum of a sheep embryo. Cerebellum of a human foetus 17 cm. long. 1. Sulcus primarius. 3. Sulcus infrapyramidalis. 2. Sulcus suprapyramidalis. " 4. Fissura post-lunata. r.l. Lateral recess ventricle IV. Mesencephalon Early cerebellum Cavity of fourth ventricle The lamella whicli forms tlie roof or dorsal wall of the ventricle in front of the plica choroidea is developed into the cerebellum, and the superior medullary velum (valve of Vieussens). The cerebellar part of this lamella consists of two thick lateral plates which meet in the middle line and are joined there by an extremely thin dorsal seam or lamina (Fig. 423, A). The inner extremities of the two cerebellar plates are thus separated by a median groove, which opens into the cavity of the hind-brain (fourth ventricle). The statement, there- fore, that the median lobe or vermis of the cerebellum is the most archaic part of the organ and is the part which IS developed nrst is not supported by fact ; indeed, the reverse of this is the case, because at this early stage the lateral portions are alone represented. In the course of time the inner ends of the cere- bellar plates become fused in the middle line, and the median furrow between them disappears. In the process of this fusion the deep part of the intervening furrow remains enclosed within the substance of the median part of the cerebellum and persists for Fiti. 424. — The Brain op an Embryo ok eleven weeks, viewed from a short time as a minute behind to show the development of the cerebellunL At this stage the cerebellar ventricle (Blake), cerebellum is in the form of a simple band or plate which arches over The cerebellum llOWDre- the hinder aspect of the fore part of the cavity of the hind brain (from . .i K jjj^x r r J sents the appearance or a simple uniform arch which bridges across the dorsal aspect of the upper part of the early fourth ventricle ; and very soon the sulci begin to appear. Of late years the development and morphological import of these sulci have received much attention. Stroud, Kuithan, Blake, Flliot Smith, and Bradley have published valuable papers on this subject, and what is written here is largely gathered from the writings of these observers. Further, the terminology suggested by Elliot Smith has been chiefly, but not entirely, followed. The first fissure to appear is the floccular fissure, which cuts off the postero-lateral corner of the cerebellar plate. The portion thus marked off is the flocculus, and its early appearance and relatively large size at this stage are significant of its high morphological 38 Medulla 530 THE NEKVOUS SYSTEM. SUR N/IED VEL. Fig. 425. A. Mesial section through the cerebellimi of an early liuman foetus (semi-diagrammatic). B. Mesial section through the cerebellum of a human foetus 17 cm. long (from Kuithan). 1. Fissura prima. 4. Fissura postnodularis. 2. Fissura suprapyramidalis. T. Transverse groove on the roof of 3. Fissura infrapyramidalis. the foiirth ventricle. Nodnle Uvula Post-nodular Assure / importance as a lobule of the cerebellum. The floccular fissure is continued inwards close to the posterior border of the cei-ebellar plate, join- ing its fellow of the opposite side in the middle line. Here it receives the name of post-nodular fissure. A narrow strip of cerebellar surface is thus marked out. The median part of this strip, by special growth, be- comes the nodulus, whilst the part which extends between this and the flocculus remains narrow and band-like, and ultimately forms a portion of the inferior medullary velum. The next furrow which appears is the sulcus prim- arius (Kuithan) or fissura prima (Elliot Smith). It cuts deeply into the vermis in a transverse direction be- tween the culmen monticuli and the clivus monticuli, and is then carried outwards over each hemisphere so as to separate the two crescentic lobules. The fissura prima is the deepest of all the fissures of the vermis, and it is developed towards the end of the third month. A little later two other fur- rows are observed in the vermis. These are the suprapyramidal and the infrapyramidal (the fissura secunda of Elliot Smith). By the former the pyramid is limited above ; by the latter the pyramid is separ- ated from the uvula. After the main fissures of the vermis are estab- lished, four important sulci on the surface of each cerebellar hemisphere come into view, viz. the postlunate post-tonsillar, the parapyramidal, and the great horizontal sulci. The fissura postlunata ap- pears in the fourth month, and curves inwards on the upper surface of the organ behind the posterior crescentic