The form and functions of the central nervous system; an introduction to the study of nervous diseases

Front matter

Open Knowledge Commons and Harvard Medical School

THE FORM AND FUNCTIONS OF THE CENTRAL NERVOUS SYSTEM

THE

Preface

FOR a number of years the authors have had the privilege of teaching neuro-anatomy to medical students in Columbia University, and also, during the war, to many of their medical colleagues assigned by the Surgeon General to the New York Neuro-Surgical School. In teaching, it has been their aim to keep in view the pertinence and value of knowledge concerning the structure of the nervous system in its actual application to clinical medicine. Not the least among the difficulties of presenting such a course is the lack of any satisfactory textbook. No single work provides a clinical and physiological interpretation of the brain and spinal cord adequate to the requirements of practical application.

In so far as possible, the method of illustrating anatomical and physiological facts by clinical examples has been adhered to in this book. The citation of actual cases caused by organic disturbances of the tissues is extensively utilized to elucidate the significance of the several divisions of the brain and spinal cord. By this method the anatomy and physiology of the central nervous system are no longer permitted to remain as independent branches of medical science, but are here incorporated as essential parts of the practical knowledge necessary to the proper diagnosis and treatment of disease.

The need of the student for the most explicit presentation of facts has been recognized in all discussions, although the danger of lapsing into unnecessarily dogmatic statement has not been overlooked.

For the most part, the interpretations given are those which have received the sanction of general acceptance. In a few instances, however, where the limits of our present knowledge concerning the functions of the nervous system are not yet discernible, certain theoretical conjectures have been advanced, both for the purpose of avoiding confusion for the student, and in the hope of stimulating further investigation. There can be no question as to the desirability of such conjectures if for nothing else than that they demonstrate

vii

Vlll PREFACE

to what extent the field of Neurology still invites the interests of future workers.

In addition to much original work, many sources have been drawn upon for neurological facts and interpretations. Chief among these have been the great modern masters of Neurology, Cajal and Dejerine. The more recent contributions of distinguished English neurologists, including such leaders as Gaskell, Elliot Smith, Hughlings Jackson, Head, Sherrington, Horsley, Holmes, Campbell and Wilson have provided a wealth of material. We are indebted to the work and influence of the American School of Neurology which has contributed extensively to the elucidation of the Component Theory of the Nervous System. In this connection, we desire especially to mention Professors H. F. Osborn, C. F. W. McClure, 0. S. Strong, C. J. Herrick, G. Carl Huber, Adolf Meyer, J. B. Johnston, F. L. Landacre and W. B. Ransom; as well as such noted clinical teachers as Professors M. Allen Starr, C. L. Dana, C. K. Mills, William Browning, C. A. Elsberg, T. H. Weisenburg, Smith Ely Jelliffe and J. Ramsay Hunt.

We also take much pleasure in expressing our sincere gratitude to a number of co-workers whose efforts and assistance have been of greatest value: To Professor F. C. Wood for his supervision and advice in the photomicrography; to Miss Regina linger for her unsurpassed technical skill in the preparation of histological sections of the brain and spinal cord; to Mr. Ivan Summers for the original drawings; to Miss Alice Goldsmith for her painstaking work on the manuscript and index. It is difficult for us to express adequately our deep sense of appreciation for the courtesy, generosity and cooperation of our publisher, Mr. Paul B. Hoeber and his editorial staff.

F. T.

October 6, 1920 .

H. A. K.

Foreword

A RECENT issue of "Science"^ records, under ''University and Educational News," a significant change in medical educational policy lately introduced at the University of Oregon with the establishment of a new chair whose first incumbent is designated as the "Professor of Zoology and Director of Fundamental Education in Medical Science." In explanation of this action of the medical faculty the reference further states that ''an attempt will be made to bring together in one course the premedical and medical years and to obliterate the divisions commonly existing between premedical, preclinical and clinical studies."

This action of the Oregon institution is interesting as an instance of a modern trend in the evolution of medical education which is beginning to make itself felt not only in this country, but also abroad. This movement is in the first place based on a fuller recognition and evaluation of the cardinal fact that morphology, physiology and biochemistry underlie all sound ideals of medical education. Upon the breadth and solidity of this supporting fundamental basis rests the security of the entire superstructure of medical teaching in the clinical branches of the later years, which is constantly expanding into greater complexity and specialization of detail with the steady advance in medical research and technique.

Coupled with this realization, and as its direct result, is a reaction on part of the teachers in the laboratory branches. While the fundamental biological sciences are accorded their full value as indispensable preparation for the study of the practical side of medicine by clinicians, the teachers of these so-called preclinical branches are in turn beginning to realize the importance of utilizing the three clinical factors of injury, disease and variation as invaluable experimental demonstrations illustrating the significance of the structural, functional and chemical facts with which they primarily are concerned.

ix

X FOREWORD

Nowhere in the entire domain of medical education are thes facts more clearly accentuated than in the adjustment of those branches of science which are grouped together to constitute the general field of vertebrate neurology. The interlocking facts of development, structure and function, and their interpretation under normal as well as pathological conditions, present an educational territory so complex in its relations and so replete with details as to call for the closest union of all the forces engaged in its cultivation.

This need of cooperative extension becomes most marked in the purely morphological aspect of the entire subject.

No experienced instructor in the anatomy of the central nervous system fails to realize fully the difficulty of adequately presenting the enormously complicated and intricate details of his subject in such form to his students for mental digestion and absorption, and with such collateral aids, as will bring the utmost possible clarity into the discussion and at the same time add a distinct realization of the interdependence of the various disciplines which combine from several sources to supply each a special part of the detailed picture forming the connected whole when brought into its proper position. For the purposes of sound morphological instruction and interpretation the neurological wards of a teaching hospital, its case-histories and other illustrative material constitute for the neural morphologist the only available authoritative laboratory of experimental zoology in which morbid conditions, altering the normal physiological reactions, point to the morphological basis and afford the final and conclusive demonstration of the functional significance underlying the details of organic structure.

The medical curriculum, charged with many crimes of both omission and commission, is perhaps nowhere blamed more justly than in its fatal heterochronic assignment of the correlated and mutually supplemental topics of morphological and clinical neurology to different parts, and mostly to different years, of the course, thus depriving each of the indispensable aid of the other which a synchronous consideration would afford.

These considerations led a number of years ago at Columbia University to the uniting of the structural, functional and clinical

FOREWORD XI

aspects of neurological teaching under the directorship of the senior author of the work now presented.

Based on the Theory of the Neural Components, in the establishment of which American Science has contributed so largely, this book offers its consideration of the vertebrate central nervous organization from the standpoints of Phylogeny, Ontogeny, Morphology, Physiology and Pathology in a thoroughly connected and clear analysis which at all times keeps in open view the ultimate main purpose of this great undertaking, the comprehensive presentation of the cardinal factors involved in their mutual relationship.

The authors sum up the fundamental concept which guided and directed their labors in their '^ Introduction to the Study of Nervous Diseases" as follows: ''This work is designed to fill the gap between morphology and the practical requirements of clinical medicine. It aims to visualize the living nervous system, to make accessible an appreciation of its vital relation to the functions which go to make up life as well as the defects in these relations which result in disease."

How well they have attained the goal thus set at the outset of the undertaking, the admirable result achieved with this publication is destined to show. Its ultimate place in scientific literature may be confided to the judgment of those who will read and study its pages.