lobule. In many cases it becomes con- fluent with its fellow of the opposite side behind the clivus monticuli. The posttonsillar fissure is seen on the under surface of the cerebellum about thcbeginningof thefifth month. It circumscribes the prominent and conspicuous tonsil and becomes confluent with the fissura infrapyi-amidalis. The parapyramidal fissure ap])cars on the under sui-face of the cerebellar hemisphere behind the bivcntral lobule, and usually joins the suprapyramidal fissiire of the inferior vermis. Ploccular fissure. Tonsil Biventral lobule. Flocculus Paraflocculus Peduncle of flocculus Post- tonsillar sulcus Parapyramidal sulcus Postero-inferior lobule Infrapyramidal fissure / Suprapyramidal fissure \ Pyramid Tuber valvula Great liorizontal sulcus Fig. 426. — Under Surface of the Cerebellum of a Human F(etus which has reached the end of the fifth month of development. the fJuhnen monticuli Clivus monticuli | Fissura prima Fissura postlunata Postero-superior lobule Fig, Suprapyramidal fissure 427. — Cerebellum of a Great horizontal Hssurii N Postero-inferior lobule Infrapyramidalis liss\ire Human Fostus which has reached THE End of the above aud behind. Fifth Month op Development. Viewed from THE MESENCEPHALON. 531 The great horizontal fissure, in spite of its depth in the adult brain — a depth which is due to the excessive growth in the later months of development of the two lobules that bound it — appears very late in the development of the cerebellum. It is first seen as a verv broad shallow gi-oove or furrow on the outer margin of the hemisphere. From this it runs forwards to the middle peduncle and backwards towards the vermis, where it usuallv joins the postlunate fissure. At this stage there is no folium cacuminis, so that tlie combined portion of the postlunate and great horizontal fissures intervenes between the clivus monticuli and the tuber valvule. Even at the time of birth the folium cacuminis is not seen on the sui'face. It rises up from the bottom of the combined portions of the great horizontal and postlunate fissures so as to form a barrier between them. Verv early a transvei-se groove appears on the smooth anterior or ventricular surface of the cerebellum (Fig. 425, B, t). This is placed much nearer the lower than the upper border of the organ, and it represents at this stage the angular peak of the tent-like roof of the fourth ventricle in the adult brain. As growth goes on, the portions of the cere- bellum in front and behind this groove approach each other, so as to deepen the groove and bring about the backward prolongation of the ventricular cavity towards the cerebellum. The leading distinctive characters of the hviman cerebellum are: (1) the small size of the flocculus : (2) the lai-ge size of the tonsil ; (3) the excessive development of the lateral hemisphere, and particularly of the postero-superior and postero-inferior lobules which bound the great hoi'izontal fissure. THE MESENCEPHALON. The mesencephalon or mid-brain is the short, narrow part of the brain -stem which occupies the aperture of the tentorium cerebelli (incisura tentorii), and connects the cerebrum which lies above with the parts which occupy the posterior cranial fossa. It is about three-quarters of an inch in length, and it consists of a dorsal part, composed of the corpora quadrigemina, and a much larger ventral part, which is formed by the two crura cerebri. In the undissected brain the corpora quadrigemina are completely hidden from view by the splenium of the corpus callosum, which projects backwards over them, and also by the superimposed cerebral hemispheres. The hinder end of each optic thalamus likewise, to some extent, overhangs the upper part of the mesencephalon on its dorsal and lateral aspect (Fig. 388, p. 482). On this portion of the optic thalamus are seen two projections, which are specially related to the mesencephalon. These are the cushion-like pulvinar, which forms the inner and hinder part of the thalamus, and the corpus geniculatum externum, an ill-defined oval swelling on the outer and under aspect of the posterior end of the thalamus. The crura cerebri can to some extent be seen on the base of the brain, where they bound the posterior part of the interpeduncular space. Encircling the upper end of each cms cerebri, where it plunges into the cerebrum, is the optic tract (Fig. 380, p. 474). The mesencephalon is tunnelled from below upwards by a narrow^ passage, caUed the aqueduct of Sylvius, which connects the fourth ventricle with the third ventricle (Fig. 429, p. 533). This channel lies much nearer the