The authors, beginning as my students, became my valued colleagues, an association which during the course of many years has grown into a close friendship. They have honored me by asking me to write a foreword to their book. I am conscious of the fact that nothing I have said can add one element of value to the great intrinsic worth of their contribution; but I feel that I cannot resist the expression of my own sense of gratitude for the privilege which I have enjoyed and the mental stimulus I have received in being permitted to observe and profit by the years of intensive and productive study in the morphological laboratory of this institution which have gone into the creation of this volume. As I have constantly profited in mind by this close association during the growth of their work, I rejoice in the fact that the same opportunities will be offered to a far wider circle of students through its pages. I am

Xll

FOREWORD confident that they will likewise find their task made lighter, their vision cleared and their mental outlook widened by the broad conception and stimulating presentation which enlivens the pages of this volume.

On behalf of my University I wish to express our grateful appreciation of this product of a ripe American scholarship and training.

Department of Anatomy

Columbia University

Octobers, 1920

Geoege S. Huntington

CHAPTER I Page

THE CENTRAL NERVOUS SYSTEM— Its Importance and Significance . . 1 The Value of the Anatomy of the Nervous System in the Practice of Medicine — Neurology and the Practice of Medicine — The Evolutional Significance of the Central Nervous System — The Centralization of the Nervous System — The Two Major Mechanisms Controlled by the Nervous System — Components of the Nervous System Controlling the Two Major Mechanisms — The Somatic Sensory or Afferent Component — The Somatic Motor or Efferent Component — The Splanchnic Sensory or Afferent Component — The Splanchnic Motor or Efferent Component — The Cooperation of the Four Components of the Nervous System — Divisions of the Nervous System.

Chapter II Embryological Development Of The Central Nervous

SYSTEM 14

Principle of Development in the Mammalian Embryo — The Formation of the Neural Plate and Groove — Appearance of the Optic, Trigeminal and Acoustico- Facial Grooves — Elevation of the Neural Folds — The Neural and Somatic Ectoderm — Changes in the Mesoderm — Probable Significance of the Neural Groove — Differentiation of the Brain End of the Neural Folds — Formation of the Roof-Plate and Neuropore — Fusion of the Somatic Ectoderm — Invasion of Mesenchymal Cells — Differentiation of Spinal Cord and Brain — Completion of the Roof-Plate — Histological Changes in the Lateral Walls — Formation of Blood Vessels — The Neural Crests — Increase in the Number and Differentiation of the Somites — Increase in Size of Brain-Vesicle — Primitive Divisions of the Brain — The Myelomeres — The Encephalomeres.

Chapter III Embryological Development Of The Central Nervous

SYSTEM {Continued) 29

The Central Canal and Primary Flexures — The Secondary Brain-Vesicles — - Differentiation of the Ventral and Dorsal Gray Columns — The Medullary Velum and Capillary Plexus — ^The Oculomotor and Trochlear Nerves — ^The Trigeminus, Facial and Acoustic Nerves — The Glossopharyngeus, Vagus, Accessorius and Hypoglossus Nerves — Ganglion of Froriep and Ganglion Accessorius — Segmentation of the Neural Crest — The Spinal Ganglia — Constituents of a Typical Spinal Segment — The Optic Stalk and End-Vesicle — The Trigeminal and Acoustico-Facial Evaginations — The Infundibular Evagination — The Otocyst — Aula and Hemispherium — The Sulcus Limitans — Formation of the Membranes — The Cranial Nerves — The Spinal Ganglia and Their Roots — The Formation of the Sympathetic Ganglia — The Hypophysis and Otocyst — The Telencephalon — The Diencephalon — The Mesencephalon — The Metencephalon and Myelencephalon — Histogenesis of the Neural Tube.

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XIV CONTENTS

CHAPTER IV Page

THE UNIT OF STRUCTURE OF THE NERVOUS SYSTEM— The Nerve-Cell

OR Neurone 50

Adaptation to the Purposes of Generating and Conducting Nerve Impulses — Structure of the Neurone — The Cell Membrane — The Cytoplasm — Intracytoplasmic Canals — Chromophilic Substances — Nissl's Bodies — Other Cell Pigments — The Neurofibrils — Absence of the Centrosome — Form of the Nerve Cell — The Dendrites — The Axone — The Neuroglia — Types of Neuroglia — Physiological Significance of the Neuroglia — Pathological Syndromes of the Nerve Cell.

Chapter V The Integration Of The Neurones To Form The Nervous

SYSTEM— The Neurone Theory 71

The Manner in Which Nerve Cells Establish Intercommunications — Classification of Cells Encountered in the Nervous System — Dynamic Polarization — The Neurone Theory — Contact Continuity — Synapsis — Interpretation of the Centralization of the Nervous System — The Essential Relation of the Receptors to the Effectors — The Receptors — Exteroceptors — Contact Receptors — Distance Receptors — Proprioceptors — Interoceptors — The Effectors — Functional Significance of the Somatic Receptors — Simple Tactile Sensibility — Critical Tactile Sensibility — Pressure Sensibility of all Grades — Muscle- Joint Sense — Pain Sensibility — Temperature Sensibility — Equilibratory Sensibility— The Special Senses of Smell, Sight and Hearing— Parts Which Amplify the Relations Between Receptors and Effectors — The Mediators— Nuclei, Tracts and Pathways — Classification of the Receptors of the Skin,

CHAPTER VI EXPOSURE AND INVESTIGATION OF THE SPINAL CORD 7i\r»S7rt/ . . 94

Significance of Spinal Relations — Incision Through the Skin and Subcutaneous Tissues — Depth of Incision in the Several Regions — Separation of Muscle Masses — Muscles and Fasciae Exposed — Arteries Encountered in the Exposure— Periosteum and Bone Exposed — Nerves Encountered in the Exposure — Removal of the Bone — Exposure of the Dura Mater — Emergence of the • Spinal Nerve Roots — Arteries of the Vertebral Canal — The Veins of the Vertebral Canal — Caudal Limit of the Dural Sac — Incision of Dura, Exposing Subdural Space, Arachnoid and Pia Mater — The Subarachnoid Space and Spinal Fluid — Ligamentum Denticulatum — Examination of the Cord and the Emergent Roots — Removal of the Cord.

CHAPTER VII THE SPINAL CORD — Its General Character and Anatomy 105

Form of the Spinal Cord — Regional Differences in the Spinal Cord — Significance of the Several Regions of the Spinal Cord — Dimensions and Weight — General Relations — Means of Fixation — Surface Markings — The Several Surfaces of the Cord — The Ventral Surface — The Dorsal Surface — The Lateral Surfaces — The Roots or Radicles of the Spinal Nerves^Differences in the Root Fibers — Length and Direction of the Spinal Roots — Relation of the Spinal Cord to the Spinal Column.

CONTENTS XV

CHAPTER VIII Page THE SPINAL CORD— Its Coverings and Circulation 119

The Osseous Covering — Spinal Dura Mater — The Upper and Lower Extremities of the Dural Sac — Spinal Arachnoid — Spinal Pia Mater — Structure of the Membranous Envelopes of the Spinal Cord — The Cerebrospinal Fluid — Circulation of the Spinal Cord — ^Lymphatics of the Spinal Cord — The Practical Significance of the Spinal Cord and its Coverings.

CHAPTER IX THE SPINAL CORD— HisTOLOGr OP THE Cord Segment 129

The Gray Columns of the Cord — Nerve-Cells in the Spinal Cord — Root Cells — Tract Cells — Arrangement of the Cells in the Different Parts of the Gray Matter — The Ventral Gray Column — The Body of the Gray Substance — The Dorsal Gray Column — The Gray Commissure — The White Matter of the Spinal Cord — Differences in the Cross Section Appearances in the Several Divisions of the Spinal Cord.