dorsal than the ventral aspect of the mesencephalon. Corpora Quadrigemina. — This name is applied to four rounded eminences on the posterior aspect of the mesencephalon (Fig. 388, p. 482). The superior pair are larger and broader than the inferior pair, but they are not so well defined nor are they so prominent. A longitudinal and a transverse groove separate the quad- rigemina! bodies from each other. The longitudinal groove occupies the mesial plane and extends upwards to the posterior commissure of the brain. The upper end of this groove widens out into a shallow depression, in which the pineal body, a small conical structure which belongs to the diencephalon, rests. From the lower end of the same groove a short but well-defined and projecting band, the frenulum veli, passes to the valve of Vieussens, w^hich Hes immediately below tjie inferior pair of quadrigeminal bodies. The transverse groove curves round below each of the superior pair of Cjuadrigeminal bodies and separates them from the inferior pair. It is also continued in an upward and forward direction on the lateral aspect of the mesencephalon. LATERAL ROOT. OPTIO TRACT 532 THE NERVOUS SYSTEM. The quadrigcmiual bodies are not marked off laterally from the sides of the mesencephalon, but each has in connexion with it, on this aspect, a prominent strand of white matter, which is prolonged upwards and forwards under the projecting pulvinar and corpus geniculatum externum. These strands are called the brachia of the corpora quadrigemina, and they are separated from each other by a continuation on the side of the mesencephalon of the transverse groove, which intervenes between the two pairs of bodies. The corpus geniculatum internum (corpus geniculatum mediale) is closely associated with the brachia. It is a small, sharply-defined oval eminence, which lies on the side of the upper part of the mesencephalon under shelter of the pulvinar of the optic thalamus. The inferior bracMum (brachium quadrigeuiinum inferius), proceeding upwards from the lower quadrigeminal body, advances towards the corpus geniculatum internum and disappears from view under cover of this prominence. Upon the opposite side of the same geniculate body the mesial root of origin of the optic tract takes shape on the surface, and the appearance is such that the conclusion might very naturally be arrived at that the inferior brachium and this root of the optic tract are continuous with each other under the genicu- ,corp:gen:ext: latc clovatlon. This is not the case, however ; the fibres of the inferior brachium, to a large extent, proceed iuto the subjacent tegmentum under cover of the internal geniculate body and help to constitute an MESIAL ROOT. ascending tract from the inferior quadrigeminal body, -corp:gen:int: wlilch procceds upwards to the optic thalamus. Of the fibres of the mesial root of the optic tract some end in 'supR. QUAD BODY; t ho gray matter of the internal geniculate body, whilst ,„rrt.QUAD:BODY. othcrs SbVi&e within it. They constitute what is called Fig. 428. -Diagram of the roots Qudden's commissure. OF THE Optic IServe. „i ■■,■•■ /i i • i • • Ihe superior bracnmm (brachium qnadrigemmum superius) is carried upwards and forwards between the overhanging pulvinar and the corpus geniculatum internum. A surface examination of the mesen- cephalon is sufficient to show that, while a large part of this strand enters the corpus geniculatum externum, a considerable portion runs into the lateral root of the optic tract. The optic tract is thus attached to the brain-stem by two roots, viz. a mesial and a lateral, which are separated from each other by a distinct groove. The mesial root disappears under the internal geniculate body. The lateral root spreads out and some of its fibres enter the superior quadrigeminal body through its brachium, whilst others find their way into the corpus geniculatum externum and the pulvinar of the optic thalamus (Fig. 428). Crura Cerebri (pedunculi cerebri). — The crura cerebri constitute the chief bulk of the mesencephalon (Fig. 429, p. 533). Upon the basal aspect of the brain they appear as two large rope-like strands, which emerge close together from the upper aspect of the pons Varolii and diverge as they proceed upwards to enter the cerebrum. At the place where each crus disappears into the corresponding side of the cerebrum, it is encircled by the optic tract. Each crus cerebri is composed of two parts, viz. a dorsal tegmental part (teg- mentum), which is prolonged upwards into the region below the optic thalamus (subthalamic tegmental region), and a ventral pedal