Chapter X

THE SPINAL CORD — The Function of the Ghat Matter in the Cord

Segment 148

General Difference in Function of the Gray and White Substance — Function of the Ventral Somatic Motor Column — Idiodynamic Control — Reflex and Tonic Control — Segmental Associative Control — Vestibulo-Equilibratory Control— Synergic Control — Associative Automatic Control — Voluntary or Vohtional Control — Influences Affecting the Ventral Gray Column and Their Possible Defects — Function of the Lateral Splanchnic Motor Cell Column — Differences in the Activities of Skeletal and Smooth Muscles — Function of the Dorsal Root Ganglion Cells — Function of the Tract Cells in the Spinal Segment — Summary of the Functions of the Gray Matter of the Spinal Cord Segment — The Cutaneous, Sensory, Muscular and Reflex Zones of the Body — The Muscles Supplied by the Several Spinal Nerves.

Chapter XI

THE SPINAL CORD — The Function of the White Matter in the Cord

Segment 185

The General Arrangement and Significance of the White Matter of the Spinal Cord — Groups of Fibers of the White Matter with Reference to the Connections Which They Establish— The Three White Columns of the Cord— Constituents of the Dorsal White Column — Intersegmental Fibers in the Dorsal White Column — Summary of the Functions of the Dorsal White Column — Constituents of the Lateral White Column — Summary of the Functions of the Lateral White Column — Constituents of the Ventral White Column — ■ Summary of the Functions of the Ventral White Column of the Cord.

CHAPTER XII THE SPINAL CORD— Its Principal Syndromes 213

Functions of the Spinal Cord in General — The Isomeric and Allomeric Functions of the Cord Segment — Clinical Differences in Lesions of the Gray and White Matter — Clinical Syndromes as a Means of Interpreting Spinal Cord Function — Syndrome of the Ventral Gray Matter — Syndrome of the Dorsal Gray Matter:

XVI CONTENTS

Page Dorsal Root Ganglion — Syndrome of the Central Gray Matter: The Gray Commissure — Syndrome of the Dorsal White Column — Syndrome of the Lateral White Column — Syndromes of the Dorsal and Lateral White Columns Combined — Syndrome of Combined Sclerosis — Syndrome of Friedreich's Ataxia — Syndrome of the Lateral White and Ventral Gray Columns — Syndrome of Hemisection of the Spinal Cord — Syndrome of Complete Section of the Spinal Cord.

Chapter XIII

REMOVAL OF THE BRAIN AND INVESTIGATION OF THE BRAIN CASE 243 The Cephalic Division of the Central Nervous System — Preliminary Procedure for the Removal of the Brain — Superficial Incision Through the Scalp and Subcutaneous Tissues — Removal of the Calvarium — Incision in the Bone — Incision in the Dura — Arachnoid and Pia Mater — Removal of the Brain — The Anterior Cranial Fossa — The Middle Cranial Fossa — The Posterior Cranial Fossa and Its Nerves — Examination of the Dura Mater Covering the Base of the Skull — Upper Limit of the Ligamentum Denticulatum of the Dura Mater — The Venous Sinuses — The Reflections of the Dura Mater — The Base of the Skull with the Dura Mater Removed — The Anterior, Middle and Posterior Fossae.

CHAPTER XIV THE MEDULLA OBLONGATA— Encephalization and a General View of

THE Medulla 253

The Prolongation of the Spinal Cord — Influences Determining the Formation of the Head — Influences Producing Modifications in the Head — The Requirements of Respiration — The Gills — Encephalomeres and Myelomeres — Control of the Medulla Over Respiration, Cardiac Action and Gastro-lntestinal Activity — The Necessary Increase of Gray Matter in the Medulla — The Development of the Fourth Ventricle — The Development of the Gustatory Sense — The Development of the Equilibratory Mechanism — The Development of Special Organs of Offense — The Primitive Functions of the Medulla — Modifications Due to the Assumption of Terrestrial Life — Recession of the Taste-Buds and Lateral Line Organs — Phonation and the Development of the Larynx — The Development of the Mobile Head and Tongue — Modifications of the Face — The Influence of Suprasegmental Structures.

Chapter XV

THE MEDUTXA OBLONGATA — Relations, Surface Appearance and Anatomy OF the Medulla 265

Situation, Boundaries and Relations — Dimensions and Coverings of the Medulla — Arteries of the Medulla Oblongata — External Markings and Surface Features of the Medulla Oblongata — The Transition from the Spinal Cord to the Medulla as Seen upon the Ventral, Lateral, and Dorsal Surfaces of the Medulla — Appearance of the Fourth Ventricle — Structures Appearing on the Surface of the Medulla Oblongata not seen in the Spinal Cord — Nerves Connected with the Medulla Oblongata — The Dorsal Root Ganglia of the Cranial Nerves Connected with the Medulla Oblongata.

CONTENTS XVll

CHAPTER XVI Pack

THE MEDULLA OBLONGATA — Internal Structure and Histology op the

Rearrangements in the Gray and White Matter in the Medulla — Changes in the Gray and White Matter at the Level of the Lower Limit of the Pyramidal Decussation — Changes in the Gray and White Matter Through the Middle of the Pyramidal Decussation — Changes in the Gray and White Matter at the Level of the Cephalic Limit of the Pyramidal Decussation — Changes in the Gray and White Matter at the Level of the Caudal Limit of the Fillet Decussation— Changes in the Gray and White Matter at the Caudal Limit of the Inferior Olive.

CHAPTER XVII THE MEDULLA OBLONGATA — Internal Structure and Histology of the

Medulla {Continued) 305

Changes in the Gray and White Matter at the Level Through the Middle of the Inferior Olive — Changes in the Arrangement of the Gray and White Matter at the Cephalic Limit of the Inferior Olive — Summary of the Changes which Occur in the Arrangement of the Gray and White Matter of the Medulla Oblongata.

Chapter XVIII

THE MEDULLA OBLONGATA— Functional Significance of the Medulla . 316 The Functions of the Gray Matter — Splanchnic Motor Functions of the Medulla — Splanchnic Sensory Functions of the Medulla — Somatic Motor Functions of the Medulla Oblongata — Somatic Sensory Functions of the Medulla Oblongata — Simple Reflexes Mediated through the Medulla Oblongata — The Medulla in its Relations to Special Functions — Its Relation to Respiration— Its Relation to Phonation — Its Relation to Deglutition and Digestion — Its Relation to Cardiac Action — Its Relation to Metabolism, Especially to Glycometabolic Control— Its Relation to Secretion— The Functions of the White Matter in the Medulla Oblongata — The Descending Tracts — The Ascending Tracts — The Principal Decussations in the Medulla — Summary of the Functions of the Medulla Oblongata.

Chapter XIX

THE MEDULLA OBLONGATA— Principal Syndromes of the Medulla . . 338 Syndrome of the Pyramidal Decussation — Syndrome of the Pyramid and the Hypoglossal Nerve — Syndrome of the Mesial Fillet, Pyramid and Hypoglossal Nerve — The Syndrome of the Nucleus Ambiguus and Nucleus Accessorius — Syndrome of the Nucleus Ambiguus, Nucleus Accessorius and Nucleus Hypoglossus — Syndrome of the Nucleus Ambiguus and Spinal Fillet (Spino-Thalamic Tract) — Syndrome of the Nucleus Ambiguus and Nucleus Hypoglossus — Syndrome of the Circumferential and Intermediate Zones — Syndrome of the Vestibular Nuclei — Syndromes Due to Multiple Lesions in the Medulla Oblongata— Syndrome of Babinski-Nageotte — Syndrome of Cestan-Chenais.

Chapter XX

THE PONS VAROLII — Significance, Anatomy and Embryology op the Pons 358 The Pons, a Structure of the Mammalian Brain — Significance of the Pons — The Pons an Index of Cortical Development — Significance of the MetencephaUc

XVlll CONTENTS

Page Tegmentum — Features in the Embryological Development of the Pons — ■ Situation, Boundaries and Relations of the Pons Varolii — Dimensions and Coverings of the Pons Varolii — -Arteries of the Pons Varolii — External Markings and Surface Features of the Pons Varolii — The Floor of the Fourth Ventricle — Features in the Floor of the Fourth Ventricle.