portion or crusta (basis pedun- culi), which, when traced upwards into the cerebrum, is seen to take up a position on the outer side of the optic thalamus and to be continuous with the internal capsule of the brain. When the base of the brain is examined it is the crusta which is seen, and it is observed to be wiiite in colour and streaked in tlie longi- tudinal direction. In the tegmentum the longitudinally-arranged fibres are, for the most part, corticipetal, or, in other words, fibres which are ascending towards the cortex of the cerebrum ; the crusta, on the other liand, is entirely composed of longitudinal strands of fibres which are coi'ticifugal , or fibres which descend from the cortex cerebri. On the surface of the mesencephalon the separation between the tegmental and IN TEEN AL STEUCTUEE OF THE MESENCErHALON. 533 pedal portions of the crus cerebri is clearly indicated by an inner and an outer groove. The inner or mesial furrow is the more distinct of the two. It looks into the interpeduncular space, and from it emerge the fascicles of the tliird or oculo-motor nerve. It is, therefore, termed the sulcus oculo-motorii (sulcus nervi oculo-motorii). The outer groove, which is placed on the lateral aspect of the mesencephalon, receives the name of the sulcus lateralis mesencephali. When traced downwards, it is observed to become continuous with the furrow which intervenes between the middle and superior peduncles of the cerebellum. A close inspection of the outer surface of the tegmental part of the crus cerebri, below the level of the quadrigeminal brachia, will reveal some faintly-marked bundles of fibres curving obliquely upwards and backwards to reach the inferior quadrigeminal body (Fig. 390, p. 484). These are fibres of the lateral fillet, coming to the surface at the sulcus lateralis and sweeping over the subjacent superior cerebellar peduncle to gain the inferior quadrigeminal body. POSTERIOR LONCITUDINAI BUNDLE AQUEDUCT OF SYLVIUS. SULCUS LATERALtS INTERNAL STRUCTURE OF THE MESENCEPHALON. When transverse sections are made through the mesencephalon the aqueduct of Sylvius is seen to be surrounded by a thick layer of gray matter, which receives the name of the Sylvian gray matter or the central gray matter of the aqueduct (stratum griseum centrale). On the dorsal aspect of the Sylvian gray matter the corpora quadrigemina form a layer which separates it from the surface, and to which the term lamina quadrigemina is applied. On the ventral and lateral aspects of the Sylvian gray matter are the tegmental portions of the crura cerebri; whilst, intervening between each of the latter and the corre- sponding crusta, there is a con- spicuous mass of dark pigmented matter termed the substantia nigra. Sylvian Aqueduct and Sylvian Gray Matter (aquseductus cerebri — stratum griseum centrale). — The aqueduct of Sylvius is the canal which leads from the fourth ventricle below, upwards through the mesen- cephalon, to the third ventricle above. It is not quite three-quarters of an inch in length, and it lies much nearer the dorsal than the ventral surface of the mesencephalon. When examined in transverse section, it presents a triangular outline as it passes into the fourth ventricle and a T-shaped outline close to the third ventricle. In the intermediate part of its course it assumes different outlines, and not always the same form at the same level in different individuals. The aqueduct of Sylvius is lined by ciliated epithelium, and outside this is the thick layer of Sylvian gray matter, which is directly continuous below with the gray matter spread out on the floor of the fourth ventricle, and above with gray matter on the floor and sides of the third ventricle. Scattered more or less irregularly throughout the Sylvian gray matter are numerous nerve-cells of varying forms and sizes, whilst in addition to these there are three definite collections or chisters of cells, which constitute the nuclei of origin of the trochlear nerve, the oculo-motor nerve, and the mesencephalic root of the trigeminal nerve. The position and relations of these will be given at a later stage. Substantia Nigra. — When seen in transverse section, the substantia nigra presents a semilunar outline. It consists of a mass of gray matter, in the midst of which are large numbers of deeply pigmented nerve-cells. It is only when this substance is examined in bulk that it appears dark ; in thin sections it does not differ much in colour from ordinary gray matter, although, under the microscope, the brown -coloured cells stand out very conspicuously, even under low powers. NERVE SULCUS OCULOMOTORIUS Fig. 429. — Diagrammatic View of the Oct Surface of A Transverse Section through the Upper Part OF THE Mesencephalon. 534 THE NEEVOUS SYSTEM. The substantia nigra is disposed in the form of a thick layer, interposed between the tegmental and pedal portions of the cms cerebri. It begins below at the upper border of the pons Varolii and extends upwards into the subthalamic region. The margins of this layer of dark-coloured substance come to the surface at the oculo-motor and the lateral sulci of the mesencephalon, and its inner part is traversed by the emerging fascicles of the oculo-motor nerve. It is not equally thick throughout. Towards the lateral sulcus it becomes thin, whilst it thickens considerably near the' inner aspect of the crus cerebri. The surface of the sub- stantia nigra, which is turned towards the tegmentum, is concave and uniform ; the opposite surface is convex and rendered irregular by the presence of numerous slender prolongations of the substance into the crusta. The morphological and physiological .significance of the substantia nigra is not fully understood, and the connexions established by its cells are imperfectly known. Inferior Quadrigeminal Bodies (colliculi inferiores). — Each of the inferior quadrigemiual bodies is largely composed of a mass of gray matter which, in transverse section, presents an oval outline (Fig. 432, p. 537). This central nucleus is, to a large extent, encapsulated by white matter. Numerous cells of different sizes are scattered throughout it, and the whole mass is pervaded by an intricate interlacement of fine fibres, which, to a large extent, are derived from the lateral fillet and the inferior brachium. In transverse sections, through this region, the lateral fillet is seen to abut against the outer margin of the central nucleus. Many of the fibres of this tract enter it at once and become dispersed amongst its cells ; others sweep over its dorsal surface, so as to give it a superficial covering ; whilst a third group is carried in the form of a thin layer inwards on its ventral aspect, so as to mark it off from the subjacent Sylvian gray matter of the aqueduct (Fig. 432, p. 537). In this manner, therefore, the inferior quadrigeminal nucleus becomes partially circum- scribed by the fibres of the lateral fillet. Several of the lateral fillet fibres, which proceed over the superficial or dorsal aspect of the nucleus, reach the mesial plane and form a loose decussation with the corresponding fibres of the opposite side. The intimate connexion wliicli is thus exhibited between the fibres of the lateral fillet and the nucleus of the inferior quadrigeminal body is very significant. It has already been shown that the lateral fillet, to a large extent, comes from the nuclei of termination of the cochlear nerve of the opjDosite side, although most of its fibres have to jjass through several nuclear inter- nodes before they reach the inferior quadrigeminal body. We must associate, therefore, the inferior quadrigeminal body, and also the corpus geniculatum internum, which likewise receives lateral fillet fibres, with the organ of hearing. This view of the inferior quadrigeminal bodies is supported both by experimental and by morphological evidence. Speaking broadly, it may be stated that the inferior quadrigeminal bodies are only present as distinct eminences in mammals, and then they are invariably correlated with a spirally-wound and well-developed cochlea. That tliey have nothing to do with sight, is shown by the fact that, when the eyeballs are extirpated in a young animal, the inferior quadrigeminal bodies remain unaft'ected, whilst the superior quadrigeminal bodies after a time atrophy (Gudden). When, on the other hand, the cochlear terminal nuclei are destroyed, fibres which have undergone atrophy may be followed to the inferior quadrigeminal bodies of both sides, but particularly to that of the opj)Osite side (Baginski, Bumm, and Ferrier and Turner). A very considerable tract of ascending fibres takes origin within the inferior quadrigeminal body . and passes upwards, in the inferior brachium, into the tegmentum subjacent to the internal geni- culate body. Within the tegmentum they proceed u}) to the optic thalamus (Ferrier and Turner). Superior Quadrigeminal Bodies (colliculi superiores). — The superior quadri- geminal body presents a more complicated structure (Fig. 431). Superficially, it is coated with a very thin layer of white matter, which is termed the stratum zonale. Underneath this there is a gray nucleus, called the stratum cinereum, which in transverse section exhiljits a crescentic outline and rests in a cap-like manner upon the subjacent part of the eminence The succeeding two strata, which respectively receive the names of stratum opticum and the stratum lemnisci, present this feature in common, that they are composed of gray matter, traversed by numerous fibres. The source from which the fibres are derived differs, however, in each case. Nerve-fibres reach the superior quadrigeminal body through — (1) the lateral and mesial fillets, and (2) through the superior brachium. Tlie fillet fibres enter INTERNAL STRUCTURE OF THE MESENCEPHALON. 