Chapter XXI

THE PONS VAROLII — Internal Structure and Histology of the Pons. . . 369 Arrangement of the Gray and White Matter at the Level of the Caudal Pontile Fibers — Arrangement of the Gray and White Matter at the Level of the Caudal Limit of the Trapezoid Decussation — Arrangement of the Gray and White Matter at the Level of the Genu of the Facial Nerve — Arrangement of the Gray and White Matter at the Level of the Nucleus Masticatorius — Arrangement of the Gray and White Matter at the Level of the Decussation of the Trochlear Nerve — Summary of the Relations of the Gray and White Matter of the Pons Varolii.

Chapter XXII

THE PONS VAROLII — Functions and Principal Syndromes of the Pons . . 383 Functions of the Gray Matter — Splanchnic Motor Functions of the Pons — Splanchnic Sensory Functions of the Pons — Somatic Motor Functions of the Pons — Somatic Sensory Functions of the Pons — Simple Reflexes Mediated Through the Pons — The Pons in its Relation to Special Functions — Its Relation to Respiration — Its Relation to Phonation — Its Relation to Deglutition — Its Relation to Secretion — Its Relation to Eye Movements and Hearing — Fun(3tions of the White Matter of the Pons — Descending Tracts Traversing the Pons — Ascending Tracts Traversing the Pons — Decussations in the Pons — Principal Syndromes of the Pons Varolii — Syndrome of the Head and Eye- Turning Contingent of the Aberrant Pyramidal System — Syndrome of the Pyramid and the Oculogyric Aberrant Pyramidal System — Syndrome of the Mesial Fillet, the Pyramidal and the Oculogyric Aberrant Pyramidal Systems — Syndrome of the Pyramidal System and the Emergent Fibers of the Abducens Nerve — Syndrome of the Pyramid, Fillet, Inferior Cerebellar Peduncle and Posterior Longitudinal Fasciculus.

Chapter XXIII

THE CEREBELLUM — A General View of Its Evolutional Significance . . 407 A Suprasegmental Portion of the Nervous System — The Phyletic Constancy of the Cerebellum — The Cerebellum in the Different Classes of Vertebrates- Generalized Pattern of the Cerebellum in Mammals — Uniformity of the Internal Structure of the Cerebellum — Primitive Connections of the Cerebellum — The Connections of the Cerebellum in Mammals — The Evolutional Significance of the Cerebellum.

Chapter XXIV

THE CEREBELLUM — Relations, Surface Appearance and Anatomy .... 427 General Relations and Boundaries — Surface Relations — Dimensions, Weight and Coverings — Arteries of the Cerebellum — Parts of the Cerebellum — Surface Appearance of the Cerebellum — Surfaces of the Cerebellum — Cerebellar Lobation in the Human Brain — Fissures and Lobes of the Superior Portion

CONTENTS XIX

Page of the Cerebellum — Fissures and Lobes of the Inferior Portion of the Cerebellum — Tabulation of the Constituents of the Cerebellar Lobes — The Arbor Vita) Cerebelli and the Medullary Nuclei of the Cerebellum.

Chapter XXV

THE CEREBELLUM — Internal Structure, Histology and Embryology . . 445 The Histology of the Gray Matter of the Cerebellar Cortex — The Molecular Layer — The Granular Layer — Summary of the Cellular Elements in the Cerebellar Cortex — The Histology of the White Matter of the Cerebellar Cortex — Mechanisms Activating the Purkinje Cell — The Medullary Nuclei of the Cerebellum — The Medullary Substance of the Cerebellum — Connections of the Cerebellum — Development of the Cerebellum.