535 InUuoi quiflrij; MeseiiceiiUalic loot of Ifftli iiei\ e ISuclcus of fourth nerve Bi ichiuiii iiiforiiis Postcrioi longitudinal \bundlo Mesial fillet the stratum lemnisci, and, in all probability, end there. The superior bracMum contains fibres of two different kinds, viz. fibres from the optic tract and fibres from the cortex of the occipital lobe of the cerebrum. By the former it is connected with the retina, and by the latter with the visual centre in the occipital region of the cerebral cortex. The retinal fibres, for the most part, spread out on the surface of the quadrigeminal body and form the stratum zonale. Most of them dip down into the substance of the body and end in connexion with the cells of the deeper layers ; several, liowever, are carried across the mesial plane, to end in the superior quadrigeminal body of the opposite side. The occipital fibres, and probably also some of the retinal fibres, enter the stratum opticum. The fibres from the occipital cortex form part of the optic radiation, and the course which they pursue will be dealt with later on. Tegmental Portions of the Crura Cerebri (tegmenta). — The tegmentum of the crus cerebri may be regarded as the continuation upwards of the formatio reticularis of the medulla and the dorsal or tegmental portion of the pons into the mesencephalon. It therefore consists of fine bundles of longitudinal fibres intersected by arch- ing fibres, which take a transverse and curved course. The interstices between these nerve- bundles is occupied by gray matter containing ir- regularly scattered nerve - cells. On its dorsal aspect the tegmentiun is con- tinuous, at the side of the Sylvian gray matter, with the bases of the corpora quadrigemina, whilst ven- trally it is separated from the crusta by the sub- stantia nigra. The two tegmenta of opposite sides are, to some extent, marked off from each other in the mesial plane by a pro- longation upwards of the median raphe of the pons and medulla, although, in the lower part of the mesencephalon, this is much obscured by the decussation of the superior peduncles of the cerebellum. The two longitudinal strands, termed the posterior longitudinal bundle and the fillet, are prolonged upwards throughout the entire length of the mesencephalon ; and they present the same relations to the tegmentum as in the lower parts of the brain. The former is placed in relation to its dorsal aspect, whilst the fillet is carried up in its ventral part. The tegmentum of the crus cerebri may be considered as presenting two parts : viz. (1) a lower part, which is placed subjacent to the inferior quadrigeminal bodies and which is largely occupied by the decussation of the superior cerebellar peduncles (Fig. 430); and (2) a superior part, subjacent to the superior quadrigeminal bodies, which is traversed by the emerging bundles of the third nerve and which contains a large and striking nuclear mass, termed the nucleus ruber or the red teg- mental nucleus (Fig. 431). In the lower part of the mesencephalon is the nucleus of the fourth nerve ; in the upper part, the nucleus of the third nerve. Superior Cerebellar Peduncles (brachia conjunctiva). — As the superior cere- Substantia nii^ra Fig. Crusta 430. — Transverse Section through the Human Mescencephalon AT the Level of the Inferior Quadrigeminal Body. 536 THE NERVOUS SYSTEM. bellar peduncles leave the pons and sink into the tegmenta of the mesencephalon, they undergo a complete decussation subjacent to the inferior quadrigeminal bodies and the Sylvian gray matter (Figs. 407, p. 505 ; 432, p. 537 ; and 430, p. 535). In this manner each peduncle is transferred from one side, across the mesial plane, to the opposite side. The decussation is completed at the level of the upper borders of the inferior quadrigeminal bodies, and then each peduncle proceeds upwards into the superior part of the tegmentum, where it encounters the red nucleus. Into this a large proportion of its fibres plunge and come to an end in connexion with the nuclear cells. Many of the peduncular fibres, how- ever, are carried around the nucleus so as to form for it a capsule which is thicker on the inner than on the outer side (Fig. 431). These are prolonged into the subthalamic region, and ultimately penetrate the ventral aspect of the optic thala- Superior quadrigeminal body External geniculate bnily Inferior bracliiuni Internal geniculate body Mesial fillet Crusta ^»w&^i / 'I ' Kt'il nucleus Optic tract ^;^j^p4- Sylvian gray matter Sj Ivian aqueduct Tegmentum - - Nucleus of third nerve Posterior longitudinal bundle Fibres of superior cerebellar peduncle Third nerve Substantia nigra Corpus mammillare Fig. 431. -Transverse Section through the Human Mesencephalon at the Level ov the Superior Quadrigeminal Body. mus, where they end in connexion with the thalamic cells. The superior cerebellar peduncle is, therefore, a great efferent tract which issues from the lateral hemisphere of the cerebellum, crosses the mesial plane in the lower part of the mesencephalon, and ends in the red nucleus and the ventral part of the optic thalamus. Red Nucleus (nucleus ruber). — This is a rounded nuclear mass, of a reddish tint in the fresh brain, which lies in the upper part of the tegmentum, and in the path of the superior cerebellar peduncle. In transverse section it presents a circular outline. It begins at the level of the lower border of the superior quadrigeminal body and it extends upwards into the subthalamic tegmental region. At first it is small and is placed at a little distance from the mesial plane ; but as it proceeds towards the subthalamic region, it increases in bulk and approaches more nearly to the mesial raphe, and its neighbour of the opposite side. The curved emerging bundles of the third nerve pass through it on their way to the surface. The relation which the fibres of the opposite superior cerebellar peduncle present to it has been described. These fibres traverse its lower part in such numbers that in Weigert-Pal specimens it presents a very dark colour ; but higher up, as the fibres IXTERXAL STRUCTUEE OF THE MESENCEPHALON. 537 Inferior qnadrigeininal nucleus Mesencephalic root of fifth nerve are gradually absorbed by the nuclear mass, they become less numerous in its midst, and the nucleus assumes a paler tint. Xumeroiis fibres which descend from the cerebral cortex and others from the corpus striatum enter the red nucleus. It likewise sends out fibres which proceed in two directions : (1) upwards into the thalamus ; (2) downwards to the spinal cord. The former may be regarded as cariying on the continuity of the superior cerebellar path after its internodal interruption in the red nucleus. The fibres to the spinal cord, called the rubrospinal tract and first described by Monakow, cross to the opposite side and then descend in the tegmentum to reach the lateral column of the cord. Posterior Longitudinal Fasciculus. — This is a very conspicuous tract of longi- tudinal fibres ^vhich extends throughout the whole length of the medulla, pons, and mesencephalon, in the formatio reticularis or tegmental part of each. Below, at the level of the decussation of the pyramids, it becomes continuous with the anterior basis-bundle of the spinal cord (p. 491), whilst, by its opposite or upper end, it establishes intricate connexions in the region immediately above the mesencephalon. Throughout its whole length it lies close to the mesial plane and its fellow of the opposite side. In the mesen- cephalon it is applied to the ventral aspect of the Sylvian gray matter, whilst in the pons and medulla it is situated immediately subjacent to the gray matter of the floor of the fourth ventricle. One of its most salient features is the intimate association which it pre- sents with the three motor nuclei from which the nerves for the supply of the muscles of the eye- ball take origin, ^iz. the oculo-motor or third nucleus, the trochlear or fourth nucleus, and the abducent or sixth nucleus. The first two of these are closely applied to its inner and dorsal aspect, whilst the ab- ducent nucleus is placed on its outer side. Into each of these nuclei it sends many collaterals, and probably also some of its constituent fibres, and these end in terminal arborisations around the nuclear cells. It would appear, therefore, that one of the most important functions of this strand is to bind together these nuclei, and thus enable them to act in harmony with each other. Fibres also enter the posterior longitudinal fasciculus from the auditory system and perhaps, also, from the facial and