CHAPTER XXVI THE CEREBELLUM— Its Functional Significance 460

Experimental Evidence — Cerebellar Localization — Experimental Evidence from Stimulation of the Cerebellar Cortex — Clinical Experimentation and Clinical Evidence — Synergia and Synergic Movements — Cerebellar Localization on the Basis of Clinico-Pathological Evidence — Synergia as Comprehending Cerebellar Functions — Analysis of Synergia into its Component Factors — The Synergic Unit — Synergia in the Light of Cerebellar Histology — Summary Concerning the Functions of the Cerebellum.

Chapter XXVII

THE CEREBELLUM — The Principal Cerebellar Syndrome and its Variations 475

History — Interpretation and Anatomical Analysis — Diagnosis and Pathology — Nomenclature — Variations of the Cerebellar Syndrome — Summary of the Cerebellar Syndrome.

CHAPTER XXVIII THE MIDBRAIN — General Significance, Anatomy and Embryology op the

Divisions of the Mesencephalon — Evolutional Changes in the Midbrain — Primitive Importance of the Midbrain in the Psycho-Associational Reflex — Relation of the Midbrain to Vision — The Tectum in Birds — The Tectum in Reptiles, Amphibia and Fish: Its Reduction in Mammals — Evolution in the Form of the Tectum Mesencephali — Morphological Limitations to Expansion of the Midbrain — Telencephalization — The Significance of the Tegmentum and Basis Mesencephali — Embryology of the Mesencephalon — Differentiation of the Corpora Quadrigemina — Histogenesis of the Midbrain — Anatomy of the Mesencephalon .

Chapter XXIX

THE MIDBRAIN — Internal Structure and Histology of the Mesencephalon 502

Section Through the Inferior Colliculus — Section Through the IntercoUicular Sulcus — Section Through the Caudal Extremity of the Red Nucleus — Section Through the Superior Colliculus and the Mesial Geniculate Body — Section Through the Superior Colliculus, Pulvinar and Lateral Geniculate Body — Gray Matter and Nuclei of the Mesencephalon of Especial Importance — Tracts of Especial Importance in the Tegmentum Mesencephali — White Matter of the Basis Mesencephali.

XX CONTENTS

CHAPTER XXX Page

THE MIDBRAIN — The Functions and Principal Syndromes of the Mesencephalon 526

Functions of the Gray Matter of the Mesencephalon — Functions of the Tectum of the Midbrain — Functions of the Tegmentum of the Midbrain — Action of the Oculomotor Nucleus in the Control of Eye Movements — Special Nuclei of the Tegmentum — Function of the White Matter of the Mesencephalon — Ascending Tracts of the Tegmentum — Descending Tracts in the Tegmentum — Descending Tracts in the Basis Mesencephali — Decussations and Commissures in the Midbrain — Syndromes of the Mesencephalon — Syndrome of the Central Gray Matter — Syndrome of the Interpeduncular Space — Syndrome of the Cerebral Peduncle — Unilateral Tegmental Syndrome of the Midbrain.

Chapter XXXI

THE INTERBRAIN — The General Significance op the Diencephalon . . . 548 Intermediate Position of the Interbrain — History of the Interbrain — Changes in and Significance of the Pars Hypothalamica — Changes in and Significance of the Pars Epithalamica — Changes in and Significance of the Pars Thalamica — The Subthalamus — The Pars Metathalamica — Summary Concerning the Significance of the Interbrain.

Chapter XXXII

THE INTERBRAIN — Anatomy and Embryology of the Diencephalon . . . 569 Situation, Boundaries and Relations of the Interbrain — Parts of the Interbrain— The Hypothalamus — The Optic Chiasm — The Post-Chiasmatic Eminence— The Stalk of the Infundibulum and Infundibular Process — The Postinfundibular Eminence — Corpora Mammillaria — The Epithalamus — The Tela Chorioidea Superior or Velum Interpositum — The Pineal Gland — Relations of the Pineal Gland — The Posterior Commissure — The Thalamus and Subthalamus— The Metathalamus — The Third Ventricle — Embryology of the Diencephalon.