other motor nuclei. The results obtained by degeneration would seem to indicate that, to a larcre extent, it is formed of fibres which run a short course within it. In spite of the large amount of attention which has been given to the study of the posterior longitudinal bundle, it must be admitted that there is little unanimity of opinion regarding its connexions and functions. That it is a brain tract of high importance, is evident from the fact that it is present in all vertebrates, and, further, that its fibres assume their medullary sheaths at an extremelv early period. In fish, amphibians, and reptiles, it is one of the most powerful bundles of the" medulla. In man its fibres medullate between the sixth and seventh months of foetal life, and at the same time as the fibres of the anterior basis-bundle of the cord, with which it stands in connexion. According to Van Gehuchten and Edinger, it extends upwards beyond the level of the oculo-motor nucleus, and in the subthalamic region its fibres take origin from a special nucleus of its o'i^-n in the gray matter of the third ventricle, immediately below the level of the corpora mammillaria. Fibres also enter the posterior longitudinal bundle from a nucleus common to it and the posterior commissure of the brain. This nucleus is placed in the fore-part of the Sylvian grav matter of the mid-brain. Held asserts that numerous fibres, arising from cells in the superior quaVlrigeminal body, curve in an arcuate manner in the tegmentum outside the Sjlvian gray Fig. 432. — Section thr(jugh the inferior Quadrigeminal BODT AN'D THE TeGMENTDM OF THE MESENCEPHALON BELOW THE LEVEL OF THE NUCLEUS OF THE FOURTH Nerve in the Orang. (The decussation of the superior cerebellar peduncles and the course of the fourth nerve in the Sylvian gray matter are seen. ) 538 THE NERVOUS SYSTEM. Decussating fibres Nucleus of in- I'erioi' quadii- geminal body Meseuceplialic root of fifth nerve Fourtli nerve Posterior longitudinal bundle Lateral fillet Superior cerebellar peduncle Mesial lillet matter, to take part on the ventral aspect of this in what is called the " fountain decussation." Reaching the opposite side tliese fibres turn downwards and join the posterior longitudinal fasciculus. Tlie same authority considers that iibres from the ventral part of the posterior commissure can also be traced down- wards into the posterior longitudinal bundle. Edinger, on the other hand, jilaces these fibres as a distinct tract on the ventral and lateral aspect of the posterior longitudinal bundle, although in apposition with it. Mendel believes that fibres from the oculo-motor nucleus are carried down in the posterior longitudinal bundle, and, from this, into the facial nerve for the supply of the orbicularis palpebrarum and the corrugator suj)ercilii, bringing these muscles therefore under the control of the same nucleus as the levator palpe- brse superioris muscle. This view has received corroboration at the hands of Tooth and Turner. It has been further suggested that fibres from the hypoglossal nucleus may, by theposterior longitudinal fasciculus, reach the facial nerve, and through it the orbicularis oris. In this manner the same nucleus would hold Fig. 433. — Section through the inferior Quadrigeminal sway over the tongue and the sphincter Body and the Tegmentum of the Mesencephalon, muscle of the lips. The close relation AT A SLIGHTLY LowER Level THAN FiG. 432. which exists between the ascending part of the intrapontine portion of the facial nerve and the posterior longitudinal bundle would render the passage of fibres from one to the other a matter which could easily be understood. Another interchange of fibres through the posterior longitudinal Ixtndle has been described by Duval and Laborde. According to these authorities, filjres from the abducent nucleus ascend in the posterior longitudinal bundle into the mesencephalon, and establish connexions with that part of the ocido-motor nucleus from which the nerve for the internal rectus of the opposite side derives its fibres. If this view be correct, it affords a ready and simple anatomical explanation of the harmonious action of the external and internal recti muscles in producing movements of the two eyeballs simultaneously to the right and to the left. From the investigations of E. H. Eraser it would appear that no fibres from the abducent nucleus go directly into the oculo-motor nerve. The same observer has sho-wTi that many filjres from Deiters' nucleus, through the patli aft'orded by the posterior longitudinal bundle, enter the third and the fourth nuclei. ^^'r^^